Circularly polarized duplex antenna with high port-to-port isolation

A circularly polarized (CP) duplex microstrip antenna with high port-to-port isolation is presented. The proposed antenna consists of a square radiating patch, two T-shaped probes to generate two orthogonal waves and a feeding network to achieve the power distribution for acquiring CP characteristics in both the transmitting (Tx) port and receiving (Rx) port. Open-circuited stub bandstop filters are adopted to enhance the isolation performance and simplify the design of the feeding network. The antenna operates on 2.22 GHz (2.20 GHz-2.24 GHz) for Tx and 2.38 GHz (2.37 GHz-2.40 GHz) for Rx. The bands are fairly close to each other. The port-to-port isolation is higher than 43 dB at upper band and 50 dB at lower band, respectively. Both of the bands of the antenna radiate LHCP waves, which could be a candidate for a frequency duplex CP antenna.