If you want to understand how radar works, a good place to start is watching a two-year-old scream in a tunnel.
In my town, there is a playground where I like to take my two-year-old son. In order to get to the playground, you have to take a short path alongside a creek and then through a long tunnel that goes under a highway. My son loves that tunnel. Every time we go through it he lets out a series of short, yelping screams that echo back to him a moment later. The echo always causes him to laugh, which in turn echoes back to him, which makes him laugh even more. He sometimes experiments with different sounds, altering the pitch and length of his screams to see how the echo reacts.
The lesson to learn from playing around with echoes is this: sound bounces. This is because sound, like electromagnetism, is a series of waves and waves bounce off objects.
This simple fact has revolutionized almost every aspect of life on earth. Because we understand how electromagnetic waves work, we’ve harnessed radio waves for communication and Wi-Fi; visible light to light our homes and watch movies; infrared waves to control our TVs; gamma rays to fight cancer; and microwaves to, among other things, revolutionize our transportation infrastructure.
Radar’s use of microwaves allows it to see vehicles that would otherwise be obstructed by low light, weather conditions, dust and other obstacles that keep visible light waves out. Understanding the electromagnetic spectrum sets up a basis for understanding how radar is used in the traffic industry, and the reasons why traffic detection systems require an evolved type of radar in order to overcome inherent problems with that technology.
Existence is full of electromagnetic waves. Walk outside on a sunny day and feel the warmth of the sun, enjoy the view – all thanks to the electromagnetic spectrum.
All electromagnetic waves travel at the speed of light, and they all have two properties, determined by their origin and the amount of energy they contain, that alter how we perceive them: wavelength, or the physical distance between the crests of waves; and frequency, or the number of waves that pass a given point per second. The higher the frequency, the shorter the wavelength and the more energy contained within the wave. Wavelength is measured using the metric system, while frequency is measured in Hertz (Hz) – named for Heinrich Hertz, the physicist who proved the existence of electromagnetic waves.
On one end of the electromagnetic wavelength are radio waves, the largest in the spectrum. Radio waves can range in size from around the size of a water bottle to larger than the planet earth. We generally use these waves for communications, like for radio and television stations.
Next in the spectrum are microwaves with wavelengths ranging from around 30 cm to 1 mm. We use microwaves for a variety of applications including heating food in microwave ovens, monitoring weather, mobile phones, and GPS. Because microwaves are able to propagate through dust, clouds, snow and rain, it is very useful for seeing the world beyond typical obstructions. Microwaves are also the basis of radar, which is utilized in the transportation industry for vehicle detection.
Because microwaves are able to propagate through dust, clouds, snow and rain, it is very useful for seeing the world beyond typical obstructions.
Further down the spectrum are infrared waves. These waves, roughly the size of a pin tip, can be sensed by humans as heat. Next comes the visible spectrum of light, which allows humans to see. These wavelengths, roughly the size of bacteria, reflect off of objects and are sensed by our eyes to form light and color. Further down are ultraviolet waves – from 400 to 10 nanometers in length. These waves contain enough energy to cause burns to humans and are the cause of sunburns. Further down are X-Rays, used most notably in the medical profession to see bones and teeth and can be no bigger than individual atoms.
Finally, there are gamma rays, deadly to humans, but used to destroy cancer cells. Gamma rays are no larger than an individual nucleus in an atom – as NASA puts it, they sail through atoms as easily as a comet sails through the solar system. Gamma rays are created through supernovas, nuclear explosions and coronal ejections from our sun as well as the standard nuclear decay of certain types of metals.
Early experiments with electromagnetic waves by the likes of Maurice Ponte, Guglielmo Marconi and Heinrich Hertz proved that these waves not only reflected off of certain objects, but that the nature of these objects could be identified by the nature of the reflection, particularly when it came to microwaves, which formed the basis for radar systems.
The advent of WWII in Britain, and the formation of the Committee for Scientific Survey of Air Defense, saw major advances in the development of radar in spotting airplanes (a technique that contributed to the defeat of the German Luftwaffe) and submarines (the capability that many claimed won the war in the Atlantic).
When the concept of creating intelligent transportation systems came into being roughly 20 years ago, the standard method of detecting vehicles was inductive loops – loops of wire with an electric charge that create a magnetic field that is disrupted by the metal in a passing car. While this method of detection is accurate, it has several drawbacks – it’s installed in the road and is prone to failure as any change in the road surface can disrupt the wires. It’s also difficult, costly and dangerous to install and replace.
In a search for a better way to sense vehicles, video detection was introduced. Video detection installs out of the road, giving a higher level of reliability than loops, but the nature of video, a technology reliant on the visible light portion of the electromagnetic spectrum, proved problematic.
Video systems fail when there is little visible light, such as at night; they also fail if there is too much light, like when the sun is glaring directly into the camera at sunrise or sunset. Because visible light waves are so small, they can be blocked by tiny objects – water droplets in the form of rain or fog, dust, snow, smog and other environmental issues can all limit visibility, and, by definition, the effectiveness of video detection. Even dirty camera lenses can bring effective vehicle detection to a halt.
Recognizing the problems inherent with video, the transportation industry sought alternatives that still offered the benefits of non-intrusive detection. Radar’s microwaves are not dependent on light, so too little or too much light makes no difference. And the wavelength of microwaves is much larger than visible light, so they easily propagate through environmental debris that hinder visible light waves.
But there were some problems with early radar detection systems, due to the fact that these early sensors were unable to maintain a constant bandwidth and a stable frequency. This is how they worked: a transmitter was used to create the actual microwave, and it was controlled by a voltage-controlled oscillator (VCO) that formed and maintained the necessary bandwidth. This process is known as an analog signal, and all wavelengths created by a transmitter in this way are subject to some fluctuation – called jitter or signal noise – that the VCO is designed to help reduce. However, there are some causes of jitter that VCOs were unable to account for, such as changes in temperature that can affect the reliability of various components in the transmitter and VCO. This caused fluctuations in the bandwidth that, over time, grew more pronounced.
The inability to maintain a constant frequency meant, first, that the sensors ability to perform accurately was diminished; and second, it was prone to drifting out of the frequency they were legally required to maintain. Electromagnetic spectrum frequencies are regulated by government agencies like the Federal Communications Commission, which regulates frequencies from 8.3 kHz – used for meteorological applications – all the way to 275 GHz – used for earth-to-space transmissions. Radar operators – including traffic sensors – have to register to use a particular frequency and then must stay there. Early radar sensors struggled to maintain a constant frequency because changes in time and temperature altered the sensors’ frequencies enough to require constant reconfiguration and calibration.
Of course, there were other issues when it came to using radar for traffic detection. Most early radar sensors operated in the low 45 MHz bandwidth, which was unable to provide reliable detection. At 45 MHz, radar returns are unfocused, meaning it’s often impossible to tell where the detected object is in relation to the unit. In traffic detection, this makes it difficult to assign a vehicle to a specific lane, leading to inaccurate per lane data; vehicles can also be blurred into a single detection, thus making count data inaccurate. Additionally, early radar sensors were unable to detect stopped vehicles, which is less of a problem on freeways or mainlines but makes them difficult to use at intersections where detecting stopped vehicles is important. Finally, early radar sensors were unable to provide speed and direction of travel information without utilizing multiple sensors.
Wavetronix took the concept of radar detection to the next level, creating radar detection devices that provide the benefits of non-intrusive design while incorporating important innovations – digital process, high definition and multi-beam radars – in order to overcome the limitations of existing radar sensors.
Perhaps the biggest change Wavetronix brought to the radar detection landscape is the creation of Digital Wave Radar. Unlike analog signals, Wavetronix’ patented process utilizes a quartz crystal-controlled digital clock (similar to the technology used to keep quartz timepieces accurate) to maintain a continuous and constant wavelength and frequency. By constantly monitoring the digital signal from the synthesizer, it’s able to maintain this consistency, resulting in a constant, accurate signal that stay within its assigned frequency.
In addition to operating in the proper frequency, Digital Wave Radar made the second innovation possible – high-definition radar with five times the resolution of previous sensors. Wavetronix’ high-definition sensors operate at the 245 MHz frequency, compared to the 45 MHz offered by other sensors. This higher frequency provides higher resolution because the microwaves can travel further and return clearer results. Higher bandwidths are more narrowly focused and can sense traffic clearly across an entire freeway; lower bandwidths return hazy results after just a few lanes. With true high definition radar, Wavetronix sensors are able to provide more distinct per vehicle detections for more accurate data.
Wavetronix created solutions to the other drawbacks of radar detection by adding more radar arrays to its sensors. With SmartSensor HD, the device used for freeway and arterial detection, dual radar beams are used to create a speed trap. By timing how long it takes for a vehicle to travel from one beam to the other, speed and direction of travel can be derived.
For intersection detection, Wavetronix added even more radar arrays. SmartSensor Matrix uses 16 radar beams to create a 90-degree field of view at the stop bar. With multiple beams, Matrix can create a two-dimensional image of the intersection stop bar and the approach that sees all vehicles, moving or stopped. This true presence detection helps make intersections operate more efficiently.
Ultimately, radar is simple to understand. You send microwaves out, they reflect off objects, and you pick up the reflection to see what is out there. The adoption of radar detection in much of the traffic industry is proof that they are the gold standard for vehicle detection, so long as they maintain a consistently high frequency and are able to utilize multiple radar beams.
After proving radar can be the best choice for vehicle detection in ITS applications, Wavetronix continues to work to improve and innovate within the radar detection industry.
