A Four-Element Microstrip Patch Antenna Array with Compact Feed Structure

A modified feed structure for a microstrip patch antenna is used to realize a four-element patch array. The two by two array consists of two of the elements fed by a standard inset microstrip feed line, while the other two elements are fed by an inset feed line extended beyond the center of the patches. In this way, again an impedance match for the single elements can be achieved, combined with a 180° phase shift in the excitation of these patches compared to the standard excitation. As a consequence, the feeding network can be concentrated to the space within the patches; resulting in reduced feed line lengths and reduced overall circuit size. Applications are compact feeds for reflector or lens antennas or building blocks for larger microstrip array antennas. An 8 by 8 element array at 10 GHz is demonstrated as an example.