Fighting a bogus ticket from a radar van

Hello everyone!

I was wondering if anyone might be able to give me some help/advice.
I was driving in Milwaukie, OR about a week and a half ago, when I noticed a white van was parked on the side of the road. Suddenly a whole bunch of flashes started going off. I said to my friend that was in the car with me, "what the hell, I am not speeding, that better not be some sort of radar ticketing machine because I am going to be so upset...I was not speeding." My friend agreed that it couldn't be that because I was indeed not speeding." Then, I promptly put it out of my mind, feeling quite confident I had nothing to worry about.

Sure enough, got a ticket in the mail today. It says I was going 11 miles over the speed limit. Not a chance in hell! I am so very upset.
I want to fight fight fight. This is so wrong on so many levels.
Any advice you could give me on beating this bogusness would be so greatly appreciated.

Thank you very much,
Ericka