Design and performance improvement of radial line slot array antennas

Rapid increase in satellite-based wireless services has created a demand for directive beam-steering antennas with wide radiation bandwidths. Commercially available parabolic reflectors provide satisfactory performance but their bulky physical appearance and nonplanar configuration make them less attractive in several applications. Microstrip array antennas exhibit poor radiation efficience at higher gain. Radial line slot array (RLSA) antennas are known for their directive radiation charateristics and planar profile but suffer from limited radiation bandwidth and lack the beam-steering feature. This thesis presents RLSA antennas with improved radiation performance, wide radiation bandwidth and beam-steering feature. Several RLSA antennas have been designed. One of these RLSA antennas has a gain of 36.9 dBic with radiation efficiency greater than 90%. By optimising near-field amplitude distortion, sidelobe level of an RLSA antenna has been reduced to -26.1 dB, which comes close to Class-2 and Class-3 ETSI antenna standards. RLSA radiation bandwidth has been enhanced by introducing permittivity variation of the dielectric materials in the cavity. Such an antenna has demonstrated a 3-dB directivity bandwidth of 19.4% and an axial ratio bandwith of 27.3%. Furthermore, this thesis also presents a methodology to steer the beam of RLSA antennas by using a pair of near-field phase-transforming metasurfaces.