rashed1880
Newbie level 5
I have been trying to measure the S-parameters of GaN HEMTs and LDMOS. but some reason I haven't been able to get expected values. I am not really sure of the reason. For example: in cold FET or below pinch-off measurement(Vgs<below pinch-off and Vds=0V), S11 parameter should be purely capacitive and if converted into Y-parameter, then Y11 should be linear. but after de-embedding, the S11 i get goes into the upper half of the smith chart and corresponding Y11 is very strange (kind of zig-zag) shape. is it because of the fixture (i designed it), calibration (i use mechanical SOTL calibration kit). does the s-parameter measurement depends on the network analyzer? If anyone here has done this before and help me out, then I would be really grateful.