phasenstarre waveguide oscillators

摘要

1,242,228. Oscillators. WESTERN ELECTRIC CO. Inc. 26 July, 1968 [27 July, 1967], No. 35713/68. Heading H3T. An oscillator has a negative resistance active element (a tunnel diode 11) disposed in energy transferring relationship to a waveguide 10, a shunt inductive element 12 being arranged close to the diode 11 to suppress oscillations below the cut-off frequency of the wavepath, thereby ensuring that oscillation at a frequency not less than the cut-off frequency is produced at the output. The spacing 11-12 is preferably a quarter of a wavelength and transverse to the direction of propagation. The waveguide 10 is tapered to match its impedance to that of the diode, to which a phase-locking input is connected by an isolator 15. The inductive element 12 is adjustable in position by a portion 13 thereof which extends through a slit 14 in the wall of the waveguide. In a second embodiment (Fig. 3, not shown) the tunnel diode (31) is arranged in an inductive iris formed by two elements (32), the frequency being adjusted by a piston (37). The microwave power is supplied by way of a circulator (38). The tunnel diode in both embodiments could be replaced by a Gunn effect or L.S.A. device. The effect of the inductive element 12(32) is explained in terms of the frequency dependent capacitive impedance curve of the diode (1, Fig. 2A, not shown) which is crossed, in the absence of the element 12, by the circuit inductive impedance curves at two points (A,B) respectively above and blow the cut-off frequency, oscillation tending to occur at the lower frequency (A). In the presence of the inductive element 12 the circuit inductive impedance curves are modified (Fig. 2B, not shown) so that a cross-over occurs only at a frequency above the cut-off frequency; and oscillation therefore occurs at this frequency (C).