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

Preface. References. Acknowledgments. Acronyms. 1 Radiation. 1.1 The Early History of Electricity and Magnetism. 1.2 James Clerk Maxwell, The Union of Electricity and Magnetism. 1.3 Radiation by Accelerated Charge. 1.4 Reactive and Radiating Electromagnetic Fields. 2 Antennas. 2.1 The Early History of Antennas. 2.2 Antenna Developments During the First World War. 2.3 Antenna Developments in Between the Wars. 2.4 Antenna Developments During the Second World War. 2.5 Post-War Antenna Developments. 3 Antenna Parameters. 3.1 Radiation Pattern. 3.2 Antenna Impedance and Bandwidth. 3.3 Polarisation. 3.4 Antenna Effective Area and Vector Effective Length. 3.5 Radio Equation. 3.6 Radar Equation. 4 The Linear Broadside Array Antenna. 4.1 A Linear Array of Non-Isotropic Point-Source Radiators. 4.2 Plane Waves. 4.3 Received Signal. 4.4 Array Factor. 4.5 Side Lobes and Grating Lobes. 4.6 Amplitude Taper. 5 Design of a 4-Element, Linear, Broadside, Microstrip Patch Array Antenna. 5.1 Introduction. 5.2 Rectangular Microstrip Patch Antenna. 5.3 Split-T Power Divider. 5.4 Transmission and Reflection Coefficients for a Corporate Fed Array Antenna. 5.5 Simulation, Realisation and Measurement. 6 The Linear Endfire Array Antenna. 6.1 Introduction. 6.2 Phase Differences. 6.3 Hansen-Woodyard Endfire Array Antenna. 6.4 Mutual Coupling. 6.5 Yagi-Uda Array Antenna. 7 The Linear Phased Array Antenna. 7.1 Linear Phase Taper. 7.2 Beam Broadening. 7.3 Grating Lobes and Visible Space. 7.4 Means of Phase Shifting. 8 A Frequency Scanned Slotted Waveguide Array Antenna. 8.1 Slotted Waveguide Array Antenna. 8.2 Antenna Design. 8.3 Validation. 9 The Planar Array and Phased Array Antenna. 9.1 Geometry. 9.2 Planar Array Antenna. 9.3 Planar Phased Array Antenna. 10 Special Array Antenna Configurations. 10.1 Conformal Array and Phased Array Antennas. 10.2 Volume Array and Phased Array Antennas. 10.3 Sequential Rotation and Phasing. 10.4 Reactive Loading. 11 Array and Phased Array Antenna Measurement. 11.1 Input Impedance, Self-Coupling and Mutual Coupling. 11.2 Radiation Pattern Measurement. 11.3 Scan Element Pattern. 11.4 Waveguide Simulator. Appendix A: Complex Analysis. A.1 Complex Numbers. A.2 Use of Complex Variables. Appendix B: Vector Analysis. B.1 Notation. B.2 Addition and Subtraction. B.3 Products. B.4 Derivatives. Appendix C: Effective Aperture and Directivity. Appendix D: Transmission Line Theory. D.1 Distributed Parameters. D.2 Guided Waves. D.3 Input Impedance of a Transmission Line. D.4 Terminated Lossless Transmission Lines. D.5 Quarter Wavelength Impedance Transformer. Appendix E: Scattering Matrix. E.1 Normalised Scattering Matrix. E.2 Unnormalised Scattering Matrix. Appendix F: Voltage Incident at a Transmission Line. Appendix :G Cascaded Scattering Matrices. Index.

Array and Phased Array Antenna Basics

Smaller physical size and wider bandwidth are two antenna engineering goals of great interest in the wireless world. To this end, the concept of external substrate perforation is applied to patch antennas in this paper. The goal was to overcome the undesirable features of thick and high dielectric constant substrates for patch antennas without sacrificing any of the desired features, namely, small element size and bandwidth. The idea is to use substrate perforation exterior to the patch to lower the effective dielectric constant of the substrate surrounding the patch. This change in the effective dielectric constant has been observed to help mitigate the unwanted interference pattern of edge diffraction/scattering and leaky waves. The numerical data presented in this paper were generated using the finite-difference time-domain (FDTD) technique. Using this numerical method, a patch antenna was simulated on finite-sized ground planes of two different substrate thicknesses, with and without external substrate perforation. The computations showed the directivity drop in the radiation pattern caused by substrate propagation was noticeably improved by introducing the substrate perforation external to the patch for the case of a patch antenna on a relatively thick substrate without any loss of bandwidth. Measurements of a few patch antennas fabricated on high dielectric constant substrates with and without substrate perforation are included for completeness. Good correlation between the computed results and measurements is observed.

Patch antennas on externally perforated high dielectric constant substrates

In order for a reflectarray to have a thin flat-plate structure, microstrip patches with microstrip transmission delay lines are proposed to form the microstrip reflectarray antenna. The results of a theoretical analysis and evaluation of this antenna are presented. It is shown that, with proper designs, this antenna can have many significant advantages over a conventional parabolic reflector. >

Microstrip reflectarray

The planar inverted-F antenna (PIFA) is popular for portable wireless devices because of its compact size and low profile. The PIFA is designed to operate with a ground plane and the ground plane is an integral part of the antenna assembly. In fact, the ground plane size is the limiting factor for the PIFA in many applications. Some work has been reported on the performance of PIFAs mounted on a conducting box of fixed size; however, what is lacking is a parametric study on the antenna behaviour as a function of geometry or antenna position and orientation on a finite ground plane. The paper presents results from a comprehensive investigation on the performance of a conventional PIFA mounted on ground planes of various sizes and shapes. The orientation and position of the antenna on a fixed-size ground plane is analysed. The influence of ground plane geometry on resonant frequency, bandwidth, gain, and radiation patterns are presented. These results are very useful in the design of a PIFA for applications requiring a small ground plane. Specifically, the results show the trade-offs between PIFA geometry and ground plane size with electrical performance. Both numerical simulation and experimental data are presented.

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Ground plane effects on planar inverted-F antenna (PIFA) performance

The uniform geometrical theory of diffraction (GTD) is employed for calculating the edge diffracted fields from the finite ground plane of a microstrip antenna. The source field from the radiating patch is calculated by two different methods: the slot theory and the modal expansion theory. Many numerical and measured results are presented to demonstrate the accuracy of the calculations and the finite ground plane edge effect.

The finite ground plane effect on the microstrip antenna radiation patterns

An X-band circularly polarized reflectarray antenna with an offset feed is designed, fabricated, and measured. The proposed design features the use of split square ring elements with a modified element rotation technique for phase compensation, which allows the rotation of the slot instead of the element itself. This is crucial in single-layer multiband reflectarray antenna designs where it is desired to minimize the effectively occupied area by individual elements. A design flow chart of the reflectarray antenna is summarized, and the element/system design procedure is presented in details. A reflectarray prototype was measured in a near field measurement system, which operates at 8.4 GHz with a gain of 30.4 dB and an aperture efficiency of 53.7%. Both the axial ratio bandwidth (AR <; 3 dB) and the 3 dB gain bandwidth are 6%.

An Offset-Fed X-Band Reflectarray Antenna Using a Modified Element Rotation Technique

An efficient computational method is demonstrated for determining the far-field patterns of reflectors illuminated by pyramidal horns. A uniform geometrical theory of diffraction (GTD) formulation is used to determine the near- and far-fields of the horn. The far-field patterns of the offset reflector are constructed using the physical optics (PO) formulation in conjunction with the Jacobi-Bessel expansion method. Many representative results are shown for the far-field patterns of the reflector. In particular, the concept of the optimum phase center for the best location of a horn illuminating a reflector is carefully studied and some useful observations are made.

J. Huang

Papers

The finite ground plane effect on the microstrip antenna radiation patterns

An Offset-Fed X-Band Reflectarray Antenna Using a Modified Element Rotation Technique

A GTD study of pyramidal horns for offset reflector antenna applications