High-Gain Open Resonator Antennas at Microwave and Terahertz Frequencies


Student thesis: Doctoral Thesis

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Award date20 Jul 2022


This thesis presents a series of high-gain open resonator antennas (ORA). Benefiting from the combined characteristics of high directivity, low profile, low cost, simple structure and lossless feeding, the open resonator antenna has aroused widespread interest. It’s regarded as a promising candidate in future wireless communication, imaging, sensing and radar systems. To solve the problems of low data rate, spectrum scarcity, and spectrum under-utilization, we designed several ORAs for operating at higher frequencies and realizing polarization division multiplexing.

First, a high-gain ORA operating at 1 THz is demonstrated. Imprinting and dry etching technologies in silicon are employed. A complementary antenna feed based on the ME dipole is proposed for enhancing the radiation characteristics of the antenna. The microfabrication technologies are compatible with the Si-based integrated circuit manufacturing process. The THz antenna is realized with over 20 dBi of antenna gain. Moreover, the antenna has the characteristic of low sidelobe level which is advantageous in many wireless applications. Although the microfabrication can achieve high-precision and smooth-morphology at THz, it is expensive and complicated, which will limit its large-scale application.

Therefore, a novel design of an open resonator antenna was proposed to fulfill the requirements of high gain, low cost and low fabrication complexity at sub-THz. A planar cavity with a loaded phase gradient metamaterial is used to imitate a spherical cavity, which helps to support higher-order modes and hence, widen the bandwidth. The design procedure is introduced in detail. With the help of high-precision three-dimensional printing technology, the planar open resonator antenna can be manufactured with a relatively lower cost and complexity. Measurements were carried out to prove that a relatively wide 3 dB gain bandwidth of 13% and a high gain over 16.8 dBi can be achieved.

The open resonator antenna not only is a potential at THz frequency but also can be applied in polarization division multiplexing to enhance the spectral efficiency. Third, a planar ORA with a thin polarizer loaded inside the cavity is proposed for millimeter wave bands. The antenna is excited by a linearly polarized magneto-electric (ME) dipole. To realize self-circular-polarizing characteristics, a polarizer with a meander line is placed between the partially reflective surface and the reflective surface. Sharing the same radiating aperture, LHCP and RHCP waves can be generated by separate input ports. After the mechanism of the circular polarization is analyzed, simulation and measurement are carried out to verify the proposed design. The operating bandwidth is 4%, from 27.4 GHz to 28.5 GHz, which covers the fifth-generation wireless communication 28 GHz band. The peak gains are 16.85 dBi and 17.20 dBi for LHCP and RHCP respectively.

However, due to the number of states limit, a dual CP antenna can only realize twofold spectral efficiency, which is not enough nowadays. Thus, the orbital angular momentum (OAM) wave, which has infinite orthogonal states, can be applied to realize infinite fold spectral efficiency theoretically. Thus, an ORA for dual orbital angular momentum (OAM) modes generation and low divergence radiation is proposed. Excitation of OAM modes is determined using open resonator theory and circular array theory. In the cavity, eight aperture-coupled patch antenna elements are used to excite two higher-order Laguerre-Gaussian modes with 90° phase difference. As verified by simulation and experiment,
the proposed low-profile antenna can radiate left-hand circularly polarized (LHCP) or right-hand circularly polarized (RHCP) waves of OAM modes l = ± 1, which have a relatively low divergence angle of ± 9º and a high gain of around 13 dBi.