how to improve vswr

dear sir :
i use one RCP2150m30 as the VSWR check device,this is a dircetional coupler,but i find the check result is not very accuracy,how to improve it?

Hi,
You expect variation at the output of PA many times. Is the gain stable?
Do check the quality of interconnections? I donto think that the DC has a problem (I assume frequency is OK).
brmadhukar

This coupler is dedicated mainly for PCS applications (1900MHz). At this frequency an important factor that will affect VSWR reading, is the layout and a proper terminations at each port of the coupler.

May be your problem is not a coupler?
For good VSWR check accuracy of the PA you need to have a good analog part of the VSWR check system, also. Check: detector, amplifier, reference source and other parts.