Patent GB-1081714-A (GB)
Title: Microwave signal processing devices
IPC: H03B19/18
Filed: 1964-09-24
Abstract: 1,081,714. Parametric amplifiers; tunnel diode circuits. RADIO CORPORATION OF AMERICA. Sept. 24, 1964 [Oct. 30, 1963], No. 39031/64. Headings H3B and H3T. [Also in Divisions H1 and H2] A resonator comprising a body of material of a high dielectric constant (e.g. rutile) is mounted in the interior of a hollow waveguide and has coupled to it at its interface with the low dielectric ambient of the waveguide one or more non-linear elements. Such a resonator is employed in harmonic generators, amplifier, mixer or oscillator of microwave frequencies. The resonator assembly 15, Fig. 1, comprises a cylindrical disc 21 of titanium dioxide positioned on a seat 22 of rod 23 at the centre of waveguide 12. A variable capacitance, semiconductor alloyed junction diode including a main body 26 of N-type material and a dot 27 of P-type is positioned at the edge of the disc and orientated for maximum coupling with the electromagnetic fields set up by the resonator, Figs. 4a, 5a (not shown). The reverse bias for the diode is provided by source 32 connected to terminals 31, 30 on cap 25 to which leads 29, 28 are also connected. A pair of R.F. by-pass capacitors 33, 34 are connected as shown and are of the form shown in Figs. 2, 3 (not shown). The resonator is positioned in the waveguide so that the broad, flat surface of the disc is parallel with the side walls of the waveguide and at right angles with the broad walls to enable maximum coupling between the fields of the waveguide and the fields of the resonator. More than one diode may be situated on the disc, Fig. 12 (not shown). Harmonic generator.-An 8 KMC signal from source 10 is supplied through isolator 14 to waveguide 12 tuned by rod 17 and is magnetically coupled to the resonator assembly 15 causing the resonator 21 to oscillate. The capacitance of the diode is effectively added to that of the rutile resonator which is so dimensioned that with the added capacitance modes of oscillation exist in the resonator at both the fundamental and the desired harmonic. The harmonic is coupled from the resonator to the waveguide 12 and through tapered waveguide 36 to load 42. Since the resonator dielectric is high the capacitance of the junction diode is small with respect thereto and the diode does not excessively load the resonator. The resonator may be in the form of a coaxial resonator, Figs. 6a, 6b (not shown), or as a pair of solid cylindrical elements, Figs. 7a, 7b (not shown), within a junction diode mounted therebetween, one of the cylinders resonating at the fundamental frequency and the other at the desired harmonic when excited by energy from the diode. Parametric amplifier.-This is essentially the same construction as the harmonic generator of Fig. 1 except that the signal to be amplified is passed through a circulator to the waveguide carrying the resonator, Fig. 8 (not shown). Pump energy is supplied through the tapered waveguide 84 and the output is taken from a part of the circulator. In operation the input signal and pump signal are magnetically coupled to the resonator which is resonant at both these frequencies and the idler frequency is produced by the interaction of these frequencies with the diode. The amplified input signal is fed back to the circulator. A tunable waveguide cavity may be mounted on the wall of the waveguide in close proximity to the resonator and is tuned to the pump frequency the resonator supporting the signal and idler frequencies. The arrangement of Fig. 7 may also be used. Mixer.-A variable capacitance diode or tunnel diode mounted rutile resonator is as shown in Fig. 9 in block form in which a signal input at a first frequency is applied across an inductor 107 connected between the diode and D.C. bias and a second frequency signal is applied to the waveguide 12 in Fig. 1. The resonator is constructed to be resonant at the sum or difference frequency. Tunnel diode amplifier.-This is the same construction as the previous embodiments, a forward biased tunnel diode mounted rutile resonator being positioned in a waveguide including a movable shorting plunger, Fig. 10, and the input signal being supplied through a circulator, from which the amplified output is taken. Tunnel diode oscillator. Fig. 11 (not shown).- In this arrangement the forward bias applied to the tunnel diode is such as to place the tunnel diode in combination with the resonator in its mode of oscillation.