Patent GB-1117348-A (GB)
Title: Microwave harmonic generator
Inventor: LUSTED ALAN RODNEY
IPC: H03B19/18
Filed: 1966-03-25
Abstract: 1,117,348. Microwave harmonic generation. MULLARD Ltd. 24 April, 1967 [25 March, 1966], No. 13293/66. Heading H2F. [Also in Division H1] A microwave fourth-harmonic generator comprises a coaxial line coupling the input signal to a varactor diode whose other terminal is connected to a waveguide having a cut-off frequency above the third harmonic of the signal but below the fourth harmonic, and a variable capacitance between the first diode terminal and the waveguide wall to form with the diode and part of the waveguide wall a circuit series-resonant at the fourth harmonic. In Fig. 3 the signal enters at the coaxial line V which has its inner conductor broadened at the inner end G to provide a length of lower impedance. A bent connector Q forms with the adjacent waveguide wall a high-impedance line to match the input to the diode K. An adjustable screw S1 forms with the diode a variable capacitance which together with the inductance from the lower terminal of the diode through the waveguide wall to the end of the screw provides a circuit series-resonant at the fourth harmonic (Fig. 2, not shown). The necessary bias for the diode is supplied via the inner conductor of the coaxial cable. A conductive member N extends from the upper terminal of the diode into a dielectric block H on the opposite wall of the waveguide. This member forms with the bottom (broad) wall of the waveguide a transmission line which can be tuned by a screw S2 (see also Fig. 4, not shown) to resonate at the second harmonic. The parts Q, K and N can be formed integrally and plugged into the end of the coaxial line F. The diode is held in position by a nylon screw (J in Fig. 4, not shown) threaded through the upper wall of the waveguide. The waveguide has an adjustable short-circuiting piston P and the energy passes up the main waveguide W1 to an output waveguide W2. The section W1 cuts off any third harmonic but passes the fourth harmonic, and the distance b should be an odd number of quarter wavelengths at the fourth harmonic. Radial chokes may be provided in the flange connecting W1 to W2 and half- or quarter-wave chokes in the piston P. This arrangement is suitable for converting 2.25 Gc/s. to 9 Gc/s. To prevent the line F from propagating fourth-harmonic energy in a waveguide mode the mean radius of the inner and outer conductors should be less than 1/2# times the wavelength and the electrical length of the parts Q and G together should be a quarter wavelength at the fourth harmonic. In a modification (Figs. 5 and 6, not shown) for converting 9 Gc/s. to 36 Gc/s. the diode is mounted eccentrically in a block which can be rotated (Figs. 7 and 8, not shown) to vary the distance of the diode from the waveguide wall and hence the capacitance; this adjustment replaces the screw S1 of Fig. 3. In addition, the lower-impedance section G is formed by reducing the diameter of the outer conductor and the member N is self-supporting without the dielectric block H. At the junction of the waveguide sections W1 and W2 a capacitive iris is provided (Figs. 5 and 12, not shown), the aperture of which has a longer dimension which is greater than the wide dimension of W1 and a short dimension which is less than the narrow dimension of W2. This iris compensates for the inductive discontinuity at the join and resonates at the output frequency.