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Antenna Tuning in Mobile Phones
Modern smart phones operate in multiple frequency bands typically in the range of 0.7GHz to 3.6GHz using multiple antennas for MIMO operation. Antenna operation is usually achieved by coupling structures within the phone to utilize the metallic chassis as an antenna. Even though this guarantees making use of the largest antenna structure available the antenna has to be impedance matched to the specific frequency bands. Furthermore, user’s hand and head interaction impairs the impedance matching and the radiation efficiency of the antenna. Impedance tuners can be used to improve the impedance matching in various desired frequency bands. Tuning strategies can be distinguished between feed port tuning and aperture tuning on the coupling element. Both, open-loop and closed-loop adaptive tuners using different tuning technologies based on semiconductor switches, varactors or MEMS switches have been investigated and implemented into products. The seminar talk will introduce the fundamentals of antennas integrated into modern smart phones as well as the impairments due to the interaction with the user. Based thereon, adequate impedance tuning strategies will be introduced and discussed. Finally, a modular evaluation kit for feed port tuning and aperture tuning of smart phone antennas will be showcased. Example evaluations using this kit will be presented.