Andy writes: Yes. The antennae used by Amtech are similar.
Obviously, the beamwidths are much wider for these antennae.
The TIRIS antennae are used to provide a much narrower beam so that lane discrimination can be done without using buried loops, lasers, etc.
To do this, they required a much narrower beamwidth, so that only one lane can be illuminated at a time. See CALTRAN Title 21 -- you can probably call it up with google, if you are interested in the requirements.
SunPass is a much simpler system. It probably works very well , as there are several other items which work in conjunction with it to determine presence of vehicle, multiple cars, multiple lanes, etc.
The TIRIS system that I built had to do all this stuff without the auxiliary stuff, so different specification were required..... If memory serves me correctly, TIRIS had to read with 99.9% accuracy in bumper to bumper cars at about 150 mph , in multiple lanes without any lane dividers or other separators. While that condition will never happen, that what the spec was........
It was tested at a race track somewhere in southwest Texas using race drivers and cars and did what it was supposed to...... That was back around 1991......... the good old days.....
A damn fun project....
Andy W4OAH