An R.F. circuit with at least one R.F. transmission line including a strip conductor (15) and a ground plane (13) on an insulating substrate (3) and having two diodes (24, 25) respectively D.C.-connected to two portions (38,39) of the ground plane (13). The two portions are mutually D.C.-isolated by a slot (37) to enable the diodes (24, 25) to be biased. The substrate (3) is mounted in a housing (1, 2) of conductive material, and the two portions (38, 39) of the ground plane (13) are mutually R.F.-coupled via the conductive material. One of the portions (39) is electrically-connected to an adjacent housing member (2) and the other portion (38) is separated therefrom by a thin insulating layer. The slot (37) inhibits coupling of R.F. energy out of the circuit into the slot (37), suitably being very narrow, e.g. 20 μm, so as to form a further transmission line with a very low characteristic impedance and also to have a high attenuation along its length for operation at mm-wavelengths.

R.f. circuit arrangement

A waveguide arrangement is formed by two conductive sections separated by an insulating substrate. The waveguide walls are delined by channels cut in the conductive sections and slots plated with conductive material in the insulating substrate.

A waveguide arrangement.

An R.F. circuit, for example an R.F. mixer circuit comprising an insulating substrate (3) in an E-plane of a rectangular waveguide (not shown) comprises an first portion including a (quasi) TEM transmission line (15, 13) for propagating R.F. energy at substantially different first and second frequencies (L.O. and I.F. respectively) and a second portion including a waveguide for propagating R.F. energy at the first frequency (L.O.). Between the waveguide and the transmission line (15, 13) area filter (14) for passing the first frequency (L.O.) and blocking the second (I.F.), and a mode transducer (11). To inhibit the mode transducer (11) from acting as a stub weakly coupled via the filter (14) to the second portion of the circuit at the second frequency (I.F.), but without affecting coupling at the first frequency (L.O.), stub means (27-30) substantially short-circuit the mode transducer (11) adjacent the filter (14). When the second frequency (I.F.) is much less than the first (L.O.), the stub means may comprise a stub (27) which is a quarter wavelength long at the first frequency (L.O.), and hence much shorter at the second frequency (I.F.), and which is short- circuited at its free end (28) by a conductive connection through the substrate (3).

Ballard Philip Mckenzie

Papers

R. F. Circuit