Active calibration target for bistatic radar cross‐section measurements

Pienaar, M.; Odendaal, J.W.; Joubert, J.; Cilliers, J.E.; Smit, Jw

doi:10.1002/2015rs005931

Cited by 14 publications

(8 citation statements)

References 16 publications

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“…Neither the trihedral corner reflector nor the reciprocity principle is usable in the bistatic case. Bistatic calibration is thus performed via other approaches, such as a modified dihedral with a varying opening angle [41], [42], a crosspolarizing cylinder [43], or an active calibrator [5], [44], [45].…”

Section: A State Of the Art 1) Bistatic Radar For Earth Observationmentioning

confidence: 99%

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Calibration and Operation of a Bistatic Real-Aperture Polarimetric-Interferometric Ku-Band Radar

Stefko

Frey

Werner

et al. 2022

IEEE Trans. Geosci. Remote Sensing

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This article presents the bistatic operation mode and the performance analysis of KAPRI, a terrestrial frequency-modulated continuous-wave (FMCW) Ku-band polarimetric radar interferometer capable of acquiring bistatic fullpolarimetric datasets with high spatial and temporal resolution. In the bistatic configuration, the system is composed of two independently operating KAPRI devices, one serving as a primary transmitter and receiver and the other as a secondary receiver. The secondary bistatic dataset is affected by possible offsets between the two devices' reference clocks, as well as distortions arising from the bistatic geometry. To correct for this, we present a two-chirp bistatic FMCW signal model, which accounts for the distortions, and a reference chirp transmission procedure, which allows correcting the clock offsets in the deramped signal time domain. The second challenge of operation of a bistatic polarimetric system is polarimetric calibration since it is not possible to employ purely monostatic targets such as corner reflectors. For this purpose, we developed a novel active calibration device Variable-Signature Polarimetric Active Radar Calibrator (VSPARC), designed for monostatic and bistatic calibration of all polarimetric channels. VSPARC and its associated novel polarimetric calibration method were then used to achieve full calibration of both KAPRI devices with polarimetric phase calibration accuracy of 20 • and 30-dB polarization purity in field conditions. This article thus presents a complete measurement configuration and data processing pipeline necessary for synchronization, coregistration, and polarimetric calibration of bistatic and monostatic datasets acquired by a real-aperture FMCW radar.

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Section: A State Of the Art 1) Bistatic Radar For Earth Observationmentioning

confidence: 99%

“…Other passive targets such as a modified dihedral proposed in [41] would likely have sufficient RCS but fail requirements 2-4 since they require precise alignment relative to position of the radar devices. For these reasons, an active calibration device was selected, similar to other bistatic campaigns [5], [45], [60].…”

Section: H Polarimetric Calibration Targetmentioning

confidence: 99%

Calibration and Operation of a Bistatic Real-Aperture Polarimetric-Interferometric Ku-Band Radar

Stefko

Frey

Werner

et al. 2022

IEEE Trans. Geosci. Remote Sensing

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“…At present, several bistatic calibration methods based on point targets have been proposed, which can be roughly divided into two categories. One idea is to use an active calibration target with a high radar cross-section (RCS) over a large frequency range that can be easily configured for different bistatic angles [7][8][9]; however, active calibration targets are expensive and complex to manufacture. The other view is to utilize passive calibration targets.…”

Section: Introductionmentioning

confidence: 99%

Feasibility, Design, and Deployment Requirements of TCR for Bistatic SAR Radiometric Calibration

et al. 2018

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The trihedral corner reflector (TCR) is widely used as the calibration device in monostatic synthetic aperture radar (SAR) calibration, and the performance of the TCR in radiometric calibration has been studied and verified in depth. As for the bistatic SAR system calibration problem, there have been few published studies. There is a lack of knowledge regarding the exact bistatic radar cross-section (RCS) pattern of TCR with different bistatic angles, and it is also not clear whether the TCR can be used as the calibration target in bistatic SAR. Moreover, the bistatic and monostatic radar cross-section (RCS) characteristics of the TCR are different, even if the bistatic angle is very small. Therefore, the feasibility, design, and deployment requirements of the TCR for bistatic SAR calibration should be carefully investigated. In this paper, we outline the theoretical and practical requirements that need to be satisfied when choosing appropriate calibration devices for bistatic radiometric calibration. Based on these requirements, we analyzed the bistatic RCS patterns using electromagnetic simulation, and concluded that the TCR is feasible for bistatic SAR calibration under relatively small bistatic angles (less than 6°). The change of TCR boresight with the bistatic angle is not considered generally. However, we found that the TCR boresight and peak RCS will change with the bistatic angle. We have also proposed that the bistatic angle can be extended to 20° by taking the change of the TCR boresight into account. In this condition, we should get the TCR boresight according to the bistatic angle and then align it during the deployment. Both of these two conditions have their own unique advantages. Different error sources of TCR RCS from manufacture, misalignment, and deformation were investigated quantitatively with simulations, which can provide a theoretical basis for how to design a suitable TCR and guarantee the calibration accuracy for bistatic calibration. In addition, simulation results are different from those of monostatic calibration. Through experiments, we have further verified the feasibility by comparing the quality of bistatic SAR images and point target energy with several typical bistatic angles as the TCR boresight is considered or not. If the bistatic angle is larger than 6°, taking the TCR optimum boresight into account can improve imaging quality and point target energy.

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“…2) The calibrator sensitive to bistatic angles cannot be used, such as dihedral and trihedral reflectors, because the polarimetric MIMO array has different bistatic angles in near-field measurement. For the sake of bistatic polarimetric calibration, several solutions have been proposed in [25]- [28]. A polarimetric monostatic and bistatic RCS facility operating at W -band can be calibrated by a wire mesh with high cross-polarization level [25].…”

mentioning

confidence: 99%

“…Mainlobe steered dihedral (MSD) object [27] with a high cross-polarization level can be applied for bistatic polarimetric calibration by adjusting the MSD design angles (ψ msd and φ msd ) over a large range of bistatic angles. A PARC [28] with two Vivaldi antennas has been designed to accomplish polarimetric calibration by aiming the maximum beam direction of the PARC transceiver antenna at the bistatic RCS measurement radar. Since the polarimetric MIMO array has 80 transceiver channels, it is quite time-consuming and complicated for calibration of the polarimetric MIMO array by adjusting the MSD design angles or the maximum beam direction of the PARC transceiver antenna.…”

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confidence: 99%

Calibration of a Polarimetric MIMO Array With Horn Elements for Near-Field Measurement

Kong

2020

IEEE Trans. Antennas Propagat.

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Polarimetric multiple input and multiple output (MIMO) radar is capable of acquiring target's high-resolution images and polarization scattering matrix (PSM). In this article, calibration of a polarimetric MIMO array of an instrumentation radar for near-field measurement is achieved at X-band by using a rotatable double-antenna polarimetric active radar calibrator (RODAPARC) and a metal cylinder quickly and accurately. The theoretical PSM of the RODAPARC with different antenna rotation angles is derived from Huygens' radiation electric field which is applicable to different bistatic angles. A polarimetric signal model is adopted to reduce the impact of the RODAPARC on calibration. Experimental studies are conducted on a polarimetric MIMO array which is measured and divided into quasi-monostatic and bistatic transceiver channels for assessment on the calibration performance. Promising calibration results are obtained with a polarization isolation improvement of about 16 dB and great reduction of the polarization channel gain error less than ±0.5 dB in amplitude and ±3 • in phase. The calibrated polarization signatures for classic objects are consistent with the theoretical results. Index Terms-Multiple input and multiple output (MIMO) radar, polarimetric active radar calibrator (PARC), polarimetric calibration. I. INTRODUCTIONW ITH the explosive development of multiple input and multiple output (MIMO) technology, more and more MIMO radars have been presented in [1]-[6]. MIMO is an enabling technique capable of imaging a target using only one snapshot [6], which is different from rail synthetic aperture radar (SAR) and turntable inverse synthetic aperture radar (ISAR). Polarimetric MIMO radar images the target rapidly, while also providing the polarization scattering matrix (PSM) of the target. Crosstalk and polarization channel gain error distort the receive signal in polarimetric radars. This distortion will be more serious for polarimetric MIMO radars in terms of multiple transceiver channels. Therefore, polarimetric calibration serves an important role in polarimetric MIMO radars.According to the different polarimetric calibrators, polarimetric calibration can be divided into passive [7]-[9] and Manuscript

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Active calibration target for bistatic radar cross‐section measurements

Cited by 14 publications

References 16 publications

Calibration and Operation of a Bistatic Real-Aperture Polarimetric-Interferometric Ku-Band Radar

Calibration and Operation of a Bistatic Real-Aperture Polarimetric-Interferometric Ku-Band Radar

Feasibility, Design, and Deployment Requirements of TCR for Bistatic SAR Radiometric Calibration

Calibration of a Polarimetric MIMO Array With Horn Elements for Near-Field Measurement

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