Svante Björklund

Evaluation of a micro-Doppler classification method on mm-wave data

Radar micro-Doppler signatures (MDS), which show how different parts of the target move, can be utilized for security and safety applications like detection and assessment of human activity at airports, nuclear power plants etc. We have evaluated a MDS classification method on measured data at 77 GHz. The important part of the method is the feature extraction, which is based on selecting the strongest parts of a Cadence-Velocity Diagram (CVD), which expresses how the curves in the MDS repeat. By our classification of MDSs of human gaits we study also how MDSs of more general target types and activities can be distinguished. We have analyzed and improved the method. The method is sound with good classification results but needs further evaluations and improvements.

On the Use of MEMS Phase Shifters in a Low-Cost Ka-band Multifunctional ESA on a Small UAV

We present a system concept for a Ka-band multi-functional electronically steerable antenna (ESA) on a small UAV that is based on using sub-arrays with low-loss RF MEMS phase shifters. Our analysis shows that low phase shifter losses are critical if the dissipated radar hardware DC power should fit within the given requirements. The results presented in this paper also indicate that adequate performance (in terms of 2 dB of average losses at 35 GHz) can be possible to achieve with a Ka- band 4-bits MEMS phase shifter design made on quartz.

Human gait parameter estimation based on micro-doppler signatures using particle filters

Monitoring and tracking human activities around restricted areas is an important issue in security and surveillance applications. The movement of different parts of the human body generates unique micro-Doppler features which can be extracted effectively using joint time-frequency analysis. In this paper, we describe the simultaneous tracking of both location and micro-Doppler features of a human using particle filters (PF). The results obtained using the data from a 77 GHz radar prove the successful usage of particle filters in tracking micro-Doppler features of the human gait.

Technical communique: An improved phase method for time-delay estimation

A promising method for estimation of the time-delay in continuous-time linear dynamical systems uses the phase of the all-pass part of a discrete-time model of the system. We have discovered that this method can sometimes fail totally and we suggest a method for avoiding such failures.

Clutter properties for STAP with smooth and faceted cylindrical conformal antennas

Conformal antennas, which assume the shape of the platform, have several advantages; like reduced weight and space, aerodynamic design and increased field of view. We are interested in detection of moving ground targets with air-borne radar with faceted or smooth vertical half-cylinder or planar antennas with different subarray sizes. We simulate radar systems and study clutter properties which are important for suppressing the clutter with STAP (Space-Time Adaptive Processing), properties by which we can compare the antennas. We use old analysis tools and propose some new which are easy to interpret and draw conclusions from. We find that the faceted and smooth half-cylinder antennas have no significant differences in clutter suppression performance. The plane antenna has poorer performance. The subarray division is more important than the antenna geometry. The number of antenna channels is related to the clutter rank and the clutter fraction of the signal space.

Refined method for terrain scattered interference mitigation

Terrain scattered interference mitigation methods for airborne radar have been described in previous papers and deconvolution methods for interference suppression have been proposed. This paper describes a refined method for terrain scattered interference mitigation and investigates performance for different conditions and limitations. An important part of the method is a threshold function to enable least squares estimation of the multipath impulse response. Least squares estimation can be applied if the impulse response is time limited or if a limited number of impulse response coefficients are required for sufficient interference suppression. The impulse response estimation can be performed either before or within the coherent processing interval. It is assumed that the direct path signal can be accurately estimated without strong multipath errors. Small relative Doppler shift errors are required between the direct path and the terrain scattered paths. Several strong jamming signal sources cannot be resolved and suppressed. Receiver blocking gives errors in the impulse response estimate and jamming signal residues in the main beam signal. Clutter signals might have to be suppressed to get accurate impulse response estimates. Bandwidth effects must be considered to get numerical stability in the inverse filtering and deconvolution operations. The refined method can suppress interference down to the receiver noise level in simple terrain scattering scenarios.

Measurement and analysis of multipath by a rough surface reflector using a digital array antenna

A receiving digital array antenna and a rough surface reflector have been used in multipath measurements, whose purpose is to learn more about undesired multipath surface reflections (surface clutter) in radar and how to suppress the reflected signals. The multipath and direct signals were analyzed by Capon power direction-of-arrival spectrum and by the eigenvalues of the spatial correlation matrix. Motion of radar, targets and jammers was simulated by moving the reflector, which also resulted in decorrelation of the multipath signals. The analysis showed that the number of large eigenvalues, and accordingly the required adaptive suppression performance, is dependent on the correlation between the signals and on the number of transmitter signals.

Fast-Time and Slow-Time Space-Time Adaptive Processing for bistatic radar interference suppression

In bistatic radar with transmitter and receiver geographically separated the interference from ground clutter and the direct path signal transmitter - receiver will be strong and must be suppressed in order to detect the target. We apply FT-STAP (Fast-Time Space Time Adaptive Processing) to the suppression, which is unusual, and compare with conventional ST-STAP (Slow-Time STAP) by simulations in order to see whether FT-STAP is an alternative to ST-STAP. The performance of FT-STAP is much worse than of ST-STAP. We give an explanation for this, which also may be the basis for large improvements of FT-STAP. Moreover, we suggest two new performance measures.

A three-dimensional displaced phase center antenna condition for clutter cancellation

In moving radar, e.g. airborne radar, the clutter from land and sea needs to be suppressed in order to detect the target. One approach to total cancellation of the clutter is Displaced Phase Center Antenna (DPCA). DPCA assumes that the antenna elements are positioned on a line parallel to the velocity vector of the radar platform so that the elements can take each others positions at different points of times. This paper theoretically investigates if it is possible with other antenna element positions, e.g. in three dimensions, for a total cancellation of the clutter. We arrive at a condition which conforms to the principle that the elements should take each others positions at different times but allows other antennas than the single line parallel to the velocity vector. Our condition could be used as constraints in an optimization problem where the target signal performance is optimized. The multipulse DPCA condition is one solution to our condition.We also give two examples of non-linear antennas fulfilling our condition.

Radar micro-Doppler parameter estimation of human motion using particle filters

Human activity monitoring and tracking around restricted areas is a very crucial issue in surveillance applications. The specific motion of different parts of the human body generates unique micro-Doppler features which can be extracted effectively using joint time-frequency analysis. In this paper, we describe the simultaneous tracking of both location and radar micro-Doppler signatures of a human target using particle filtering (PF). The results obtained using the data from a specifically developed radar for these kind of applications operating at 77 GHz frequency, prove the successful usage of particle filters in tracking micro-Doppler features of the human gait.