Research On Duplex Antennas With High Isolation

Wireless communication technology is under rapid development,and wireless communication devices are undergoing continuous improvement.Realizing small volume,light weight,high integration and multi-function has become a new development trend of wireless communication devices.Using the duplex antenna that enables transmitting and receiving signals in one device in the antenna-feeder system helps realizing a smaller and more integrated wireless communication device.The design idea of the filtering antenna is taken when designing the duplex antenna,and that makes the antenna structure more compact.The bandwidths,frequency selectivity and out-band suppression of the duplex antenna are also improved.For the duplex antenna,the mutual interference level between the receiving and transmitting signals should be as low as possible,so the isolation level of the designed duplex antenna should be as high as possible.This paper studies high isolation duplex antennas.Filtering structures are introduced in the feeding networks to enhance port-to-port isolation and decrease the mutual interference between the transmitting and receiving signals.The following three high isolation duplex antenna designs are completed:1.A duplex antenna based on T-shape probe-fed microstrip patch structure is proposed.First,a dual-band antenna based on T-shape probe-fed microstrip patch structure is proposed,and the dual-band antenna is used as the public radiation structure of the transmitting and receiving signals.The feeding networks of the low-band channel and the high-band channel are both band-pass filters composed of two half-wavelength hairpin resonators.They are coupled to the dual-band antenna through slots,thus two third-order filtering antennas that work in corresponding frequency bands are formed.Through this design method,the bandwidths of the two operating bands are increased,and high isolation level is reached.2.A duplex antenna introduced a transmission zero in one frequency band is proposed.A rectangle microstrip patch with U-shape slot is used to realize dual-band antenna.The feeding networks of the transmitting channel and the receiving channel are both composed of two halfwavelength hairpin resonators,and they are coupled to the dual-frequency patch through independent slots on the ground plane.Two third-order filtering antennas that work in corresponding frequency bands are formed,and the bandwidths and frequency selectivity are enhanced.An open-circuited stub is loaded into the feeding port of the transmitting channel and a transmission zero is generated in high frequency band.The transmission zero is adjusted into the receiving band and the isolation is greatly improved.3.A duplex antenna introduced one transmission zero in each frequency band is proposed.A two-port radiation structure based on stack patches is used,and there is isolation between the two ports.The transmitting channel filter is a band-pass filter composed of two hairpin resonators.The feeding port of the transmitting channel filter loads an open-circuited stub and the transmission zero generated by the open-circuited stub is adjusted into the receiving band.There is mixed electric and magnetic coupling between the resonators in the receiving channel filter and the generated controllable transmission zero is adjusted into the transmitting band.The bandwidths and frequency selectivity are improved and high port-to-port isolation is realized.