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This is part 42 of the LoRa/LoRaWAN tutorial.

In this tutorial I will explain what a monopole antenna is and why a ground plane is needed.

A ½λ dipole antenna has two elements (each element L = ¼λ), but a monopole antenna has only one element (L = ¼λ).
A monopole antenna relies on a good conducting plane for its operation.
This plane is used as a mirror to create a "second imaginary" element.
The ground (earth) is a conductor and RF energy is reflected from the ground.
The monopole antenna performance can be improved by using a plane made of a better conductive material instead of using the earth itself.
This conducting plane is called the ground plane or counterpoise.
The ground plane must have a radius greater than ½ wavelength from the base of the monopole antenna.
For a ¼λ monopole antenna the reflected radiation from the ground is in phase with the direct radiation.
The receiving antenna (RX) gets energy from the direct path AND from the reflected path which is in phase.
A ¼λ monopole antenna will have twice the gain (3 dB) of a ½λ dipole antenna (in free space).
A ½λ dipole antenna has a gain (G) of 1.64 and an impedance (Z) of 73 Ω at its centre, which is the radiation resistance.
A ¼λ monopole antenna has a gain (G) of 2.15 + 3 = 5.15 dBi (or 3 dBd) and a radiation resistance of 0.5 x 73 = 36.5 Ω when positioned over a large conductive ground plane.

½λ dipole antenna 4NEC2 card deck:
https://www.mobilefish.com/download/l...
¼λ monopole antenna 4NEC2 card deck:
https://www.mobilefish.com/download/l...

By default a monopole antenna will perform poorly without the use of a ground plane.
A ground plane can be a network of horizontal wires or a metal plate.

More information about the end node, see:
https://www.mobilefish.com/developer/...
The end node uses the MCCI LoRaWAN LMIC Library:
https://github.com/mcci-catena/arduin...
The end node uses the following sketch:
https://www.mobilefish.com/download/l...

One or more gateways were able to receive my transmitted sensor data, see:
https://drive.google.com/open?id=18SK...

The logged data can be found at:
https://www.mobilefish.com/download/l...
https://www.mobilefish.com/download/l...

A ¼λ monopole without ground plane has a bad antenna performance.
A ¼λ monopole with ground plane with a radius GREATER than ½λ has a good antenna performance.

As demonstrated using a metal plate (radius greater than ½λ) or radials as the ground plane produces approximately the same result.
Using radials is often preferred:
- The radials are lighter than a metal plate.
- The radials are cheaper than a metal plate.
- The radials are more resistant to weather conditions (wind, rain).
When using a metal plate or radials as a ground plane, in both cases the impedance is around 75Ω instead of 50Ω.
When radials are used, bend it to a certain angle and the impedance will be 50Ω and the VSWR will remain below 2.

The effect of a ground near any antenna (for example: monopole, dipole, Yagi-Uda, Moxon, etc) can be significant.
The antenna performance can be positive or negative.
The effect can be simulated using an antenna modelling software (see tutorial 38).

Check out all my other LoRa/LoRaWAN tutorial videos:
   • LoRa/LoRaWAN tutorials  

Subscribe to my YouTube channel:
   / @mobilefish  

The presentation used in this video tutorial can be found at:
https://www.mobilefish.com/developer/...

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