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.

Studies on Microwave Antennas: Passive Intermodulation Distortion in Antenna Structures and Design of Microstrip Antenna Elements

Sami Hienonen

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 18th of March, 2005, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7485-X)   [1279 KB]
Dissertation is also available in print (ISBN 951-22-7484-1)


Passive intermodulation (PIM) measurements of antennas and the design of dual-polarised microstrip antenna elements are investigated in this thesis. The emphasis is on the development of a passive intermodulation source localisation method and on the studies of the PIM source behaviour under various impedance loading conditions.

Passive intermodulation distortion can be harmful in wireless communication systems where the difference between the transmitted and the received power is large such as in GSM base stations. One of the most critical components is the antenna. As the antennas become more complex, the risk of getting excessive PIM distortion increases. Therefore, the antenna designer needs to have knowledge about the PIM phenomenon and proper tools to investigate various antenna structure configurations.

The concept of PIM near-field measurement is introduced and the implementation of the equipment for the GSM 900 frequency band is presented. The performance of the scanner is analysed and demonstrated with measurements. The scanner is capable of locating PIM sources in antennas and other open structures down to −110 dBm when the transmitted power is 43 dBm. The limiting factors of the scanner sensitivity are considered and several sensitivity measurements are performed. An analysis of the impedance loading effects on PIM measurements is carried out. The conducted measurements support the theory that the loading impedance effects can be several decibels, when the source or load return loss is less than 20 dB, which is the case with many filters and antennas used in base stations.

Dual-polarised antenna elements are needed in various array antenna applications. Two compact antenna element designs with moderate bandwidth and dual polarisation are introduced in the 12 GHz frequency band. The elements use a dual-resonant structure in order to achieve an impedance bandwidth of 16 % (Lretn > 10 dB). The arrangement of the antenna feeds results in an isolation of 35 dB between the ports.

This thesis consists of an overview and of the following 6 publications:

  1. Hienonen S., Golikov V., Vainikainen P., and Räisänen A. V., 2004. Near-field scanner for the detection of passive intermodulation sources in base station antennas. IEEE Transactions on Electromagnetic Compatibility 46, number 4, pages 661-667. © 2004 IEEE. By permission.
  2. Hienonen S., Vainikainen P., and Räisänen A. V., 2003. Sensitivity measurements of a passive intermodulation near-field scanner. IEEE Antennas and Propagation Magazine 45, number 4, pages 124-129. © 2003 IEEE. By permission.
  3. Hienonen S. and Räisänen A. V., 2004. Effect of load impedance on passive intermodulation measurements. Electronics Letters 40, number 4, pages 245-247. © 2004 IEE. By permission.
  4. Hienonen S. and Räisänen A. V., 2004. Passive intermodulation near-field measurements on microstrip lines. In: Proceedings of the 34th European Microwave Conference (EuMC 2004). Amsterdam, The Netherlands, 12-14 October 2004, pages 1041-1044. © 2004 European Microwave Association. By permission.
  5. Hienonen S., Lehto A., and Räisänen A. V., 1999. Simple broadband dual-polarized aperture-coupled microstrip antenna. In: Proceedings of the 1999 IEEE Antennas and Propagation Society International Symposium. Orlando, FL, USA, 11-16 July 1999, volume 2, pages 1228-1231. © 1999 IEEE. By permission.
  6. Hienonen S., Lehto A., and Räisänen A. V., 2001. Compact wideband dual-polarized microstrip antenna. Microwave and Optical Technology Letters 28, number 6, pages 396-398.

Errata of publication 2

Keywords: passive intermodulation, near-field measurement, microstrip antennas, dual-polarization, sensitivity, bandwidth, cross-polarization, phased-array antenna, base station, mobile communications

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© 2005 Helsinki University of Technology

Last update 2011-05-26