A Ka-Band (26 GHz) Circularly Polarized 2x2 Microstrip Patch Sub-Array with Compact Feed

A Ka-Band (26 GHz) 2x2 sub-array with square-shaped microstrip patch antenna elements having two truncated corners for circular polarization (CP) is presented. In addition, the layout for a new compact microstrip feed network for the sub-array is also presented. The compact feed network offers a footprint size reduction of near 60% over traditional sub-array at 26 GHz. Experimental data indicates that a truncation amount alpha = 0.741 mm for an isolated patch element results in a return loss (S-11) of -35 dB at 26.3 GHz. Furthermore, the measured S-11 for the proof-of-concept sub-array with the above elements is better than -10.0 dB at 27.7 GHz. However, the impedance match and the operating frequency can be fine-tuned to 26 GHz by adjusting the feed network dimensions. Lastly, good agreement is observed between the measured and simulated S-11 for the sub-array for both right hand and left hand CP. The goal of this effort is utilize the above sub-array as a building block for a larger NxN element array, which would serve as a feed for a reflector antenna for satellite communications.