International Journal of Antennas and Propagation

The key to decreasing reradiation interference (RRI) of power transmission lines on adjacent radio stations is to clarify the RRI resonance mechanism. Aiming at the defects of existing RRI resonance analysis methods, including frequency limitation and lack of physical explanation, a RRI resonance analysis method based on characteristic mode (CM) theory is proposed in this paper. Firstly, based on the generalized eigenvalue equation, a set of characteristic currents with orthogonal relationship and their eigenvalues for power transmission lines are solved, and combined with Poynting’s theorem, the CM radiation characteristics are analyzed. Secondly, under specific external excitation, CM-related parameters are obtained through modal decomposition. Finally, the total energy radiated by power transmission lines is decomposed into the superposition of energy radiated by each CM, and the mechanism of RRI resonance is clarified from the perspective of CM. The simulation results show that compared with the IEEE guide and the generalized resonance theory, the method in this paper is effective and independent of observation points, which can provide a theoretical support for further research on the RRI suppression measures.

For WLAN/WIMAX applications, a brand-new tree-shaped metamaterial-loaded microstrip antenna is suggested. The reduced ground plane size and 4.4 dielectric constant (r) and 0.02 loss tangent (δ) dielectric are used to manufacture the 15 × 16 × 1.6 mm³ microstrip antenna. Two X-shaped slots are added to achieve the characteristics needed for WIMAX applications at 5.5 GHz. Additionally, a split-ring resonator is added to the structure to increase its bandwidth. It runs for WLAN applications with a center frequency of 5.8 GHz. The proposed structure’s measured impedance bandwidth is 45.39% with SRR and 53.48% without SRR, respectively. The proposed antenna is capable of satisfying the major requirements of modern wireless devices such as multiband operation, compact size, large bandwidth, and planar structure. The best outcomes are attained with the aid of parametric analysis of feed width, ground height, and slot width. All electromagnetic simulations were performed using CST Studio software. The measured results and the simulation agree. The waveguide extraction approach is used to demonstrate the SRR’s permeability property. The suggested antenna had adequate impedance matching, was small, and had a wide bandwidth.

Accurate modeling of relativistic electromagnetic scattering characteristics from high-speed motion of plasma coated objects is crucial for the development of hypersonic aircraft and their applications in the identification and surveillance of moving stealth targets. Nevertheless, a solution for bistatic polarized radar cross sections (RCSs) from a 3-D object with plasma coated layer in motion has yet to be obtained. This manuscript proposes a solution to this problem by employing a combination of the auxiliary differential equation (ADE) method with Lorentz finite-difference time-domain (FDTD) method. Utilizing the Lorentz transformation, this paper presents the transformation of parameters of the incident plane wave and dimensions of the object between the laboratory system that remains static and the rest system that remains stationary relative to the object in high-speed motion. The near-zone electromagnetic fields near the object are computed using the ADE method in the rest system, after which the near-field to far-field (NF-FF) transformation is employed to obtain the far-zone polarized scattered field. By applying Lorentz transformation to the coordinates, this paper presents a solution for the polarized scattering from moving plasma coated objects. Especially, radial components of the polarized scatterings are analyzed. The proposed method is validated through several numerical experiments, demonstrating its efficiency and accuracy.

This paper presents an efficient decoupling network using a single directional coupler and transmission lines for closely spaced Tx/Rx antennas in single polarized radar applications. The isolation between both antennas can be enhanced by controlling the phase of the Tx leakage signal and the coupling coefficient of the directional coupler. Its structure provides no loss of Tx/Rx paths excepting minute loss due to the coupling of the directional coupler. The Tx leakage is more insensitive to the antenna impedance variation compared with a conventional monostatic system. The design process is as follows: First, closely separated Tx/Rx antennas were designed and their isolation () was extracted. Second, the directional coupler was designed with its coupling coefficient . Finally, both were connected by transmission lines, of which phases were adjusted for the coupled and antenna-isolated signals with 180° phase difference. The Tx/Rx antennas without and with the decoupling network have 15-dB bandwidths of 23.98–24.43/23.98–24.50 GHz and 23.80–24.36/23.80–24.45 GHz, respectively. Gains of 8.17/8.39 and 8.72/8.73 dBi and efficiencies of 60.56%/60.77% and 63.0%/61.8% in the Tx/Rx antennas without and with the decoupling network were achieved at 24.1 GHz, respectively. The dimension of the proposed antenna is 1.62λ₀ 2.09λ₀ 0.0204λ₀. The K-band antennas show a good Tx-Rx isolation of 29.3–67.9 dB which was superior at least 9 dB to the conventional antennas.

In this article, an 8 × 8 MIMO antenna system with multidecoupling structures is proposed for the fifth-generation (5G) terminal applications. First, an antenna element consisting of an L-shaped open slot with dimensions of 5.6 × 5 mm² and two bent-L-shaped monopoles with dimensions of 12.7 × 6.1 mm² is introduced. Due to coupling feed technology, the initial open slot owns a wide bandwidth from 3.62 GHz to 4.82 GHz. For broadening the bandwidth of the initial antenna element, two bent-L-shaped monopoles are added to the open slot to adjust the input impedance. By optimizing the parameters of monopoles, the proposed antenna element has been finally determined and the bandwidth of the antenna element has been broadened (2.82 GHz to 5.23 GHz). Second, a dual antenna pair is constructed by placing the two antenna elements with an edge-to-edge distance of 27 mm in a mirror image placement; the 8 × 8 MIMO antenna system is brought about by symmetrically disposing four such antenna pairs with an edge-to-edge distance of 47 mm. Moreover, the isolation of two closely placed antenna elements is achieved by the parasitic strip-loading technique and defective ground techniques. Due to the decoupling techniques used in the 8 × 8 MIMO antenna system, the average isolation has been optimized from 13.2 dB to 21.9 dB and the total efficiency of each antenna element has been improved from a worst 20% to over 45%. Besides, the calculated mean efficiency gain is less than 1 dB, and the calculated envelop correlation coefficient (ECC) is lower than 0.01 for desired frequency bands. Furthermore, the proposed 8 × 8 MIMO antenna system has the measured broadband bandwidth from 3.28 GHz to 5.05 GHz (covering N77, N78, and N79 bands) and a compatible dimension for ultra-thin mobile phones. The simulated results of this work are all obtained from EM software CST STUDIO SUITE 2019. In general, the proposed 8 × 8 MIMO antenna system with a high-isolation property provides a hopeful solution to 5G ultra-thin mobile phones.

A novel super wideband (SWB) dual port antenna with second-order Hilbert branches and a modified T-decoupling structure is proposed. The overall size of the antenna is only 32 mm × 26 mm × 1 mm. The SWB antenna front comprises a “house” shaped radiating patch and a trapezoidal-shaped microstrip line. Two SWB antenna units are placed symmetrically on FR4 dielectric substrate to form the SWB-MIMO (multiple-in multiple-out) antenna. Two second-order Hilbert branches expand the wideband of the SWB-MIMO antenna. The antenna decoupling is mainly achieved by loading a fence-like “T” decoupling structure on the ground plane. The antenna is also miniaturized and isolated by adjusting the distance between the radiating patches of the units. The simulations and measurements show that the SWB-MIMO antenna operates in the frequency band of 1.98-30.8 GHz (175.84% relative bandwidth). The bandwidth dimensional ratio (BDR) (BDR is a measure of the compactness of the antenna, the higher the BDR, the better the compactness of the antenna, and the wider the working bandwidth of the antenna.) is 14653.33. The overall isolation is below −16.4 dB, and the important part (8.5–24.1 GHz) is below −20 dB. The envelope correlation coefficient (ECC) is less than 0.03, and the radiation characteristics are excellent.