| 摘要 |
1,180,866. Aerials. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 17 May, 1968, [18 May, 1967], No. 23706/68. Heading H4A. An aerial which is stated to have broadband proportions comprises first and second dipole groups of elements 1b and 3b, Fig. 6b, positioned parallel to each other and spaced apart less than #/5, where # is the wavelength corresponding to the centre frequency F of the operating band. The group 1b is designed to have its first anti-resonance at the frequency F, and the group 3b at a frequency from 1À1 F to 1À8 F. The juxtaposed ends of one group of elements are connected to a receiver, and those of the other group are left unconnected. As described, the elements of group 1b are triangularly shaped sheets and those of group 3b are a pair of straight coaxial rods. In other embodiments (e.g. Fig. 6a, not shown) both groups have elements consisting of a pair of straight coaxial rods. In another embodiment (Fig. 5, not shown) one group consists of a pair of straight coaxial rods and the other consists of a pair of V-shaped elements, each formed by a pair of straight rods joined at an apex from which they diverge. Particulars of dimensions of typical aerials are given. 1,180,878. Light modulators; pulse radar. UNITED AIRCRAFT CORP. 9 Sept., 1968 [4 Oct., 1967], No. 42738/68. Headings H4D and H4F. To produce an output signal which is a time function of an input signal, an acoustic wave is produced in acoustic cell 18 by applying the input signal to transducer 20, and a laser beam from laser 10 is arranged to scan across the acoustic cell to intersect the acoustic wave, whereby an undiffracted zero order signal and at least one frequency shifted diffracted order signal are produced, detected by detector 24, and heterodyned to produce an output signal which is a time function of the input signal. If the scan velocity V l of the laser beam is less than zero (V l being defined positive in the direction of the acoustic velocity V s ), the output signal is compressed in time and unshifted in frequency. If V s >V l >O the signal is expanded and downshifted in frequency. If V l =V s the acoustic diffraction grating appears stationary and yields no Doppler shifted light. If V l >V s the output signal is reversed in time (back-tofront inversion), and where 2 V s >V l >V s the output signal is also expanded and downshifted, and where V l >2V s it is also compressed and upshifted. Where V l =2V s the output signal is the identical pulse but reversed in time. To further vary the output signal the laser beam may be intensity modulated, e.g. by means of a Kerr or Pockels cell 12. Optical scanner 14 may comprise an acoustic cell in which an acoustic wave produces a refractive index change which causes refraction and therefore scanning of the laser beam. If the scanning angle of the laser beam is small, lenses 16 and 22 may not be required. A lens 11 may apply a small convergence angle to the laser beam to thereby focus the beam on to the cell 18. If the convergence angle is slightly larger than the diffraction angles, the diverging diffracted and undiffracted beams will overlap and heterodyne to produce the Doppler frequency shift. The arrangement may be used in a " chirp " radar system. |
