A bandwidth intelligent tunable filter based on filter theory is designed in this article. By selecting a special interstage coupling structure and using a varactor circuit, dual frequency band tunable transmission could be achieved within the broadband range. The final design results show that the insertion loss of the filter is reduced to below 1.65dB and the return loss is greater than -15dB. In addition, the fixed frequency of the filter is 290MHz and the bandwidth is greater than 5MHz. The adjustable operating frequency ranges from 228-275.7MHz, the bandwidth is greater than 4.5MHz and the insertion loss is not greater than 1.2dB. The above parameters meet the filter requirements. This filter could achieve effective signal filtering in communication systems, which could ensuring system electromagnetic compatibility.
In this paper, a new type of electrically tunable filter is designed based on the long hole structure. The results show that the frequency adjustable range of the new filter is from 210MHz to 350MHz, the bandwidth is more than 3%, the insertion loss is not more than -3dB and the insertion loss is better than - 14dB, respectively. The electrical performance of the new filter is better than that of the original comb line filter and the weight is 0.3Kg, which is only 30% of the original electrically tunable filter. The results show that the design method of the long hole structure is reasonable and has excellent performance. This new kind of filter would have good application prospect in EMC design.
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