Endre søk
Begrens søket
1 - 31 of 31
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Amin, Shoaib
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. University of Gävle, Sweden.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rönnow, Daniel
    ATM, University of Gävle.
    Digital Predistortion of Single and Concurrent Dual BandRadio Frequency GaN Amplifiers with Strong NonlinearMemory Effects2017Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 65, nr 7, s. 2453-2464Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electrical anomalies due to trapping effects in gallium nitride (GaN) power amplifiers (PAs) give rise to long-term or strong memory effects. We propose novel models based on infinite impulse response fixed pole expansion techniques for the behavioral modeling and digital predistortion of single-input single-output (SISO) and concurrent dual-band GaN PAs. Experimental results show that the proposed models outperform the corresponding finite impulse response (FIR) models by up to 17 dB for the same number of model parameters. For the linearization of a SISO GaN PA, the proposed models give adjacent channel power ratios (ACPRs) that are 7-17 dB lower than the FIR models. For the concurrent dual-band case, the proposed models give ACPRs that are 9-14 dB lower than the FIR models.

  • 2.
    Amin, Shoaib
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. Högskolan i Gävle.
    Landin, Per
    Chalmers University of Technology.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rönnow, Daniel
    Högskolan i Gävle.
    Behavioral modeling and linearization of crosstalk and memory effects in RF MIMO transmitters2014Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 62, nr 4, s. 810-823Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper proposes three novel models for behavioral modeling and digital pre-distortion (DPD) of nonlinear 2 x 2 multiple-input multiple-output (MIMO) transmitters in the presence of crosstalk. The proposed models are extensions of the single-input single-output generalized memory polynomial model. Three types of crosstalk effects were studied and characterized as linear, nonlinear, and nonlinear & linear crosstalk. A comparative study was performed with previously published models for the linearization of crosstalk in a nonlinear 2 x 2 MIMO transmitter. The experiments indicate that, depending on the type of crosstalk, the selection of the correct model in the transmitter is necessary for behavioral modeling and sufficient DPD performance. The effects of coherent and partially noncoherent signal generation on the performance of DPD were also studied. For crosstalk levels of 30 dB, the difference in the normalized mean square error and adjacent channel power ratio was found to be 3-4 dB between coherent and partially noncoherent signal generation.

  • 3. Anttila, Lauri
    et al.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Valkama, Mikko
    Joint Mitigation of Power Amplifier and I/Q Modulator Impairments in Broadband Direct-Conversion Transmitters2010Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 58, nr 4, s. 730-739Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a novel digital predistorter structure for joint mitigation of frequency-dependent power amplifier (PA) and in-phase and quadrature (I/Q) modulator impairments in direct-conversion radio transmitters. The predistorter is based on an extended parallel Hammerstein structure, yielding a predistorter that is fully linear in the parameters. In the parameter estimation stage, the indirect learning architecture is utilized. The proposed technique is the first technique in the literature to consider the joint estimation and mitigation of frequency-dependent PAand I/Q modulator impairments. Extensive simulation and measurement analysis is carried out to verify the operation and efficacy of the proposed predistortion structure. It is shown that the adjacent channel power ratio is increased by more than 20 dB in all experiments when using the proposed method, and that the performance of the reference techniques is clearly exceeded.

  • 4.
    Baghaei Nejad, Majid
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektronik- och datorsystem, ECS.
    Radiom, Soheil
    Katholieke Universiteit Leuven.
    Vandenbosch, Guy A. E.
    Katholieke Universiteit Leuven.
    Tenhunen, Hannu
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektronik- och datorsystem, ECS.
    Zheng, Li-Rong
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Elektronik- och datorsystem, ECS.
    Gielen, Georges G. E.
    Katholieke Universiteit Leuven.
    Miniaturization of UWB antennas and its influence on UWB-transceiver performanceInngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670Artikkel i tidsskrift (Annet vitenskapelig)
  • 5.
    Baghchehsaraei, Zargham
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Oberhammer, Joachim
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Parameter Analysis of Millimeter-Wave Waveguide Switch Based on a MEMS-Reconfigurable Surface2013Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 61, nr 12, s. 4396-4406Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a novel concept of a millimeter-wave waveguide switch based on amicroelectromechanical (MEMS)-reconfigurable surface with insertion loss and isolation very similar to high performance but bulky rotary waveguide switches, despite its thickness of only 30 mu m. A set of up to 1470 micromachined cantilevers arranged in vertical columns are actuated laterally by on-chip integrated MEMS comb-drive actuators, to switch between the transmissive state and the blocking state. In the blocking state, the surface is reconfigured so that the wave propagation is blocked by the cantilever columns short-circuiting the electrical field lines of the TE10 mode. A design study has been carried out identifying the performance impact of different design parameters. The RF measurements (60-70 GHz) of fabricated, fully functional prototype chips show that the devices have an isolation between 30 and 40 dB in the OFF state and an insertion loss between 0.4 and 1.1 dB in the ON state, of which the waveguide-assembly setup alone contributes 0.3 dB. A device-level yield analysis was carried out, both by simulations and by creating artificial defects in the fabricated devices, revealing that a cantilever yield of 95% is sufficient for close-to-best performance. The actuation voltage of the active-opening/active-closing actuators is 40-44 V, depending on design, with high reproducibility of better than (sigma = 0.0605 V). Lifetime measurements of the all-metal, monocrystalline-silicon core devices were carried out for 14 h, after which 4.3 million cycles were achieved without any indication of degradation. Furthermore, a MEMS-switchable waveguide iris based on the reconfigurable surface is presented.

  • 6.
    Bagheriasl, Mohammad
    et al.
    Sorbonne Univ, L2E, UR2, F-75005 Paris, France..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Valerio, Guido
    Sorbonne Univ, L2E, UR2, F-75005 Paris, France..
    Bloch Analysis of Artificial Lines and Surfaces Exhibiting Glide Symmetry2019Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 67, nr 7, s. 2618-2628Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Glide-symmetric structures have recently emerged as a smart choice to design planar lenses and electromagnetic bandgap materials. We discuss here the conditions under which a glide-symmetric structure is equivalent to a nonglide-symmetric structure with a reduced period. To this aim, we propose an analysis method based on network theory to efficiently derive the dispersive behavior of these periodic structures. Both phase and attenuation constants can be determined, with potential applications to both guiding and radiating structures. Retaining higher order modal interactions among cells helps to derive the dispersive behavior of periodic structures more accurately. Furthermore, we take advantage of the higher symmetry of these structures to decrease the computational cost by considering only one half or one-quarter of a unit cell instead of the entire cell. We study one and 2-D glide-symmetric structures and confirm the validity of our analysis with comparisons from commercial software.

  • 7.
    Berglind, Eilert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Björk, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Humblet's Decomposition of the Electromagnetic Angular Moment in Metallic Waveguides2014Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 62, nr 4, s. 779-788Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In a seminal paper, Humblet decomposed the angular momentum of a classical electromagnetic field as a sum of three terms: the orbital angular momentum (OAM), the spin, and the more unfamiliar surface angular momentum. In this paper, we present the result of such decomposition for various metallic waveguides. We investigate two hollow metal waveguides with circular and rectangular cross sections, respectively. The waveguides are excited with two TE eigenmodes driven in phase quadrature. As references, two better known modes are also analyzed: a plane, a circularly polarized wave (a TEM mode), and a TE-Bessel beam, both of infinite transverse extent and with no metallic boundaries. Our analysis shows that modes carrying OAM and spin can also propagate in the metallic waveguides, even when the cross section of the waveguide is distinctly non-circular. However, the mode density of orthogonal modes carrying OAM is at most equal to that of the waveguides' eigenmodes.

  • 8.
    Chen, Qiao
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion. Southeast Univ, State Key Lab Millimeter Waves, Nanjing 210096, Jiangsu, Peoples R China.
    Ghasemifard, Fatemeh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Valerio, Guido
    Sorbonne Univ, Lab Elect & Electromagnetisme, F-75005 Paris, France..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Modeling and Dispersion Analysis of Coaxial Lines With Higher Symmetries2018Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, nr 10, s. 4338-4345Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, 1-D periodic structures possessing higher symmetries are proposed and investigated in terms of their dispersion properties. The proposed structures are coaxial lines with coaxial rings periodically loaded on their inner or outer conductors. The higher symmetries, namely, glide and twist symmetries, are obtained by performing an additional geometrical operation within the unit cell of the periodic structure. We demonstrate that the propagating modes exhibit a lower frequency dispersion in higher symmetric coaxial lines. Moreover, the conventional stopbands of periodic structures at their Brillouin zone boundaries can be controlled by breaking the higher symmetry or changing the order of the twist symmetry. A circuit-based analytical method is proposed to calculate the dispersion diagram of the glide-symmetric coaxial lines. The results are validated with a full-wave simulation. Moreover, several prototypes of the twist-symmetric coaxial lines are manufactured and measured. A remarkable agreement is achieved between the measurements and simulations, validating the theoretical results. The proposed structures find potential applications in leaky-wave antennas and fully metallic reconfigurable filters and phase shifters.

  • 9.
    Ebrahimpouri, Mahsa
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Rajo-Iglesias, Eva
    Sipus, Zvonimir
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Cost-Effective Gap Waveguide Technology Based on Glide-Symmetric Holey EBG Structures2018Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, nr 2, s. 927-934Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a novel electromagnetic bandgap (EBG) structure, which can be used to manufacture low-cost waveguiding structures at high frequencies. The unit cell of the proposed EBG consists of glide-symmetric holes in parallel plate waveguide. Using this unit cell in groove gap waveguide technology has a number of advantages over pin-type EBG at high frequencies, such as acquiring higher accuracy because of larger periodicity as well as an easier and cheaper manufacturing process. The performance of the proposed waveguiding structure is demonstrated using both a straight and a double 90 degrees bent lines through simulation and measurement.

  • 10.
    Glubokov, Oleksandr
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Xinghai, Zhao
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Campion, James
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Beuerle, Bernhard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Shah, Umer
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Oberhammer, Joachim
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Mikro- och nanosystemteknik.
    Investigation of Fabrication Accuracy and Repeatability of High-Q Silicon-Micromachined Narrowband Sub-THz Waveguide Filters2019Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 67, nr 9, s. 3696-3706Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the fabrication accuracy and repeatability of micromachined quadruplet filters designed at a center frequency of 270 GHz with a 5-GHz bandwidth using a versatile multilayer chip platform which allows for axially arranged waveguide ports. A large number of narrowband silicon-micromachined filters arranged on multiple chips are investigated for fabrication imperfections, assembly misalignment, and fabrication yield, employing fabrication-prediction and different chip-to-chip self-alignment feature strategies. A numerical technique for characterization of the entire fabrication process of the filters through extracting the error statistics for coupling coefficients of a large number of different samples from separately assembled chips is proposed. A total of 47 test filters in effectively 15 different design variants have been fabricated in two fabrication runs, evaluated, and analyzed. The most critical sources of errors are determined. The expected accuracy of the entire filters fabrication process is demonstrated through the yield analysis based on the collected error statistics.

  • 11.
    Isaksson, Magnus
    et al.
    University of Gävle.
    Wisell, David
    University of Gävle.
    Rönnow, Daniel
    University of Gävle.
    A Comparative Analysis of Behavioral Models for RF Power Amplifiers2006Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 54, nr 1, s. 348-359Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A comparative study of nonlinear behavioral models with memory for radio-frequency power amplifier (PAs) is presented. The models are static polynomial, parallel Hammerstein (PH), Volterra, and radial basis-function neural network (RBFNN). Two PAs were investigated: one was designed for the third-generation (3G) mobile telecommunication systems and one was designed for the second-generation (2G). The RBFNN reduced the total model error slightly more than the PH, but the error out of band was significantly lower for the PH. The Volterra was found to give a lower model error than did a PH of the same nonlinear order and memory depth. The PH could give a lower model error than the best Volterra, since the former could be identified with a higher nonlinear order and memory depth. The qualitative conclusions are the same for the 2G and 3G PAs, but the model errors are smaller for the latter. For the 3G PA, a static polynomial gave a low model error as low as the best PH and lower than the RBFNN for the hardest cross validation. The models with memory, PH, and RBFNN, showed better cross-validation performance, in terms of lower model errors, than a static polynomial for the hardest cross validation of the 2G PA.

  • 12.
    Isaksson, Magnus
    et al.
    University of Gävle.
    Wisell, David
    Ericsson AB, Gävle.
    Rönnow, Daniel
    University of Gävle.
    Wide-band dynamic modeling of power amplifiers using radial-basis function neural networks2005Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 53, nr 11, s. 3422-3428Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A radial-basis function neural network (RBFNN) has been used for modeling the dynamic nonlinear behavior of an RF power amplifier for third generation. In the model, the signal's envelope is used. The model requires less training than a model using IQ data. Sampled input and output signals were used for identification and validation. Noise-like signals with bandwidths of 4 and 20 MHz were used. The RBFNN is compared to a parallel Hammerstein (PH) model. The two model types have similar performance when no memory is used. For the 4-MHz signal, the RBFNN has better in-band performance, whereas the PH is better out-of-band, when memory is used. For the 20-MHz; signal, the models have similar performance in- and out-of-band. Used as a digital-predistortion algorithm, the best RBFNN with memory suppressed the lower (upper) adjacent channel power 7 dB (4 dB) compared to a memoryless nonlinear predistorter and 11. dB (13 dB) compared to the case of no predistortion for the same output power for a 4-MHz-wide signal.

  • 13.
    Khan, Zain Ahmed
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. Högskolan i Gävle.
    Zenteno, Efrain
    Universidad Católica San Pablo.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Isaksson, Magnus
    Högskolan i Gävle.
    Digital Predistortion for Joint Mitigation of I/Q Imbalance and MIMO Power Amplifier Distortion2016Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, nr 99, s. 1-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper analyzes the joint effects of in-phase and quadrature (I/Q) imbalance and power amplifier (PA) distortion for RF multiple input multiple output (MIMO) transmitters in the presence of crosstalk. This paper proposes candidate models for the digital predistortion of static I/Q imbalanced sources exciting a dynamic MIMO Volterra system. The proposed models are enhanced using a novel technique based on subsample resolution to account for dynamic I/Q imbalance distortions. Finally, the computational complexity of the proposed models is analyzed for implementation suitability in digital platforms. It is shown that the error spectrum for the proposed models in subsample resolution reaches the noise floor of the measurements. The proposed models achieve a normalized mean squared error of -50 dB and an adjacent channel power ratio of -57 dB for signal bandwidths upto 65 MHz and crosstalk levels ranging to -10 dB. These results demonstrate the effectiveness of the proposed techniques in the joint mitigation of I/Q imbalance and PA distortion with crosstalk for a typical 2x2 MIMO telecommunication setup.

  • 14.
    Khan, Zain Ahmed
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Zenteno, Efrain
    Universidad Católica San Pablo.
    Händel, Peter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Teknisk informationsvetenskap.
    Isaksson, Magnus
    University of Gävle.
    Extraction of the Third-Order 3x3 MIMO VolterraKernel Outputs Using Multitone Signals2018Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, nr 11, s. 4985-4999Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper uses multitone signals to simplify theanalysis of 3×3 multiple-input multiple-output (MIMO) Volterrasystems by isolating the third-order kernel outputs from eachother. Multitone signals fed to an MIMO Volterra system yielda spectrum that is a permutation of the sums of the inputsignal tones. This a priori knowledge is used to design multitonesignals such that the third-order kernel outputs are isolated inthe frequency domain. The signals are designed by deriving theconditions for the offset and spacing of the input frequency grids.The proposed technique is then validated for the six possibleconfigurations of a 3x3 RF MIMO transmitter impaired bycrosstalk effects. The proposed multitone signal design is usedto extract the third-order kernel outputs, and their relativecontributions are analyzed to determine the dominant crosstalkeffects for each configuration.

  • 15.
    Landin, Per N.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Van Moer, W.
    Isaksson, M.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Peak-power controlled digital predistorters for RF power amplifiers2012Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 60, nr 11, s. 3582-3590Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the issue of predistorter blow-up, i.e., uncontrolled peak expansion caused by the predistorter. To control the peak expansion, an extension of the multistep indirect learning architecture (MS-ILA) is proposed by adding a constraint that describes the allowed peak power of the predistortion signal. The resulting optimization problem is shown to be convex and an optimization method is formulated to solve it.

  • 16.
    Landin, Per Niklas
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Fritzin, Jonas
    University of Linköping.
    Van Moer, Wendy
    Vrije Universiteit Brussel.
    Isaksson, Magnus
    University of Gävle.
    Alvandpour, Atila
    University of Linköping.
    Modeling and digital predistortion of class-D outphasing RF power amplifiers2012Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 60, nr 6, s. 1907-1915Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a direct model structure for describing class-D outphasing power amplifiers (PAs) and a method for digitally predistorting these amplifiers. The direct model structure is based on modeling differences in gain and delay, nonlinear interactions between the two paths and differences in the amplifier behavior. The digital predistortion method is designed to operate only on the input signals' phases, to correct for both amplitude and phase mismatches. This eliminates the need for additional voltage supplies to compensate for gain mismatch.

    Model and predistortion performance are evaluated on a 32 dBm peak output power, class-D outphasing PA in CMOS with on-chip transformers. The excitation signal is a 5 MHz downlink WCDMA signal with peak-to-average power ratio (PAPR) of 9.5 dB. Using the proposed digital predistorter, the 5 MHz adjacent channel leakage power ratio (ACLR) was improved by 13.5 dB, from -32.1 dBc to -45.6 dBc. The 10 MHz ACLR was improved by 6.4 dB, from -44.3 dBc to -50.7 dBc, making the amplifier pass the 3GPP ACLR requirements.

  • 17. Mohottige, Nandun
    et al.
    Glubokov, Oleksandr
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Jankovic, Uros
    Budimir, Djuradj
    Ultra Compact Inline E-Plane Waveguide Bandpass Filters Using Cross Coupling2016Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 64, nr 8, s. 2561-2571Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents novel ultracompact waveguide bandpass filters that exhibit pseudoelliptic responses with the ability to place transmission zeros on both sides of the passband to form sharp rolloffs. The filters contain E-plane extracted pole sections (EPSs) cascaded with cross-coupled filtering blocks. Compactness is achieved by the use of evanescent mode sections and closer arranged resonators modified to shrink in size. The filters containing nonresonating nodes are designed by means of the generalized coupling coefficients' extraction procedure for the cross-coupled filtering blocks and EPSs. We illustrate the performance of the proposed structures through the design examples of third-and fourth-order filters with center frequencies of 9.2 and 10 GHz, respectively. The sizes of the proposed structures suitable for fabricating using the low-cost E-plane waveguide technology are 38% smaller than ones of the E-plane extracted pole filter of the same order.

  • 18.
    Nader, Charles
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Landin, Per Niklas
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Van Moer, Wendy
    Vrije Universiteit Brussel, ELEC department.
    Björsell, Niclas
    University of Gävle, Radio center for measurement technology.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Performance Evaluation of Peak-to-Average Power Ratio Reduction and Digital Pre-Distortion for OFDM Based Systems2011Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 59, nr 12, s. 3504-3511Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we evaluate the effect of applying peak-to-average power ratio (PAPR) reduction and digital pre-distortion (DPD) on two types of radio frequency power amplifiers when an orthogonal frequency division multiplexing (OFDM) signal is used. The power amplifiers under test are a standard class-AB amplifier and a Doherty amplifier. The PAPR reduction methods are based on a state-of-the art convex optimization formulation and on the standard clipping and filtering technique. The DPD method consists of modeling the behavior of the power amplifier using a parallel Hammerstein model, and then extracting the inverse parameters based on the indirect learning architecture. To achieve better DPD performance, extracting the DPD parameters based on multiple-step iterations is investigated. The cases where PAPR reduction and DPD are applied separately and combined are studied and investigated. Power amplifier figures of merit are evaluated. Good performance is shown when combining both pre-processing techniques up to a certain operating point where DPD performance deteriorates due to generation of strong peaks in the signal. In addition, a difference in the power amplifier behavior is reported and analyzed.

  • 19.
    Nader, Charles
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Landin, Per Niklas
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Van Moer, Wendy
    Vrije Universiteit Brussel, ELEC department.
    Björsell, Niclas
    University of Gävle, Radio center for measurement technology.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Rönnow, Daniel
    University of Gävle, Radio center for measurement technology.
    Peak-power controlling technique for enhancing digital pre-distortion of RF power amplifiers2012Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 60, nr 11, s. 3571-3581Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we present a method to limit the generation of signal peak power at the output of a digital pre-distorter that is applied to a RF power amplifier (PA) operating in strong compression. The method can be considered as a joint crest-factor reduction and digital pre-distortion (DPD). A challenging characteristic of DPD when applied to a PA in strong compression is the generation of relatively high peaks due to the DPD expansion behavior. Such high peaks generation, which may be physically unrealistic, can easily damage the amplification system. Such a phenomenon, referred in this study as DPD-avalanche, is more noticed when the signal exciting the PA is compressed due to crest-factor reduction. The suggested method for controlling such DPD-avalanche is based on shaping the input signal to the DPD in such a way to keep the pre-distorted signal peak power below or near the maximum allowed peak power of the PA. The suggested method is tested experimentally on a Class-AB and a Doherty PA when excited with a wideband orthogonal frequency-division multiplexing (OFDM) signal. Scenarios for an OFDM signal with and without crest-factor reduction are evaluated. Measurement results when using the proposed DPD-avalanche controller show smooth deterioration of the in-band and out-of-band linearity compared to steep deterioration when no controller is used. In addition, the suggested controller offers a higher operating power range of the DPD while fulfilling out-of-band distortion requirements and preserving low in-band error.

  • 20.
    Nader, Charles
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. University of Gävle, Sweden; Vrije Universiteit Brussel, Belgium.
    Van Moer, Wendy
    Vrije Universiteit Brussel, Belgium.
    Barbé, Kurt
    Vrije Universiteit Brussel, Belgium.
    Björsell, Niclas
    University of Gävle, Sweden.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. University of Gävle, Sweden.
    Harmonic Sampling and Reconstruction of Wideband Undersampled Waveforms: Breaking the Code2011Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 59, nr 11, s. 2961-2969Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, a method for measuring wideband waveforms correctly when undersampling is used as a digitizing technique is presented. Two major challenges arise when undersampling wideband waveforms: overlapping of aliased spectral bins of the digitized waveform and ambiguity in spectral bins standing on multiples of the Nyquist frequency. Those challenges are more pronounced when using wideband modulated signals to excite nonlinear devices. The theory behind a correct undersampled measurement is based on the use of an irrational relation between the undersampling frequency and the spectral resolution of the waveform to measure. This is the key to a successful harmonic sampling used today in large-signal network analyzers when wideband modulated waveforms are to be measured. Inverting the problem, such theory is also the solution for reconstructing wideband undersampled waveforms based on a single measurement and with a relatively short record of measured data. It is a solution for RF sampling and cognative radios where the digital processing is moving toward the antenna of the receiver.

  • 21.
    Norgren, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Chebyshev collocation and Newton-type optimization methods for the inverse problem on nonuniform transmission lines2005Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 53, nr 5, s. 1561-1568Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A frequency-domain inverse problem for the nonuniform LCRG transmission line is considered. The parameters of the nonuniform line are interpolated by Chebyshev polynomials, and the Telegraphers equations are solved by a collocation method using the same polynomials. The interpolation coefficients for the unknown parameters are reconstructed by means of Newton-type optimization methods for which the Jacobian matrix has been calculated explicitly. For the reconstruction of one or two parameters, the algorithm is tested on synthetic data, and the necessity to use regularization is discussed. Finally, the algorithm is tested with measured reflection data to reconstruct shunt capacitances with piecewise constant profiles.

  • 22.
    Shah, Umer
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Sterner, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Oberhammer, Joachim
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    High-Directivity MEMS-Tunable Directional Couplers for 10–18-GHz Broadband Applications2013Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 61, nr 9, s. 3236-3246Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports on two novel concepts of areaefficient, ultra-wideband, MEMS-reconfigurable coupled line directional couplers, whose coupling is tuned by mechanically changing the geometry of 3-D micromachined coupled transmission lines, utilizing integrated MEMS electrostatic actuators. Concept 1 is based on symmetrically changing the geometry of the ground coupling of each signal line, while Concept 2 is simultaneously varying both the ground coupling and the coupling between the two signal lines. This enables uniform and well predictable performance over a very large frequency range, in particular a constant coupling ratio while maintaining an excellent impedance match, along with high isolation and a very high directivity. For an implemented micromachined prototype 3-to-6 dB coupler based on Concept 1, the measured isolation is better than 16 dB, and the return loss and directivity are better than 10 dB over the entire bandwidth from 10 to 18 GHz. Concept 2 presents an even more significant improvement. For an implemented 10-to-20 dB prototype based on Concept 2, the measured isolation is better than 40 dB and the return loss is better than 15 dB over the entire bandwidth from 10 to 18 GHz for both states. The directivities for both states are better than 22 dB and 40 dB, respectively, over the whole frequency range. The measured data fits the simulation very well, except for higher through-port losses of the prototype devices. All devices have been implemented in an SOI RF MEMS fabrication process. Measured actuation voltages of the different actuators are lower than 35 V. Reliability tests were conducted up to 500 million cycles without device degradation.

  • 23.
    Shah, Umer
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Sterner, Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Oberhammer, Joachim
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Multi-Position RF MEMS Tunable Capacitors Using Laterally Moving Sidewalls of 3-D Micromachined Transmission Lines2013Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 61, nr 6, s. 2340-2352Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a novel concept of RF microelectromechanical systems (MEMS) tunable capacitors based on the lateral displacement of the sidewalls of a 3-D micromachined coplanar transmission line. The tuning of a single device is achieved in multiple discrete and well-defined tuning steps by integrated multi-stage MEMS electrostatic actuators that are embedded inside the ground layer of the transmission line. Three different design concepts, including devices with up to seven discrete tuning steps up to a tuning range of 58.6 to 144.5 fF, (C-max/C-min = 2.46) have been fabricated and characterized. The highest Q factor, measured by a weakly coupled transmission-line resonator, was determined as 88 at 40 GHz and was achieved for a device concept where the mechanical suspension elements were completely de-coupled from the RF signal path. These devices have demonstrated high self-actuation robustness with self-actuation pull-in occurring at 41.5 and 47.8 dBm for mechanical spring constants of 5.8 and 27.7 N/m, respectively. Nonlinearity measurements revealed that the third-order intermodulation intercept point (IIP3) for all discrete device states is above the measurement-setup limit of 68.5 dBm for our 2.5-GHz IIP3 setup, with a dual-tone separation of 12 MHz. Based on capacitance/gap/spring measurements, the IIP3 was calculated for all states to be between 71-91 dBm. For a mechanical spring design of 5.8 N/m, the actuation and release voltages were characterized as 30.7 and 21.15 V, respectively, and the pull-in time for the actuator bouncing to drop below 8% of the gap was measured to be 140 mu s. The mechanical resonance frequencies were measured to be 5.3 and 17.2 kHz for spring constant designs of 5.8 and 27.7 N/m, respectively. Reliability characterization exceeded 1 billion cycles, even in an uncontrolled atmospheric environment, with no degradation in the pull-in/pull-out hysteresis behavior being observed over these cycling tests.

  • 24.
    Somjit, Nutapong
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikrosystemteknik.
    Stemme, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Mikrosystemteknik.
    Oberhammer, Joachim
    KTH, Skolan för elektro- och systemteknik (EES), Mikrosystemteknik.
    Binary-Coded 4.25-bit W-Band Monocrystalline-Silicon MEMS Multistage Dielectric-Block Phase Shifters2009Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 57, nr 11, s. 2834-2840Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a novel concept of a microwave microelectromechanical systems (MEMS) reconfigurable dielectric-block phase shifter with best loss/bit at the nominal frequency and best maximum return and insertion loss ever reported over the whole W-band. A seven-stage phase shifter is constructed by lambda/2-long high-resistivity silicon dielectric blocks, which can be moved vertically by MEMS electrostatic actuators based on highly reliable monocrystalline silicon flexures on-top of a 3-D micro-machined coplanar transmission line. The dielectric constant of each block is artificially tailor made by etching a periodic pattern into the structure. Stages of 15 degrees, 30 degrees, and 45 degrees are optimized for 75 GHz and put into a binary-coded 15 degrees + 30 degrees + 5 x 45 degrees configuration with a total phase shift of 270 degrees in 19 x 15 degrees steps (4.25 bits). Return and insertion losses are better than -17 and -3.5 dB at 75 GHz, corresponding to a loss of -0.82 dB bit, and a phase shift efficiency of 71.1 degrees/dB and 490.02 degrees/cm. Return and insertion losses are better than 12 and 4 dB for any phase combination up to 110 GHz (98.3 degrees/dB; 715.6 degrees/cm). The intercept point of third order, determined by nonlinearity measurements and intermodulation analysis, is 49.15 dBm for input power modulation from 10 to 40 dBm. The power handling is only limited by the transmission line itself since no current-limiting thin air-suspended metallic bridges as in conventional MEMS phase shifters are utilized. This is confirmed by temperature measurements at 40 dBm at 3 GHz with skin effect adjusted extrapolation to 75 GHz by electrothermal finite-element method simulations.

  • 25.
    Töpfer, Fritzi
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Dudorov, Sergey
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Oberhammer, Joachim
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Millimeter-Wave Near-Field Probe Designed for High-Resolution Skin Cancer Diagnosis2015Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 63, nr 6, s. 2050-2059Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a detailed technical characterization of a micromachined millimeter-wave near-field probe developed for skin cancer diagnosis. The broadband probe is optimized for frequencies from 90 to 104 GHz and consists of a dielectric- rod waveguide, which is metallized and tapered towards the tip to achieve high resolution by concentrating the electric field in a small sample area. Several probes with different tip sizes were fabricated from high-resistivity silicon by micromachining and were successfully characterized using silicon test samples with geometry- defined tailor-made permittivity. The probes show a high responsivity for samples with permittivities in the range of healthy and cancerous skin tissue at 100 GHz (from 3.2 - j2.3 to 7.2 - j8.0, loss tangent of approximately 1.26). The sensing depth was determined by simulations and measurements from 0.3 to 0.4 mm, which is adapted for detecting early-stage skin tumors before they metastasize. The lateral resolution was determined to 0.2 mm for a tip size of 0.6 x 0.3 mm, which allows for resolving small skin tumors and inhomogeneities within a tumor.

  • 26.
    Valerio, Guido
    et al.
    Sorbonne Univ, Lab Elect & Electromagnetisme, UR2, F-75005 Paris, France..
    Ghasemifard, Fatemeh
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Sipus, Zvonimir
    Univ Zagreb, Fac Elect Engn & Comp, HR-10000 Zagreb, Croatia..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Glide-Symmetric All-Metal Holey Metasurfaces for Low-Dispersive Artificial Materials: Modeling and Properties2018Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, nr 7, s. 3210-3223Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the wave propagation between two glide-symmetric metallic plates drilled with periodic rectangular holes. A mode-matching method is proposed in order to derive efficiently the dispersive properties of these periodic structures. The method takes advantage of the higher symmetry of the structure reducing the computational cost by enforcing boundary conditions on the field on only one of the two surfaces. Physical insight on specific symmetry properties of Floquet harmonics in glide-symmetric structures is also gained. The code is validated with commercial software assessing its accuracy when varying the most influential/critical parameters. We confirm the potential of glide-symmetric structures to tune the effective refractive index. Specifically, we demonstrate that glide-symmetric structures with rectangular shapes can be employed to synthesize anisotropic refractive indexes with a large band of operation, which makes such metasurface structures applicable for the realization of ultrawideband planar lenses.

  • 27.
    Wang, Lei
    et al.
    Hamburg Univ Technol TUHH, Inst Electromagnet Theory, D-21079 Hamburg, Germany..
    Luis Gomez-Tornero, Jose
    Tech Univ Cartagena, Dept Commun & Informat Technol, Cartagena 30202, Spain..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Substrate Integrated Waveguide Leaky-Wave Antenna With Wide Bandwidth via Prism Coupling2018Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 66, nr 6, s. 3110-3118Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    New communications systems require high-speed data transfer and need high frequency, wideband, and directive antennas. Leaky-wave antennas are a desirable type of antennas for millimeter and submillimeter waves, since they can produce a high directive radiation with a single feeding. The latter is an enormous advantage to reducing the cost and losses at high frequency. Despite these advantages, their dispersive nature inherently produces a beam squint effect in their radiation patterns. Here, we propose the use of a lens that compensates for the dispersion of the leaky wave, making the overall antenna broadband. This concept is demonstrated in substrate integrated waveguide technology at Ka-band, and the lens is integrated in the same technology. Full-wave simulations and experimental results are presented to demonstrate the potential of our proposal. Our manufactured prototype has more than 20% frequency bandwidth for the 3-dB pattern at (sic) = 31 degrees, and the main radiating direction steers only +/- 0.5 degrees from 35 to 40 GHz with a half-power beamwidth of 8 degrees.

  • 28.
    Wang, Lei
    et al.
    Hamburg Univ Technol, Inst Electromagnet Theory, D-21079 Hamburg, Germany..
    Luis Gomez-Tornero, Jose
    Tech Univ Cartagena, Dept Commun & Informat Technol, Cartagena 30202, Spain..
    Quevedo-Teruel, Oscar
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknisk teori och konstruktion.
    Substrate Integrated Waveguide Leaky-Wave Antenna With Wide Bandwidth via Prism Coupling (vol 66, pg 3110, 2018)2019Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 67, nr 1, s. 262-262Artikkel i tidsskrift (Fagfellevurdert)
  • 29.
    Willen, Bo G.
    et al.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Rohner, M.
    Schnyder, I.
    Jackel, H.
    Improved automatic parameter extraction of InP-HBT small-signal equivalent circuits2002Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 50, nr 2, s. 580-583Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An improved automatic extraction technique for determination of the element values of an InP heterojunction-bipolar-transistor small-signal T-model is presented. Numerical optimization is shown to yield reproducible and physically relevant results when using a suitable figure-of-merit. The outcome of such an extraction is displayed for a range of operation points and the resulting bias dependencies of the element values is shown to be in good agreement with theoretical effects. The technique is further used to validate the quality of the extraction itself by showing a significant sensitivity to a deliberate error in the value of each element.

  • 30.
    Zenteno, Efrain
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre. University of Gavle.
    Isaksson, Magnus
    University of Gävle.
    Händel, Peter
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Output Impedance Mismatch Effects on the Linearity Performance of Digitally Predistorted Power Amplifiers2015Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 63, nr 2, s. 1-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper analyzes the effects of load impedance mismatch in power amplifiers which linearity has been enhanced using various digital predistortion (DPD) algorithms. Two different power amplifier architectures are considered: a class AB and a Doherty amplifier and three model structures for the DPD model are compared: memoryless polynomial (MLP), general memory polynomial (GMP) and Kautz-Volterra functions (KV). This paper provides a sensitivity analysis of the linearized amplifiers under load mismatch conditions and reports the performance when dynamic parameter identification for the DPD is used to compensate for the changes in the load impedance. In general,power amplifiers linearity is sensitive to load impedance mismatch. Linearity may degrade as much as 10 dB (in normalized mean square error) according to the magnitude and the phase of the reflection coefficient provided by the load impedance. However, depending on the amplifier design, the sensitivity toload impedance mismatch varies. While the Doherty amplifier studied show significant linearity degradations in the in-band and out-of-band distortions, the out-of-band distortions of the studied class AB were less sensitive to the load impedance mismatch. In adaptive DPD schemes, the performance obtained in the MLP model does not benefit from the updating scheme and the performance achieved is similar to a static case, where no updates are made. This stresses the memory requirements in the predistorter. When employing the GMP and the KV models in an adaptive DPD scheme, they tackle to a larger extent the linearity degradations due to load impedance mismatch.

  • 31.
    Zenteno, Efrain
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Ronnow, Daniel
    MIMO Subband Volterra Digital Predistortion for Concurrent Aggregated Carrier Communications2017Inngår i: IEEE transactions on microwave theory and techniques, ISSN 0018-9480, E-ISSN 1557-9670, Vol. 65, nr 3, s. 967-979Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a multiple-input multipleoutput (MIMO) nonlinear mitigation technique for closely spaced concurrent aggregated carrier systems. The transmitter architecture considers band-limited sources, where the predistorter and signal bandwidth are the same, thus reducing transmitter hardware cost and power consumption. The technique relies on multirate processing and linear filtering and uses the carrier frequencies to isolate the contribution of linear and nonlinear basis functions to the desired bands. This approach can be used with any MIMO model structure. In particular, models are linear in the parameters of low computational complexity. The technique was evaluated using three concurrent carriers of 50 MHz each fed to a Doherty amplifier. The results show significant reduction in the error vector magnitude and improvements for the transmitter efficiency using the proposed compensation technique.

1 - 31 of 31
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf