2.5. VLF & LF AntennaΒΆ

VLF (Very Low Frequency) Band take place from 3kHz to 30 kHz in the frequency spectrum [18].

Advantages Disadvantages
EM waves penetrate more than higher frequencies such as in the sea water High background noise levels
Low atmospheric attenuation Communication needs large amount of power at the output of the transmitter
Appropriate for long range communication  
Diffract around objects that would block higher frequencies  
Less prone to multipath  

VLF antennas operate on VLF band. They are electrically small and this simplifies analysis. They are physically large structures. In other words, they generally have a number of towers that 200-300 m high and cover areas of up to a square kilometer or more. The VLF antennas support worldwide communication [18].

The VLF antennas have some problems that listed below [18]:

  • Bandwidth is less than 200 Hz.
  • Small radiation resistance.
  • They are expensive structures.
  • Antenna system covers a large area.
  • Designing an efficient transmitting antenna is difficult.
  • High power levels are needed for transmission.

Marris produced a ferrite core loopstick antenna for receiving application as shown in Fig. 2.4. He said VLF antenna but operating frequency band is 50 kHz to 195 kHz, so it was a LF antenna. MMG F14 grade nickel-zinc material was used. The antenna compared with a traditional 20 x 1.25 cm diameter loopstick and he noted that increased signal strength and reduced noise [39].


Fig. 2.4 : Loopstick antenna.

1939 The Screened Loop Aerial