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Does this look to be excessive ripple? What caues it?

Question asked by drkirkby on Apr 19, 2013
Latest reply on Apr 27, 2013 by Dr_joel

1 ) Stuck a couple of 3.5 mm to N adapters on the 3.5 mm test cables of my 8720D VNA. One gave me a female N, the other a male 
2) Performed a full 2-port calibration of the VNA from 50 MHz to 6 GHz with an 85032B cal kit. I used no averaging, but did reduce the IF bandwidth to 1 kHz from the default 3 kHz.
3) Promptly measured S21 of an attenuator rated to 1 GHz.surprising 

The result is as shown. I know that S11 and S12 are of the order of 20 dB at 6 GHz, which is not given this attenuator is rated to 1 GHz.

There is a very noticable rippled on the device, which may be real, but may be not. Does the frequency of this ripple indicate anything useful? Is this excessive, or to be expected?