This communication presents a low-profile, compact, high gain dual-band and dual-circularly polarized (CP) folded transmitarray antenna (FTA) with independent beam control at Ku-band. The element with independent phase control capability in two bands is designed to achieve the functionality of linear polarization to different circular polarization conversion. To reduce the profile of the whole FTA, a dual-band and dual-linearly polarized patch antenna is adopted as the feed source. By controlling the phase distribution and circular polarization of the transmitarray (TA) according to the phase compensation principle, the proposed antenna can radiate left-hand CP (LCP) waves and right-hand CP (RCP) waves at 12 and 15 GHz, respectively. On the basis, three typical FTA prototypes with different beam directions are simulated to validate the capability of independent beam control. Two of the prototypes are fabricated and measured, and the results are shown in reasonable agreement with the simulation. The proposed antenna not only reduces the profile by 2/3 compared to the traditional TA antenna, but also has the advantages of compact planar structure, low cost, high gain, and easy integration, which presents great application potential in two-way satellite communication systems with limited volume and space.

A new decoupling scheme named three-port coupled resonator decoupling network (CRDN) is proposed. The matching and decoupling conditions for the three coupled antennas are proposed, and the decoupling condition for the real part of the mutual admittances between three coupled antennas is derived. More importantly, a comprehensive synthesis theory for the three-port CRDN is proposed. In order to prove this concept, three different configurations of three-element are designed for verification, including not only triangular arrays but also linear antenna arrays. Simulated and measured results show that in all three examples, multiple types of coupling between antennas can be reduced to below $-$ 20 dB. Furthermore, the total efficiency and envelope correlation coefficient of the decoupled antennas are significantly improved compared with the coupled counterparts. The proposed three-port CRDN is easy to implement and is attractive for multiple-input multiple-output (MIMO) applications.

A second-order coupled resonator decoupling network (CRDN) with source-load coupling is proposed in this article. Based on the characteristic analysis of different types of coupled antennas, a general decoupling theory from the network point of view for the CRDN with source-load coupling is developed, in which the coupling coefficients of all couplings in the CRDN can be analytically obtained. To demonstrate the effectiveness of the proposed theory, two design examples are elaborated. Two identical triangular sheet antennas of the same frequency, as well as two monopoles operating in adjacent frequency bands, are decoupled by a CRDN with the source-load coupling realized by coupled microstrip lines. Two prototypes and their counterparts in which antennas are strongly coupled without CRDNs are fabricated and measured. The measurement results show that in both cases, the CRDN with the source-load coupling can suppress the mutual couplings between antennas to below $-$ 20 dB within the band of interest while maintaining key performances such as matching, radiation patterns, total efficiencies as well as envelope correlation coefficients (ECCs) and available throughput in a given propagation channel. The proposed decoupling design shows great potential to be applied to antenna coexistence problems with broader bandwidth demand.

The analysis of the target's broadband electromagnetic scattering characteristics plays an important role in radar stealth and recognition areas. The traditional method of moments (MoM) needs to calculate each frequency point when analyzing the target. With the increase of the target electrical size and complexity, the radar cross section (RCS) of the target changes drastically with frequency, it is necessary to calculate the accurate frequency response with a small frequency interval, which is very time-consuming in calculation and not feasible. This paper proposes to combine the subdomain method of moments (SMoM) with the Chebyshev approximation technique (CAT) to efficiently analyze the electromagnetic scattering of arbitrary shaped objects over a broad frequency band. In the SMoM technique, the whole object can be divided into several regions, each of which can be independently solved by the method of moments (MoM). The CAT technique is employed to expand the unknown current coefficients into a Chebyshev series for achieving fast frequency sweeping. Instead of direct point-by-point simulations, it is only necessary to calculate the currents by SMoM at several Chebyshev-Gauss frequency sample points. Furthermore, the Chebyshev series are matched via the Maehly approximation to a rational function to improve the accuracy. Numerical examples show that the hybrid technique can greatly reduce the computation time without loss of accuracy.

The Adaptive Cross-Approximation (ACA) technique is presented to speed up the conventional MoM-PO for analyzing antenna array in the vicinity of an electrically large platform. In the hybrid ACA-PO method, the ACA technique, which is based on the specific properties of the Green’s function, can be employed to compress the self-impedance matrix of the MoM region, as well as the interaction matrices between the MoM and PO regions. By introducing the ACA into MoM-PO, the initial dense matrices are compressed which resulting in a substantial reduction in memory consumption. In addition, the hybrid ACA-PO method utilizes the decomposed low-rank matrix to solve the current, which can efficiently perform matrix-vector multiplication (MVM) related to MoM and PO regions. Several numerical examples are given to illustrate the efficiency and accuracy of the proposed hybrid method in comparison to the conventional MoM-PO and Adaptive Cross-Approximation (ACA) methods.

An efficient hybrid method based on subdomain adaptive integral method (SAIM) and Chebyshev approximation technology (CAT) is proposed for analyzing the wideband radar cross section (RCS) of complex multiscale objects in this letter. The SAIM cannot only be used to effectively deal with the difficulty of slow convergence caused by the mutiscale problems, but also greatly reducing the computational memory. By introducing the CAT into SAIM, we can use the currents at a few frequency sampling points to predict the currents at any frequency point over the entire band. In addition, the application of the Maehly approximation can obtain a better accuracy. Numerical examples show that the proposed SAIM-CAT can significantly improve the calculation efficiency without loss of accuracy.