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Spreading and Underground Antennas

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ANTENTOP- 01- 2019, # 023

Spreading and Underground Antennas

 

 

Figure 2

Spreading Antenna

 

 

 

Figure 3

Underground Antenna

 

 

In the theory the underground antenna may be considered as a kind of coaxial feedline being created by antenna (center wire of the coaxial) and ambient soil, as lossy braid of the coaxial. Termination shown on the end of the coaxial line is the theoretical load that shows losses on radiation of the center wire and losses of the electromagnetic energy in the ground.

 

In the real life the termination load may be a real resistor that serves to eliminate high stand waves in the antenna wire and improve tuning of the antenna in wide or certain frequencies range. Determination of input impedance of spreading and underground antenna, both theoretically and practically, is very sophisticated task. Reference [2] gives information on the methods and ways how to do this.

 

Depending on the conductance and the dielectric property of the real soil and practical design of the underground or spreading antenna, the termination load may have resistance of 100-500 Ohms on frequencies from 2-30 MHz.

 

 

Sometimes for the underground and spreading antenna is used not loaded at the end wire, as shown on the Figure 1. It is so named Quasiresonance Antenna. Distribution of current and voltage along the wire of the antenna is almost similar to current distribution that is normally present in resonant antenna. In contrast to an aperiodic antenna see Figure 2, 3) having a large bandwidth and stable parameters, the non-loaded antenna's parameters and resonance band are rather unstable.

 

It is happened because the electrical length and input impedance of the quasiresonance antenna depends on state of soil, on or in which the antenna is installed. As usual, conditions of the soil are vared over season of the year and dictate by the weather- cold or hot and rain or snow. But, sometimes, with stable soils (desert sands, frosted soil) it is possible to have quasiresonance antenna with stable parameters.

 

 

 

 

 

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Last Updated:

December 29, 2019 23:15

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