This paper presents a general overview of substrate integrated transmission lines, from the perspective of historical background and progress of guided-wave structures and their impacts on the development of microwave circuits and integration solutions. This is highlighted through a technology roadmap involving the categorized five generations of microwave circuits. In particular, the substrate integration technologies are reviewed and discussed with focus on technical features, design highlights, component developments, structures evolution, and systems integration. A number of examples are presented to showcase some of the selected milestone research and development activities and accomplishments in connection with substrate integrated transmission line technologies, with particular focus on substrate integrated waveguide (SIW) techniques. Practical applications and industrial interests are also presented with key references and technical results, which show more and more product developments in the end-user sectors. It can be found that the popularity of SIW techniques is closely related to the achieved seamless integration of planar and non-planar structures into a unified design space, thereby allowing the possibility of combining major advantages of all the structures while alleviating their potential drawbacks. The future perspectives of the substrate integration technology are discussed through five major research directions, which suggest potential impacts in the development of future generations of circuits and systems such as system-on-substrate (SoS).

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Substrate Integrated Transmission Lines: Review and Applications

In this paper, a compact, broadband, planar array antenna with omnidirectional radiation in horizontal plane is proposed for the 26 GHz fifth-generation (5G) broadcast applications. The antenna element is composed of two dipoles and a substrate integrated cavity (SIC) as the power splitter. The two dipoles are placed side-by-side at both sides of the SIC, and they are compensated with each other to form an omnidirectional pattern in horizontal plane. By properly combing the resonant frequencies of the dipoles and the SIC, a wide impedance bandwidth from 24 to 29.5 GHz is achieved. To realize a large array while reducing the complexity, loss, and size of the feeding network, a novel dual-port structure combined with radiation and power splitting functions is proposed for the first time. The amplitude and phase on each element of the array can be tuned, and therefore, the grating lobes level can be significantly reduced. Based on the dual-port structure, an eight-element array with an enhanced gain of over 12 dBi is designed and prototyped. The proposed antenna also features low profile, low weight, and low cost, which is desirable for 5G commercial applications. Measured results agree well with the simulations, showing that the proposed high-gain array antenna has a broad bandwidth, omnidirectional pattern in horizontal plane, and low side-lobes.

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Planar Sub-Millimeter-Wave Array Antenna With Enhanced Gain and Reduced Sidelobes for 5G Broadcast Applications

This letter presents a compact dual-layer 4 × 8 Butler matrix (BM) with sidelobe level (SLL) suppression in substrate-integrated waveguide (SIW) technology. Addressing the excessive crossovers in the classic 4 × 8 BM, a novel dual-layer configuration is proposed here. Such a configuration can help reduce the required crossovers from original five sets to merely one set. Therefore, the 4 × 8 BM can be significantly simplified to achieve better compactness. Based on this configuration, a SIW dual-layer 4 × 8 BM is designed with a dimension of 6.1 λ × 4.1 λ . To evaluate its SLL suppression effect, a multibeam array fed by the proposed BM is designed, simulated, and measured.

Compact Substrate-Integrated 4 × 8 Butler Matrix With Sidelobe Suppression for Millimeter-Wave Multibeam Application

This article presents a low-cost, high-efficiency, and full-metal reflectarray (RA) antenna with mechanical beam-steerable capabilities. A unit cell (UC) implemented by a metal cylinder with a cuboid-shaped notch is proposed to achieve a 1 bit reflection phase (0 and $\pi $ ) for the transverse electric (TE) and transverse magnetic (TM) normal incidence waves. The proposed UCs can be employed to construct an RA antenna with 2-D beam-steerable abilities. For demonstration, the RA antennas with six different beam directions are presented as examples, by simply adjusting the rotations of the UCs. The impedance matches of the RA antenna are all below −10 dB from 22 to 33 GHz, and the measured radiation patterns of the RA antenna are all highly consistent with the simulated counterparts for the six different beam direction scenarios. A 1.5 dB gain drop bandwidth of approximately 20% from 24.7 to 30 GHz and a peak realized gain of 18.9 dBi at 26 GHz are experimentally obtained for the RA antenna with radiation patterns at broadside. Compared to the substrate-based UCs loaded with p-i-n diodes, the proposed UCs have full-metal structures without using any active RF components and dielectric substrates, leading to the high total efficiency of the proposed RA antenna. Due to the low-cost, high-efficiency, and high-power handling properties, the proposed RA antenna can provide a fixed or scanning beam and is a good candidate for 5G millimeter-wave communication applications.

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A Low-Cost, High-Efficiency and Full-Metal Reflectarray Antenna With Mechanically 2-D Beam-Steerable Capabilities for 5G Applications

In this paper, a 2-D scanning magnetoelectric (ME) dipole antenna array fed by printed ridge gap waveguide (PRGW) Butler matrix is proposed. The ME dipole antenna is designed to achieve a bandwidth wider than 20% at 30 GHz and stable gain of 6.5 ± 0.8 dB over the operating frequency bandwidth. A $4\times 4$ planar PRGW Butler matrix is designed and constructed using a four PRGW hybrid couplers having a wide bandwidth performance. The overall performance of the Butler matrix exhibits about 5° phase error over the operating frequency bandwidth. The integration of ME dipole antennas with the designed Butler matrix results in four fixed beams, one in each quadrant at an elevation angle of 35° from the broadside to the array axis. The proposed passive beam switching network (BSN) has a wide bandwidth of 20% with radiation efficiency higher than 84% over the operating bandwidth. The proposed BSN shows a stable radiation pattern with a stable gain of 10.3±0.2 dB, where the sidelobe level is less than −15 dB over the whole operating frequency band. The fabricated prototype of the proposed BSN is tested, where the measured and simulated results show an excellent agreement.

2-D Scanning Magnetoelectric Dipole Antenna Array Fed by RGW Butler Matrix

A planar millimeter-wave 2-D beam-scanning multibeam array antenna fed by compact 16-way beam-forming network (BFN) in multilayered substrate integrated waveguide (SIW) technology is addressed. The BFN is formed by connecting two stacks of sub-BFNs, the E-plane sub-BFN and the H-plane sub-BFN. The H-plane sub-BFN is realized by a traditional H-plane $4 \times 4$ Butler matrix (BM). The key point of this design is to propose an E-plane $4 \times 4$ BM which realizes a planar E-plane sub-BFN. These two sets of sub-BFNs can joint directly without resorting to any connectors or connecting networks to form such a compact 16-way BFN with a reduced area of merely $3\lambda \times 12\lambda $ . After that, to be compatible with the proposed BFN, a ladder-type $4 \times 4$ slot antenna array is employed, which is comprised of four linear $1 \times 4$ slot antenna arrays. Different from traditional array, the four subarrays are distributed in separate layers for the purpose of jointing to the BFN more conveniently. Transition network are also required to connect the BFN with the antenna array. Finally, a compact 2-D scanning multibeam array antenna based on the planar SIW BFN are fabricated and measured, which would be an attractive candidate for 5G application.

Liang-Kui Sun

Papers

Planar Millimeter-Wave 2-D Beam-Scanning Multibeam Array Antenna Fed by Compact SIW Beam-Forming Network