The evolution of Fifth Generation (5G) communications networks from earlier cellular wireless systems is being realized worldwide. Mobile internet access with voice, video, and data communications is being provided by combining diversified terrestrial and satellite-communications (satcom) equipment. However, despite 5G’s generous bandwidth, it is being consumed quickly by people as well as by devices in the form of streaming apps, the Internet of Things (IoT), sensors, appliances, and more.
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6G Planning Underway
However, before 5G network infrastructure has even been completed, applications are being planned for Sixth Generation (6G) technology. With 5G occupying frequency spectrum below 6 GHz and approaching 72 GHz, 6G will extend towards 1 THz.
For all that 5G wireless networks promise, growing use of sensors for safety, surveillance, and monitoring as part of IoT devices is just one of the ways in which massive amounts of data will be generated. 5G networks will certainly not lack for bandwidth, with systems operating within three distinct frequency ranges (FR) of FR1 (˂6 GHz), FR2 (24.25 to 71.0 GHz), and FR3 (7.125 to 24.250 GHz).
But with a rapidly growing number of IoT devices being added to 5G networks — along with a steadily growing number of human users — pressure will be on 5G networks (even with their enhanced bandwidths) to provide low-latency data transfers as part of security systems, surveillance, and business meetings, as examples.
Typical data transfer latency for 5G networks is about 4 milliseconds, which may seem like an insignificant delay. But for some of the applications projected for 6G networks (such as holographic, three-dimensional (3D) imaging on telephone calls, and remote virtual reality (VR) business meetings), almost zero latency is required for practical, real-time responses.
The transformation of 5G technology into 6G networks, or at least to 5G advanced systems, will require sophisticated use of frequency spectrum encompassing the entire millimeter-wave frequency spectrum (30 to 300 GHz) not previously considered of practical use for any form of commercial communications. Growing use of emerging electronic technologies such as artificial intelligence (AI) and machine learning (ML) will help manage network access points as people and things compete for spectrum.
Make It Mechanical
By employing AI, 6G wireless communications networks will gather sensory data on the operating environment, detecting the reflection of obstacles and instantly mapping optimum propagation paths for high-frequency signals. But getting users’ signals to cells and switching points — whether above ground, underground, or from space —will still require components such as array antennas able to form beams of directed energy that can transfer large amounts of data through crowded airspaces.
Mechanical design and development will contribute to the creation of 5G/6G networks well matched to the operating ecosystem and capable of providing practical, reliable long-term operation. As 5G extends into 6G services through the addition of thousands of low Earth orbit satellites (LEOS) for space-based communications, lightweight components will be needed for ever smaller satellites.
With the increasing density of components and functionality contained on smaller PCBs for LEOS and terrestrial small cells, effective thermal management techniques will be needed to minimize any build-up of heat within small metal enclosures. Also, high-resolution photolithography will be required to realize the fine circuit linewidths supporting the small wavelengths of millimeter-wave signal frequencies.
The choice of antennas and interfacing them to 5G/6G infrastructure is an example where mechanical engineering will play a key role in supporting antenna designers. Antennas for 5G/6G networks will make use of many configurations, including highly directional beamforming devices, omnidirectional antennas, active phased arrays with multiple elements, flexible printed-circuit-board (PCB) antennas for base stations or mobile cellular products, and massive multiple-input, multiple-output (mMIMO) antennas to handle extensive signal traffic at small cells (Fig. 1).
These many different antennas must interconnect with 5G/6G receivers and transmitters and process signals with a diversity of modulation forms across a wide total frequency range, with larger antennas for the “under-6-GHz” portion of 5G/6G networks and smaller antennas for millimeter-wave and higher frequency signals. Precision in the mechanical design of the antennas, especially at millimeter-wave frequencies, is essential for 5G/6G systems, which will require centimeter positioning accuracy for management of billions of manned and unmanned users.
The Design of 5G/6G Antennas
The design of 5G/6G antennas may start with S-parameter data (or simulations) on a commercial computer-aided-design (CAD) software tool (Fig. 2), but physical prototypes of the antennas are mostly likely realized through additive manufacturing methods such as 3D printing (Fig. 3). In this approach, materials are melted at high temperatures and formed into shapes and sizes according to CAD drawings and parameters. This contrasts with traditional subtractive manufacturing methods where material which is not needed is removed by laser or mechanical cutting and drilling.
Many varied materials, including dielectric plastics and conductive metals, can be formed by 3D printing layer upon layer and with great precision, resolution, and repeatability. Specialized 3D printing techniques, such as direct metal printing (DMP), form pure copper and copper alloys into precise circuit shapes. When low-oxygen DMP systems are used, 3D metal parts can be produced with excellent surface finishes for use at millimeter-wave frequencies. In addition, laser direct imaging (LDI) is a technique for applying laser energy to fabricate circuit lines and spacings with better than 25-µm resolution, which is also beneficial for millimeter-wave circuits.
With the expected complexity of 6G systems and design goals for low-latency signal switching for billions of IoT devices, many distinct types of antennas will contribute to 5G/6G signal routing. Radio-frequency identification (RFID) antennas will be components within many electronic devices, marking their roles within the network. For both humans and IoT devices, wearable and implantable antennas will provide measurements of physical quantities, such as humidity, temperature, gas and liquid concentrations, and force.
Energy-harvesting antennas are also expected to be key components within 5G/6G systems to contribute power to the network by conversion of environmental components (such as wind and sunlight) and to be the energy source for what will be termed “zero-energy” components.
Antenna Evolution with Mechanical Design
Antenna technologies continue to evolve as demand for voice, video, and data communications increases. Passive phased-array antennas have long been a solution to achieve the high-energy pulses needed for military radar transmitters by adding the signal powers of many in-phase antenna elements together. The separate elements of a phased-array antenna are designed and fabricated to be in phase with each other, requiring minimal variations in phase for maximum output power.
In contrast, active phased array antennas provide electrical control of the phase and amplitudes of the separate antenna elements to achieve maximum output power when the separate signal components are summed. Beam steering of active antenna arrays continues to develop to where experimental antennas are being designed so that the direction, frequency, and amplitude of the directed beam can be controlled by different software coding formats, such as space-timecoding (STC) software.
Advanced antenna architectures will contribute to low-latency wireless communications in 5G and 6G networks. By switching arrays of active antenna systems, remote radio heads (RRHs) will increase the number of channels possible with smaller cells. With the small signal wavelengths, large numbers of small cells will be needed at higher frequencies to achieve acceptable wireless cellular coverage in areas with large populations and with operating environments containing multiple propagation obstacles.
Antenna performance and functionality will differ according to the antenna’s application within the network. Antennas for mobile robotic IoT devices, for example, will connect to the network within short distances through small cells at millimeter-wave frequency bands but will require omnidirectional radiation patterns for maximum connectivity.
Due to the nature of robotic IoT devices, zero-latency interconnections with 5G/6G networks will be required whether the robots are underground or above ground. Antennas for biomedical and healthcare applications — such as remote real-time patient organ monitoring — may require the wide bandwidths available at millimeter-wave frequencies, but with the highly focused and directed electromagnetic (EM) beams enabled by active array antennas.
In the case of a mobile robotic IoT application, the mechanical attachment of the omnidirectional antenna to the robotic device must meet military requirements for withstanding shock, vibration, and a wide temperature range to ensure dependable communications with the network. For the biomedical antenna, the antenna must be installed with instrument-grade alignment precision to ensure the proper calibration of the directed EM beams.
Electronic design accounts for some beam correction, but mechanical design provides antenna design, installation, and positioning so that it can achieve a “0-deg” starting point. The same type of antenna installation and alignment precision will be essential for the 3D holographic communications expected to be a popular feature of 6G networks.
Integrating Electronic, Mechanical Engineering
Both 5G and 6G networks will feature dense circuitry with high-performance circuit materials supporting printed-circuit boards (PCBs) tightly packed with active and passive electronic devices. Highly integrated mixed-signal devices — such as system-on-chip (SoC) components and system-in-package (SiP) designs — will provide subsystem functionality in package sizes once associated with single-function components (i.e., receivers in packages formerly the size of amplifiers with low-loss materials contributing to effective thermal management with reduced size, weight, and power). Some components, such as antennas, will still be wavelength-related and will operate at millimeter-wave frequencies with the aid of active beamforming techniques. The repeatable manipulation of the EM spectrum will depend upon precise mechanical engineering, fabrication, and assembly to achieve channel frequency assignments, especially at the shrinking wavelengths of higher frequencies.
Designing and producing practical 5G/6G networks with the advanced antenna and other electronic technologies will require strong mechanical engineering efforts to achieve the physical components and tolerances required in support of millimeter-wave signal frequencies and beyond. The integration of electronic and mechanical engineering efforts (Fig. 4) will begin with the human design imagination and, from there, CAD software simulations. Those simulations will save the time and cost of building multiple prototypes. Not to be forgotten is the importance of accurate measurement capabilities for both electrical performance and mechanical tolerances.
For all the engineering skills, the measurements will verify that the prototype designs are ready for use in the field if manufacturing methods exist to produce them repeatably, reliably, and cost-effectively.