Microstrip Ridge Gap Waveguide Research Articles

Development of Reconfigurable High-Frequency Devices Using Liquid Crystal in Substrate-Integrated Gap Waveguide Technology

This article presents the theoretical study, numerical simulation and fabrication of a phase shifter and a stub resonator for use in microstrip ridge gap waveguide (MRGW) technology, using a liquid crystal (LC) in the substrate as a reconfigurable material. The phase shifter and the stub resonator are filled with LC, and thanks to the LC’s dielectric anisotropy properties, the phase shift and the resonance response can be easily controlled using an external electric or magnetic bias field. The phase shifter was designed to operate in the range of 10 to 20 GHz, and the resonator was designed to operate in the range of 7.8 to 8.8 GHz. The phase shifter’s responses (including both phase shift and insertion losses), associated with both the parallel and perpendicular permittivity values of the LC, were computed and measured, and then the corresponding figure of merit (FoM) was extracted. The resonator’s frequency responses, associated with both the LC’s parallel and perpendicular permittivity, were computed. The resonator’s frequency responses, which provided different polarization voltages, were measured and compared to the simulation results. All technological issues related to both prototypes are also discussed here. The good agreement between the simulation and measurement results confirm this technology as a viable approach to the practical implementation of these microwave reconfigurable devices.

Compact dual‐band inverted‐microstrip ridge gap waveguide diplexer

A compact dual-band inverted microstrip ridge gap waveguide (IMRGW) diplexer composed of four dual-mode IMRGW resonators and an IMRGW T-junction matching network is proposed in this letter. The dual-band diplexer is based on a dual-mode IMRGW resonator which can produce both the inverted microstrip resonant mode and the cavity resonant mode. Two resonant modes of the IMRGW resonator are highly independent, so the passbands of dual-band IMRGW diplexer can be easily tuned to the desired frequencies. A second-order dual-band IMRGW diplexer is designed and simulated. The simulated passbands of the second-order dual-band IMRGW diplexer are 13.13-13.38, 14.85-15.26, 18.57-19.42, and 20.85-21.35 GHz with fractional bandwidth of 2%, 2.7%, 4.8%, and 2.4%. A prototype is fabricated and measured to verify the feasibility of the proposed IMRGW diplexer. The measured passbands of the second-order dual-band IMRGW diplexer are 13.07-13.35, 14.88-15.35, 18.45-19.37, and 20.82-21.28 GHz with fractional bandwidth of 2.1%, 3.1%, 4.9%, and 2.2%. The measured isolation is better than 23 dB over 12-22 GHz. The measured results agree well with the simulations.

Efficient Procedure to Design Large Finite Array and Its Feeding Network With Examples of ME-Dipole Array and Microstrip Ridge Gap Waveguide Feed

An efficient procedure to design a large planar array and its corporate feeding network is presented. The procedure is verified by $8 \times8$ and $16\times16$ arrays of magnetoelectric dipoles (ME dipole) fed by microstrip ridge gap waveguide (MRGW) through a narrow slot. This procedure is based on using the frequency-dependent effective input impedance at the port of each element, which includes the effect of the mutual coupling between the antenna elements, which is used to design the corporate feeding network. In addition, the far-field characteristics of the array parameters such as directivity, gain, and the radiation patterns are predicted using the pattern multiplication method including the mutual coupling. The results are verified with the full-wave numerical solution. The procedure requires limited resources and speed up the design cycle. In the presented examples, the array elements are directly excited by the MRGW, which provides more flexibility to design complicated feeding networks and allow for distances between the elements less than a wavelength. Therefore, grating lobes are avoided. To accommodate such constraints, special designs of the power dividers are performed to provide the symmetric location of MRGW lines to avoid coupling between the feeding network lines. Furthermore, a transition from waveguide WR-15 to the MRGW is proposed to differential feed of the array antenna. The $16 \times 16$ array of ME dipoles has been fabricated. The measurement results show a 19% matching bandwidth ( $\vert \text{S}11\vert dB) and measured gain above 30 dBi with radiation efficiency better than 71%, all within a common bandwidth of 56–66 GHz.

Compact Dual-Band Inverted-Microstrip Ridge Gap Waveguide Bandpass Filter

A compact dual-mode inverted microstrip ridge gap waveguide (IMRGW) resonator and a series of dual-band IMRGW bandpass filters (BPFs) with easily controllable passbands are proposed for the first time in this article. The resonator is embedded into the ridge of the IMRGW without disturbing the placement of the mushroom-type bed of nails. A metalized via-hole is introduced to the center of the IMRGW resonator to ground a central patch, resulting in an inverted microstrip resonance mode and a cavity resonance mode simultaneously. The cavity resonant mode is relatively insensitive to the dimensions of the central patch, while the inverted microstrip resonance is insensitive to the dimensions of the cavity enclosed by electromagnetic band-gaps (EBGs) and two rows of metalized via-holes. Therefore, the resonant frequency of the two modes can be tuned independently. The resonators can be cascaded easily with a short IMRGW transmission line. A series of IMRGW based dual-band BPF with different orders are designed, fabricated, and measured. The third-order BPF’s simulated passbands are 13.07–13.41 and 18.46–18.91 GHz with a fractional bandwidth of 2.5% and 2.3%. Low insertion losses better than 1.7 and 2.1 dB are obtained on the two passbands. The measured passbands are 13.52–13.86 and 18.9–19.34 GHz with a fractional bandwidth of 2.3% and 2.2% while the insertion losses are better than 2.5 and 2.3 dB for the third-order BPF.

Millimeter-Wave Dual-Mode Filters Realized in Microstrip-Ridge Gap Waveguide Technology

In this paper, we propose novel microstrip-ridge gap waveguide (MS-RGW) millimeter-wave bandpass filters based on a dual-mode resonator. The resonator represents a rectangular patch grounded by a set of vias, whose pair of fundamental degenerate modes are separated in the spectrum using the via position perturbation. MS-RGW feeding lines are realized as periodically grounded microstrip lines inserted into a perfect magnetic conductor (PMC) structure, which are fed via the 2.92-mm connector through the specifically designed transition. A detailed analysis of the filters is provided together with the analysis of their building blocks—mushroom-based PMC surface, MS-RGW with periodically grounded microstrip line, and dual-mode resonator. The proposed filters are fabricated using standard PCB technology and the measured results show that the filters exhibit low losses, good in-band and out-of-band characteristics, and good selectivity. As such, the proposed filters represent excellent candidates for millimeter-wave filtering applications since they reconcile the requirements for high performance, low loss, and low cost.

Modeling and Design Empirical Formulas of Microstrip Ridge Gap Waveguide

Recently, interest in the microstrip ridge gap waveguide (MRGW) has increased due to the need for a self-packaged and low-loss structures for millimeter-wave applications. The MRGW consists of a grounded textured surface, which is artificially representing a perfect magnetic conductor surface loaded with a thin low dielectric constant substrate with a printed strip. This is topped with another dielectric substrate covered with a conducting plate at the top as a ground plane. Currently, the full-wave and optimization tools are used to design the MRGW structure. Consequently, an efficient modeling and design tool for the MRGW is proposed in this paper via curve fitting. Closed form empirical expressions for the effective dielectric constant, characteristic impedance, and the dispersion effect are provided. The developed expressions are generalized for arbitrarily chosen MRGW parameters. The expressions are verified with the full-wave solution. The results show the potential of the proposed approach in modeling the MRGW structure

Microstrip-Ridge Gap Waveguide Filter Based on Cavity Resonators With Mushroom Inclusions

In this paper, we propose a novel microstrip-ridge gap waveguide (MS-RGW) filter configuration, which is based on cavity resonators with mushroom inclusions. The resonators are realized as defects in surrounding mushroom-based perfect magnetic conductor (PMC), and thus, the filter configuration does not require additional conductive layers nor rearrangement of the PMC elements. The hosting MS-RGW is fed through transition from SMA to microstrip ridge, enabling simple fabrication and excellent impedance matching in a wide frequency range. To demonstrate the potential of the proposed structure, four narrowband filters have been designed, fabricated, and measured. The filters exhibit excellent in-band characteristics and small dimensions.

Microstrip-Ridge Gap Waveguide–Study of Losses, Bends, and Transition to WR-15

This paper presents the design of microstrip-ridge gap waveguide using via-holes in printed circuit boards, a solution for high-frequency circuits. The study includes how to define the numerical ports, pin sensitivity, losses, and also a comparison with performance of normal microstrip lines and inverted microstrip lines. The results are produced using commercially available electromagnetic simulators. A WR-15 to microstrip-ridge gap waveguide transition was also designed. The results are verified with measurements on microstrip-ridge gap waveguides with WR15 transitions at both ends.

2<formula formulatype="inline"><tex Notation="TeX">$\times$</tex> </formula>2-Slot Element for 60-GHz Planar Array Antenna Realized on Two Doubled-Sided PCBs Using SIW Cavity and EBG-Type Soft Surface fed by Microstrip-Ridge Gap Waveguide

A wideband 2x2-slot element for a 60-GHz antenna array is designed by making use of two double-sided printed circuit boards (PCBs). The upper PCB contains the four radiating cavity-backed slots, where the cavity is formed in substrate-integrated waveguide (SIW) using metalized via holes. The SIW cavity is excited by a coupling slot. The excitation slot is fed by a microstrip-ridge gap waveguide formed in the air gap between the upper and lower PCBs. The lower PCB contains the microstrip line, being short-circuited to the ground plane of the lower PCB with via holes, and with additional metalized via holes alongside the microstrip line to form a stopband for parallel-platemodes in the air gap. The designed element can be used in large arrays with distribution networks realized in such microstrip-ridge gap waveguide technology. Therefore, the present paper describes a generic study in an infinite array environment, and performance is measured in terms of the active reflection coefficient S11 and the power lost in grating lobes. The study shows that the radiation characteristics of the array antenna is considerably improved by using a soft surface EBG-type SIW corrugation between each 2x2-slot element in E-plane to reduce the mutual coupling. The study is verified by measurements on a 4x4 element array surrounded by dummy elements and including a transition to rectangular waveguide WR15.