Wrong S parameters of a shunt MEMS switch

[emmagood]

Hi,


I am new to MEMS switch. Presently, I am trying to simulate for the S parameters of a shunt MEMS switch. I am trying to find out the S11 value in upstate position. The structure is the basic shunt switch given in Rebeiz book (I am using the corresponding paper for the dimensions) and the software is CST Microwave Studio.

I am getting two problems:

1. The S parameters are not coming as per the paper. Infact the curve for a frequency range of 2 to 40 Ghz is between -1 dB to -5 dB (As per the paper, it should be between -30dB and -10dB).

2. While I am connecting the ports in the CST Microwave studio, during simulations, its impedance is showing to be more than 50 ohms (around 150-200 ohms for various simulation runs). I checked the manual of CST and I am giving the port dimensions as per the recommended values for a CPW (width = 2 *(G+W+G) of CPW and height=(G+W+G) of CPW.)

Can anyone pls. help me with these issues. I will be very grateful for any suggestions/ideas.

Thanking in advance,

Emma.

 

[CPW_Enlighten]

Did you use the right substrate material? You might want to post the details of model and parameters used.

 

[emmagood]

Did you use the right substrate material? You might want to post the details of model and parameters used.

Well, the first problem of incorrect S parameters is somewhat solved by increasing the port impedance to near about 50 ohms. I am still not able to get exact 50 ohms port in CST. Initially I got 38 ohms. Later, I increased the port width and height to get impedance upto 44 ohms. I think, if I can get 50 ohms ports in CST, I will be able to replicate the results. Do you know how to do so.

BTW , I used the the right substrate.. in the papers it was mentioned silicon, so I tried with bot lossy and lossless materials. They are giving almost the same results. I am making a shunt switch with beam length of 300 um on 60/100/60 (G/W/G) CPW.

 

[danial_1860]

hi
i have problem simulating mems shunt switch in hfss. i dont know how to obtain the s-parameters. please help me in excitation and defining proper ports to get s11 and s12

thanks