GB1259395A - - Google Patents

Abstract

1,259,395. Radar. BRITISH IRON & STEEL RESEARCH ASSOCIATION. 13 Feb., 1970 [14 Feb., 1969], No. 8126/69. Heading H4D. The distance between a datum point and a surface is measured by transmitting a signal compounded from two microwave signals having a predetermined frequency difference from the datum point to the surface, receiving a reflected signal from the surface, and measuring the phase difference between the transmitted and received difference frequency component of the compounded signal. The level of a liquid or solid load in a hopper or the thickness of a steel billet placed on a reference surface may be measured. As shown in Fig. 2, two microwave generators 30, 31 generate microwave signals # 10 GHz with a known frequency difference in the range 10 MHz to 150 MHz maintained by a phaselock loop (not shown). The generators 30, 31 are connected to a magic T 35 through isolators 32, 33 and one or two level-set attenuators 34. A reference difference frequency signal is detected at 38. The received reflected signal is channelled through directional coupler 40 to a detector 41. Both detected signals are then fed to a phasemeter 42. Preferably the detected signals are mixed with another frequency so that the phase measurement can be made at a lower frequency (# 1 MHz). The 1 MHz signals may be further heterodyned to produce signals at 150 kHz. The phase-lock loop may operate at the 1 MHz frequency (Fig. 3, not shown). In this arrangement, the range may be changed by altering the frequency of oscillator (51) so that the wavelength of the difference signal may be set initially large for search purposes and then progressively reduced for increased accuracy.