Patent GB-778446-A (GB)
Title: Improvements relating to the measurement of power flow or energy transmitted in an electromagnetic field
IPC: G01R21/00
Filed: 1952-09-23
Abstract: 778,446. Power measurements; semiconductor devices. BARLOW, H. E. M. July 23, 1953 [Sept. 23, 1952], No. 23888/52. Class 37. Apparatus for determining the power due to a field of high frequency waves transmitted along a predetermined path (which may be a transmission line or waveguide) comprises a Hall plate inserted in the path or such waves to be traversed along mutually perpendicular axes by the transverse magnetic component of the field of H.F. waves and by a current proportional to the transverse electric component of such waves, to develop a pulsating or alternating E.M.F. between faces of the Hall plate lying on an axis perpendicular to both the said mutually perpendicular axes, whose true mean value is measured by a suitable instrument as a function of the power of the H.F. field. In Fig. 3 a germanium or silicon Hall plate 1 has its ends symmetrically connected between parallel strip conductors 2, 3 of a H.F. (exceeding 20 Kc/s) transmission line by means of non- rectifying soldered or welded points and disposed with faces parallel to the plane of axial symmetry of the conductors so that it is traversed along its y axis by a current proportional to the electric field across the conductors and along its z axis by a magnetic component proportional to the magnetic field between them so that a voltage developed between the broad faces of the plate and measured by a galvanometer G (or valve voltmeter) is proportional to the power transmitted. Multiple Hall plates may be adjacently disposed between the conductors of a H.F. transmission line to be traversed by the inter-conductor magnetic field, and separately supplied with currents proportional to the accompanying alternating electric field through series condensers of small impedance compared with the plate resistance ; the several Hall voltages being connected additively in series with the galvanometer and the plates being orientable to neutralize any unbalance rectified E.M.F.'s developed at the contacts between individual plates (Fig. 4, not shown). A Hall plate 1 may be also connected (Fig. 5) in a coaxial line with its ends connected between the inner and outer conductors 3, 4 and its faces parallel to the longitudinal plane of symmetry of the line to develop a voltage between its sides proportional to the H.F. power in the line, while series plural Hall plates 1 (Fig. 6) radially spaced round the central conductor 3 in a fixed transverse plane with their interconnecting leads perpendicular to the electric field enable the several output voltages to be connected in cascade and the individual plates to be adjustable to cancel out rectified voltages. Sensitivity may be increased by disposing the Hall plate 1 in close proximity to the inner conductor 3 of a coaxial line and midway along a constricted halfwave section of the outer conductor 4, impedance matched to the remainder of the line with the output leads disposed perpendicularly to the electric field whereby the electro magnetic field at the plate is intensified (Fig. 7). The Hall plate may be connected along its y axis between the broad faces of a rectangular wave guide carrying H.F. power in the Hol wave mode with its x axis along the axis of the guide (Fig. 9, not shown) or disposed in a constricted section 8 of the guide, dimensioned to have a cut-off frequency below the waveguide operating frequency and matched thereto by tuning screws 7 and dia- A A phragms 6 spaced respectively - and - from 4 2 the constriction. The Hall plate is disposed centrally within the constriction to receive the transverse component of the magnetic field perpendicularly to its faces while its ends may receive currents proportional to the electric field over leads connected to the narrower faces of the constriction and disposed perpendicularly to the electric field, and the Hall voltage developed between the faces is proportional to the transmitted power (Figs. 10, 11). A plurality of plates disposed in a transverse plane near the guide axis may have their Hall voltages connected in cascade for measurement.