A Compact Planar Quasi-Yagi Antenna With Bandpass Filtering Response

A planar quasi-Yagi antenna with bandpass filtering response is presented. The quasi-Yagi antenna consists of a double-sided printed driven dipole, an offset double-sided parallel-strip line (DSPSL) director, a DSPSL reflector, and an offset DSPSL parasitic element. Both the reflector and the parasitic element can produce an extra radiation null at the band-edges of the passband, and the parasitic element can also generate an additional resonance within the passband. As a result, a compact wideband quasi-Yagi antenna with quasi-elliptic bandpass filtering response is obtained, without requiring any extra filtering circuit. In addition, the antenna is fed by a balanced DSPSL, and therefore, no balun is needed, leading to a very simple feeding structure. For demonstration, a prototype operating at 2.4 GHz was designed and measured. The prototype has a low profile of 0.006 lambda(0), a - 10-dB impedance bandwidth of 30.4%, an average gain of 5.7 dBi over the passband, and an out-of-band suppression level of about 20 dB in the near stopbands.