Editor’s Note: Welcome to our weekly Reality Check column. We’ve gathered a group of visionaries and veterans in the mobile industry to give their insights into the marketplace.
As wireless devices evolve, so must their antenna systems, which play a critical but underappreciated role in both the user experience, original equipment manufacturers’ capability to make it all work and operators’ ability to turn a profit. To understand why, it helps to look at the concept of antenna tuning, which affects everything from download speeds, to dropped calls to spectrum usage.
Antenna tuning is a hot topic because it’s a technology whose time can’t come soon enough. It’s critical for designing smartphones and tablets that can meet user expectations about LTE’s speeds and their preference for thin, sleek devices with big screens and batteries that last at least a full day. Multiple input, multiple output adds another layer of complexity with its two antenna requirement in LTE devices. The need for two antennas operating at the same frequencies while located fairly close together makes achieving isolation difficult. Low-performance antennas lead to significant interference – causing dropped calls and/or slow data rates.
Antenna tuning uses impedance-matching techniques to optimize the antenna’s performance for both the frequency and environmental conditions, all in real-time. In the process, antenna tuning helps the operator’s profitability by making more efficient use of its spectrum and network infrastructure. For example, it enables fast downloads and uploads, so each device spends less time tying up spectrum and base station resources. The end result is a high-performance wireless device that provides optimal connectivity regardless of how many bands the phone has to service or how the user holds it.
Equally important to understanding the benefits of antenna tuning is a discussion on its limits. An antenna tuning circuit can’t overcome a poorly designed, inefficient, low-performance antenna. Nor can the tuning circuit increase the bandwidth of the antenna itself. For example, antenna tuning doesn’t make an antenna radiate more efficiently, so it can’t compensate for the noticeable performance degradation that comes with an antenna with low efficiency. Nor can it overcome an antenna that’s electrically too small to cover a wide frequency range, as is the case with LTE.
Given all of the benefits of antenna tuning, several vendors are now launching active impedance matching tuning circuits. There are two main approaches. The first is an active antenna system where the tuning circuit is co-located at the antenna’s feed point. With this approach, the antenna and active components are designed together, as an integrated system, for superior performance.
The second approach is to co-locate the tuning circuit in the baseband chip, transceiver or power amplifier, at the opposite end of the RF chain from the antenna. With the second approach, you are tuning not only the antenna, but also parasitics and losses. There is also an electrical delay with this approach given the distance between the antenna and the tuning circuit. When a tuning circuit is designed independently, the circuit topology and tuning component characteristics (reactance values for example) will place limitations on the type of antenna it can support. As a result, the antenna designer and device OEM have less design flexibility. The antenna and tuning circuit must be designed simultaneously as an integrated system solution for optimal performance.
The figures below compare the active antenna systems approach to tuning with tunable components located at the antenna feed point:
The future is active antenna systems
That’s where active antenna systems come in. Unlike passive antennas, an active antenna system automatically adjusts itself to compensate for changes such as frequency and the detuning effects that occur due to the user’s head and hand. As a result, smartphones and tablets that use active antenna systems are better equipped to provide consistently fast uplink and downlink connections, as well as significantly fewer dropped calls.
Active antenna systems will be a key driver in ensuring that OEMs meet carrier specs, and that consumers are pleased with their wireless experiences. Tunable matching circuits, from which active impedance matching techniques are derived, address form factor and frequency coverage challenges, and provide many benefits including the ability to reduce the antenna’s physical volume by up to 50% without compromising performance. This significant size reduction is critical, especially as additional antennas are integrated into the device and the display and battery sizes continue to grow. Alternatively, these techniques can be used to cover a wider bandwidth in the same antenna volume.
Innovations will continue with AIM. The number of input parameters will be substantially increased to dynamically keep the antenna matched over a wide variety of use cases, using a feedback loop, including body effects and phone placement, such as on a table or in the palm of a hand. Forward and reflected power can be sampled at the antenna port and an algorithm can be implemented to quickly adjust the matching circuit to re-match the antenna.
The antenna acts as a sensor and is the key to connectivity and LTE performance since it is the only air interface for the device. Tunable antenna approaches, without the antenna as part of the design, won’t provide the performance expected in today’s demanding LTE world. Active antenna systems will be required with dynamic tuning to cover significantly wider bandwidths, achieve smaller physical volumes and provide more degrees of freedom in the design process helping OEMs to bring products to market faster and deliver a superior user experience.
Jeff Shamblin is the Chief Scientist at Ethertronics, and is responsible for overseeing all research and development projects for the corporation. Shamblin brings 29 years experience in antenna engineering to this position. Before joining Ethertronics, Shamblin worked for two RFID start-up companies, SCS and Claridy Solutions. At Claridy he was the manager in charge of antenna development and assisted in all aspects of RFID relating to antenna and scattering issues. Shamblin previously worked as an antenna consultant providing design and analysis services to several wireless start-ups in the Southern California area. Prior to his work in RFID Shamblin spent more than 20 years in antenna design and development in the aerospace industry at Lockheed and Northrop where he was responsible for several antenna designs on various aircraft and missile programs. He holds seven patents relating to antenna technology. Shamblin earned a bachelor’s degree in physics from California State University, Northridge.
