The Design Of Millimeter Wave Duplexer

With the development of the mobile Internet data services and the updating ofscience and technology, communication system obtains rapidly development. However,it faces the problem that the frequency spectrum is getting more and more crowded atthe same time. Therefore, Frequency Division Duplex communication and TimeDivision Duplex communication system will be integrated to satisfy the urgent demandof modern communication. In order to solve the problem that signal is received and sentvia an identical antenna, Diplexer is designed. It is widely used in microwave andmillimeter wave communication, satellite communication, radar, electronic warfaresystem and so on. In the case of a crowed frequency spectrum, it is very necessary that atypical duplex device is applied in the communication system to obtain an appropriatefrequency spacing and isolation between the transmitting and receiving channels, so asto improve the capacity of the system.Based on the practical demand, this paper firstly analyses the diplexer theory, filtertheory, circulator theory and the characteristics of the ferrite which is a key material tobuild a circulator. After the analysis, two solutions are presented based on substrateintegrated waveguides and waveguide technology. Related theoretical analysis of thesolutions is also presented. After electromagnetic simulation, the two solutions arefabricated and tested.During the designing of substrate integrated waveguide devices, an inductive metalwindow is proposed in the circulator part, which not only makes the circulator achieve asmaller voltage standing-wave ratio (VSWR), but also makes all the vias to be throughvias that greatly reduces the processing difficulty. As for the filters, they are designedusing a cross-coupled structure to generate a transmission zero-band so that its stopbandattenuation can be improved. The testing results of the designed duplexer agree withsimulation expect for its insertion loss is larger than the simulation.As the tested insertion loss of substrate integrated waveguide components is a littlebit larger than simulation, this paper designs the duplexer with waveguide technology.In order to achieve a good circular properties, the circulator uses a1/4wavelength Y type steps and tuning screws for matching. And the designed waveguide filter gets ahigh rejection level which is almost higher than40dB within0.2GHz outside ofpass-band. Simulation results show that this waveguide diplexer has characteristics ofsmall insertion loss, good rejection band attenuation and it gets a cross band betweenthe upper and lower pass-band so as to make it support the co-working of both TDD andFDD systems. However, millimeter-wave waveguide duplexers require relatively highfabrication accuracy, the fabrication tolerances are inevitable. The testing results showthat it has a frequency offset, but through tuning the screws, the duplexer can beadjusted to fulfill the system’s requirement.In addition, in order to integrate the planar circuits and the waveguide component,two kinds of the waveguide to microstrip transitions of90-degree arc bend and90-degree step bend are designed in this paper. Both of the transitions can make inputport and output port in the same direction and they get low insertion loss, widebandwidth. Also, the test results agree well with the simulation. But the90-degree stepbend structure gets an advantage of easier manufacturing compared with arc bendstructure.