Design Of Filtering Couplers With Reconfigurable Frequency

This work reports on,for the first time,the design of filtering couplers with reconfigurable frequency.The reconfigurable filtering transmission lines(RFTLs)with 90oor-90ophase shift are firstly designed,and then the reconfigurable filtering couplers are constructed by substituting the basic unit of quarter-wavelength(?/4)transmission line in the conventional couplers with the proposed RFTL.RFTLs consist of coupled half-wavelength(?/2)resonators,and the tunable capacitors loaded at two ends of half-wavelength resonators are used to tune the center frequency of RFTL.By properly controlling the electric or magnetic coupling between the resonators,the phase shift of 90oor-90oof the RFTLs can be realized,respectively,while maintaining a near constant bandwidth.The external coupling along with a pair of transmission zeros is achieved by asymmetric tap feeding of the RFTLs.For verification,a class of frequency-reconfigurable filtering couplers is designed and fabricated.1)A reconfigurable filtering rat-race coupler is designed and fabricated on a Rogers RT/Duroid 5880 with?_r=2.2 and h=0.787 mm.The measured center frequency is tuned from 700 MHz to 1840 MHz while maintaining a 3-d B fractional bandwidth of 13%±0.5%/13.7%±0.6%,insertion loss of 8.1?6.9/8.3?5.9 d B,return loss of better than 13 d B,and isolation of better than 21 d B.2)A reconfigurable filtering quadrature coupler is designed and fabricated on a Rogers RT/Duroid 5880 with?_r=2.2 and h=0.508 m.The measured center frequency is tuned from 947 MHz to 1775 MHz while maintaining a 1-d B bandwidth of 75±5/65±10 MHz,insertion loss of 8.3?6.9/8.3?7.1 d B,return loss of better than 14 d B,and isolation of better than 14 d B.