A Wide Range Microwave Sweeping Oscillator

Basically, the rf circuit consists of a tunable cavity for a grid-anode resonant circuit, a means for feedback to an untuned grid-cathode circuit, and a means for coupling the cavity to a waveguide output. The gridanode cavity is the only sharply tuned circuit, and it was found that oscillations could be obtained over the entire band by changing the resonant frequency of that cavity alone. In this application, the electronic conductance between the grid and cathode is so high that this portion of the circuit has an inherent broad band such that separate tuning is unnecessary. The necessity for continuous, rapid tuning virtually requires that there be no sliding contacts in the tuning mechanism. A type of cavity was chosen so that tuning could be accomplished by a simple variable capacitor of the non-contacting type. Reduced to its simplest elements, it consists of a short coaxial line, resonant in the half-wave mode. Actually the line is much shorter than a half wavelength because of excess capacitance at both ends. At one end is the capacitance of the grid-anode gap, and at the other end is the variable capacitor used for tuning. 553