Radars capable of measuring targets' Polarimetrie characteristics provide valuable supplementary information for a more reliable detection, identification and physical parameters estimation. The novelty of this work lies in that it had not been previously possible to perform measurements for a comparison of polarimetric orthogonal simultaneous vs time-multiplexed sequential sounding signals in real-time, because of the time delay required to reconfigure a system to cater for the different waveform types. During this time delay, an observed non-stable target(s) would have had substantially moved, yielding both measurements not directly comparable. In this paper we present the polarimetric interleaved simultaneous-time-multiplexed waveform, justifications for the PARSAX radar setup upgrade, and the system implementation with a focus on the receiver FPGA. Preliminary results from the comparison are revealed. The data and results will be used for a future detailed comparative analysis of sounding waveforms and their impact on polarimetric target characteristics.@en

A reconfigurable range-Doppler processing method for FMCW radar is presented. By concatenating beat-frequency signals from more than one sweep, a continuous beat-frequency signal for the whole coherent processing interval (CPI) can be created. As a result, continuous targets' observation time is extended beyond that of a single chirp duration, leading to range resolution improvement. The created continuous beat-frequency signal can be split in the digital domain to any two-dimensional slow-time and fast-time matrices with the same number of elements as in the original signals, which offers a realization of a software-defined pulse/sweep repetition rate in range-Doppler processing. The signal concatenation is done in the short-time Fourier transform (STFT) domain, where the beat-frequency slices are extrapolated to compensate for the observation time lost in the transient region between sweeps, and then a phase correction is applied to each frequency-slice as appropriate, followed by an inverse STFT (ISTFT). The proposed technique is verified with simulation and experiments with an FMCW radar for stable and moving target scenarios. We found that the method allows for range resolution improvement without the transmission of additional bandwidth and also allows for the ability to observe different resolution granularities in parallel from one CPI. It additionally allows the decoupling of the transmitted PRF from the Doppler processing PRF, permitting the facility to observe different unambiguous Doppler velocity intervals from one CPI, without compromising on the total CPI processing gain.@en

A frequency-modulated continuous-wave (FMCW) radar interference mitigation technique using the interpolation of beat frequencies in the short-time Fourier transform (STFT) domain, phase matching, and reconfigurable linear prediction coefficients estimation for Coherent Processing Interval processing is proposed. The technique is noniterative and does not rely on algorithm convergence. It allows the usage of the fast Fourier transform (FFT) as the radar's beat-frequency estimation tool, for reasons such as real-time implementation, noise linearity after the FFT, and compatibility with legacy receiver architectures. Verification is done in range and in range-Doppler using radar experimental data in two ways: first by removing interferences from interference-contaminated data and second by using interference-free data as the reference data, and processing it--as if it had interferences--using the proposed technique, inverse cosine windowing and zeroing for comparison. We found that processing with the proposed technique closely matches the reference-data and outperforms the inverse cosine windowing and zeroing techniques in 2-D cross correlation, amplitude, and phase average errors and phase root-mean-square error. It is expected that the proposed technique will be operationally deployed on the TU Delft simultaneous-polarimetric PARSAX radar.@en

Classical saw-tooth Frequency Modulated Continuous Wave (FMCW) radars experience a coupling between the maximum unambiguous Doppler-velocity interval, maximum operational range, range-resolution and processing gain. Operationally, a trade-off is often necessarily made between these parameters. In this paper, we propose a waveform and a processing method that decouples the aforementioned parameter dependencies at the price of using multiple receiver channels within the radar. The proposed method exploits the fact that beat-frequency signals have the same baseband frequency, even if the transmitted and received chirps occupy different radio frequency bands, and have different center-frequencies. We concatenate those baseband signals in the time-frequency domain to restore the range-resolution and processing gain. An overview of FMCW parameters trade-off for related waveforms and a feasibility and limitations analysis of implementing the proposed processing method are presented. The method is verified by simulations and experiments with an FMCW radar for stable, moving and extended-moving targets. We additionally have highlighted its non-idealities in the simulations and experiments. We found that the proposed method indeed alleviates the trade-off between FMCW operational parameters and allows the extension of the Doppler ambiguity interval without compromising on those parameters.@en

Real-time reconfigurable digital heterodyne LFMCW radar systems offer degrees of flexibility in selecting parameters for the transmitted waveform and for the digital receiver signal processing chain. These parameters are tightly-coupled and a change in any of them will affect the rest, and subsequently the entire system. We listed these parameters and performed an analysis to aid radar system designers to optimally select suitable permutations of them depending on their reconfigurability and system requirements. Deramping of a real-sampled up-going LFMCW signal was used as a basis of this study. This paper presents a brief abstract of the analysis results, with examples of the effects of different parameter permutations. We found that this analysis has enabled us to assess FPGA signal processing blocks' reconfiguration parameters, and to identify radar system boundaries/limitations. These findings will be applied to future reconfigurable radar receiver research at TuDelft.@en

There is a requirement for waveform orthogonality on dual or multiple channel radars to avoid cross-channel interferences. It is additionally favored that dual-channel polarization-orthogonal radars are capable of estimating target Polarization Scattering Matrix (PSM) elements simultaneously, that is within one Pulse/sweep/frame Repetition Interval (PRI). The current solution for simultaneity in Linear Frequency Modulated Continuous Wave (LFMCW) radars is to use a pair of nearly-orthogonal waveforms within the same frequency band with opposite frequency excursion slopes. This solution does not provide full orthogonality because of its susceptibility to some cross-channel interferences, where their mitigation result in difficult-to-suppress unwanted artifacts after range compression, in addition to opposite sign residual video phases which are difficult to compensate for. We propose a new pair of independent waveforms - along with their required processing steps - which satisfy both the orthogonality and simultaneity requirements, but with less undesirable artifacts than the opposite slope chirps. In this paper we present results from experimentation with simulated and radar-measured data for the new waveform. We found closely comparable results with the baseline of standard LFMCW processing. We aim to operationally use the new waveform-pair on the TuDelft PARSAX polarimetric radar.@en