Strip-line filters and diplexers with the housing of complicated cross section form for mobile communication systems

A novel easy-to-manufacture design of filters and diplexers providing frequency band 2–7% between pass-band and stop-band is proposed which is suitable for mass production. Main features of the proposed design are following: (i) the entire circuit of frequency selective components is a single branched strip conductor which may be made by punching technology; (ii) the branched strip conductor is disposed inside of metal housing and separated from one by foam substrates; (iii) the metal housing has a shape of plane tube with complicated cross section which may be made by extrusion technology; (iv) coaxial cables are soldered to the metal housing and ends of the branched strip conductor. The open-ended stubs disposed in the region of the housing with the largest distance between the wide walls have significantly higher impedances in comparison with impedances of connected in series strip-line sections disposed in the region of the housing with the small distance between the wide walls. This structure creates narrow bands of attenuation in vicinity of attenuation poles therefore one can provides a narrow frequency band between the pass-band and the stop-band of filters. The use of the open-ended stubs in a shape of flat spiral provides additional increasing their impedance. Due to the use of open-ended stubs in a shape of flat spiral and the housing having complicated cross section the open-ended stubs with very high impedances are created and frequency band between the pass-bands of diplexer is reduced. The proposed filters don’t include the metal parts touching each other since the branched strip conductor made as an all-metal plate is isolated from the conductive housing which is the plane metal tube with complicated cross section. As a result the filter of this simple structure provides lower level of the passive intermodulation distortions and lower fabrication cost in comparison with known filters. The punching and extrusion technologies provide very small fabrication tolerances therefore the proposed frequency selective components are manufactured without tuning procedure and don’t contain tuning screws. As a result their fabrication cost is lower in comparison with the known frequency selective components providing low insertion loss.