Technical report | A High Performance Active Antenna for the High Frequency Band
The design of an active antenna with an operational frequency range from low- to high-frequency is presented. The main cause of inter-modulation distortion is identified and recommendations are given to minimize their generation. A detailed analysis is carried out into the various sources of noise generated within the active antenna and how their summation affects the total noise seen at the output. Lightning protection is also discussed.
This report describes the design of a high performance high frequency (HF) active antenna starting from the antenna rod and finishing with the output buffer stage which drives the co-axial transmission line feeding a receiver. The main source of inter-modulation products is identified and steps that can be taken to reduce their magnitudes are described and implemented. Internal noise generated within the design, which can limit the antenna's sensitivity, is also examined in detail and the main source of this noise identified across the antenna's usable frequency range. Recommendations are given on how to install these types of antennas in an antenna site with the resonance formed by the mast together with the active antenna readily calculated. Operating an active antenna at frequencies higher than this resonance will result in a monotonic decrease in sensitivity.
The completed design is a compact receive only active antenna covering the frequency range from LF to HF. It is broadband with a constant antenna factor over this frequency range. It can be used to measure the vertical E field strength of a signal, perform general surveillance work (either fixed or vehicle mounted) or used to create a quickly deployable antenna array for the geo-location of signals in the HF band.