S11 and gain relation

i have simulated patch antenna at 2.65 ghz in hfss. i am getting s11 less than -10 db at 2.65 ghz, 4.88ghz and 6.88 but when i look at the gain associated with those freq. i get gain at 3.33 db at 2.65 ghz. but at 4.88ghz and 6.88 ghz ,i am getting gain in minus.what can be the reason for that?are these freq. called harmonics? fr4 is used as substrate.

what is the standard gain of patch antenna when fr4 is used?

fr4 doesn't good work on frequency bellow 4Ghz. You have a big losses at 4.88ghz and 6.88, so you have a good S11 and bad gain.
You can try to use rogers 4003 or other substrates with similar characteristics.

Hi,

First of all, you need to know your frequency range of intereset. I assume you know that already, now collect S21 transimission data (remember it's a two PORT measurement, S21) of that freq. range...I believe your S21 data should be not far if it's a narrow band design.

Harmonics is is product of your fundamental frequency, if your fundamental freq=2.65GHz then your

2nd harm.=2.65x2 GHz
3rd harm.=2.65x3 GHz
.
.
.
so on


Good luck!

Why two threads with the exact same question?
https://www.edaboard.com/threads/268306/

MK28 said:

Hi,

First of all, you need to know your frequency range of intereset. I assume you know that already, now collect S21 transimission data (remember it's a two PORT measurement, S21) of that freq. range...I believe your S21 data should be not far if it's a narrow band design.

Harmonics is is product of your fundamental frequency, if your fundamental freq=2.65GHz then your

2nd harm.=2.65x2 GHz
3rd harm.=2.65x3 GHz
.
.
.
so on


Good luck!

Click to expand...

Thank u sir,

but normally we use only one port to feed the antenna,than how to find S21?
I just wonder why S11 is better and gain is in minus?

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Thank u sir,
this big loss of what?i mean this loss is known as what name?

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sorry i am new to this site so i thought thread was not posted ..thats y...really sorry for multiple copies

@falguni_raval: you dont have to call us Sir, nobody is your Sir...you are on your own Boss.

There are few articles on-line on how to measure S21, but note: it's not a straight forward. If you need more information then please look up on google.

S11: good S11 indicates your incident power is deliverd to the your load( in this case ANT) and somefraction of it might reflected back to the source.

S21: as I've said it's a two port measurement and if you are doing 1-port (S11) on network analyzer you should not expect to have a +ve number. However, when you see -ve number (lets assume its an amplifier) meaning your DUT has no gain @certain frequecny, meaning it's not acting as a DUT that amplifying its input signal anymore.

Gain=output/iput ,,it's a raio..ANT has no input/output ratio, it will not provide you any gain. What it does is, it takes RF signal that applied to its inout and it will radiate that signal at certain direction (energy level will be stronger in one direction than others).

I hope these helps, if not then read more.

@MK28
I think i got confused with your last post.
Lets take a practical example, I simulated a rectangular patch for certain resonant frequency say 5.1 GHz. And I will optimize the design to get least possible S(1,1), in my problem statement, I got S(1,1) = -49 dB (as shown in graph below) and my guide said it is good to good and take the dimensions to go for fabrication.

Can you explain bit more or find me a document/link to get more insight of this?
Thank you for helping

@akc185: you have designed an ANT where your S11=-49dB...it is good enough.

Could you pls be more specific with your question?

@MK28 Sorry, while explaining the experimental design we did, I lost touch with the main question.
So getting back on question, my teacher only looked for S(1,1) only while in your previous posts you have also mentioned about gain and s(2,1).
It will be good if you can provide with document/link regarding 'considerations of various parameters while antenna designing'

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@MK28 Sorry, while explaining the experimental design we did, I lost touch with the main question.
So getting back on question, my teacher only looked for S(1,1) only while in your previous posts you have also mentioned about gain and s(2,1).
It will be good if you can provide with document/link regarding 'considerations of various parameters while antenna designing'

I do not have any documents on me at the moment, but pls google your need and I am sure you will find something. But.........

Assuming you are good with your simulation tool now here are the tips:

1. Dimension your patch, Length and width
2. feeding point
3. Width of your short circuit plate (if any) to the GND
4. Your PCB material, thickness of it (total thickness)
5. if you are going to implement your ANT inside of any products i.g. plastic cover over your ANT then consider that
6. Total GND plane

You see there are lots of parameters to look at to tune your final product....you need to do lot of simulations with one at a time and make sure you list down what you are doing.

GOOD LUCK!