In brief

Short-slot couplers are a particular type of waveguide directional coupler commonly used due to their compact size in comparison with other waveguide configurations. The common short-slot Riblet coupler is used as a 3 dB hybrid (equal power division to the coupled and the through ports) in microwave networks supporting high power and providing good performance over a moderate bandwidth. In this article, the general case of short-slot couplers with arbitrary power division is presented, in E- or H-plane configuration. Moreover, it is shown that the port closer to the input can handle either more or less power than the further port, depending on the design parameters and the length of the main guide of the coupler. Several designs in E- and H-plane are shown to introduce the concept. In addition, two experimental prototypes, with either rectangular waveguide interfaces or coaxial input/output, are manufactured and tested showing good agreement with the expected results.

In this letter, a quad-band shared-aperture antenna with multibeam in millimeter wave (MMW) is proposed. The antenna is realized by integrating a microwave (MW) electromagnetic transparent tri-band filtering antenna with an MMW multibeam substrate-integrated waveguide (SIW) slot array antenna. By stacking the low-band (LB) and high-band (HB) antennas, the quad-band shared-aperture antenna is achieved. The LB antenna is realized by embedding a dual-band U-slot patch into a perforated patch, and the filtering function is achieved by introducing a stub-loaded resonator into the feeding layer. To achieve electromagnetic transparency in MMW, the LB radiator is discretized by bandpass frequency-selective surface cells. The HB antenna is formed by a 4 × 5 SIW slot array and a 4 × 4 stacked Butler matrix, which achieves four independent beams in MMW. For verification, a prototype is fabricated and measured. In the MW band, the antenna operates well at 2.55 GHz, 3.5 GHz, and 4.9 GHz, with peak gains of 6.8 dBi, 7.7 dBi, and 8.5 dBi, respectively. In the MMW band, the beam directions of the antenna at 26 GHz are ±14° and ±44°, with peak gains of 15.2 dBi and 14.1 dBi, respectively.

This paper presents a new balanced-to-unbalanced (BTU) hybrid ring with arbitrary power division ratio. Standard S-parameters and mixed-mode S-parameters are adopted to describe the performance requirements of the BTU hybrid ring. A simple configuration composed of transmission lines is developed to achieve desired functions of the BTU hybrid ring with arbitrary power division ratio. The design equations are given to guide the design. A prototype with the power division ratio of 3:1 is designed to verify the theoretical prediction. The fabricated BTU hybrid ring is matched well for both balanced and unbalanced ports. The BTU power division with arbitrary power division ratio and high mode conversion suppression are also achieved.

A planar miniaturized asymmetrical four-port circuit structure based on the composite left- and right-handed transmission lines (CLRHTLs) is proposed in this paper to design a balanced-to-single-ended (BTSE) power divider (PD) with arbitrary power division. The two outputs of the power divider are in-phase, hence, the proposed circuit can be seen as the cascade of a balun and a Gysel power divider with arbitrary power division. The matrix conversion between the single-ended scattering parameters and the mixed-mode scattering parameters along with the circuit analytical formulation are presented. Finally, a prototype of the PD with 2 dB magnitude difference between its output ports is designed and fabricated. The measured results validate the proposed design approach.

An ${S}$ -/ ${K}$ -band metasurface-based antenna with a shared aperture is proposed for 5G applications. The metasurface is designed with the dual-band characteristics for two antennas to work in the same aperture without interference. Based on the characteristic mode analysis, $3\times 3$ metasurfaces are proposed for the ${S}$ -band radiation. To radiate the ${K}$ -band electromagnetic wave without blocking, the metasurfaces are discretized by the subcell of a square ring and an inner square patch to achieve a frequency selective function. Then, as an example, the microstrip-fed slot is used to drive the metasurfaces at the ${S}$ -band, while an $8\times 8$ substrate integrated waveguide slot array antenna between microstrip and metasurface is designed at the ${K}$ -band. The measurement shows the 10 dB return loss bandwidths of 23.45% and 4.8% and the realized gain of 7.52–10.88 and 21.3–22.4 dBi over the ${S}$ -band (3.2–4.05 GHz) and the ${K}$ -band (25.22–26.46 GHz), respectively.

A compact unequal Wilkinson power divider with arbitrary power division is analyzed and demonstrated in this paper. The power divider can be designed with arbitrary power division in theory and achieves large power dividing ratio in practice. The proposed structure is compatible with single layer integration by using the normal PCB fabrication process. The complete analytical procedures of the proposed power divider are presented. To verify our proposed design approach in theory, one 11:1 unequal power divider is designed and fabricated. The measured bandwidth at 20 dB return losses is about 6%, while the isolation of the two output ports is better than 20 dB. Good agreement between the measured and simulated amplitude distributions is observed. The phase difference between outputs ports are about ±2.5 degree, over the 10% relative frequency bandwidth.

This paper presents a novel dual-band filtering balanced-to-unbalanced impedance transforming out-of-phase power divider using a simple admittance inverter with an extreme high frequency ratio and arbitrary power division, which is composed of stepped-impedance transmission lines. Based on the traditional transmission-line theory and ABCD/V matrix, the closed-formed analytical equations and complete design procedure are derived and provided for the filtering differential-mode transmission with high frequency ratio and good dual-band common-mode suppression. For demonstration, a designed prototype operating at 1 and 6.4 GHz are simulated, fabricated, and measured. The measured results agree well with the EM simulation perfectly.

In this letter, we present theoretical and experimental investigations of a rat-race coupler with negative group delay (NGD) characteristics and an arbitrary power division ratio. From the theoretical analysis, the NGD characteristics can be obtained through various transmission paths and have small variations with the power division ratio. The power division ratio is controlled by only the characteristic impedance of the transmission lines. Ideal port isolation and return loss characteristics are obtained at a center frequency for any arbitrary power division ratio. For experimental demonstration, a microstrip line rat-race coupler is implemented with center frequency of 2.14 GHz. The measurement results agree well with simulation results and theoretically predicated values.

To satisfy the requirements of the emerging wireless communication system, the simultaneous implementation of large frequency ratio and tight coupling is demanded for a dual-band coupler. But most of the existing dual-band coupler structures can only achieve one of them. In this paper, a new coupled line based dual-band coupler structure is proposed. The detailed theoretical analysis is conducted for different ranges of frequency ratio. It was shown that a wide frequency ratio from 1.4 to 11.7 can be achieved even for the designs which require a tight coupling of 3 dB. For higher flexibility, the same circuit topology is further investigated to implement the arbitrary power division ratios over the two bands. More importantly, the design parameters for the large frequency ratio and arbitrary power division ratio are found to be almost independent resulting in a simple design procedure. For demonstration purposes, a dual-band 3 dB coupler with a large frequency ratio of 6 is designed, fabricated and measured. Furthermore, another dual-band coupler with coupling coefficients of 3 dB and 6 dB at 2 GHz and 4 GHz is designed, fabricated and measured. Good agreement between simulation and measurement can be observed for both prototypes.

This study describes a new class of couplers using single‐layer microstrip lines that reduce the occupied area, suppress the harmonic components and provide arbitrary power division ratios. It consists of lumped reactances between transmission lines to reach realisable impedances and shorten line lengths. To provide a design guideline, closed‐form formulas are derived and five different designs are produced and built to investigate the couplers performance and design accuracy. The simulation results prove to be in good agreement with measurements. More than 70% size reduction with respect to the conventional structures, 12 dB harmonic suppression and high power division ratios (9:1) achieved in various presented branch line, rat race and multi‐section Wilkinson dividers. This proposed class of coupler structures can effectively be used in miniaturised and/or arbitrary power division ratio couplers with harmonic suppression.

To achieve multi‐function integration and independent performance regulation of microwave and millimetre‐wave (mm‐Wave) shared‐aperture antennas, a design method based on embedded structure fusion is proposed. In the Sub‐6G band, a high‐order mode annular‐ring patch antenna is designed. To transform the non‐broadside characteristics, the current distribution of TM31 and TM12 modes is reconstructed by slotting in the centre of the patch. Additionally, the electric field distribution is modified by loading shorting pins to achieve beam broadening. In the 5G mm‐Wave band, a four‐element high‐gain substrate integrated waveguide (SIW) slotted cavity backed antenna array with low‐sidelobe characteristics is obtained using the element interleaving technique. The SIW slotted cavity backed antenna array is integrated into the central area of the annular‐ring patch to achieve aperture‐sharing fusion. Experimental results demonstrate that the antenna operates in the Sub‐6G dual‐band of 2.1–2.2 GHz and 5.2–5.4 GHz, respectively. Furthermore, the widest half‐power beamwidth measured in these two bands is 126° and 140°. In the mm‐Wave band, the operating bandwidth is 26.5–29.5 GHz, with a gain of up to 18.8 dBi. Notably, the performance of different bands does not impact the other, and the measured isolation exceeds 40 dB. Furthermore, the antenna profile is only 0.008 λ0. Therefore, an ultra‐low‐profile microwave and mm‐Wave shared‐aperture antenna with multi‐function integration and independent performance control is realised, which has great potential for application in 5G intelligent connected vehicle communications.

A generalized two-way two-section dual-band Wilkinson power divider with two absorption resistors and its size-reduced model are presented. Design equations for dual-band and arbitrary power division are derived from modified even- and odd-mode analysis. The frequency ratio of the lower and upper band frequencies must be lower than three. The channel bandwidth is presented as a function of frequency ratio with mathematical expressions. A coupled line section is introduced to reduce circuit size based on the assumptions of linear phase characteristics and equal phase velocities of the even and odd modes. Two two-way dual-band power dividers, one three-way planar dual-band power divider, and one size-reduced dual-band power divider were fabricated. Experimental results were in good agreement with predicted values.

Abstrct A novel coupled-line impedance-transforming structure with two parallel short-circuit stubs is proposed to design a wideband branch-line coupler with arbitrary power division in this article. In order to design this modified wideband branch-line coupler, analytical synthesis equations are obtained. As typical examples, four wideband branch-line couplers with different power dividing ratios are presented. The widest 20-dB return loss and isolation fractional bandwidth in these four numerical examples is almost 38%. Finally, two microstrip branch-line couplers operating at 1 GHz are fabricated and measured. One of these couplers has equal power division and a measured 13.9-dB return loss and isolation fractional bandwidth of 32.8%. The other one has 3-dB unequal power division and a measured 12.7-dB return loss and isolation fractional bandwidth of 37.6%. Obviously, this proposed branch-line coupler has several advantages, including a wide band, a compact size, an unequal power division, easy implementation (simple structure), and an analytical design method.

Coupled resonator circuits are the basis for the design of many bandpass microwave filters. Design techniques used for two-port coupled resonator circuits are extended here to multiple output circuits such as power dividers and diplexers. The design approach is based on synthesis of coupling matrix for multiple coupled resonators with multiple outputs using gradient-based optimisation. It allows the synthesis of power dividers with arbitrary power division, as well as diplexers and multiplexers with novel topologies. Since there is no need to use separate energy distribution networks such as circulators, manifolds or other junctions, the components can be miniaturised. An X-band unequal power divider and diplexer have been designed and realised using waveguide cavity resonators to confirm the new design methodology.

Although epsilon-near-zero (ENZ) media have emerged as a promising platform for power dividers, the majority of existing designs are confined to fixed power splitting. In this work, two dynamically tunable power dividers using waveguide ENZ media are proposed by precisely modulating the internal magnetic field and the widths of the output waveguides. The first approach features a mechanically reconfigurable ring-shaped ENZ waveguide. By continuously re-distributing the magnetic field within the ENZ tunneling channels utilizing rotatable copper plates, arbitrary power division among multiple output ports is constructed. The second design integrates a rectangular-loop ENZ cavity into a substrate-integrated waveguide, with four positive–intrinsic–negative diodes embedded to dynamically activate specific output ports. This configuration steers electromagnetic energy toward output ports with varying cross-sectional areas, enabling on-demand control over both the power division and the number of output ports. Both analytical and full-wave simulation results confirm dynamic power division, with transmission efficiencies exceeding 93%. Despite differences in structure and actuation mechanisms, both designs exhibit flexible field control, high reconfigurability, and excellent transmission performance, highlighting their potential in advanced applications such as real-time wireless communications, multi-input–multi-output systems, and reconfigurable antennas.