A planar millimeter-wave two-dimensional (2-D) beam-scanning multibeam array antenna fed by compact 16-way beam-forming network (BFN) in multi-layered substrate integrated waveguide (SIW) technology is addressed. The BFN is formed by connecting two stacks of sub-BFNs, the E-plane sub-BFN and the H-plane sub-BFN. The H-plane sub-BFN is realized by a traditional H-plane 4 ×4 Butler matrix (BM). The key point of this design is to propose an E-plane 4 ×4 BM which realizes a planar E-plane sub-BFN. These two sets of sub-BFNs can joint directly without resorting to any connectors or connecting networks to form such a compact 16-way BFN with a reduced area of merely 3 λ×12 λ. After that, to be compatible with the proposed BFN, a ladder-type 4 ×4 slot antenna array is employed, which is comprised of four linear 1 ×4 slot antenna arrays. Different from traditional array, the four sub-arrays are distributed in separate layers for the purpose of jointing to the BFN more conveniently. Transition network are also required to connect the BFN with the antenna array. Finally, a compact 2-D scanning multibeam array antenna based on the planar SIW BFN are fabricated and measured, which would be an attractive candidate for 5G application.

This letter presents acompact dual-layer 4 $\times$ 8 Butler matrix (BM) with sidelobe level (SLL) suppression in substrate integrated waveguide (SIW) technology. Addressing the excessive crossovers in the classic 4 $\times$ 8 BM, a novel dual-layer configuration is proposed here.Such a configuration can help reduce the required crossovers from original five sets to merely one set. Therefore, the 4 $\times$ 8 BM can be significantly simplified to achieve better compactness. Based on this configuration, a SIW dual-layer 4 $\times$ 8 BM is designed with a dimension of 6.1λ $\times$ 4.1λ. To evaluate its SLL suppression effect, a multibeam array fed by the proposed BM is designed, simulated and measured.

A simple internal antenna design for WWAN/LTE operations is investigated, and it can be incorporated into a mobile phone that has an unbroken metal rim of height 5 mm. The proposed antenna is mainly composed of two parallel slots (dual-loop) embedded on the system ground, and by feeding them with an L-shaped coupled feedline with matching networks, good excitation of multiple loop resonant modes can be obtained, which is capable of covering the GSM850/900 (824–960 MHz), DCS/PCS/UMTS2100 and LTE2300/2500 (1710–2690 MHz) operating bands. In addition, the feasibility of realizing decoupled multi-antennas (2 ×2 MIMO antenna system) is also demonstrated and its performances are acceptable for smartphone applications.

A near field communication (NFC) dual-loop antenna with a miniaturized size of 15 mm × 25 mm is initially proposed for full metal-cover smartphone applications. To achieve a small clearance zone on the metal-cover, a small rectangular slot of size 8 mm × 16 mm is loaded into the metal-cover. To allow good inductive coupling, the NFC antenna is only 0.37 mm beneath the center of the rectangular slot. Because of that, the direction of the eddy current induced on the metal cover will be the same as the dual-loop NFC antenna. It is noteworthy that the prototype NFC antenna integrated with a single rectangular slot loaded full metal-cover was certified by the Europay, MasterCard and Visa (EMV) test.

When a hypersonic vehicle flies in the atmosphere, plasma sheath and trails are configured around the vehicle due to aerodynamic heating and ablation, which distort the radar echo signal and then influence the target range information and Doppler frequency extracted from the echoes. In order to examine the impact of plasma laminar wake on radar detection, this article is primarily aimed to establish a laminar wake echo model based on a linear frequency-modulated continuous wave (LFMCW) radar, which takes into account the reaction control system of laminar wake by employing the Born approximation solution and the characteristics of the inhomogeneous and nonunique velocity of the wake medium. An echo signal processing method is also developed, in which the stretch processing technique is combined with the keystone transform of the target range walk correction. Such a treatment not only reduces the sampling rate and bandwidth, but also eliminates the cross-range cells phenomenon caused by hypersonic; finally, the range-Doppler (RD) image of the wake is achieved by 2-D fast Fourier transform (2-D FFT) processing, and radar range and velocity measurement results in the presence of plasma are obtained.

When a hypersonic object reenters the atmosphere, the formation of an ionized plasma sheath and wake will significantly change its scattering characteristics, causing a significant impact on detection, identification, and tracking. To investigate the relationship between the scattering characteristics of a hypersonic object in ground tests and real flights, in this article, the scaling laws of a hypersonic object with plasma sheath and underdense turbulent wake are derived from the binary scaling law for hypersonic flows, combined with an impedance matching method and the first-order Born approximation method, respectively. We find the radar cross section (RCS) scaling law of a hypersonic object with ionized flow is $\sigma _{1} /\sigma _{2} =\eta ^{2}\xi $ , while the scaling law for an underdense turbulent wake is $\sigma _{1} /\sigma _{2} =\eta ^{4}$ when they satisfy the binary scaling law, where $\sigma _{1} $ and $\sigma _{2}$ are the RCS of a real flight and ground test, $\eta $ is a scaling factor, and $\xi $ is dependent on the dielectric parameters of the plasma sheath. The derived scaling laws can explain the phenomenon of the RCS of the underdense turbulent wake being higher than that of the hypersonic object with plasma sheath under certain conditions and are applied to the RCS simulation of a hypersonic object with ionized flow and underdense turbulent wake.