Design And Research Of Negative Group Delay Filter

With the rapid development of microwave/RF communication,the requirements for phase and signal distortion of the transmission system performance are gradually increasing.The negative group delay filter(NGDF)has drawn more and more attention because of it's special properties.But people have not yet formed a design theory for NGDF so far,and there is little related research achievements aimming at NGDF which uses microstrip lines,especially tunable NGDF.Based on the synthesis method of the traditional bandpass filter,a new synthesis method in view of lossy filter and bandstop filter of NGDF is proposed.The design theory of NGDF is analyzed and researched based on the two programs.Two structures of NGDF are designed in this thesis,which are used to implement the fixed NGDF and single/dual band tunable NGDF,respectively.Firstly,a novel structure of open loop resonator(OLP)which is implemented by an electric coupling method is proposed in this thesis.A fixed NGDF is designed using this structure,and the loss characteristics of the filter are improved by input/output impedance matching.The measured results show that the center frequency and negative group delay(NGD)of the filter are 2.149 GHz and-15.22 ns,respectively.Meanwhile,the insertion loss is less than 27.43 dB.Compared with the related studies,the proposed filter can achieve a larger NGD with smaller attenuation.Based on the design of the non-adjust NGDF,this thesis proposes a single/dual band NGDF with tunable center frequency and NGD using microstrip lines and short-circuit coupled lines.The proposed tunable filter have the advantage of flexible adjustability.The center frequency and NGD can be tunable independently.Meanwhile,all the parameters can be tuned at the same time.The maximum tunable ranges of center frequency and NGD of the single tunable band filter are 1.450 ~1.870 GHz and-2 ~-30 ns,respectively.The center frequencies of dual band tunable filter can adjusted from 1.435 to 1.855 GHz and 2.395 to 2.695 GHz,respectively.The maximum adjustable ranges of NGD are-4 ~-22 ns and-4 ~-32 ns,respectively.The measured results are agreement with the simulated results,which shows that the tunable ranges of center frequency and NGD in this work are wider than that of the preview studies,while the SA are lesser than the preview works.