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Neuroimaging characteristics of dementia with Lewy bodies
Alzheimer's Research & Therapy volume 6, Article number: 18 (2014)
This review summarises the findings and applications from neuroimaging studies in dementia with Lewy bodies (DLB), highlighting key differences between DLB and other subtypes of dementia. We also discuss the increasingly important role of imaging biomarkers in differential diagnosis and outline promising areas for future research in DLB. DLB shares common clinical, neuropsychological and pathological features with Parkinson’s disease dementia and other dementia subtypes, such as Alzheimer’s disease. Despite the development of consensus diagnostic criteria, the sensitivity for differential diagnosis of DLB in clinical practice remains low and many DLB patients will be misdiagnosed. The importance of developing accurate imaging markers in dementia is highlighted by the potential for treatments targeting specific molecular abnormalities as well as the responsiveness to cholinesterase inhibitors and marked neuroleptic sensitivity of DLB. We review various brain imaging techniques that have been applied to investigate DLB, including the characteristic nigrostriatal degeneration in DLB using positron emission tomography (PET) and single-photon emission computed tomography (SPECT) tracers. Dopamine transporter loss has proven to reliably differentiate DLB from other dementias and has been incorporated into the revised clinical diagnostic criteria for DLB. To date, this remains the 'gold standard' for diagnostic imaging of DLB. Regional cerebral blood flow, 18 F-fluorodeoxygluclose-PET and SPECT have also identified marked deficits in the occipital regions with relative sparing of the medial temporal lobe when compared to Alzheimer’s disease. In addition, structural, diffusion, and functional magnetic resonance imaging techniques have shown alterations in structure, white matter integrity, and functional activity in DLB. We argue that the multimodal identification of DLB-specific biomarkers has the potential to improve ante-mortem diagnosis and contribute to our understanding of the pathological background of DLB and its progression.
Dementia with Lewy bodies (DLB) is the second most common form of neurodegenerative dementia following Alzheimer’s disease (AD), accounting for approximately 15% of cases at autopsy . Characterised by cognitive fluctuations, visual hallucinations, and motor Parkinsonism, DLB shares both clinical and pathological features with other dementia types, including Parkinson’s disease dementia (PDD) and AD. Hence, DLB is a frequently misdiagnosed condition, and previously established consensus criteria are limited by low sensitivity. In light of this uncertainty in diagnosis, and with important implications for subsequent patient management, more reliable imaging markers are needed to help distinguish DLB from other subtypes of dementia. In this review, we provide a literature summary of the principal neuroimaging techniques used to investigate DLB in terms of its differentiation from other dementia types. The diagnostic standard for all mentioned studies is clinical criteria except where otherwise stated.
Radionuclide imaging techniques
Nuclear imaging modalities such as single-photon emission computed tomography (SPECT) and positron emission tomography (PET) represent well established, reliable imaging methods to assess molecular changes in DLB (Table 1).
Single-photon emission computed tomography
The focus of SPECT on DLB has been on the demonstration of alterations in the dopamine transporter (DAT), reflecting changes in the nigrostriatal pathway, and the analyses of cerebral perfusion and metabolism.
Dopamine transporter loss
Imaging ligands, such as 123FP-CIT, have been developed for SPECT to visualise DAT loss in vivo. Reduced binding in the striatum reflects dysfunction or loss of nerve terminals in the substantia nigra. Previous autopsy literature has established that nigrostriatal degeneration and subsequent DAT loss is far more severe in DLB compared to AD . In healthy volunteers and patients with AD, the ligand is taken up in the caudate and putamen where neurons expressing the DAT are concentrated. In DLB, however, ligand uptake is almost absent in the putamen, and is reduced in the caudate (Figure 1). Consistent with an earlier single-site study , a phase III multicentre imaging study demonstrated a sensitivity and specificity of 78% and 90%, respectively, to distinguish DLB from AD . The effectiveness of 123FP-CIT-SPECT in the distinction between DLB and AD is further confirmed in another autopsy study (88% sensitivity and 100% specificity) .
DAT loss is related to the clinical feature of motor parkinsonism though, as DAT loss can be demonstrated before clinical parkinsonism is apparent, it may also be present in those without motor features. In addition, one study reported decreased DAT levels to be associated with visual hallucinations in DLB , suggesting the possible involvement of mesocortical dopaminergic pathways in the clinical phenotype of DLB. Recognition of the diagnostic value of dopaminergic SPECT in DLB is reflected in its incorporation in the revised consensus criteria for DLB, which allow for the diagnosis of probable DLB with evidence of a low DAT uptake in SPECT or PET imaging in the presence of one (rather than the usual two) core feature of DLB .
Several radiopharmaceuticals are available for regional cerebral blood flow SPECT: 99mTc hexamethylpropyleneamineoxime, N-isopropyl-p-[123I]iodoamphetamine and 99mTc-ethyl cysteinate dimer. The majority of studies have consistently highlighted a distinctive pattern of occipital hypoperfusion in DLB when compared to AD, affecting both primary visual cortex and visual association areas, and including the precuneus [8–10]. Lobotesis and colleagues  reported that blood perfusion in DLB and AD differed only in occipital regions and distinguished DLB from AD and from control subjects with 65% sensitivity and 87% specificity. Another SPECT study using N-isopropyl-p-[123I]iodoamphetamine also demonstrated relatively preserved medial temporal lobe perfusion in DLB in addition to occipital hypoperfusion in DLB when compared with AD . In an earlier study by Colloby and colleagues , a region of interest (ROI) analysis revealed decreased cerebral blood flow in AD compared to DLB in the medial temporal lobe, bilateral striatum and in the right thalamus. More recently, the same group used a spatial covariance analysis approach and concluded that multivariate analysis of blood flow SPECT data showed good diagnostic accuracy for distinguishing DLB from AD .
In summary, the two different SPECT methods (DAT and perfusion) are both useful in diagnosing DLB, but DAT imaging appears to be more robust and accurate compared to perfusion . On the contrary, SPECT was unable to discriminate between DLB and PDD, thus supporting the concept that these two forms of dementia belong to the same continuum spectrum, but are distinct diseases from AD .
Positron emission tomography
PET also allows molecular investigation of dementia subtypes but is less widely available and more expensive than SPECT. In addition, the versatility of PET imaging is due to the variety of different radioisotopes available, allowing investigation of different functional systems; for example, energy metabolism with 18 F-fluorodeoxygluclose (FDG), cholinergic pathways with N-11C-methyl-4-piperidyl acetate, the dopaminergic system with 18-fluorodopa and other ligands for the vesicular monoaminergic transporter, and cerebral amyloid deposition with Pittsburgh compound B and18F labelled compounds, such as 18flurodopa, 18 F Flutemetamol and 18 F Flubetapir.
Consistent with SPECT findings of occipital hypoperfusion in DLB patients, FDG-PET studies have established a distinctive pattern of hypometabolism in the occipital cortex [16, 17] and visual association cortices, with relative preservation of the posterior cingulate, which is normally markedly affected in AD (the so-called 'cingulate island' sign). Furthermore, occipital hypometabolism has been linked by some to visual hallucinations in DLB . Using 18fluorodopa, Klein and colleagues  did not reveal any differences in dopaminergic deficit profiles between DLB and PDD.
Most of the research done with amyloid PET imaging has been focused on AD, which is consistently associated with elevated levels of uptake, especially in the prefrontal cortex, midline and lateral parietal cortex, temporal cortex and striatum. Although the pathological hallmarks of DLB are Lewy bodies and Lewy neurites, cortical amyloid-beta deposition is often seen. The importance of amyloid-beta burden in DLB and cognitive impairment remains to be elucidated. Amyloid imaging studies in DLB have yielded variable results. While some studies have reported similar amyloid-beta deposition in DLB and AD, most studies report lower mean cortical amyloid-beta ligand binding in DLB patients, with both AD and DLB patients showing elevated amyloid burden compared to their healthy controls .
Differences in cortical amyloid burden between DLB and PDD have been investigated in recent amyloid PET studies. Edison and colleagues  demonstrated that cortical amyloid load is significantly raised in over 80% of DLB patients, while amyloid pathology is infrequent in PDD. This finding is largely in accordance with the literature reporting elevated cortical amyloid deposition in DLB compared to PDD , which is aligned with the presence of greater cortical Alzheimer pathology in DLB . Clinically, it is also noteworthy that increased amyloid deposition has also been found to be associated with a more aggressive rate of cognitive deterioration and visuospatial impairments in DLB [21, 22]. Future research clarifying the influence of amyloid deposition might be important for informing treatment decisions with the potential availability of effective anti-amyloid agents.
Autopsy findings of profound cholinergic deficits in DLB (greater than in AD) have led to the application of PET ligands to evaluate the cholinergic system in DLB in vivo, such as N-[11C]methylpiperidin-4-yl acetate and propionate. Klein and colleagues  have demonstrated widespread reductions of acetylcholinesterase activity in DLB, particularly affecting the posterior regions, while similar reductions have also been reported in the thalamus . This pattern of cholinergic deficiency is comparable to that seen in Parkinson’s disease [24, 25]. On the other hand, choline acetyltransferase activity, particularly in the neocortex, is markedly reduced in DLB compared to AD, consistent with the autopsy findings . The spatial distribution of cholinergic deficiencies also appears to be different from AD, where deficits are most prominent in the temporal lobes while the thalamus is relatively spared .
PET studies using 11C-dihydrotetrabenazine have also examined nigrostriatal projections in DLB and AD, and previous studies have demonstrated its potential to differentiate DLB from AD. Compared to controls, significantly decreased binding of 11C-dihydrotetrabenazine was predominantly found in the posterior and anterior putamen and caudate nucleus in DLB, while differences were found between AD and controls .
Structural magnetic resonance imaging
Besides nuclear imaging methods, the clinical utility of structural neuroimaging with magnetic resonance imaging (MRI) for differential diagnosis of dementias is also well established. Structural MRI has been widely used to compare regional structural changes in patients with DLB against AD, PDD and their healthy controls. In this section, we summarise the principal findings using MRI to distinguish DLB from other subtypes of dementia (Table 1).
Comparison between dementia with Lewy bodies and Alzheimer’s disease
Both cross-sectional and longitudinal studies have shown that DLB is associated with less pronounced global atrophy than AD . The most consistent finding is the relative preservation of the medial temporal lobe (MTL) in DLB compared to AD  (Figure 2). Burton and colleagues  demonstrated the clinical significance of MTL atrophy for distinguishing DLB from AD in pathologically confirmed cases, although another autopsy study argued that the presence of MTL atrophy may not rule out a diagnosis of DLB, especially amongst patients in the oldest old-age category (>85 years) . In addition, Burton and colleagues  reported a strong correlation between hippocampal atrophy and amyloid-beta plaques and neurofibrillary tangles but not Lewy body-associated neuronal inclusions, suggesting that gray matter (GM) loss in DLB could be due to concomitant AD pathology. Hippocampal atrophy in DLB and AD has also been investigated, showing less severe atrophy in DLB than in AD when compared to healthy controls . Similarly, other studies have demonstrated that the entorhinal cortex, CA1, and subiculum areas of the hippocampus may be most affected in AD compared to DLB [28, 32].
In parallel with the MTL findings, patients with DLB generally demonstrate relative preservation of episodic memory capabilities compared to AD while experiencing impairments in attentional and visuospatial tasks. Hence, Ballmaier and colleagues  hypothesised that frontal lobe structures could be spared in DLB and the reciprocal connections with relatively preserved temporal regions would be affected to a lesser extent too. Although their study revealed greater frontal GM loss in AD relative to DLB , other studies have not found differences between these patient groups .
Conversely, the midbrain appears to be more affected in DLB than in AD, with the substantia innominata showing greater atrophy [35, 36]. The substantia innominata contains the nucleus basalis of Meynert, which is highly involved in the cholinergic neurotransmitter system. In addition, Whitwell and colleagues  demonstrated that increased dorsal mesopontine GM atrophy distinguished patients with clinically diagnosed DLB and AD, and this finding was further confirmed in an autopsy study involving patients with high likelihood DLB . These findings are thus in agreement with greater cholinergic dysfunction in DLB, and perhaps relate to the presence of midbrain synuclein pathology (see the 'Cholinergic pathways' section).
In light of the 123FP-CIT SPECT functional changes involving the loss of DAT in DLB , associated subcortical structures have also been investigated relative to AD. Cousins and colleagues  have observed reduced putamen volume in patients with DLB, which may be associated with the striatal synuclein pathology.
Comparison between dementia with Lewy bodies and Parkinson’s disease dementia
There have also been attempts to compare GM loss between DLB and PDD. These results have converged to reveal a pattern of more pronounced GM loss in DLB compared to PDD. This is in agreement with the PET and pathological findings of greater amyloid burden in DLB. It is noteworthy that localisations of GM reductions in DLB relative to PDD appear to be variable amongst studies. While Burton and colleagues  did not detect different cortical atrophy profiles between DLB and PDD, a voxel-based morphometry (VBM) study by Beyer and colleagues  of PDD, DLB, AD, and healthy controls revealed GM reductions in the temporal, parietal and occipital lobes in DLB. Besides the temporal and parietal areas, Lee and colleagues  also identified striatal and occipital GM reductions. A different pattern of structural and functional correlations between DLB and PDD was recently revealed . In particular, decreased GM volume in associative areas, namely the left precuneus and inferior frontal lobe, correlated with visual hallucinations in DLB but not in PDD patients. The variation in patient population, sample size and subtle differences in imaging analysis methodology may account for such mixed effects in comparing GM reduction between the DLB and PDD groups; for example, VBM has been shown to be highly sensitive to co-registration and normalisation errors.
Cortical thickness analyses
Recent advances in image processing allow automatic extraction of whole brain cortical thickness information from structural MRI. Cortical thickness has been shown to demonstrate high precision and sensitivity in detecting alterations in morphology resulting from neuropathological changes. Hence, it has been used in increasing numbers of studies as a marker to separate AD and PDD from healthy controls. Recently, a multivariate classification study of cortical thickness demonstrated 82% sensitivity and 85% specificity for differentiating AD from DLB . Specifically, AD was characterised by regional thinning of the parahippocampal, subgenual cingulate regions and temporal pole, whereas cortical thinning in DLB was localised in the middle and posterior cingulate, superior temporo-occipital and lateral ortibofrontal regions. It is interesting to note that the greater temporal involvement in AD compared to DLB has been one of the most consistent findings on structural imaging whether on visual inspection, ROI or VBM studies [33, 44].
White matter hyperintensities
White matter hyperintensities (WMHs) are areas of high signal intensity commonly detected using T2-weighted or fluid inverted recovery sequences in periventricular and deep subcortical white matter regions. In older people they are often a marker of cerebral small vessel disease, accumulating over time. WMHs are commonly attributed with loss of myelin and axons, and mild gliosis , but can also reflect amyloid angiopathy and other pathologies. Over the past decade, visual rating scales and volumetric assessments have been developed to quantify WMH load. Although the clinical significance of WMHs in dementia remains to be determined, several studies have found WMHs to be associated with cognitive impairments. A longitudinal study comparing progression of WMHs in AD, DLB and PDD revealed a greater burden at baseline of WMHs in AD compared to healthy controls, DLB and PDD, with no subsequent differences in the rate of progression between groups . The importance of WMHs in DLB remains poorly understood. Thus, future research is needed to investigate region-specific WMHs and examine potential differences in functional correlations between dementia subtypes.
Active task and resting state functional MRI (fMRI) are the main neuroscience tools to examine cerebral function related to cognitive tasks or during rest through changes in blood oxygen level-dependent signal. There are still relatively few fMRI studies in DLB, but different patterns of functional connectivity between AD and DLB have been reported (Table 1). A recent resting-state fMRI study showed both increased connectivity between the precuneus and regions in the dorsal attention networks and decreased connectivity with prefrontal and visual cortices in DLB compared to the AD group . Another data-driven independent component analysis study demonstrated increased connectivity in the default mode network in DLB compared to AD . This finding contrasts with reported connectivity dysfunctions between the posterior and anterior portions of the default mode network in AD . Kenny and colleagues  found greater connectivity between the putamen and frontal, temporal and parietal regions in DLB patients compared with AD patients, and argued that this might be associated with Parkinsonian features in DLB. Consistent with relative preservation of memory function in DLB compared with AD, hippocampal connectivity was not found to be different in DLB compared to healthy controls. Conversely, the left hippocampal connectivity was greater in AD compared with controls, which might reflect potential compensatory mechanisms.
Given the high prevalence of visuoperceptual impairments in DLB patients, task-based fMRI studies have investigated the functional integrity of the visual system in DLB. A task-based fMRI study involving visual presentations of colour, face and motion paradigms found greater activation in the superior temporal sulcus in DLB compared to AD during the motor part of the tasks . Another task-based fMRI study did not find any significant differences in functional response between DLB and healthy controls to checkerboard, objects or motion stimuli in V1 and V2/V3, suggesting a relative preservation of function in lower visual areas. Interestingly, ROI analysis revealed decreased V5/MT (middle temporal) activation in response to motion stimuli in the DLB group . Whether these abnormalities at higher levels of the visual system contribute towards the characteristic visuoperceptual impairment and visual hallucinations needs further empirical evidence. In summary, these results seem to indicate that functional abnormalities in DLB affect the visual association areas rather than the primary visual cortex.
Diffusion tensor imaging
Diffusion tensor imaging (DTI) provides in vivo information about white matter microstructural integrity by utilising the anisotropic nature of diffusion in neuronal white matter tracts . White matter diffusion characteristics are commonly assessed by means of mean diffusivity (MD) and fractional anisotropy (FA). MD increases with the degeneration of structural barriers that normally restrict the Brownian motion of water molecules, and reductions in FA occur as diffusion consequently becomes less directionally oriented.
DTI studies in AD have consistently found elevated MD in the hippocampus and decreased FA in the main limbic pathways. Much less is known about DTI changes in DLB. Previous DTI studies on DLB used ROI-based or voxel-based techniques with considerable variability in their findings. Some studies have reported diffusion abnormalities of the corpus callosum and the frontal, parietal, occipital, and, to a lesser extent, temporal white matter when compared to controls, while other studies have found very little change in DTI parameters compared to controls and AD patients [53, 54]. The modest involvement of the temporal lobe is consistent with the relative preservation of global neuropsychological measures and memory domain in DLB compared to AD. Two DTI studies in DLB patients have also identified white matter alterations in the longitudinal fasciculus [54, 55]. Considering the significant role of longitudinal fasciculus in ventral visual pathway, these abnormalities could be associated with visuospatial impairment and visual hallucinations in DLB patients. In addition, elevated MD in the amygdala was also found in DLB, which was associated with Unified Parkinson’s Disease Rating Scale scores . However, AD was not accompanied by loss of GM in this brain region, implying a different pathologic mechanism, such as vacuolisation. However, no changes in diffusivity measures were identified between DLB and AD . On the contrary, a recent DTI study demonstrated distinct patterns of white matter alterations between DLB and AD, with a more focal posterior predominance of FA change in DLB (parieto-occipital) as opposed to a more diffuse pattern of change in AD. DLB was also associated with reduced FA in the pons and the left thalamus compared to AD .
Magnetic resonance spectroscopy
1H magnetic resonance spectroscopy (MRS) measures the peak signals from several different metabolites within a single examination period, and it has increasingly been used in differential diagnosis of dementia through the identification of respective spectroscopic profiles of various dementia subtypes (Table 1). In AD, the metabolite N-acetylaspartate is consistently found to be reduced in temporal lobe tissue (approximately 15%) , and is associated with disease severity . In addition, increases in myo-inositol (15%) are also commonly reported . In comparison, DLB is characterised by relatively normal N-acetylaspartate/creatine and myo-inositol levels, suggesting neuronal integrity and a lack of gliosis, respectively . Further research with larger sample sizes will determine the clinical utility of these findings in distinguishing DLB from other types of dementia.
At present, neuroimaging findings in dementia are generally derived from group-level analyses. While these have enriched our understanding about the neurobiological differences between DLB and other dementia types, the diagnostic value of most neuroimaging methods is still limited due to the lack of sensitivity and specificity when applied at the individual subject level. As such, there has been increased emphasis on maximizing the utility of more advanced data analysis methods to bridge the gap between the basic research and clinical practice. In this regard, novel machine learning techniques have been developed to allow individual classification of patients. Machine learning techniques extract features from neuroimaging data and construct models of different dementia types and healthy population. These models have been used to differentiate AD from controls, mild cognitive impairment, and frontotemporal lobar degeneration , while the potential of this approach in classification among dementia types has been highlighted by a recent autopsy-based machine-learning study by Vemuri and colleagues  involving pathologically confirmed dementia patients (AD, DLB, and frontotemporal lobar degeneration). Besides the advent of machine learning techniques, multimodal neuroimaging studies have become increasingly popular as researchers are recognising the benefits from integrating more than one imaging modality (for example, jointly analysing brain volume with perfusion or white matter changes). Recent multimodality strategies have shown superior predictive power than using any single modality domain in the diagnosis of AD [62–64], and distinguishing AD from frontotemporal lobar degeneration  and mild cognitive impairment . Similar approaches have recently been applied also to the differentiation of DLB from other conditions. Goto and colleagues  integrated MRI striatal volumetric data with occipital perfusion SPECT to distinguish patients with mild DLB from patients with mild AD with high sensitivity and specificity. Kantarci and colleagues  achieved increased accuracy (98%) for distinguishing DLB from AD by combining information from occipital FDG uptake, global Pittsburgh compound B retention, and hippocampal volume. Given the multifactorial nature for pathological involvement in patients with DLB, differentiation between DLB and other dementia types will be aided by combining imaging modalities that are sensitive to different components of the disease process.
Longitudinal analyses of neuroimaging data will also provide information about the trajectory of the disease and its underlying neurobiological changes. By allowing the assessment of brain changes over time in individual subjects using multiple serial MRI scans, longitudinal designs have the advantage of reducing within-subject variation. Different rates of cerebral atrophy in dementia types could also inform differential diagnosis. In fact, DLB patients showed a much slower rate of global atrophy (0.4%) compared to AD patients (1.1%) .
This review summarises the current imaging literature of DLB in the context of its differentiation from other causes of dementia, discusses the increasingly important role of imaging biomarkers in differential diagnosis, and outlines promising areas for future research. Collectively, the imaging findings have yielded important insights into the underlying pathophysiology of this condition while showing potential promise in improving clinical differentiation of DLB from other types of dementia.
To date, the marked reduction of dopaminergic activity in the basal ganglia is the most characteristic imaging finding of DLB, and has been considered as a significant step in aiding the clinical diagnosis of DLB. Cerebral perfusion studies have also revealed a distinctive pattern of deficits in parietal and occipital regions. At the structural level, another robust observation concerns the relative preservation of MTL in DLB that is consistent with preserved memory functions. Other techniques such as DTI, MRS, and fMRI coupled with novel analytical approaches have also revealed information for differential diagnosis of DLB.
While the field has made substantial progress in delineating the imaging characteristics associated with dementia subtypes, the ability to detect structural patterns that enable accurate prediction of diagnosis for specific individuals ultimately determines the clinical value of MRI and the measurements obtained from it. The reliable application of these methods in routine radiological practice may be facilitated by non-expert-dependent, automated methods of analysis.
In terms of practical considerations, SPECT and PET are both generally well tolerated investigations with few contra-indications, though both involve radiation exposure, limiting the number that any one subject should have. In most countries, SPECT is more widely available than PET. MRI is now widely accessible but more unsuitable for those with claustrophobia, pacemakers or metallic implants in or around the head. fMRI requires specialist stimulus presentation, which limits its applicability to research studies. In addition, some computerized paradigms in task-based fMRI might not be suitable for elderly dementia patients. Other modalities, particularly DTI and MRS, require extensive post-processing analysis time, also potentially limiting their routine application for clinical use.
It is worth mentioning the limitations of the current research. At present, the overwhelming majority of neuroimaging studies in DLB are cross-sectional, relatively small in size, and in participants in established stages of the disease. Therefore, larger prospective longitudinal studies are warranted to confirm the utility of many imaging techniques and monitor disease progression in early disease stages as well as at risk individuals and patients with mild cognitive impairment. Furthermore, studies involving multimodal neuroimaging data and larger cohorts are likely to make novel contributions in evaluating the utility of combined biomarkers in DLB.
This article is part of a series on Lewy Body Dementia, edited by Ian McKeith and James Galvin. Other articles in this series can be found at http://alzres.com/series/LewyBodyDementia.
Dementia with Lewy bodies
Diffusion tensor imaging
Functional magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance spectroscopy
Medial temporal lobe
Parkinson’s disease dementia
Positron emission tomography
Region of interest
Single-photon emission computed tomography
White matter hyperintensity.
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This work was supported by the NIHR Biomedical Research Unit in Dementia and the Biomedical Research Centre awarded to Cambridge University Hospitals NHS Foundation Trust and the University of Cambridge. EM was in receipt of a Gates Cambridge PhD studentship. We thank Dr Sean Colloby and Dr Michael Firbank for their assistance with the figures.
EM, LS and GBW have no competing interests. JTO’B has acted as a consultant for GE Healthcare and Lilly.
About this article
Cite this article
Mak, E., Su, L., Williams, G.B. et al. Neuroimaging characteristics of dementia with Lewy bodies. Alz Res Therapy 6, 18 (2014). https://doi.org/10.1186/alzrt248
- Fractional Anisotropy
- Diffusion Tensor Imaging
- Dementia With Lewy Body
- Default Mode Network
- Diffusion Tensor Imaging Study


|Publication number||US4806934 A|
|Application number||US 07/040,399|
|Publication date||Feb 21, 1989|
|Filing date||Apr 20, 1987|
|Priority date||Apr 20, 1987|
|Also published as||EP0288232A2, EP0288232A3|
|Publication number||040399, 07040399, US 4806934 A, US 4806934A, US-A-4806934, US4806934 A, US4806934A|
|Inventors||John E. Magoon|
|Original Assignee||Raytheon Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (20), Referenced by (9), Classifications (21), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to tracking circuits, and more particularly to a circuit capable of tracking a signal returned from a moving object as the signal passes through antenna nulls.
It is well known that radar and other electronic direction finding systems make use of the physical property that a transmitted radio frequency signal is reflected by surrounding objects. One important application for such systems is object tracking. An object tracking system's primary purposes are to determine the position and speed of a moving object by monitoring the reflected radio frequency signal as received by an antenna. The object's position is determined by using a directional receiving antenna. Such directional antennas are characterized by an antenna pattern consisting of a narrow or highly focused main lobe and attendant sidelobes. The main lobe is steered towards the moving object by feeding the antenna's electrical output to a control circuit. The control circuit controls a motor arranged for rotating the antenna. When the electrical output is at a maximum, the antenna is known to be pointing at the moving object. If the electrical output's amplitude decreases, the control circuit uses a resulting phase change in the electrical output to activate the motor so the antenna will be realigned. The object's speed is determined by using the physical property that a reflected radio frequency signal returned from a moving object exhibits frequency shift. This frequency shift, or Doppler frequency, can be detected in the electrical output to determine the object's speed.
A problem occurs with Doppler frequency tracking systems when the object moves too quickly for the antenna to be realigned, thus allowing the reflected radio frequency signal to be received through a sidelobe rather than through the main lobe. This causes an abrupt change in the antenna's electrical output as the reflected signal moves through the antenna nulls. One way of solving this problem is to use a signal processing circuit to filter abrupt changes in the electrical output. Thus, the rotation direction and Doppler frequency as determined before the abrupt amplitude or phase change occurred is used until the antenna is again aligned with the moving object. Although this technique works well, for some applications there is a period of time when the moving object is not being directly tracked. Also, Doppler frequency information may be lost by the filtering process.
Another solution to the object tracking problem is to use multiple antenna elements arranged as a phased array and beamforming techniques on outputs of the phased array to develop a plurality of steerable antenna lobes in a plurality of directions. Such systems work well for their intended purpose, but tend to be more expensive than single antenna systems.
A somewhat analogous problem is that of recovering data in a phase modulated communication signal. As is well known, a phase modulated communication signal is one where the phase of a carrier signal is modulated in accordance with data to be transmitted. In one such technique, known as biphase modulation, the communication signal consists of a carrier signal at a particular frequency transmitted with a particular phase, for example 0°, to indicate a logic 0 data bit, and with another phase, for example 180°, to indicate a logic 1 data bit. The receiver then reconstructs the data by demodulating the phase shifts in the communication signal. This demodulation problem is analogous to the object tracking problem in that they both process signals containing abrupt phase shifts. An example of one such system is shown in the United States patent granted to DeLong et al., U.S. Pat. No. 3,883,806, issued May 13, 1975 and assigned to Rockwell International Corporation of Dallas, Texas. This circuit provides a local reference signal remaining phase-continuous despite phase modulations in an input signal. The circuit operates by reversing the output of a phase lock loop each time the input signal reverses phase. However, such a circuit is not directly applicable to the present problem since the purpose of such a circuit is to detect and remove such abrupt phase transitions, whereas in the present invention it is important not only to detect and remove transistions, but also to provide a continuous and smooth indication of the instantaneous phase of the reflected signal for tracking purposes.
It is therefore an object of this invention to provide a circuit capable of continuously maintaining phase lock with a signal reflected from an object moving with a high velocity with respect to a receiving antenna.
A further object is to provide such a circuit without the need for multiple antenna elements or beamforming or other associated circuits commonly necessary for operating an array of antenna elements.
Yet another object is to provide an apparatus for outputting a Doppler frequency tracking signal without the abrupt phase reversals caused by the object passing through antenna nulls.
A still further object is to provide an apparatus capable of maintaining Doppler frequency tracking of an object even when its receiving antenna is not properly aligned with the object.
Briefly, these and other objects of this invention are accomplished by a phase lock loop circuit arranged to output an object tracking signal having a continuous phase despite discontinuous phase reversals in an input signal. The circuit combines a phase detector, for indicating if an abrupt phase change in an input signal has occurred, such as when a signal returned from a moving object has passed through an antenna null; a phase reversing circuit, controlled by the phase detector, for operating on the input signal to reverse its phase when the detector indicates that an abrupt change has occurred; and various components of a phase lock loop. In particular, the low pass filter component of the phase lock loop has a time delay greater than the time delay associated with the phase detector, so that the output of the phase detector is stable and readily available before the output of the low pass filter is fed to control the other phase lock loop components.
In accordance with one particular embodiment of the invention, the phase detector is a conventional mixer fed by a signal in phase quadrature with the phase lock loop input signal, a low pass filter with small time delay, and a Schmitt trigger arranged to provide a digital control signal for indicating when the phase lock loop input signal has gone through an abrupt phase reversal.
These and other objects, advantages and novel features of this invention become apparent from the following detailed description when considered together with the accompanying drawings, where:
FIGS. 1A through 1E depict a series of events occurring as a moving object passes a directional antenna at a speed much faster than rotational speed of motors associated with such an antenna;
FIG. 2 is a plot of the frequency and phase of a signal reflected from the moving object as it passes the antenna;
FIG. 3 shows tracking control circuits associated with such an antenna and in particular a tracking signal phase lock loop in accordance with this invention; and
FIG. 4 shows the outputs of a detector mixer and loop mixer shown in FIG. 2 as a function of the phase difference between their input signals.
Referring now to the drawings, where like reference characters designate corresponding parts throughout the several figures, there is shown in FIG. 1A a representation (not to scale) of a radio antenna 10, its associated directional antenna pattern 15, and an airborne moving object 12 such as an airplane. The moving object 12 in this case is travelling in the direction of arrow 14. The antenna pattern 15 is seen to include a main lobe 16 and one or more sidelobes such as those indicated by reference numerals 17a and 17b. The antenna 10 is normally positioned so that the highly focused main lobe 16 aims at the moving object 12. Thus, if a bearing line 18 is drawn from the antenna 10 towards moving object 12, the bearing line 18 passes through a point near the center or boresight 19 of main lobe 16. This boresight 19 is the point at which a signal reflected by the moving object 12 is received by antenna 10. As shown in FIG. 1B, moving object 12 eventually changes its position thus causing bearing line 18 to pass through a point 20 to one side or the other of boresight 19 of main lobe 16. In such an instance, circuits associated with the electrical signal output of antenna 10 (not shown in FIG. 1) detect this offset of main lobe 16 as a reduction in amplitude and change in phase of the electrical signal output from antenna 10. Such signal processing circuits, well known in the art, make use of this amplitude reduction and phase shift of the electrical signal output to develop a control signal. This control signal in turn is fed to a motor (not shown) associated with antenna 10 to cause antenna 10 to rotate in the direction of arrow 22. In this manner the boresight 19 of main lobe 16 becomes realigned with the bearing line 18. The bearing of moving object 12 is thus determined to be the same as the particular direction in which the boresight 19 of antenna 10 is pointing.
A problem occurs when moving object 12 has a very high velocity with respect to the maximum rotating speed of antenna 10. Such a situation, depicted in FIG. 1C, may occur when the moving object 12 is moving with high speed or, perhaps more commonly, when moving object 12 is passing very close to antenna 10. Although antenna 10 has begun to swing in the direction of arrow 22 to become realigned with bearing line 18, the reflected signal is now being received in a portion of antenna pattern 15 known as a null 24. This has occurred because, although antenna 10 has begun to rotate in the direction of arrow 22, moving object 12 is moving too fast for antenna 10 to remain aligned with it. The situation may continue to a point, as shown in FIG. 1D, where the reflected signal is received by antenna 10 through a point 26 on a portion of a side lobe 17b of antenna pattern 15. This is a problem because the electrical signal output from antenna 10 is now reduced in amplitude and has undergone a 180° phase reversal. The electrical signal may undergo additional phase reversals, such as in the situations shown in FIG. 1E, if another null 25 is passed. In this situation, the direct use of the electrical signal output to develop a motor control signal for antenna 10 leads to erroneous movement commands.
A plot of this effect on the electrical signal output from antenna 10 is shown in FIG. 2. The upper graph is frequency versus time. This is a typical Doppler curve, with frequency, f1, above a center frequency, f0, before a time t1. During this period, moving object 12 is approaching the antenna 10, so the electrical signal indicates a positive Doppler frequency, f1 -f0. Between times t1 and t2, moving object 12 passes and begins to recede from antenna 10, and the frequency of the electrical signal begins to roll off to f2, below f0. This causes the electrical signal to indicate a negative Doppler, f2 -f0.
The lower graph in FIG. 2 shows the phase of the electrical signal versus time. It illustrates the problem, occurring between times t1 and t2, when the antenna 10 does not remain aligned with the moving object 12. One or more 180° phase reversals occur as the moving object 12 aligns with one or more antenna nulls.
What is needed then is a circuit for recognizing that these phase changes have occurred. The circuit would then obtain the true phase change due only to Doppler frequency rolloff. The true phase change can then be used to track the moving object 12 even while the antenna 10 is misaligned.
FIG. 3 shows a block diagram of an object tracking system, generally indicated as 30, for solving this problem. Object tracking system 30 includes a radio antenna 10, rotatably mounted upon a mast 32, and with its direction controlled by a motor 34. Antenna 10 outputs an electrical return signal 33 to a receiver 36. The receiver 36 demodulates the return signal 33 and provides an output 37 to a phase tracking circuit 50. The phase tracking circuit 50 provides a voltage at an output 77 corresponding to the relative phase of a signal reflected from a moving object 12 (FIG. 1). The output 77 of phase tracking circuit 50 is returned to receiver 36. Receiver 36 then uses the tracking circuit output 77 and the return signal 33 to track the position and speed of moving object 12. Receiver 36 may also provide such tracking information to a display or utlization device (not shown). Receiver 36 forwards this tracking information on an output signal 51 to a controller 38. Controller 38 develops a control voltage, or other electrical control signal 40, to cause motor 34 to rotate antenna 10 to allign its boresight 19 (FIG. 1) with moving object 12. Controller 38 is comprised of signal processing circuits, well known in the art, for making use of the phase information provided by output signal 51 and amplitude information present in receiver output 37 to develop the control signal 40.
Now more particularly, phase tracking circuit 50 in accordance with the present invention is seen to comprise components of a conventional phase lock loop and additional components. The phase lock loop includes a loop mixer 52, loop low pass filter 54 (also referred to as a slow low pass filter) and a voltage controlled oscillator (VCO) 56. The receiver output 37 is fed to loop mixer 52 together with the 0° output 57b of VCO 56. Thus, loop mixer 52 acts as a phase difference detector providing a signal 53 indicating the difference in phase between the receiver output 37 and the VCO 0° output signal 57b. In turn, this signal 53 is fed back to the input terminal of VCO 56 through loop low pass filter 54 to maintain the VCO 0° output signal 57b in phase lock with receiver output 37.
A phase tracking circuit 50 in accordance with the present invention also includes a phase reversal detector 60 and a phase reversing circuit 70. Phase reversal detector 60 comprises detector mixer 62, detector low pass filter 64 (also referred to as the fast low pass filter), and Schmitt trigger 66. Detector mixer 62 is fed both the receiver output 37 as well as a 90° VCO output signal 57a. While this signal 57a is shown to be fed from a 90° output terminal of VCO 56, it should be understood that such a signal 57a might also be developed at the output of a 90° phase shifter attached to the 0° output of VCO 56. The output of detector mixer 62 is in turn fed to detector low pass filter 64 through Schmitt trigger 66 to provide a phase reversal control signal 67. It is the purpose of phase reversal detector 60 to provide such a phase reversal control signal 67 when the return signal 33 has experienced an instantaneous phase shift of approximately 180°. It is seen that the detector mixer 62 provides such a control signal 67 indicative of an abrupt phase change by using a detector low pass filter 64 and a Schmitt trigger 66. Schmitt trigger 66 has a lower threshold voltage V1 and upper threshold voltage V2. The control signal 67 is a digital signal where level transitions indicate phase reversals in the receiver output 37. Preferably, it has a level change in the positive going direction (that is from a logic 0 level to a logic 1 level) when the phase of return signal 36 has abruptly changed from 0° to 180°, and has a level change in the negative direction (from logic 1 to logic 0) when the return signal 36 undergoes an abrupt negative phase change from 180° to 0°.
Phase reverser 70 is essentially a pair of amplifying circuits, including inverting amplifier 72 and non-inverting amplifier 74, and also a switch 76. The inputs of both inverting amplifier 72 and non-inverting amplifier 74 are fed by the loop phase difference signal 53 from loop detector 52. The outputs of amplifiers 72 and 74 are each fed to a corresponding input terminal of switch 76. Switch 76 is operated to select either the inverted loop phase difference signal 73 or the non-inverted loop phase difference signal 75, in accordance with the level of phase reversal control signal 67.
Having described the various components of phase tracking circuit 50 its operation can now be understood. In particular, as previously mentioned, phase tracking circuit 50 is primarily operated as a phase lock loop with the loop mixer 52 serving to provide a loop phase difference signal 53 indicating the difference between the phase of the 0° output 57b of the VCO 56 and the phase of the receiver output 37. The loop phase difference signal 53 is then fed through non-inverting amplifier 74 via switch 76 to loop low pass filter 54 and then to the control input of VCO 56. A slight variation in the phase of receiver output 37 results in a change in the voltage of loop difference signal 53. This voltage change is in turn fed through loop filter 54 to adjust the VCO 56. VCO 56 continues adjusting in this manner until such time as its 0° output 57b becomes phase aligned with the phase lock loop input, namely receiver output 37.
An important function of phase tracking circuit 50 is provided by phase reversal detector 60 and phase reverser 70. In particular, phase reversal detector mixer 62 compares the receiver output 37 with 90° phase shifted VCO output signal 57a and provides a phase reversal difference signal 63 indicating their difference. This signal 63 drives detector low pass filter 64 and Schmitt trigger 66. The output of Schmitt trigger 66, namely phase reversal control signal 67, is fed to switch 76 and serves to select one of the inverted loop mixer control signal 73 and non-inverted loop mixer control signal 75 as a selected loop control signal 51 to be fed to loop low pass filter 54. In the event that detector filter output 65 exceeds the threshold voltage V2 of Schmitt trigger 66, phase reversal control signal 67 becomes a logic "1" level and causes switch 76 to move to the "1" position shown as a dashed line in FIG. 3. In this instance, the inverted loop mixer signal 73 output from inverting amplifier 72 is now fed to loop low pass filter 54. The loop then continues to operate using inverted loop mixer signal 73 until such time as the phase of receiver output 37 changes sufficiently in the negative going direction to comprise a -180° phase shift, at which time the detector filter output signal 65 decreases below the voltage V1 threshold of Schmitt trigger 66. This changes the loop control signal 67 to a logic 0 level and thus causes switch 76 to return to the "0" position. The non-inverted loop mixer control signal 75 is now fed to loop low pass filter 54.
Most importantly, however, phase tracking circuit 50 operates so that phase reversal control signal 67 must be stabilized before any change occurs in the selected loop control signal 77 fed to loop filter 54. In other words, the time delay associated with phase reversal detector 60, including the detector mixer 62, detector low pass filter 64, and Schmitt trigger 66, is less than the time delay associated with slow loop filter 54. It is also desirable for changes in the VCO IN control signal 55 to occur more slowly than changes in the phase reversal control signal 67. Thus, the loop low pass filter 54 preferably has a time delay greater than the detector low pass filter 64. This insures that any changes due to the abrupt phase reversal of receiver output 37 are minimized at the VCO IN control signal 55. That is switch 76 has changed states before the slow loop filter 54 has changed its output voltage 55.
Further understanding of the operation of phase tracking circuit 50 can be understood by referring to FIG. 4. Shown are plots of the outputs of loop mixer 52 and detector mixer 62 versus the difference in phase between the signals fed to their respective inputs. In particular, a dashed curve 80 shows the loop mixer signal 53 output from loop mixer 52 as a function of the phase difference of its inputs, receiver output 37 and VCO 0° output 57b. The upper row of numerals along the abscissa are used for interpreting dashed curve 80. As seen in FIG. 3, this loop mixer signal 53 varies between a voltage greater than V2 and less than V1 about a mean voltage V. Output voltages V1 and V2 here are shown to correspond to points at input phases ±22.5° and ±157.5°, but it should be understood that other voltage thresholds for "maximum 0°" and "minimum 180°" may be used. The mean voltage V may or may not be zero volts. Thus, when the phase difference between the reference signal 36 and VCO 0° output signal 57b is 0°, loop mixer 52 provides an output of V volts. If the phase difference between these signals increases in magnitude, the loop mixer 52 output voltage also increases (or decreases) in magnitude to a maximum (or minimum) at a point where the input phase difference is 90° (or -90°).
The detector mixer output 63 from detector mixer 62 is shown in FIG. 4 as a solid curve 84. The lower row of numerals along the abscissa are used for interpreting solid curve 84. This solid curve 84 similarly varies between a maximum above V2 and a minimum below V1 about a mean V volts. Detector mixer output signal 63 has maximum negative and positive magnitude when the difference between its inputs, namely receiver output 37 and VCO 90° output 57a, is -90° or +90°, respectively.
Referring now to FIGS. 3 and 4 together it can be seen that when phase tracking circuit 50 is adjusted so that VCO 56 has its 0° output substantially phase aligned with the phase of receiver output 37, little or no change is needed in the VCO input to maintain the stability of the loop. Loop mixer output signal 53, via non-inverting amplifier 74 and switch 76 in the zero position, is then used directly by loop low pass filter 54 to control VCO 56. The switch 76 is held in the "0" position in this instance, as the detector mixer output 63 is well below the threshold voltage V2 at which it would change to a logic level 1. This situation corresponds to having the antenna 10 positioned so that the main lobe 16 of its antenna pattern 15 is intersecting bearing line 18. However, when an abrupt phase change of, say, 180° occurs, such as when the return signal 33 passes through a null 24 (FIG. 1C) of the antenna pattern 15, several things occur. The phase lock loop 50 (FIG. 3) is now unstable because the slope of the loop mixer output 80 (FIG. 4) is reversed at the 180° point of the horizontal axis. An ordinary phase lock loop (not shown) would correct this unstable loop condition by adjusting the phase through 180° in either direction back to the 0° point of the horizontal axis by changing the frequency of the VCO. As a result of this correction process, an ordinary phase lock loop would send false doppler information to the receiver 36 (FIG. 3), creating system loop instability, and, thus cause the loss of doppler tracking at the antenna null during the rapid doppler rolloff shown in FIG. 2. The improved phase lock loop 50 eliminates, or at least minimizes, the false doppler being sent to the receiver 36 without interruption of the doppler roll off information (as provided in phase tracking output 77) needed to maintain doppler tracking. Now, as the propagation delay through phase reversal detector 60 is less than the propagation delay through the VCO control loop (including slow loop filter 54), detector mixer 62 begins operating in a region such that its output voltage is greater than V2, as the difference between the 90° output of VCO 56 and the receiver output 37 is now approximately 180°. Thus, Schmitt trigger 66 provides a logic signal level 1 at its output, thereby causing switch 76 to move to the "1" position. This in turn has the effect of making the loop stable by inverting the loop mixer output signal 53, which by now is only a slight positive or negative voltage. Any change caused in the output of mixer 53 is filtered by loop low pass filter 54. Since the propagation delay of loop low pass filter 54 is greater than the propagation delay of phase reversal detector 60, however, this change is not present in the VCO control signal 55. As switch 76 has switched much more rapidly than any change in voltage fed back to VCO through loop filter 54, the VCO control signal 55 eventually fed to VCO 56 changes only by a small amount. When receiver output 37 makes an opposite change in phase (i.e., as return signal 18 (FIG. 1E) again passes through a null 25 as main lobe 16 fails to becomes realigned with moving object 12), the detector mixer output 63 again changes to a voltage more negative than V1, causing the Schmitt trigger 66 to provide a logic "0" level at phase reversal control signal 67. This in turn flips switch 76 back to the "0" position where the non-inverted loop mixer output 53 is then fed to slow loop low pass filter 54. Again, only a small disturbance will be fed forward to VCO 56.
It has thus been seen that the effect of adding a phase reversal detector circuit 60 and a phase reversing circuit 70 has been to eliminate the need for the phase tracking circuit 50 to seek a stable operating state after an abrupt 180° phase shift in the antenna output signal. This alleviates the problem caused by antenna 10 not being able to rotate quickly enough to remain aligned with moving object 12.
While what has been shown and described is considered to be the preferred embodiment of this invention, several modifications become readily apparent to those of skill in the art. In particular, various other arrangements may be used to obtain the same result. The fast low pass filter 64 might be eliminated, trading rejection of unwanted signals (ground clutter, other aircraft, etc.) during signal fade outs for further reduction of false Doppler during phase reversals. Additionally, the slow low pass filter 54 might be placed before amplifiers 72 and 74, directly after the loop mixer 52. Also, amplifiers 72 and 74, rather than being placed after loop mixer 52, might be placed at one of the inputs of loop mixer 52, either operating on receiver output 37 or on VCO 0° output signal 57b. It is possible to take the output 77 of phase tracking circuit 50 after the slow loop filter rather than before it. It is felt therefore, that this invention should not be restricted to the aforementioned embodiments but rather should be limited only by the scope and spirit of the following claims.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US3109143 *||Apr 1, 1960||Oct 29, 1963||Hughes Aircraft Co||Synchronous demodulator for radiotelegraph signals with phase lock for local oscillator during both mark and space|
|US3444556 *||Dec 15, 1967||May 13, 1969||Gen Electric||Electronic phase-difference counter-circuit|
|US3600700 *||Jun 6, 1969||Aug 17, 1971||Nippon Electric Co||Circuit for phase locking an oscillator to a signal modulated in n-phases|
|US3716802 *||Apr 5, 1971||Feb 13, 1973||Muratani T||Phase locked loop with rapid phase pull-in circuit|
|US3727227 *||Sep 15, 1970||Apr 10, 1973||Mitsubishi Electric Corp||Tracking antenna system|
|US3728730 *||Sep 16, 1970||Apr 17, 1973||Mitsubishi Electric Corp||Apparatus for detecting incident angle of radio wave|
|US3772695 *||Mar 22, 1972||Nov 13, 1973||Harris Intertype Corp||False null detection in automatic tracking systems|
|US3787775 *||Mar 28, 1973||Jan 22, 1974||Trw Inc||Phase correction circuit|
|US3859658 *||Oct 16, 1972||Jan 7, 1975||Itt||Conical scan tracking system|
|US3883806 *||Mar 7, 1974||May 13, 1975||Rockwell International Corp||Demodulator circuit for phase modulated communication signals|
|US3906376 *||Jun 3, 1974||Sep 16, 1975||Rockwell International Corp||Synchronous differentially coherent PSK demodulation|
|US3956748 *||Dec 29, 1972||May 11, 1976||The United States Of America As Represented By The Secretary Of The Navy||Omnidirectional tracking weapon control system|
|US3961172 *||Dec 5, 1974||Jun 1, 1976||Robert Stewart Hutcheon||Real-time cross-correlation signal processor|
|US4010467 *||Mar 2, 1972||Mar 1, 1977||The United States Of America As Represented By The Secretary Of The Navy||Missile post-multiple-target resolution guidance|
|US4029900 *||Jan 26, 1976||Jun 14, 1977||Bell Telephone Laboratories, Incorporated||Digital synchronizing signal recovery circuits for a data receiver|
|US4135191 *||Jun 13, 1977||Jan 16, 1979||The Bendix Corporation||Coherent demodulator|
|US4217551 *||Jul 25, 1977||Aug 12, 1980||Intech Laboratories, Inc.||Phase modulated data transmission system|
|US4257007 *||Apr 16, 1979||Mar 17, 1981||The United States Of America As Represented By The Secretary Of The Navy||Active high-power bandpass filter|
|US4346477 *||Aug 1, 1977||Aug 24, 1982||E-Systems, Inc.||Phase locked sampling radio receiver|
|US4394626 *||Dec 1, 1980||Jul 19, 1983||Fujitsu Limited||Phase synchronizing circuit|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5099477 *||Jul 19, 1990||Mar 24, 1992||Fujitsu Limited||Phase matching circuit|
|US5166689 *||Nov 25, 1991||Nov 24, 1992||United Technologies Corporation||Azimuth correction for radar antenna roll and pitch|
|US5168277 *||Nov 25, 1991||Dec 1, 1992||United Technologies Corporation||Radar tracking system having target position dead reckoning|
|US5220293 *||Dec 19, 1991||Jun 15, 1993||Sun Microsystems, Inc.||High reliability phase-locked loop|
|US6556165 *||Nov 5, 2001||Apr 29, 2003||Mitsubishi Denki Kabushiki Kaisha||Antenna apparatus and waveguide rotary coupler|
|US9411039 *||Jan 21, 2011||Aug 9, 2016||Freescale Semiconductor, Inc.||Phased-array receiver, radar system and vehicle|
|US20070139261 *||Dec 19, 2005||Jun 21, 2007||Honeywell International Inc.||Systems and methods for self-calibrating a radar altimeter|
|US20090262008 *||Jun 23, 2009||Oct 22, 2009||Honeywell International Inc.||High accuracy radar altimeter using automatic calibration|
|US20130293411 *||Jan 21, 2011||Nov 7, 2013||Freescale Semiconductor ,Inc.||Phased-array receiver, radar system and vehicle|
|U.S. Classification||342/103, 331/17, 331/25, 327/231, 342/77, 342/442, 329/345, 375/327|
|International Classification||H03L7/087, H03L7/10, G01S13/68, G01S13/58, G01S13/66|
|Cooperative Classification||G01S13/68, H03L7/087, H03L7/10, G01S13/586|
|European Classification||G01S13/58G2, H03L7/10, H03L7/087, G01S13/68|
|Apr 20, 1987||AS||Assignment|
Owner name: RAYTHEON COMPANY, LEXINGTON, MASSACHUSETTS 02173,
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:MAGOON, JOHN E.;REEL/FRAME:004709/0434
Effective date: 19870416
|Sep 5, 1989||CC||Certificate of correction|
|Sep 22, 1992||REMI||Maintenance fee reminder mailed|
|Feb 21, 1993||LAPS||Lapse for failure to pay maintenance fees|
|May 4, 1993||FP||Expired due to failure to pay maintenance fee|
Effective date: 19930221


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domain: design


text:
Bank jobs update! HDFC Bank adds over 21,400 employees in FY 2021-22
HDFC Bank reported its Q4 earnings results for FY22 on Saturday. Among other things, the bank hired over 21,400 in the financial year gone by. The bank said, as of March 2022 end, it had 141,579 employees as against 120,093 as of March 31, 2021.
ET Now Digital
Updated Apr 16, 2022 | 09:18 PM IST
Photo : PTI
While IT sector giants frequently hog the headlines for their ambitious yearly hiring figures, companies from other sectors go under the radar. India’s largest private bank HDFC Bank, on Saturday, reported its quarterly earnings results for Q4 of financial year 2021-22 (FY22); among other things, the bank said it hired 21,483 employees during the FY22. While the figure may not be as significant as those churned out by a TCS or an Infosys, it points towards improving business environment as the economy recovers from the impact of Covid-19.
The private lender also reported a dip of 29% in bad loan provisioning and improvement in asset quality— yet another sign of an improvement in business climate.
As of March 31, 2022, the bank's distribution network consisted 16,342 branches and 18,130 ATMs,cash deposit and withdrawal Machines (CDMs) across 3,188 cities and towns as against 5,608 branches and 16,087 ATMs, CDMs across 2,902 cities and towns as of March 31, 2021. 50% of its branches are in semi-urban and rural areas, the bank said in a statement.
“The number of employees were at 141,579 as of March 31, 2022 (as against 120,093 as of March 31, 2021); in addition, we have 15,341 business correspondents, which are primarily manned by Common Service Centres (CSC),” it added.
HDFC Bank reported a 22.8% yearly jump in standalone net profit during the fourth quarter of the financial year 2021-2022 (Q4FY22) to Rs 10,055.20 crore on the back of a 29% dip in bad loan provisioning during the period. Net profit in the corresponding March quarter of FY21 stood at Rs 8,186.51 crore. The banking sector bellwether’s Q4FY22 reported net profit figure was lower than an ET Now poll of Rs 10,200 crore.
The increase in profits were boosted by robust interest income, better asset quality and lower provisions.
Net interest income, the difference between interest earned by lending and interest given on deposits to customers, rose by 10% to Rs 18,872.70 crore from Rs 17,120.20 crore in the FY21 March quarter. The private lender reported Rs 17,543 crore interest income in the preceding December 2021 quarter.
End of Article
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domain: finance


text:
I was very pleased with the service I got when hiring the car from you and as we are on holiday in Nerja once a year I will definitely hire from you again.
From: Alec Thrippleton
I can't say I was overly impressed by your service. Given that the Elderly rep who served me was rude and arrogant.
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From: Peter Mcneil
We rented a Fiat Punto from 14 - 28 September 2011 and were very satisfied.
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Booked a car through your company for the first time in September 2011. The car condition and personal service was as advertised. I will certainly book through malagacar.com again
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Hello, beginning with the reservation and ending with the transportation to the airport for the return trip, everything worked out perfectly.
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From: Milan Duvnjak
Address: Av. del Comandante García Morato, 34, 29004 Málaga.
Telephone: +34 952 17 60 30. E-mail: email@example.com.
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domain: travel