Browsing by Author "Ala-Laurinaho, Juha, Dr., Aalto University, Finland"

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    Advances in Beam-Steerable and Low-Scattering Antennas for Communications and Sensing
    (Aalto University, 2021) Leino, Mikko K.; Ala-Laurinaho, Juha, Dr., Aalto University, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Assoc. Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    Communication networks are being developed to handle the increased wireless data traffic that the existing systems cannot handle. Fifth-generation mobile networks (5G) are adopting millimeter-wave (mm-wave) frequencies for higher spectral efficiency and wider spectral bands in order to increase network capacity. Additionally, the number of network antennas will increase exponentially, since the propagation at mm-waves suffers from intrinsic atmospheric attenuation. Furthermore, the mm-wave antennas are required to be highly efficient, and beam-steering capabilities are also necessary to focus capacity where it is needed. The first part of this thesis discusses phased array designs for the mm-wave base-station applications and tools for the analysis and optimization of the antennas. The presented antennas operate in Ka- and E-bands, and they combine low-loss, waveguide-based power division networks and antenna elements with phase shifters that are integrated on a printed circuit board (PCB). The resulting proposals are antennas with high efficiency, where the majority of the losses are caused by the used phase shifters. The performances of both antennas (e.g., their beam-steering capabilities) have been validated with measurements. Furthermore, the antenna diagnostic results based on the holography data are presented, along with optimization methods that allow performance enhancement in terms of higher antenna gain and lower side lobes. Because antenna development can be a time-consuming and costly process, utilizing the same antenna in multiple different scenarios is desirable. The second part of the thesis explains how the previously presented Ka-band antennas, which were initially developed for communications, can be used in imaging applications. A frequency-diverse imaging method is explained, in which a computational algorithm is used to reconstruct the image from the observation data. A theoretical evaluation and experimental test results are presented. The proposed method has been used successfully to reconstruct an image of the scene locating a conducting sphere, and future research paths are discussed. Modern radar applications may require co-locating multiple antennas together, especially if the area or the volume reserved for the antennas is limited. Therefore, electrically invisible or transparent antennas that do not affect the performance of the co-existing antennas are required. The third and final part of the thesis focuses on this topic and describes the design steps required to realize a low-scattering antenna, i.e., an inductively loaded, chopped dipole that is transparent at a higher frequency than where it operates. It is experimentally demonstrated how the radar cross section of the designed antenna is reduced at the higher frequency 15 dB, while the radiation efficiency of the dipole decreases 0.4 dB at its operation frequency due to the inductive loading.