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Microwave Theory and Techniques, IEEE Transactions on

Issue 8 • Date Aug. 2014

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  • Table of contents

    Publication Year: 2014 , Page(s): C1 - C4
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  • IEEE Transactions on Microwave Theory and Techniques publication information

    Publication Year: 2014 , Page(s): C2
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  • Editorial

    Publication Year: 2014 , Page(s): 1569
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  • An FDTD Model of Graphene Intraband Conductivity

    Publication Year: 2014 , Page(s): 1570 - 1578
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1913 KB) |  | HTML iconHTML  

    A novel finite-difference time-domain (FDTD) model of magnetized graphene gyrotropic conductivity is proposed in this paper. The model, derived with the aid of auxiliary differential equations, takes into account intraband electron transitions, which are prevailing over interband conductivity terms up to terahertz frequencies. It is shown on the basis of equivalent circuit representation that a static magnetic bias changes a Drude dispersion characteristic of graphene into an extended Lorentz model supplemented with an additional branch accounting for the induced gyrotropy. The proposed FDTD updated equations are successfully validated with analytical results available in the literature. Computational efficiency of the algorithm is also tested. View full abstract»

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  • Approximate Evaluation of the Integration of Green's Function for Parallel Interconnects

    Publication Year: 2014 , Page(s): 1579 - 1589
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    An approximate analytical scheme is proposed in this paper to evaluate the integration of the Green's function, on the background of parallel interconnects. The free-space Green's function is expanded in Taylor's series and integrated term-wise. Instead of handling double-volume integrals directly by numerical or purely analytical means, the expressions of double-line integrals for two parallel filaments are first derived. Following the clue to geometrical mean distance, for the expanded terms of nonnegative orders, a second-order mean distance is introduced to represent the role of the cross section so that the volume integration can be evaluated by using the formulas of line integration. Numerical results show that the presented method bears better performance than existing approaches. View full abstract»

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  • Symmetrical Large-Signal Modeling of Microwave Switch FETs

    Publication Year: 2014 , Page(s): 1590 - 1598
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2195 KB) |  | HTML iconHTML  

    This paper presents a new symmetrical field-effect transistor (FET) model suitable for microwave switches. The model takes advantage of the inherent symmetry of typical switch devices, justifying a new small-signal model where all intrinsic model parameters can be mirrored between the positive and negative drain-source bias regions. This small-signal model is utilized in a new and simplified approach to large-signal modeling of these type of devices. It is shown that the proposed large-signal model only needs a single charge expression to model all intrinsic capacitances. For validation of the proposed model, small-signal measurements from 100 MHz to 50 GHz and large-signal measurements at 600 MHz and 16 GHz, are carried out on a GaAs pHEMT. Good agreement between the model and the measurements is observed under both small- and large-signal conditions with particularly accurate prediction of higher harmonic content. The reduced measurement requirements and complexity of the symmetrical model demonstrates its advantages. Further, supporting operation in the negative drain-source voltage region, the model is robust and applicable to a variety of circuits, e.g., switches, resistive mixers, oscillators, etc. View full abstract»

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  • Microwave Properties of MAPTMS Sol-Gel Films for High-Speed Electrooptic Devices

    Publication Year: 2014 , Page(s): 1599 - 1604
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    This paper measures the dielectric constant and loss tangent of methacryloyloxy-propyltrimethoxysilane (MAPTMS) sol-gel films over a wide range of microwave frequencies. Samples were prepared by spin-coating sol-gel films onto metallized borosilicate glass substrates. The dielectric properties of the sol-gel were probed up to 50 GHz with several different sets of coplanar waveguide transmission lines electroplated onto sol-gel films. The dielectric constant and loss tangent are determined to be approximately 3.1 and 3×10-3 at 35 GHz, respectively. This demonstration shows that MAPTMS sol-gel is a viable material for integration with high-speed electrical and electrooptic devices. View full abstract»

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  • Enhanced Modelling of Split-Ring Resonators Couplings in Printed Circuits

    Publication Year: 2014 , Page(s): 1605 - 1615
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    An enhanced equivalent circuit approach for the magnetic/electric interaction of single split-ring resonators (SRRs) with printed lines is presented in this paper. A very simple and efficient lumped-element network is proposed to model the behavior of metamaterial-based printed lines over a wide frequency band. The same circuit topology can be used for the single- and two-mirrored SRRs loaded microstrip line. The corresponding circuit parameters are obtained from the multiconductor transmission line theory as well as from closed-form expressions that make use of just the resonance frequency and minimum of the reflection coefficient (which should be previously extracted from experiments or full-wave simulations). The comparison of our equivalent circuit results with measurements and full-wave simulations has shown a very good agreement in a considerably wider frequency band than other previously proposed simple equivalent circuits. View full abstract»

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  • Analysis and Design of a Novel Low-Loss Hollow Substrate Integrated Waveguide

    Publication Year: 2014 , Page(s): 1616 - 1624
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1396 KB) |  | HTML iconHTML  

    In this paper, a novel hollow substrate integrated waveguide (HSIW) is presented for realizing low-loss millimeter-wave (mm-wave) transmission lines embedded in multi-chip modules. A new analysis method for the HSIW is proposed by treating it as a combination of a two-dielectric loaded rectangular waveguide (RWG) and standard substrate integrated waveguide, where an effective dielectric constant, εe, is introduced. An HSIW prototype in the Ka-band is fabricated using a progressive-lamination low-temperature co-fired ceramic technique. The measured results agree well with theoretical calculations and simulations. An average of 0.009-dB/mm loss is achieved in Ka-band, which is comparable to an air-filled RWG. This shows that the technique has great potential for further development to realize highly integrated mm-wave modules. View full abstract»

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  • Slow-Wave Substrate Integrated Waveguide

    Publication Year: 2014 , Page(s): 1625 - 1633
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1783 KB) |  | HTML iconHTML  

    This paper describes a new concept of substrate integrated waveguide (SIW): a slow-wave substrate integrated waveguide (SW-SIW). Compared to a conventional SIW, the proposed topology requires a double-layer substrate with a bottom layer including internal metallized via-holes connected to the bottom conductive plane. The slow-wave effect is obtained by the physical separation of electric and magnetic fields in the structure. Electromagnetic simulations show that this topology of SIW allows decreasing the longitudinal dimension by more than 40% since the phase velocity is significantly smaller than that of a classical SIW. Simultaneously, the lateral dimension of the waveguide is also reduced. By considering a double-layer technology, SW-SIWs exhibiting a cutoff frequency of 9.3 GHz were designed, fabricated, and measured. The transversal dimension and the phase velocity of the proposed SW-SIW are both reduced by 40% as compared to a classical SIW designed for the same cutoff frequency, leading to a significant surface reduction. Moreover, an original kind of taper is proposed to achieve a good return loss when the SW-SIW is fed by a microstrip transmission line. View full abstract»

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  • Dimensional Synthesis of Coupled-Resonator Pseudoelliptic Microwave Bandpass Filters With Constant and Dispersive Couplings

    Publication Year: 2014 , Page(s): 1634 - 1646
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1831 KB) |  | HTML iconHTML  

    In this paper, we propose a novel technique for the dimensional synthesis of coupled-resonator pseudoelliptic microwave filters with constant and dispersive couplings. The proposed technique is based on numerical simulations of small structures, involving up to two adjacent resonators, and it accounts for a loading effect from other resonators by replacing them with terminations coupled through appropriately scaled inverters. The dimensions of the resonators and coupling elements are determined by an optimization process that matches the zeros and poles of the simulated response of a low-order circuit consisting of one or two coupled resonators connected to a source and to matched loads with the eigenvalues of a submatrix obtained from the coupling matrix of the lumped-element model of the filter. To assure high accuracy and rapid convergence, a zero-pole optimization algorithm was used. The application of this method is illustrated with four examples involving a simple fourth-order open-loop microstrip filter with two transmission zeros, through a triplet with one transmission zero, a quadruplet with two asymmetric transmission zeros located on both sides of the passband, to a fourth-order waveguide filter with three transmission zeros. The validity of the method is confirmed by an experiment involving a filter with dispersive coupling realized in substrate-integrated waveguide technology. View full abstract»

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  • Synthesis Model and Design of a Common-Mode Bandstop Filter (CM-BSF) With an All-Pass Characteristic for High-Speed Differential Signals

    Publication Year: 2014 , Page(s): 1647 - 1656
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2064 KB) |  | HTML iconHTML  

    A new common-mode bandstop filter (CM-BSF) with an all-pass performance (from dc to 9 GHz) for differential signals is proposed by using a C-shaped patterned ground structure (PGS) with meandered signal lines on a two-layer printed circuit board (PCB). This technique can successfully generate two close transmission zeros in common-mode within the frequencies of concern. A corresponding equivalent circuit model is established to predict the filter behaviors, and a formula for common-mode transmission zeros is derived based on the circuit model. Next, a design method is developed and a synthesis procedure is proposed. According to the procedure, a wideband CM-BSF is synthesized and fabricated on a two-layer PCB. In addition, the simulation and experiment results are demonstrated to verify the technique and show excellent performance of the proposed CM-BSF. It is shown that common-mode noise can be suppressed over 10 dB from 1.9 to 8.9 GHz with 130% fractional bandwidth (FBW) while the insertion loss of differential-mode can be kept less than 3 dB from dc to 9 GHz. The electrical size is only 0.21 λg ×0.21 λg, where λg is the wavelength of the stopband central frequency. To sum up, the proposed CM-BSF has merits of low cost (two layer), a simple geometric structure, a compact size, and a large common-mode FBW. Most importantly, the filter can keep good signal integrity of the digital differential signals due to its all-pass characteristic. View full abstract»

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  • Investigation of Higher Order Reentrant Modes of a Cylindrical Reentrant-Ring Cavity Resonator

    Publication Year: 2014 , Page(s): 1657 - 1662
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    Analysis of the properties of resonant modes in a reentrant cavity structure comprising of a post and a ring was undertaken and verified experimentally. In particular we show the existence of higher order reentrant cavity modes in such a structure. Results show that the new cavity has two re-entrant modes, one of which has a better displacement sensitivity than the single post resonator and the other with a reduced sensitivity. The more sensitive mode is better than the single post resonator by a factor of 2 to 1.5 when the gap spacing is below 100 μm. This type of cavity has the potential to operate as a highly sensitive transducer for a variety of precision measurement applications, in particular applications which require coupling to more than one sensitive transducer mode. View full abstract»

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  • Reconfigurable Waveguide Filter with Variable Bandwidth and Center Frequency

    Publication Year: 2014 , Page(s): 1663 - 1670
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    This paper presents a center frequency and bandwidth reconfiguration mechanism for waveguide microwave bandpass filters. The filters are designed to be used in the output section of a satellite communication system. While the center frequency of a bandpass filter can be tuned by changing the lengths of the filter resonators, the coupling irises as practical realizations of the impedance inverters cannot easily be adapted to a new value. The novel approach chosen in this paper is to replace the impedance inverters by a novel type of coupling structure. This coupling structure allows adjustment of the coupling by changing the length of a transmission line, which is equivalent to changing the resonant frequency of a coupling resonator. Design equations are presented to transform an impedance inverter into the proposed coupling structure. A synthesis procedure for bandwidth reconfigurable filters is proposed. The feasibility of coupling adaptation is proven based on a full-wave model of the coupling structure. The synthesis process is applied to a four-pole Chebyshev sidewall-coupled circular waveguide filter with 54- and 72-MHz bandwidth settings. The filter is built up and measured. The measured results prove that the filter can be tuned to both bandwidths over a center frequency range of 200 MHz with excellent return loss and insertion loss. View full abstract»

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  • Optimized Synthesis of Self-Equalized Microwave Filters

    Publication Year: 2014 , Page(s): 1671 - 1677
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    In this paper, a new methodology for synthesizing self-equalized filters is introduced. The methodology consists of optimizing the polynomial transfer and reflection functions considering amplitude and phase constraints simultaneously. The algorithm gives access to a more general class of functions than generalized Chebyshev (also called quasi-elliptic) functions. Two self-equalized filters are designed using this new methodology, and their performances are compared to general Chebyshev filters in order to put into evidence the interest of the proposed optimization algorithm. The first design leads to reduced group-delay variations, and the second one leads to a simplification of the hardware, reducing the number of resonators. View full abstract»

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  • High-Resolution Passive Phase Shifters for Adaptive Duplexing Applications in SOS Process

    Publication Year: 2014 , Page(s): 1678 - 1685
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2212 KB) |  | HTML iconHTML  

    Two high-resolution passive delay line phase shifters in silicon-on-sapphire are compared. Both make use of digitally tuned capacitor loaded π sections to obtain 360 ° phase control. The first has a nominal resolution of 9-bit and uses ten sections, yielding an insertion loss (IL) of 12.6 dB at 1.4 GHz. The second employs a center tapped auto-transformer to provide 180 ° of phase shift, reducing both size and the IL while enabling a further 1-bit improvement in resolution. The measured IL in the 1.8-2.4-GHz frequency range is less than 7.3 dB. Stacked field-effect transistors were employed as switches to increase the power-handling capability. An input referred third intercept point (IIP3) of +39 and +54 dBm were measured for the first and second circuits, respectively. View full abstract»

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  • High-Power High-Efficiency Class-E-Like Stacked mmWave PAs in SOI and Bulk CMOS: Theory and Implementation

    Publication Year: 2014 , Page(s): 1686 - 1704
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4387 KB) |  | HTML iconHTML  

    Series stacking of multiple devices is a promising technique that can help overcome some of the fundamental limitations of CMOS technology in order to improve the output power and efficiency of CMOS power amplifiers (PAs), particularly at millimeter-wave (mmWave) frequencies. This paper investigates the concept of device stacking in the context of the Class-E family of nonlinear switching PAs at mmWave frequencies. Fundamental limits on achievable performance of a stacked configuration are presented along with design guidelines for a practical implementation. In order to demonstrate the utility of stacking, three prototypes have been implemented: two fully integrated 45-GHz single-ended Class-E-like PAs with two- and four-stacked devices in IBM's 45-nm silicon-on-insulator (SOI) CMOS technology, and a 45-GHz differential Class-E-like PA with two devices stacked in IBM's 65-nm low-power CMOS process. Measurement results yield a peak power-added efficiency (PAE) of 34.6% for the two-stacked 45-nm SOI CMOS PA with a saturated output power of 17.6 dBm. The measurement results also indicate true Class-E-like switching PA behavior. A peak PAE of 19.4% is measured for the four-stacked PA with a saturated output power of 20.3 dBm. The two-stacked PA exhibits the highest PAE reported for CMOS mmWave PAs, and the four-stacked PA achieves the highest output power from a fully integrated CMOS mmWave PA including those that employ power combining. The 65-nm CMOS differential two-stacked PA exhibits a peak PAE of 28.3% with a saturated differential output power of 18.2 dBm, despite the poor ON-resistance of the 65-nm low-power nMOS devices. This paper also describes the modeling of active devices for mmWave CMOS PAs for good model-hardware correlation. View full abstract»

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  • Design and Analysis of Broadband Darlington Amplifiers With Bandwidth Enhancement in GaAs pHEMT Technology

    Publication Year: 2014 , Page(s): 1705 - 1715
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    This paper presents a bandwidth enhancement technique for broadband Darlington amplifiers. A detailed analysis of the high-frequency performance of the Darlington amplifier and the effect of bandwidth enhancement is provided. A design procedure is also given for broadband feedback Darlington amplifiers with bandwidth enhancement and gain flattening. A single- and a three-stage feedback amplifier with the proposed improvements are designed and implemented in a 0.25- μm AlGaAs-InGaAs pHEMT technology. The single-stage amplifier provides 6±0.4 dB of small-signal gain in the frequency band of 1-30 GHz. The three-stage amplifier features 17.8±0.8 dB of small-signal gain in the frequency band of 2-29 GHz. It provides a gain-bandwidth product of 217 GHz, which is 3.3 times larger than the unity gain frequency (fT) of the process. View full abstract»

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  • A 2G/3G/4G SAW-Less Receiver Front-End Adopting Switchable Front-End Architecture

    Publication Year: 2014 , Page(s): 1716 - 1723
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1457 KB) |  | HTML iconHTML  

    In this paper, a surface acoustic wave (SAW)-less receiver (RX) front-end adopting switchable front-end architecture has been presented for second-generation/third-generation/fourth-generation cellular applications. Depending on the RX-transmitter (TX) frequency separation, a favorable down-mixing architecture is selected between a current-sampling mixer and a voltage-sampling mixer. The proposed switchable architecture meets the specification of an input-referred second-order intercept point (IIP2) for the SAW-less RX while minimizing the power consumption. The implemented RX front-end consists of a wideband capacitor cross-coupled common-gate low-noise amplifier, a 25% duty-cycle passive mixer with IIP2 calibration circuitry, a baseband transconductor, and a trans-impedance amplifier. Fabricated in a 65-nm CMOS process, the SAW-less RX front-end provides conversion gain of 42 dB, and achieves noise figure of below 3.3 dB, out-of-band input-referred third-order intercept point of -2 dBm, and IIP2 of more than 56 dBm. It draws an average current of 14.8 mA from 1.2 V. The die area is 1.71 mm2. View full abstract»

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  • A Low-Power Analog Baseband Section for 60-GHz Receivers in 90-nm CMOS

    Publication Year: 2014 , Page(s): 1724 - 1735
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    A low-power analog baseband section suitable for 60-GHz receivers using orthogonal frequency-division multiplexing (OFDM) with 16 quadrature amplitude modulation (16-QAM) modulation is presented in this paper. Power efficiency is achieved by combining active-RC with source-follower-based topologies in order to synthesize a custom sixth-order transfer function. The complete chain consists of the cascade of a first-order transimpedance amplifier with finely programmable gain, a fourth-order source-follower-based filter, and a coarse gain first-order programmable gain amplifier. The prototype is implemented in 90-nm CMOS. It achieves a 1-GHz cutoff frequency and programmable gain from 0 to 20 dB with 1-dB step control, drawing 9.5 mA (0-9 dB gain range) or 10.8 mA (10-20 dB gain range) from a 1-V supply. An 8.2-dBm third-order input intercept point and a -145-dBm/Hz input-referred noise power density are measured at 0- and 20-dB gain, respectively. The entire circuit occupies an area of 400 × 390 μm2. View full abstract»

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  • Modeling and Jitter Improvement of SRD-Based Ultra-Wideband Pulse Generator

    Publication Year: 2014 , Page(s): 1736 - 1747
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2056 KB) |  | HTML iconHTML  

    Step recovery diode (SRD)-based ultra-wide band (UWB) pulse generators (PGs) suffer from jitter caused by AM-to-PM conversion, SRD shot noise, and clock jitter. These noise sources significantly impact the accuracy of UWB systems if very high precision ranging/positioning is required. Jitter behavior caused by the transmitter and receiver is mostly detrimental in the equivalent time-sampling receiver. Thus, a mathematical model for simulation of the jitter and amplitude variation effect in the equivalent time-sampling technique has been developed and used in SystemVue simulations. A criterion as an estimate of system accuracy is defined as signal-to-distortion ratio (SDR) and used. Similarly, a model for AM and PM noise analysis for an SRD-based UWB PG is developed that was validated experimentally. In addition, SRD shot-noise contribution on output jitter was evaluated using the proposed model. Based on these models, methods to reduce the output jitter of the system have been recommended. Simulation showed that clock jitter and SRD shot noise led to pronounced output jitter, with shot noise the primary cause. For a typical SRD-based UWB PG, an output jitter of around 3 ps has been achieved using improvement techniques based on the proposed method, compared to a 15-ps jitter before improvement. These measured results are in good agreement with our predictions. View full abstract»

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  • Crosstalk Corrections for Coplanar-Waveguide Scattering-Parameter Calibrations

    Publication Year: 2014 , Page(s): 1748 - 1761
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3204 KB) |  | HTML iconHTML  

    We study crosstalk and crosstalk corrections in coplanar-waveguide vector-network-analyzer calibrations. We show that while crosstalk corrections can improve measurement accuracy, the effectiveness of the corrections depends on a number of factors, including the length of the access lines, transverse dimensions, the separation between the crosstalk standards, and the substrate configuration. View full abstract»

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  • Millimeter-Wave Material Characterization Using Laminated Waveguides

    Publication Year: 2014 , Page(s): 1762 - 1771
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2235 KB) |  | HTML iconHTML  

    This paper presents a material characterization method in the millimeter-wave (mm-wave) range. Laminated waveguides (LWGs), a “quasi” planar form of the metallic rectangular waveguide, were chosen as transmission lines for the test structures. Using transmission lines with a metallically surrounded cross section, the difficulty of calculating the relative permittivity ε r from the measured effective relative permittivity εr,eff (which arises in microstrip-line (MSL)-based methods) can be avoided. Employing transmission lines with different cross-sectional geometries for the characterization, separation of the dielectric loss from the conductor loss is possible, the parameters such as surface impedance and roughness factor of the conductor need not to be determined in advance. Compared to choosing strip-lines, using LWGs is more accurate and less sensitive to fabrication tolerances. LWGs of different lengths and thicknesses were designed for the characterization. For S-parameter measurements based on air-coplanar probes, three MSL-to-LWG transitions were designed to guide the signal into the LWGs. The test structures were realized in a low-temperature co-fired ceramics (LTCC) technology. After co-firing, the LTCC materials were characterized at a working frequency of 79 GHz. The results show that the conductor and the dielectric losses have been separated and the accuracy of the derived loss tangent has been well improved. This method can also be applied to organic materials and offers opportunities for further research on the roughness factor of conductors in the mm-wave range. View full abstract»

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  • A Peak-Search Algorithm for Load–Pull Optimization of Power-Added Efficiency and Adjacent-Channel Power Ratio

    Publication Year: 2014 , Page(s): 1772 - 1783
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2251 KB) |  | HTML iconHTML  

    Power amplifiers in modern wireless systems must meet increasingly stringent spectral constraints while still operating with high power efficiency. A new peak-search algorithm is demonstrated to find the Pareto optimum of power-added efficiency (PAE) while producing an adjacent channel power ratio (ACPR) value under a specified maximum. A peak-search is first performed for the maximum PAE, and then a small-step steepest descent walk in the ACPR is taken from the PAE maximum toward the ACPR minimum until ACPR requirements are met. This approach reasonably approximates the Pareto optimum for the device. Simulation and measurement data are presented for searches from multiple starting points, and good correspondence is obtained for the Pareto optimum reflection coefficient, as well as the optimum PAE and ACPR values. This measurement-based algorithm is expected to find useful application in real-time adaptive radio and radar transmitters, as well as in bench-top measurements for amplifier design. View full abstract»

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  • RF Head Coil Design With Improved RF Magnetic Near-Fields Uniformity for Magnetic Resonance Imaging (MRI) Systems

    Publication Year: 2014 , Page(s): 1784 - 1789
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1408 KB) |  | HTML iconHTML  

    Higher magnetic field strength in magnetic resonance imaging (MRI) systems offers higher signal-to-noise ratio, contrast, and spatial resolution in magnetic resonance (MR) images. However, the wavelength in ultrahigh fields (7 T and beyond) becomes shorter than the human body at the Larmor frequency with increasing static magnetic field (B0) of the MRI system. At short wavelengths, an interference effect appears, resulting in nonuniformity of the RF magnetic near-field (B1) over the subject and MR images may have spatially anomalous contrast. The B1 near-field generated by the transverse electromagnetic RF coil's microstrip line element has a maximum near the center of its length and falls off towards both ends. In this study, a double trapezoidal-shaped microstrip transmission line element is proposed to obtain uniform B1 field distribution by gradual impedance variation. Two multi-channel RF head coils with uniform and trapezoidal shape elements were built and tested with a phantom at 7-T MRI scanner for comparison. The simulation and experimental results show stronger and more uniform B1+ near-field with the trapezoidal shape. View full abstract»

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The IEEE Transactions on Microwave Theory and Techniques focuses on that part of engineering and theory associated with microwave/millimeter-wave components, devices, circuits, and systems involving the generation, modulation, demodulation, control, transmission, and detection of microwave signals. This includes scientific, technical, and industrial, activities. Microwave theory and techniques relates to electromagnetic waves usually in the frequency region between a few MHz and a THz; other spectral regions and wave types are included within the scope of the Society whenever basic microwave theory and techniques can yield useful results. Generally, this occurs in the theory of wave propagation in structures with dimensions comparable to a wavelength, and in the related techniques for analysis and design..

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