Research On Negative Group Delay Microwave Circuit Based On Coupled Patch

Group delay distortion is one of the challenging issues in a radio frequency circuit or microwave communication system,which may cause the inter-symbol interference of wideband communication systems and the pseudo-range error of global navigation satellite systems.The negative group delay(NGD)microwave circuit has the characteristic that the group delay value is negative,which can compensate for the group delay distortion.This feature effectively solves the problem of group delay distortion in radio frequency circuits and microwave communication systems,so that NGD circuits are often widely used in radio frequency devices and microwave systems.But traditional NGD circuits have large insertion loss(more than 10 d B),which limits their applications.Therefore,the research on the low insertion loss NGD microwave circuit based on the coupled patch in this thesis has important significance and a wide range of applications.The main works completed include:(1)A compact NGD circuit based on asymmetric coplanar striplines and double-sided parallel striplines(DSPS)is designed.The NGD circuit is fed by asymmetric coplanar striplines.The characteristic of the proposed NGD circuit is generated by the open-circuited DSPS combined with the connecting hole.The measurement results show that the compact NGD circuit has an NGD value of-2.42 ns at the center frequency of 1.577 GHz,and the NGD bandwidth is 36 MHz.The insertion loss in the NGD bandwidth is lower than 4.75 d B,and the return loss is higher than 11.7 d B.The proposed NGD circuit has the advantages of compact structure,low insertion loss,and flexible design.(2)A compact dual-band NGD circuit with independently adjustable characteristics is designed.The proposed NGD circuit generates NGD characteristics through different lengths of rectangular patches coupled on the upper and lower sides of the main transmission line.The measurement results show that the compact NGD circuit has an NGD value of-4.8 ns at the center frequency of the lower band of 1.228 GHz and the NGD bandwidth is 11 MHz.The center frequency of the higher band is 1.575 GHz,the measured NGD value is-5.3 ns,and the NGD bandwidth is 14 MHz.In both NGD bands,the measured insertion loss and return loss are better than 2.7 d B and 12.6 d B,respectively.The measurement results are in good agreement with the simulation results,and the dual-band NGD function is realized.(3)A wideband NGD circuit based on coupled patch is designed.This circuit generates the NGD phenomenon through the double layer patches coupled with the main transmission line.The measurement results show that the wideband NGD circuit has an NGD value of-0.51 ns at the center frequency of 2.45 GHz,and the NGD bandwidth is 112 MHz(the fractional bandwidth is 4.7%).In the NGD band,the insertion loss is lower than 4.3 d B,and the return loss is better than 10.0 d B.It has the advantages of low insertion loss and flexible design,and the wideband NGD function is realized.(4)A reconfigurable NGD circuit based on coupled patch is designed.The NGD characteristic is realized by loading a grounding resistor on the short-circuited end of the Ushaped coupled patch and a variable capacitor on the open-circuited end.The measurement results show that the reconfigurable NGD circuit can realize the operating frequency adjustment range of 0.8 GHz ～ 1.2 GHz,and the group delay adjustment range of-0.9 ns ～-3.9 ns.During the adjustment process of the center frequency and the NGD value,the insertion loss in the NGD band is lower than 2.3 d B,and the return loss is higher than 12.6 d B.The designed circuit realizes the function of reconfigurable negative group delay.