| 摘要 |
745,269. Radar; aerials. RAYTHEON MANUFACTURING CO. Sept. 25, 1953, No. 26515/53. Classes 40 (5) and 40 (7). An aerial construction suitable for use in a radar having separate transmitting and receiving units comprises an electrical ground plane 10 having two spaced apart apertures therein which form the mouths of two electromagnetic horns 11 and 12, the distance between the apertures being such with respect to the wavelength of operation that the aerials are isolated to a high degree from one another. The horns may be substantially matched to free space and excited in TE 01 mode with the electrostatic lines perpendicular to the line intersecting the axes of the horns. As shown, horn 12 is the transmitting horn and is excited by offset probe 13 surrounded by a sheath of dielectric 15. The probe is fed by coaxial line from magnetron oscillator 19 resiliently mounted between the horns. Horn 11 is used for reception and contains a pair of crystal rectifiers 33 forming a balanced mixer from which an output signal is derived. These crystals are fed out of phase by the received signals and in phase by a signal derived from horn 12 over a coaxial line. This line has a central conductor 36 fed by coupling loop 37 in horn 12 and terminated by attachment to the mixer in horn 11. Part of conductor 36 is surrounded by a layer of lossy material 40 to attenuate the signal and the outer conductor of the line is made up of two halves 41 and 42 designed to form a rigid assembly preventing relative movement of the horns. A cover 45 is provided surrounding the horns and this is attached to a ring 47 which is in turn attached to the support structure 52 which may be the skin of an aircraft. The ring 47 is designed to have a half wavelength slot 48 in it, one side of which is formed in part by the edge of ground plane 10. As the plane 10 is a substantial part of a quarter wavelength thick the junction between it and the ring 47 will be at a relatively high impedance point along the slot and any looseness of the securing screws will thus have little effect in modulating the current flow between the ground plane and the structure 52 and is unlikely to produce spurious signals. The slot is preferably filled with dielectric material. A modified choke structure for use at the edge of the ground plane 10 is described with reference to Figs. 8, 9 and 10 (not shown). The arrangement of the aerial structure with reference to the other units of an F.M. radar is described in connection with Fig. 5 and with reference to a pulse radar in connection with Fig. 6 (Figs. 5 and 6, not shown). Fig. 7 shows the aerial structure 54 fastened to a cylindrical support member 66 rotatable about a vertical axis 67. This form of mounting may be used for a marine navigational radar. |
