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Antenna - Air impedance matching?

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fonograph:
I have read conflicting information,one is that matching impedance of antenna to air is not needed,that full power transfer will happen no matter what the impedance antenna is,becose the reflection is in phase with the outgoing signal.Second opinion is that matching is needed,which one is true?

I does not make sense to me that at RF frequencies,we must always impedance match everything but somehow large impedance discontinuity when transitioning to air is somehow not causing any issues.

Futhermore,even if the antenna - air impedance mismatch doesnt affect frequency domain or power,wont the "in-phase reflections" cause time domain smearing of somethe sorts? For example in case of pulse position modulation that depends on short  pulses in time domain,would it not cause  some ringing or some time domain pulse shape degradation?

tautech:
 :)
Have been down this road and I'm certainly no expert even still finding my way and still somewhat lost at times.

Have a little read of something I'm working on again now I've got the right tools.......and some small understanding.  :(
https://www.eevblog.com/forum/testgear/siglent-sva1015x-1-5ghz-spectrum-vector-network-analyzer-(coming)/msg1686137/#msg1686137

tautech:
Simply for antenna construction you must satisfy 3 main requirements.

Resonance frequency, where the antenna emits the most energy at the desired frequency.
Impedance, so the antenna matches the feedline and its source impedance at the desired frequency.
50 Ohms is normal.
SWR so the antenna is the most efficient at the desired frequency with the energy available.

Easy, no it isn't ! Hard, not terribly with the right gear and/or some experimentation.

D-Jack:

--- Quote from: fonograph on July 30, 2018, 01:40:35 am ---I does not make sense to me that at RF frequencies,we must always impedance match everything but somehow large impedance discontinuity when transitioning to air is somehow not causing any issues.

--- End quote ---

An impedance mismatch when designing an RF circuit will affect the power and range of your signal. If it is bad enough, it will not transmit at all. The majority of circuits will "work" without tuning (as long you follow the basic layout recommendations) but instead of having a 10 meter range, you will have 1 meter. This can deeply impact your product since you will either have to increase output power increasing power consumption or you will have a product with poor signal performance.

Some people may say the a tuning process for antenna-air is not need because they often assume the circuit will be enclosed somehow, so in that case the tuning must take into account the enclosure.

This is an excellent application note that will walk you through the various steps of designing and tuning an RF circuit: http://www.cypress.com/file/136236/download

GregDunn:
Not sure what is meant by matching the antenna to the air?  What you want is for the native impedance of an antenna to approximately match the impedance of free space (about 377 ohms).  It's most important if you're trying to deliver prodigious amounts of power; if the impedance is reasonably close you'll get some power transfer regardless, but if lots of power is being sent, much of it may come back down the line to your transmitter and that's generally not good.

Most antenna cookbooks take 300 ohms as a starting point, and unless you're trying to couple directly to a receiving antenna rather than actually broadcast or transmit RF, you'll want to use an antenna element designed for that approximate impedance.  There are lots of special cases, so if you're trying to design a VLF high power system or a microwave point-to-point link, it's best to consult the literature.  But in general, even these types of systems take the free space impedance into account at some point in the design.

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