Antennas and Antenna Measurement Techniques for Mobile Communication Terminals

Doktorsavhandling, 2004

Mobile communication is expanding rapidly, finding new uses and pushing the development of terminals. There are many systems in use today, for example mobile phone systems for voice communication, satellite navigation/positioning systems, and short range data communication. Soon new systems for high speed data communication are expected to emerge, and also systems that use much higher frequencies than today. When it comes to the mobile terminals, some general trends in the development are: shrinking size, more advanced antennas with carefully designed radiation characteristics, larger production volumes, and shorter lead times. This dissertation presents three new antenna types for mobile communication terminals, each studied experimentally. These are the dual feed monopole antenna, a broadband dual RC-loaded loop antenna, and the capacitance-short-load antenna, suitable for different applications. The dual feed monopole antenna is with its two ports suitable for example in satellites where redundancy is required. The RC-loaded loop antenna and the capacitance-short-load antenna are suitable in mobile terminals that are very small compared to the wavelength, e.g. ear plugs and wrist watches. The capacitance-short-load antenna is also highly suitable for electrical tunability over a very wide frequency range. Furthermore, reverberation chamber antenna measurement techniques are studied theoretically and experimentally. The studies include measurement of correlation coefficient between antennas, reflective measurements of free-space reflection coefficient and radiation efficiency, models for mechanical and frequency mode stirring efficiency, a chamber with a Rice distributed signal amplitude, a chamber with an anisotropic signal environment, and a finite probability distribution for random signals with limited power. All these studies serve to expand the usefulness of reverberation chambers as a means for fast, accurate, and cheap antenna characterization, in both product development and production. Finally, information retrieval from phaseless radiation measurements is studied theoretically. Phaseless measurements are common when characterizing the radiation properties of complete mobile terminals, for example in production tests.