The Research And Design Of Narrow-band Dual-mode Filter

With the fast development of communication systems in recent years, higherdemand for the performance of filters has been put forward in microwave andmillimeter wave wireless communication systems. Such filters with high quality factor,low insert loss, sharp out of band rejection, high power capacity together with small sizeare in great need. Compared with the traditional full polar point filter whoseperformance can only be improved by increasing its orders, leading to the increase inboth size and loss, the research of the dual-mode filter with one cavity plays a vital rolein the design of filters with high performance. This paper aims at designing narrowbandwidth dual-mode filters guaranteeing its selectivity. The main characteristics are asfollows:1. The relative bandwidth is narrow enough.2. The filters use rectangulardual-mode resonators, in which the coupling of the modes don’t apply for screws, thus,it is convenient for the machining.3. The filters utilizing circularr waveguide dual-mode resonators apply for new structure to realize coupling of adjacent cavities, whichis of great convenience to adjust resonance.The work of paper is organized as follows:Firstly, the meaning of research and the development at home and aboard isillustrated based on the narrow band dual-mode filters. Then the fundamental workingprinciples of microwave band pass filters is analyzed, following the design formulatogether with kinds of narrow-band pass filters.Secondly, some basic theory related to the design of dual-mode filter is introducedbriefly, including the realization of resonators, the couplings of its inner modes, theimplement of coupling of adjacent dual-mode resonators, the calculations of input andoutput couplings and its respondent structure.Finally, three patterns of narrow band dual-mode filters are designed.1.Ultra-narrow band dual-mode filter in millimeter wave band is designed with its centerfrequency at25GHz. Relative band0.2%based on the rectangular resonator, in whichmodesTE₁₀₂andTE₂₀₁are applied for. The input and output structure utilize thestructure transitioned from coaxial to rectangular waveguide and its outside dimension is65mm×25mm×15mm.2. The narrow band dual-mode filter at10GHz is designedwith relative band4%applying for rectangular resonators with modesTE102andTE₃₀₁.. The return loss is less than-20dB and insert loss is less than1dB. There are threetransmission zeros at the low frequency side of the pass-band.3. Narrow banddual-mode circular waveguide filter is fabricated with center frequency15.19GHz,relative bandwidth0.3%using theTE111mode in circular waveguide. And a novelcoupling structure is proposed to realize the couplings of adjacent cylinder waveguidedouble mode resonators.