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.
Mobile consumers are being promised — and want — 3G and 4G smartphones and other wireless devices that deliver noticeably superior data, video, call performance and battery life. Naturally, they desire all of these features in smaller form factors that can easily fit in a front pocket or the palm of their hand.
In general, smartphone size is hovering around 125 millimeters x 60 mm x 9 mm. Thickness is the one dimension that is seeing some change as smartphone vendors compete for the “thinnest” phone. While device size is relatively stable, the number of antennas/RF components required is increasing to meet LTE MIMO requirements and battery size is increasing to power the additional components. Real estate inside the device is already at a premium creating a challenge for original equipment manufacturers to make all the components fit, meet carrier compliance requirements and specifications, and deliver a superior user experience.
Given the number of antennas in a device, sometimes up to five, and the limited space available, antennas are frequently located in less than optimal locations and close to other components. This results in interference and ultimately detuning. Additionally, performance can be compromised by body effects and phone placement, causing further detuning and dropped calls.
Innovating in an industry that hasn’t changed in two decades
These challenges, as well as new trends in the wireless space, such as accessing the cloud in a mobile environment, have created an opportunity for the RF and antenna systems space to re-architect technologies that haven’t changed much in 20 years. The “passive” antennas that had been used for 2G and 3G devices have reached their limits and now with the proliferation of 4G networks, the requirements for MIMO and global roaming can’t fully be achieved with “passive” approaches. Instead, active antenna systems — in which the antenna dynamically interacts with the RF system — are needed.
In many cases, active impedance matching techniques 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, are not new. In fact, they have been around for about 50 years and were originally used in military applications. While they worked for military devices, they were extremely large and expensive and certainly not scalable for today’s wireless smartphones.
Continued improvements in antenna design techniques, along with recent developments in small form factor, cost-effective tuning components, have made active impedance matching a reality in today’s smartphone.
Furthermore, applying active impedance matching techniques to the antenna provides solutions to the handset designer for form factor and frequency coverage challenges. Applying tuning techniques to the antenna provides many benefits:
–Reducing the antenna’s volume while maintaining the same frequency coverage.
–Keeping the same antenna volume and covering additional frequency bandwidth.
–Tuning the antenna dynamically to compensate for body effects using a “closed loop” technique.
Active impedance matching techniques can reduce the antenna’s physical volume by 50% without compromising performance. This significant size reduction is critical, especially as additional antennas are integrated into the device and the battery size continues to grow. Alternatively, these techniques can be used to cover a wider bandwidth in the same antenna volume. Active impedance matching also speeds up time-to-market, since it allows more degrees of freedom in the antenna structure design phase. Unlike “passive” antennas that require tuning with each design iteration process, active antennas can dynamically re-tune themselves when changes are made to the device. This is important for OEMs especially as they battle it out to come to market with new devices ahead of their competition.
Innovations will continue with active impedance matching. The first iteration of this technique consists of an open-loop design, whereby limited inputs of information are processed, and then decisions are made on the best state for the antenna system to be in. These decisions will meet one of the design goals cited above.
The next iteration is an HD open-loop design. This design has the benefits of the open-loop design but increases the number of input parameters substantially. Doing so will add capability, particularly offsetting the effects of being adjacent to the body.
A closed loop design will be implemented in the future, whereby the active impedance matching circuit will 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.
This set of techniques has several elements in the architecture to realize an active impedance matching design. Some key components enable flexible reactance values to be used, but getting a design point fixed is the challenge of the system design and more specifically, the designer of the antenna. This lesson is quickly learned when this technique is applied to a mobile phone product.
Advanced antenna architecture, combined with extensive design experience will yield optimal performance and connectivity, which is becoming increasingly critical for enterprises and consumers in general who are moving toward the cloud and need real-time access to their productivity tools.
Jeff Shamblin is the chief technology officer at Ethertronics and is responsible for overseeing all research and development projects for the corporation. Shamblin brings 29 years experience in antenna engineering to the position.
