Vhf Band Duplexer And Multiplexer

Nowadays the communication system becomes more and more complex. As aresult, the phenomenon of several receivers and transmitters of different frequencyworking at the same time in it can be found from time to time. Multiplexer can be usedto divide certain wide frequency signal into serial bands or combine differentfrequency signals into one channel in reverse. Duplexer is the simplest example ofthem. They are the important modules which many receivers and transmitters can useto work by one antenna at the same time. Furthermore they are widely used in manysystems at present. Compared with the traditional scheme that the functions of systemwere realized through installing several independent antennas in limited field, it caneffectively avoid the antennas’ mutual coupling which deteriorates the system’sperformance. Then the structure of system becomes compact and the cost of maintainalso be reduced. The widely application of duplexer and multiplexer is the tendency ofdeveloping modern communication system.Now some needs of middle-width multiplexer which can endure middle power ofcontinuous power are called for in radio communication of VHF-band. Although thevolume can be reduced through the technology of capacity-loaded or SIR, it can notmeet the demand of project. Based on the theory of multiplexer which has thecharacteristic of continuous passband, the lumped constant duplexer and multiplexerhave been designed and made in this paper. They can be used in the real project ofvehicle-mounted multiplexer of VHF-band. They have the characteristics of smallsize、low insert loss(≤1.1dB)、sharp transition band(the rectangular coefficient(50dB/3dB)≤1.4)、contiguous passband and the capability of enduring middle powerwave(50W CW). It is a completely new product of company which I work in.The main work about the realization of VHF-band duplexer and multiplexer inthis paper is generalized as follow:1.Some typical network-structures of duplexer and multiplexer are analyzed. Bothadvantages and disadvantages of them are also compared.2.Focused on the application of high power、narrow band and miniature volume,the key technology used in coaxial cavity duplexer、 tubular duplexer and helix duplexer are discussed. Then the CT structure of linear type and resonator which lookslike a stool are also given.3.Focused on the application of enduring middle power、middle bandwidth、contiguous passband and miniature volume, the parallel LC resonant is used assusceptance network to design lumped constant multiplexer’s susceptance network.Then the tuning method is introduced. The test results correspond with the simulationresults. It verifies the validity of design method.4.A topological structure of bandpass filter which has the characteristic of highrectangular coefficient is designed. It can be easily realized in low frequency.Furthermore it can also endure continuous wave of middle power (50w). The structureis adopted to enhance the design of multiplexer’s selectivity in this paper.5.Based on the theory of circuit, the software of Designer is used to analyze boththe transient enduring voltage and current of every component of LC multiplexer. Theresults indicate that the “guard-band” is very important in LC filter with powercapability. The method is practical and fast. It can also help to choose the type ofcomponents.