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S11 and Z-parameter of Spiral Antenna Design in HFSS

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ashuroks

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I am stucked with my result of the design which i am preparing in HFSS

I am preparing an antenna which is 4 Arm Microstrip Spiral Antenna with 4 SMA feeds at 50 Ohms but since the impedance of antenna as theory says is not equivalent to 50 Ohms So i renormalize it to 300 Ohms Can you please check my design and let me know if there is any problem with my design of Antenna. If you also Calculate S parameter using Z parameter from the formula S11 = 20 log (Zin-Zo/Zin+Zo) Which is coming out to be wrong ..

I checked the results from the Solution Data by checking the Z-parameter and Zo but still i am not able to figure out where the error is
freq S-parameter Z-parameter Zo
Do not renomalize 1.9682GHz -2.58dB 527.66 +455.64j (49.755 +0.0248j) Ohms
Renormalize to 300 Ohms 1.9682GHz -15.8dB 527.66 + 455.64 (300+0j) Ohms

if using formula i backcheck the results like s11 = gamma = (Z-Zo)/(Z+Zo) then the results is not giving me the desired S-parameter Results .

I am not clear with what is happening here ?

I would be grateful if anyone can reply to this query

Thank your very much
 

Can you verify your s11 formula. S11 =((Z11-Z0)(Z22+Z0)-(Z12*Z21))/((Z11+Z0)(Z22+z0)-Z12Z21)
Here Z11 are the impedance parameters at the input and the output side.

The value you have there gamma is the input side reflection coefficient. gamma_out =S22 will give you the output side reflection coefficient.

You have to make correponding changes to all the Z parameters when you renormalize.
 

but sir i have 4 sma feeds so Is all the data is going to effect my net effective S parameter or not ? like Z11 Z21 Z31 Z41 is every other Z parameters are also affecting my antennna design ..coz i have 4 SMA feeds ..

Thank you for your reply
 
If your practically designing an antenna YES.
If your making a theoretical design..you can assume Z21 to be zero etc...But you will have to consider all the input/output ports in your computation.
 

No sir i am asking whether HFSS does the same ..Like i am simulating this antenna in HFSS so i am not very clear how does HFSS calculates the S parameter for the array antenna ..This is array antenna only with four arms interleaved and four SMA connectors are there ..

My problem is When i am calculating the S11 parameter using Z11-parameter it is not giving me correct results as compared with HFSS S11 parameter result .

Also if you see HFSS help you will find that HFSS calculates S parameter first and then Z parameter using the S parameter only So if they are the conversion of one another only then why it is giving error ?

I would be highly grateful to you
 

HFSS considers all the mutual effects and takes the full equation into account. I presume you have specified all the impedance parameters. And your S- parameters your using "renorm". Your model parameters, considering it is four port you would want to verify all the S parameters. I am not able to emulate your error on the HFSS model either.

Good luck
 

hi
i know its an old thread but if possible can you tell me how did you get this formula?i am also thinking of desingng spial antenna can you plz guide me about it i-e how to take its impedance computation thanks
ashuroks said:
I am stucked with my result of the design which i am preparing in HFSS

I am preparing an antenna which is 4 Arm Microstrip Spiral Antenna with 4 SMA feeds at 50 Ohms but since the impedance of antenna as theory says is not equivalent to 50 Ohms So i renormalize it to 300 Ohms Can you please check my design and let me know if there is any problem with my design of Antenna. If you also Calculate S parameter using Z parameter from the formula S11 = 20 log (Zin-Zo/Zin+Zo) Which is coming out to be wrong ..

I checked the results from the Solution Data by checking the Z-parameter and Zo but still i am not able to figure out where the error is
freq S-parameter Z-parameter Zo
Do not renomalize 1.9682GHz -2.58dB 527.66 +455.64j (49.755 +0.0248j) Ohms
Renormalize to 300 Ohms 1.9682GHz -15.8dB 527.66 + 455.64 (300+0j) Ohms

if using formula i backcheck the results like s11 = gamma = (Z-Zo)/(Z+Zo) then the results is not giving me the desired S-parameter Results .

I am not clear with what is happening here ?

I would be grateful if anyone can reply to this query

Thank your very much
Click to expand...
 

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