# How to design variable resistors R0 to represent the frequency-dependent loss in ADS

#### thundrous

##### Newbie level 4 I am trying to replicate a result of a paper in Advanced Design System software. It is mentioned that the resistance is variable and its equation is 10e-9f (GHz) + 5. When I drew the resistance in the software and wrote the formula, a syntax error showed up.

Would you please guide me on how to enter this equation? Is there any specific module I need to enter inside the equation field?

Here is their equivalent circuit: and here is the equivalent circuit that I drew: #### dick_freebird Seems like it just wants a wee bit of series L?

#### BigBoss Use equation based s-parameter blocks.
Define first s-parameters matrix of a series resistor then enter these values into equation based blocks with the variable "freq". Otherwise it will not recognize.

#### thundrous

##### Newbie level 4 Use equation based s-parameter blocks.
Define first s-parameters matrix of a series resistor then enter these values into equation based blocks with the variable "freq". Otherwise it will not recognize.
Thank you very much for your response, until now I updated the equivalent circuit as follows, but still I cannot reach the proper data. Do you have any idea where the problem is? Also, i do not know how to introduce the frequency as the variable "freq". I tried to but the software does not accept it.
any suggestion appreciated.   #### thundrous

##### Newbie level 4 Seems like it just wants a wee bit of series L?
I do not know, would you please explain more?

#### thundrous

##### Newbie level 4 #### BigBoss S-parameters matrix of a series resistance ; Then use equation based s-parameter block like this. then you will see that s-parameters are not constant versus frequency. (If the resistance was constant, s-parameters should have been constant too but they aren't due to frequency dependence of the resistance) #### thundrous

##### Newbie level 4 S-parameters matrix of a series resistance ;
View attachment 180869
Then use equation based s-parameter block like this.
View attachment 180870
then you will see that s-parameters are not constant versus frequency. (If the resistance was constant, s-parameters should have been constant too but they aren't due to frequency dependence of the resistance)
View attachment 180872
Thank you very much for your guidance I did what ever you mentioned in the previous comment as follows based on my current device and here is my Equivalent circuit: S21, S11 are my experimental results and S65, S55 are for the simulation I've got a good verification between S21 and S65, However the S55 does not seems good and it starts from -10dB
So based on the article I changed the frequency loss resistance depedance as follows: I eleiminated R=50 then the slope of S55 changed but still it starts from -10dB. It seems the variable Rlossy has lots of effect on our measurments and by changing the formula i even needed to change the capacitance C4 for validation between simulation and experiment results. Would you please guide mewhich one is current and where did I made a mistake because S55 should start from zero.

#### BigBoss It was my own example, not real/your one. You have to define your own formulae by yourself. It might
be anything as you desire. I dont know the process that you've been working on.

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