E-Plane Metal Insert Filters With Improved Stopband Characteristics

Abstract

Microwave filters find their application in all modern communication systems, including RADARs, satellites, cellular communication and other wireless applications. Different resonator configurations are used to implement these filters with their pros and cons. Microstrip filters are low cost, there is ease in integration and these are smaller in size but they face additional dielectric and radiation losses. Coaxial filters are compact in size with moderate quality factor but their performance is sensitive to fabrication tolerances at frequencies of x-band and other higher bands. Waveguide filters are very useful for the applications where high quality factor and high power handling capability is required. Microwave filters are based on transmission line and waveguide theory so there is periodicity in their response. Due to which practically their second stopband performance is poor which is not acceptable for image rejection and multiplexer applications. So extensive research has been done to improve the stopband performance. Since waveguide filters have high quality factor and high power handling capability so they are favourable for space applications. In waveguide filters E-plane metal insert filters are low cost and mass producible but their stopband performance is poorer. Different techniques are used to improve their stopband performance. One of the techniques is to use triple inserts. This technique involves multiple interfaces in the mechanical assembly due to which its measured passband performance deteriorates severely. To resolve the issue a novel structure for the coupling section or the inverter is proposed, in this research. Our proposed design is based on novel configuration of coupling structure. So the proposed design achieves an excellent broadband performance specially in terms of attenuation and broadness of second stopband. It implements standard waveguide cavity resonators to secure higher quality factor and power handling capability of the waveguide filter. It also achieves the characteristic features of conventional E-plane metal insert filter i.e. mass producibility by using very thin single metal insert. Overall size of the proposed filter is smaller than conventional E-Plane filter. Its passband IL and RL are better than triple metal insert filter, as there are minimum interfaces in the proposed design.