GB1190549A - Improvements in Electrical Waveguide Arrangements - Google Patents

Abstract

1,190,549. Isolators and filters. STANDARD TELEPHONES & CABLES Ltd. 24 March, 1969, No. 15206/69. Heading H1W. A dual-purpose waveguide device comprises a combination of a field-displacement ferrite isolator and a band-pass filter. A section 3 of rectangular waveguide is provided with lateral strips 4, 5 of ferrite, one of which (4) carries a resistive coating 6, whereby, on application of a transverse magnetic field H dc , the section behaves as a conventional field-displacement isolator over a certain band of frequencies. At frequencies below this band, the section 3 is effectively dimensioned beyond cut-off by virtue of the effect of the polarized ferrite strips 4, 5. Energy incident from section 1 propagates as an evanescent wave in section 3 and each length I of the section presents an inductive reactance to the wave. Each length l is associated with an E-plane stub 8 dimensioned to provide a series capacitative reactance which is the conjugate of the reactance of the corresponding length l, whereby the whole section 3 behaves as a three-section band-pass filter within a band of frequencies below that within which it behaves as an isolator. In the latter band, the stubs 8 approximate in length to #g/2 and present a short circuit to the waveguide. In a modification (Fig. 6, not shown), having two sections only, the stubs (two in number) lie parallel, instead of at right-angles, to the waveguide section 3.