A Compact Printed Filtering Antenna With Good Suppression of Upper Harmonic Band

In this letter, a printed planar filtering antenna composed of the stepped-impedance dipole (SID), stepped-impedance resonator (SIR), and low-pass filter (LPF) is presented. The SIR is used as a parasitic element in proximity to the SID radiator to improve its upper band-edge selectivity and to widen its operation bandwidth. Our extensive study is at first conducted to exhibit that the upper harmonic band of radiation can be tremendously pushed upward by appropriately replacing the main dipole radiator and the parasitic resonant element with the SID and SIR. Next, a stepped-impedance LPF is employed to further effectively suppress the high-order harmonic band of radiation as quantitatively demonstrated. The measured reflection coefficient has achieved a wide fractional bandwidth up to 27.5%, covering a frequency range of 2.5-3.3 GHz, with vertical bar S-11 vertical bar < 10 dB. In particular, its first harmonic band for radiation has been significantly extended from 7.2 GHz beyond 14.0 GHz as confirmed in simulation and experiment.