A Compact Printed Filtering Antenna Using a Ground-Intruded Coupled Line Resonator

A compact printed filtering antenna with high bandedge gain selectivity is presented. Occupying about the same substrate area as a conventional antenna, the proposed structure not only serves as a radiator but also a second-order bandpass filter, with one filter pole provided by a Gamma-shaped antenna and the other by a newly proposed coupled line resonator. High band-edge selectivity is achieved due to two additional stop-band transmission zeros provided by the coupled line resonator. To minimize the required area and reduce the spurious radiation, a coupled line structure composed of a microstrip line and a coplanar waveguide by broadside coupling is adopted and intruded into the Gamma-shaped antenna area. According to the filter specifications, a design procedure for the proposed filtering antenna is depicted in detail. One example at 2.45 GHz with a second-order Chebyshev bandpass filter of 0.1 dB equal-ripple response is tackled. As compared to the conventional Gamma-shaped antenna, the proposed filtering antenna not only possesses a similar antenna gain but also provides better bandedge gain selectivity and flat passband gain response. The measured results, including the S-parameters, total radiated power, and antenna gains versus frequency, have good agreement with the designed ones.