Wire Antenna Calculator

A random wire antenna [1] is comprised of a long wire above ground that is used to transmit and receive signals. This is a quick way to add an antenna to radio equipment.

However, it is not an optimal antenna design and so when it is used with a transmitter or receiver, the radio range performance can vary greatly.

To calculate the physical length of a wire antenna

Enter

  • Upper and Lower Frequencies
  • Wavelength

To design an antenna at a single frequency, enter the same value for both upper and lower.

Example Antennas

The picture below shows a wire antenna soldered on to a PCB to provide 2.4 GHz Wi-Fi connectivity. In this particular case it is a quarter wavelength wire with a length of approximately 3 cm.

Use the above calculator to confirm this by entering 2400 MHz (Lower) and 2500 MHz (Upper) and quarter wavelength.

A random wire antenna does not follow any specific pattern or design. Due to the random nature of its length and placement, these antennas can have a wide range of impedance values. However, they tend to have a low feed point impedance, which makes them easier to match to the transmitter or receiver. This makes them a popular choice for many amateur radio operators.

Example Calculation

A wire antenna that is used for both Wi-Fi bands (2400 MHz and 5800 MHz) has the following lengths depending

Wire Antenna TypePhysical Length (cm)
λ7.3
λ/23.7
λ/41.8

A commercial low-cost wire antenna shown below has a length of 8.5 cm including the external enclosure. While the structure itself is that of a monopole antenna, the dimensions are closer to that of a 7.3 cm wire antenna from the table above (dimensions are a little larger on account of the plastic enclosure).

Bingfu Dual Band WiFi 2.4GHz 5GHz 5.8GHz 3dBi MIMO RP-SMA Male Antenna (2-Pack) for WiFi Router Wireless Network Card USB Adapter Security IP Camera Video Surveillance Monitor

General Precautions

In general we do not recommend the use of a wire antenna for a Power Amplifier or transmitting radio equipment without a good matching network design. A poor match at the output of the transmitter can result in reflections (use the SWR to Reflected Power calculator to find the percentage) and damage the radio electronics.

Related Calculators

References

[1] Wire antenna on Wikipedia