The Development Of Broadband LC Frequency-hopping Filter

Now frequency spectrum use ratio is getting higher and higher in the information society, raises the use ratio is one of communications essential requirements. The frequency -hopping communications can hold many frequency-hopping communications system work in certain band width, achieve the goal resource sharing, raises the frequency spectrum use ratio greatly. In this article, the filter works in the VHF frequency band and UHF frequency band, coverage area 108MHz-174MHz and 225MHz-400MHz. It is as the chooses filter in the receiver located at between the antenna and the mixer.This article prime complete design two mini-type tunable filters, and used in systems, their tuning range are 108MHz-174MHz and 225MHz-400MHz. They will be low insert loss, broad bandwidth, almost constant bandwidth and small size. So it is a little difficult. I use the network theory and add the ideal transformer in the filter design. Design in practice and use simulation software, get a good result at the end on the base of the theories of the network design and coupling-resonator filter design, i introduce the processes from the lowpass filter prototypes to the bandpass coupling-resonator filter. I add the ideal transformer, change the bandpass coupling-resonator filter to the equivalent LC model, then put the precise model of the varactor into the simulation software, adapt a special method to optimization the filter.At last, i test and adjust fiters. The possible causes of the problem is analyzed and offer ideas to the later works.In brief, this article has make research to tunable filter module in the system. The designed sample performance is fine and has good project application value.