Design, Production And Application Of A Sideband Steep Microwave Dielectric Filter

Recent years, with the development of wireless communication, RF/microwave circuit have been paid more and more attention and development. While the microwave band-pass filters are the most important wireless communication system RF front end passive devices, so the band microwave band-pass filter device electrical performance indexes, filters reliability of wireless communication system have an important effect on overall performance. This article based on a company "TD-SCDMA base station with a band-pass filter" project as the background and the research object, research and design and production of two types of filters from the actual project application.The project takes the basic design theory as the guide, bases on the asymmetric Generalized Chebyshev filter prototype and as well as draws on the theory foundation of transmission zeros, to design a double transmission zero microwave band pass filter. The band of the two controllable transmission zeros, thereby realizing that guarantees the in-band flatness and insertion loss in the case of smaller realized edge with steep characteristic. Zero is produced by the cross coupling between the non-adjacent resonators and parallel LC resonant circuit to form an energy barrier.TD-SCDMA base station with a band pass filter uses microwave dielectric materials with the dielectric constant of21(magnesium titanate series). The two band-pass filters’sizes are3.8mm*12mm*8.2mm, center frequency are2017.5MHz,1900MHz respectively and the corresponding respectively named3017S3,1900S4.2017S3Electrical Characteristics:Insertion loss:≤3.5dB;BW:±7.5MHz; V. S.W. R:≤1.5(13.98dB); Ripple (in BW):≤0.5dB; Attenuation:≥11dB(@1995MHz);≥30dB(@1980MHz);≥11dB(@2040MHz)≥32dB(@2067MHz)1900S4Electrical Characteristics:Insertion loss:≤3.0dB;BW:±20MHz; V. S.W.R:≤1.7(11.7dB);Ripple (in BW):≤0.5dB; Attenuation:≥11dB(@1935MHz);≥30dB(@1955MHz);≥11dB(@1865MHz)≥25dB(@1848MHz)The difficult of side band steep is2017S3, and the low-end stop-band in deviation from the band edge1.48%(30MHz/2017MHz) reached the30dB attenuation as well. As it known in the microwave dielectric filter is a relatively steep. Filters after microwave ceramic manufacturing process and batch test meet the technical requirements of the project. Filter already under the mass production process and deliver to users already.