GB640848A - Improvements in the stabilizing, or measuring, of the frequency of microwave oscillations - Google Patents

Abstract

640,848. Frequency measurements. RADIO CORPORATION OF AMERICA. Sept. 9, 1948, No. 23750. Convention date, Jan. 8. [Class 37] [Also in Groups XL (b) and XL (c)] The molecular resonance of certain gases such as ammonia, carbonyl sulphide and methyl halides is utilized for measuring or stabilizing the frequency of micro-wave oscillations. In the micro-wave generator system shown in Fig. 5, the sharply resonant characteristic of a resonant cavity tuned to a desired operating frequency and containing a gas exhibiting molecular resonance at that frequency is utilized to stabilize the frequency of a multicavity magnetron 10. The gas 12 is contained in a cavity 11 which is coupled to the magnetron so as to appear thereto as a highly reactive load capable of pulling the frequency of the generated oscillations to the desired value. This is effected by adjustment of the distance a, from the wave-guide 9 to the window 17 of the cavity 11 and the distance b from the cavity 11 to the magnetron 10. Two cavities 13, 14, Fig. 6, may be provided, the cavity 13 being filled with gas and the cavity 14 being identical therewith but not filled with gas. The cavities 13, 14 are spaced apart by a distance c such that the reflection at the junction of the cavity 14 with the wave-guide 9 cancels out the reflected wave at the junction of the cavity 13 and the waveguide 9 so that only the impedance component due to gas resonance remains. A screw 15 is provided for fine adjustment of the electrical distance c. The chambers 11, 13 for containing the gas are each provided with a window 17 of thin mica, which is transparent to the microwave energy from the generator. The gas pressure may be less than one-tenth of a millimeter of mercury. The frequency-stabilizing element may be a length of gas-tight concentric line 18, Fig. 8, filled with gas and connected to a valve 19 so as to form a tuned grid circuit. A resonant cavity 20, Fig. 9, or a length of wave-guide 21, Fig. 10, filled with a gas exhibiting molecular resonance at the fundamental or higher modes of the cavity or guide may be used as an absorption wavemeter for adjusting an oscillator to operate at a molecular resonance frequency of the gas or to check whether the frequency of generated oscillations corresponds with that of the precision wavemeter. A set of precision wavemeters or frequency standards for a large number of discrete frequencies may be made by suitable choice of the gas, and of the dimensions of the associated cavities. Each wavemeter unit, Figs. 9 and 10, may be provided with a crystal rectifier for connection with a sensitive meter 22.