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

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    Advances in the Analysis and Design of Electrically Small Antennas
    (Aalto University, 2018) Hannula, Jari-Matti; Lehtovuori, Anu, Dr., 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, Ass. Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    The increasing number of frequency bands used in wireless communications results in added challenges for antenna designers. This challenge is further increased by the limited volume available for antennas in modern wireless devices. The inclusion of multiple-input multiple-output (MIMO) techniques requires multiple antennas in a device, which further reduces the maximum size of an individual antenna. The upcoming fifth generation of mobile communications promises improvements for three aspects of mobile communications: mobile broadband, massive internet of things, and mission critical services. Of those three, this thesis focuses on the first two. The enhanced mobile broadband promises data rates above gigabits per second, and the capacity to serve even larger number of users. For this to be possible, the spectral efficiency of the devices must be sufficiently large. The first part of this thesis describes the intermodulation measurement technique. The technique enables contactless measurement of passive transponders that contain a nonlinear load. It is used in this work to characterize the realized gain of a harmonic transponder, but the technique can also be used for other passive transponders, such as radio frequency identification (RFID) tags. The second part of the thesis introduces the antenna cluster concept developed in this work. The concept involves using multiple closely spaced antenna elements together to create an antenna that can be tuned to operate across a large number of frequency bands. The basic principle of the concept is described and the necessary theory is formulated. The concept is experimentally verified as part of a mobile antenna prototype and it is further extended to an eight-element MIMO antenna design that can operate across a wide frequency range. Transceiver design is an important part of the cluster concept, as the method is highly dependent on the capabilities of the transceiver. The final part of the thesis analyzes the effect of the transceiver on the overall cluster performance. Both the transmitter and receiver properties are investigated. The transmitter is modeled using the performance data of an existing integrated transmitter and the receiver is investigated using the equivalent circuits of common receiver architectures.