GB1020043A - Cavity resonator apparatus - Google Patents

Abstract

1,020,043. Cavity resonators. VARIAN ASSOCIATES. March 27, 1963 [April 9, 1962], No. 12147/63. Heading H1W. A cavity for operation in the TE 0,1, n modes (n > o) has a hemispherical end wall and a further end wall which is other than symmetrical with the hemispherical wall about a diametral plane through its edges. Such a cavity has a high Q for TE 0,1, n modes and supports no other modes except the TM 1,1, n. These latter, however, are resonant at a frequency different from the resonant frequency of the desired modes. As shown in Fig. 2, the cavity comprises a hemispherical end wall 13, a short cylindrical side wall 12 and a further end wall 14 of ribbed planar form. Frequency adjustment is obtained by screwing the end wall 14 into the cylindrical wall 12 and locking with a ring 17. Waveguides may be coupled to the cavity through apertures 15, 16. If necessary, the cylindrical side wall 12 may be dispensed with. Additional suppression of undesired TM modes may be obtained by providing an annular gap 24, Fig. 2A, partly filled, if desired, with lossy material, between the end wall 14<SP>1</SP> and the side wall 12<SP>1</SP>. A modified method of tuning consists in laterally displacing the axes of the end walls from each other. For this purpose, the walls are respectively provided with interengaging, mutually-rotatable flanges, the flanges being provided with eccentrically arranged shoulders. In a further tuning method, the two axes are angularly displaced by means of interengaging, mutually-rotatable, tilted flanges. Small changes in resonant frequency may be produced by perturbations such as dents or screws extending into the cavity. The cavity may be temperature stabilized by making the side wall and the hemispherical wall out of a material having a low thermal coefficient of expansion and the flat end wall out of a material having a high coefficient.