GB1088171A - Circuit arrangements for eliminating ground return echoes in radar systems - Google Patents

Abstract

1,088,171. Pulse radar. COMPAGNIE FRANCAISE THOMSON HOUSTONHOTCHKISS BRANDT. April 23, 1965 [April 23, 1964], No. 17327/65. Heading H4D. Pulse radar apparatus is provided with means whereby clutter can be removed from an echo signal 1, Fig. 1b, without removing any target echoes protruding above said clutter. The echo signal shows three target echoes having a width T equal to the transmitted pulse width, two outside the area of clutter, and the third inside but of greater magnitude than the clutter. After I.F. amplification and detection at 11, Fig. 1a, the echo signal 1 is applied directly and with a delay T (waveform 2) to respective inputs of an AND gate 12. The output S1 of the gate has an amplitude equal to that of the lower of the two input signals. The output S1 is used as a first control signal, and is also applied to one input of a subtractor circuit 15 having the echo signal with a delay 2# (waveform 4) applied as the subtractor to its other input. The output of the subtractor circuit is such as to pass only positive signals, such that the output is S2, the second control signal. The first control signal S1 is used to control the attenuation of an attenuator 16, Fig. 2a (not shown), attenuating the I.F. echo signal 6, Fig. 2b (not shown). The variation of the attenuation is such that the clutter overlapped by the control signal is reduced in level to noise level, leaving an initial unattenuated portion of clutter, and the third echo signal (waveform 7). This waveform is then delayed by T and the remaing clutter portion removed by a second attenuator 18 under the control of the second control signal to give waveform 9, which after detection shows only the target echoes (waveform 10). In order that the arrangement described should have a dynamic range large enough to accept the full range of echo signals, I.F. amplifier 11 has a large dynamic range with a logarithmic amplitude response and the attenuators also have a logarithmic amplitude response.