A new dual mode cavity concept

A new dual mode cavity concept is presented based on the independent tuning of two orthogonal resonant modes inside a cavity. The use of this principle has been claimed in the past very frequently but violated in practice due to a confusing association between the electromagnetic system and its equivalent network representation. It is shown that the desired coupling effect inside the cavity is simply obtained when both resonant modes are simultaneously excited and tuned to different frequencies. A generic network representation for the dual mode cavity is proposed which is more clearly associated to the real electromagnetic system. The relation of this network with the standard filter synthesis network is shown and some fundamental design implications are derived that are not in full agreement with the classical design techniques. Based on this new understanding a simple tuning mechanism has been experimentally verified on typical channel filters.