Multi-beam antennas are critical components in future terrestrial and non-terrestrial wireless communications networks. The multiple beams produced by these antennas will enable dynamic interconnection of various terrestrial, airborne and space-borne network nodes. As the operating frequency increases to the high millimeter wave (mmWave) and terahertz (THz) bands for beyond 5G (B5G) and sixth-generation (6G) systems, quasi-optical techniques are expected to become dominant in the design of high gain multi-beam antennas. This paper presents a timely overview of the mainstream quasi-optical techniques employed in current and future multi-beam antennas. Their operating principles and design techniques along with those of various quasi-optical beamformers are presented. These include both conventional and advanced lens and reflector based configurations to realize high gain multiple beams at low cost and in small form factors. New research challenges and industry trends in the field, such as planar lenses based on transformation optics and metasurface-based transmitarrays, are discussed to foster further innovations in the microwave and antenna research community.

/pdf/quasi-optical-multi-beam-antenna-technologies-for-b5g-and-6g-1gpf5orbnv.pdf

Quasi-Optical Multi-Beam Antenna Technologies for B5G and 6G mmWave and THz Networks: A Review

A dual-broadband dual-polarized magnetoelectric dipole (ME-dipole) antenna with a shared aperture for 5G applications is proposed in this communication. The antenna is operated at the 2.35–3.93 GHz (N41 and N78) and 24–34 GHz (N257 and N258) dual fifth-generation (5G) bands. Each band exhibits a dual-polarized radiation, and more importantly, the two bands shared the same radiation aperture. In the millimeter-wave (MM-wave) band, the proposed antenna can generate two-dimensional (2-D) multiple beams with dual-polarization, and the switching range at each plane is about ±20°. The antenna is composed of two kinds of ME-dipole. The MM-wave band uses an ME-dipole feeding through the substrate-integrated waveguide (SIW) as the source to excite four horn antennas with inclined inner walls to achieve high-gain 2-D switching with dual-polarization. The lower frequency band combines the four horn antennas to achieve a large dual-polarized ME-dipole antenna. The antenna operating mechanism and the design procedure are illustrated in detail. The measured results show that a −10 dB impedance bandwidth of 33.91% (24–33.91 GHz) and 50.31% (2.35–3.93 GHz) is achieved. The peak gain of the proposed antenna in the two bands is 10.67 dBi (3.8 GHz) and 14.85 dBi (32.2 GHz), respectively. Due to the robust characteristics of the ME-dipole and horn antenna, the antenna shows a stable pattern and a wide impedance bandwidth, which covers most of the current 5G microwave and MM-wave bands. The antenna features a shared aperture, large frequency ratio, dual-broadband, dual-polarization, and 2-D multiple beams, which are well suited for the 5G base station applications.

Dual-Broadband Dual-Polarized Shared-Aperture Magnetoelectric Dipole Antenna for 5G Applications

Digital Metasurfaces have recently offered tremendous opportunities in real-time manipulation of terahertz (THz) waves in programmable ways to reach special applications that cannot be achieved using conventional architectures. Unlike the previous demonstrations at this spectrum, which only exploit spatial modulation, in this paper, we propose a spatiotemporally modulated graphene-based digital metasurface (STGDM) to carry out different missions in both space and frequency domains. Applying proper time-variant Fermi level controlling signals turns a 2-bit phase-only meta-atom into a powerful sub-wavelength scatterer with the ability to modulate both phases and amplitudes with arbitrary high quantization levels at center or harmonic frequencies. Several illustrative examples have been presented to demonstrate the excellent capability of our STGDM to dynamically realize different THz scattering behaviors, including beam deflection, vortex beam generation, spatial power dividing, harmonic focusing, and airy beam generation with a single digital interface. The employed space-time coding strategy reveals an additional knob for lifting some fundamental limitations of the previous graphene-based metasurfaces to achieve functionalities requiring both phase and amplitude modulations. Meanwhile, by facilitating the structural design to obtain high quantization levels, the proposed STGDM may be a reliable component in highly-efficient THz imaging and information systems.

Reprogrammable Spatiotemporally Modulated Graphene-Based Functional Metasurfaces

This research targets the robust routing protocols in airborne networks (ANs). Particularly, we target the AN which is equipped with the latest antenna technology, called Multi-Beam Directional Antenna (MBDA) [1]. MBDA allows the simultaneously packet delivery in multiple directions without RF interference between directions/beams. We have found that MBDAs can actually bring new opportunities to enhance a popularly used AN routing scheme, i.e., optimized link state routing protocol (OLSR). In particular, MBDAs enable OLSR to better achieve low probability of detection (LPD), a critical requirement in many military applications with adversary nodes nearby which try to eavesdrop the signals. Therefore, we propose a multi-path enhanced OLSR, which is able to exploit the advantages of multi-beam transmissions and select the proper multi-point relays (MPRs) to easily reach all nodes by using only a small number of message broadcasts. An innovative method based on social network concept is used for the selection of MPRs in multi-beam OLSR. Finally, we have conducted the simulations and showed that the enhanced OLSR is suitable for mobile and dense airborne networks with LPD requirements.

Enhanced OLSR routing for airborne networks with multi-beam directional antennas

A multiple beam parasitic array radiator (MBPAR) antenna is proposed in this letter. The MBPAR antenna can cover all angles in horizontal plane by generating six wide beams with angle-step of 60° in 2.4 GHz wireless local area network (WLAN) bands. The MBPAR antenna consists of six active elements, a center parasitic reflector, twelve parasitic isolation elements, and a ground structure. Six active elements located in the ground edge use a common center parasitic reflector to realize six beams. The parasitic isolation elements located on the angular bisectors are used to improve the isolation between adjacent ports. Unlike the traditional electrically steerable parasitic array radiator antenna, the MBPAR antenna can realize six beams at the same time, which remarkably increase the communication capacity. To validate the proposed design, an MBPAR antenna has been designed and prototyped at 2.45 GHz. The MBPAR antenna exhibits VSWR <2 and isolations better than −20 dB in 2.4G-WLAN bands. The peak realized gain of 7.3 dBi and efficiency of 95.7% of the MBPAR antenna are obtained. The MBPAR antenna with large communication capacity and low wind resistance is suitable for the outdoor WLAN applications.

Multiple Beam Parasitic Array Radiator Antenna for 2.4 GHz WLAN Applications

This article presents a novel triband dual-polarized shared-aperture antenna with frequency-selective function for sub-6 GHz base station applications. The proposed antenna is composed of a dual-polarized square loop antenna with two parasitic loops for 2G/3G/4G (1710–2690 MHz) and a differentially fed dual-polarized planar antenna for 5G (3300–3600 and 4800–5000 MHz) base station applications. These two antennas are placed coaxially but different altitudes for saving the installation space. In order to achieve good individual performance for these two antennas in the same aperture without interference or blocking, the lower band (LB) antenna is designed as a frequency-selective surface (FSS) for the nether mid/upper bands (M/UBs) antenna. The measured results show that the proposed antenna achieves a high port isolation (>20 dB) between LB and M/UBs and a −10-dB impedance bandwidth of 50.4% (1.60–2.70 GHz), 14.9% (3.28–3.80 GHz), and 8.6% (4.75–5.18 GHz). To further validate the design concept, an antenna array composed of four LB elements and eight M/UBs elements with the corresponding spacing is fabricated and measured, which demonstrates the application of the triband shared-aperture antenna in array form.

Triband Dual-Polarized Shared-Aperture Antenna for 2G/3G/4G/5G Base Station Applications

This communication presents a beam-deflection short backfire antenna (BD-SBA). The proposed BD-SBA differs from the conventional SBA in that the main reflector of the BD-SBA is a phase-modulated metasurface instead of a perfect electric conductor (PEC). The phase-modulated metasurface consists of 15 columns of unit cells which are designed to change the phase of the reflected waves. Therefore, the beam of the BD-SBA can be deflected to a certain angle. First, several BD-SBAs with linear phase-modulated metasurfaces are studied, which indicates that the beam of antennas point at different directions. Second, the BD-SBAs with nonlinear phase-modulated metasurfaces are studied to compare the difference between metasurfaces with linear and nonlinear width variation of patch. The simulated results show that the metasurface with nonlinear variation can obtain better performance than the former. To verify this design method, the BD-SBA with $\Delta \theta = 10^{\circ }$ was fabricated and measured at ${X}$ -band. The overall height of the proposed antenna is 0.35 wavelength at 10 GHz. The measured and simulated results are in good agreement; the measured beam-deflection angle, realized gain, and aperture efficiency are 10°, 14.8 dBi, and 68.3% at the center frequency, respectively. Due to the beam-deflection function, medium-to-high gain characteristics, and low profile, the proposed BD-SBA can be expected to find potential applications in wireless backhauling.

Beam-Deflection Short Backfire Antenna Using Phase-Modulated Metasurface

A compact Rotman lens is presented in this paper. The compact Rotman lens consists of a lens body and truncated ports with the energy distribution slots. By truncating the long triangular transitions of the traditional Rotman lens, the lengths of lens ports are reduced effectively. However, the impedance discontinuity problem is caused by truncating the triangular transition. To solve this problem, the energy distribution slots are designed between the feed lines and the truncated lens body apertures. The energy distribution slot is evolved from the 1-2 power divider, which creates a transition process for the wave energy propagating from the feed lines and realizes good impedance match between the lens body and the feed lines. To validate the proposed design, a 4×7 Rotman lens has been designed and prototyped at 10 GHz. The Rotman lens exhibits a scanning range of ±33°, 27% bandwidth for VSWR <; 2, and the isolation between beam ports better than 17.2 dB within the operation bandwidth. Basing on the advantages of compact size, low cost, easy processing, and wide bandwidth, the proposed compact Rotman lens may have wide applications in the multi-beam antenna systems.

Design of Compact Rotman Lens Using Truncated Ports With Energy Distribution Slots

A compact microstrip Rotman lens is proposed in this paper. The microstrip Rotman lens consists of a lens body and Chebyshev impedance transformers. The Chebyshev impedance transformers are used as beam ports, array ports and dummy ports. Compared to the traditional linear tapered transition, the Chebyshev impedance transformer is shorter, which leads to the size reduction and insertion loss improvement for the Rotman lens. An X-band 4 × 7 Rotman lens using Chebyshev impedance transformers is designed and fabricated. Compared to a traditional Rotman lens, the proposed Rotman lens shows a size reduction of about 56% and an insertion loss improvement at 10 GHz. The measured results demonstrate that better than 15 dB return loss throughout the bandwidth from 8 to 12 GHz is obtained.

/pdf/compact-microstrip-rotman-lens-using-chebyshev-impedance-2jqe3lvhpm.pdf

Qiuyan Liang

Papers

Triband Dual-Polarized Shared-Aperture Antenna for 2G/3G/4G/5G Base Station Applications

Multiple Beam Parasitic Array Radiator Antenna for 2.4 GHz WLAN Applications

Beam-Deflection Short Backfire Antenna Using Phase-Modulated Metasurface

Design of Compact Rotman Lens Using Truncated Ports With Energy Distribution Slots

Compact Microstrip Rotman Lens Using Chebyshev Impedance Transformers