The computational complexity of the conventional adaptive beamformer is relatively large, and the performance degrades significantly due to both the model mismatch errors and the unwanted signals in received data. In this paper, an efficient unwanted signal removal and Gauss-Legendre quadra-ture (URGLQ)-based covariance matrix reconstruction method is proposed. Different from the prior covariance matrix recon-struction methods, a projection matrix is constructed to remove the unwanted signal from the received data, which improves the reconstruction accuracy of the covariance matrix. Considering that the computational complexity of most matrix reconstruction algorithms are relatively large due to the integral operation, we proposed a Gauss-Legendre quadrature-based method to approximate the integral operation while maintaining the accu-racy. Moreover, to improve the robustness of the beamformer, the mismatch in the desired steering vector is corrected by maximizing the output power of the beamformer under a constraint that the corrected steering vector cannot converge to any interference steering vector. Simulation results and prototype experiment demonstrate that the performance of the proposed beamformer outperforms the compared methods and is much closer to the optimal beamformer in different scenarios.

In this paper, a double-lossy-layer frequency-selective rasorber (FSR) with an ultrawide reflection suppression band is presented based on the equivalent circuit approach with a clear, concise, and effective design process. First, the general equivalent circuit model (ECM) of double-lossy-layer FSRs is established and studied to reveal the mechanism of the operation band extension of the absorption-transmission (A-T) FSRs to the lower frequency. Second, a single-polarized FSR is designed inversely based on the optimized circuit parameters to fulfill the ideal desired performances. The evolution process is exhibited step-by-step and the equivalent-circuit-based design guideline is summarized. Simulation results show the single-polarized FSR achieves a low reflection band (|S ₁₁ | ≤ -10 dB) from 1.07 GHz to 12.66 GHz, with a ratio bandwidth of 11.83:1. The 80% absorption band covers 0.99-7.11 GHz (151.1%) and the -1-dB transmission bandwidth is 43.0%, ranging from 7.97 GHz to 12.33 GHz. Then, a dual-polarized FSR is further presented and optimized to preserve excellent frequency responses. In addition, the proposed FSR also achieves ultra-miniaturization and thus improves angular stability partly. Finally, a dual-polarized FSR prototype of 20 × 20 unit cells is fabricated and measured to verify the design and the measurement results coincide well with the simulation ones.

This paper describes the design of microwave/millimeter wave dual-band patch antenna array with shared aperture. The antenna array is designed of stack structure of three printed circuit boards. The Ka-band patches are fed directly with microstrip lines of the Ka-band power divider network and the E-band patches are coupling fed by the E-band power divider network through slots cut in the antenna ground. An antenna unit is studied, fabricated and measured firstly to verify the feasibility of the shared aperture structure. Finally, a shared aperture antenna array consists of a 2 × 4 Ka-band array and an 8 × 16 E-band array is designed based on the antenna unit. The E-band and the Ka-band feeding network are carefully designed to reduce the reflections, and the Ka-band feeding network combines series feed and parallel feed in order to save space. The shared aperture antenna array is fabricated and measured, and the results are presented. In order to measure the E-band array, the main port of the E-band power divider is connected to a standard WR12 waveguide through an antipodal fin-line waveguide to microstrip transition.

A compact printable multibeam antenna array is studied in this paper. The antenna system is composed of a printed Rotman lens and an antipodal dual elliptically tapered slot antenna array; both of the two components are studied, respectively, at first, and then integrated on a single printed circuit board to make up the integrated unit of the multibeam antenna array. Measured results of all components are presented.

In this letter, a low-profile circularly polarized double-folded transmitarray antenna (CP-DFTA) at Ka-band with low radar cross section (RCS) performance is proposed by introducing a novel absorptive frequency-selective polarization converter (AFSPC). The proposed AFSPC comprises an upper lossy layer and a lower linear-to-circular polarization converter (LCPC) with an air gap between them, which achieves not only in-band linear-to-circular polarization conversion but also out-of-band absorption performance with a low profile of only 0.058 $\lambda _{L}$ ($\lambda _{L}$ is the free-space wavelength of the lowest absorption frequency). Then, a double-folded transmitarray antenna (DFTA) is designed and integrated with the AFSPC to achieve the low profile of the antenna. A prototype of the low-RCS CP-DFTA is finally fabricated and measured. The measured results show that the proposed antenna achieves a peak CP gain of 25.85 dBic at 31GHz, a 3-dB gain bandwidth of 20.7% covering 26-32GHz, and a 3-dB axial ratio bandwidth of 15.9% ranging from 26 to 30.5GHz. Simultaneously, an ultra-wide 8-dB RCS reduction band of 105.2% covering 6.8-21.9GHz is achieved. The measured results are in convincing agreement with the simulated ones.

Antennas in the ultra low frequency (ULF, 300 Hz to 3 kHz) and very low frequency (VLF, 3∼30 kHz) bands are usually very large. In this study, we developed a very small antenna, which can radiate electromagnetic waves in these frequency bands. The antenna consisted of two rotating charged plates (RCPs), which were charged by the voltage source. Numerical results of the radiated far field and its frequency spectrum are presented for three cases: (a) the antenna is charged with DC voltage, (b) the antenna is charged with AC voltage, and (c) the antenna rotates with variable speed and is fed with DC voltage. The predominant frequency component was equal to the rotating frequency of the RCPs fed with DC voltage. If the RCPs were fed with AC voltage two dominant frequencies were generated, which were determined by the difference in frequency between the RCP rotation frequency and the AC source frequency. When the RCPs rotated with variable speed and were fed with DC voltage, many frequency components were generated, which were determined by the initial rotational speed of the RCPs and their acceleration.