The terahertz frequency modulation continuous-wave (THz FMCW) imaging technology has been widely used in non-destructive testing applications. However, THz FMCW real-aperture radar usually has a small depth of field and poor lateral resolution, thus restricting the high-precision imaging application. This paper proposes a 150-220 GHz FMCW Bessel beam imaging system, effectively doubling the depth of field and unifying the lateral resolution compared to the Gaussian beam quasi-optical system. Moreover, a THz image restoration algorithm based on local gradients and convolution kernel priors is proposed to eliminate further the convolution effect introduced by the Bessel beam, thereby enhancing the lateral resolution to 2 mm. It effectively improves the image under-restoration or over-restoration caused by the mismatch between the ideal and actual point spread function. The imaging results of the resolution test target and semiconductor device verify the advantages of the proposed system and algorithm.

Passive multifrequency microwave sensors frequently struggle with difficulties of nonuniform spatial resolution among multiple channels. The raw measurements in the land-sea transition zone are seriously contaminated. Conventional analytical deconvolution techniques suffer from the tradeoff between spatial resolution enhancement and noise amplification, leading to low data integrity in the practical spatial resolution matching application. To provide multichannel microwave radiometer (MWR) data with matching levels of spatial resolution, a method based on iterative deconvolution with close loop priors (ICLP) is proposed. Specifically, a destriping module is first utilized as a preprocessing step to maintain high data integrity. Then, the close loop mechanism using sparse adaptive priors is proposed to balance the spatial resolution and data integrity enhancement. Also, progressively iterative deconvolution is introduced to realize controllable levels of spatial resolution enhancement (spatial resolution matching) for multichannel data to reach a consistent level. Experiments performed using both simulated and actual microwave radiation imager (MWRI) data demonstrate the validity and effectiveness of the method.

An improvement of the wide-angular scan-loss compensation (SLC) and sidelobe level (SLL) in a small linear array with 23 elements is discussed. The array integrates small subarrays with an optimized pattern for SLC, while the SLL suppression is obtained by using a combination of elements with phase steering only and elements with amplitude/phase control in the center. This combination leads to a less number of T/R module. When the antenna is scanned to ±60°, a maximum first and peak SLL (FSLL and PSLL) of -15.1 dB are obtained. In addition, a -4.6 scan-loss is obtained, it means that the SLC is 2.4 dB with a Cavity-backed U-slotted Patch (CUP) antenna. These performance results are very attractive in particular for a small linear array with wide angular scanning capability.

A novel approach is proposed for building a planar array derived from linear arrays using a toolbox of different types of subarrays located parallel and perpendicular to the linear array axes. The array design assumes constant element patterns and focuses on rectangular array applications with one dimensional, wide-angular beam scanning. Optimization criteria concern a trade-off between side lobe level performance, directive gain scan-loss, reducing the number of element controls and maximizing the use of phase-only elements for beam steering. All subarray configurations and functionalities, for improving the full array performance in sidelobe level and scan-loss compensation, are analyzed and validated in detail. The step-by-step integration of different subarrays starts from the center part of the array. This center part is a linear subarray along the major axis of the rectangular array with uniform maximum amplitude and spatially stretched. This subarray is combined with cross-line subarrays perpendicular to this center axis. At both edges of the center array, two in-line, uniform-amplitude and stretched subarrays are added and combined with cross-line subarrays. The amplitude distribution of the 3 in-line subarrays and the cross-line subarrays allows for lowering the sidelobe level in the plane of scanning. Finally, at both ends of the three in-line subarrays, subarrays with two and five elements are applied for reducing the scan-loss. By assuming cos(\vartheta) element pattern results are given for a planar rectangular array with 41 elements length and 3 elements width. To lower cost and higher power efficiency, the array uses only 33 multi-bit phase shifters, 12 1-bit phase switches, and 4 attenuators for amplitude control. Optimized broadside and 60° scanning patterns are compared and show improved performance in directive gain D=24.4 dBi (broadside), D=19.9 dBi (60°) and in \text {SLL}=-21.6 dB (broadside), \text {SLL}=-19.5 dB (60°).

An advanced design, adding a significant first sidelobes level (FSLL) improvement to a previously introduced wide-angular-scanning, linear array prototype with demonstrated scan-loss compensation (SLC) and sidelobes suppression features is discussed. The linear array makes use of in-line subarrays for SLC and an additional amplitude taper in its central, uniform region for lowering the FSLL with as much as 4\mathrm{d}\mathrm{B} at \pm 60 {\mathrm{o}} scanning (13\mathrm{d}\mathrm{B} at \pm 20 {\mathrm{o}} scanning). Several Taylor-type amplitudes tapers are compared, the best overall performance improvement being observed for a -18dB prototype taper. The advocated solution is highly suitable to high-sensitivity radars requiring a fast-scanning, fan-beam.

A new technique to enhance the indication of moving targets is proposed, which makes use of randomized Stepped Frequency Continuous Wave (SFCW) modulations, where the frequency order is changed from pulse to pulse. This kind of signals gives the possibility to discriminate target responses whose Doppler spectrum is folded back into the clutter region. The discrimination is performed directly during the range compression, so avoiding spectrum aliasing in the Doppler domain. For the range compression, the deramping technique, commonly used with linear SFCW, is extended to the case of non linear stepped modulations. In this way, the sampling constraints can be relaxed also when using randomized SFCW signals, allowing the same sampling frequency as with deramped linear SFCW, and reducing therefore the system complexity. Compared to linear modulations, randomized SFCW signals give also the advantage to suppress range ambiguities and therefore the capability to look at further range.

A novel approach is proposed for compensating the scan loss in wide-angular scanning array antennas due to the pattern falloff of physical radiators. The method is based on replacing elements in (linear) arrays with sub arrays with enhanced radiation intensity at large angles. This strategy is best applicable in the case of sparse arrays that intrinsically provide the space for accommodating sub arrays. An optimised linear sub array, with 5 dB radiation intensity enhancement at 60° is designed. This sub array is then incorporated in linear array antennas with (approximately) 50% thinning factors. An up to 1.2 dB improvement of the maximum directivity at 60° beam scanning is obtained. The obtained results allow conjecturing that a similar strategy, when applied to planar arrays, will lead to an even more significant scan-loss reduction, this yielding a substantial performance enhancement for wide-angular scanning radar array antennas.

A full-scale concept demonstrator for the scan loss mitigation via integrating subarrays in sparse, linear arrays is presented for the first time. The array uses technologically attractive cavity-backed, U-slot, patch antennas. An effective computational philosophy is proposed, validated and applied for a full electromagnetic characterisation of the resulting very large, non-uniform array. The computational results highlight impressive improvements when compared to the performance of sparse arrays comprising elementary radiators, exclusively. These results provide compelling arguments for the superiority of a physical concept demonstrator designed along these lines.