Browsing by Author "Ala-Laurinaho, Juha, Dr., Aalto University, Department of Radio Science and Engineering, Finland"
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- Development of Characterization Methods for Antennas and Quasi-Optics
School of Electrical Engineering | Doctoral dissertation (article-based)(2015) Du, ZhouThis dissertation focuses on the development of characterization methods for antennas and quasi-optical components. The dissertation presents three new methods to deal with certain limitations occurred during the antenna measurement processes. First, a new technique using the Chebyshev polynomials has been proposed to process the antenna measurements obtained in non-anechoic sites to obtain equivalent free space radiation patterns. This new technique combines the principle of a FFT-based method with the special relationship between coefficients of the Bessel-Chebyshev polynomials. Experimental results are presented to demonstrate the potential of this approach over conventional time gating techniques for a certain class of problems. Second, a new antenna pattern retrieval method is proposed. In this method, the antenna reflection coefficient is measured many times when a unique reflective load with known spatial reflection properties is placed near the antenna in each measurement. The antenna pattern is obtained from the measurements with an inversion algorithm. Simulations have been used to verify the theoretical basis and the method has been experimentally demonstrated at 30 GHz. The results show that the method could enable sufficient accuracy with low gain antennas or in the vicinity of main lobe with directive antennas. Third, a new technique is presented to realize a wideband hologram compact antenna test range (CATR) by linearly adjusting the feed location. The wideband formulas for linearly adjusting the feed have been discussed and verified. The performance of the wideband operation has been demonstrated by the measured results at W (95 GHz) and D (170 GHz) bands for the hologram aperture diameter of 350 mm. The dissertation also discusses characterization of quasi-optics, namely, MEMS-based high-impedance surface (HIS) and reflectarray elements. First, the reflection properties of the single unit cell structure of MEMS-based HIS is studied, tunability of the MEMS varactors and beam steering of a large structure at 80 GHz has been demonstrated with a simplified model. The structure allows steering of the beam within the range from -45º to +45°. A quasi-optical measurement setup has been built for the experimental characterization. Second, the design and optimization process of reconfigurable reflectarray element integrated with MEMS-based phase shifter at 120 GHz is studied. Also, the dielectric properties of SU-8 substrate have been characterized with on-wafer measurements. Several design parameters which could affect the modulation efficiency have been studied. - Reconfigurable antennas and radio wave propagation at millimeter-wave frequencies
School of Electrical Engineering | Doctoral dissertation (article-based)(2016) Semkin, VasiliiFor the last decades we have been witnessing the evolution of wireless radio networks. Since new devices appear and the mobile traffic, as well as the number of users, grows rapidly, there is a great demand in high capacity communications with better coverage, high transmission quality, and more efficient use of the radio spectrum. In this thesis, reconfigurable antennas at micro- and millimeter-wave frequencies and peculiar properties of radio wave propagation at mm-wave frequencies are studied. Reconfigurable antennas can improve radio link performance. Recently, many different concepts have been developed in the reconfigurable antenna design to control the antenna bandwidth, resonant frequency, polarization, and radiation properties. In the first part of the thesis, we investigate mechanically tunable antennas operating at microwave frequencies with the ability to change the shape of the conductor element and, consequently, to control the radiation properties of the antenna. Also in the first part, we study conformal antenna arraysfor 60 GHz applications based on cylindrical structures. Beam switching technology is implemented by realizing several antenna arrays around the cylinder with a switching network.Scanning angles of +34˚/-32˚ are achieved. Moreover, it is vital to study radio wave propagation peculiarities at mm-wave frequencies in indoor and outdoor environments to be able to deploy wireless networks effectively. The propagation part of the thesis focuses on several aspects. First, we investigate how the estimation of optimum antenna configurations in indoor environment can be done usingrealistic propagation models at 60 GHz. Ray tracing simulations are performed and realistic human blockage models are considered. Second, we present the results from a measurement campaign where reflection and scattering properties of two different built surfaces are studied in the millimeter-wave E-band (71-76 and 81-86 GHz). Next, we present a geometry based channel model for a street canyon scenario, using angular-domain measurement results to calculate realistic power angular spectra in the azimuth and elevation planes. Then, we evaluate propagation effects on the radio channel on the rooftop of the buildings bymeasurements and simulations. We have used unmanned aerial vehicles and photogrammetrytechnique to create a highly accurate 3D model of the environment. Based on a comparison of the measured and simulated power delay profiles, we show that the highly accurate 3D modelsare beneficial in radio wave propagation planning at mm-wave frequencies instead of using simple geometrical models.