LoRa/LoRaWAN tutorial 41: Dipole Antenna

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This is part 41 of the LoRa/LoRaWAN tutorial.
In this tutorial I will explain what a dipole antenna is.
A dipole antenna is the simplest and most widely used class of antenna.
A dipole antenna consists of two identical conductive elements such as copper wires, rods or tubes.
The two elements contribute to the radiation.
If the total length of the dipole is ½ wavelength, than each element has a length of a ¼ wavelength.
When we speak of a ½λ dipole antenna, the total length of the antenna is a ½λ.
A nice animation where you can see the radiation pattern vs current distribution when you increase the dipole length:
• 3D Dipole Radiation Pa...
The equation to calculate the wavelength:
c = λ x f
c = speed of light = 299792458 m/s
λ = wavelength in m
f = frequency in Hz
If antenna f = 868 MHz:
λ = c / f = 299792458 / 868000000 = 0.34538 m = 345.38 mm
As explained earlier a ½λ dipole is a good antenna.
This means both elements of the antenna are 0.25 λ in length.
If f = 868 MHz and λ = 345.38 mm, L= 0.5 x 345.38 = 172.69 mm
Do not forget the velocity factor.
If the dipole is made of stainless steel (VF=0.9): l = 0.9 x 172.69 = 155 mm
A ½λ dipole antenna has a power gain of 1.64 (or 2.15 dBi) over an isotropic antenna (see tutorial 39).
At its feed point ½λ dipole antenna has an impedance consisting of 73 Ω resistance (R) and a reactance of 42.5 Ω (X).
4NEC2 card deck:
www.mobilefish...
Note:
Initially the length was set to 0.155 m then I used the 4NEC2 optimising functionality to improve the design.
The optimised length = 0.160 m.
The 4NEC2 model element length = 160 mm.
The real ½λ dipole antenna length = 146 mm (= 2 x 73 mm).
I used the N1201SA Vector Impedance Analyser to tune the antenna.
Why this discrepancy?
The real antenna is not 100% accurately modelled in the 4NEC2 program.
Think of the gap between the elements, terminal with screws, the type N female chassis.
All these influences the antenna behaviour.
Please be aware that the generated radiation patterns are merely a ROUGH indication how the real dipole antenna behaves.
As explained earlier the real ½λ dipole 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.
The ½λ dipole 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...
The end node uses the MCCI LoRaWAN LMIC Library:
github.com/mcc...
The end node uses the following sketch:
www.mobilefish...
I have NOT modified the end node transmission power when using the ½λ dipole 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 ½λ dipole antenna is attached to an end node at location A and transmitted data and I have done the same with a sleeve dipole antenna.
In both cases two messages per minute were transmitted.
The logged data can be found at:www.mobilefish...
Several nearby gateways were able to receive my transmitted sensor data, see:
drive.google.c...
I have conducted another test whereby the ½λ dipole antenna is directly connected to the end device. No coax cable is used.
Again the same tests were conducted using the same ½λ dipole antenna and sleeve dipole antenna at location A.
Two messages per minute were transmitted and both logged data can be found at:
www.mobilefish...
Note: The tests were conducted approximately 1.5 months later.
The RF coaxial cable with type N male plug right angle to SMA male connector is probably not working correctly.
I have replaced it with another setup.
Looking at the results I can conclude that my self build ½λ dipole antenna performs the same as the purchased sleeve dipole antenna.
Check out all my other LoRa/LoRaWAN tutorial videos:
• LoRa/LoRaWAN tutorials
Subscribe to my KZbin channel:
/ @mobilefish
The presentation used in this video tutorial can be found at:
www.mobilefish...
#mobilefish #lora #lorawan

[@ristomatti]

Your tutorials are great! There's no room for misunderstanding as every step is clearly explained unlike on pretty much all other tutorials I've ran across. I've learned a lot already by watching 3 videos. Thanks for sharing the knowledge!

[@Lexdrumz]

Awsome tuturials! Great stuff! will you build an 5/8 wave antenna for 868mhz? Very much interested what the impedance would be and vswr. The radiation lobes should be a little bit longer and flatter compared to 1/2 wave dipole. More range for lorawan! But it should be more difficult to feed them I think?

[@j86t25]

sir please make tutorial about folded dipole

[@miguelangelgalindo3124]

Do you have any video on how does affect the diameter of the antenna wire to the range?

[@thekambing]

Sir why should we cut the other 3 ground sma connector feet??is it affecting the result?i am new to lora, especially this radio things...thank you for sharing this knowledge sir.

[@Mobilefish]

Sorry, but I do not understand your question.

[@thekambing]

@@Mobilefish on 23:45 sir, but i understood now. i have one more question, is it possible to make lora dipole antenna just by print it on PCB?and what is the dimension?thank you

[@Mobilefish]

You are asking the same question as with the moxon antenna. Theoretical you can, but I do not see the advantage. Printing a dipole or Moxon antenna on a PCB is more a hassle. Are the circuits on the same PCB as the antenna? If so, depending where the circuit is located on the PCB, it can impact the antenna performance. And how is the antenna feeded? By a PCB trace, which can act as an antenna (=interference). As you can see it is not a simple question to answer. Building an antenna (not printing on PCB) is easy to make, easy to test with an antenna analyser and easy to feed (using a coax cable with SMA connector). So, having said this, to answer your question: the same dimensions as mentioned in my tutorial. Keep an eye on the PCB trace thickness.

[@thekambing]

@@Mobilefish thank you sir..yes actually i'm looking for best fitted internal box antenna for my node.

[@Mobilefish]

Okay, please watch kzbin.info/www/bejne/kIfSY4Whd7hkatE and checkout: github.com/FabienFerrero/UCA_Board Please note: I have NOT build a PCB antenna myself, so I can not tell you if it is good or not.