Research And Design Of Broadband And Harmonic Suppression Branch Line Directional Coupler

With the rapid development of mobile communication,at present,the fourth generation of mobile communication technology,the rapid development of China,the transmission receiving equipment have become increasingly demanding,microwave devices which has a very crucial role in these devices,Branch line directional couplers are also to be broad-band and harmonic suppression.The traditional branch line directional coupler is simple,but the bandwidth is very narrow,and the relative bandwidth of the branch line coupler for 3dB is only 10%.In this paper,a 3dB two branch line coupler with dumbbell shaped DGS is designed which bandwidth increased to 26%,a 3dB three branch line coupler with rectangular shaped DGS is designed which bandwidth increased to 50%,and then a 10 dB branch line coupler adding 1/4 wavelength impedance converter at each port to achieve broadband matching is proposed.The measure data showed that the relative bandwidth increased to 42.6%.a design method of 10 dB broadband branch line coupler which can suppress the third harmonic is.Meanwhile,traditional branch line coupler is composed of 1/4 wavelength transmission line,which has periodic frequency response.Therefore,the higher order harmonic generation generated by nonlinear devices,especially the three harmonic,could not be suppressed.A broadband branch line coupler based on 1/4 wavelength impedance converter by adding single open circuit stab to each branch line and main line is proposed,T type junction is formed to suppress the three harmonic.In order to be easier to fabricate the coupler,the dumbbell shaped DGS structure is embedded in this coupler.The frequency center of the proposed coupler is 3GHz,the relative bandwidth is 43.6%,it has a wide bandwidth and can suppress the third harmonic,at the third harmonic frequency S21?S31and S41 are less than-15 dB.A wideband branch line coupler with Defected Ground Structure(DGS)low pass filter is designed,which can suppress the 2th and 3th harmonic by using the filter characteristic of DGS filter.Finally,the bending properties of Flexible traditional branch line coupler and Flexible broadband branch line coupler with open circuit stab are simulated and measured,the result show that the performance Flexible branch line coupler will not change basically,however there will influence central frequency,and the frequency bias is about 100 MHz.