Contents I. Introduction
Planer waveguide slot array antennas and microstrip patch array antennas have been an interesting research topic among the antenna professionals since 1970s. Typical printed antennas can be compact, lightweight and can offer low cost but these types of antennas suffer usually from high dielectric losses at high frequencies. Also, when an array of printed antenna is built for high gain or multiple beam application, the antenna efficiency decreases even more because of increased losses in feeding network. The steps and discontinuities in the feeding network also tend to give spurious radiation [1]. Planar waveguide-type slot array antennas do not suffer from the above disadvantages, and is therefore an attractive candidate for high frequency applications requiring high gain [2]–[4]. But waveguide slot arrays are associated with complex feed network under the radiating waveguide array and high manufacturing costs of standard rectangular waveguide at high frequency. Apart from the cost of waveguide array itself, the integration of high frequency MMIC with rectangular waveguide is also very challenging at high frequencies [5]–[6].
