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Equipment Solutions: Antennas

LF and VLF antennas are very large structures, some as tall as 1,500 feet, that are tuned to resonate at a desired operating frequency. The challenge for an antenna design is to maximize the effective height of the antenna – and therefore maximize the radiated signal - and minimize the losses in the antenna and associated ground system.

Due to the physics of launching electromagnetic waves at low frequencies, and the need to radiate many hundreds of kilowatts, or sometimes megawatts, to communicate with under water receivers, LF and VLF transmitting antennas are physically very large structures. At the same time they are electrically short compared to the wavelength of the transmitted signal. As a consequence, they exhibit very low resistance, very high reactance, and very high voltages and currents are present in the antenna. The physically large characteristics make the antennas quite effective at capturing incident higher-frequency signals, both from nearby man-made transmitters and natural sources such as lightning. Tuning such an antenna is not a trivial task, but measuring and characterizing such an antenna is also challenging so as to avoid destruction of the measuring equipment and/or injury to personnel.

Hi-Q engineers have created a customized approach to antenna measurement and characterization that is as effective and comprehensive as measuring a component on a workbench. The antenna complex impedance is measured at hundreds of frequencies in just seconds, and from that data we derive equivalent circuit models, define tuning and impedance matching requirements, and determine required voltage and current ratings. Hi-Q can develop the electrical design parameters of an antenna to meet broadcast requirements, and utilizing our partners we can have them built as needed.

 

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