VLF transmitting antenna radiation efficiency: Measurement principle and data processing

Measurement principle and data processing method are introduced for VLF transmitting antenna efficiency evaluation. According to wave propagation theory, antenna efficiency can be calculated by using field strength measured in the groundwave-dominant range. Selection of test equipment, method to calibrate the antenna factor and directional gain of a test antenna are also introduced. The calculated field strengths agree well with the measured data. As an example, the radiation efficiencies of a VLF antenna at different distance and frequencies are calculated.