Frequency Hopping Filter Based On Varactor And Design

With the rising complexity of electromagnetic environment the interference of communications is becoming more and more serious. In this case, frequency-hopping communications is applied to communications field, especially in military communications. Because of its strong anti-jamming performance, artificially blocking capability and anti-interception ability, frequency-hopping is an effective means against radio interference.The performance of frequency-hopping communications primarily depends on the tuned filter-the more frequency produced by filter and the faster the hopping frequency, the more difficulty the interference and reconnaissance. With the continuously adjustable center frequency, rapid tuning, small size and low cost, the tuned filter based on varactor is wildly applied to frequency-hopping communications. This paper focuses on the studies of four different structural types of tunable filter based on varactor.Firstly, according to the principal of coupled resonator filter a RF LC tuned filter is designed. The test results show that in the range of 100MHz-260MHz the filter is adjustable,its VSWR is less than 2 and it can be well used in communication station.Secondly, according to combline filter and interdigital filter, microstrip combline tuned filter which is adjustable in 800MHz-1450MHz and interdigital tuned filter which is adjustable in 1000MHz-1500MHz are designed. The insertion loss, VSWR and square ratio of these two types of tuned filter are all at the hopeful plane.At last, on the basis of a large number of scientific literature about the dual-mode resonator, in this paper, a dual zero tuned filter is designed. Because of the hole can not only be the grounding contact of varactor, but also achieve dual-mode resonant structure, this dual zero tuned filters which have the dual zero with dual- mode resonator structure and the high inhibit degree outside the band shows a significant advantage.