Patent GB-1336587-A (GB)
Title: Microwave circuit assembly for operation above
IPC: H03D9/00
Filed: 1970-12-11
Abstract: 1336587 Microwave circuits; detectors; amplitude modulation THOMSON-CSF 11 Dec 1970 [16 Dec 1969] 59158/70 Headings H3T H3Q and H3R [Also in Division H1] In a microwave circuit assembly comprising first and second conductive layers 3, 2 on opposite faces of an insulating panel 1, a hole 9 in the panel divides the first layer 3 into two portions and an electrically conductive block 4 is inserted in the hole 9 and is connected to the second layer 2. The circuit assembly further comprises a low-pass filter T section, having two inductive series arms La, Ld, each consisting of a portion of elongate electrically conductive material and a capacitive shunt arm Cd comprising a discrete capacitor, the free extremity of one of the arms La is connected to only one of the portions of the first layer, the capacitor Cd has one electrode connected to the block 4 and the other electrode connected to the junction of the series arms and the other inductive arm is connected to a terminating arm which includes a variable impedance semi-conductor diode D1 and electrical means is provided for controlling the impedance of the diode. Oscillations from a local oscillator are applied to line conductors 2, 3, Fig. 1, shown as X1, X2 in the equivalent circuit, Fig. 3, together with a switching bias to switch the diode D1 from a blocked state to a conductive state. Switching of the biasing potential causes a shift by almost 180 degrees in the relative phase of the incident and reflected waves at relatively low carrier frequencies. The components La, Ld and Cd act as a LPF and are selected so that the effect of the capacitive termination D 1 on the phase shift resulting from alternate blocking and unblocking of the diode D1 is compensated for to produce a flat response characteristic (Fig. 4, not shown). The bias applied to the diode D1 may also be such as to clip half of the cycles of a modulated carrier so as to operate as a detector. Alternatively a modulating signal may be fed into the bias circuit so that the circuit operates as a modulator or mixer. In the micro-strip arrangement (Fig. 1) the ribbon or wire section La is shorter than section Ld, the condenser Cd may be ceramic or M.O.S. type and the diode D1 may be Schottky snapoff varactor or semi-conductor PIN diode. In an alternative arrangement (Fig. 2, not shown), a conductor (5) connected to section La, is sandwiched between two dielectric strips (1<SP>1</SP>, 1<SP>11</SP>), such as of aluminium oxide, whose outer surfaces are covered by a pair of ground layers (6A, 6B). Either arrangement may be placed in a sealed enclosure 10. The elements Cd and D1 may be soldered on to a block 4 by gold silicon or gold germanium alloys and the block 4 may be of gold-plated copper or a similarlyplated nickel-cobalt-iron alloy. In a further modification (Figs. 5 and 6, not shown) a coupling condenser (C2) is connected in series with the diode D1 (D2) and the bias is applied from (7) to the junction of the diode (D2) and condenser (C2). This arrangement preferably uses a tunnel or Schottky diode for (D2) and operates as a mixer for modulating or demodulating the incoming carrier frequency. In a modification (Figs. 8-10, not shown) a HPF (Lm, C1, Lp) is included in the input between X1, X2 and the section La. This may be further modified by alternatively applying the bias voltage from (8) via a wire Lp to the section La. The bias voltage may be an I.F. signal to modulate the high frequency input oscillation or a continuous or alternating D.C. potential for biasing the diode D1 as a detector or as a switchable terminating impedance. A common metal block 4 may carry two such circuits operating as a balanced modulator with control leads (7) and/or (8) energized in push-pull.