Browsing by Author "Ala-Laurinaho, Juha, Dr., Aalto University, 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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    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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    Developments in imaging at millimeter and submillimeter wavelengths
    (Aalto University, 2013) Tamminen, Aleksi; Ala-Laurinaho, Juha, Dr., Aalto University, Finland; Radiotieteen ja -tekniikan laitos; Department of Radio Science and Engineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Räisänen, Antti, Professor, Aalto University, Finland
    This thesis presents novel experimental results in the fields of millimeter- and submillimeter-wave imaging, reflectivity studies, as well as power detector characterization. The overlapping topics share key concepts of beam steering, holography, and antenna measurements. Indirect holographic imaging technique is verified experimentally for the first time. This method allows for coherent detection of a target, using a reference wave and simple direct detection receivers. This is very promising, since receiver complexity is seen as the greatest hindrance to the realization of large imaging arrays. In the holographic method, coherent detection and focusing of the image is a post-detection task. A novel computational technique is introduced, which removes the restrictions on the reference-wave direction. In the experimental work at 310 GHz, the slanted-edge method is applied for estimating the point spread function. Experimental data indicate a decrease in resolution of 20-30 % compared to a diffraction limited case. The noise-equivalent reflectivity difference (NERD) is found to be approximately constant (NERD = 0.002), down to the received signal SNR of 26 dB. Reflectarrays (RAs) are developed and characterized at 120 GHz. The RAs enable beam-steering, and they are designed to be compatible with MEMS microfabrication. Three static RAs are characterized in a near-field measurement range. The measured beamwidths are within 10 % of the simulated ones. The specular reflection from RAs is studied, and the concept of RA efficiency is introduced. The experimentally determined efficiency is found to be 0.11 while simulation results suggest an average efficiency of 0.54. Reflection- and transmission-type phase holograms are used to create a planar wave front, quiet zone (QZ), in a compact test range at both 310 and 650 GHz. The measured QZ variation is ±1.5 dB and ±5° at 310 GHz and ±3 dB and ±25° at 650 GHz. The holograms are suitable for use in radar-cross-section (RCS) measurements. The reflectivity of different radar-absorbing materials (RAMs) is studied in a RCS range. Commercial RAM and low-cost materials are compared for their monostatic reflectivity in an angular range of 45° and 12° at 310 and 650 GHz, respectively. It is found that common materials, such as carpets have reflectivity from −60 to −30 dB, and are suitable for use as RAM. Bolometers used in a submillimeter-wave imager are studied at 321-782 GHz. The antenna-coupled microbolometers are characterized in room temperature. They are coupled with an equi-angular spiral antenna and a silicon substrate lens. The beamwidth of the bolometers is found to follow an 8.5°/THz –relation across the band. A low-cost infrared detector is compared with dedicated power meters. It is found to have a sensitivity of 1700 V/W and noise-equivalent power (NEP) of 0.4 uW/rtHz. As such, it can be used as an ad hoc power detector.
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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.
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    Millimetre and submillimetre wave antenna design using ray tracing
    (Aalto University, 2013) Karttunen, Aki; Ala-Laurinaho, Juha, Dr., Aalto University, Finland; Radiotieteen ja -tekniikan laitos; Department of Radio Science and Engineering; Sähkötekniikan korkeakoulu; School of Electrical Engineering; Räisänen, Antti, Prof., Aalto University, Finland
    The millimetre and submillimetre wave frequency ranges have many current and potential applications for example in satellite technology and telecommunications. Electrically large antennas are needed in several applications, e.g., in order to achieve high antenna gain with a narrow beam. Reflector and lens antennas, with all dimensions large compared to the wavelength, are commonly designed using ray tracing. Ray tracing is based on a high frequency approximation of Maxwell’s equations. The main advantage of ray tracing is the decreased computational effort as compared to more accurate full-wave methods. In this thesis, ray tracing is used in both synthesis and simulation of electrically large antennas. In the first part of this thesis, a 650 GHz dual reflector feed system (DRFS) is designed, tested, and used in a hologram-based compact antenna test range (CATR). The DRFS provides shaped illumination that simplifies the hologram manufacturing. A ray-tracing based numerical synthesis method is used to design the 650 GHz DRFS. It is tested with antenna measurements prior to the compact range measurements. The designed DRFS is used successfully in a full scale compact range, in which a 1.5-m antenna is tested at 650 GHz. In the second part of this thesis, several beam-steering integrated lens antennas (ILAs) are designed with ray-tracing simulations. Antenna prototypes are designed, fabricated, and tested at 77 GHz with antenna measurements. Electrical beam steering is demonstrated with integrated feed arrays and switching networks. Also, beam-steering properties of ILAs with a wide range of different lens permittivities and feed element directivities are studied with ray-tracing simulations. Lens shapes are developed for improvement of the beam properties at large beam-steering angles. With a low permittivity ILA, an intermediate eccentricity, compared to those of the conventional hemispherical and elliptical lenses, is found to have smaller scan loss and lower side-lobes with large beam-steering angles of about 30°. Placing the feeds on a spherical surface of an extended hemispherical ILA is found to result in a beam shape and gain that remain nearly constant at beam-steering angles up to about 25°. A typical disadvantage of a beam-steering ILA is the increase of the internal reflections with the increase of the feed offset. It is shown that the extension of a low permittivity extended hemispherical ILA can be shaped to significantly reduce the internal reflections. It is also shown that it is possible to design an integrated lens antenna with low reflection loss (< 1 dB), for moderate beam-steering angles (< 15°), with any lens permittivity and with any feed element directivity. The reduction of internal reflections is based on the selection of the original ellipse radius larger than the final lens radius and designing the shape of the extension for minimal reflections.