Millimeter Wave Sensors: Basics, Features, and Manufacturers

This application note covers the fundamentals of millimeter wave sensors, including the features of millimeter wave radar sensors from Texas Instruments (TI), key manufacturers and vendors, and the advantages they offer.

Introduction

A millimeter wave sensor operates within the millimeter wave frequency band, ranging from 30 GHz to 300 GHz. These sensors are broadly categorized into two types: active and passive.

• Active Sensors: These sensors emit their own electromagnetic (EM) waves and receive the reflected waves from the object being measured. Examples include communication satellites and radar systems.
• Passive Sensors: These sensors simply receive EM energy within their field of view and perform measurements based on the received energy. Examples include remote sensing satellites and passive motion sensors.

Millimeter wave radar sensors fall under the active sensor category.

Millimeter Wave Radar Sensor: How it Works

As shown in the figure below, a millimeter wave radar sensor comprises a transmitter and a receiver.

Millimeter wave radar sensor (Image courtesy: Texas Instruments Incorporated)

The transmitter uses a synthesizer module to emit an EM signal at its operational frequency and then receives the reflected echo from the target object. Radars often use a special type of signal called a chirp signal. The receiver antenna picks up the reflected echo. This received signal is then downconverted using an RF mixer, which is fed by an appropriate Local Oscillator (LO) frequency. After downconversion, the analog Intermediate Frequency (IF) signal is low-pass filtered and converted into a digital signal. Digital signal processing is then applied to the received digital signal for further analysis.

The transmitter can employ different types of waveforms, such as pulsed, Frequency Shift Keying (FSK), Continuous Wave (CW), and Frequency Modulated Continuous Waveform (FMCW). Texas Instruments’ mmwave sensors utilize FMCW for their operation.

TI Millimeter Wave Radar Sensors

Texas Instruments has developed two main families of mmwave sensors:

• AWR Family: Primarily used for automotive applications.
• IWR Family: Designed for industrial, drone, and medical applications.

These sensors can:

• Determine the distance or range to an object and provide range resolution to distinguish between multiple objects.
• Measure velocity by transmitting two chirp signals separated by a time interval ($T_c$) and measuring the phase difference between the received echoes.
• Estimate the angle of arrival (AoA) by measuring the angle of the reflected signal with respect to the horizontal plane.

Features of the TI IWR1642 Single-Chip Millimeter Wave Radar Sensor

The IWR1642 from Texas Instruments offers the following features:

• Frequency of Operation: 76 GHz to 81 GHz with 4 GHz continuous bandwidth.
• Number of Channels: 4 receive channels, 2 transmit channels.
• Transmit Power: 12.5 dBm.
• Receiver Noise Figure: 15 dB (77 to 81 GHz).
• Phase Noise at 1 MHz: -93 dBc/Hz (77 to 81 GHz).
• Other Peripherals: 6 ADC channels, 2 SPI channels, 3 UARTs, CAN, I2C, GPIOs, 2-lane LVDS, etc.

Millimeter Wave Sensor Manufacturers and Vendors

The following table lists some key manufacturers and vendors of millimeter wave sensors:

Benefits and Advantages of Millimeter Wave Sensors

Millimeter wave sensors utilize millimeter wave frequencies, resulting in very short wavelengths in the EM spectrum. This leads to several benefits:

• Penetration: Ability to penetrate various materials, including drywall, plastic, and clothing.
• Focusing and Steering: mmwaves can be focused and steered using optical techniques, similar to light signals.
• Directionality: Highly directional with an angular accuracy of approximately 1 degree.
• Resolution: Due to large absolute bandwidths, mmwave sensors can distinguish between very closely spaced objects.

For more detailed information, refer to advantages and disadvantages of millimeter wave radar.