Designs of Wide-Angle Scanning Phased Array Antennas

Abstract

Phased array antennas are widely used in various applications, including radar systems, wireless communications, and satellite communications. The ability to scan over a wide angle is crucial for these applications to achieve optimal performance. However, traditional phased array designs often suffer from considerable gain fluctuations as the scanning angle increases. To extend the scan range, a widely used approach is to construct antenna elements with broad beam coverage. However, this approach has separated the design of antenna element and array. When the optimized wide-beam element is adapted to the array design, the element pattern usually deteriorates due to the mutual coupling, leading to a challenging and time-consuming optimization of array performance. To mitigate these problems, a novel design methodology is proposed in this thesis by taking mutual coupling effect into account in the design stage of element pattern.

Chapter 1 conducts a comprehensive literature review of existing techniques for wide-angle scanning phased array antennas. Chapter 2 proposes a novel phased array design approach. In this approach, a guiding isolated element pattern (IEP) is derived from the beam envelopes of desired scanning patterns and real array factors that incorporate the mutual coupling effect. For an ideal phased array with a stable peak gain across the scan range, a wide-beam IEP with beam shaping capability is needed. To demonstrate the idea, an aperture-coupled dielectric resonator antenna (DRA) is studied for beam shaping. This shaped-beam DRA is further utilized to build a 1-D scanning DRA array. The DRA element exhibits measured 3-dB beamwidths of 172° and 149° in the E- and H-planes, respectively. Notably, the H-plane main beam of the DRA array demonstrates a scanning capability from -72° to +72°, with minimal gain fluctuation of less than 0.9 dB.

Chapter 3 introduces a low-profile linear phased array antenna that features an extensive scan range. Each array element is designed with broad-beam multi-slots, which can be divided into y-directed magnetic currents with the same direction and x-directed magnetic currents with different directions. The y-directed magnetic currents contribute to a broadside radiation pattern, while the x-directed magnetic currents enhance the radiation in the low-elevation areas. By combining these two types of currents, a flexible wide-beam H-plane radiation pattern is achieved. The prototype of the array element demonstrates an exceptionally wide 3-dB H-plane beamwidth of 217°. Subsequently, an H-plane linear array antenna is constructed using our multi-slot elements. The main beam of this antenna is capable of steering from -90° to +90°, maintaining a gain fluctuation of less than 2.1 dB.

Chapter 4 investigates a 2-D wide-angle scanning DRA phased array based on complementary active element patterns (AEPs). First, a single-layer grounded coplanar waveguide (GCPW) feeding structure is proposed for slot-coupled DRA with a small backlobe. Based on this feeding network, a simple wide-beam isolated DRA operating at quasi-HEM₁₁₂ mode is presented by introducing an equivalent magnetic surface at the bottom of the DRA. This DRA element is used to build a small 3×3 array to quickly evaluate its AEP characteristics for beam scanning. However, unwanted scan blindness occurs in the E-plane AEP of the center element, which will greatly deteriorate the scanning performance. To solve this problem, a higher-order HEM₁₁₃ mode with complementary AEP is introduced to combine with the quasi-HEM₁₁₂ mode. As a result, a broad-beam center AEP is obtained in the 3×3 array. Next, an 8×8 DRA phased array with dummy elements is accordingly designed, exhibiting wide scan ranges of ±72° and ±74° in the E- and H-planes, respectively.

Overall, a novel design methodology and three wide-angle scanning phased array antennas are investigated in this thesis. The improved design procedure and competitive scanning performance make our proposed designs suitable for radar and various wireless communication systems.

Date of Award	19 Sept 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kwok Wa LEUNG (Supervisor)