Radar tutorial: Distance measurement with radar sensors

The most important tips for the optimal use of radar sensors for distance measurement.

OndoSense radar sensors for distance measurement can be used profitably in many industrial applications. For optimal use of our distance radar sensors, we have summarized the most important practical tips in this tutorial for you. With this, we make sure you achieve the best results quickly with radar technology for distance measurement in your industrial environment!

1. Correctly align radar sensor to target object

If you start operating your radar sensor for the first time, you will see how important it is to correctly align the radar to the target object. Assuming an object is facing the radar with a flat surface, the following applies: The more precisely in the right angle this surface is aligned to the center of the radar beam, the stronger the radar signal.

Radar tip #1

To get a strong signal, align the radar sensor as far as possible at right angles to the target object.

With increasing tilting of the surface or object, the signal strength decreases, as the radar radiation is increasingly not thrown back to the radar sensor. The roughness of the surface also plays an important role: The rougher the surface, the higher the degree of tilting that just allows a stable radar signal.

For smooth surfaces, on the other hand, the maximum possible tilting is lower, because the radar beams are more scattered and reflected in different directions. Radar sensors are therefore better suited to detect objects with very rough surfaces in comparison to laser sensors.

Radar tip #2

The smoother the surface, the more important the correct alignment of the radar sensor.

2. Measuring spot size: Key factor for stable, precise measurements

The measuring spot size of the radar sensor, which depends on the opening angle, has a large influence on the detection of the target object and possible interference reflections, similar to optical systems. A large opening angle leads to a large measuring spot, so that the distance measurement is averaged over a wide range of the measuring object and the distance measurement becomes inaccurate.

A larger radar beam also leads to more interference reflections as well as to a weakened receiving signal at equal transmitting power. The radar sensor is thus less able to distinguish small or distant objects from the background.

Radar tip #3

If possible, reduce the measurement spot size by measuring closer to avoid potential interference reflections.

A small aperture angle leads to a small measuring spot size, which leads to fewer interference reflections, especially for small or far away target objects. This enables reliable distance measurement with strong receiving signals and higher accuracy. At the same time, a small opening angle reduces the maximum tilting rate at which a stable radar signal is possible.

Rada tip #4

Choose a radar sensor with a narrow opening angle to achieve precise and reliable measurement results.

The measuring spot size is an important parameter for distance measurements with radar sensors. With the OndoSense radar spot size calculator, you can calculate the measurement spot size of your radar sensor (depending on the distance from the target object) in just a few clicks! Just select your OndoSense radar sensor or enter the opening angle and lens diameter of your radar sensor.

Radar tip #5

Calculate the measuring spot of your radar sensor for your distance measurements, e. g. with our radar spot size calculator.

3. Radar sensor resolution: Distinguishing objects from each other

The resolution is a crucial parameter of radar sensors. It is of great importance when it comes to the question of the suitability of the sensor for a specific measurement challenge. The resolution indicates at which distance from each other two objects are detected separately by the radar. Only if the radar signals (so called peaks) of these objects can be clearly distinguished from each other, the distance of both objects may be determined.

This is relevant if several objects are located at a similar distance from each other and are detected by the radar sensor. For example:

  1. The objects lie next to each other and are both detected by the opening angle of the radar sensor or covered by the radar spot. In addition, the first object does not completely cover the second object. One possible application is the width measurement of a thin steel strip, which moves on a roller conveyor and is detected laterally by the radar. The distance value to the steel strip can be clearly determined if the distance from the steel strip to the rolling gear corresponds at least to the resolution of the radar sensor.
  2. The objects are in a row. The first object is partially permeable for radar waves, i. e. it is made out of a non-conductive (dielectric) material such as plastic, rubber, cardboard, etc.

Radar tip #6

Pay attention to how many objects your measuring spot covers and which objects are relevant for your measurement.

If the radar sensor cannot detect two or more target objects separately and thus resolve them, then the distance to neither object can be reliably determined. A powerful distance resolution therefore has many advantages and is in some cases necessary.

Radar tip #7

If you want to detect objects that are close to each other, your radar sensor should have a good distance resolution.

4. Averaging of distance value for multiple objects or complex surfaces

In certain cases, the opening angle of the radar sensor detects several objects or structures with a complex surface gradient – e. g. in contrast to a flat surface. If the distance between the reflection points of these objects or structures is smaller than the resolution of the radar sensor, the radar sensor can no longer detect the different distance values. The result is an averaging of the distance values of all detected reflection points.

Radar tip #8

Consider whether your measurement value results from the averaging of the distances of different reflection points in the radar opening angle.

The stronger the reflection at a specific position of the object or surface, the higher the weight of this reflection point in the displayed distance value. If the surface curve of the measuring object is known, the measured distance can be corrected to detect the exact distance value. This is the case with round objects or surfaces, for example. If necessary, OndoSense provides support in the development of an algorithm for correct distance calculation.

Radar tip #9

If you want to capture the distance to complex surfaces with very high precision, you may need to correct the measured distance value

5. Radar penetrates non-conductive materials

Using a radar, it is possible to penetrate non-conducting materials such as plastic, rubber, cardboard, glass, etc., since the radar waves only partially reflect these dielectric materials. On the other hand, when the radar beams encounter metals or continuous water films, they are fully reflected.

Radar tip #10

Radar allows you to measure through non-conductive materials. For more information, take a look at our overview table:

Being able to penetrate certain substances or objects with radar sensors makes sense for a wide range of applications:

Radar sensors can detect the distance to objects behind glass, plastic or other non-conducting materials. At the boundary layer of the dielectric material there is a weak reflection, which also determines the distance to the glass or plastic. However, most of the radar waves radiate unhindered through this material, so that the distance to the target object behind it is detected.

To protect the radar sensor from enormous heat radiation or explosions, glass, heat-resistant plastic or a mica plate can be used. Only a limited amount of the radar signal is reflected, so that the radar sensor detects the distance to the object behind it with high accuracy.

Radar tip #11

Do you need to protect your sensor from great heat? Radar also measures through heat-resistant plastic windows!

6. Radar reflector for amplified radar signals

Radar reflectors are mirror-like retroreflectors that ensure that the radar beams are always thrown back in the direction of the radar sensors regardless of the direction of incidence. Even at a small size, a radar reflector can reflect a relatively high amount of energy due to the large effective reflective surface (also called radar cross section).

Radar reflectors usually consist of three surfaces arranged at right angles. Due to the resulting cube shape, they are also referred to as angle reflectors or corner cubes. The advantage of these three-surface radar reflectors is that the radar beams are accurately reflected back to the radar source even if there is no right angle orientation to the radar.

Radar tip #12

You cannot align your target object right-angled to the radar? Consider using a radar reflector.

With the help of radar reflectors, the precision of distance measurement can be significantly increased. In addition, reliable distance measurements over long distances can be realized, as the radar signal is significantly amplified by the enlarged radar cross-section.

Radar tip #13

Use a radar reflector to increase the stability or precision of your measurement.

Radar tip #14

At long distances, you can significantly increase the range and signal strength of your measurements with a radar reflector.