The foundational-attack theory
California case law (People v. Goulet, People v. Ellis) requires the prosecution to lay foundation before radar readings come in: (1) the officer was certified on the unit, (2) the unit was calibrated within the manufacturer’s interval, (3) a tuning-fork or self-test was performed at the start of shift, and (4) the speed-zone was supported by a recent Engineering & Traffic Survey per VC 40802(c).
What "speed trap" means in California
Under VC 40801–40802, a "speed trap" is a prima-facie zone without a current E&T Survey. Radar evidence from a speed trap is inadmissible. The E&T Survey must be no more than 5 years old (7 with a Traffic & Engineering Investigation, 10 with a supplemental survey).
Drafting the declaration
Your TBWD should state that the officer’s declaration does not establish foundation on each element, then demand that the court confirm a current E&T Survey exists for the stretch of road where you were cited. Many roads in California do not have a current survey on file — especially smaller county roads and streets where speed limits were last resurveyed a decade ago.