Abstract: An isolator is described for use in a low-noise maser amplifier, which provides low loss across a wide bandwidth and which can be constructed at moderate cost. The isolator (40) includes a train of garnet or ferrite elements (50, 52) extending along the length of a microwave channel (14) parallel to the slow-wave structure (24), with the elements being of staggered height, so that the thin elements (50) which are resonant to the microwaves are separated by much thicker elements (52). The thick garnet or ferrite elements reduce the magnetic flux passing through the thin elements (50), to permit altering of the shape of the thin elements so as to facilitate their fabrication and to provide better isolation with reduced loss, by increasing the thickness (T) of the thin elements and decreasing their length (L) and width (W).

Abstract: A dielectrically loaded four-port waveguide circulator is used with a reflected-wave maser connected to a second port between first and third ports to form one of a plurality of cascaded maser waveguide structures. The fourth port is connected to a waveguide loaded with microwave energy absorbing material. The third (output signal) port of one maser waveguide structure is connected by a waveguide loaded with dielectric material to the first (input) port of an adjacent maser waveguide structure, and the second port is connected to a reflected-wave maser by a matching transformer which passes the signal to be amplified into and out of the reflected-wavemaser and blocks pumping energy in the reflected-wave maser from entering the circulator. A number of cascaded maser waveguide structures may thus be housed in a relatively small volume of conductive material placed within a cryogenically cooled magnet assembly.