This article focuses on the experimental validation of probing signals designed to enable radar operation in spectrally crowded environments using an S-band software defined radar (SDR). The tested waveforms ensure spectral coexistence between the sensing system and frequency-overlaid emitters, while optimizing radar performance. This is achieved through a bespoke notching of the radar signal spectrum to control the amount of interference injected by the radar in each shared frequency interval. In addition, some relevant features of the probing signal that influence radar performance are controlled via a similarity index, describing the maximum allowable distance between the spectrally notched waveform and a prescribed radar signal. In a first stage, the study is aimed at verifying whether the transmit and receive chains of the SDR system impair the spectral and temporal features of the designed waveforms. Subsequently, the tested signals are radiated into the environment to investigate their effectiveness to detect targets in the illuminated scene, as well as to ensure spectral coexistence in the presence of frequency-overlaid emitters. The results demonstrated that by exploiting the designed radar probing signals, the SDR system is capable of sharing spectrum with other radio frequency wireless systems while also allowing to detect both stationary and moving targets.

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This paper investigates the possibility of transmitting waveforms designed to enable spectral coexistence between radar and other Radio Frequency (RF) wireless systems via a Software Defined Radar (SDR). The design technique tested in this study nominally enables the placement of notches in the spectrum of the synthesized probing radar signal. Their widths and depths are set during the design stage so as to accounting for the interference into each shared frequency interval, allowing for spectral coexistence. At the assessment stage, the synthesized signal is used with the PARSAX radar system, an SDR capable of operating in the S frequency band. The analysis first focuses on studying the compliance of the signal generated by the PARSAX radar with its theoretical counterpart. Subsequently, open-air experiments are conducted in the presence of stationary and moving targets. The results show that the spectral characteristics of the probing radar signal adhere well to the theoretical spectral mask, and prove the system ability to detect both stationary and moving targets.

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The phase coded FMCW and its properties for joint sensing and communication are studied. Two different receiver structures for the sensing properties of this waveform are compared theoretically and experimentally. It is shown both by simulations and experiments that the phased coded FMCW combines communication capabilities of PMCW and sensing capabilities of FMCW while using a realizable hardware complexity for an automotive 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

Weather radar is well recognized as an effective sensor for obtaining the microphysical and dynamical properties of precipitation at high spatial and temporal resolution. Radar calibration is one of the most important prerequisites for achieving accurate observations. In this article, a portable, cost-effective and repeatable radar calibration technique, namely, unmanned aerial vehicle (UAV)-aided radar calibration, is proposed. A UAV serves as the stable aerial platform carrying a metal sphere, flying over the radar illumination areas to complete the calibration process. The flying routine of the UAV can be pre-programmed, and thus, the antenna pattern regarding different elevation and azimuth angles can be retrieved. To obtain the position of the sphere, the real-time single-frequency precise point positioning-type global navigation satellite system solution is developed. In addition, the radar constant is calculated in the range-Doppler domain, and only the data where the metal sphere separates from clutter and other objects are selected. The S-band polarimetric Doppler transportable atmospheric radar (TARA) is used in the calibration campaign. The experiments demonstrate the following results: 1) antenna pointing calibration can be completed and 2) antenna pattern can be retrieved and weather radar constant can be accurately calculated.@en

This paper outlines the work on the design of a reconfigurable receiver for the PARSAX radar. The FPGA based digital receiver samples incoming signals at intermediate frequency (IF) and processes signals digitally instead of using more conventional analog approaches. In this way it offers more robust system stability and avoids unnecessary multi-channel calibrations of analog circuits. The processing algorithms implemented in the FPGA chips can be reconfigured adaptively regarding to different transmitted waveforms, and without changing of hardware. The successful development of reconfigurable receiver has been verified by experiment and yields maximum flexibility for the whole radar system.@en

The article describes the IRCTR PARSAX radar system. It is an S-band high-resolution Doppler polarimetric FMCW radar utilizing dual-orthogonal sounding signals. The signals allow for measuring in one sweep all elements of the radar targets polarization scattering matrix simultaneously. PARSAX characteristics are: modular system set-up, highly-optimised linearity and sensitivity of the RF front-end receiver, use of a flexible multi-channel arbitrary waveform generator as sounding waveforms source, high-resolution analogue to digital conversion of the received signals at sufficiently high intermediate frequency and FPGA-based programmable digital multi-channel receiver. The paper shows that PARSAX is a unique radar research platform for studying arbitrary sounding waveforms with bandwidth up to 50 MHz and processing algorithms in Doppler-polarimetric radar.@en

An FPGA-based digital receiver has been developed to perform real-time processing for the PARSAX radar. It is a fully polarimetric FMCW radar with dual-orthogonal sounding signals, which has the possibility to measure all elements of the radar targets polarization scattering matrix simultaneously, in one sweep. This paper presents the design principles including the range profile interpretation, optimal parameters selection and processing gain analysis. A novel parallel deramping processing architecture suitable for FPGA implementation is introduced; the overall digital de-ramping processing has been implemented in one chip of FPGA and verified by experimental results.@en

Polarimetric agile radar is able to measure all elements of the polarization-dependent backscattering matrix (BSM) simultaneously. Polarimetric calibration is an important issue to determine the BSM accurately. This paper focuses mainly on the internal and semi-external calibration of the dual-channel polarimetric agile radar system. The paper presents a novel approach based on very up to date methods used for cross-validation between simulations and measurements. Error models of all parts of the radar system will be derived from the approach and implemented in the radar system calibration. After calibration, the good matching performance for relative measurement between two channels demonstrates the validity of the here-proposed calibration approach.@en

Polarimetric agile radar is able to measure all elements of the polarization-dependent backscattering matrix (BSM) simultaneously. Polarimetric calibration is an important issue to determine the BSM accurately. This paper focuses mainly on the internal and semi-external calibration of the dual-channel polarimetric agile radar system. The paper presents a novel approach based on very up to date methods used for cross-validation between simulations and measurements. Error models of all parts of the radar system will be derived from the approach and implemented in the radar system calibration. After calibration, the good matching performance for relative measurement between two channels demonstrates the validity of the here-proposed calibration approach.@en