Flow Measurement

Radar Level Transmitter

What is Radar Level Transmitter?

Radar Level Transmitter are instruments that utilizes radio waves to measure the distance between the sensor and the surface of liquid or solid. Two main types of Radar Level Transmitter are Non contact FMCW (Frequency Modulated Continuous Wave) and Pulse Radar level transmitter. Both types of radar level transmitter are not affected by pressure, temperature, and dust. Therefore both are widely used in solid and liquid level measurement.

Working Principles

FMCW (Frequency Modulated Continuous Wave) Radar

FMCW radar works by emitting a signal which is reflected off the target object and received by the radar.The signal emitted is at a high frequency with frequency sweep (frequency increases linearly during the measurement phase,). The signal emitted is reflected off the measuring surface and received with a time delay.

Frequency difference Δf is calculated from the actual transmit frequency and the receive frequency. The difference is directly proportional to the distance. A large frequency difference corresponds to a large distance and vice versa.

The frequency difference Δf is transformed via a Fourier transformation (FFT) into a frequency spectrum and then the distance is calculated from the spectrum. The level results from the difference between tank height and measuring distance.

The frequency difference that is processed by Fast Fourier Transformation (FFT) to identify the signal in Inter-medium Frequency (IF). This FMCW radar is innate with signal / noise enhancement and filtering of echo-back via Phase-Lock Loop (PLL) circuit that is the best solution for complex environment and high accuracy measurement.

Source: “FMCW Radar Level Transmitter Working Principle.”  Inst Tool, S Bharadwaj Reddy, https://instrumentationtools.com/fmcw-radar-level-transmitter-working-principle/

Pulse Radar

Pulse radar emits short and powerful pulses and in the silent period receives the echo signals. In contrast to the continuous wave radar, the transmitter is turned off before the measurement is finished.

The extremely narrow microwave pulse emitted by the antenna of the radar level transmitter can travel at the speed of light and part of its energy, which is reflected off the surface of the target medium, is received again by the same antenna. The time lapse between pulse emission and reception by the antenna is proportional to the distance between the surface of the target medium and the reference point on the antenna.

However, as the electromagnetic wave is transmitted at extremely high speed, which leads to a short time lapse (nanosecond level) making it difficult to be detected, radar level transmitters have adopted a special demodulation technology, enabling accurate detection of the time lapse between pulse emission and reception, thus generating accurate measurement results.

Level Measurement (Liquids)

rd780 76-81ghz radar level measurement

RD780 (76-81GHz)

FMCW With Narrow Beam Angle
Up to 30m


Up to 10m
HART Available

RD800 radar level transmitter exia 30 meter range


Up to 30m
HART Available


Flood Monitoring
IP68 Rating
up to 30m

Level Measurement (Solids)

RD980 (76-81GHz)

FMCW With Narrow Beam Angle
Up to 120m


Up to 80m
HART Available