Millimeter Wave Circularly Polarized Antennas Based on Printed Ridge Gap Waveguide Technology

The growing demand for higher data rates in wireless communication systems has built a significant momentum toward the fifth-generation (5G) of mobile communications as there are more uncongested frequency bands compared to the sub 6 GHz band. Circularly polarized (CP) antennas are highly required for the 5G millimeter-wave (mm-wave) systems due to their attractive features like reducing the polarization mismatch between transmitting and receiving antenna and suppressing multipath interference. The printed ridge gap waveguide (PRGW) technology exhibits desirable features at high frequencies due to its air-filled guiding medium. Therefore, the implementation of antenna arrays with these state-of-the-art guiding structures can enhance the efficiency of communication systems, which is highly required at mm-wave frequencies. This research can be divided into two main parts: First, development of wideband mm-wave CP antenna array based on PRGW. Two designs for CP antenna arrays with distinct features of wideband bandwidth of more than 22.5%, simple structure, compact size, and high radiation efficiency better than 85% are presented. Cavity-backed slot spiral and spiral antenna are chosen as radiating elements to achieve RHCP beam. The mentioned antennas benefit from their inherently broadband features. However, their traditional feeding procedures are quite challenging and require complicated balun circuits and external matching networks. To alleviate this issue, simple feeding techniques for both spiral and slot spiral antennas have been proposed in this research. In the second main part of the research, a PRGW wideband dual CP antenna array is developed to increase the system capacity further. The dual sense of circular operation is achieved by using a shared radiating aperture of a 2×2 45◦ ME dipole array and a two-port feeding network. The proposed dual port feeding network provides equal power division and the phase difference of -90° and +90° between adjacent output ports to generate RHCP and LHCP beams, respectively. The feeding network components (rat-race couplers, directional couplers, and crossover) are designed based on PRGW technology with broadband performance. The proposed design solves the problem of limited operating bandwidth and low radiation efficiency of low profile dual CP arrays in the mm-wave band. All proposed antenna arrays are fabricated and measured to verify the simulated results. Good agreement between simulation and measured results is obtained. In all designs, the wideband performance, compactness, high radiation efficiency, and integration capability are considered significant to make them suitable for mm-wave applications