Miniaturization of array antennas with superdirective excitation

A simple superdirective antenna structure that does not require an impedance tuner is proposed. The proposed design concept for broadside superdirective antennas was used to fabricate five-element arrays of d = 0.2/spl lambda/ and 0.3/spl lambda/ by combining self-resonating dipole elements, /spl lambda//4 parallel line matching circuits and a feed network. A d = 0.3/spl lambda/ antenna realized the designed radiation pattern with a theoretical gain (8.1 dBi) which confirmed the exact superdirective excitation. However, when d = 0.2/spl lambda/, the radiation pattern was deformed and the gain was about 4.5 dB lower than the designed value for lossless material. This decrease in gain is consistent with the calculated ohmic loss of the antenna elements and the loss caused by pattern synthesis errors, which is higher when the Q factor is high.<>