The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Design and Implementation Techniques of Wideband Mobile Communications Antennas

Jani Ollikainen

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S4 at Helsinki University of Technology (Espoo, Finland) on the 26th of November, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7381-0)   [1198 KB]
Dissertation is also available in print (ISBN 951-22-7380-2)

Abstract

Wireless communications has been a major motivator of small antenna research during the last decade. New communication systems with wider system bands have been introduced, single-band terminals have evolved into multiband and multimode terminals, the average terminal size has decreased drastically, and internal antennas have been developed into standard solutions. All this combined with strict limitations set for the energy absorbed by the users of mobile terminals has created needs for improved antenna solutions and better understanding of small antennas on small complex platforms. In response to these challenges, it is studied in this thesis how the frequency band, over which the combination of an electrically small antenna and a small radio device efficiently transmit and receive radiowaves, can be systematically maximized.

When a small antenna is attached to a small metal object, like the metal chassis of a mobile phone, the size and shape of the object and the position of the antenna on it can have a strong effect on the antenna performance. The thesis shows that the behavior of a radiating system formed by a small antenna and the metal chassis of a small radio device can be studied by approximating the system as a combination of the separate resonant wavemodes of its components. The modes of the antenna and the chassis are described with resonant circuits that are combined into one dual-resonant equivalent circuit model. It is shown with the model that the characteristics of the antenna-chassis combination depend on the unloaded quality factors and the relative amplitudes of the resonant modes of the antenna and the chassis. Based on the results obtained with the circuit model, several important conclusions on the significant properties of the system can be drawn.

The effect of the metal chassis on the bandwidth, radiation efficiency, and SAR (specific absorption rate) of internal mobile phone antennas is also studied with electromagnetic simulations in the thesis. The results support those of the resonator-based analysis and show that in addition to the impedance bandwidth, the radiation efficiency in talk position and SAR depend strongly on the parameters of the phone chassis.

When the size and efficiency are fixed, making a small antenna dual-resonant or multiresonant is a very effective method of increasing its bandwidth. The method is extensively studied in this thesis, which presents for the first time a unified theory for the impedance bandwidth optimization of small antennas comprising two coupled resonators with arbitrary unloaded quality factors (Q01 and Q02). Simulated and measured results are presented to support the theory. In addition, results for novel antenna designs that were developed based on the theory are presented. An example of the results is the first published single-feed internal mobile phone antenna that covers the frequencies of E-GSM900, GSM1800, GSM1900, and UMTS with a return loss of at least 6 dB and high radiation efficiency.

One of the main problems of increasing the effective bandwidth of a small resonant antenna with electrical frequency tuning is power loss in the tuning circuit. A systematic method for the minimization of RF power loss in certain frequency-tuning circuits of small resonant antennas is developed and demonstrated in the thesis. The design principles are also adapted to the design of a novel frequency-tuning circuit for internal mobile phone antennas. It enables adding a new band of operation to an existing dual-band antenna structure.

This thesis consists of an overview and of the following 9 publications:

  1. Ollikainen J. and Vainikainen P., 2002. Design and bandwidth optimization of dual-resonant patch antennas. Helsinki University of Technology, Radio Laboratory publications, Report S 252. Espoo, Finland, 41 pages. © 2002 by authors.
  2. Ollikainen J. and Vainikainen P., 1998. Radiation and bandwidth characteristics of two planar multistrip antennas for mobile communication systems. Proceedings of the 48th IEEE Vehicular Technology Conference (VTC 1998). Ottawa, Ontario, Canada, 18-21 May 1998, volume 2, pages 1186-1190. © 1998 IEEE. By permission.
  3. Ollikainen J., Fischer M. and Vainikainen P., 1999. Thin dual-resonant stacked shorted patch antenna for mobile communications. Electronics Letters 35, number 6, pages 437-438. © 1999 IEE. By permission.
  4. Kivekäs O., Ollikainen J. and Vainikainen P., 2003. Wideband dielectric resonator antenna for mobile phones. Microwave and Optical Technology Letters 36, number 1, pages 25-26.
  5. Vainikainen P., Ollikainen J., Kivekäs O. and Kelander I., 2002. Resonator-based analysis of the combination of mobile handset antenna and chassis. IEEE Transactions on Antennas and Propagation 50, number 10, pages 1433-1444. © 2002 IEEE. By permission.
  6. Kivekäs O., Ollikainen J., Lehtiniemi T. and Vainikainen P., 2003. Effect of the chassis length on the bandwidth, SAR, and efficiency of internal mobile phone antennas. Microwave and Optical Technology Letters 36, number 6, pages 457-462.
  7. Ollikainen J., Kivekäs O., Toropainen A. and Vainikainen P., 2000. Internal dual-band patch antenna for mobile phones. Proceedings of the AP2000 Millennium Conference on Antennas & Propagation. Davos, Switzerland, 9-14 April 2000, CD-ROM SP-444, paper p1111.pdf. © 2000 European Space Agency (ESA). By permission.
  8. Ollikainen J., Kivekäs O. and Vainikainen P., 2002. Low-loss tuning circuits for frequency-tunable small resonant antennas. Proceedings of the 13th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC 2002). Lisboa, Portugal, 15-18 September 2002, pages 1882-1887 (CD-ROM, paper cr1593.pdf). © 2002 IEEE. By permission.
  9. Kivekäs O., Ollikainen J. and Vainikainen P., 2002. Frequency-tunable internal antenna for mobile phones. Proceedings of the 12èmes Journées Internationales de Nice sur les Antennes, 12th International Symposium on Antennas (JINA 2002). Nice, France, 12-14 November 2002, volume 2, pages 53-56 (CD-ROM, paper 124.pdf). © 2002 SEE-GRéCA. By permission.

Errata of publications 1, 4, 8 and 9

Keywords: small antenna, patch antenna, PIFA, efficiency, bandwidth, quality factor, dual resonance, frequency tuning, mobile phone, mobile communications

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© 2004 Helsinki University of Technology

Last update 2011-05-26