Valentine Research, Inc. holds several patents related to radar detection. The one in question here about two antennae is US Patent 5083129, which expires this month. The abstract:
A police radar detector detects both the presence of radar signals incident upon a motor vehicle using the detector and also determines the direction of origin of the source of detected radar signals and signals the operator of the motor vehicle of the presence and source direction of the radar signals. Preferably, the radar detector includes two antennas with shared circuitry in a single housing. One of the antennas is directed generally toward the front of the motor vehicle and the other antenna is directed generally to the rear of the motor vehicle. As the police speed radar frequency bands are scanned or swept, each potential radar signal which is detected is processed to determine the direction of origin of the signals. To determine the direction of origin of incident radar signals, the signals are detected in both antennas with the signal strengths in the two antennas being compared to determine the direction of origin of the signals. It is preferred to identify the direction of the radar source as being to the front of the vehicle, to the rear of the vehicle or to the side of the vehicle. Empirically determined tables assist in the determination of thresholds for use in the detector to determine direction of the source of detected radar signals.
It says, "Preferably, ... in a single housing." I'm no patent lawyer but I have a few patents to my name so I know a little about this. I can tell you that this does not exclude external antenna for Mr. Valentine so K40 does not have exclusive use of this. I've searched but cannot find the K40Electronics patent for multiple antennae. Could you please point me in the right direction to it. I'm kind of surprised they have this kind of patent.
P.S. Perhaps K40 Electonics goes by another name for their detector patents. Would you happen to know what this name is? A "Communication system for vehicles" patent is the only patent listed for K40 Electronics. It has nothing to do with multiple radar antennae but with wireless communication of sensors to annunciation devices.