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Microwave Theory and Techniques, IEEE Transactions on

Issue 12 • Date Dec. 2003

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Displaying Results 1 - 25 of 40
  • A reduced intermodulation distortion tunable ferroelectric capacitor-architecture and demonstration

    Publication Year: 2003 , Page(s): 2568 - 2576
    Cited by:  Papers (26)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (980 KB) |  | HTML iconHTML  

    A ferroelectric tunable capacitor device architecture is presented that allows for a reduction of intermodulation distortion (IMD), while maintaining high tunability at low bias voltages. The tunable capacitor is fabricated from epitaxial thin-film barium-strontium-titanate deposited on a sapphire substrate. The RF portion of the capacitor is a conventional planar gap capacitor with a 12-14-μm gap. However, rather than superimposing the dc bias on the RF pads, a separate bias structure is fabricated within the RF gap. The interdigital bias structure has narrowly spaced high resistance (2-3×104 Ω/sq) oxide conductor electrodes, such as indium-tin-oxide electrodes or lanthanum-strontium-cobalt-oxide electrodes spaced 1-2 μm apart. The high resistivity of the bias electrodes decouples the dc bias from the RF signal path. This bias structure allows high dc fields to be developed with less than 30 V applied to tune the material permittivity (1 : 1.4), but is sufficiently resistive to avoid affecting the Q factor of the RF capacitor. Since the RF gap is wide, the IMD performance remains good, even at modest tuning voltages. The following three classes of gap capacitor have been fabricated for concept verification: 1) a conventional gap structure (without additional bias structure); 2) the proposed RF gap capacitor with the dc-bias structure; and 3) a narrower conventional RF gap-capacitor structure used as an IMD reference. The proposed RF gap capacitor with dc-bias structure has been fabricated in two versions: one in which the highly resistive bias electrodes are electrically connected to the RF electrodes (the attached-bias-electrode (ABE) scheme) and one in which the highly resistive electrodes are provided with a separate port for further control (the isolated-bias-electrode (IBE) scheme). In addition, parallel and perpendicular orientation of the bias electrodes relative to the RF field is investigated. The frequency response of the proposed gap capacitor with the dc-bias structure is characterized and its analysis shows that the highly resistive bias lines are serving as a dc-bias path for high tunability, but are not attenuating the RF signal. While the IBE structure has more degrees of freedom for bia- sing as compared to the ABE structure, the overall tunability at 30 V and IMD performance of both the ABE and IBE structures are similar. Two-tone IMD tests show that the IMD performance for the gap capacitor with the bias structure is improved by 6 dB over the conventional reference structure at the same tunability. View full abstract»

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  • Tailoring double-negative metamaterial responses to achieve anomalous propagation effects along microstrip transmission lines

    Publication Year: 2003 , Page(s): 2306 - 2314
    Cited by:  Papers (20)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (517 KB) |  | HTML iconHTML  

    The design of a double-negative metamaterial loaded microstrip transmission line (DNG MTM-TL) to tailor the propagation characteristics at S- and C-band frequencies is presented. Guided-wave propagation along this DNG MTM-TL was studied numerically. The scattering parameters of the DNG MTM-TL were obtained with Ansoft's High Frequency Structure Simulator. A two-port network realization of the DNG MTM-TL is established. The effective permittivity and permeability for the DNG MTM-TL is extracted using this two-port network representation. It is shown that both a negative permittivity and a negative permeability and, hence, a negative index of refraction exist in the design frequency range. These material parameters are dispersive and conform to a two-time derivative Lorentz material model type of resonance behavior. This form of the index of refraction may be very suitable for applications dealing with phase and dispersion compensation along a microstrip transmission line. View full abstract»

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  • A 16-element two-dimensional active self-steering array using self-oscillating mixers

    Publication Year: 2003 , Page(s): 2476 - 2482
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB) |  | HTML iconHTML  

    A 16-element two-dimensional (2-D) retrodirective array using self-oscillating mixers (SOMs) is presented. SOMs allow for easier implementation of larger 2-D arrays by eliminating the complex local-oscillator (LO) feed structure. A 4 × 4 element retrodirective array using SOMs is demonstrated at an LO frequency of 7.68 GHz. Each element is phased locked at the LO frequency with an accompanying RF frequency isolation of 17.9 dB between adjacent horizontal elements and 22.2 dB between adjacent vertical elements. A -10-dBm external injection-locking signal is applied to reduce the phase noise of the 16-element array to -68.2 dBc/Hz at 10-kHz offset. Retrodirectivity is observed in the φ=0°, φ=-45°, and φ=-90 plane for scattering angles of θ=-15°, θ=0°, and θ=+30°. View full abstract»

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  • A novel modified-T equivalent circuit for modeling LTCC embedded inductors with a large bandwidth

    Publication Year: 2003 , Page(s): 2327 - 2333
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB) |  | HTML iconHTML  

    This paper presents a new modified-T model for three-dimensional inductors embedded in the multilayer low-temperature cofired-ceramic substrate with a remarkably large bandwidth. This model combines a core circuit, a five-element modified-T model, to include the effects of a transmission line with an electrical length up to π, and several resonators to consider the effects due to coil coupling and the finite ground plane. It is emphasized that most of the elements in this equivalent-circuit model can be extracted directly from the measured S-parameters. Compared to the conventional PI-section model that is valid only up to the fundamental self resonant frequency (SRF), this model can include more higher-order SRFs and ground resonant frequencies effectively, which results in several times larger bandwidth. View full abstract»

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  • Thermal analysis of AlGaN-GaN power HFETs

    Publication Year: 2003 , Page(s): 2445 - 2452
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (445 KB) |  | HTML iconHTML  

    In this paper, we present a thermal analysis of AlGaN-GaN power heterojunction field-effect transistors (HFETs). We report the dc, small-signal, large-signal, and noise performances of AlGaN-GaN HFETs at high temperatures. The temperature coefficients measured for GaN HFETs are lower than that of GaAs pseudomorphic high electron-mobility transistors, confirming the potential of GaN for high-temperature applications. In addition, the impact of thermal effects on the device dc, small-signal, and large-signal characteristics is quantified using a set of pulsed and continuous wave measurement setups. Finally, a thermal model of a GaN field-effect transistor is implemented to determine design rules to optimize the heat flow and overcome self-heating. Arguments from a device, circuit, and packaging perspective are presented. View full abstract»

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  • An 8-GHz continuous-time Σ-Δ analog-digital converter in an InP-based HBT technology

    Publication Year: 2003 , Page(s): 2555 - 2561
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (510 KB) |  | HTML iconHTML  

    We report an 8-GHz clock-rate, second-order continuous-time Σ-Δ analog-digital converter (ADC) that achieves 57.4-, 51.7-, and 40.2-dB SNR at signal sampling rates of 125, 250, and 500 Ms/s, respectively. The integrated circuit occupied 1.45-mm2 die area, contains 76 transistors, is fabricated in an InP-based HBT technology, and dissipates ∼1.8 W. We also study the effect of excess delay on modulator performance, and show that excess delay does not affect performance as long as the centroid-in-time of the digital-analog converter pulse remains stationary. View full abstract»

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  • Efficient modal analysis of arbitrarily shaped waveguides composed of linear, circular, and elliptical arcs using the BI-RME method

    Publication Year: 2003 , Page(s): 2378 - 2390
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (734 KB) |  | HTML iconHTML  

    This paper deals with the accurate and efficient modal analysis of arbitrarily shaped waveguides whose cross section is defined by a combination of straight, circular, and/or elliptical arcs. A novel technique for considering the presence of circular and/or elliptical segments within the frame of the well-known boundary integral-resonant mode expansion (BI-RME) method is proposed. This new extended BI-RME method will allow a more accurate solution of a wider number of hollow conducting waveguides with arbitrary profiles, which are usually present in most modern passive waveguide components. To show the advantages of this new extended technique, the modal chart of canonical (circular and elliptical) waveguides, as well as of irises with great practical interest (i.e., cross-shaped irises with rounded corners) has been first successfully solved. Next, a computer-aided-design software package based on such a novel modal analysis tool has first been validated with the accurate analysis of a referenced complex dual-mode filter, and then applied to the complete design of a novel twist component for K-band application based on circular and elliptical waveguides. A prototype of this novel device has been manufactured and measured for verification purposes. View full abstract»

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  • A novel ultra-compact resonator for Superconducting thin-film filters

    Publication Year: 2003 , Page(s): 2290 - 2296
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (439 KB) |  | HTML iconHTML  

    This paper proposes a novel thin-film resonator structure, which combines the microstrip resonator and the coplanar resonator to form an integrated resonator. This resonator structure has an extremely compact size, as compared to the thin-film resonator structures from the literature, and its resonant frequency was shown theoretically to be less sensitive to, or even insensitive to, the thickness of the substrate. An eight-pole quasi-elliptic filter based on this novel resonator was designed. The exact filter layout was simulated and optimized by full-wave electromagnetic simulation using IE3D software. The full-wave simulated filter response was in good agreement with the theoretical filter response. A filter was fabricated on a double-sided YBa2Cu3O7 thin film epitaxially grown on a 2-in-diameter MgO wafer. The measured filter response showed a bandwidth of 1.5 MHz and a center frequency of 850.3 MHz at 78 K. The insertion loss at the passband center was 1 dB, corresponding to a filter Q of 28 000. Steep rejection slopes were obtained at the band edges and rejections reached over 70 dB in approximately 300 kHz from the passband edges. No pronounced changes were observed for input power levels between -20-0 dBm, indicating a relatively high power-handling capability of the filter. View full abstract»

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  • State-space Integral-equation method for the S-domain modeling of planar circuits on semiconducting substrates

    Publication Year: 2003 , Page(s): 2315 - 2326
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB) |  | HTML iconHTML  

    This paper presents a new and very efficient integral method for the electromagnetic modeling of planar circuits on multilayered semiconducting substrates. Differently from standard integral approaches, the method leads to a state-space model of the circuit. This model directly permits to find the admittance matrix in the form of a reduced-order pole expansion in the S-domain through standard Krylov sub-space techniques. Three examples demonstrate the really good performances of the method in terms of accuracy and rapidity. View full abstract»

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  • A high-speed adaptive antenna array with simultaneous multibeam-forming capability

    Publication Year: 2003 , Page(s): 2483 - 2494
    Cited by:  Papers (9)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2119 KB) |  | HTML iconHTML  

    A new type of adaptive beamforming antenna system architecture is proposed for multichannel wireless communications. Multibeam communication with high data throughput is accomplished using the proposed beamformer architecture. The system consists of analog mixers, a multitone direct digital synthesizer (DDS), and a digital signal processor (DSP) controller. The essential idea of multibeam forming is based on a multitone weighting scheme combined with analog-digital hybrid signal processing. While the real-time multibeam construction is realized by the analog mixer circuits and a DDS, the complicated adaptive beamforming and direction-of-arrival estimation algorithms are carried out by the DSP. In this architecture, only one beamformer circuit is required to handle multiple beams, leading to significant reduction in hardware counts. A 5.8-GHz eight-element adaptive beamforming array successfully demonstrates two-beam simultaneous beamforming with less than three degrees of peak and steering errors and more than 20-dB interference suppression. The test-bed exhibits successful two-channel data recovery at 25-Mb/s data throughput in each channel with binary phase-shift keying modulation, for simultaneous dual-beam reception. The bit-error-rate measurement validates the robustness of the communication quality under strong interferences. View full abstract»

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  • On deembedding of port discontinuities in full-wave CAD models of multiport circuits

    Publication Year: 2003 , Page(s): 2355 - 2365
    Cited by:  Papers (26)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (531 KB) |  | HTML iconHTML  

    A systematic numerical methodology is proposed for the accurate deembedding of multiport discontinuities in full-wave numerical models of multiconductor microwave and millimeter-wave passive structures and high-speed digital interconnects. The discussed methodology is based on the earlier-proposed short-open calibration (SOC) procedure. The latter being a numerical analog of the experimental transmission-thru-reflection technique provides a consistent removal of the feed networks of the device-under-test over a wide range of frequencies. The treatment of multiport topologies is achieved through the continuation of the original scalar SOC method into the vector space. The new vector SOC method is easily combined with integral-equation-based method-of-moments electromagnetic-field solvers and allows for substantial flexibility in the choice of excitation mechanisms. Such commonly used method-of-moments driving schemes as ports locally backed up by a vertical conducting wall, ungrounded-internal differential ports, and via-mounted ports can be accurately deembedded within the framework of the vector SOC. Several numerical experiments are provided to validate the proposed multiport deembedding methodology and demonstrate its application. View full abstract»

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  • Broad-band high-power amplifier using spatial power-combining technique

    Publication Year: 2003 , Page(s): 2469 - 2475
    Cited by:  Papers (16)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1019 KB) |  | HTML iconHTML  

    High power, broad bandwidth, high linearity, and low noise are among the most important features in amplifier design. The broad-band spatial power-combining technique addresses all these issues by combining the output power of a large quantity of microwave monolithic integrated circuit (MMIC) amplifiers in a broad-band coaxial waveguide environment, while maintaining good linearity and improving phase noise of the MMIC amplifiers. A coaxial waveguide was used as the host of the combining circuits for broader bandwidth and better uniformity by equally distributing the input power to each element. A new compact coaxial combiner with much smaller size is investigated. Broad-band slotline to microstrip-line transition is integrated for better compatibility with commercial MMIC amplifiers. Thermal simulations are performed and an improved thermal management scheme over previous designs is employed to improve the heat sinking in high-power application. A high-power amplifier using the compact combiner design is built and demonstrated to have a bandwidth from 6 to 17 GHz with 44-W maximum output power. Linearity measurement has shown a high third-order intercept point of 52 dBm. Analysis shows the amplifier has the ability to extend spurious-free dynamic range by N23/ times. The amplifier also has shown a residual phase floor close to -140 dBc at 10-kHz offset from the carrier with 5-6-dB reductions compared to a single MMIC amplifier it integrates. View full abstract»

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  • Predistortion technique for cross-coupled filters and its application to satellite communication systems

    Publication Year: 2003 , Page(s): 2505 - 2515
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB) |  | HTML iconHTML  

    This paper presents a novel adaptive predistortion technique for general cross-coupled microwave/RF filters with improved insertion loss and group-delay equalization. The method enables many potential applications of an almost abandoned technique, and permits a lower Q implementation technology to emulate the performance of a higher Q filter. 10-4-4 filters were built and tested at C- and Ku-band to verify the validity of the new method. The impact to satellite communication channels was also analyzed. Another novel concept of over-predistortion was proposed and evaluated and should lead to significant improvement for applications such as satellite transponder input multiplexers, where insertion loss can be traded off for in-band flatness, mass, volume, and even overall system performance. View full abstract»

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  • Nonreciprocal wave propagation in multilayer semiconductor films at frequencies up to 200 GHz

    Publication Year: 2003 , Page(s): 2453 - 2460
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1070 KB) |  | HTML iconHTML  

    Three multilayer gyrotropic thin-film semiconductor waveguides comprising S-I GaAs/AlAs/n-GaAs/AlGaAs in a static magnetic field of 0.15 T have been analyzed over the frequency range of 0-200 GHz. The dispersion diagrams and field distributions show nonreciprocal propagation, and forward waves and backward waves depending on the order in which the films are stacked. Potential applications such as miniature phase shifters and isolators in the frequency range of 50-100 GHz with lengths of the order of micrometers are briefly discussed. View full abstract»

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  • An alignment insensitive separable electromagnetic coupler for high-speed digital multidrop bus applications

    Publication Year: 2003 , Page(s): 2597 - 2603
    Cited by:  Papers (3)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (683 KB) |  | HTML iconHTML  

    A separable electromagnetic coupler was designed, simulated, fabricated, and tested as part of a prototype eight-module multidrop memory bus. The coupler consists of broadside coupled traces, one on a rigid motherboard and the other on a flex circuit soldered to a daughter card. The zig-zag geometry of the traces reduces variation in the coupling coefficient due to horizontal and vertical misalignment of the coupler halves. Simulation and testing indicates that a target capacitive coupling coefficient of 0.34, which has been selected to balance signal-transmission-level requirements against motherboard impedance discontinuity effects, can be achieved with little variation over +/-12-mil alignment tolerance. In addition, custom interface circuitry was designed in conjunction with the coupler to enable 1.6-Gb/s data rate per differential pair. The prototype system was tested for an extended period executing read and write memory transactions for an estimated bit error rate less than 2.0e-17. View full abstract»

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  • Power density and temperature distributions produced by interstitial arrays of sleeved-slot antennas for hyperthermic cancer therapy

    Publication Year: 2003 , Page(s): 2418 - 2426
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (561 KB) |  | HTML iconHTML  

    A graded-mesh finite-difference time-domain (FDTD) code, together with an alternate-direction-implicit finite-difference (ADI-FD) solution of the bioheat equation, are used for studying arrays of sleeved-slot antennas imbedded in a brain-equivalent phantom. The FDTD code allows efficient and accurate modeling of the fine structure of each antenna and of a sufficiently wide surrounding region. The ADI-FD solution of the bioheat equation allows evaluation of transient and steady-state temperature distributions in the brain-equivalent phantom with acceptable computational costs. The solution of the dosimetric-thermal problem in the volume irradiated by the antenna array permits the assessment of dimensions of the region where the temperature increase is above 43°C (the threshold for an effective hyperthermia treatment) as a function of the array input power. Arrays made of three identical antennas placed at the vertices of equilateral triangles of 10-, 15-, and 20-mm sides have been studied. The temperature of 43°C is reached in approximately 3 min in a deep-seated tumor region, from 10 to 40 mm in diameter, by applying input power levels between 2-32 W. View full abstract»

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  • An efficient electromagnetic-physics-based numerical technique for modeling and optimization of high-frequency multifinger transistors

    Publication Year: 2003 , Page(s): 2334 - 2346
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1515 KB) |  | HTML iconHTML  

    We present a fast wavelet-based time-domain modeling technique to study the effect of electromagnetic (EM)-wave propagation on the performance of high-power and high-frequency multifinger transistors. The proposed approach solves the active device model that combines the transport physics, and Maxwell's equations on nonuniform self-adaptive grids, obtained by applying wavelet transforms followed by hard thresholding. This allows forming fine and coarse grids in the locations where variable solutions change rapidly and slowly, respectively. A CPU time reduction of 75% is achieved compared to a uniform-grid case, while maintaining the same degree of accuracy. After validation, the potential of the developed technique is demonstrated by EM-physical modeling of multifinger transistors. Different numerical examples are presented, showing that accurate modeling of high-frequency devices should incorporate the effect of EM-wave propagation and electron-wave interactions within and around the device. Moreover, high-frequency advantages of multifinger transistors over single-finger transistors are underlined through numerical examples. To our knowledge, this is the first time in the literature a fully numerical EM-physics-based simulator for accurate modeling of high-frequency multifinger transistors is introduced and implemented. View full abstract»

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  • Implementation of nonquasi-static effects in compact bipolar transistor models

    Publication Year: 2003 , Page(s): 2531 - 2537
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (473 KB) |  | HTML iconHTML  

    Large-signal implementation of nonquasi-static (NQS) effects in bipolar transistors is reviewed. An approach is proposed to introduce first-order NQS correction to typical quasi-static phenomenological models. Both charge- and noncharge-conserving implementations are considered. The resulted large-signal equivalent-circuit model compares well with the two-dimensional physical model in simulating HBT transient response under high-current operations. The present approach advances the state-of-the-art by allowing arbitrary bias dependence of transit times in large-signal NQS models. View full abstract»

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  • Baseband impedance and linearization of FET circuits

    Publication Year: 2003 , Page(s): 2523 - 2530
    Cited by:  Papers (11)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (537 KB) |  | HTML iconHTML  

    Baseband impedance has been identified as having a positive or negative effect on the intermodulation distortion of microwave circuits. The effect can be assessed or utilized with the aid of previously proposed figures-of-merit. Under certain situations, intermodulation cancellation can be achieved simply by adding resistance to the bias network. The impact of baseband impedance on the performance of derivative superposition amplifiers is analyzed. A bias region was studied that exhibits a good second- and third-order intermodulation with minimal intermodulation dependence on baseband impedance. This allows the effective use of the derivative superposition technique in baseband amplifiers, as well as giving wide-band linearization performance in RF amplifiers. View full abstract»

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  • Flip-chip assembly and liquid crystal polymer encapsulation for variable MEMS capacitors

    Publication Year: 2003 , Page(s): 2562 - 2567
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (805 KB) |  | HTML iconHTML  

    Packaging is a well-known barrier to the advancement of microelectromechanical systems (MEMS) for RF applications. To pave the way for the removal of this barrier, we have developed a flip-chip assembly technology to transfer foundry-fabricated MEMS devices from the host silicon substrate to a ceramic substrate. Specifically, posts have been designed and fabricated to assure excellent RF performance by achieving a precise gap between the device and ceramic substrate. In addition, a novel liquid crystal polymer (LCP) encapsulation technology has been developed to protect the RF MEMS device. LCP is a good encapsulation material for nonhermetic packaging because it significantly reduces the packaging cost. We have demonstrated excellent RF performance of variable MEMS capacitors that have been flip-chip assembled and LCP encapsulated. The quality (Q) factors of such capacitors were measured to be higher than 300 at 1.0 GHz. View full abstract»

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  • An optimal vector-network-analyzer calibration algorithm

    Publication Year: 2003 , Page(s): 2391 - 2401
    Cited by:  Papers (51)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (515 KB) |  | HTML iconHTML  

    We present an iterative algorithm for calibrating vector network analyzers based on orthogonal distance regression. The algorithm features a robust, yet efficient, search algorithm, an error analysis that includes both random and systematic errors, a full covariance matrix relating calibration and measurement errors, 95% coverage factors, and an easy-to-use user interface that supports a wide variety of calibration standards. We also discuss evidence that the algorithm outperforms the MultiCal software package in the presence of measurement errors and accurately estimates the uncertainty of its results. View full abstract»

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  • Negative refraction, growing evanescent waves, and sub-diffraction imaging in loaded transmission-line metamaterials

    Publication Year: 2003 , Page(s): 2297 - 2305
    Cited by:  Papers (40)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (761 KB) |  | HTML iconHTML  

    We present an analytical formulation that shows the negative refraction of propagating waves and the growth of evanescent waves within a negative refractive index (NRI) lens made of a periodically L, C loaded transmission-line (TL) network, referred to as the dual-TL structure. A transformation known as the "array scanning method" is then employed to analytically demonstrate the sub-diffraction imaging capability of a dual-TL lens. In essence, the two-dimensional (2-D) periodic Green's functions corresponding to the voltages and currents excited by a vertical elementary current source are derived. The developed theory is utilized to plot the 2-D voltage magnitude distribution for the case of focusing an elementary current source. The analysis reveals that a resolution limit is imposed by the periodicity of the NRI medium used. Moreover, the periodicity of the NRI medium bounds the amplitude of the growing evanescent waves in a realizable NRI lens and prevents them from growing to unphysically large values. View full abstract»

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  • Passive parameterized time-domain macromodels for high-speed transmission-line networks

    Publication Year: 2003 , Page(s): 2347 - 2354
    Cited by:  Papers (49)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (850 KB) |  | HTML iconHTML  

    There is a significant need for efficient and accurate macromodels of components during the design of microwave circuits. Increased integration levels in microwave devices and higher signal speeds have produced the need to include effects previously neglected during circuit simulations. Accurate prediction of these effects involve solution of large systems of equations, the direct simulation of which is prohibitively CPU expensive. In this paper, an algorithm is proposed to form passive parametrized macromodels of large linear networks that match the characteristics of the original network in time, as well as other design parameters of the circuit. A novel feature of the algorithm is the ability to incorporate a set of design parameters within the reduced model. The size of the reduced models obtained using the proposed algorithm were less than 5% when compared to the original circuit. A speedup of an order of magnitude was observed for typical high-speed transmission-line networks. The algorithm is general and can be applied to other disciplines such as thermal analysis. View full abstract»

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  • A UTD/FDTD investigation on procedures to assess compliance of cellular base-station antennas with human-exposure limits in a realistic urban environment

    Publication Year: 2003 , Page(s): 2409 - 2417
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (794 KB) |  | HTML iconHTML  

    In this paper, different exposure situations for a subject standing inside a room of a building with a window facing a rooftop-mounted base-station antenna are analyzed. The study is accomplished by using a technique combining the uniform asymptotic theory of diffraction and the finite-difference time-domain method, suitable to characterize human exposure in realistic urban environments at a reasonable computational cost. The different exposure conditions examined are analyzed to highlight the problems related to compliance assessment procedures in complex exposure scenarios and to suggest some possible solutions. A comparison of the results obtained in these scenarios with those computed neglecting the presence of the room walls (free-space situations) evidences that, under certain conditions, average exposure field levels and specific absorption rates (SARs) in the realistic environments can be higher than in free space, thus demonstrating that compliance assessment carried out in free space can yield nonconservative results. As concerns implications of field nonuniformities, typical of realistic urban environments, on SAR values, the results show that the whole-body averaged SAR is related to the average field value, provided the averaging procedure is appropriately chosen to cover all the volume occupied by the subject (VS) and not only a vertical surface. Local SAR values, instead, show a more complex relation with the exposure field, such that considering only the VS-averaged field value for compliance assessment might lead to an underestimation of the real exposure level, while using the peak of the field in VS leads to a remarkable overestimation. View full abstract»

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  • Design and testing of SMA temperature-compensated cavity resonators

    Publication Year: 2003 , Page(s): 2284 - 2289
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (413 KB) |  | HTML iconHTML  

    In this paper, we present a method for designing temperature-compensated cavity resonators using shape memory alloys (SMAs). This paper gives an expression for the temperature drift of resonant frequency, which is valid for any conductor-loaded cavity regardless of its shape. This formula, combined with a field perturbation model, is used to derive the resonant frequency of an SMA-compensated resonator subject to temperature fluctuation. Experimental results are given that confirm the feasibility of the proposed design approach. A design method is proposed for specifying SMA alloys to build the actuator. An expression is derived to accurately predict the performance of an actuator design. View full abstract»

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Aims & Scope

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..

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Dominique Schreurs
Dominique.Schreurs@ieee.org

Editor-in-Chief
Jenshan Lin
jenshan@ieee.org