R1D narrow beam distance sensor: Technology

Radio waves detect, locate, and track objects

Radar, which stands for Radio Detection and Ranging, is a technology using radio waves to detect, locate, and track objects. It has a wide range of applications, including aviation, meteorology, maritime navigation, traffic control and object detection in the industrial world. The basic principle behind radar involves the transmission of radio frequency (RF) signals and the reception of their reflections from objects in the environment.

A radar sensor consists of a transmitter that emits electromagnetic waves in the microwave frequency range. The emitted radio waves travel through the air at the speed of light. When the waves come across an object in their path, some of the energy is reflected back to the receiver of the sensor and processed by the microprocessor and distance is calculated.

ifm radar sensors transmit RF waves in the microwave frequency range

Distance is proportional to the frequency change between transmitted and received signals

FMCW technology measures distance and velocity

ifm’s radar position sensor utilizes FMCW (Frequency Modulated Continuous Wave) technology to measure distance and velocity of one or multiple objects. The sensor continuously transmits a signal with a frequency that varies linearly over time. The modulation allows the radar sensor to achieve better range resolution, accuracy and sensitivity compared to other technologies.

The range to the target is determined by analyzing the frequency difference between the transmitted and received signals. This frequency difference is related to the round-trip time of the signal and can be used to calculate the distance to the target(s).

Doppler effect allows radar to determine velocity

Radar can also make use of the Doppler effect to determine the velocity of the target. RF signals are transmitted by the sensor and are reflected back to the sensor after hitting a target. If the target is moving toward or away from the sensor, the frequency of the reflected waves change, increasing if the target is moving toward the sensor and decreasing if the target is moving away from the sensor.

This shift in frequency is detected and measured by the sensor and it is directly proportional to the speed of the target. The greater the shift, the faster the target is moving.

Reflected frequency changes as an object is moving toward or away from the sensor

RCS as a function of distance and target

Radar cross-section (RCS)

The radar cross-section (RCS), also known as radar signature, is a measure of how well an object is detectable by radar. RCS is a measure of reflective characteristics of an object when irradiated by radar waves.

• Effective area that a target reflects signals back to the sensor
• Often expressed in m²
• Highly dependant on frequency of the radar waves
• Object shape and geometry have an influence. Flat and angled surfaces tend to have larger RCS than round surfaces
• Object material and coating have an influence

As a general rule of thumb, the higher the dielectric constant and the larger the object size, the higher the RCS and, therefore, the better the visibility to a radar sensor.

Ground speed measurement

To measure the relative speed between the sensor and the ground, the sensor must be mounted at an optimized angle. The radar sensor measures the frequency shift of the radar waves as they reflect off the ground. If the sensor is pointed directly down at the ground, the Doppler shift might be too small to be detected. The angle ensures that the radar waves are more effectively interacting with the moving surface, resulting in a measurable Doppler shift.