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Best tools for analysing Receiving (Active) Antennas?

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nctnico:
Are you sure that using two identical antennas will work? From what I've read, antennas may have different RX & TX gains so splitting the result in half won't work. A while ago I found a paper from R&S on this subject and they proposed a method where you use 2 different antennas in 4 different combinations in order to get to the RX & TX gain of each antenna.

Berni:

--- Quote from: nctnico on January 26, 2023, 01:51:07 pm ---Are you sure that using two identical antennas will work? From what I've read, antennas may have different RX & TX gains so splitting the result in half won't work. A while ago I found a paper from R&S on this subject and they proposed a method where you use 2 different antennas in 4 different combinations in order to get to the RX & TX gain of each antenna.

--- End quote ---

Yep i agree.
Antennas can have loss inside them that eats up some of the energy and it could even be non linear with power. They can also have horizontal vs vertical polarization or even circular polarization and a lot more RF black magic i will likely never understand.

However if you just do a simple dipole out of metal rods, the response of it is going to act pretty predictable, and there is no worries about directionality as long as you stay away the two null points on the ends.

Ideally you would also be doing this in an anechoic RF room and use special calibrated antennas, but most of the time you don't need super accurate results within single digit dBs. Taking the simple dipole antenna outside in an open area of the yard is close enough to get a good idea of how well your antenna is performing.

switchabl:
If the objective is to characterize antenna gain, the simplest approach is probably the substitution method where you measure the same signal with a reference antenna (with known gain, probably a dipole) and then mount your AUT in the same location and compare power levels. The advantage is that the transmitter is relatively uncritical, as long as it provides a stable signal and is reasonably far away and you don't need perfectly predictable propagation conditions. You could even use something like a commercial broadcast.


--- Quote from: nctnico on January 26, 2023, 01:51:07 pm ---Are you sure that using two identical antennas will work? From what I've read, antennas may have different RX & TX gains so splitting the result in half won't work. A while ago I found a paper from R&S on this subject and they proposed a method where you use 2 different antennas in 4 different combinations in order to get to the RX & TX gain of each antenna.

--- End quote ---

There isn't really anything wrong with the two antenna method (based on the Friis formula P2 / P1 = G1 G2 (λ / 4πd)2, solve for G1 = G2). But there are a number of underlying assumption and these may not always be practical:
- the antennas are actually identical
- the antennas are reciprocal (usually true for passive antennas)
- the distance is sufficient for far-field approximation to hold
- free space propagation, no reflections
- polarization is known a priori

tautech:

--- Quote from: vinlove on January 26, 2023, 11:27:53 am ---
--- Quote from: wasedadoc on January 26, 2023, 11:14:51 am ---A SWR meter reveals nothing about the gain of an antenna (transmit or receive) which is achieved through its directivity.  What parameters of receiving antennas are you wanting to analyse?

--- End quote ---

Resonance for the receiving frequency.

--- End quote ---
What frequency are we looking at ?
There are a few options depending on what info you need from the antenna and I have found the actual resonant frequency the most important to have correct.

Rather than work with any live signal source with an SA or VNA I prefer to use the antenna reciprocity principles and use a VNA to provide the stimulus to initially get the resonance/emissivity tuned in with Log Mag and then engage SWR and Smith charts to further tune it to near perfection.

I have a antenna project I did a few years back documented here with a couple of screenshots using a SA and reflection bridge but the real grunt work was all done with a VNA.
https://www.eevblog.com/forum/rf-microwave/antenna-project-log/

There I only needed excellent sensitivity but right on frequency as I was working with a small 200m range remote.
The results were better than expected and I again thank the members that pointed me in the right direction with their pearls of wisdom.

vinlove:
To reiterate the OP,

1. Is it possible to analyse Rx antennas especially the active antennas for the resonance and efficiency for the given band or frequency using measuring equipment or tools such as NanoVna or Tiny Spectrum Analyser?

2. If it is, then what would be the parameters? - What are we measuring and against what etc?

3. Which tester / measuring tool would be best for the job?

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