I N D U S T RY P E R S P E C T I V E S
ANTENNA DESIGN CHALLENGES FOR 4G
FRANK M. CAIMI, PH.D.
The trend in mobile wireless devices has been to provide faster access, improved processors, more memory, brighter and higher resolution screens, additional connectivity with Wi-Fi, GPS, third generation (3G), and fourth generation (4G) world access — all with longer battery life in thinner, sleeker packages. Compound this with the desire of mobile operators to expand their available band allocations, and what results is a difficult industrial design arena, where suppliers are vying afor physical space within the confines of a smartphone or similar device to accommodate necessary components. One such component is the antenna — essentially a transducer that converts time varying electrical current to radiated energy, and often considered a last minute addition to the physical structure. Now with the introduction of 4G and 1 × 2 or 2 × 2 multiple-input multiple-output (MIMO) communications protocols, not one but two antennas are needed, each with specific requirements typical of any transducer: bandwidth, efficiency, mutual coupling, size, and cost. With newer Third Generation Partnership Project (3GPP) definitions for carrier aggregation, simultaneous band coverage will be also be necessary. These trends introduce significant challenges for effective antenna design. the phone will excite nearly the same current modal distribution, and therefore produce virtually the same radiation pattern. Since both antennas are coupled to the same mode, they experience mutual coupling so that power introduced into one antenna is partially coupled to the opposite antenna’s source resistance, and is subsequently lost. A common solution is to relocate one antenna to excite a different radiation mode on the chassis, which can result in smaller bandwidth and efficiency depending on the chassis width-to-length ratio. For 1 × 2 MIMO configurations rolling out now, this approach can meet...
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