What Is Millimeter Wave Technology?

Millimeter wave (mmWave) technology operates in the frequency band from 30 gigahertz to 300 gigahertz, where free-space wavelengths range from ten millimeters to one millimeter. This spectral region offers large swaths of unused or lightly used spectrum, enabling data rates and radar resolutions that are unattainable at lower frequencies. Signal propagation at mmWave frequencies is characterized by higher free-space path loss and greater sensitivity to atmospheric absorption, particularly near the 60 GHz oxygen absorption peak and 183 GHz water vapor line, which shapes both the challenges and the opportunities of practical deployment.

Circuit Technologies for mmWave

Building efficient circuits at millimeter-wave frequencies requires transistors with high transit frequencies and maximum oscillation frequencies. Indium phosphide and gallium arsenide high-electron-mobility transistors have historically led in noise figure and gain, but silicon-based technologies including SiGe BiCMOS and advanced CMOS processes at 22 nanometer nodes and below have closed the gap sufficiently to enable cost-effective consumer products. Silicon millimeter-wave integrated circuits in 28 GHz and 39 GHz bands now achieve output powers and noise figures competitive with III-V solutions for base station and handset applications.

Millimeter-wave circuits use transmission lines and waveguides scaled to millimeter and sub-millimeter dimensions. Rectangular waveguide remains the medium of choice for low-loss interconnects and high-power feeds, while substrate-integrated waveguide and grounded coplanar waveguide allow planar integration at the cost of somewhat higher loss. Packaging is a critical challenge: bond-wire and flip-chip interconnects that are acceptable at microwave frequencies become significant impedance discontinuities at 60 GHz and above, motivating wafer-level packaging and antenna-in-package approaches.

5G mmWave Communications

The 5G New Radio standard defines mmWave operation in frequency range 2 (FR2), initially spanning 24.25 to 52.6 GHz, with further extensions anticipated in the upper FR2 and 60 GHz bands. The large available bandwidth, up to 400 MHz per carrier in FR2, supports peak downlink rates exceeding 10 gigabits per second in ideal conditions. 5G mmWave beam management is one of the key protocol innovations enabling this: the base station and device continuously search, select, and maintain directional beams to compensate for the short propagation range and susceptibility to blockage by the human body, foliage, and building materials.

Dense deployments of small cells with active phased-array antennas, often mounted on street furniture or building facades, are needed to deliver coverage in urban areas. The high penetration loss of mmWave signals through walls means outdoor-to-indoor coverage requires dedicated in-building systems, which in turn creates demand for mmWave repeaters and reconfigurable intelligent surfaces that redirect signals around obstructions.

Millimeter-Wave Imaging Radar

Radar operating at 76 to 81 GHz achieves range resolutions below five centimeters and can resolve point targets separated by a few degrees in angle, enabling detailed sensing of the environment around a vehicle. Automotive imaging radar at 77 GHz uses frequency-modulated continuous-wave waveforms and multiple-input multiple-output antenna configurations to generate three-dimensional point clouds of surrounding objects, providing a low-cost complement to lidar for autonomous driving perception. Security screening systems at airport checkpoints use 70 to 80 GHz imaging to detect concealed objects beneath clothing without ionizing radiation.

Applications

• 5G cellular: FR2 base stations and user equipment deliver gigabit wireless connectivity in dense urban environments using phased-array beamforming.
• Automotive radar: 77 GHz radar sensors provide adaptive cruise control, emergency braking, lane-change assistance, and parking automation in passenger vehicles.
• Security imaging: Millimeter-wave portal scanners reveal concealed weapons and contraband on the human body in airports, courthouses, and correctional facilities.
• Satellite broadband: V-band (40-75 GHz) and E-band (71-86 GHz) feeder links connect satellite gateways to space segment with multi-gigabit capacity.
• High-rate wireless backhaul: E-band point-to-point links replace fiber for last-mile backhaul between cellular base stations and the core network.
• Non-destructive testing: Millimeter-wave reflectometry and tomography detect subsurface voids, delaminations, and moisture in composite structures and road pavements.