A compact printed filtering antenna with flat gain using annular slot and UIR

Design, fabrication and measurement of a filtering antenna are presented for WLAN / WIFI/ LTE communication systems in this paper. The filtering antenna consists of a feeding network, half-wavelength (λ/2) uniform impedance resonator (UIR) with a cambered structure and an annular slot. UIR with cambered structure is employed as the first stage resonator to improve the frequency selectivity in necessary passband. An annular slot etched on the back of substrate is excited by UIR through an inset coupling structure. The annular slot acts as a radiator as well as the last stage resonator. The inset coupling structure can be treated as the admittance inverter in the filter design. Compared to conventional antenna, the proposed filtering antenna has wide bandwidth, low cross polarization and good frequency skirt selectivity in passband. Measurement results show that the filtering antenna can operate at 2.5GHz with 550MHz, peak gain can be obtained to 1.2dBi, cross polarization can be suppressed to -30dB, respectively. The filtering antenna only occupies 0.23λ_g × 0.29λ_g.