Ripple Effect on RF Amp Design

Hi, I have designed a RF amp at frequency 5.3GHz. Would like to know what is the root cause for the ripple effect along the band? Is it the unstable of the amplifier? or the not matching? or there is too much reflection?

Please refer to it

It seems to me this effect could be due to a long (referred to lambda) poorly matched transmission line. Is your network analyzer calibrated at the end of the connecting cables ? Can't you measure S11 and/or S22 ?

Hi, yes, i have measured S11 too. as per attached is the result of measured value for S11.

May be caused by poor match of your RF amplifier on the input or output, i.e. VSWR.
You can insert a PI attenuator at the input to see what happens.

It is oscillating at out of band.

Yeah looks like some weak oscillation or other interfering signal. Try reducing your IF bandwidth and see if it changes.

Hi, is there any term for this problem? Is there any suggestion for the reading?