A dipole antenna with calculable gain over the frequency range 20 MHz to 2.2 GHz

The precise measurement of antenna gain in the lower half of the VHF range presents many challenges. Half-wave, or shorter, dipole antennas possess a near uniform H-plane pattern which creates difficulties in achieving a reflection free measurement site, particularly below 150 MHz. By measuring VHF dipole-like antennas over a large flat outdoor ground plane, the reflections can be precisely controlled. The principles of the VHF antenna are extended into the UHF range to cover mobile communications applications. A calculable dipole antenna has been developed which is used to provide traceability for antenna factor over the frequency range 20 MHz to 2.2 GHz, to uncertainties as low as ± 0.15 dB. The use of electro-optic transducers further reduces the uncertainty of measurement of E-field phase and amplitude by replacing the electrically conducting feed cable by non-reflecting optical fibre.