Novel unilateral circuits for MMIC circulators

A circuit which is equivalent to a four-port circulator with one port terminated, called a quasi-circulator, is proposed. The quasi-circulator can replace a conventional circulator even though it is not a complete circulator. Examples of novel three-port unilateral circuit modules, called quasi-circulator modules, which are the main part of the quasi-circulator are presented to realize very wide band circulators in monolithic microwave integrated circuit (MMIC) form without using ferrite materials and external magnets. The proposed modules are composed of an active out-of-phase divider and an active in-phase combiner or an active in-phase divider and an active out-of-phase combiner. The modules have many variations. All are very small and operate over a very wide frequency range. Two types of quasi-circulator modules that have very broadband operation up to X or Ku band are demonstrated. A quasi-circulator is also demonstrated. It is shown how an active circulator is realized by quasi-circulator modules