Is a radar gun a witness against a speeding motorist? Can you request to have your experts examine it?

You are in court, accused of speeding, but the only witness against you is a radar gun, because the peace officer who pulled you over, is only accepting the display of his radar gun. So, because the device is the real (and only) witness against you, it should be required to be sworn in and testify, like any other witness, and you should be able to have that device given to your own panel of experts, to determine that the device is functioning perfectly, right?

There have been cases where radar guns were proven to be inaccurate, and the radar gun itself should be subpoenaed as a witness, just like any other witness. Don’t you agree?