mixer result problem...need opinion urgently

I have designed a mixer to operate in 4-9 GHz range. but I've dne tht using a single FET ..the simulation results were not tht great but once I fabricated in microstrip the results were worse...the single FET device I am using can be used upto 20 GHz as per the datasheet...my question is...is it even reasonable fr me to expect a gain or atleast a loss of about -3 or -4 in the entire 4-9 GHz range when using a single lone transistor for obtaining mixer operation? I will be grateful fr an opinion on the issue..thnx