GB715399A - Directional wave antenna for marine radar use - Google Patents

Abstract

715,399. Aerials. KATCHKY, N., and BYERS, H. G. Jan. 4, 1952 [April 18, 1951], No. 370/52. Class 40 (7) A directive antenna assembly comprises a sectoral horn having upper and lower walls diverging from a throat to a mouth portion and a waveguide situated at the throat with its longitudinal axis parallel to the respective planes of the walls and having an array of slots cut in the side of the guide facing the mouth of the horn. In one embodiment intended for use as a radar scanner the radiator is a horizontally mounted slotted waveguide 10 in the throat of a flared horn 20. The waveguide is mounted by bolts and nuts 25 on the back wall of a casing 60 and spring clips 24 secure together the throat end of the horn walls and the guide between which spacing pieces 23 are interposed to provide a quarterwavelength choke section. The front edges of the horn sides are located in channel pieces 63 running along the top and bottom of the rectangular front aperture of the casing. Also located between the channel pieces is a vertical grating consisting of thin plates 71 extending in parallel planes perpendicular to the plane of the aperture and threaded on to rods along which they are regularly spaced by spacing elements 64. The plates 71 are spaced less than #/2 apart and the grating serves to attenuate the component of vertical polarization where substantially vertical but inclined slots are provided in the waveguide. A window 63a of radiation permeable material may be provided to seal the horn structure. The assembly is mounted for rotation and fed through wave-guide joint 50 and guides 40 and 81 leading to one end of the radiating guide 10. The arrangement may be resonant or non-resonant but it is preferred to make it non-resonant to achieve a greater bandwidth and to provide a power absorbing termination 30, Fig. 5 (not shown) on the opposite end of guide 10 to the feeder input. The slots in the front narrow face of the guide are approximately half a wavelength apart (200 degrees) and inclined alternately to right and left Fig. 4 (not shown). The ratio of field intensity at the waveguide ends is made an eighth of that at the centre to reduce side lobes and the specification contains theoretical discussions and graphs re'ating to the choice of amplitude taper, slot spacing, and slot inclination.