Design considerations of broadband circular microstrip antennas with embedded reactive loading

By using reactive loading, inserting a microstrip-line section at the radiating edge of a rectangular patch or inside a slot cut of a circular patch, a patch antenna can be excited in two resonant modes near the fundamental mode of the original unloaded microstrip antenna. The two resonant modes can be designed close to form a wide operating bandwidth. By modifying the inserted microstrip-line structure, various kinds of antennas are proposed. Although the broadband operation is greatly sensitive to small variations in the dimensions of the inserted microstrip structure, a good impedance condition for the broadband operation can be achieved. The good antenna performance of various types of antennas within the operating bandwidth is also observed. It is seen that a proposed broadband antenna with a wide antenna bandwidth may not have a good gain performance with gain variation less than 3 dBi. This shows that there exists a trade-off between the antenna bandwidth and gain performance. Details of designs are presented.