Patent GB-1318615-A (GB)
Title: Range detection system
IPC: G01S13/64
Filed: 1970-06-22
Abstract: 1318615 Pulse radar BABCOCK ELECTRONICS CORP 22 June 1970 [23 June 1969] 30263/70 Heading H4D  A range detection system comprises means for transmitting signals for a period corresponding to the time taken for said signals to traverse a selected fraction of the range of the system, and detecting means, which may make use of the Doppler effect, for detecting a signal from a target. The detecting means comprises a plurality of gating means each having as one input said detected echo signal, and as another input a signal of duration substantially equal to the period of the transmitted signal, the time of beginning of application of said other input signal to each gating means being different. A system which operates at a frequency such as 1800 MHz, and which is particularly suitable for installation in a target drone to determine the miss-distances of bullets (e.g. from 5 to 200 feet) for telemetering to a ground station, is described with reference to Fig. 2. An oscillator 34 is controlled by a master pulse generator 36 and is coupled through a first circulator 38, a switch 40, and a second circulator 32 to an aerial 30. Part of the output of the oscillator 34 is coupled to one input of a mixer 56, and another part is coupled to a series arrangement of a rectifier 45 and resistors 46, 47. Voltage developed across the resistor 46 controls the operaton of a pulse generator 42 and of a slow switch 50. Signals received on the aerial 30 are coupled through the circulator 32, the slow switch 50, and an R.F. amplifier 54 to the other input of the mixer 56. Output from the said mixer is coupled through a video amplifier 58 to the paralleled first inputs of a series of gates 64, 66, 68 (in practice, more than three gates may be provided). The second inputs of said gates are respectively connected through one, two, and three of similar delay elements, 70, 72, 74 to the output side of the pulse generator 42. The master pulse generator 36 provides a relatively long pulse to the oscillator 34, but the enabling pulse from the pulse generator 42 is comparatively short, e.g., 10 nano-seconds. This enabling pulse operates the switch 40, so that an R.F. pulse is transmitted from the aerial 30. It also successively energizes the second inputs of the gates 64, 66, 68 at, for example, 10 nanosecond intervals, as it passes through the delay elements 70, 72, 74. A received pulse from a moving target leads to a corresponding output from the mixer 56, since it has a frequency difference from the oscillator 34, owing to the Doppler effect. One of the gates 64, 66, 68 is enabled if the delays due to the delay elementsin series with its second input are equivalent to the transit delay in the go-return path of the received pulse arriving at its first input. Output from a gate is taken through a box-car detector, an audio amplifier, and a limiter to an output terminal for processing. The slow switch 50 is a device which becomes increasingly conductive with time, so that strong echoes from near-by objects are attenuated as compared with weaker echoes from more distant objects. A solid state device may be used (Fig. 4, not shown). In a second embodiment a separate detector, or radio frequency gate, is used for each increment of range, and separate aerials 116, 118, Fig. 5, are provided for transmission and reception. Some of the energy directed to the aerial 116 is coupled to a power divider 132, which supplies respective first inputs of detectors 126, 127, 128 through delay elements of progressively increasing delay times. Signals received on the aerial 118 are coupled through an R.F. amplifier 120 and a slow switch 124 to a power divider 122, which supplies respective second inputs of the detectors 126, 127, 128. Simultaneous application of an echo signal from a moving target and of the delayed transmitted pulse to a detector results in a Doppler output signal being applied through an amplifier to one of the output terminals 151, 153, 154.