GB1278306A - Improvements in or relating to antennas - Google Patents

Abstract

1278306 Aerials HUGHES AIRCRAFT CO 23 Oct 1969 [28 Oct 1968] 51988/69 Heading H4A In a horn aerial first and second electromagnetic waves are respectively launched within a first portion thereof. The second wave is slower than the first, but it is converted into a third electromagnetic wave which is faster than the first, and with which it travels through a second portion of the horn to its aperture. The first and third waves combine to provide a radiation pattern having reduced side lobes over a wide frequency range. As described, a conical horn 22, Fig. 3, includes a throat section 23 with an arm 24. Longitudinal rods 25, 26 extend from the centre conductors 27, 28 of coaxial lines 29, 30 through the throat section 23 and then fan out along the inner surface of the conical portion of the horn. A disc 30 at the end of throat section 23 provides a termination for the outer conductors of the lines 29, 30. The inner conductors of said lines are taken to opposite polarity outputs of a hybrid junction 32, input to which is provided from a line 36 through a power divider 34 and a variable phase shifter 33. A TEM wave is thereby launched along the rods 25, 26. Another output from the power divider 34 is taken to a probe in the arm 24, and this sets up a TE 11 wave in the throat section 23. At the ends of the rods 25, 26 the TEM wave therealong is converted into a TM 11 wave, which combines with the TE 11 wave. In another embodiment, a TE 11 wave is launched from the end of a throat section of a conical horn and energy is abstracted from it by means of two oppositely disposed inwardly directed radial probes, which are connected to respective rods extending towards the aperture of the horn, and along which a TEM wave is developed (Fig. 1, not shown). More than two TEM launching rods may be used, and to maintain a constant characteristic impedance the diameters of the rods and their spacings may be increased with the flaring out of the horn, so as to give geometrical similarity at any cross-section (Figs. 5A, 5B, not shown). The relative phases of the signals applied to N rods may be progressively increased by 2#M/N from rod to rod (where M is an integer). For impedance matching purposes discontinuities, such as ferrules or undercuts, may be provided at or near the ends of the rods (Fig. 6, not shown). Embodiments using pyramidal horns are also described (Figs. 7A, 7B, 8, not shown).