With the demanding system requirements for the fifth-generation (5G) wireless communications and the severe spectrum shortage at conventional cellular frequencies, multibeam antenna systems operating in the millimeter-wave frequency bands have attracted a lot of research interest and have been actively investigated. They represent the key antenna technology for supporting a high data transmission rate, an improved signal-to-interference-plus-noise ratio, an increased spectral and energy efficiency, and versatile beam shaping, thereby holding a great promise in serving as the critical infrastructure for enabling beamforming and massive multiple-input multiple-output (MIMO) that boost the 5G. This paper provides an overview of the existing multibeam antenna technologies which include the passive multibeam antennas (MBAs) based on quasi-optical components and beamforming circuits, multibeam phased-array antennas enabled by various phase-shifting methods, and digital MBAs with different system architectures. Specifically, their principles of operation, design, and implementation, as well as a number of illustrative application examples are reviewed. Finally, the suitability of these MBAs for the future 5G massive MIMO wireless systems as well as the associated challenges is discussed.

Multibeam Antenna Technologies for 5G Wireless Communications

By covering a metal ground plane with a periodic surface texture, we can alter its electromagnetic properties. The impedance of this metasurface can be modeled as a parallel resonant circuit, with sheet inductance L, and sheet capacitance C. The reflection phase varies with frequency from +/spl pi/ to -/spl pi/, and crosses through 0 at the LC resonance frequency, where the surface behaves as an artificial magnetic conductor. By incorporating varactor diodes into the texture, we have built a tunable impedance surface, in which an applied bias voltage controls the resonance frequency, and the reflection phase. We can program the surface to create a tunable phase gradient, which can electronically steer a reflected beam over +/- 40/spl deg/ in two dimensions, for both polarizations. We have also found that this type of resonant surface texture can provide greater bandwidth than conventional reflectarray structures. This new electronically steerable reflector offers a low-cost alternative to a conventional phased array.

Two-dimensional beam steering using an electrically tunable impedance surface

A multilayer reflectarray composed of two stacked arrays with rectangular patches of variable size is demonstrated. A progressive phase distribution on the reflector surface is achieved by adjusting the dimensions of the patches. The phase of the reflection coefficient at each element is computed by the method of moments in the spectral domain, assuming local periodicity. A technique is presented for the design of dual polarization reflectarrays that yields all the dimensions for the photo-etching mask. A prototype has been design, built and measured, and a superior bandwidth performance has been verified, compared to conventional single layer reflectarrays.

Design of two-layer printed reflectarrays using patches of variable size

Advances in reflectarrays and array lenses with electronic beam-forming capabilities are enabling a host of new possibilities for these high-performance, low-cost antenna architectures. This paper reviews enabling technologies and topologies of reconfigurable reflectarray and array lens designs, and surveys a range of experimental implementations and achievements that have been made in this area in recent years. The paper describes the fundamental design approaches employed in realizing reconfigurable designs, and explores advanced capabilities of these nascent architectures, such as multi-band operation, polarization manipulation, frequency agility, and amplification. Finally, the paper concludes by discussing future challenges and possibilities for these antennas.

Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review

This paper demonstrates a novel means of achieving cophasal far-field radiation for a circularly polarized microstrip reflectarray with elements having variable rotation angles. Two Ka-band half-meter microstrip reflectarrays have been fabricated and tested. Both are believed to be the electrically largest reflectarrays ever developed using microstrip patches. One, a conventional design, has identical square patches with variable-length microstrip phase-delay lines attached. The other has identical square patches with identical microstrip phase-delay lines but different element rotation angles. Both antennas demonstrated excellent performance with more than 55% aperture efficiencies, but the one with variable rotation angles resulted in better overall performance. A brief mathematical analysis is presented to validate this "rotational element" approach. With this approach, a means of scanning the main beam of the reflectarray over a wide angular region without any RF beamformer by using miniature or micromachined motors is viable.

A Ka-band microstrip reflectarray with elements having variable rotation angles

This paper presents the study and prototype demonstration of the concepts of antenna focusing, cross-polarization reduction, and multiple-polarization capability of a planar microstrip reflectarray antenna. A square patch with two equal microstrip delay lines connected to its two orthogonal feeding points is used as the antenna element of the planar reflectarray. The length of the delay lines, which varies from patch to patch, is schematically designed to focus the plane wave to the feed point. The measured overall efficiency of the prototype antenna is above 50% in the normal operating band, and in some frequency ranges the efficiency has reached 70%. The experimental patterns show that the measured cross polarization due to special arrangement of the delay lines is quite low at the direction of the main beam. X-polarization and Y-polarization measured data show that the antenna is suitable for multiple-polarization applications (dual linear and dual circular). Surprisingly, the antenna has achieved approximately greater than 7% of gain bandwidth (-3 dB gain drop). These results demonstrate the feasibility of such an antenna for radar and communication system applications. >

Multiple-polarization microstrip reflectarray antenna with high efficiency and low cross-polarization

We propose the improved CPW-fed configurations with dual-mode double-square-ring resonators (DMDSRR) for quad-band applications. The resonant frequency equations of DMDSRR are introduced for simply designing quad-band bandpass filter (BPF). Resonant frequencies can be controlled by tuning the perimeter ratio of the square rings. To obtain lower insertion loss, higher out-of-band rejection level and wider bandwidth of quad-band, the improved CPW-fed and dual-mode perturbations are designed. The proposed filter is successfully simulated and measured. It can be applied to 0.95, 1.26, 1.89 and 2.29 GHz systems.

CPW-Fed Dual-Mode Double-Square-Ring Resonators for Quad-Band Filters

Using configuration synthesis and design map, the CPW-fed circular fractal slot antennas are proposed for dual-band applications. In practice, the experimental results with broadband and dual-band responses (47.4% and 13.5% bandwidth) and available radiation gains (peak gain 3.58 and 7.28 dBi) at 0.98 and 1.84 GHz respectively for half-wavelength design are achieved firstly. Then, the other broadband and dual-band responses (75.9% and 16.1% bandwidth) and available radiation gains (peak gain 3.16 and 6.62 dBi) at 2.38 and 5.35 GHz for quarter-wavelength design are described herein. Contour distribution patterns are applied to figure out the omni-directional patterns. The demonstration among the design map and the EM characteristics of the antenna is presented by current distributions.

CPW-Fed Circular Fractal Slot Antenna Design for Dual-Band Applications

Blooming in data-communication applications is beyond all expectations. Smart antennas as now regarded as one of enabling technologies for next-generation wireless communication systems with its promised performance on enhancing network capacity. This paper presents a detailed analysis of the classes of smart antenna systems (SASs), including adaptive arrays, multibeam multiple-input-multiple-output (MB-MIMO) antennas, and diversity-antenna systems. This study also demonstrates practical examples of communication system with developed smart antennas, and shows that using smart antennas instead of traditional antennas highly improves the system performance.

Smart Antennas for Advanced Communication Systems

A novel planar monopole antenna designed with tulip-shaped structure is proposed for UWB applications. The corolla of tulip-shaped structure is constructed with petal and calyx by the EM-mode synthesis. By tuning the petal structure, wideband performance covering 2.55 to 40.5 GHz (1:16) with −10-dB return loss is measured. The radiation patterns are omnidirectional patterns. Antenna gain is 0.2 to 4.0 dBi in the operating range. The current distributions are simulated for demonstration. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 307–312, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21334

Dau-Chyrh Chang

Papers

Multiple-polarization microstrip reflectarray antenna with high efficiency and low cross-polarization

CPW-Fed Dual-Mode Double-Square-Ring Resonators for Quad-Band Filters

CPW-Fed Circular Fractal Slot Antenna Design for Dual-Band Applications

Smart Antennas for Advanced Communication Systems

A novel tulip-shaped monopole antenna for UWB applications