Design Of Miniaturized Dual-band Branch-line Couplers And Rat-race Couplers With Harmonic Suppression

Microstrip directional coupler have been widely used in microwave and millimeter wave regions.Branch-line couplers and rat-race couplers as basic elements are often used in power divider,phase shifter,balanced mixer,power amplifier circuit etc..With rapid development of modern wireless communication technology,traditional microstrip directional coupler has been unable to meet performance requirements of system.The research of single frequency,narrow bandwidth,large volume and the existence of high harmonics of directional couplers is essential.In order to overcome these defects,novel microstrip directional couplers are designed in this paper:novel miniaturized dual-band branch-line couplers and rat-race coupler with harmonic suppression.Main research work of the thesis can be summarized.1.The novel miniaturized dual-band branch-line coupler has been designed to solve the problems of single frequency and large volume.The branch-line coupler structure is adapted to the dual-band operation by loading extended transmission line through the ports.T-type transmission line structure equivalent to the traditional quarter-wavelength transmission line is analyzed,and the passive component circuit in another direction is also miniaturized.Moreover,with microstrip via-transition connected to top and bottom of PCB layers,a sandwich structure is formed,and the coupler circuit size is more reduced.With folded technology,size of port extensions is further reduced.Finally,the overall size of the coupler is 0.14?*0.16?.In order to validation,the proposed coupler operating at 0.98 and1.81 GHz is designed,simulated,fabricated and measured.Size of the novel coupler is8.6%,15.1%and 42.4%of area of the branch-line couplers[24,36,29].The measured results are in good agreement with the simulation.The new structure accomplish the goals of multi-band and miniaturization.2.The thesis presents a novel type of miniaturized rat-race coupler with harmonic suppression to solve the problem of large volume and high harmonics.Traditional rat-race coupler is composed of transmission line 3/2 wavelength,physical transmission line length of the novel design is reduced by loading T-type structure.In addition,as the result of the transmission zero introduced by the T-type stub,harmonic suppression is very effective.Then,a sandwich structure is formed with microstrip via-transition connected to top and bottom of layers to further reduced the size.The operating frequency of the rat-race coupler is 2.2 GHz,and the bandwidth of transmission suppression is from 4.7 dB to 20 dB,which can reach 10 dB.The size of the rat-race coupler is 26*13mm~2,and is 42.8%and17.8%of area of the rat-race couplers[38,40].Finally,the new structure is processed and measured,measured results are in good agreement with simulation results.The new design achieves the purpose of miniaturization and harmonic suppression.