Could we all just take a break from the post-Antennagate blame game? Let’s go up a level and look objectively at RF issues and their effect on smartphone performance and user experience. It’s particularly important as the wireless industry transitions to 4G technology. Since multifunction smartphones like the Apple iPhone4 require multiple antennas for full broadband connectivity, the always-tricky balance between form and function will become even tougher to strike.
Yes, it’s true that antennas in smartphones and other handheld wireless devices are affected by the way in which the user holds the device. All antennas have low and high impedance regions that are particularly sensitive to changes in dielectric loading. The magnitude of the effect is inversely proportional to the distance between the antenna and the dielectric interference. The closer you get to the antenna, the bigger the effect. If you can touch the antenna conductor directly, you could get a significant change in performance.
Since every single phone model is different, hand effect must be minimized through an iterative design process of moving and adjusting the antenna structure until the device meets mobile operator and regulatory performance goals established for that particular device in multiple usage cases.
For today’s complex multiband smartphones, antenna designers must balance the technical challenge of designing antenna elements that are effective radiators of the signals transmitted and received in as many as 10 operating frequency bands with the mechanical challenge of placing these antenna elements into a device that fits in a consumer’s pocket, is mostly a metal and glass screen, and also has cameras, speakers, a keyboard, and a big battery.
On the mechanical side, the antenna must be small enough to allow sleek, thin, and compact phone designs. It must also be located to maximize its ability to get signals into and out of the phone without exceeding government power and RF exposure limits. Also, antennas can’t create interference or be affected by nearby objects such as transceiver modules, speakers, and digital cameras.
On the electrical side, the antenna must be large enough to radiate efficiently over multiple frequency bands. Today, a typical smart phone’s main antenna covers five bands from 824 MHz to 2170 MHz. New advanced communication protocols like LTE and WiMAX will require the main antenna to cover frequencies as low as 700 MHz and as high as 2700 MHz. In addition, connectivity antennas for WiFi, Bluetooth, and GPS must operate without interfering with the main antenna function. The impact of these requirements on a devices electrical, mechanical, and industrial design cannot be overstated.
An integrated antenna design that wraps around the outside of the phone is an innovative approach to eliminate the need to reserve dedicated volume for internal antennas, making the phone more compact. This approach allows the screen and battery to be as large as possible. It also enables the user to have a bigger impact on the performance under some usage conditions.
Although difficulties often arise with new design concepts, continued innovation in the form of frequency agile and adaptive control technologies can mitigate these effects. SkyCross is pioneering these techniques to address challenges of increased complexity and need for support of up to 10 frequency bands in new 4G handset, notebook, and USB designs.
Device designers are constantly pressured to trade RF performance for other features. It’s easy to forget that today’s smartphones are multiband, multifunction radios. As we move into 4G protocols like LTE and WiMax, research in antenna designs that incorporate frequency agility and multiple feed points to compress the physical size of the antenna and consolidate multiple antennas into a single part will become more important. These techniques will allow the antennas to become smaller so designers can add more features without affecting the performance of the device as a multiband, multifunction radio transceiver.
About the author
Paul Tornatta is Chief Technical Officer at SkyCross, which specializes in optimizing wireless connectivity in consumer electronics devices. Last year SkyCross shipped more than 100 million antennas to device manufacturers worldwide. Tornatta has more than 25 years of experience the aerospace, wireless, telecommunications, and automotive industries. He earned a BSEE from New Mexico State University.