Frequency tunable microwave apparatus having a variable impedance hybrid idler circuit

Claim 1

A broad-band frequency tunable microwave apparatus of the type including a transmission line, a semiconductor element in said line for generating, in response to a threshold signal, a microwave signal having fundamental, second and third harmonically related frequency components, means for applying said threshold signal to said semiconductor element, and output means to provide a substantially resistive impedance electrically connected to said semiconductor element for transmitting a signal component at the second harmonic frequency to a terminating load impedance, wherein the improvement comprises: a variable input impedance idler circuit connected in parallel with said semiconductor element including a distributed transmission line having a predetermined characteristic impedance serially connected to a lumped variable capacitor connected to ground, said input impedance of said idler circuit being substantially reactive and determining the fundamental and harmonic frequencies of said apparatus, said fundamental frequency and its harmonics being tunable over a selected frequency range by changing the input circuit impedance of said idler circuit by varying the capacitance of said variable capacitor, whereby said apparatus provides said microwave signal to said terminating load impedance only at said second harmonic frequency throughout the tunable frequency range.