Radar sensors

01

Choose what the radar must measure and how finely

Texas Instruments' white paper explains that radar systems transmit electromagnetic waves that objects reflect, and by capturing the reflected signal determine the range, velocity and angle of the objects. Its mmWave devices use frequency-modulated continuous wave (FMCW) operation: the transmitted chirp rises in frequency linearly with time, characterised by start frequency, bandwidth and duration — its example uses 77 GHz, 4 GHz and 40 µs. Range resolution, the ability to separate two nearby objects, depends only on the bandwidth swept by the chirp, so a chirp bandwidth of 4 GHz gives 3.75 cm. Velocity resolution is inversely proportional to frame time, and at least two receive antennas are needed to estimate angle of arrival; antennas spaced half a wavelength apart give the widest field of view, ±90°. [1]

The paper adds that the short wavelength — about 4 mm at 76–81 GHz — keeps antennas small and lets the radar detect movements as small as a fraction of a millimetre, and that TI's industrial range covers 76–81 GHz and 60–64 GHz single-chip sensors with on-chip processing for object tracking and classification. [1]

Editorial calculation: using the same relation (resolution = speed of light ÷ twice the bandwidth), a sensor confined to the 100 MHz-wide 24.075–24.175 GHz band could separate targets no closer than about 1.5 m, compared with 3.75 cm for a 4 GHz chirp — which is why simple 24 GHz sensors suit motion detection while fine distance work uses wider mmWave bands. [1] [2]

A 60 GHz part shows what a presence and gesture sensor chip states. Infineon's product page for the XENSIV BGT60TR13C lists a 58–63.5 GHz frequency range, one transmit and three receive antennas in package in an L-shaped array (giving angle of arrival), 5 dBi antenna gain, a 90° half-power field of view, detection from 0.2 m to 15 m, a chirp ramp speed of 400 MHz/µs and bandwidth above 5 GHz. It runs from 1.8 V at 200 mA current consumption, is qualified to industrial JEDEC20/22 for −20 to +70 °C, comes in a 6.5 × 5.0 × 0.9 mm package, and Infineon states under 5 mW with duty cycling according to a released FCC waiver. Its listed uses include presence detection, people counting and tracking, sleep and heart monitoring, and smartphone gestures. [4]

Editorial calculation: using Texas Instruments' relation that range resolution is c ÷ 2B, the 5.5 GHz span from 58 to 63.5 GHz gives about 3 × 10⁸ ÷ (2 × 5.5 × 10⁹) ≈ 2.7 cm, finer than the 3.75 cm TI gives for 4 GHz; at 400 MHz/µs a full 5.5 GHz sweep takes about 13.75 µs. Whether a module reaches this depends on the chirp it is configured for, so ask for the configured bandwidth and chirp time. [1] [4]

Give the supplier the targets (people, vehicles, liquid surface, objects), the task (motion, presence, distance, speed, counting, level), detection range, required range resolution and accuracy, field of view in azimuth and elevation, update rate, the frequency band and the countries of sale, output interface (relay, UART, CAN, RS-485, 4–20 mA, Ethernet), supply voltage and power, operating temperature and IP rating, mounting and housing, certifications, and quantity.

02

Check the radio band and licence rules

Radar sensors are radio transmitters, so the band must be allowed where the sensor is sold. In the United States, 47 CFR 15.245 limits operation in 902–928 MHz, 2435–2465 MHz, 5785–5815 MHz, 10500–10550 MHz and 24075–24175 MHz to field disturbance sensors, excluding perimeter protection systems. It sets field strength of the fundamental at 500 mV/m in the three lower bands and 2,500 mV/m in the 10.5 and 24.1 GHz bands, measured at 3 metres, with harmonic limits, and requires emissions outside the band to be at least 50 dB below the fundamental or within the general limits of 15.209. Sensors for motor vehicles or aircraft must include features to prevent continuous operation unless their restricted-band emissions fully comply; continuous operation is permitted for farm equipment, indoor fork lifts and railway equipment. [2]

Editorial note: other countries apply their own radio rules and frequency bands; ask the supplier which certification and band each model holds for every market in the order.

A 24 GHz module shows what that band allows in practice. RFbeam's K-LC2 is a K-band I/Q Doppler transceiver with a 2 × 4 patch antenna, an asymmetric beam of 80° by 34°, 15 dBm EIRP, a 140 MHz FM sweep input that lets it be used for ranging, dual I/Q channels for direction estimation, and a 25 × 25 mm footprint under 6.5 mm thick, in 5 V and 3.3 V versions; RFbeam now marks both versions as not recommended for new designs. [3]

Editorial calculation: with the 140 MHz sweep, range resolution is about c ÷ 2B = 3 × 10⁸ ÷ (2 × 140 × 10⁶) ≈ 1.07 m, against 3.75 cm for a 4 GHz-wide 77 GHz chirp; also check a part's lifecycle status before designing it in. [3] [1]

03

Compare what suppliers offer

Suppliers linked to this page list radar or microwave sensors; each card links to the page reviewed.

Listings include a radar level sensor offered alongside magnetostrictive level gauges, a microwave sensor for door release in access control, and a 360° microwave sensor; ask each for the band, detection range, resolution, field of view and radio certification.

04

Trace the radar signal chain

This is a functional reference built from the sources cited; it is not one maker's design.

05

Fill the specification fields with values for your project

A radar sensor quotation needs values for your project. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the target, task and markets together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Target: [people; vehicles; liquid; objects]
Task: [motion; presence; distance; speed; level]
Range: [max; resolution; accuracy]
Coverage: [azimuth; elevation; update rate]
Radio: [band; countries of sale; certification]
Interface: [relay; UART; CAN; RS-485; 4–20 mA]
Site: [temperature; IP; mounting]
Quantity: [units]

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