The title of this article speaks to a design consideration in radio technology that we learned many decades ago. It is smarter to acquire gain by using larger antennas than to achieve gain with more powerful amplifiers. This is a first principle of radio design. Amplifiers require power and power is expensive and fickle. Whereas, passive antennas are low cost, and need nothing more to generate signal gain. They give us free gain.
However, with the advancement of Internet of Things (IoT) technology and the miniaturization of radios to fit anyplace, this rule is beginning to become obsolete. It is not that we no longer care about active gain coming with costs for power consumption, we probably care more today then ever before. But with other technological advancements, such as tiny circuits, longer life batteries, and compact form factors for new products, we simply have other pressing design matters that make the advantage of gain from larger antennas a thing of the past.
If we look back to the 1920-1930, in the UK, they built massive acoustic mirrors. These sound mirrors collected noise and focused it towards people’s ears and later at sensitive microphones. As they developed, this gigantic technology permitted the pinpointing of invading airplanes in the sky. These early airplane attackers were slow flying and low flying, so the acoustic mirrors gave early warning of the invaders to allow actions to be taken to protect citizens and launch defending countermeasures such as getting allied airplanes up in the air ready for combat.
Different sizes and types of concrete parabolas were constructed to increase resolution to pinpoint the distance of the invading aircraft. A wide curving reflector as is seen in the two images above and below was one such experiment to provide more directional focus by widening the beamwidth to scan the broader shoreline.
These vast concrete dishes, which can be found along the northern and easterly British coastline, are sound mirrors. Originally designed to capture the sounds of incoming enemy aircraft as they approached the United Kingdom from across the English Channel and the North Sea (although one was also built at Baħar iċ-Ċagħaq in Malta), these military listening devices acted as a rudimentary early warning system in the decades before radar was developed and deployed.
Conceived by William Sansome Tucker, and operated at differing scales between around 1915 and 1935, the acoustic mirrors were able to signal an aircraft from up to 24 kilometers (15 miles) away. The concave structures responded to sound by focusing the waves to a single point, whereupon a microphone would be positioned. Not only were the structures able to announce the arrival of an aircraft, but they could also determine the incoming direction of attack of the plane to an accuracy of 1.5 degrees. With the development of faster aircraft in the 1930s, these sound mirrors became obsolete.
Serious developmental work on radar began in the 1930s, but the basic idea of radar had its origins in the classical experiments on electromagnetic radiation conducted by German physicist Heinrich Hertz during the late 1880s. Hertz set out to verify experimentally the earlier theoretical work of Scottish physicist James Clerk Maxwell. Maxwell had formulated the general equations of the electromagnetic field, determining that both light and radio waves are examples of electromagnetic waves governed by the same fundamental laws but having widely different frequencies. Maxwell’s work led to the conclusion that radio waves can be reflected from metallic objects and refracted by a dielectric medium, just as light waves can. Thus, the invention of the antenna.
Most of the countries that developed radar prior to World War II first experimented with other methods of aircraft detection. These included listening for the acoustic noise of aircraft engines and detecting the electrical noise from their ignition. Researchers also experimented with infrared sensors. None of these, however, proved effective.
Radar used a different frequency compared to acoustic mirrors, but built upon this same work. It added movement of the antenna to sweep the skies instead of building larger curved antennas.
Dipole Antenna Development
In the early 1960s saw the advent of the miniature handheld transistor radios. So, smaller antennas were needed to be appropriate for the compact size of these transistor radios.
A transistor radio is a small portable radio receiver that uses transistor-based circuitry. Following the invention of the transistor, the first commercial transistor radio was released in 1954. The mass-market success of the smaller and cheaper Sony TR-63, released in 1957, led to the transistor radio becoming the most popular electronic communication device of the 1960s and 1970s. Transistor radios are still commonly used as car radios. Billions of transistor radios are estimated to have been sold worldwide between the 1950s and 2012.
These radios relied on small 1/4 or 1/8 wavelength antennas. They were often compact and telescoped out of the radio for better performance.
Internet of Things
Modern IoT devices use tiny circuit boards often smaller than the batteries that power them. The antennas are built-in to these circuit boards. Of course, the PCB trace length determines the antenna resonant frequency. Each antenna requires a keep-out area around the antenna trace where no copper traces or ground fill can exist on any layer of the PCB. The trace can either be gold flashed or covered with solder mask. The antenna’s electrical performance will be determined by the type of substrate material, its thickness, relative dielectric constant (εR), and metallization resistivity.
The integration of antennas within the packaging dictated by product form and function should be a team effort between RF engineering and Industrial-Mechanical design. Common considerations amongst the co-development team should be harmony with the industrial and mechanical design, while maintaining a firm observation of best-practices for antenna placement and implementation for radio performance and success of regulatory testing and compliance. This effort can be synthesized from raw materials and design know-how or can be implemented with off-the-shelf solutions that reduce design risk and cycle-time.
The promise of higher speed for high data rate communication and lower latency for real-time interaction is alluring for users. This combination will not only provide for new video formats like 360 degree video (video traffic is expected to account for 73% of all mobile data traffic by 2023), but also enable new technologies such as autonomous driving, augmented or virtual reality interaction, and a tactile internet with applications in fields ranging from industry automation and transport systems to healthcare, education and gaming.
Antenna design for mobile phones has always been a challenging topic for engineers, and designing antennas to support the new 5G frequency bands will raise the bar further. Two frequency ranges are of most interest: frequency range 1 for sub 6 GHz bands communication and frequency range 2 for communication at the millimeter (mm) wave frequencies above 24 GHz. Some of the bands are still under discussion, and the exact frequency designations will vary geographically. Initial mobile phone integration will focus on sub 6 GHz antennas, with mm-wave support being considered for providing broadband links to homes or other fixed infrastructure initially, before finding its way into mobile phones in the near future too.
With 8×8 MIMO and beamforming coming in 5G radios, the need for intelligence to manage these new features is critical. The advent of the smart antenna is now upon us.
We have come a very long way since the ear was used against a concrete parabola to capture signals. The current and next generation of miniature antenna technology is almost invisible to see and is nested deeply inside the devices. The performance for these micro antennas far exceeds what we used in the past. With beanforming coming, the intelligence will drive the gain with directional capabilities similar to what was done in the 1930s, except now it is fully automated, offers better gain, and excels at delivering crisp and clear signals to your device.
Arch Daily. (2017). These Enormous Concrete Acoustic Mirrors Pepper the British Coastline. ArchDaily.com. Retrieved on February 3, 2020 from, https://www.archdaily.com/875917/these-enormous-concrete-acoustic-mirrors-pepper-the-british-coastline
Rutschlin, M. (2019). 5G Antenna Design for Mobile Phones. Dassault Systemes. Retrieved on February 3, 2020 from, https://blogs.3ds.com/simulia/5g-antenna-design-mobile-phones/
Skolnik, M. (2020). History of Radars. Encyclopaedia Britannica. Retrieved on February 3, 2020 from, https://www.britannica.com/technology/radar/Advances-during-World-War-II
Teschler, L. (2019). Hidden Pitfalls of IoT Antenna Design. WTWH Media LLC. Retrieved on February 3, 2020 from, https://www.microcontrollertips.com/hidden-pitfalls-of-iot-antenna-design/
Wikipedia. (2020). Transistor Radio. Retrieved on February 3, 2020 from, https://en.wikipedia.org/wiki/Transistor_radio
About the Author:
Michael Martin has more than 35 years of experience in systems design for broadband networks, optical fibre, wireless, and digital communications technologies.
He is a business and technology consultant. He is employed by Wirepas Oy from Tampere, Finland as the Director of Business Development. Over the past 15 years with IBM, he has worked in the GBS Global Center of Competency for Energy and Utilities and the GTS Global Center of Excellence for Energy and Utilities. He is a founding partner and President of MICAN Communications and before that was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation (CYN: TSX).
Martin currently serves on the Board of Directors for TeraGo Inc (TGO: TSX) and previously served on the Board of Directors for Avante Logixx Inc. (XX: TSX.V).
He has served as a Member, SCC ISO-IEC JTC 1/SC-41 – Internet of Things and related technologies, ISO – International Organization for Standardization, and as a member of the NIST SP 500-325 Fog Computing Conceptual Model, National Institute of Standards and Technology.
He served on the Board of Governors of the University of Ontario Institute of Technology (UOIT) [now OntarioTech University] and on the Board of Advisers of five different Colleges in Ontario. For 16 years he served on the Board of the Society of Motion Picture and Television Engineers (SMPTE), Toronto Section.
He holds three master’s degrees, in business (MBA), communication (MA), and education (MEd). As well, he has three undergraduate diplomas and five certifications in business, computer programming, internetworking, project management, media, photography, and communication technology. He has earned 15 badges in next generation MOOC continuous education in IoT, Cloud, AI and Cognitive systems, Blockchain, Agile, Big Data, Design Thinking, Security, and more.