A Low-Cost Technique for improving Angular Scan Range of Phased Array Antennas

Abstract

With the emergence of modern communication technologies, there has been an increasing demand for faster and higher-quality communication, which necessitates higher bit rates and, consequently, greater bandwidth. This shift has driven the adoption of higher operational frequencies, such as millimeter-wave bands. For instance, 5G mobile communications operate in the K band (18–27 GHz) and Ka band (27–40 GHz), while satellite communications often use the Ku band (12–18 GHz) and Ka band. However, as the operational frequency increases, path loss becomes significantly higher, requiring the use of higher-gain antennas to compensate for this loss. A key drawback of using high-gain antennas, such as parabolic reflectors, is the difficulty in steering the beam to cover a wider angular range. Phased array antennas provide an excellent solution as transmitting or receiving antennas for that reason, as they provide a high gain with the ability to electronically steer the beam to other directions by changing the progressive phase shift between the array elements. Designing a high-performance broadband phased array antenna with a wide angular scanning range is challenging, as the antenna parameters are interrelated and require tradeoffs. For example, increasing the distance between elements reduces mutual coupling and increases the effective aperture of the array, thereby enhancing its gain. However, this also causes grating lobes to appear at lower scan angles, thereby limiting the angular scanning range. Additionally, a larger element spacing necessitates a wider electronic phase shift range, requiring a more linear phase shifter with frequency, which complicates the design of the feeding network. The focus of this research is to investigate a low-cost approach to improving the angular scanning range of phased array antennas through the use of a wide angle impedance matching layer (WAIM), employing two techniques. First, A general analytical method is provided to characterize the array’s scan impedance variation in the presence of nearby reflecting surfaces, such as a ground plane or WAIM layers. Second, the generalized Smatrix technique is used to model the array unit cell and transmission line (TL) models for WAIM layers. The WAIM layer offers a low-cost, scalable solution to increase the angular scanning range of phased array antennas without altering their lattice configuration or feeding network. This makes it a modular solution, simpler than other techniques. In this thesis, Both main WAIM modeling techniques are investigated, applied to different array examples (slot and dipole arrays). Then, the GSM method is used to design a fully dielectric WAIM layer