Small Low-Profile Loop Wideband Antennas With Unidirectional Radiation Characteristics

Small low-profile wideband loop antennas featuring unidirectional radiation characteristics are presented. Directive radiation characteristic is achieved by proper combination of fields radiated by symmetric and anti-symmetric current components supported by any loop antenna. Relative strengths of the symmetric and the anti-symmetric radiations change according to shape of the loop. Prototype loop antennas are fabricated and their impedance and radiation gain patterns are measured. The gain patterns show directive characteristics in both major planes. It is shown that the gain measured in the desired direction of maximum radiation exceeds the maximum achievable practical gain for omnidirectional antennas of the same dimensions over wide frequency band.