The Research And Design Of Multiple Bandpass Filter

With the rapid development of information technology, WCDMA, WLAN, LTE, etc. update very soon, which makes the spectrum resource crow more and more. At present, a single filter can’t satisfy the demand of multiple channel application, the application of multi-band filter is more and more important. In the wireless communication system, the multi-band filter can effectively make the circuit of the system more simple and can also reduce the volume of communication equipment, which can simplify the system structure and reduce the equipment cost. Therefore, researching of the multi-band filter design has very important significance.This article has a detailed introduction about the microwave filter, which is the basis of multi-band filter. According to the need of practical engineering application, a method of making multiple band-pass filter in parallel about the multi-band filter is put forward. By this method, the bandpass filter in the multi-band filter can be designed independently, and transmission zeros can be introduced in the multi-band filter to meet the demand of the high isolation, low insertion loss, and the sideband suppression of the multi-band filter can get controlled. In order to verify the effectiveness of the method, an example of 1730-1780&1780-1875 MHZ dual-band filter is given in this paper. According to the design index, transmission zeros with CT implementation structure are introduced in the first passband and second passband, and then use the AWR to simulate and optimize the circuit, finally use Ansoft HFSS to make 3D models simulation. The electricity coupling structure and the input/output structure in the 3D model are changed innovatively, which make the physical debugging easier. And the physical test results can well meet the design requirementsConsidering the increasing of the taps in the multi-band filter may lead to the questions like that the mutual influence between passband will be more worse and the physical debugging become more difficult, a new structure of dual-band filter is puts forward in this paper, which is based on the duplexer with common cavity. By introducing the common cavity, the filter tap number can be reduced effectively and the filter performance can be more better. Finally, the article gives an example of dual-band filter with common cavity, and a comparation between the dual-band filter with common cavity and a dual-filter with no common cavity is given.Finally, the paper puts forward a combiner with a frequency range of GSM&DCS, TD F&TD E based on the research of multi-band filter. According to design requirements, the GSM&DCS channel is designed through two band-pass filter in parallel and the TD F&TD E channel is a dual-band filter with common cavity, then combine the two dual-band filters. With the novel structure, the combiner structure is more simple, the tap number is reduced. The combiner has been used in the market and its reaction result is good.Based on the design principle of filter and with the demand of practical engineering application, the design of multi-band filter is discussed deeply. And the author has made some work on how to realize the miniaturization of multi-band filter with low insertion loss and high restraint outside the band.