An integrated low frequency ratio wideband filtering duplex slot antenna

Abstract

An integrated low frequency ratio wideband filtering duplex slot antenna with high isolation is proposed in this letter. The antenna consists of two layers: four circular slots are sequentially introduced between two layers, four orthogonal slotlines are etched to connect them, which are used as radiation structures; two pairs of split-ring resonators (SRRs) are inserted into two orthogonal microstrip line baluns ending in open stubs on both top and bottom layers, respectively, which is considered as the feeding network. Then, two independent broad operation bands are achieved by employing two orthogonal broadband resonator-based filtering feeding lines to excite circular slot mode. Furthermore, both filtering characteristic and polarization diversity help to improve port isolation, which contributes to frequency duplex function. The antenna is fabricated and tested. The measured results indicate that the impedance bandwidths of the lower-and-upper-band channels are 24.5% (2.29-2.93 GHz) and 17.5% (3.11-3.71 GHz), respectively. Low frequency ratio (1.05) is achieved. Port isolation is better than 42 dB and the cross polarization level is below 26 dB.