Remember that RADAR is an acronym for [RA]dio [D]etection [A]nd [R]anging. The detection part is important, it involves signal to noise ratio, information discrimination, directionality and polarization.
Antennas and their mounts are usually conductive, so is the aircraft, vehicle or structure. To make sure that the radio waves are received from known directions, which are clear and precisely known without being “smeared around” care is taken in how and where the antenna is placed with conductive items nearby.
A Radar on a vehicle has perhaps the windshield surround, the hood, dashboard and the mount itself nearby. Without validation by putting a vehicle in an anechoic chamber like the one above with the Typhoon aircraft and testing the direction of the radio waves then no one knows with any confidence where the radar is pointing.
The antenna radiation pattern above shows an example where the radio signal direction is “smeared around” just by having a simple conductive metal plate nearby.
The pattern and smearing is likely much more complicated and the direction much less likely to be in the desired direction with a windshield, hood, dash and mounting as you will find in vehicle mounted radar that have not been tested in an anechoic chamber.
Has the vehicle and the mounted radar been tested in an anechoic chamber?