A multi-frequency microstrip-fed annular slot antenna

A single feed multi-frequency annular slot antenna is analyzed with an integral equation program and experimentally. Experimental impedance bandwidths of the first three operating frequencies range from 6.6 to 10.8 percent. At these frequencies, the antenna displays a broadside bi-directional radiation pattern, with directivity on the order of 5 dB. Tuning the antenna is examined by changing the width of the slot ring and adjusting the open-circuited microstrip feed line.