An Elliptic Function Combline Filter using Electric Probe to Realise Capacitive Coupling

A four-pole elliptic function combline filter is discussed. In this filter, an electric probe is used between the two crossed coupled resonators in order to realise the required capacitive coupling. Unlike a method introduced recently for the same type of filters, this realisation reduces the need for resonators with long posts, providing filter compactness and offering flexible and wide range of couplings. Experimental results show good agreement with the theoretical analysis.