Gap Waveguide Technology Research Articles

A Half-Mode Groove Gap Waveguide for Single-Layer Antennas in the Millimeter-Wave Band

This letter presents an alternative to significantly reduce the time and difficulty in designing and fabricating antennas in gap waveguide (GW) technology by using a novel half-mode groove GW. GW is often criticized within the subtractive manufacturing field for the high fabrication time required to mill many pins with the waveguides in the same piece. To demonstrate the possibilities of this new approach, two different antennas have been designed, fabricated, and measured. Both antennas, formed by only two pieces with no contact, operate from 29 to 31 GHz and present reflection coefficients below <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 10 dB and high antenna efficiency above 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> . In addition, both prototypes can reuse the bed of nails, which favors shorter manufacturing times and lower costs in the development phase.

Development of a compact transverse slot array antenna using corrugation in groove gap waveguide technology

SummaryWe present the proof of concept of a compact slot array antenna with proper side lobe level in groove gap waveguide (GGW) technology. Four transverse slots are etched at the GGW broad wall along with the nulls of standing TE10 wave existing inside the shorted GGW. To decrease the sidelobes and antenna size, corrugations are applied through the wave path inside the GGW. Proper use of corrugations can reduce the wavelength inside the GGW leading to reduction of the distance between adjacent transverse slots, which can help to suppress the grating lobe problem and consequently enhance the radiation efficiency, which is a challenge in transvers slot array antennas. The designed antenna is optimized to achieve maximum gain, lowest grating lobe level, and return loss at 15 GHz using HFSS simulator. The achieved gain is about 13 dBi, and the SLL is better than 15 dB. To confirm the simulation results, the designed antenna was fabricated and tested. Both simulation and measurement results confirm that the grating lobes are well suppressed at the antenna operating frequency.

Dual-Circularly Polarized Array Antenna Based on Gap Waveguide Utilizing Double-Grooved Circular Waveguide Polarizer

This article presents a dual-circularly polarized array antenna based on gap waveguide technology operating at E-band. Double-grooved circular waveguide polarizers that utilize two annulus grooves placed at 45° and 135° offset from both excitation ports are used in this work. The operating principles of the polarizer are analyzed. Multilayer design using gap waveguide is implemented on the basis of the polarizer. The antenna consists of six layers, including three layers for the feeding networks, one layer for the polarizer, one layer of back cavity, and another layer of radiating grid. A 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 unit cell is proposed first and employed to realize an 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 planar array. Corporate feeding networks that use compact E-plane T-junctions and H-plane T-junctions are proposed. The antenna has been fabricated and verified by measurements. The measured results of S-parameters agree well with the simulation and show that reflection coefficients are better than −10 dB for both circular polarizations (CPs) from 76 to 81 GHz. The measured isolation between the input ports is larger than 25 dB in the operating band. The far-field measurements show that the antenna has realized gain larger than 24 dBi and axial ratios less than 1.5 dB from 76 to 81 GHz at boresight direction.

Three-Dimensional Printed, Dual-Band, Dual-Circularly Polarized Antenna Array Using Gap Waveguide Technology

A gap waveguide (GW)-based 4 × 4 dual-band, dual-circularly polarized antenna array is proposed. The antenna is composed of two stacked layers which are responsible for right-handed circularly polarized (RHCP) radiation in K-band and left-handed circularly polarized (LHCP) radiation in Ka-band. Each stacked layer consists of a GW power distribution network to excite 16 radiating units from a single input. A waffle grid is mounted on top of the array structure to increase effective aperture areas and reduce grating lobes. A prototype was fabricated using stereo lithography appearance (SLA) 3D printing and metallization technology, which significantly decreased the fabrication cost and complexity. Measurement results for the antenna prototype demonstrate the operating bandwidths of 19.91–20.52 GHz in K-band and 28.26–29.19 GHz in Ka-band, over which the reflection coefficients of &lt;−10 dB and axial ratios of &lt;3 dB are achieved. The prototype provides peak gains of 20.1 and 20.3 dB with total efficiencies of &gt;90% in the two respective bands. The combination of dual-band, dual-circularly polarized capability, high gain, high efficiency, lightweight, low cost and compact size renders the proposed design a potential candidate for commercial millimeter wave communication applications.

Broadband millimeter-wave metasurface antenna array with printed ridge gap waveguide for high front-to-back ratio

A novel broadband metasurface (MTS) antenna array with high front-to-back ratio (FBR) is proposed for 28 GHz millimeter-wave applications. With slot pairs loaded on patch cells, an aperture-coupled slotted-mushroom MTS antenna is designed to obtain broadband radiation characteristics with a compact size. To suppress the backward radiation of this antenna, the printed ridge gap waveguide (PRGW) technology with a perfect magnetic conductor (PMC) shielding made of mushroom unit-cells underneath the microstrip feeding line is applied. On this basis, a 4 × 4 MTS antenna array with the PRGW feed network is developed. Simulated results show that the FBR can be highly improved by over 16 dB within the entire bandwidth. To validate the design, a prototype of the proposed antenna is fabricated. Measured results show that an FBR greater than 28 dB can be obtained over a 24% impedance bandwidth (from 24.9 GHz to 31.7 GHz) with the reflection coefficient less than −10 dB. The measured antenna gain ranges from 17 dBi to 19.2 dBi and the corresponding measured aperture efficiencies are 35% and 45.6%. The measured results also suggest that the proposed MTS antenna possesses −35 dB cross-polarization level and stable radiation patterns. In addition, the proposed antenna remains a very low profile of 1.7 mm (0.17λ0 at 28 GHz). All the achieved features indicate that the proposed MTS antenna is an important candidate for B5G and 6G wireless communication.

Design of an E-sectoral horn based on PRGW technology for 5G applications

AbstractE-plane sectoral horn antenna based on printed ridge gap waveguide (PRGW) technology is designed for 5G applications. It is implemented on the top plate of the PRGW structure to avoid the losses and dispersion associated with conventional feeding mechanisms. The quasi-transverse electromagneticPRGW-based antenna is excited through a planar microstrip transition. First, the single horn antenna element is introduced with the microstrip feeding section. It shows an impedance bandwidth of fractional bandwidth 26% from 45.7 to 55.4 GHz with the realized gain of 12.7 dBi and radiation efficiency of 90%. In order to maximize the realized gain, a four-element linear horn array is introduced. The same impedance bandwidth is maintained with the array having a gain of 18.6 dBi from 45.7 to 55.4 GHz. The overall antenna array performance in the entire operating frequency range is stable with a radiation efficiency around 85%. Three matching sections are implemented to achieve better impedance matching. One is used to match the horn with the feeding aperture via the PRGW line. Another section is designed to match microstrip transition with PRGW ridge. Finally, two-stage quarter wavelength transformers are required to match the power divider with the array feeding network. A prototype of single-element horn antenna was fabricated to verify the concept of the design. Simulated and measured results show that the proposed antenna can operate in the frequency band of 45–55 GHz with good agreement of radiation performance. Moreover, the proposed designs are implemented and simulated using two microwave simulation tools (CST and HFSS) to verify the radiation performance, which exhibits good agreement. The design of an E-sectoral horn antenna and its array with high gain based on PRGW is demonstrated for the first time which is considered a novel issue. It can be integrated with other passive and active elements in communication systems. Thus, it can be a valuable component in 5G communication due to its high gain, compact size and ultra-wide band.

Dual circular polarization 2 × 2 slot array antenna based on printed ridge gap waveguide technology in Ka band

In this paper a novel multi-layer slot array antenna based on printed ridge gap waveguide (PRGW) technology with dual circular polarization (CP) at Ka band is proposed. This antenna consists of five layers, two dielectric substrates as a transition from PRGW to coax line and a branch line coupler (BLC) as an antenna feeding network, and three metal layers as a coupling slot, 2 × 2-element slot array antenna and ground layer. Feeding network has two individual ports consists of a BLC that based on PRGW implemented. The operating frequency band of the antenna for S11 < −10 dB with the gain more than 11.5 dBi is 27–29 GHz which covers the 27.5–28.35 GHz band proposed by Federal Communications Commission (FCC) and can be a suitable antenna for 5G applications at this frequency band. Total aperture size of the array antenna is less than 1.15 × 1.15 λ2 at 28 GHz and total efficiency of it is better than 80 %. Two individual ports of the proposed antenna provide two isolated left- and right-hand CP with axial ratio (AR) less than 2 dB for each port in aforementioned frequency range, and the measured results indicated that the antenna can provide isolation more than 15 dB between two input ports.

Inverted Microstrip Gap Waveguide Coplanar EBG Filter for Antenna Applications

The possibility of making compact stopband filters using coplanar-coupled EBG resonators in inverted microstrip gap waveguide technology is studied in this work. To do this, the filtering characteristics of different configurations of mushroom-type elements are shown in which the short-circuit element is placed on the edge of the resonator’s patch. The behavior of the structure as well as its main advantages such as: low losses, self-packaging, low level of complexity, flexibility and easy design are illustrated in the paper. To evaluate the possibility of integrating these structures in gap waveguide planar antennas feeding networks, a 5-cell EBG filter was designed and built at the X band. The proposed filter reached a maximum rejection level of −35.4 dB, had a stopband centered at 9 GHz and a relative fractional bandwidth below −20 dB of 10.6%. The new compact filter presented a flat passband in which it was well matched and had low insertion losses that, including the connectors, were close to 1.5 dB in most of the band. These results are enough to improve low-complexity future antenna designs with filter functionalities in this technology.

A novel design of printed ridge gap waveguide‐based 0‐dB backward‐wave coupler

This article presents the design and implementation of a 0-dB coupler based on Gap Waveguide (GW) technology. The proposed coupler is considered as the first backward-wave 0-dB realized using this technology. It operates at a central frequency of 30.5 GHz and maintains good performance regarding isolation and directivity all over the band. A parametric sweep is carried out to study the effect of the coupling section dimensions on the coupler performance to achieve nearly 0-dB coupler. The design is based on finite difference time domain (FDTD) analysis using CST microwave studio and Finite Element Method (FEM) using Ansoft HFSS for validation. The novelty of this article is that the achievable coupling section structure is considered as a genuine design for most 0-dB couplers for different operating frequency bands with its corresponding unit cell design based on GW technology. To validate this concept, the design steps are applied to four different frequency bands without changing the shape of the coupling section. The corresponding GW feeding networks are implemented on different materials for different couplers: Rogers RT5880, Rogers RO3003, and Rogers RO4350B. Furthermore, one of the couplers is fabricated and tested. The measured and simulated results show an acceptable agreement.

W-Band Binary Phase-Controlled Multibeam Antenna Array Based on Gap Waveguide Magic-Tee

In this article, a compact 94 GHz multibeam antenna array based on the binary phase-controlled concept is proposed. The feeding network is composed of four unconnected layers, and the ridge or groove gap waveguides are adopted as the guided wave structures. A key planar gap waveguide Magic-Tee is designed to obtain 0° and 180° phase states and then integrates with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\,\times \,8$ </tex-math></inline-formula> slot antenna array to achieve multibeam operation for the first time. Compared with the traditional phased array and passive beamforming networks (BFNs), the feeding design is simple in construction, consisting of only Magic-Tees and cascaded power dividers without any phase shifters. Benefiting from the gap waveguide technology, the antenna array does not require electrical contact among the metal layers, so it is simple and low cost to manufacture. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times8$ </tex-math></inline-formula> slot antenna array can easily switch among one-beam and three different dual-beam states that point to ±7°, ±17°, and ±38°. The measurement results of 6.6% bandwidth from 91.7 to 98 GHz for both reflection coefficients <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; -10$ </tex-math></inline-formula> dB and isolations >25 dB are achieved. The proposed multibeam antenna array would be an attractive candidate for millimeter-wave multiuser communication where it requires multiple beams simultaneously.

Differentially Fed Dual-Polarized 2-D Multibeam Dielectric Resonator Antenna Array Based on Printed Ridge Gap Waveguide

In this article, a differentially fed dual-polarized dielectric resonator antenna (DRA) subarray excited by a substrate integrated waveguide (SIW) cavity is proposed. A #-shaped slot etched on the top wall of the SIW cavity is used to achieve the differential excitation due to the intrinsic field distribution of TE120 mode in the SIW. Based on the proposed antenna subarray, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> 2 dual-polarized 2-D multibeam DRA antenna array with simple structure is designed, fabricated, and measured, which can achieve high cross-polarization discrimination (XPD) in the direction of maximum radiation. To reduce substrate loss, the printed ridge gap waveguide (PRGW) technology is used to feed the SIW cavity. Two orthogonal PRGW Butler matrices are placed at different layers so as to realize 2-D beamforming scanning with dual-polarization. The SIW cavity is placed in the air gap of PRWG, which can increase the stability of the antenna structure. By cleverly combining the SIW cavity and PRGW structure, the proposed multibeam antenna array has the advantages of high XPD and high radiation efficiency. Measured results show that an impedance bandwidth of 10% (28.5–31.5 GHz) and a peak gain of 11.8 dBi are obtained. Also, the measured XPDs are 28.3 dB at the center frequency and larger than 19.2 dB over the band of operation. Besides, the measured radiation efficiency of 67% is achieved for both the polarizations at 30 GHz.

Design and development of broadband gap waveguide‐based 0‐dB couplers for Ka‐band applications

The design and fabrication of a wideband millimetre-wave 0-dB coupler is proposed in this paper using gap waveguide technology for low-loss and high-power applications in 30-GHz frequency band. To overcome the fabrication challenges in millimetre-wave frequencies, the gap waveguide technique is utilised. Two gap waveguide-based coaxial- and waveguide-fed 0-dB couplers are designed with broadband performance, high return loss, acceptable coupling flatness and high isolation. For verifying the performance of the proposed structures, a prototype of the waveguide-fed 0-dB coupler is manufactured and measured. The measurement results show that the return and insertion losses and the isolation of the fabricated 0-dB coupler is better than 18 dB, 0.5 and 18 dB, respectively, in the specified frequency range from 26.2 to 34 GHz. Moreover, the breakdown power level of the proposed millimetre-wave structures is in kW orders to satisfy the high-power requirements.

A Shared-Aperture Dual-Band High-Efficiency Antenna Based on Groove Gap Waveguide

A shared-aperture dual-band antenna at 2.4 GHz Wi-Fi and Ku-bands is proposed in this letter. The antenna in the high-frequency band is featured by a slotted cavity configuration based on the gap waveguide technology. The slotted antenna consists of 3 × 3 slots incorporated into the top metal of the cavity. The periodic structure is loaded into the proposed antenna, which reduces the resonant frequency of the cavity. The top metal of the cavity is enlarged and four shorted screws are loaded, which achieve four half-mode cavities operated in the Wi-Fi band. Two antennas (slotted cavity antenna and dual-band antenna) are designed, fabricated, and tested. Measured results show that a −10 dB impedance bandwidth of 18.3% (13.15–15.8 GHz), a 3 dB gain bandwidth of 17.7% (13.1–15.65 GHz), and a peak gain of 14.8 dBi are realized for the cavity antenna. The impedance bandwidth of the proposed dual-band antenna covers 2.4–2.5 and 13.4–16.2 GHz. A 2 dB gain bandwidth of 16.4% (13.4–15.8 GHz) is realized. Owing to an all-metal structure that exhibits no dielectric loss, the radiation efficiency of the antenna is better than −1 dB in the whole working band. The proposed antenna shows the characteristics of high gain, high efficiency, and low cost, which is suitable for simultaneous satellite communication and Internet of Things applications.

A D-Band Corporate-Feed Gap-Cavity Slot Array Antenna Using Virtual PEC Method

A D-band corporate-feed gap-cavity slot array is proposed with wide bandwidth and high aperture efficiency. The cavity with higher order modes is implemented by using the gap waveguide (WG) technology, namely, a gap cavity. To ensure that the gap cavity is operating with the desired higher order mode over a wide bandwidth, the corporate-feed architecture is applied for uniform excitation and with alternating-phase between adjacent slots. The gap cavity is split into multiple elements by using zero-thickness virtual perfect electric conductor (PEC) walls. With this unique approach, the design, fabrication, and assembly complexities are reduced. For experimental verification, a gap cavity with an 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 slot array is designed in the 120 GHz band, and an E-plane WG feeding network is proposed to excite the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">880</sub> -mode. Two metal fences are introduced on either side of the radiating slot, and an inductive metal pin is introduced below the radiating slot to improve the radiation performance and broaden the bandwidth. The measured impedance matching bandwidth is around 110–144.8 GHz (27.3%). The measured peak gain is 26.22 dBi at 137.64 GHz, and the measured peak aperture efficiency is 86.2% at 115.325 GHz. The 3 dB gain bandwidth is the same as the impedance matching bandwidth.

Slow Wave Gap Waveguide With Bandpass Filtering Functionality

Gap waveguide (GW) technology, taking advantage of contactless electromagnetic band-gap (EBG) structures, solves the contact issue of conventional rectangular waveguides and provides a reliable method for packaging with planar circuits. Herein, a slow wave GW (SW-GW) structure with bandpass filtering functionality is presented. Utilizing the low-frequency cutoff characteristic of the GW and band-stop effect of the quasi-periodic transverse corrugations inside the GW, the lower and upper stopbands of the SW-GW can be easily achieved and reconfigured for different bandwidth requirements. The relationship between the dispersion diagram and the filtering characteristics, including the pass and stop bandwidths and group delay (GD), is studied to provide a simple but effective design guideline. The presented SW-GW reduces the design and implementation difficulties of conventional filters, especially wideband filters. A prototype operating at 24–30 GHz is designed and manufactured to validate the idea, and a good agreement is achieved between the measurement and simulation results.

Fully Metallic Glide-Symmetric Leaky-Wave Antenna at Kₐ-Band With Lens-Augmented Scanning

A fully metallic leaky-wave antenna (LWA) with enhanced scanning rate is presented. The leaky waveguide is implemented in groove gap waveguide technology and is periodically loaded to produce backward radiation. Furthermore, glide-symmetric pins are placed inside the leaky waveguide to increase the dispersion. A parallel-plate waveguide metasurface prism lens is used to disperse the backward radiation and increase the scanning rate of the LWA. The designed antenna can steer the radiation from −26° to 26° from 27 to 35 GHz, and an average total efficiency of 74% is achieved. A prototype of the designed antenna is manufactured, and measurements corroborate the simulated results. The proposed concept is applicable to other frequency-scanning antennas and can be used to increase the scanning rate in radar and imaging systems.

Wideband mm-wave high-gain multibeam antenna array fed by 4 × 4 groove gap waveguide butler matrix with modified crossover

This paper presents a wideband millimeter wave (mm-Wave) high-gain multibeam antenna array fed by Butler Matrix (BM) based on groove gap waveguide (GGW) technology. First, the components of 4 × 4 GGW BM have been designed and analyzed, especially the proposed modified crossover, which greatly improves the performance of BM as feeding network. Then a 2 × 2-element subarray with three layers has been proposed, combined with the 4 × 4 GGW BM to form a 1 × 4 broadside antenna array. Finally, the prototype of high-gain wideband four-beam antenna array has been manufactured and measured. The measured results verify the superior performance of the multibeam antenna array between 26.3-29.7 GHz. The return loss (RL) can reach 15 dB and isolation between ports is also less than 15 dB, and the measured maximum gain of radiation patterns and the maximum radiation efficiency can also reach 19.05 dBi and 86.8%, respectively. The measured results have a good agreement with the simulated results.

Ka-Band Integrated Multilayer Pyramidal Horn Antenna Excited by Substrate-Integrated Gap Waveguide

This work proposed a solution of structures built from stacking several dielectric substrates with the conducting cladding, aiming for electrical contact between them [perfect electric conductor (PEC)–PEC]. At mm-wave frequencies, surface roughness or imperfect flat surfaces present possible gaps that cause severe unexpected leakage. Many engineers overlooked this problem. To prevent this leakage, we propose transforming one of the PEC–PEC surfaces into artificial magnetic conductors (AMCs), creating a PEC–AMC layer that suppresses any leakage even with no contact between the surfaces where the gap is less than a quarter wavelength. A wideband multilayer pyramidal horn antenna using substrate-integrated gap waveguide (SIGW) technology is proposed as an example that highlights the proposed solution. In each layer of the horn, the opening is surrounded by periodic cells to suppress leakage and surface waves. In addition, the upper surface surrounding the horn’s opening is surrounded by EBG mushroom cells to act as a soft surface that suppresses the surface waves and reduces the edge diffraction, and, in turn, improves the radiation characteristics of the horn. The horn achieved a gain of 11.5 dBi and 20.5% bandwidth (28.5–35 GHz). The simulated and measured results show excellent agreement with each other.

High-Gain and Low-Loss Dual-Polarized Antenna Array With Reduced Sidelobe Level Based on Gap Waveguide at 28 GHz

In this letter, a 16×16-element dual-polarized antenna array with a reduced sidelobe level is proposed at 28 GHz for fifth-generation (5G) communication systems. The dual linear polarization operation is carried out through cross-shaped waveguide slots and multilayer feeding networks. Low-loss gap waveguide technology and Taylor distribution are applied in the feeding networks. A ridge unequal power divider with flexible power ratio and phase difference is devised and applied in the gap waveguide feeding network to reduce the complexity of unequal power structural design. A prototype of the proposed dual-polarized antenna array is manufactured by milling technology. Measured results show that the realized gains are higher than 28 dBi over the operating frequency band of 27.4–28.6 GHz. Moreover, the sidelobe level is lower than −18.5 dB for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -direction polarization and −19.5 dB for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -direction polarization.

Dispersion Analysis of Periodic Structures in Anisotropic Media: Application to Liquid Crystals

This paper presents an efficient method to compute the dispersion diagram of periodic and uniform structures with generic anisotropic media. The method takes advantage of the ability of full-wave commercial simulators to deal with finite structures having anisotropic media. In particular, the proposed method extends the possibilities of commercial eigenmode solvers in the following ways: (i) anisotropic materials with non-diagonal permittivity and permeability tensors can be analyzed; (ii) the attenuation constant can easily be computed in both propagating and stopband regions and lossy materials can be included in the simulation; and (iii) unbounded and radiating structures such as leaky-wave antennas can be treated. The latter feature may be considered the most remarkable, since the structures must be forcefully bounded with electric/magnetic walls in the eigensolvers of most commercial simulators. In this work, the proposed method is particularized for the study of liquid crystals (LCs) in microwave and antenna devices. Thus, the dispersion properties of a great variety of LC-based configurations are analyzed, from canonical structures, such as waveguide and microstrip, to complex reconfigurable phase shifters in ridge gap-waveguide technology and leaky-wave antennas. Our results have been validated with previously reported works in the literature and with commercial software CST and HFSS.