The tetrahedral antenna

The tetrahedral antenna was proposed as a result of a general requirement for an easily deployable radar transmitting element radiating efficiently in the HF range (3-30 MHz). The tetrahedral antenna is a development of the biconical antenna in common use in the VHF/UHF bands. The two conical halves are held coaxially with apices adjacent at the feed point, forming a dipole. The bicone operates satisfactorily over a wide frequency range with a typical impedance of 200-300 Ω, the lower end of the band occurring at a frequency where the antenna is approximately a wavelength long. At lower frequencies the bicone operates satisfactorily but with a lower impedance, and its resistance at its lowest resonant frequency is of the order of 50 Ω. The tetrahedral antenna uses, instead of cones, two tetrahedra, each made of six tubular elements or rods. The measurement results show that this antenna is an efficient radiator of vertically polarised waves at frequencies at which it is approximately a quarter-wavelength high, without the need for an earth mat. Measurements also showed an input SWR of better than 2:1 within a band of 34% around the resonant frequency. It was found that the resonant frequency could be reduced by the addition of a tuning coil, with a small reduction in gain, the height then being one sixth of a wavelength