| With the rapid expansion of wireless communication services,the data transmission rate has significantly increased,and the limited spectrum resources have been difficult to meet the needs of high-speed wireless communication.The research on the key technology of full duplex can effectively alleviate the problem of shortage of wireless spectrum resources,and realize high-speed data transmission in a limited frequency band.Applying full-duplex technology to A WLAN improves the transmission rate,transmission distance,and reliability.Circulator,bandpass filter and power amplifier are important devices in the full-duplex RF front end.This thesis mainly studies the circulator,bandpass filter and power amplifier in the full-duplex RF front end of WLAN.The work completed in this thesis mainly includes:(1)Design two kinds of high isolation transceiver duplexer structure working in WLAN,one is the combination of circulator,power distributor andBarron;The other is a combination of directional coupler and circulator.The isolation degree is improved by amplitude and phase cancellation.Wilkinson power splitter and wideband planar Barron are designed.The structure of transceiver duplexer based on Barron is designed by power splitter,Barron and circulator.The measured isolation value of the whole structure is greater than 40 dB in 2.02～2.79 GHz band,and greater than 50 dB in 2.42～2.68 GHz band.The maximum isolation value is 60.7 dB.Subsequently,a three-branch line microstrip coupler was designed.The Defective Ground Structure(DGS)was adopted and a one-half wavelength parallel open circuit branch was loaded at the port to reduce the machining difficulty and expand the working bandwidth.A transceiver duplexer Structure based on directional coupler was designed using the coupler and circulator.The measured isolation value of the whole structure is greater than 25 dB in 2.25～3.1 GHz frequency band,and the maximum isolation value is 47 dB at 2.6 GHz.Compared with the simulation results,the measured results have certain frequency offset and larger insertion loss.(2)Considering the deviation between the measured results and the simulation results of the high isolation transceiver duplexer structure,a rat-race coupler based circuit topology is designed.Based on the phase characteristics of 180° rat-race coupler,the isolation degree of the whole structure is improved by amplitude and phase cancellation technology.Double-sided Parallel Strip Line(DSPSL)is used to replace microstrip line,and DSPSL inverting unit is used to replace transmission line,thus reducing the size of rat-race coupler.On this basis,a high impedance parallel resonant branch is used to replace the traditional transmission line,which can further reduce the size of the rat-race coupler and suppress the high harmonics.The measured results show that the isolation degree is greater than 35 dB in the 1.5～3.5 GHz frequency band and greater than 50 dB in the center frequency of 2.4 GHz,showing good isolation performance and realizing the protection of the transceiver system.(3)A band-pass filter and a power amplifier are designed.A band-pass filter was designed using a microstrip transmission line loaded with a stepped impedance resonator and a Hilbert fractal DGS element.The measured results show that the stopband of the filter is suppressed,the transition band is steeper,the insertion loss at the center frequency of 2.4 GHz is 1.71 dB,and the relative bandwidth is 10.8%.The return loss of the filter is greater than 10 dB in the passband.The 2.4 GHz power amplifier is designed based on Ga N transistor NPTB00004 A.The measured results show that the maximum output power is 35.81 dBm and the PAE is46.89%.(4)The full duplex RF front-end system is tested.The results show that the full duplex RF front-end system achieves good isolation and stable power output. |
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