GB1064846A - Improvements relating to radar equipment - Google Patents

Abstract

1,064,846. Height finding radar. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. June 25, 1964 [June 27, 1963], No. 25684/63. Heading H4D. A height-finding radar comprises antenna means providing a plurality of overlapping beams stacked in elevation and defining crossover axes between adjacent lobes, means determining which cross-over axis is nearest a target, means determining the height of the determined cross-over axis at the range of the target, means determining the amount by which the target differs in height from the determined cross-over axis and means for adding said height difference to said determined cross-over axis height to obtain the actual target height. Three adjacent antennµ are shown in Fig. 2 (not shown) which produce the three overlapping lobes shown in Fig. 1 (not shown). Antenna (1) radiates on frequency f1 and receives on both frequencies f1 and f2 by means of active and passive receivers respectively. Antenna (2) radiates on frequency f2 and receives on frequencies f2 and f1 by means of active and passive receivers respectively whilst antenna (3) radiates and receives in the same manner as antenna (1). If a target is at an elevation between the cross-over axis between beams (2) and (3) and the axis of beam (2), maximum echo energy will be received by antenna (2) at its own frequency of f2 by its active receiver. The energy radiated by antenna (2), reflected by the target and received by the passive receiver of antenna (3) will be greater than that received by the passive receiver of antenna (1). These facts determine which cross-over axis is nearest the target. Comparison of the energies received by the active receiver of antenna (2) and the passive receiver of antenna (3) then gives the angular distance of the target from the determined cross-over axis. If the antennµ are spaced a phase comparison may be used to determine the angular distance. In the arrangement of Fig. 3 the means shown in the left half of the figures are duplicated for each beam, the means shown being provided for the N<SP>th</SP> beam, the target for convenience being supposed to be positioned in the N<SP>th</SP> beam and nearer to the cross-over axis between the N<SP>th</SP> and N + 1<SP>th</SP> beam. The beams have a Gaussian energy distribution such that the variation of the logarithmic signed strengths is beams N and N+ 1 due to a target at an angle # from the cross-over axis between the two beams, may be written:- where # is the angle between the two beam axes. The difference between the logarithmic signal strengths is thus 2K# or proportional to the required angular distance. The active receiver of beam N feeds the received signal in logarithmic form to a beam selector 5, common to all the beams, via a gate and store unit 2. The beam selector detects that a larger signal is being received by beam N than by any of the other beams and accordingly adjusts a two-pole switch 6. The passive receivers of beams N - 1 and N + 1 pass their outputs in logarithmic form to a comparison circuit 10 via gate and store units 3 and 4. The comparison circuit 10 determines which output is greatest and passes it to a difference circuit 9. The other input of the difference circuit is fed with the logarithmic output from the active receiver of beam N, such that the difference circuit 9 produces a signal representing the angular distance #. The outputs of the passive receivers of beams N - 1 and N + 1 are also passed to an arrangement 11 which produces a signal indicating beam N - 1 or beam N +1 depending on which is near to the target. This signal is fed to a cross-over selection circuit 12 via switch 6, together with a signal from beam selector 5 representing beam N. The cross-over selection means indicates that the target is nearest to the cross-over axis between beams N and N+1, and produces a signal representing the height of this cross-over axis at the range of the target, with the aid of height/range waveforms from generator 13. When there are N beams, N - 1 height/range waveforms are produced by generator 13 each having the form h=kR+1R<SP>2</SP>, and commencing with the transmission of a radar pulse. The two terms of the equation may be produced by successive integration, Fig. 4 (not shown). The height representing signal is applied to one input of an adder circuit 15. The signal representing the angular distance # is fed via switch 6 to means 14 where the angular distance # is converted into a height difference which may be positive or negative. The height difference signal is fed to adder circuit 15 to produce a pulse signal representing the total height of the target by its amplitude. The height pulses may be used to feed a height/ range display or may be sorted in means 17 into height layers for various control purposes. If the height of a particular target is required the height pulses may be sampled by a suitable gate. The height pulse occurs at the same time as the corresponding video pulse in the normal PPI display which is fed by the outputs of the active receivers of the antennµ via circuits 1 and OR combiner circuit 16.