Substrate Integrated Waveguide Butler Matrix Research Articles

Multimode CRLH SIW Transmission Lines for Wideband Multiport Directional Couplers and Miniaturized Beamforming Networks

In this article, a multimode composite right/ left-handed (CRLH) substrate-integrated waveguide (SIW) transmission line technology is proposed, which aims to broaden the operating bandwidth of the multiport directional couplers (DCs) and solve the oversize of the beamforming network (BFN). Its core is to etch multiple interdigital slots (IDSs) on the conductor surface of the multimode SIW transmission line, which can control the electromagnetic fields of different modes in the transmission line under the condition of less electromagnetic energy leakage. By adjusting the position and size of the IDSs, the desired phase constants and electromagnetic field distributions of different modes can be obtained simultaneously. Based on the proposed multimode CRLH SIW transmission line, the six-port, the eight-port, and the ten-port DCs are designed, respectively. Compared with the traditional multiport DCs based on the SIW, the bandwidth of the proposed six-port and eight-port DCs is broadened by about 87.3%. Based on the proposed multiport DCs, the miniaturized BFNs and the miniaturized multibeam array antennas (MBAs) can be realized by adding appropriate fixed phase shift. Finally, to verify the feasibility of applying multiport DCs based on the multimode CRLH SIW transmission lines to the miniaturized BFNs and the miniaturized MBAs, a 3 <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> 3 BFN, a 4 <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> 4 BFN, and a three-port MBA are fabricated, measured, and discussed. Their sizes are reduced by 58%, 49%, and 60%, respectively, compared with their SIW butler matrix (BM) counterparts.

Investigation on Beam Alignment of a Microstrip-Line Butler Matrix and an SIW Butler Matrix for 5G Beamforming Antennas through RF-to-RF Wireless Sensing and 64-QAM Tests.

In this paper, an intuitive approach to assessing advantages of beamforming in 5G wireless communication is proposed as a novel try and practical demonstration of importance of alignment between the transmitter’s and receiver’s beams working in millimeter-wave frequency bands. Since the diffraction loss of millimeter-wave signals matters seriously in propagation, the effects of the misalignment and alignment between beams need to be checked for, which was conducted with a horn antenna and the 4 × 4 Butler matrix which mimic the relationship of the base station and handset antennas. Designing and using the microstrip-line and the substrate integrated waveguide (SIW) Butler matrices, RF-to-RF wireless connectivity between the horn and the microstrip line beamformer as case 1 and the horn and the SIW beamformer as case 2, concerning the changing angle of the beam from either of the two Butler matrices, was tested, showing over 12 dB enhancement in received power. This direct electromagnetic link test was accompanied by examining 64-QAM constellations for beam-angle changing from −30° to +30° for the two cases, where the error vector magnitude in the QAM-diagram becomes less than 10% by beam-alignment for the changing angle.

Design of a 4×8 Substrate Integrated Waveguide Butler Matrix with Sidelobe Suppression at 60 GHz

Design of a 4×8 Substrate Integrated Waveguide Butler Matrix with Sidelobe Suppression at 60 GHz

Design and evaluation of a vertically integrated passive two‐dimensional beam switching antenna array at 60 GHz

A millimeter-wave two-dimensional (2D) beam switching planar microstrip patch antenna array excited by a 4 × 4 substrate-integrated waveguide Butler matrix (BM) is presented in this article. The BM architecture is modified to feed the planar array in a vertically integrated multilayer design to minimize parasitic effects due to junction discontinuity and reduce the radio frequency (RF) front-end footprint. This feed architecture enables the designer to control the phased array inputs to achieve a set of beam directions in four quadrants of radiation space at a desired elevation angle. For verification of beam switching via over-the-air measurements at 60 GHz, a bench-top anechoic chamber with proper transmitter and receiver antenna positioners was designed and fabricated using in-house laboratory resources. 2D beam steering was confirmed in the intended four quadrants of radiation space at ϕ0 = 50°, 140°, 220°, and 300° and θ0 = 30° ± 5°, meeting the design specifications with a very good margin. Each switched beam demonstrated between 5 and 6 dBi gain at 60 GHz, which is within 1 dB deviation from the simulated results.

V-Band Wideband Circularly Polarized Endfire Multibeam Antenna With Wide Beam Coverage

A V -band wideband circularly polarized (CP) endfire multibeam antenna array with the wide beam coverage is presented in this letter. First, a wideband compact endfire CP element with the wide axial ratio (AR) beamwidth is proposed. The design procedure and working principle of the element are discussed in detail. Besides, connected holes are used to reduce the mutual coupling and improve the AR performance. After that, a wideband substrate integrated waveguide Butler matrix is designed to feed the antenna array. Finally, the multibeam antenna is fabricated, measured and investigated. The measured results demonstrated that the proposed multibeam antenna provides a wide −10 dB impedance bandwidth of 28.5% (55.5 to 74 GHz) and a wide 3 dB AR bandwidth of 24.6% (57 to 73 GHz). Additionally, a wide beam coverage ranging from 45°–66° is achieved. Good agreement achieves between measured results and simulated ones.

Characterization of a 4 × 4 substrate integrated waveguide Butler matrix at 60 GHz for two‐dimensional beam steering

A 4x4 substrate integrated waveguide (SIW) Butler matrix for two-dimensional (2-D) beam steering operating at 60 GHz is developed and experimentally evaluated in this article. The SIW beamforming network is a Butler matrix that is implemented with new designs of its constituent components in order to achieve a compact design. Namely, an SIW phase shifter that uses periodic rectangular slots is introduced for the first time at 60 GHz to replace the more area-consuming meandered SIW. The phase shifter prototype, fabricated and measured as a proof of concept, demonstrates achieving an additional 20.3° of phase shift with using only 3 apertures without increasing the length or meandering the SIW line. The hybrid coupler and crossover sections of the SIW Butler matrix are also optimized to reduce the overall area of Butler matrix by 53.9%. The SIW Butler matrix prototype is fabricated and measured demonstrating achieving the differential output phase values needed to switch the beam of a 2-D array in four quadrants while keeping the insertion loss magnitude imbalance of below 1.47 dB from simulations and 3.34 dB from measurements.

Millimeter-Wave Multibeam Endfire Dual-Circularly Polarized Antenna Array for 5G Wireless Applications

A broadband multibeam endfire dual-circularly polarized (CP) antenna array using dielectric-loaded stepped slot antennas for millimeter-wave (mmWave) applications is proposed. First, a dual-CP endfire antenna element is designed for broadband mmWave applications. Additional loaded dielectric is utilized to improve the interelement isolation, the polarization purity, and the gain performance. Second, a substrate integrated waveguide (SIW) feeding network is designed for multibeam array applications. The broadband $4\times 4$ SIW Butler matrix, interconnections, and transitions are designed and applied in the antenna array. Third, mutual coupling and its influence on the array performance are investigated. Additional air gaps between elements are designed for axial ratio performance enhancement. Finally, the proposed multibeam array is designed, fabricated, and measured. The fabricated prototype achieves wide impedance bandwidth of 29.3% with the interbeam isolation greater than 15 dB, and a wide axial ratio bandwidth of 22.5%. The proposed multibeam endfire dual-CP antenna array would be a very attractive candidate for 5G mmWave wireless applications.

A Compact Multi-Beam End-Fire Circularly Polarized Septum Antenna Array for Millimeter-Wave Applications

In this paper, a novel circularly polarized end-fire septum antenna based on substrate-integrated-waveguide (SIW) is proposed in the 60-GHz band. By introducing four symmetrical tapered curved air slots in three stacked open-ended SIW layers, the antenna can obtain an operating bandwidth from 57.2 to 63.4 GHz for both AR $\vert S_{11}\vert dB. Besides, the half-power-beam-width and 3-dB axial-ratio (AR) beam-width are all wider than 79°, and a stable gain of 7.57 dBic with a variation of 0.15 dBic can be achieved in the working band. A $4 \times 4$ SIW Butler matrix based on SIW with three same substrates is then designed. The modified two-layer phase shifters realized by the different path distance are employed in the folded Butler matrix. By combining the antenna element and the Butler matrix together, a four-beam antenna array with circular polarization wave is realized. The proposed array has been fabricated and measured. The measurement results show that the antenna gain up to 11.01 dBic, −10 dB impedance and isolation bandwidth from 57.8 to 62.5 GHz (except at around 58.3 GHz), stable radiation pattern and a wide angular range of ±37° can be obtained. The measured AR values of the main lobe range of four beams are all less than 5 dB from 58 to 60 GHz.

A 60 GHz Horizontally Polarized Magnetoelectric Dipole Antenna Array With 2-D Multibeam Endfire Radiation

A novel substrate integrated waveguide (SIW) fed horizontally polarized endfire magnetoelectric (ME) dipole antenna composed of an open-ended SIW with broad walls vertical to substrates and a pair of electric dipoles realized by four metallic patches is proposed. Simple configuration and excellent performance including an impedance bandwidth of 46.5%, stable gain of around 6 dBi, and symmetrical cardioid radiation patterns with low backward radiation and low cross polarizations are achieved. An SIW 90° twist integrated in three-layered substrate is implemented in order to connect the ME-dipole antenna conveniently to the SIW beam-forming network with broad walls parallel to substrates. A $4 \times 4$ SIW Butler matrix with a three-layered zigzag topology is then designed, which enables a size reduction of 45% for the matrix compared with conventional single-layered configuration but not affecting its operating characteristics. By employing a $2 \times 4$ ME-dipole array with 90° twists, two-folded Butler matrices and four SIW 3 dB E-plane couplers, a multibeam endfire array that can radiate eight beams scanning in two dimensions is designed at the 60 GHz band. The fabricated prototype verifies that a wide impedance bandwidth of 22.1%, gain varying from 10 to 13 dBi and stable radiation beams can be obtained. Due to good performance and the compact structure with low fabrication costs, the proposed design would be attractive for future millimeter-wave wireless applications including 5G communications and the WiGig system.

A Multibeam End-Fire Magnetoelectric Dipole Antenna Array for Millimeter-Wave Applications

A novel substrate integrated waveguide (SIW)-fed end-fire magnetoelectric (ME) dipole antenna is proposed. The antenna consisting of an open-ended SIW and a pair of electric dipoles has a simple structure that can be integrated into substrates conveniently. Both the open-ended SIW and the electric dipoles are effectively radiated together. Excellent performance, including a bandwidth of 44%, symmetrical radiation patterns that are almost identical in two orthogonal planes, low backward radiation, low cross polarizations, stable gain of around 5 dBi, and wide beamwidth of around 110°, are also obtained. An $8 \times 8$ SIW Butler matrix is then designed. Modifications to the geometry of the matrix provide more spacing to locate SIW phase shifters and phase compensation structures with wide bandwidth. By employing the proposed end-fire ME-dipole antenna array and the $8 \times 8$ Butler matrix, an eight-beam antenna array is realized. The fabricated prototype demonstrates that wide bandwidth, stable radiation patterns with cross polarizations of less than −28 dB and gain varying from 9 to 12 dBi can be obtained. The proposed multibeam end-fire ME-dipole antenna array would be an attractive candidate for millimeter-wave wireless applications due to its good performance, ease of integration, and low fabrication cost.

SIW Butler Matrix with Modified Hybrid Coupler for Slot Antenna Array

This paper presents a substrate integrated waveguide Butler matrix with a modified hybrid coupler, operating from 28 to 32 GHz. The modified hybrid coupler is realized by using 90° hybrid coupler followed by a -45° compensating phase shifter. Thus, 45°/135° output phase differences can be obtained using this type of coupler. Compared with the equal-length unequal-width phase shifter, the compensating phase shifter exhibits better phase characteristics, with only 3° phase error over 28-32 GHz. Because the phase of compensating phase shifter is not realized by taking the phase introduced by the crossover as a reference, it gives great flexibility to the design of compensating phase shifter. Adopting the modified hybrid coupler, the designed Butler matrix features the output phases with peak to peak error of 13° and wideband performance from 28 to 32 GHz. The slot array fed by the Butler matrix can radiate four slanted beams with acceptable measured gains, in the range of 9.7~12 dBi for port 1 excitation and 8.4~11.1 dBi for port 2 excitation. The radiated beams can reach a wide azimuthal coverage between ±61°.

MINIATURIZED MULTILAYER FOLDED SUBSTRATE INTEGRATED WAVEGUIDE BUTLER MATRIX

Recently, substrate integrated waveguide (SIW) technol- ogy attracts more and more attention in the development of millimeter- wave integrated beamforming network (BFN) depending on its inher- ent advantages. However, the SIW-based BFN usually has a large cir- cuit size. To overcome this weakness, we propose a novel multi-folded SIW Butler matrix at the center frequency of 60GHz. Two difierent full-wave simulation tools are employed to validate our design. This folded BFN ofiers a number of beneflts, such as highly compact con- flguration, low coupling between adjacent paths, and wide operation bandwidth. For convenient use, the SIW ports can be converted to the microstrip line ports arranged in order through a special broad- band two-layer transition network. Such a miniaturized SIW Butler matrix can reduce the circuit area by more than 60% compared with the conventional single-layer version.

Design of a 60-GHz Substrate Integrated Waveguide Butler Matrix—A Systematic Approach

A 60-GHz substrate integrated waveguide Butler matrix designed based on a systematic approach is fabricated by a standard single-layer print circuit board process, which is more economical for mass production than are the advanced processes such as low-temperature co-fired ceramic, thick-film process, etc. The systematic approach involves design equations, simulations, and measurements. Starting with a set of explicit design equations for the short-slot couplers, one calculates the structure dimensions. The calculated dimensions are then optimized with full-wave simulation to finalize the design of the key components, including the couplers and phase shifters. With the use of a noncoaxial multiport measurement technique, the characteristics of the components are acquired through a probe station and a two-port vector network analyzer. Measurement technique plays a critical role in the systematic design approach. By measuring at the intrinsic ports or the wave ports defined in the full-wave simulations, the components are unambiguously verified and then integrated to complete the design of the Butler matrix. The resulting Butler matrix is also verified by the measured eight-port <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -matrix, which is shown in good agreement with the simulated one. As the measured results of the Butler matrix show, for the operating bandwidth from 58 to 62 GHz, the reflections and isolations are lower than -13.5 dB and the insertion losses are below 2.5 dB. Much like the measured results of the components, the measured eight-port <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -matrix not only verifies the design of the Butler matrix, but also will facilitate the follow-on design of a switched-beam antenna array.