Browsing by Author "Viikari, Ville, Assoc. Prof., Aalto University, Department of Electronics and Nanoengineering, Finland"

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    Adaptive Multiport Antennas for Handsets
    (Aalto University, 2021) Luomaniemi, Rasmus; Lehtovuori, Anu, 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
    Generally, the main factors driving the evolution of modern handset antennas are the requirements for increasing the data capacity and the visual appearance restricting the volume of the antennas. To increase the data transfer rates, new bands with wider frequency ranges are used together with an increasing number of multiple-input multiple-output (MIMO) antennas. The appearance of the device is an important factor in the smartphone industry. However, nearby conductive objects, such as the screen or metal rim of the device, hinder the operation of the antennas. Therefore, new innovations and techniques are required to reach these difficult goals. This thesis studies whether multiport antenna techniques can be used to address the aforementioned challenges. In the first part of this thesis, new design methods for multiport handset antennas are presented. The first method can be used to design switch-reconfigurable antenna systems. The rim is used for MIMO operation on different frequency bands with switches and the proposed design method makes the optimization process efficient. The proposed antennas achieve 30-40 % total efficiency in the 700-960 MHz band and 25-75 % total efficiency in the 1.7-2.7 GHz and 3.0-4.0 GHz bands. The second method utilizes multiport antennas and characteristic modes to utilize an unbroken metal rim for MIMO antennas. The proposed antennas achieve an efficiency of 15-59 % at low band and 25-80 % at higher bands. The second part of this thesis focuses on the interaction between the user and multiport antennas. First, the effect of the user's hand on the operation of the antennas designed in the first part is investigated. Given the promising results obtained, the study is extended to include the user in the design process from the beginning. A design process for hand-immune antennas based on the characteristic modes of both the metallic antenna structure and lossy dielectrics of the user is presented. The resulting antennas achieve a total efficiency of more than 30 % at low band with the user holding the device. A common problem even with multiport antennas is the ability to achieve a wide enough bandwidth. The third part of this thesis presents a method for realizing antennas in extremely small volumes inside smartphones by taking advantage of the gap between the battery and the back cover of the device. An average total efficiency of 35 % is achieved across the 3.3-4.2 GHz band with an antenna height of only 0.75 mm. Following that, a more general design tool for accelerating the design process of multiport antennas is presented. Using the quality factor combined with a proper choice of feeding signals, the achievable performance of a structure can be estimated without the need for time-consuming matching network optimization. The new and computationally efficient design methods developed in this work enable the realization of antennas with improved performance. Moreover, the presented antenna designs demonstrate the benefits of multiport antennas in comparison to traditional solutions.
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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.
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    Beam-switching antennas for millimeter-wave communications
    (Aalto University, 2021) Karki, Sabin Kumar; 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
    Millimeter-wave frequencies, i.e. 30-300 GHz, are being widely adopted in commercial applications such as communication systems, radar, and imaging. At millimeter-wave frequencies, the antennas need to be directive to mitigate the higher free-space loss and atmospheric attenuation. In addition, the beam steering capability helps to extend the coverage to a wide angular range. The objective of the thesis is to develop high-gain and wide beam-steering antennas based on the beam-switching topology. The thesis contributes to the improvement of the integrated lens antenna (ILA) and the feed beam-switching network (BSN) performance. The ILAs are evaluated in terms of form-factor and scan-loss reduction and efficiency improvement. The study of BSN is aimed towards insertion loss reduction and enabling beam reconfigurability. An elliptical ILA with a focal length to diameter ratio, f/d, of 1.1 and a diameter of 160 mm is designed to meet the gain and beam-steering regulations for the point-to-point link antennas operating at 71-76 GHz. The f/d of an elliptical ILA is reduced to 0.88 by using the high permittivity material. An integrated metal-plate lens (IMLA), a combination of the dielectric and metal-plate lens, is proposed to reduce the focal length. The IMLA with 0.69 f/d is designed to achieve a total efficiency of 64% in comparison to 45% of the traditional ILA. The radiation pattern tilting of the offset feeds along the focal plane improved the scan loss of the IMLA by 3.5 dB compared to a traditional ILA. Furthermore, the reduction of scan loss and the extension of the beam steering range of the hemispherical ILA is achieved by positioning the feeds along the spherical surface. The second part of the thesis focuses on the BSN. The numerical study demonstrates that the ILA radiation properties are mostly affected by the radiation pattern distortion of the beam-switching feed array rather than the coupling between the feed ports. The BSN of the Rotman lens fed array is implemented with the 4-channel vector modulator (VM) instead of the RF-switch to minimize the insertion loss. The Rotman lens-based array uses the 1×4 SIW-fed microstrip patch antenna arrays as the radiating elements and a novel easy-to-implement admittance control mechanism is demonstrated for the SIW-fed series arrays. The beam-configurability of the Rotman lens-based array is attained by simultaneous excitation of the beam ports with the VM, which varies the half power beamwidth from 18° to 75°.
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    Co-Existing Antennas in Modern Handsets
    (Aalto University, 2020) Kurvinen, Joni; Lehtovuori, Anu, 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
    Fifth generation (5G) mobile networks significantly increase the data transfer rates of wireless communications. This increase is achieved by utilizing multiple-input multiple-output (MIMO) systems at sub-6 GHz frequencies. Furthermore, 5G introduces new millimeter-wave (mm-wave) frequencies in which more bandwidth is available for high-capacity communications. A common factor for both frequency ranges is that handsets should be equipped with more antennas than before. Another challenge for antenna designers is the limitations set by the phone industry. Current smartphones are already densely packed, with a maximized screen-to-body ratio. Due to the limited volume, antennas must be integrated into the handset body. However, phone manufacturers are strict about the visual appearance of the device, which further restricts the placement of the antennas. The first part of this thesis presents methods to integrate antennas into the handset body at both the sub-6 GHz and the mm-wave frequencies. The sub-6 GHz antennas are implemented in the metal frame of a handset with a fully metallic back cover according to industry requirements. The antenna performance is confirmed with antenna measurements. 5G mm-wave antennas are desired to be dual-polarized and to operate at two frequency bands. The effect of the handset chassis on the antenna performance is investigated. The second part of the thesis considers the co-existence of mm-wave and sub-6 GHz antennas with a focus on effective volume utilization. To fit all the required antennas into a handset, antennas must be able to perform in a shared volume. A mm-wave antenna is designed and located within the same space as the traditional LTE antenna, and the mm-wave antenna is enclosed with plastic and radiates through an opening in the metal frame of the phone. The plastic isolates the two antennas and allows adequate performance for both. The presented co-design method is verified, and the beam-steering capability of the mm-wave antenna is demonstrated experimentally. Integrating mm-wave antennas into the metal frame of a phone might short-circuit the sub-6 GHz antennas and thus destroy the LTE performance. To prevent the short-circuiting, a design method for a capacitively-loaded feed line is developed. The loaded feed line behaves like a transmission line at mm-waves frequencies but presents as a small common-mode capacitance at the sub-6 GHz range. This behavior allows sub-6 GHz antennas to operate normally. The presented method enables improved integration of mm-wave antennas into the metal frame of a phone.
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    Millimeter-wave antennas for 5G handsets and base stations
    (Aalto University, 2020) Montoya Moreno, Resti; 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
    The massive increase in the number of connected devices is making it necessary to use higher frequencies and wider bandwidths. The use of frequencies in the 20-300 GHz will enable achieving higher capacities and data rates. In order to compensate for the higher free-space path loss and increased atmospheric absorption directive antenna elements have to be used and, thus, beam-steering and beam-forming capabilities are needed. In this thesis, mm-wave antennas in the 24-35 GHz range are developed. The designs include both mobile phone and base station antennas since both of them will have to evolve to meet the demands of 5G networks. The first part of this thesis focuses on finding mm-wave antenna solutions for 5G mobile handsets. The mobile phone antennas radiate towards the end-fire direction with respect to the mobile phone. The designs present dual-polarized operation and wide-angle beam-steering for increased reliability. Moreover, the mm-wave antennas are designed so that they do not heavily degrade the performance of the already present sub-6 GHz antennas. The proposed solutions include 3 and 4-element arrays which are either integrated in the metal frame of the mobile phone, or radiate through a small window in it. The second part of this thesis introduces 5G base station antennas and their challenges. The base station antennas presented are scalable in the number of antenna elements in order to adapt to different use cases. Moreover, and as a huge amount of base stations are going to be required with the development of 5G, the antennas are energy efficient and relatively cheap to manufacture. They present beam-steering or beam-switching capabilities in order to keep track of the mobile users, as well as high directivity. The designs presented include an efficient 16-element horn antenna phased-array, and a wide-angle dual-polarized beam-switching lens antenna.