how to reduce the spurr

I use ADF4154,PD frequency is 4.096MHz,and I want to output 184.1MHz,but I found the spectrum exist two spurr at about 160KHz offset the ouput frequence.the spur is very serious,which up to -30dB.when i change the BW from 18k to 80kHz,the spurr dont change,I want to know why this spurr and how can i reduce it? thank you.
Another question, when I use 3 order loop filter,according to the simmulation result,loop resistor's value is 74.8m,I don't know whether such a big resistors is right? or whether I made some mistakes? Hope anyone could help me,thanks again.