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S11 vs antenna gain in patch antenna

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daniels_here

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i have designed a patch antenna with a gain of 16db but only a maximum of -8db s11 for the frequencies i want. will this antenna be able to still transmit or do i have to get the s11 lower? i have heard that max should be -10db for the s11. i only want it to go max 100m
 

antenna factor gain s11

hi daniels_here,
S11 and gain are two important figures of merit. The former one is used to evaluate the quality of match with the feed. And the latter, the gain, could both enbodies the radiation and the efficiency.
what i'm wondering is how a relatively high gain(16dB) could be achieved in your design in a not very good match condition? could you describe your structure roughly?
 

gain vs s11

16 dBi sounds very suspicious. That is too high and I wanted to concur with the previous comment. It is almost as if the two values were reversed.

Check your results carefully.

BTW -10 dB s11 or less in my mind is a reasonable level. I prefer to shoot for -15 dB reflection coefficient when I can get it. Work out the loss due to each and you will see the impact and then can make up your mind as to what you really need.
 

s11 antenna power

Hi:

It is possible to achieve 16 dBi gain if it is a patch antenna array. For S11 = - 8 dB, you still have about 1.5 dB room or you can still improve the gain by 1.5 dB. I don't think it is necessary to make S11 below - 10 dB. If S11 is below - 10 dB, it means that you get extra 0.6 dB more gain. Reducing S11 is one of the best ways to achieve higher gain because it costs you nothing for extra gain.

Regards,
 
can s11 in gain?

s11 must be above -40, then only you will get the same radiated power and received power,and also the VSWR=1.02
 

good antenna s11

This is interesting. You are getting a variety of "answers".

Here are several general guidelines:

Individual patch gain range: 6 to 10 dBi typically
Array of patch antennas: 4 to 8 elements to achieve 16 dBi (estimated)
Spacing, feed efficiency, element gain are all factors, maybe scan angle too.
S11 below -20 dB over a significant bandwidth might be problematic


I would suggest that you evaluate the impact of the various characteristics on your situation and decide what is really needed. The guidelines are just that and not rigid requirements.
 

vs antenna

I have not seen any commercial patch type antennas with an S11 of better than 10 dB. Maybe if you buy one from a military house that tunes and tests antennas, you can do better. But the cheap commercial ones are all dog pooh for VSWR! 8 dB is fine, unless you are talking about a lot of power transmitted.
 

acceptable s11 for antennas

hey guys thanks alot you have cleared alot up for me.
I am using a patch array of 8 strip lines,

I have been trying to impedance match it using the ansoft designer SV program. But i am not having to much luck with that what i have done is got the impedance value for one patch antenna say it is roughtly 30 -45j (real / imaginary) from HFSS. Than i have set up a microwave port with 50 ohms impedance and the othere with 30 -45j in Designer. Than used the smith tool to impedance match it but i am not having too much luck with it. Am i on the write track or am i way off with this method of impedance matching a Antenna?
 

s11 in db

In case of Patch Antenna array,Returnloss(RL) of the antenna not only reflects the RL of Array elements it also reflects RL of feed network.

Single antenna element returnloss should be good (RL ≤ -10dB).

And the Spacing between Antenna elements should be between 0.72 to 0.8λ.

u can check out these.
 

s 11 for antenna

Hello,

the return loss has to be minimize, first of all to reduce the overall losses. For example

S11 = -10 dB => link loss of 0.45 dB (10% of input power lost)
S11 = -15 dB => " " 0.14 dB ( 3 % of input power lost)
S11 = -20 dB => " " 0.04 dB ( 1 % of input power lost)

S11 of -10dB can be good for commercial usage. It is better at least -15dB.

Second point an excessive RL (> -10) introduces also S12 distortions since they are not independent : (S11)^2+(S12)^2 = 1.

Bye.
 
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