RF MEMS switches mask undesired frequency bands in smartphones
A team of researchers at UCSD Jacobs School of Engineering has taken advantage of radio frequency micro-electro-mechanical systems to improve smartphone performance in the near future by way of higher antenna efficiency. Commonly found in satellite and defense applications, RF MEMS can pave the way to enhanced download speeds, better voice quality and improved energy efficiency in smartphones.
"If you can make smartphone antennas 2dB or 3dB more efficient, you basically halve your download times. Truly, if we accomplish this with RF MEMS technologies, it's a huge deal," said Gabriel Rebeiz, electrical engineering professor at UCSD JSE. This work has advanced RF MEMS to the point where large-scale incorporation into smartphone antennas appears probable if not inevitable.
"We demonstrated that you can get a better antenna, a better filter, a better power amplifier using RF MEMS. These were the first demonstrations. Industry took this work and adapted it to their own situations," said Rebeiz.
Figure 1: Metal contact RF MEMS switches. This technology could be incorporated into smartphones as tunable filters that mask undesired frequency bands.
In addition to antennas, RF MEMS technology could find its way into tunable filters for smartphone radios that might one day replace the tens of individual filters built into today's smartphones. With the rise of carrier aggregation-which is the use of multiple frequency channels to divide data, such as a video, that is being sent or downloaded in today's advanced wireless networks-filters are increasingly important, explained Bilgehan Avser, an electrical engineering graduate student in the Rebeiz lab.
"Metal-contact and capacitive switches could turn out to be extremely important for tunable RF front ends of next-generation communication systems," said Avser.
Cellphone base stations could also see RF MEMS implementations. But applications beyond tunable antennas could take more time to be implemented in commercial handsets and tablets, Rebeiz noted.
In recent years, antenna size-and by extension RF performance-has lost ground in phones to larger screens and thinner form factors that exclude larger antennas. At the same time, the demands placed on these antennas have increased. For example, even though antennas have gotten smaller, they are being asked to cover lower-frequency bands that would normally require larger antenna form factors.
"The smartphone antenna, which has long been neglected, now is of prime importance for how to make the smartphone more efficient," said Rebeiz. Incorporating RF MEMS into smartphone antennas yields "tunable" antennas that work efficiently across one or two frequency bands at a time. The frequency at which they function most efficiently, however, can be changed-and RF MEMS metal-contact switches and variable capacitors are used to make the antennas tunable.
"With RF MEMS, you can take an inefficient wideband antenna and turn it into an efficient tuned antenna," said Rebeiz. In this context, RF MEMS serves as a low-loss switched variable capacitor capable of changing the antenna's resonant frequency, which is the frequency at which the antenna operates most efficiently.
"We laid out the fundamental work to make RF MEMS a reality, through investigation of so many fundamental problems of MEMS. We solved a lot of these problems and transferred the advances to industry," said Rebeiz.
His research group's contributions include making MEMS robust in the face of process stresses incurred during micro-fabrication, as well as temperature extremes. They also helped demonstrate the vast potential that RF MEMS hold for commercial applications.