Browsing by Author "Viikari, Ville, Assoc. Prof., Aalto University, Department of Electronics and Nanoengineering, Finland"

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    Conformal and multi-band antennas for future mobile handsets and wireless sensors
    (Aalto University, 2017) Rasilainen, Kimmo; Viikari, Ville, Assoc. Prof., Aalto University, Department of Electronics and Nanoengineering, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Assoc. Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    Desired performance of handsets and wireless sensors used in communications systems of current and future generations places significant challenges also on designing the antennas used in these devices. The antennas must adhere to requirements of existing frequency allocations, and in the case of handsets, must be compatible with multi-band and multi-antenna implementations for enhanced performance. This thesis studies the operation of electrically small antennas for particular implementations and radio systems, and gives ideas for a conceptually new class of devices. The first part of the thesis investigates the design and performance of harmonic transponders, wireless sensors that utilise two different, harmonically separated frequencies for communication. Compared to systems with the same transmission and reception frequencies, the harmonically separated case is beneficial for detection in clutter-rich environments. Two different techniques for implementing the required harmonic matching are studied and verified experimentally. General design rules and figures of merit are presented for the suitability of particular antennas and diodes for transponder applications. Antennas for conformal sensing and handset applications are considered in the second part of the thesis. Efficient antenna performance requires taking into account the intended usage case and environmental effects already during the design process. Bending the handset is modelled using equivalent circuit models for better physical understanding, and the results show that the most significant effects take place at frequencies below 1 GHz. Case studies are also made for a conformal, wrist-worn handset application, in which the effect of the user is also considered. The final part of the thesis deals with the design and implementation of well-performing multi-element (MIMO) antennas. The proposed antenna structures utilise combinations of fed, passive, and parasitic elements to obtain good impedance matching and efficiency across the LTE low band (698-960 MHz). Performed computational and experimental studies show that this can be achieved using antennas with large volume but moderate surface area and fully passive matching circuits. The last point is beneficial for Carrier Aggregation implementations. The concept of physical antenna diversity can help to improve the multi-antenna performance, especially at the low band.