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

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    Advances in Wideband Phased Antenna Array Design and Manufacturing at Millimeter Waves
    (Aalto University, 2022) Kähkönen, Henri; Ala-Laurinaho, Juha, Dr., Aalto University, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    Fifth-generation (5G) telecommunication networks have shifted to millimeter-waves (mm-waves) to provide a broader spectrum of available frequency for the increasing number of wireless devices and to meet the demand for higher data rates. Antenna arrays are key components of these new radio-frequency (RF) systems. The antennas become physically smaller, and electrically larger arrays become feasible with an entire array fitting into the same volume as a single dual-polarized sub-6 GHz antenna element, the type previously used. Larger antenna arrays enable massive multiple-input and multiple-output (MIMO) and beam steering, increasing the potential available data rates even further. Furthermore, the technology in beam-steerable antenna arrays in telecommunication applications converges with the hardware used previously only in sensors, such as radars. In future, sensing could become an integrated part of multipurpose antenna arrays and used together with telecommunication applications, to increase the safety of autonomous vehicles, for example. This thesis presents antenna arrays for mm-wave handset and base station applications at Ka- and E-bands, which are portions of the radio spectrum in the microwave range of frequencies at 26–40 GHz and 60–90 GHz, respectively. Three different antenna array designs are discussed: a dual-polarized Vivaldi antenna array for Ka-band; a co-designed Vivaldi antenna array for handsets; and a dielectric-filled waveguide antenna array. The dual-polarized Ka-band Vivaldi antenna is an element design that can be made from a single metal piece or by using additive manufacturing processes. The antenna is surface-mounted on a printed circuit board (PCB) and does not require separate RF connectors, enabling more cost-efficient devices. The antenna is characterized by a beam-steerable, 8×8 element configuration. Additionally, a modular design with 4×4 elements and beamforming integrated circuits (ICs) with the same footprint has been developed. The antenna array design is demonstrated using both conventional machining and additive manufacturing processes. The mm-wave Vivaldi antenna array for metal-rim handsets is co-designed with the 4G Long Term Evolution (LTE) antenna. The antenna array is implemented within the same volume as the LTE antenna without affecting the performance of either antenna. The mm-wave antenna radiates through an aperture in the metal rim of the handset and is suitable for 25–30 GHz frequencies with good electrical performance. The dielectric-filled waveguide antenna is designed for E-band. The developed antenna uses dielectric-filled waveguides to decrease the waveguide dimensions and to enable an element spacing of λ/2. The proposed design is a four-element array that is fed from a single WR-12 waveguide port. It uses a 1-to-4 waveguide power division network.
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    Antenna mutual coupling and amplifier effects in transmission
    (Aalto University, 2024) Kutinlahti, Veli-Pekka; Lehtovuori, Anu, Dr., Aalto University, Department of Electronics and Nanoengineering, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    The oncoming fifth generation (5G) telecommunication standard utilizes multi-antenna systems to implement multiple-input multiple-output and beam-steering capabilities in most wireless devices, including mobile devices. This shift in transceiver architecture will introduce each antenna element with its own feed control, along with an amplifier and phase shifter chain. The high integration level of these components prohibits the use of traditional ferrite circulators as isolators between the components, introducing the non-ideality of active reflections in the antenna elements to the amplifier outputs. The change in amplifier load impedance causes variation in amplifier output power, linearity, efficiency and can possibly even cause breakage of components in extreme cases. This development is parallel to the fact that 5G will use higher frequencies and wider bandwidth signals, driving the development of innovative design methods to achieve wide-band high-gain antennas with beam-steering capability. The first part of the thesis describes optimizing different aspects of amplifier-antenna systems with mutual-coupling-induced mismatch. First, the equivalent isotropic radiated power (EIRP) of a 2x2 patch antenna array in an amplifier-antenna system is optimized through phase tuning. Phase tuning achieves a maximum 0.7-dB improvement in EIRP within the -3-dB beam steer range at 2.5 GHz, compared to progressive phase shift. Second, the 3rd order intermodulation is minimized with respect to the carrier by adjusting input feed power and phase in a two-tone excited 1x4 amplifier-antenna array, where the beam at each tone is independently steered. Optimization results in a 25-dB improvement in the signal-to-3rd-order-intermodulation ratio without decreasing far-field power density. However, this improvement comes at the cost of sacrificing beam integrity in terms of side-lobe level. Third, 3rd order intermodulation with respect to the carrier is minimized by antenna impedance matching using co-simulations of the amplifier and antenna. The second part considers the optimization of realized gain in antenna arrays. First, an antenna array driven with element-specific amplifiers with varying output impedance is examined. Changes in amplifier gain may lead to altered output impedance and increased mismatch in the antenna interface, a phenomenon often neglected. An iterative method that accounts for the change in impedance is introduced, resulting in increased realized gain. Second, a cluster array concept is proposed to achieve high coverage gain over a wider band compared to a simple patch antenna array with similar elements. The cluster array utilizes patch elements with different resonant frequencies and high inter-element coupling to achieve wide-band matching with feeding weight tuning.
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    Design and Optimization Methods for Multiport Antennas
    (Aalto University, 2022) Kormilainen, Riku; Lehtovuori, Anu, Dr., Aalto University, Finland; Liesiö, Juuso, Assoc. Prof., Aalto University, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    Modern wireless communications has evolved greatly within the past 30 years, and antennas are a significant part of the today's society. Almost everyone has a smartphone equipped with multiple antennas, and antennas are found in many everyday household objects and devices such as washing machines, coffee makers, and robotic vacuum cleaners. Furthermore, wearable antennas (such as those in medical devices, clothes, and watches) are becoming increasingly popular. In summary, antennas are placed in unconventional locations demanding new antenna design methods. Multiport antennas may provide benefits as compared to traditional single-port antennas. Therefore, this thesis discusses novel design methods for multiport antennas which requires new design methods. This thesis is divided into three part The first part studies using practical decoupling and matching networks (DMNs) in multiple-input-multiple-output (MIMO) antennas and antenna arrays. A DMN for a four-port MIMO antenna is realized with sufficient bandwidth, and a method is presented for optimizing a DMN of an antenna array with a commercial circuit synthesis tool by applying a unit cell model. The second part of the thesis discusses a method to optimize the radiation efficiency of a multiport antenna. The method provides an ultimate efficiency limit for a given multiport antenna in terms of its port characteristics. The developed method can be viewed as a design tool of sorts, and its practicality is demonstrated by designing a mobile MIMO antenna based on the results obtained with this method.  The third part of the thesis focuses on extending the multiport antenna method discussed in the second part. The method is extended to optimize the partial radiation efficiency of multiport antennas and the realized gain of an antenna array comprising multiport elements. Although these methods are based on theoretical formulation, they enable a systematic way to realize practical multi-port antennas. The methods developed within this thesis provide a basis for developing multiport antennas. This hopefully advances the use of multiport antennas and enables the design of better and more complex antennas for future needs.
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    Multi-band 5G Antenna Designs for Smartphones
    (Aalto University, 2024) Chen, Quangang; Lehtovuori, Anu, Dr., Aalto University, Department of Electronics and Nanoengineering, Finland; Ala-Laurinaho, Juha, Dr., Aalto University, Department of Electronics and Nanoengineering, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    In the pursuit of increasing data transmission rates, mobile communications have rapidly evolved into the 5G era. With more and more frequency bands being specified and utilized, one of the longstanding challenges in mobile phone antenna design has been to cover multiple communication bands within the limited internal space of a phone. The introduction of Multiple-Input Multiple-Output (MIMO) technology and millimeter-wave (mm-wave) technology, together with the attractive visual appearance of handsets, has presented new challenges for mobile phone antenna design. The first part of this thesis concentrates on frequency-reconfigurable antennas, specifically utilizing lumped components. A full metal-rimmed model serves as a basis in the antenna designs covering hepta-band of 4G and C-band of 5G. A decoupling method of 5G MIMO antennas is also proposed based on the current suppression in a ring slot. Subsequent designs in this part focus on the frequency-reconfigurable antennas in the mm-wave frequency band. Required capacitance is first studied in the frequency band from 24 to 43.5 GHz, and practical antenna design is then implemented with commercially available tunable components, covering a frequency band from 23.2-30.2 GHz with total efficiency larger than -2.5 dB. A novel cluster array concept is introduced in the second part for frequency tunability through the adjustment of feeding weights. Realized gains of antenna arrays are maximized using eigenvalues of electric-field results. The proposed approach can be applied to various antenna designs to improve the spherical coverage in a wide frequency range. For instance, diverse patch and dipole elements, which can be seen as multiple-resonance circuits, are employed to illustrate this concept. The third part presents a dual-polarized end-fire antenna array as a supplement to broadside antennas achieving full spherical coverage required for the 5G mm-wave applications. Multiple resonant modes are generated through the use of a novel stacked antenna with a low profile for vertical polarization. The overlapped bandwidth of the vertical polarization and horizontal polarization ranges from 24 to 43.5 GHz. The methods developed in this thesis achieve the multiple frequency bands for 5G mobile communications. This work contributes to the antenna designs for modern smartphones, incorporating the research between practical applicability and innovative approaches.
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    Novel Modulated Backscattered Communication Techniques for Transponder Based on Multiple Antennas
    (Aalto University, 2022) Siddiqui, Tauseef Ahmad; Holopainen, Jari, Dr., Aalto University, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    Recently, existing ambient radio frequency (RF) signals such as those from Wi-Fi APs, Bluetooth devices, TV towers, FM broadcasting stations and cellular base stations have been proposed to be reused for backscatter communication as they can, in principle, provide power continuously. In this context, an advanced version of RFID technology with sensing capabilities can play a pivotal role in the large-scale deployment of the Internet of Things (IoT). However, the RF sources in ambient backscatter communications systems (ABCSs) are unpredictable regarding transmission powers, frequencies and locations. Therefore, the design and deployment of an ambient backscatter device to achieve optimal performance is often more complicated. Clearly, a single antenna will not be sufficient, given the requirement for a long read range with high-speed data communication in sensor nodes operating over a wide range of frequencies. Multiple antennas should instead be employed for efficient operation. Smart antenna solutions such as frequency-reconfigurable antennas, beam-and-polarization steerable antennas are needed with more advanced modulators.The first part of the thesis presents a new concept of transponder that can independently perform amplitude and phase modulation. Such a modulator enables modulation schemes that necessitate multiple states. Multi-state modulation schemes can possibly carry more bits per a unit time at the same modulation frequency. The second part of the thesis introduces a broadband transponder concept that enables the device to select the frequency band with the highest power density. Multiple, closely spaced antenna elements with adjustable phase weighting are combined to create a transponder that can be tuned to function across many frequency bands. The theory necessary to support this objective is formulated, and the concept is experimentally verified. The last part of the thesis aims to design a beam-steerable transponder capable of independently steering at least two beams simultaneously by adjusting modulator delays. This allows the device to receive signals from one direction and re-scatter them to another. Alternatively, the device can gather energy from two directions simultaneously. The operation principle with an analytical model is explained for both monostatic and bistatic cases and the most feasible structure and control circuit are demonstrated in practice.
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    Space-Saving Antenna Solutions for Mobile Devices
    (Aalto University, 2024) Varheenmaa, Harri; Lehtovuori, Anu, D.Sc. (Tech.), Aalto University, Department of Electronics and Nanoengineering, Finland; Ylä-Oijala, Pasi, Ph.D., Aalto University, Department of Electronics and Nanoengineering, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    Smartphones are an essential part of modern society and antennas have a vital role in the operation of the phone and mobile communications infrastructure. In recent years, smartphones with a full edge-to-edge screen and a metal rim have been the goal of the phone manufacturers but designing the antennas on such devices is demanding task. A full edge-to-edge screen significantly reduces the available room for antennas since antennas can then only be located on the rim. Compared to plastic rim, the metal rim increases the coupling, which decreases efficiency. Additionally, modern handhelds require multiple antennas to cover all of the required fifth-generation (5G) frequency bands, increase the data transfer rate, and reduce the hand effect. Implementing all necessary 5G antennas is challenging due to limited space, manufacturing cost constraints, and unavailability of decoupling structures. This thesis proposes non-conventional ways to implement antennas in limited space. First, still unused space for antenna is identified in back cover. The designed antenna achieves good performance despite the challenging position where there is only a 1-mm gap between the radiating element and the metallic battery. Noteworthily, as the back-cover antenna radiates toward the user the specific absorption rate (SAR) must be considered. This thesis proposes the following three different strategies for reducing the SAR by almost half without affecting the radiated power: specific geometry, a matching circuit, and an antenna cluster with properly calculated feeding weights. The second space-saving design is an eight-element sub-6 GHz multiple-input multiple-output antenna design that is suitable for a smartphone with a highly desirable full edge-to-edge screen and metal rim. Its compact size (17.9mm × 7mm) is achieved by bending the antenna slots. Due to three excited current modes, the frequency band is wide (3.4–6.1 GHz) and the total efficiency is high (58–95%). Additionally, manufacturing costs and even more space are saved with a simple structure that does not require any decoupling solutions. The third design proposed in this thesis saves space by integrating a sub-6 GHz antenna and a millimeter-wave (mmWave) antenna into the same volume. This shared-aperture antenna requires even less room since the sub-6 GHz and mmWave antennas have a wide frequency band (3.4–6 GHz and 26.5–29.5 GHz, respectively). Attributable to the high isolation (15.3 dB), these antennas do not interfere each other’s operation and the total efficiency is good (65–95%). Furthermore, the beam steering range of the mmWave antenna is ±}40◦. Additionally, the proposed shared-aperture antenna design is suitable for mobile devices with a full edge-to-edge screen and a metal rim. The antenna solutions developed in this thesis demonstrate how antennas can be integrated into crowded devices, where the usable space is minimal, by retaining the required technical performance while also considering the implementation aspects.
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    Towards Power Autonomous Wireless Sensors
    (Aalto University, 2019) Mc Caffrey, Colm; Pursula, Pekka, Dr., Technical Research Center of Finland VTT, Finland; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    To enable widespread deployment of sensor systems in our world, they must be wireless and power autonomous. There is no universal solution to achieve such a device. Instead a system level approach must be taken that considers the sensor, its readout, wireless communications and powering methods available in the context of the application requirements and sensor system lifetime. Achieving power autonomy requires a two front approach; addressing both the need and the supply. The optimisation of power consumption in this work focuses on the radio communications, highlighted as one of the most power critical subsystems. A power-optimised system enables the exploitation of application appropriate energy sources; whether they be battery power in the case of short lifetime devices, energy harvesting where reliable sources exist, wireless power transfer where it can be applied, or passive radio backscattering techniques. This thesis presents four independent systems, each a power autonomous solution in the context of its application requirements. The first system integrates a voltammetric electronic tongue sensor for gastrointestinal disease diagnosis, with power provided by a high-density lithium manganese dioxide primary cell, ample for the 72 hours operation time of the capsule. The capsule contains an electrically small loop antenna and communicates wirelessly at 433 MHz to a remote receiver. The second system applies a MEMS acoustic emission sensor for online condition monitoring of valve leakage in the petrochemical industry, utilising thermal energy harvesting in the sensor node, and industrial current loop harvesting in the gateway to achieve power autonomy for continuous operation. The device communicates at 2.45 GHz and includes an ultra-low power wake-up radio based on passive down converting receiver to enable the sensor to be in an ultra-low power mode and asynchronously interrogated by the gateway. The third system exploits resonant inductive coupling for the actuation of a wirelessly powered soft robotic caterpillar which itself is potentially a fully passive wireless sensor platform. The system utilises a frequency sweeping power transmission mechanism, around 8.5 MHz, to wirelessly transfer energy to multiple shape memory alloy actuators, enabling the generation of a wave of force through the caterpillar body providing locomotion. The fourth system employs a fully passive wireless sensing platform based on radio backscattering at UHF frequencies (around 868 MHz), and a harmonic resonant sensor based on the third order intermodulation principle. In its entirety, this work represents progress on multiple fronts on the key challenge of powering the next generation of IoT devices.
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    UHF RFID Transponder Antenna Solutions for Enhanced Performance and Producibility
    (Aalto University, 2019) Jaakkola, Kaarle; Elektroniikan ja nanotekniikan laitos; Department of Electronics and Nanoengineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Viikari, Ville, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland
    As a means of automatic identification, passive UHF RFID technology provides clear benefits over its competitor technologies, such as optical codes or RFID technologies operating at lower frequencies. Perhaps the greatest of these benefits is the long read range that can be achieved with a tag that is relatively simple and small. However, the exploitation of the radiating far field as the coupling method between the reader and the transponder, which enables the long read range, also makes the tags sensitive to their near environment. Consequently, the combination of a metallic use environment, long read range and a small, low-cost tag is difficult to achieve in practice. In this thesis, new concepts of implementing UHF RFID transponders are studied and presented. Additionally to performance and versatility, the production cost is always an important parameter for a means of automatic identification. Therefore, in this thesis, a special emphasis has been put on the producibility of the presented tags. In practice, this means that the tags developed are suitable for mass production and their performance is not too sensitive to the parametric variation that always occurs in the industrial fabrication processes. The tag solutions presented in this thesis are divided into two main categories: small all-platform tags and tags implemented with alternative conductor materials. The small all-platform tags are fabricated with printed circuit board and inlay technologies. The alternative conductor materials studied are graphene and aluminium-doped zinc oxide (AZO). Graphene is an interesting new material that is eco-friendly and printable. Additionally to the raw material itself being non-toxic, fabricating the transponder by printing can replace the currently used etching process that produces toxic waste. Thin-film AZO is a transparent conductor material that enables transparent antennas and thus invisible transponders to be used on e.g. windows or windshields. Even though these new materials provide new features and benefits, they both set special challenges that mainly relate to the conductivity that is remarkably lower than that of bulk metal. The attachment of the microchip is another challenge that, in order to keep the tags commercially viable, should not form a bottleneck in the fabrication process. Even though the radiating far-field is the main coupling method for a UHF RFID system, for some applications that do not require a long read range, inductive near-field coupling is an attractive option. Two near field tag solutions are presented in this thesis; the first one is a solution for tagging metal items that form a challenge to conventional near-field tags. The second one combines graphene as the conductor material and the chip attachment by glue-bonding, providing a small, eco-friendly and mass-producible tag.