Patent GB-1013294-A (GB)
Title: Apparatus for providing information on characteristics of electromagnetic wave loads
IPC: G01R27/32
Filed: 1962-03-19
Abstract: 1,013,294. Measuring impedance; frequency characteristics. DIELECTRIC PRODUCTS ENGINEERING CO Inc. March 19, 1962 [March 20, 1961], No. 10493/62. Heading G1U. An apparatus for providing information on the characteristics of an electromagnetic wave load test comprises an electomagnetic wave generator, a circuit via shich the e.m. wave from the generator is applied to the load under test, and arrangement for sensing the wave transmitted over the circuit. The sensing arrangements incorporate an impedance network which establishes in response to an e.m. wave four reference voltages at four network terminals, these voltages being in quadrature with one another with respect to the load. Circuit elements are connected between the load and each network terminal to provide output signals proportional to the quadrature components of a characteristic of the load. In an arrangement for determining the reflection coefficient as a function of frequency of a network e.g. a coaxial line, a test signal from a sweep frequency generator 10 (Fig. 1) is combined with suitable marker pulses and applied to an impedance plotter network 16 to which is connected the network 18 under test. Outputs from the plotter are applied to both horizontal and vertical deflection systems of an oscilloscope, on the face of which will be displayed a Smith Chart impedance plot. In the impedance plotter network are provided four resistance-capacitance phase shifters connected between the point of application of the sweep generator voltage 40 (Fig. 2) and ground. These phase shifters are selected so that the voltages at their mid points ABCD at the middle of the frequency range under examination are 90 degrees out of phase one with another, and thus the voltages AB, CD are in quadrature. The input I is applied via a matching resistor 38 to a coaxial line at 0, the outer sheath of which is connected to ground. Square law detectors are connected from 0 to the points A, B, C, D, and D.C. output voltages proportional to the square of the sensed R.F. voltages are produced and applied over lines 20, 24 to the oscilloscope 22, whose beam position will represent a polar plot of the reflection coefficient. When an engraved transparent Smith Chart face plate is placed in front of the cathode ray tube a measure of the R.F. impedance at the point measured on the coaxial line may be obtained. An alternative arrangement using distributed constant components (e.g. identical transmission lines terminated by different lengths of open and short circuited sections of transmission line) is described (Fig. 3 not shown) and a mechanical construction of this arrangement is discussed (see division H3). In order to measure transmission coefficients the modified arrangement of Fig. 6 is used. A signal is applied from generator 10<SP>1</SP> to a transmission coefficient bridge 16<SP>1</SP> which has a matched load resistor normally connected between point 0 and ground, and which applies outputs in quadrature over lines 20<SP>1</SP>, 24<SP>1</SP> to the oscilloscope. From the input a signal is applied to the network 18 under test, after which the transmitted signal is applied via the phase shifter 122 to the transmission coefficient bridge. When the test is in progress it is arranged that the input to the network is applied from the generator through a matching resistor while the phase shifted output is applied to the point 0 and the resistor 120. The display will be similar to that obtained for reflection coefficients.