Patent GB-735315-A (GB)
Title: Improvements in radio direction finders
Inventor: RAMSAY JOHN FORREST
IPC: H01Q19/195
Filed: 1952-09-02
Abstract: 735,315. Directional radio systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 23, 1953 [Sept. 2, 1952], No..22102/52. Class 40 (7). In a C.W. radar system with a wide angle transmitting or receiving focusing element, e.g. lens or reflector, the radio or modulation frequency is dependent on the direction of transmission or reception so that the direction of the target can be determined by measuring the appropriate frequency at the receiver. Alternatively the direction-dependent receiver may be used for determining the direction of any transmitter. Fig. 1 illustrates a system in which the Dopple effect of a moving reflector in the path of the transmitted energy is utilized to vary the radio frequency. As shown the radiation from a fixed horn FH coupled to a C.W. transmitter T is reflected by a polarized mirror M on to a #/4 plate P backed by a elliptical reflector R located in the focal surface of the lens L, the plate P serving to rotate the plane of polarization through 90 degrees so that the energy reflected by R is transmitted through the mirror M. The reflector R is rotated about an axis through the focus F of the lens perpendicular to the plane of the paper so that each time the reflecting surface coincides with the focal surface a wide-angle beam is transmitted, the energy transmitted in different directions within the beam coming from elements of the reflectors R moving with different linear velocities so that the radio frequencies as modified by the Doppler effect of the moving mirror will also be different, Figs. 4 and 5 (not shown). Energy reflected by a target is received by a wide-angle horn RH and heterodyned with an output from transmitter T to give a beat frequency indicative of the target direction which is detected by head-phones HP and/or a frequency meter. Alternatively the reflector R may be oscillated, it may be a zoned reflector or lens-connected mirror or it may be replaced by an array of small oscillating or reciprocating reflectors, Fig. 6 (not shown); the #/4 plate P may also be separate from the reflector R and stationary. If the transmitter and receiver are interchanged, the energy received from any particular direction will be incident on a corresponding element of the reflector R and hence the energy reflected by R to the receiving element FH will have a frequency characteristic of the direction of reception. The system illustrated in Figs. 2 and 3 comprises a wide-angle transmitter (not shown) and an array of small horns RH in the focal plane of a wide-angle receiving lens L<SP>1</SP>, the horns being connected in parallel to a detector D. An apertured disc S, Fig. 3, rotating about the axis A of the lens is mounted in front of the horns so that the energy received by a particular horn corresponding to a particular direction of reception is amplitude modulated at a frequency characteristic of the direction left or right ambiguity can be resolved by shifting the axis of rotation of S to one side of the focal region. Alternatively the horns RH may function as transmitters in which case the modulation frequency of the transmitted energy is direction-dependent; the array of horns may be replaced by a single element located in the focal plane of the lens. Specification 720,154 is referred to.