Millimeter waves (MMW) are extremely high-frequency electromagnetic waves in the 30GHz to 300 GHz frequency (10mm -1mm wavelength) range. Lying between the microwaves and the infrared waves, millimeter waves have the potential to provide a solution to the growing demand for bandwidth and high-speed communication needs.
Over the last few decades, affordable technologies have enabled more widespread use of the millimeter waves. This has resulted in the expansion of wireless communications and fast data applications while easing the pressure on the lower frequencies.
With data rates reaching 10Gbps, some of the possible applications include high-speed point-to-point WLANS and broadband access, mobile and wireless networks, streaming high-resolution video, automotive radar solutions, and more.
Advantages and Challenges
The demand for bandwidth has continued to grow over the last few decades, largely due to an increased use and number of communication devices. However, meeting these global communications needs and the requirement for high-speed wireless data transfers has been a challenge due to the limited spectrum (though plenty of that hype has been overblown in the past).
Most applications have been restricted to frequencies of up to 30 GHz. This range is currently congested, hence limiting development of newer technologies. The good news is that the millimeter wave’s spectrum, which was previously reserved for the military and scientific applications, is slowly becoming available for consumer and commercial applications.
This has the potential to ease the demand for the lower frequencies and allowing expansion of frequency-dependent technologies and applications.
Beyond the controlled allocation of the frequencies in the 30 - 300GHz range, in the past, there haven't been many components that work at high frequencies. Now, however, there are more manufacturers who are producing components that can handle millimeter waves.
Manufacturers are now developing affordable components that are increasingly making the millimeter waves practical in a variety of applications. New technologies and semiconductor materials such as indium phosphide (InP), gallium nitride (GaN), gallium arsenide (GaAs) are making it possible to build components like transistors at the submicron size of about 40nm or smaller.
Miniaturized Silicon Radars 120GHz radar. Image courtesy of SEMICON Europa
Here are some lightning-round, hypothetical advantages and challenges associated with millimeter wave technology:
Advantages of Millimeter Waves
- Large bandwidth: The large bandwidth translates to better data transfer rates, attaining speeds of about 10Gbps or more compared to the 1Gbit/s limit when using the microwave frequencies. This makes high-quality video streaming, real-time gaming, and other bandwidth intensive applications a reality.
- Small components sizes: The components and antennas for the higher millimeter wavelengths are usually very small compared to those for lower frequencies. This makes it possible to design physically smaller circuitry and equipment. For example, a half-wave dipole operating at a 900MHz cellular frequency is about six inches long but this would reduce to 2.5 mm at 60GHz in free space or less if on a dielectric substrate. As such, it is possible to make very small and lightweight radio equipment comprising the radio and antenna or build multiple elements phased arrays on a chip.
- Greater resolutions: The narrow beam could allow the ability to achieve greater resolutions.
- Low interference and increased security: The narrow beam and short range can be a benefit since there is less interference from nearby radios. In addition, it is much harder to intercept the signals and there is also increased security since the signal is only restricted to a small area.
Challenges in Using Millimeter Waves
- Limited range: The millimeter waves, due to the short wavelength, have a short transmission range of about 10 meters for most low power applications. However, the range is extended by using high transmit power and antenna gains, and receivers with high sensitivity. In addition, the short wavelengths of between 10 and 1 millimeter suffer high atmospheric attenuation; with fog, rain and moisture attenuating the waves the highest, and shortening the transmission distances. All these factors reduce the possible range to about one kilometer. Sometimes, designers may use high-gain antenna arrays to boost the effective radiated power and increase the transmission range.
- Requires line of sight: Physical objects such as trees and buildings will block the waves, leading to weak wave signals and a reduced range.
- Costly components: Manufacturing the small components requires more precision and care, hence increasing costs.
Commercial Applications of Millimeter Waves
The three main characteristics that influence the use of the MMW are its wide bandwidth, short wavelengths, and how it interacts with the atmosphere. These may translate to either advantages or disadvantages depending on the target application.
The millimeter waves are used in astronomy, medicine, and meteorology, as well as communications. Millimeter waves with frequencies in the license range 71-76, 81-86, and 92 to 95 GHz are usually used for the high bandwidth, point-to-point communication links while the 60 GHz frequency is used for the unlicensed short-range data links such as the Wireless Gigabit (WiGig), based on the standard 802.11ad protocol.
High-Definition (HD) Video Applications
The ability to transmit huge amounts of data at high data rates makes the MMW favorable for the transmission of high-definition (HD) video which requires several gigabits per seconds. The MMW provides a superior alternative since it retains the video quality unlike the alternative method of first compressing the data and then transmitting at Mbits/ rate range.
Typical applications include transmitting video from a set-top-box, tablet, or laptop to an HDTV, from a game or DVD player to a TV set. Other applications include wireless video cameras, wireless HD projectors, etc.
IEEE 802.11ad WiGig Technology
The WiGig (wireless Gigabit) technology enables devices to communicate at high data rates of up to 7 or 8Gb/S. The short range communication standard is based on the 60GHz spectrum, but can but has a limited distance of about 10 meters. One advantage of the WiGig is the high data transmission rates with little latencies. The WiGig devices can be used in conjunction with antenna arrays to provide dynamic beamforming. For now, there's only a handful of Wi-Fi certified WiGig products, but its proponents hope to expand that list over the coming months and years.
Single-Chip Radar ICs for Communication and Automotive Radar Solutions
Advanced semiconductor technology now allows packaging MMW circuits into an integrated circuit. This makes it possible to develop single-chip circuits for a variety of applications.
For example, a chip designed for smartphone and tablet applications comprises of an embedded antenna array, a 60 GHz RF transceiver, and a baseband processor. This allows wireless transmission of high definition video between devices and large display screens.
The fine resolutions of millimeter wave radars make them ideal for detecting small movements and objects, allowing them to determine a position with a millimeter precision. The millimeter radars in the 76 to 81 GHz range are widely used in vehicle control and safety devices. The specific applications include sensors for automatic braking, lane intrusion, applications blind spot detection, forward collision detection, cruise control, and more. A typical automotive radar chipset is the PRDTX11101 from Freescale Semiconductor. The radar chipset has a detection range of between 20 and 200 meters and customizable to perform various automotive applications.
Passenger detection using a millimeter-wave radar and a camera. Image courtesy of Toyota.
Human Body Scanners
The millimeter waves are used in body scanners in airports and other installations. The scanners provide an outline of the human’s body and will reveal any hidden object. Initially, there were major concerns in regard to safety and privacy. These have been addressed by using low power waves that only gets an outline of the body as opposed to performing a whole-body imaging.
Currently, the TSA uses millimeter wave scanners in most US airports to assess threats, stating that it has "no known adverse health effects".
Millimeter Wave Therapy
Millimeter waves in the frequency range of between 40 and 70GHz, or the 7.5 - 4.3 mm wavelength are used in a wide variety of medical processes to treat various diseases and to treat pain. The therapy is known as Millimeter Wave Therapy, (MMW therapy), or extremely high frequency (EHF) therapy.
Wireless Data Communication in Virtual Reality Headsets
Researchers such as MIT are even working on a technology that will use millimeter waves to wirelessly transmit high-quality video to the VR headsets, hence eliminating the need for wires. Currently, high video quality Virtual Reality headsets are tethered to fast computers. This restricts the user movement to the length of the cables to the computer. Enabling wireless connectivity will improve user experience without decreasing the video quality.
Millimeter waves can open up a large spectrum for a wide range of applications, hence easing pressure on the already congested 0-30 GHz spectrum.
Regulations and lack of affordable components that could produce and receive millimeter waves were at one time a challenge that limited the use of the spectrum. However, designers and manufacturers have now made significant progress in developing affordable semiconductor devices for commercial high-speed communications and other millimeter wave applications.