| 摘要 |
In a microwave device, for example a microwave local oscillator with a harmonic mixer for feedback control, problems of coupling the mixer circuit to the R.F. cavity are overcome by providing a d.c. blocking capacitor of the mixer on a planar surface of a support extending across an aperture in one wall of the cavity. In preferred embodiments the capacitor is a planar device formed by a plurality of interdigitated fingers. These fingers are oriented to couple magnetically with the R.F. energy at the aperture in the cavity. The support conveniently comprises a printed circuit board having a ground plane on the same surface as the capacitor, which is located in a small opening in the ground plane. A second ground plane is provided on the opposite side of the printed circuit board, overlying the opening. The two ground planes are interconnected by plate-through-holes.
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