There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Gain enhancement methods for printed circuit antennas

A low side-lobe substrate-integrated-waveguide (SIW) antenna array is presented at the 28-GHz band using broadband unequal feeding network for millimeter-wave (mm-wave) handset devices. The ground-plane size of the proposed antenna is fixed to half of the size of the Samsung Galaxy Note 4. The antenna array has been implemented with a multilayer structure created by stacking three substrates and a copper plate. An 8-way SIW feeding network with broadband 4-stage T-junction dividers and a cavity-backed antenna are investigated to obtain broadband performance. The proposed unequal T-junction dividers with phase compensation are introduced and designed for various output ratios. Applying Taylor beam-pattern synthesis in the 8-way SIW feeding network, low side-lobe performance is achieved. The measured result of the fabricated antenna has 2.3 GHz bandwidth within $\text{S}_11\,{ . The fabricated antenna can be performed with a gain up to 13.97 dBi with a low cross-polarization and symmetrical fan beam radiation patterns with low side-lobe levels. Most of the measured results are validated with the simulated results. The proposed antenna array provides low cost, broadband performance, and good radiation performances with low side-lobe levels for mm-wave handset devices.

Low Side-Lobe Substrate-Integrated-Waveguide Antenna Array Using Broadband Unequal Feeding Network for Millimeter-Wave Handset Device

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-layer multibeam conformal slot array antenna operating at a center frequency of 10 GHz is proposed in this paper. The antenna consists of a microstrip Rotman lens and a substrate-integrated waveguide (SIW) array of $10{\times} 10$ radiating slots, which is axially mounted onto a cylindrical surface with a radius of 90 mm, i.e., $3\lambda _{0}$ . The Rotman lens feeds the slot array through the coupling slots in the broad sides of the SIWs. An improved design process is introduced for realizing a conformal Rotman lens for cylindrically conformal arrays. There are unique requirements for the phase distribution and phase compensation in cylindrically conformal applications. The Rotman lens and slot antenna are built and optimized in full-wave simulation software. To validate the proposed concepts, a conformal antenna prototype is implemented and measured. The experimental results demonstrate a scanning range of ±46°, with a −3 dB crossover level between adjacent radiation beams in the E-plane and a −20 dB sidelobe level in the H-plane. The measured and simulated radiation patterns of all the scanned beams are in good agreement. This type of multibeam conformal slot array has been theoretically and experimentally studied, and it demonstrated the potential for applications in aircraft, missiles, and high-speed vehicles.

A Multibeam Cylindrically Conformal Slot Array Antenna Based on a Modified Rotman Lens

A single-layer substrate integrated waveguide slot array is presented for use in low sidelobe applications. A compact three-level power divider is developed to provide the required phase distribution and enhanced co-phase bandwidth. Then, the Elliott’s design procedure is employed taking accurately into account both the external coupling and the high-order mode internal coupling. The measured radiation pattern and the frequency response are in very good agreement with design specifications and with simulated results provided by CST Microwave Studio. The measured sidelobe level at the center frequency is below $-$ 32.3 dB in the E-plane and below $-$ 33.8 dB in the H-plane for a design goal of $-$ 35 dB.

Improved Design of Low Sidelobe Substrate Integrated Waveguide Longitudinal Slot Array

The Elliott’s procedure for the design of planar waveguide arrays of longitudinal slots has been extended to the cylindrical conformal case. The presented procedure has been devised to deal with the most general case of a cylindrical conformal substrate integrated waveguide (SIW) longitudinal slot array with a dielectric cover. Both external and internal mutual coupling have been accurately and effectively taken into account. The results of the synthesis procedure have been validated using both Ansys HFSS simulations and experimental results, showing a good agreement with the design specifications.

Design Equations for Cylindrically Conformal Arrays of Longitudinal Slots

A novel wideband cavity-backed slot antenna operating at X-band is proposed. Compared to conventional cavity-backed slot antennas, both the bandwidth and gain of the proposed antenna are significantly increased by adding a multilayer dielectric cover. This antenna offers a 40% (|S
 11
| <; -10 dB) impedance bandwidth. Meanwhile, the gain of a single antenna within this band is 6-9.5 dBi, 2-3 dB higher than those without that multilayer dielectric cover at most of the bandwidth. To further validate the capability of the proposed antenna, a 4 ×4 antenna array is designed, fabricated, and tested. The measurement results corroborate with simulations well. Taking advantage of its wider bandwidth and higher gain compared to the counterparts, this antenna could find great potential application in the future.

Design of Wideband Cavity-Backed Slot Antenna With Multilayer Dielectric Cover

An accurate and efficient procedure is devised to evaluate the mutual coupling in dielectric-covered planar arrays of longitudinal slots. This approach takes full advantage of the discrete complex image method to cast the spatial-domain Green's functions into closed forms, and hence a direct calculation of mutual coupling in the spatial-domain is available. The computation time reduces significantly compared to the previous spectral-domain procedure, without any loss in the accuracy, rendering this approach very attractive for the design of large dielectric-covered planar arrays.

/pdf/efficient-evaluation-of-the-external-mutual-coupling-in-4k875jlxmv.pdf

Hu Yang

Papers

A Multibeam Cylindrically Conformal Slot Array Antenna Based on a Modified Rotman Lens

Improved Design of Low Sidelobe Substrate Integrated Waveguide Longitudinal Slot Array

Design Equations for Cylindrically Conformal Arrays of Longitudinal Slots

Design of Wideband Cavity-Backed Slot Antenna With Multilayer Dielectric Cover

Efficient Evaluation of the External Mutual Coupling in Dielectric-Covered Waveguide Slot Arrays