How much current can you draw from a resonant loop antenna

In summary, the conversation discusses the behavior of current in loop antennas with different characteristics. In the case of an uncompensated inductance, the current in the antenna cancels out the incoming magnetic field, leading to a maximum current that can be drawn. However, in resonant antennas, there is a 90 degree phase shift between the current and the incoming EM wave, and the limit on the current may behave differently depending on the situation. It is implied that there is always a limit on the current due to the finite energy contained in the fields. This is further reduced by the fact that receiving antennas can only capture a portion of the incident fields. The conversation also suggests using the equation for a resistive LRC circuit to calculate
  • #1
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In the case of a loop antenna with uncompensated inductance, the magnetic field generated by the current in the antenna is in antiphase to the incoming magnetic field of the EM wave. So it is believable that the current which causes cancellation of the flux through the antenna is the maximum current that you can draw.
But in the case of a resonant antenna, there is 90 degrees phase shift between the magnetic field generated by the current in the antenna and the magnetic field of the incoming EM wave. In the idealized situation (no resistance, neglecting radiation by the receiving antenna) is there any limit on the current?
(Or does it behave like I0*t*sin(2*Pi*f*t) if the induced voltage is U0*sin(2*Pi*f*t) ?).
 
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  • #2
There is always going to be some implied limit on the current. For example, there is only a finite amount of energy contained in the fields that can be extracted to generate the currents. One can consider the equivalent sources of the fields to be in the form of currents and charges and given that the total energy contained in the fields is finite then the equivalent energy from the sources must also be finite. This ignores the fact that any receiving antenna can only capture the fields incident upon their effective aperture which further reduces the amount of energy that can be extracted out of the fields.
 
  • #3
You could use the equation for a (parallel or series) resistive LRC circuit, and use R as the resistance (load) of the external circuit. The circulating current for a series R in the loop is then I = Vout/R.

Bob S
 

1. What is a resonant loop antenna?

A resonant loop antenna is a type of radio antenna that uses a loop of wire to receive or transmit radio signals. It works by creating a magnetic field that interacts with the electromagnetic waves in the air, allowing for efficient transmission and reception of radio signals.

2. How does the current drawn from a resonant loop antenna affect its performance?

The amount of current drawn from a resonant loop antenna is directly related to its performance. The higher the current, the stronger the magnetic field, resulting in stronger reception or transmission of signals. However, there is a limit to the amount of current that can be drawn from the antenna before it becomes inefficient and starts to generate excess heat.

3. What factors determine the maximum current that can be drawn from a resonant loop antenna?

The maximum current that can be drawn from a resonant loop antenna is determined by several factors, including the physical dimensions of the loop, the frequency at which it is operating, and the material used to make the loop. The design and construction of the antenna also play a role in determining the maximum current it can handle.

4. Is there a standard or recommended maximum current for a resonant loop antenna?

There is no standardized or recommended maximum current for a resonant loop antenna. The maximum current will vary depending on the factors mentioned above and the specific purpose of the antenna. It is important to carefully design and test the antenna to determine its safe and optimal current drawing capabilities.

5. Can too much current damage a resonant loop antenna?

Yes, too much current can damage a resonant loop antenna. If the amount of current drawn exceeds the antenna's capabilities, it can result in overheating and potential damage to the wires or other components. It is important to properly design and monitor the current drawn from the antenna to prevent damage and ensure optimal performance.

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