GB1368879A - Waveguide antenna - Google Patents

Abstract

1368879 Aerials STANDARD TELEPHONES & CABLES Ltd 24 May 1973 [8 June 1972] 26760/72 Heading H4A An aerial arrangement comprises a radiating element or radiating elements each in the form of an open-ended waveguide which is so terminated as to be able to operate at a frequency below cut-off, an evanescent mode being then sustained, as well as at a frequency above cutoff. In one embodiment, a rectangular waveguide 1, Fig. 3, is divided over part of its length by a metal septum 8 (on E-plane bifurcation) into two waveguides of reduced height, each of which is fed by a respective input 6 or 7. The input at 6 has a frequency below cut-off (e.g. 1À3 GHz, in the L-band) whilst the input at 7 has a frequency above cut-off (e.g. 3À6 GHz, in the S-band). In each reduced height waveguide there is a respective tuning screw 9A or 9B, and a respective matching obstacle 10A or 10B. The obstacle 10A prevents coupling of higherfrequency towards the lower-frequency input 6, whilst lower-frequency fields rapidly decay in the reduced height waveguide containing the higher-frequency input 7. The open end of the waveguide 1 terminates at a ground plane 3 in which there is an aperture 2. A dielectric material plug 4 is contained in the said open end, and provides a conjugate reactance match for the waveguide at the lower frequency. A plurality of such radiating elements may be arranged in rows and columns, using a common ground plate, to form an array (Fig. 1, not shown). Electronic scanning can be effected by introducing progressive phase differences in rows and/or columns. In another embodiment, Fig. 2 (not shown), a length of rectangular crosssection waveguide has a common input at one end for signals of two different frequencies, and has a radiating aperture at the other end which is backed by a dielectric material slice. The width of the waveguide is such waves at the higher of the two frequencies are propagated normally, whilst the length of the waveguide and the thickness of the dielectric material slice are such that waves at the lower of the two frequencies are propagated in an evanescent mode. Specifications 1,129,185 and 1,312,506 are mentioned.