Antenna & Sticker Placement

The angle between sticker and antenna makes all the difference when installing vehicular RFID. Here is how you can achieve great RFID connectivity through optimal placement.

Before understanding the role of positioning in an RFID system, it helps to know exactly how the system works.

The antenna emits passive energy in a particular direction. When a passive tag (e.g. HeadlightSticker™) receives this energy, it stores this power to power up its chip. Once enough power is stored, the sticker transmits its signal forward.

This whole process takes a fraction of a second and repeats continually as long as the antenna can power the sticker.

This process is directional. This means that the tag and reader must face each other. The more they face each other, the better the read.

Think of it like shining a flashlight at a mirror: your antenna is the flashlight, and the sticker is the mirror. You need the mirror to point in such a way that the light is reflected back at the reader.

It may help to think of it as RF energy “bouncing” off the sticker. (although strictly speaking this is not exactly how it works.) If the energy bounced off the sticker, where would it go? Will most of it bounce back towards the reader, or will it simply bounce up into the sky?

The most intuitive way to remember this is to use the Rule of Thumb.

Because the antenna and sticker want to be parallel, it is generally recommended that you pick one standard and stick with it. If you try to get both form factors with the same antenna, you will reduce performance and consistency for the entire system.

A low mounted reader will have trouble with most windshield tags. A high mounted reader will have trouble with many headlight tags.

Instead of implementing a hybrid system with both headlight and windshield tags, you should pick a single standard. If a hybrid system is necessary, we recommend using two antennas. (The Plug&Go Reader™ can support two antennas running simultaneously.)

HeadlightStickers™ work well with a low mounted reader, mostly level and parallel with the approaching headlights. Windshield RFID requires high mounted readers (often directly over the driver’s lane for best results.) Again, as with all RFID, the goal is to have a face-to-face conversation between the tag and antenna.

Overhead mounting for windshield tags has been the go-to solution for most vehicular RFID implementations. Unfortunately, there are several drawbacks with high mount points:

1. Readers mounted directly overhead reduce maximum vertical clearance.
2. High mount points require a sturdy base, which requires heavy duty poles and pouring concrete.
3. Aesthetically speaking, high mounted readers call attention to themselves.

Furthermore, there are two major flaws with windshield mounted RFID:

1. Metallized windshields interfere with RF signals and are increasingly common.
2. Windshields significantly vary in height and angle. An angle that works for a standard sedan may fail on a higher SUV with a more vertical facing windshield.

Because of the variance in windshield angles, face to face reading is far easier to achieve with a headlight mounted RFID tag than on a windshield.

Simply put, Headlight shape is far more consistent than windshield shape, and headlight RFID completely avoids the conflict with metallized windshields.

With that said, headlights are still three dimensional.
When installing a HeadlightSticker™ one must account for the location of the reader.

So before HeadlightSticker™ placement, ask yourself these questions:

1. Where is the antenna?
2. During the vehicle’s approach, where will the antenna and sticker best interface?

The major requirements of sticker placement are that they be placed horizontally, and that they be 2″ or further from the car’s metal body. As long as those conditions are satisfied, your top consideration should be ensuring that the sticker is in a place where it will interface with the reader at your ideal range.

The HeadlightSticker™ system is considerably more consistent and leads to a marked improvement in overall success rates compared to windshield stickers.

The angle between the sticker and antenna makes up 95% of your experience. We have accounted for most of the other usual RFID variables (wireless interference, antenna settings, etc.) by designing the Plug&Go Reader™ to automatically adjust antenna settings on the fly. The only major variable left is where the sticker goes.

The variance in headlight shape and sticker placement accounts for variable experiences. A Jeep with relatively flat headlights and a well placed sticker may open the gate from 40+ feet away. A sleek Corvette with steeply angled headlights and a poorly placed sticker may not read until it is right in front of the gate. To some extent, that’s going to happen. No system is perfect.

But keep in mind that a vehicle with a metallized windshield may never have a successful windshield tag read. With HeadlightStickers, every vehicle has a solid chance. If you properly install a HeadlightSticker™ and take reader position into account, a successful read is almost a certainty.