Research And Design Of The Quad-Polarization-Agile Antenna

The increasingly complex wireless channel environment and spectrum resource shortage put forward new and higher requirements for the design of wireless communication system.As the transceiver of wireless communication system,the design of antenna also faces new challenges,and it is developing towards multi-function.In recent years,the rapid development of semiconductor devices promotes the research of reconfigurable antenna.The research object of this paper,polarization reconfigurable antenna(PRA),is a kind of antenna whose polarization states can be adjusted dynamically.In other words,polarization reconfigurable antenna integrates multiple antennas with different polarization states into one topology.It means that PRA not only improves the performance but also reduces the number of antennas utilized in a system,which favors the miniaturization design of the wireless communication system.In addition,PRAs are useful for frequency reuse and multipath fading,so it has broad application prospects.Focusing on the feeding network,this thesis conducts some research on PRA.The main research contents and achievements of this paper are summarized as follows:A wideband reconfigurable feeding network for polarization reconfigurable antenna is designed.The feeding network is composed of an amplitude-and-phase-switchable network with specific phase difference between two output ports and an impedance matching circuit.The amplitude-and-phase-switchable network is based on the structure of a quadrature hybrid coupler.The phase difference between output ports is improved by loading terminal resistance,and diodes are loaded to make the network available to switch between four output modes.The input impedances of the network in different modes are studied by using odd and even mode analysis method,and a reconfigurable impedance matching circuit with simple structure is designed based on simulation results.The measured results show that the impedance matching bandwidth(S₁₁<10 d B)of the feeding network in single-output modes and orthogonal-output modes can reach 45.8%and 30%respectively,and the phase difference of the output ports can be kept within90±5°in a relative bandwidth of 25.4%in the orthogonal modes.A dual-polarized L-shaped probe patch antenna is designed to verify the performance of the feeding network.By analyzing the coupling of the antenna probes,an optimization method of the feeding network is proposed.The overlapped bandwidth of all polarization modes of the whole reconfigurable antenna is 25.4%,and the maximum gain reaches 8.1 d Bi.Compared with the existing broadband schemes in PRA design,the proposed one has advantages in size and design complexity.A dual-band quad-mode polarization reconfigurable antenna is proposed.The antenna consists of a reconfigurable feeding network and a dual-band dual-polarized antenna.In this thesis,the design complexity of the feeding network is reduced by using the dual-band characteristic of the proposed antenna.The feeding network is designed based on the structure of quadrature-hybrid coupler.Dual-band performance is achieved by adding open stubs,four output modes are implemented by the load of PIN diodes,and the phase difference of outputs is improved by the load of terminal resistors.By analyzing operating states of the diodes,the number of controlling dc voltages is reduced to minimum.Based on the parameter analysis,the adjustment method of the outputs of two operating frequency band is given.In terms of the antenna,an L-shaped probe dual-polarized dual-band antenna is designed.By analyzing the working principle of the antenna,the matching optimization method is given.The experimental results show that the antenna achieves four polarization states simultaneously in the frequency band of 0.94GHz–1.07 GHz and 1.99 GHz–2.27 GHz.According to the author's knowledge,the proposed antenna realizes dual-band quad-mode polarization reconfiguration for the first time,which is of great significance.Through the aforementioned research,this thesis provides new methods and ideas for the design of polarization reconfigurable antenna based on reconfigurable feeding network.