Galina Babur

Basics and first experiments demonstrating isolation improvements in the agile polarimetric FM-CW radar – PARSAX

The article describes the IRCTR PARSAX radar system, the fully polarimetric FM-CW radar with dualorthogonal sounding signals, which has the possibility to measure all elements of the radar targets polarization scattering matrix simultaneously, in one sweep.

Nearly Orthogonal Waveforms for MIMO FMCW Radar

Herein is proposed a set of nearly orthogonal waveforms based on offset linear frequency modulated (LFM) signals for multiple-input, multiple-output frequency modulated continuous wave (MIMO FMCW) radar operation. The orthogonality of sounding signals is a critical point for many multi-channel radar applications because the interference between signals can significantly limit the radars ability for observation of weak targets in the presence of strong targets and clutter. High orthogonality for the proposed waveforms can be obtained by using de-ramping processing in the MIMO FMCW radar receiver. The experimental results presented demonstrate that a high orthogonality level is achievable for a specific multi-channel FMCW radar.

Antenna Coupling Effects for Space-Time Radar Waveforms: Analysis and Calibration

In this paper, we investigate the impact of mutual coupling between the antenna array elements on the performance of a multiple-input multiple-output (MIMO) radar with colored waveform transmission (collocated coherent MIMO system). Simulation results confirm the decrease in system performance when antenna mutual coupling is taken into account. A dedicated scan-dependent calibration technique is proposed for elimination of the coupling effect. The experiments with a real X-band antenna array validate the coupling analysis and the calibration procedure presented in this paper.

Space-time radar waveforms: circulating codes

This paper describes a concept of the circulating codes covering the whole class of the space-time codes. The circulating codes do not narrow the radiated pattern of the antenna array, thus providing a wide angular coverage, possibly tunable. In turn, the beam-forming on transmit is achievable by means of the signal processing in one (or each) receiver channel. The modelling results demonstrate the efficiency of the circulating codes based on their multidimensional ambiguity functions.

Optimization of low sidelobes radar waveforms: Circulating codes

This paper presents two techniques as well as their combination for optimization of the low side-lobes space-time waveforms: circulating LFM signals. Matched filtering is implemented for the pulse compression. The ambiguity functions of the modified waveforms are analyzed for demonstration of the optimization efficiency. The simulation results show that the proposed techniques decrease the range side-lobes, with no penalty on the signal-to-noise ratio, and restore the range resolution in the beam-formed angular direction where the circulating LFM signal previously had a resonance effect. Typical sidelobe levels lower than -50dB are demonstrated over the whole angular coverage, with an 8 element antenna and 256 length codes.

Design and implementation of cross-channel interference suppression for polarimetric LFM-CW radar

This paper presents design and practical implementation of the method for cross-channel interference suppression in polarimetric LFM-CW radar with dual-orthogonal sounding signals. Simultaneously transmitted and received signals have limited orthogonality, what results in the interfering signals in the processing channels of the radar receiver. The suppression of the interfering signals is implemented in real time, characterized by simplicity and low increase of computational resources. The efficiency of the cross-channel interference suppression is demonstrated experimentally.

Reconfigurable digital receiver design and application for instantaneous polarimetric measurement

This paper presents the development of a reconfigurable receiver to undertake challenging signal processing tasks for a novel polarimetric radar system. The field-programmable gate arrays (FPGAs)-based digital receiver samples incoming signals at intermediate frequency (IF) and processes signals digitally instead of using conventional analog approaches. It offers more robust system stability and avoids unnecessary multichannel calibrations of analog circuits for a full polarimetric radar. Two kinds of dual-orthogonal signals together with corresponding processing algorithms have been investigated; the digital implementation architectures for all algorithms are then presented. Processing algorithms implemented in FPGA chips can be reconfigured adaptively regarding to different transmitted waveforms without modification of hardware. The successful development of such reconfigurable receiver extends our radar capacity and thus yields tremendous experimental flexibility for atmospheric remote sensing and polarimetric studies of ground-based targets.

Low-Cost Digital Beamforming on Receive in Phased Array Radar

This paper presents a novel low-cost technique for digital beamforming on receive in phased array radar. The presented technique can be used to synthesize multiple beam patterns in different angular directions and can be implemented after analog summation of the received signals using only one received pulse. Since the digital beamforming in our work is implemented after summation of the received signals, a reduction of the overall cost, size, and power consumption of the phased array front-end becomes possible in comparison to standard digital beamforming. The performance and effectiveness of the here-proposed beamforming technique are assessed by means of modeling and experimental verification.

Improved calibration technique for the transmit beamforming by a coherent MIMO radar with collocated antennas

In this paper we present a calibration method for mitigating the effects of mutual coupling affecting the signal radiated by MIMO radar with collocated antennas. The paper contains the measurement results that verify the proposed method. The improved scan-dependent calibration technique is proposed for elimination of the coupling effect. The experiments with a real X-band antenna array validate the calibration procedure presented in this paper.

Monopulse on transmit by means of orthogonal probing signals: Theoretical and experimental validations

Multiple-Input Multiple-Output (MIMO) radars represent a new class of sensors which combine orthogonal waveform transmissions and multichannel designs to improve specific performance of the system. Well known benefits are achieved in terms of either angular resolution, in the coherent MIMO scenario, or higher detection probability, in the statistical MIMO approach. In this paper the authors investigate the properties of the MIMO concept from another perspective. By exploiting the waveform agility characteristic of such systems, the simultaneous transmissions are used to synthesise independent channels which are then combined as for an angular monopulse detector. In fact, leading to a monopulse on transmit configuration. The analysis shows the theoretical improvement, in terms of angular accuracy, achieved by the MIMO array and the experimental results obtained by a monopulse on transmit with a simplified radar set-up.