Low profile filtering antenna with high selectivity without extra circuit

A novel microstrip filtering antenna with high selectivity is presented. A shorting SIR stub and a square patch with a rectangular ring slot are designed to produce a couple of radiation nulls near the passband, respectively. The bandwidth (3.44GHz-3.94GHz) is wider than that in a traditional antenna. In the presented antenna, the selectivity of the right side of passband is 30.3 dB, and the selectivity of the left side of passband is 18.2dB without an extra circuit. The proposed antenna consists of three layers of stacking structure connected tightly up and down, so it has an easy fabrication structure. Flat gain, compact size 0.49λ*0.49λ*0.07λ, and higher front and back ratio (>20dB) are obtained than the conventional antenna.