What parameters should be taken care of when designing a receiving antenna.

[shmily0447]

Hi all,

For my understnading, we are usually designing transmitting antennas when talking about antenna design. 'Cause we usually look into the S11 and gain of the antenna.

Can anyone with experience suggest that what parameters we should look at when designing a receiving antenna? The S11 does not make sense anymore I think. So in that case, is that right that we should only look at the gain?

 

[E Kafeman]

S11 is a parameter describing impedance matching situation between a RF circuit and antenna.
Absolute antenna gain is the directivity of the antenna*antenna efficiency. A common absolute reference is the isotropic antenna [dBi].
Sometimes is high directivity wanted and sometimes do we want a more omnidirectional radiation pattern (lower peak gain).
A part of achieving high system efficiency is to keep good impedance match (S11).
Selecting an antenna type with low resistive losses and high radiation resistance makes higher efficiency possible.
These parameters are not depending on if the system is using antenna for Rx or Tx.

Some exceptions when Rx and Tx situation not is equal:
Sometimes can a minor Rx impedance mismatch be to prefer for achieving better snr in a LNA at a minor cost of system efficiency.
Also for TX can sometimes a mismatch be to prefer. It will reduce peak power output but maybe also increase DC power efficiency or reduce harmonics as reflecting signal can act as a kind of frequency selective negative feedback.
If transmitting with very high power level, must antenna be designed to handle the heat loss. That is seldom a problem for Rx.

 

[biff44]

most receivers are receiving low level signals. So the antenna has specific gains it needs to meet. That may mean a very high gain but only in one direction, or a low gain that is uniform in all directions.

So one wants to make sure that is accomplished. To test such a thing, u buy a "standard gain horn" or other known performance antenna to transmit a signal, and use your designed receive antenna to pick it up as the relative geometries are changed.

In general one wants a good return loss, so that there are not cable reflections to deal with (real trouble in high speed comm systems) or excess insertion loss due to the reflected signal. In practice, fancy systems like cell towers might have return losses in the 15 to 30 dB range. An RFID antenna might get by with a return loss of 4 dB, though.

 

[shmily0447]

If we are designing a Rx antenna, singal will propagate from the antenan to the circuit. In this case, does the S11 of the antenna still important?

- - - Updated - - -

Is the S11 of the antenna still important if it works as a Rx antenna? In this case, the singal will propagate from the antenna to the circuit. So does a perfect match when looking into the antenna's input port still count?

 

[tony_lth]

What's your application?
For RX antenna, you can directly match the antenna S11 to LNA if the distance between antenna and LNA is short and you can accurately simulate it, otherwise, how can you do the match?

 

[rodgerwxh]

In EM/antenna/signal processing theory, they all mentioned one called reciprocal principle, that means for linear system, Tx -> Rx should be equivalent as Rx -> Tx, thus in principle, well matched S11 of Tx means that it will equally doing well in receiving the signal at that sink of S11. So yes, S11 is equally important for both Tx and Rx.

However, as above experts well commented, practical designs need to consider many other things, For example, in certain cases, due to space limit, Rx can be very small in size since it focuses on receiving clean signal but not strong signal, (LNA will take care of the rest), Tx require thicker feeding due to high power. And most of the time, Tx and Rx are not working at the same frequency, since high power Tx will severely interfere Rx if they are close and working at the same band. Thus there are a lot of things between books and real devices on platforms

 

[sindhuvel92]

refer
https://www.mhprofessional.com/downloads/products/0071612882/0071612882_chap01.pdf
https://www.techdesignforums.com/practice/technique/antenna-design-considerations



Receiving Antennas

A better receiving antenna can only come from three things:

1.) Reducing common mode noise. Common mode noise is from an antenna being electrically "wired", or connected, to noise sources. This occurs even if the connection is an indirect path we cannot easily understand. It is caused by poor antenna to feedpoint interface, a bad feedline or connection, or a poor antenna design.

2.) Altering and reducing near field coupling. If an antenna is near noise sources, or conductors radiating noise from noise sources some distance away, the near field response of an antenna can be important. The field impedance of an antenna, or the ratio of magnetic to electric fields, varies with distance and position with any antenna. There isn't any antenna that is purely electric or purely magnetic, and even if there was there is no noise source that is purely electric or magnetic. Some antennas, just through luck, might couple less to very close noise radiators. At a relatively small distance every antenna works the same so far as ratio of magnetic to electric fields!

3.) Directivity, or the antenna pattern, can reduce noise. An antenna does this by being more sensitive in the direction or polarization of desired signals, and less sensitive in the direction or at the polarization of noise.

With any low-height receiving antenna, like an EWE, K9AY, loop, or Beverage, the antenna responds to vertically polarized signals! Even a long, low, horizontal wire, like a Beverage, is a vertically polarized receiving antenna.

Keep all of this in mind, as you look at antenna choices.

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