A 4×1 L-band receiving phased array with full digital beamforming for four simultaneous polarizations is presented. The array is based on a reconfigurable quad-polarization antenna consisting of four patches with secondary patches to increase the bandwidth. The resulting 16 channels are combined into eight channels using hybrid couplers that provide a layer of fixed phasing. The eight channels are digitized using a Xilinx radio frequency system-on-chip (RFSoC) and the polarizer for the four polarizations (V, H, LHCP, and RHCP) and the beamformer are implemented in the RFSoC. The beamforming performance for the four simultaneous polarizations is demonstrated.

Isoflux antenna is a kind of antenna with earth coverage radiation pattern, aiming to give equal power to different areas of the earth’s surface. Previous antennas with isoflux pattern are either bulky or lack multi-polarizations, making them unsuitable for small satellite applications. This paper presents a compact polarization reconfigurable antenna with isoflux pattern. The proposed antenna consists of a dielectric cylinder with a small cylinder cut off from the top, a circular patch antenna with four feeding ports. Through proper phasing of the four ports, the antenna can realize two orthogonal linear polarizations and two circular polarizations. With the use of the dielectric block above the circular radiating patch, the broadside radiation pattern can be enhanced. A 1 × 8 array is designed to validate the performance of the beam steering ability with small gain variation.

In this paper, we investigate a local average sampling and reconstruction problem using the fractional Fourier transform (FRFT). We present certain necessary and sufficient conditions under which there is an average sampling theorem for signals bandlimited in the FRFT domain.

A $4\times 1$ L-band conformal receiving array with full digital beamforming for four simultaneous polarizations and sidelobe suppression is presented. The array is based on a reconfigurable quad-polarization antenna featuring four primary patches with secondary patches to enhance the bandwidth. The resultant 16 channels are combined into eight channels through hybrid couplers which introduce the required fixed phasing. The eight channels are digitized and processed in an AMD radio frequency system-on-chip (RFSoC). The polarizer for the four polarizations (HP, VP, LHCP, and RHCP) and the beamformer are implemented in the RFSoC as well as suppression of sidelobe levels (SLL). The beamforming performance of the conformal array is demonstrated for several beamsteering cases.

An L-band 4x4 dual-polarization array with full digital receiving beamforming using two synchronized radio frequency system-on-chip (RFSoC) is presented. The array has 32 dipoles, 16 for each polarization, connected to the 2x16 channels of the two RFSoCs. The constituting element for the array are two dipoles placed orthogonal to each other. Details of the dipoles, the antenna array, the synchronized RFSoCs, and the calibration are provided. The digital beamformer is first compared with an analog beamformer for measured boresight patterns. Subsequently, digital beamsteering is demonstrated in elevation. The array provides the building block for larger arrays with application in synthetic aperture radar (SAR).

A flexible dual linear polarized $\mathbf{H}$-shaped aperture coupled S-band array is presented. The array uses flexible polyimide printed circuit board (FPC) technology and polyethylene foam (PF-4). The antenna comprises an aperture FPC layer, two separate FPC layers for the feed networks of the orthogonal polarizations, and an FPC patch. These layers are separated by PF-4 foam to enable conformability. The antenna is tested on a flat surface and conformed to cylindrical surfaces with radius of $\mathbf{2 0 0} \mathbf{~ m m}, \mathbf{1 5 0} \mathbf{~ m m}$, and $\mathbf{1 0 0} \mathbf{~ m m}$. The measured antenna provides conformability, dual linear polarization, high impedance bandwidth (20-25%), and port isolation larger than $\mathbf{3 0} \mathbf{d B}$.

Radio frequency system-on-chip (RFSoC) has be-come a promising candidate for replacing traditional analog and digital front-ends in the development of fully digital phased arrays. As the sampling frequency is limited to a few GHz, RFSoC can't be used for direct sampling at X-band. In this contribution, an X-band phased array receiver system with RFSoC is presented, which includes down-conversion to L-band, in which all the channel imperfections are incorporated in the beamforming algorithm. A rigid-flexible $4\times 4$ antenna array, consisting of four subarays, is designed and fabricated for demonstration and verification. The proposed method is demonstrated using minimum variance distortionless response (MVDR) beamforming applied in the Xilinx RFSoC ZCU111.

Compact and low profile shared aperture dual-band antennas are presented for space applications. The shared aperture antennas consist of a regular stacked patch for the high band and two channel shaped patch antennas with differential feed for the low band. The mutual coupling between antennas working at two bands is suppressed by using antennas with dual-resonance for out-of-band radiation suppression. A prototype operating at low band (1.04–1.11 GHz) and high band (1.19–1.35 GHz) is fabricated and measured. The measured results generally agree with the simulated results, making it a candidate for shared aperture dual band applications.

A foldable dual linear polarized antenna with gamma match at L band is presented. Two crossed dipoles are fed by two feed networks with gamma match to achieve the two polarizations. Since the gamma match uses the ground in the center of the radiator, it is relatively easy to extend the conventional single polarization to dual polarization. The feed networks are printed on two sides of a rigid PTFE substrate, while the radiators are printed on one side of flexible copper cladded polyimide substrate. Taking advantage of feed network’s planar configuration and the use of flexible substrate, the dualpolarized antenna can be folded with low profile. Thus the proposed dual polarized dipole antenna is a good candidate for L-band space applications where the antenna must be stowable and deployable.

A stowable and deployable 4×4 bowtie array at L-band is presented. The 16 bowtie antennas are fabricated using standard FR-4. The bowtie array uses flexible copper-clad kapton with supporting narrow aluminum channels to replace the conventional rigid ground plane. A size reduction of about 85% is achieved when the antenna is stowed. The measured gain, excluding the losses of the feed network, is between 16 dBi and 19.5 dBi over the frequency band of interest from 1.2 GHz to 1.5 GHz.

Compact and low-cost antennas with reconfigurable patterns are of great interest for communication and observation systems. This type of antenna can enable main beam tilting and provide wide angle beam steering as compared to the narrow beam of a high gain antenna [1]. Pattern reconfigurable antennas also have drawn significant attention for improving the performance of satellite communication systems. Various designs are presented in literature for pattern reconfigurable antennas [2]. Most of the designs are based on conventional rigid substrates, which is not useful for compact stowage and deployment in space [3].

Recently, synthetic aperture radar (SAR) image change detection has become an interesting yet challenging direction due to the presence of speckle noise. Although both traditional and modern learning-driven methods attempted to overcome this challenge, deep convolutional neural networks (DCNNs)-based methods are still hindered by the lack of interpretability and the requirement of large computation power. To overcome this drawback, wavelet scattering network (WSN) and Fourier scattering network (FSN) are proposed. Combining respective merits of WSN and FSN, we propose Stockwell scattering network (SSN) based on Stockwell transform (ST), which is widely applied against noisy signals and shows advantageous characteristics in speckle reduction. The proposed SSN provides noise-resilient feature representation and obtains state-of-the-art performance in SAR image change detection as well as high computational efficiency. Experimental results on three real SAR image datasets demonstrate the effectiveness of the proposed method.

A low-cost L-band antenna with reconfigurable quad-polarization is presented. The antenna consists of four identical radiating elements. Each element comprises two stacked rectangular patches to achieve more than 10% bandwidth. Through proper phasing of the four elements, the antenna can realize two orthogonal linear polarizations and two circular polarizations. To demonstrate the concept, an antenna is realized using FR-4 substrate. The measured 10-dB input return loss bandwidth is 11%. And the measured 3-dB gain bandwidth is from 1.21 GHz to 1.36 GHz, with a maximum gain of 8.8 dBi for both linear polarization and circular polarization.

The synchrosqueezed wavelet transform (SSWT) has been proven to be a powerful time-frequency analysis tool. However, this transform is unable to deal with signals with fast varying instantaneous frequencies. The objective of this paper is to overcome this deficiency using the fractional wavelet transform (FRWT), which is a generalization of the conventional wavelet transform. We first propose a synchrosqueezed FRWT (SSFRWT), which shares many properties of its SSWT counterpart while offering attractive new features. Then, we present a theoretical analysis of the SSFRWT, including the derivation of its basic properties. Moreover, we show that the discrete form of the SSFRWT admits efficient numerical implementation akin to that of the SSWT. Finally, the theoretical derivations are validated via simulations.

This paper proposes a novel circular polarized microstrip array with high gain for satellite communication in X-band. In order to extend the impedance bandwidth, the novel single-feed unit element is created without adding the profile. The proposed antenna employs the sequential rotation technique to improve the axial ratio bandwidth with high circular polarization purity. The final design, with an overall size of 91.6 mm x 45.8 mm×1.7 mm is simulated. The proposed antenna can provide an impedance bandwidth of 62.1% from 8.83 GHz to 16.78 GHz, and 3 dB axial ratio bandwidth from 9.84 GHz to 11.52 GHz. The realized gain at the center frequency is 16.4 dBi (with 3-dB gain in band ranging from 9.70 GHz to 12.18 GHz, covering the whole axial ratio bandwidth). Thus, the proposed low-profile circular polarized antenna is suitable for X-band satellite applications.

The wavelet scattering convolution network (SCN) have recently developed as a kind of effective feature extractor, which has achieved a great performance in signal and image processing applications. Unfortunately, as feature extractor, SCN is not appropriate to mimic the visual system of mammals in image classification tasks, so that STFT-based time-frequency scattering convolution network (TFSCN) is proposed. However, TFSCN is limited by a major drawback: it is only available for stationary signals’analysis but not for non-stationary ones, since STFT can viewed as linear translation-invariant filters in the FT domain intrinsically. The aim of this paper is to overcome this weakness using the short-time fractional fourier transform (STFRFT) which is a bank of linear translation-variant bandpass filters and thus may be used for non-stationary signal analysis. First, We present the fractional time-frequency scattering transform based upon the STFRFT. Then a generalization of TFSCN’s structure dubbed FRTFSCN is illustrated. The significant performance of FRTFSCN are shown via experiment simulations.

This paper proposes a new wide-beam bifilar helix antenna with earth coverage beam for satellite communication. Former helix antennas for micro-satellites are focused on narrow-beam high-gain purpose and hard to realize the desired beam pattern within a wide angle range, making them unsuitable for earth coverage applications. This novel antenna realizes the uniform illumination of the earth's surface with miniaturized structure. (The earth coverage radiation pattern is obtained within the beamwidth of θ in the range of ±56°). According to the calculation, the antenna is modeled and simulated. The simulation results show good agreement.