| 摘要 |
813,168. Radar. TELEFUNKEN G.m.b.H. Dec. 17, 1957 [Dec. 22, 1956], No. 39182/57. Class 40 (7). The invention relates to an apparatus for measuring the speed of moving targets and has provision to make the apparatus responsive only to approaching or to receding targets. In one embodiment a radar transmitter S feeds an aerial SA by means of a waveguide H1. Echo signals received by reflection of the transmitted waves from a moving target are passed from aerial EA to a guide H2 which is split as shown in Fig. 1. Detectors D1 and D2 are placed at the ends of these branches, the two paths from the aerial to the detector being equal or differing by a whole number of wavelengths at the frequency of transmission. A portion of the transmitter energy is fed to the branches of the guide H2 by means of directional couplers R1 and R2, the arrangement being such that the transmitted oscillations at the couplers are in phase quadrature. At the output of the detectors appear the sum and difference frequencies of the transmitted and received frequencies and each detector feeds a narrow-band amplifier V1 or V2 which amplifies the difference, or Doppler, frequency only. The outputs from the amplifiers will be, for example, E1 and E2 and will be in phase quadrature, E1 lagging or leading E2 depending upon the direction of motion of the target, Figs. 2a and 2b (not shown). By means of a phase shifter P a further shift of 90 degrees is given to E1 or E2 and this signal combined with the non-shifted signal in a combining transformer T. Means, not shown, may be provided in one of the channels to the transformer to ensure that the amplitudes of the two signals fed to the transformer are equal, the signals will then either add in phase or cancel each other. The transformer feeds to a frequency meter which is used to measure the speed of the target. The apparatus thus distinguishes between approaching and receding targets and indicates the speed of the former or the latter dependent on the position of the switch U. The phase-shifter P is described in the Specification with reference to Fig. 3 (not shown) and a preferred form of phase-shifter with reference to Fig. 4 (not shown). |
