Microstrip extracted-pole lossy filters

In the chapter, the design of microstrip lossy extracted-pole filters has been described. This type of filter can have both of high selectivity and flat passband. The high selectivity is contributed by using extracted-pole technique and the flat passband is achieved by introducing RCCs in the inline network. The independently controllable extracted-pole transmission zeros result in an inline asymmetrical filter topology with asynchronously tuned resonators. The direct circuit synthesis of this type of filter has been described with numerous examples providing a more direct insight into the theory. The proposed equivalent circuit and tabulated elements are ready to hand with most commercially available circuit modelling tools. Two six-pole microstrip filters of this type have been designed and demonstrated experimentally showing promising filtering characteristics. The improvement of passband flatness is more significant and obvious in the narrowband than that of the wideband.