| Application of mobile internet and multimedia technology in the21st century stimulates the evolution and development of wireless communication. Wideband communication system, which can compatible with a variety of communication standards and provide high-quality communication, will become inevitable in the future development of wireless communication. As one of the key components of the RF front-end, wideband filter performance will directly affect the quality of the communication system. In order to meet the requirements of miniaturized microwave integrated circuit, filters not only have good performance, but also have to be small, compact, easy integration and interconnection. For such small size, high-performance wideband filter needs, this paper does exhaustive research on wideband filter based on the lateral signal interference method and bending-type anti-coupled line structure.Innovative research results of this paper include:1) We propose a high selectivity wideband band-stop filter based on lateral signal interference method. This lateral signal interference is formed by anti-coupled line loaded by a quarter-wavelength open-circuited transmission line stub, in parallel with IT-type coupled line which is loaded by two symmetrical quarter-wavelength open-circuited transmission line stubs. Because of the symmetry of the proposed filter structure, we analyze and deduce the filter structure through the symmetrical two-port network odd-and even-mode analysis, and eventually get the scattering parameter expression of the filter structure. Based on obtained scattering parameters, we have a detailed discussion about how transmission and reflection zeros change with characteristic impedance of coupled line and open-circuited transmission stub. The results of discussion shows that we can adjust the location of stop-band transmission zeros and pass-band reflection zeros by changing characteristic impedance of the coupled line and open-circuited transmission stub. In order to validate the feasibility of the filter structure and the effectiveness of the design theory, we finally fabricate, simulate and measure a wideband band-stop filter, which have a center frequency of3GHz and20dB attenuation bandwidth of up to94%. Compared with other similar filter, the proposed filter has a wider bandwidth and higher selectivity.2) We further propose a novel wideband band-stop filter. The filter is designed using signal interference technology which is formed by a bending-type anti-coupled line loaded by a quarter-wave length open-circuited transmission line stub, in parallel with two symmetrical half-wavelength open-circuited transmission line stubs. By using the bending-type anti-coupled line loaded by a quarter-wavelength open-circuited transmission line stub, in parallel with two symmetrical half-wavelength open-circuited transmission line stubs, we can introduce five transmission zeroes into the stop-band of the filter, and also produce four reflection zeroes at the pass-band. Because of these transmission and reflection zeroes, we get steep transition-band characteristic, wide stop-band, and better stop-band rejection. Because of the symmetry of the proposed filter structure, we analyze and deduce the filter structure using the symmetrical two-port network odd-and even-mode analysis, and eventually get the scattering parameter expression of the filter structure. Through the analysis of transmission and reflection scattering parameters, we can get the expression of transmission and reflection zeroes. Based on the expression of transmission and reflection zeroes, we have a detailed discussion about how transmission and reflection zeros change with characteristic impedance of coupled line and open-circuited transmission stub. The results of discussion shows that we can adjust the location of stop-band transmission zeros and pass-band reflection zeros by changing characteristic impedance of the coupled line and open-circuited transmission stub. In order to validate the feasibility of the filter structure and the effectiveness of the design theory, we finally fabricate, simulate and measure a wideband band-stop filter, which have a center frequency of3GHz and10dB attenuation bandwidth of up to115%, also have165.9dB/GHz attenuation slope of the transition-band at the right side of stop-band. The agreement of simulation and measurement results validate the feasibility of the filter structure and the effectiveness of the design theory3) We propose a wideband filter based on bending-type anti-coupled line structure. By using the bending-type anti-coupled line loaded by a II-type coupled line and two symmetrical open-circuited transmission line stubs, we can introduce six transmission zeroes into the stop-band of the filter. Because of these stop-band transmission zeroes, we get steep transition-band characteristic, wide stop-band, and better stop-band rejection. Because of the symmetry of the proposed filter structure, we analyze and deduce the filter structure using the symmetrical two-port network odd-and even-mode analysis, and eventually get the transmission and reflection scattering parameter expression of the filter structure. In order to verify the feasibility of the filter structure and reliability of design theory, we design and construct a compact wideband band-pass filter prototype, which has a center frequency of3GHz and10dB attenuation bandwidth of up to61.4%. The agreement of simulation and measurement results validate the feasibility of the filter structure and the reliability of design theory. Meanwhile, in order to further improve the selectivity of the filter edge and improve the stop-band rejection level, we directly cascade two identical filters prototype. The cascaded filter obtains a competitive attenuation slope, which has100.8dB/GHz at the left edge of the pass-band and has109.4dB/GHz at the right edge of the pass-band.4) We further propose a novel and simple structure wideband band-pass filter. The filter structure is very simple, just composed of a bending-type anti-coupled line and half-wavelength open-circuited transmission line stub. Because of the symmetry of the proposed filter structure, we analyze and deduce the filter structure using the symmetrical two-port network odd-and even-mode analysis, and eventually get the scattering parameter expression of the filter structure. Through the analysis of transmission and reflection scattering parameters, we can get the expression of transmission and reflection zeroes. Based on the expression of transmission and reflection zeroes, we have a detailed discussion about how transmission and reflection zeros change with characteristic impedance of coupled line and open-circuited transmission stub. The results of discussion shows that we can adjust the location of stop-band transmission zeros and pass-band reflection zeros by changing characteristic impedance of the coupled line and open-circuited transmission stub. Eventually, we design, simulate, measure and compare two band-pass filters with different transmission and reflection zeroes. The center frequency of the filter is3GHz,3dB bandwidth of45%. Test results show that the band-pass filter has a steep transition-band characteristics and low insertion loss. |
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