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This is part 44 of the LoRa/LoRaWAN tutorial.
In this tutorial I will explain how to build a ¼ wave ground plane antenna.
The ¼ wave ground plane antenna (aka spider antenna) has radials.
Often four ¼ wave radials are used to sufficiently simulate a complete circular conductive ground plane which works as a reflector as already explained in tutorial 42.
The current in the reflected image has the same direction as the current in the real antenna.
If the radials are straight, meaning not bend, the impedance at the feed point will be around 37Ω.
If the radials are bend down at an angle of 40° the impedance at the feed point will be around 50Ω.
The ¼ wave ground plane antenna is an unbalanced antenna thus a 50Ω coax cable, which is an unbalanced feed line, can be directly attached to it.
The ¼ wave ground plane antenna has only one radiating element which is fed in the lower end which is near the conductive surface.
The radiating element length LRadiating = ¼ x λ and the radials are slightly longer.
The radiating element is also called the driven element, radiator or resonator.
4NEC2 card deck:
www.mobilefish.com/download/l...
Please be aware that the generated radiation patterns are merely a ROUGH indication how the real quarter wave ground plane antenna behaves.
The real quarter wave ground plane antenna is not 100% accurately modelled.
If you want accurate radiation patterns of real antennas than the antenna radiation patterns measurements should be performed in an anechoic chamber.
Based on the 4NEC2 antenna model results, the ½ wave dipole antenna has a slightly higher maximum gain compared to the ¼ wave ground plane antenna.
You might think by placing the antenna near the ground you will get the best antenna performance (= higher gain).
But placing the antenna near the ground is not a good idea because of the Fresnel Zone.
If you do not know what the Fresnel Zone is, watch tutorial 7.
¼ wave ground plane antenna pros:
- Provides good performance.
- Easy to build with consistent results.
- Can be used at all frequency bands including LF, MF, HF, VHF and beyond.
- Omnidirectional radiation.
- Vertically polarised signals.
- Low cost.
- Low angle of radiation which means the signal is not directed towards the sky.
- The radiation pattern is fairly uniform both vertically and horizontally.
¼ wave ground plane antenna cons:
- It requires a ground plane (radials)
- A ½ wave dipole antenna has a slightly higher maximum gain compared to a ¼ wave ground plane antenna.
The ¼ wave ground plane antenna performance is compared with a sleeve dipole antenna.
More information about sleeve dipole antennas, see tutorial 43.
For this test I am using the end node and antenna C as demonstrated in tutorial 33.
More information about this end node, see:
www.mobilefish.com/developer/...
The end node uses the MCCI LoRaWAN LMIC Library:
github.com/mcci-catena/arduin...
The end node uses the following sketch:
www.mobilefish.com/download/l...
I have NOT modified the end node transmission power when using the ¼ wave ground plane antenna.
In my area there are several gateways and I know that these gateways, which are connected to The Things Network, can receive my transmitted data.
The ¼ wave ground plane antenna is attached to the end node at location A and transmits data.
I have done the same with the sleeve dipole antenna.
In both cases two messages per minute were transmitted.
The logged data can be found at:
www.mobilefish.com/download/l...
One or more gateways were able to receive my transmitted sensor data, see:
drive.google.com/open?id=18SK...
If you look at the results you may notice there is no significant difference in the average RSSI values.
When using the ¼ wave ground plane antenna it took 17.5 minutes to transmit 30 messages.
When using the sleeve dipole antenna, which is my reference antenna, it took 18.5 minutes to transmit 15 messages.
The Arduino sketch is configured to transmit 2 messages per minute.
So looking at the results I can conclude that my self build ¼ wave ground plane antenna performs the same as the sleeve dipole antenna.
Check out all my other LoRa/LoRaWAN tutorial videos:
• LoRa/LoRaWAN tutorials
Subscribe to my RU-vid channel:
/ @mobilefish
The presentation used in this video tutorial can be found at:
www.mobilefish.com/developer/...
#mobilefish #lora #lorawan
2 июл 2024
