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This work presents a collection of millimeter-wave (mmWave) quasi-elliptical bandpass frequency selective surface (FSS) designs. First, an emerging dual-mode filtering circuit with separate electric and magnetic coupling paths is established, enabling high-order bandpass and quasi-elliptical responses. Three types of long-period substrate-integrated waveguide (SIW) FSS, embedding four identical criss-cross slot elements in one period, are used to implement the circuit resonators and their coupling mechanisms. Second, a shared metal via array delineates two SIW cavities within one macro cell, forming another FSS, thus significantly improving the out-of-band suppression. Third, an improved multipath coupling circuit topology allows the designed elliptical FSS to provide an extended passband while maintaining angular stability up to 50°. Fourth, this approach can extend to developing dual- and tri-band configurations with high roll-off properties in the passband. Finally, experimental results confirm the simulations, highlighting these FSSs exhibit notable features, including low cost, low profile, low transmission loss, wide passband, and improved filtering selectivity approximating the ideal filter response.

This article presents a new design of an endfire phased array antenna (PAA) using heterogeneous beam elements (HBEs) for wide-angle scanning. The HBEs are specially designed elements with inclined and controllable beam directions, which incorporate a printed dipole and a rotary ground to achieve the desired beam inclination. Then, the PAAs are constructed based on the proposed HBE, and the array arrangement is realized by adjusting the beam-inclined angle of each element. As a result, the proposed HBE PAAs effectively maintain a stable effective aperture across various scanning angles and thus achieve a wide scanning range with a low gain variation. Prototypes of $1\times4$ and $1\times8$ -element HBE PAAs are designed, fabricated, and measured. The simulated and measured results reveal a significant improvement within the scanning range for the proposed HBE PAAs compared to their standard counterparts. The $1\times4$ and $1\times8$ -element HBE PAAs achieve impressive scanning ranges of $\ge \pm 70^{\circ }$ and $\ge \pm 80^{\circ }$ , respectively, within a wide impedance bandwidth of 24.25–29.5 GHz (19.8%), at the cost of a slight decline in normal-direction gain (< 1.2 dBi). This design offers a promising solution to enhance the performance of PAAs for mmWave mobile terminals.

Switchable frequency selective rasorbers (FSRs) have gained significant attention for their ability to switch passbands into absorption bands. However, increasing their functionality or switchable state while maintaining stable wideband transmission and low reflection remains challenging. Therefore, this work proposes a three-layer FSR architecture that achieves switchable wide-passband in wide low-reflection bands and state-of-the-art independent switchability under dual polarization. First, for the bottom layer, a second-order inductively coupled frequency selective surface (FSS) with active diode loading on the uppermost layer can switch from wide passband to reflections. Second, for the middle layer, the switchable impedance layer with a low- ${Q}$ parallel resonator can preserve the passband or absorb previous in-band electromagnetic (EM) waves. Third, for the top layer, theoretical analysis confirms that an additional nonswitchable impedance layer must be introduced to achieve extended low reflection bandwidth during various switching states. Note that a polarization-isolated bias network is merged into the structural design to provide polarization-independent switchability for the passband. Finally, experimental results agree with simulations, demonstrating the proposed FSR device exhibits excellent performance, including four switching operating states, a wide 1-dB passband, 45° transmission angular stability, and a consistently wide low-reflection band in all rasorbing or absorbing states.

A phased array antenna (PAA) incorporating a dielectric dome lens (DL) extends its scanning range but concurrently experiences a notable reduction in broadside gain due to the inherent diverging lens characteristics near the broadside. Instead of using a whole dielectric DL, this article proposes a dielectric top-truncated dome lens (TTDL) to address this issue. The approach mitigates broadside gain reduction by eliminating the dielectric DL’s inherent diverging characteristics near the broadside through truncation of its upper portion. The study elucidates the design fundamentals for the dielectric TTDL, encompassing an analysis of the truncation impact and the corresponding phase compensation strategy aimed at mitigating this truncation effect. Utilizing ray-tracing methods and full-wave simulations, this work comprehensively evaluates the performance disparity between the TTDL and conventional DL, revealing the effectiveness of the proposed approach. Additionally, the structural flexibility of the TTDL is discussed to facilitate a more compact architecture. Experimental validation of a TTDL antenna, incorporating a feed array and a compact dielectric TTDL, is presented. Results demonstrate that within the 26.5 to 29.5 GHz operating band, the compact TTDL effectively extends the scanning range from 60° to 80° while avoiding broadside gain reduction and maintaining a gain fluctuation within 5 dB.

Heterogeneous beam element (HBE)-based phased array antenna (PAA) technology leverages the pattern shape of each element as a novel design degree of freedom (DoF) to optimize the scanning performance of PAAs. Through strategic arrangements of HBEs, an equivalent wide beam can be synthesized, thereby enabling wide-angle scanning. This article provides a theoretical analysis of this technology, encompassing theoretical foundations and design methodologies, and offers experimental validations. First, we introduce the average active element pattern (AAEP) approach to analyze HBE PAA technology, establishing its theoretical foundations. Subsequently, a numerical and theoretical analysis is made of the effects of the element spacing, array aperture size, element beamwidth, and element heterogeneity on the scanning performance of the HBE PAA, formulating essential design guidelines. Moreover, the HBE PAA technology is extended from 1-D heterogeneity to 2-D, highlighting its effectiveness in 2-D wide-angle scanning. Finally, the HBE PAA technology is experimentally validated, with assessments conducted on the linear and planar HBE PAAs. The results demonstrate that the HBE PAA technology applies to linear and planar PAAs, 1-D and 2-D wide-angle scanning, and can achieve excellent broadband wide-angle scanning performance in mmWave compared to their traditional counterparts.

A novel planar heterogeneous design strategy of a reflectarray antenna (RA) from the perspective of an equivalent medium is presented. A weak resonance criterion for constructing and selecting elements is proposed accordingly. Three types of weak resonance heterogeneous elements and element libraries are constructed to achieve fully continuous phase shift and low loss, which further contribute to realizing high-efficiency RA. To validate the design strategy, high-efficiency low-profile RAs using LTCC technology are designed for demonstration. The measured results indicate the heterogeneous RA achieves a maximum aperture efficiency of 46.32% and a high gain of 31.40 dBi at 140 GHz. Compared with conventional homogeneous RA, the maximum aperture efficiency is improved by 11%. The proposed high-efficiency low-profile RAs are promising candidates for short-distance communication in sub-millimeter wave and terahertz (THz) bands.

This communication introduces an innovative distributed integrated antenna (DIA) architecture for millimeter-wave (mmWave) mobile terminals. The DIA discretizes the antenna into multiple components: basic structures and auxiliary structures, which are located on different parts of the mobile terminals, including chip, package, PCB, and shell. Meanwhile, the signal pathway between these components is achieved by the antenna’s internal electromagnetic coupling rather than a conductive connection, leading to lower radiation loss and larger availability in design space. This communication, moreover, presents several representative schemes of the DIA architecture and compares them with conventional architectures. In particular, a new scheme using the same basic structure is proposed to further reduce manufacturing costs and simplify the production cycle. To demonstrate this new scheme, three antenna examples using the same dipole on the package are designed. By combining different auxiliary structures on PCB/shell, varying radiation patterns, including beam steering, gain enhancement, and polarization conversion, are achieved. The simulated and measured results both show that all antennas can reach a wide impedance bandwidth of 24.25–29.5 GHz, with a high radiation efficiency exceeding 70%; therefore, the feasibility of the new scheme for DIA architecture is sufficiently verified.