# ADS design guidecell：fmax vs VGS & VDS problem

Question asked by lolicer on Jan 13, 2018

hello,guys:
I am using ADS the design guide-amplifier-DC and bias point simulation-FET_ft_fmax_vs Bias cell to simulate the Fmax variance with the sweep of VGS and VDS. when I use the original schmatic with original ideal GaAs FET, this cell works and I can get the results like below: but when I change the FET from the ideal one to the UMS foundry HEMT, I can't get the full result(only get two) like below: I check the error from the plot:Maximum frequency of oscillation (fmax) and other plot(shown in the above figure)
, all the reported error are the same as below: While evaluating "LcsGetNewExpName1":
Operation "[ ] sweep access", index out of range in dimension 1, independent "freq" must use an index in the range 0 <= index < 0

I also check the variable fmax infomation as below: there is a irreg which obvious not normal. and I check the help manual and get the only one matched searched result as below:

sweep_size()
Returns the sweep size of a data object

Syntax
y = sweep_size(x)

Arguments

Examples
Given 2-port S-parameters versus frequency, and given 10 frequency points, there are then ten 2 X 2 matrices. sweep_size() is used to return the sweep size of the S-parameter matrix, and its companion function size() returns the dimensions of the S-parameter matrix itself:
a = sweep_size(S) returns 10
a = size(S) returns {2, 2}
Irregular data:
Assume that the data is 3 dimensional with the last dimension being irregular. The independents are: Vsrc, size, time with dimension [3,2,irreg]. Then:
SwpSz=sweep_size(data) would return:
__SIZE SwpSz
Vsrc=1.0,size=1.0
1 20
Vsrc=1.0,size=2.0
1 21
Vsrc=2.0,size=1.0
1 59
Vsrc=2.0,size=2.0
1 61
Vsrc=3.0,size=1.0
1 76
Vsrc=3.0,size=2.0
1 78
where __SIZE is an independent added by the sweep_size() function.
sweep_size(SwpSz) would return the correct size of the two outer variables:
(1) (2) (3)
3 2 1

as long as I tried, I can't understand what I can do to make it right....

Can anyone knows what is going on and how to solve this?