28 GHz High Efficiency Planar Array Antenna with Hybrid Feed Network

Microstrip antennas and arrays have been widely used in military and commercial applications because of their ease of fabrication, low profile and low cost. In any microstrip array antenna, design of the feed network is always the most challenging task for which many different methods have been proposed. One method is to distribute the power to individual array elements by a coplanar microstrip network. A corporate (parallel) feed structure is the easiest to design, however, at higher microwave frequencies, antenna gain and aperture efficiency deteriorate significantly due to increase in losses of microstrip lines and unwanted radiation from the power distributing circuit [1]. A series-fed microstrip array can achieve a more compact size and better efficiency but still suffers from substantial losses in connecting transmission lines [1].