Patent GB-592119-A (GB)
Title: Improvements in or relating to apparatus for measuring high frequency power
IPC: G01R21/00
Filed: 1943-07-23
Abstract: 592,119. Coil-less resonators. SPERRY GYROSCOPE CO., Inc. July 23, 1943, No. 12048. Convention date, Feb. 4, 1942. [Class 40 (iii)] [Also in Group XXXVI] Ultra-high-frequency to be measured (see Group XXXVI) is introduced into a coaxial line element 41, 42, Fig. 2, and is conducted into a resonant chamber 43, which is adjusted by means of a sliding end wall 44 to match the impedance of the hot wire 9 so that the entire electromagnetic energy introduced into the coaxial line is dissipated in the hot wire 9. To permit D.C. to be introduced into the hot wire 9, the resonant chamber 43 is provided with a cap 45 between which and the body of the chamber 43 is an insulating layer which forms the dielectric of a blocking condenser 48. The inner conductor 42 passes through a slot 51 in the outer conductor and is attached to a sleeve 46 which is slidable by means of a knob 46<1> to adjust the impedance coupling of the transmission line, 41, 42 to the resonant chamber 43. In a modification, Fig. 9, the hot wire 74 is a low current, fuse held in clips 76, 77. The clip 76 is attached to the end wall 79 which is insulated from the outer tubular conductor 81 for unidirectional voltages by a ribbon 80 of dielectric material. Attached to the tube 81 is an outer concentric tube 86 having an end wall 87 in which is a socket 88 for the lead wires 57<11> connected to the end wall 79 and to opposite ends of the compensation resistance 101. A direct current lead for the end 77 of the fuse 74 is provided by a concentric line 90<1>, 91, preferably a quarter-wave long. The concentric line 78, 84 may be joined to a line of different diameter by a tapered section 89, matching being effected by means of a sleeve 90 which is a quarter wavelength long. For higher power measurement the fuse 75 may be replaced by an incandescent lamp, which may be either of the vacuum or gas-filled type. Fig. 3 shows a current or energy dividing transformer for diverting a known proportion of the high-frequency energy for heating the hot wire 9. Two hollow end conductors 25, 26 are spaced apart by a member 27 and terminated by tapered concentric line adapters 28, 28<1> adapted to receive concentric transmission line terminals. A central member 29 is slidably mounted between the two end members 25, 26 and can be fixed in adjusted position by a screw 30 slidable in a slot in the member 27. The inner conductor of the central member 29 has a varying diameter, whilst the outer conductor is of constant diameter. The diameter of the inner conductor increases from the ends to the centre, thus lowering the impedance of the concentric conductors from a value corresponding to a high voltage and low current at the ends to a much lower value at the centre 33 corresponding to a low voltage and high current. The central member 29 is provided with a high impedance tap 34 at its lowest impedance point, where the inner conductor has a sudden reduction in diameter, corresponding to an increase in impedance. The tap 34 has attached to it an outer conductor 54 of constant inner diameter and an inner conductor 53 of slowly increasing diameter, so . that at the point 55 the impedance of the line 53, 54.is equal to that of the line 41, 42, Fig. 2, to be attached. In order to allow for the effect of standing waves due to energy reflections, the position of the tap between the two fixed end sections 25, 26 is varied so as to obtain maximum and minimum readings from which the actual energy transfer along the transmission line may be determined. An alternative form of current or energy dividing device having a fixed tap is shown in Fig. 6. Energy to be divided is introduced into a tapered matching end 59 and is divided into calculable portions at the tap 34<1>, the portion of the energy tapped by the branch 49<1> being fed to the coaxial line 41, 42, Fig. 2. The unused portion of the energy is absorbed in a terminating impedance 36, which may be composed of carbon or graphite. In another modification, Fig. 7, the inner conductor is stepped at 62, 63, 64, 65, 67, 68, 69, and the inner conductor of the branch is stepped at 66, 71, 72, 73. The highfrequency power to be measured may alternatively be reduced to a value suitable for measurement by the attenator or energy dissipator shown in Fig. 21. A section of concentric transmission line has an inner conductor 121 and an outer conductor 123 with insulating spacers 125. A concentric line 127 is joined to the line 121, 123 by a joining member 129 and an outer sleeve 131, insulating supports being spaced at a quarter the operating wavelength apart. The energy is dissipated and attenuated in resistance elements 133, 135 comprising a thin coating of carbon &c. on an insulating disc. These resistance elements are spaced apart by a quarter wavelength. Further resistance elements spaced at quarter wave intervals may be added. Specifications 581,972 and 592,161 are referred to.