HMC1044 SPI Clock freq and RF Behavior


I am using HMC1044 in one of my application. Using STM32F417 controller to configure HMC1044 through its SPI. 

I tried with 1MHz to 20Mhz as SPI clock but not able to configure HMC1044. What is the supported SPI clock frequency ? in data sheet I see its 20ns minimum clock time which is (50MHz) is this true?

And for every band selection I do, Filter behavior is same. 

RF behavior with default Band-15:

With the default band-15 configuration I am unable to see the required filter performance.

I am feeding -20dBm as in put level, fed frequencies from 900MHz-4GHz, but filter output is not uniform in pass band, that is at 1.2GHz its giving -50dBm at 2GHz its giving -48dBm.

Variation is not at all linear in the pass band. Can you share its behaviors Gain vs Frequency for different bands.