@article{wilkerson_kilgore_gard_steer_2015, title={Passive Intermodulation Distortion in Antennas}, volume={63}, ISSN={["1558-2221"]}, DOI={10.1109/tap.2014.2379947}, abstractNote={An analytic formulation of passive intermodulation distortion (PIM) in antennas is presented for PIM introduced by electro-thermal modulation of conductivity by current-related losses. A silver rectangular patch antenna was fabricated using a sapphire substrate isolating the thermal process from other possible sources. Two-tone testing at 990 MHz using a sweep of the tone separation from 3 Hz to 100 kHz is reported. Both transmitted and reflected PIM are characterized using a high dynamic range two-tone test system incorporating an analog canceler achieving a dynamic range of 125 dB at 1-Hz tone separation for reflection measurements, and 100 dB at 10-Hz tone separation for transmission measurements with each tone set to 32.3 dBm.}, number={2}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Wilkerson, Jonathan R. and Kilgore, Ian M. and Gard, Kevin G. and Steer, Michael B.}, year={2015}, month={Feb}, pages={474–482} }
 @article{ding_gard_steer_2012, title={A Highly Linear and Efficient CMOS RF Power Amplifier With a 2-D Circuit Synthesis Technique}, volume={60}, ISSN={["1557-9670"]}, DOI={10.1109/tmtt.2012.2206824}, abstractNote={A 2-D circuit synthesis technique (2DCST) is introduced that simultaneously linearizes the AM-AM and AM-PM distortions of CMOS RF power amplifiers (PAs). A class-AB nMOS RF PA fabricated in a 0.18-μm CMOS process is reported. With a WCDMA signal, the amplifier achieved 41.6% power-added efficiency (PAE) with -33-dBc single-adjacent channel power ratio (ACPR1) and 38.5% PAE with -40-dBc ACPR1 at output powers of 24.9 and 24.0 dBm, respectively. This state-of-the-art linearity and efficiency performance is comparable to that of GaAs HBT linear RF PAs. The 2DCST is applicable to a broad range of analog circuits and other semiconductor technologies.}, number={9}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Ding, Miaofu and Gard, Kevin G. and Steer, Michael B.}, year={2012}, month={Sep}, pages={2851–2862} }
 @article{hu_gard_steer_2011, title={Calibrated non-linear vector network measurement without using a multi-harmonic generator}, volume={5}, ISSN={["1751-8725"]}, DOI={10.1049/iet-map.2010.0580}, abstractNote={The current generation of non-linear vector network analysers (NVNA) relies on a multi-harmonic generator to establish an absolute phase reference. Such a reference may not be readily available or, more importantly, may impose limitations on tone spacing in multi-tone testing for one type of NVNA based on a four-port VNA. The latter is a severe limitation when characterising memory behaviour in RF non-linear circuits. Here a hybrid NVNA is proposed that combines a sampling oscilloscope, a four-port VNA and phase-locked signal generators. A signal generator, phase locked to generators that are combined as the multi-tone excitation, provides the relative phase reference during swept power measurements using the VNA. The high dynamic range VNA-based measurements are corrected in absolute phase using the oscilloscope-based NVNA measurement at a specific power level. The hybrid NVNA has high dynamic range and the lower bound on tone spacing is determined by the memory depth of the oscilloscope, the windowing effect of the VNA receivers and the phase noise of the multi-tone sources. At 2 GHz, the hybrid NVNA has a dynamic range of 40 dB at 200 Hz tone spacing for a two-tone signal, increasing to more than 80 dB for tone spacings of 200 kHz and greater.}, number={5}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Hu, J. and Gard, K. G. and Steer, M. B.}, year={2011}, month={Apr}, pages={616–624} }
 @article{wilkerson_lam_gard_steer_2011, title={Distributed Passive Intermodulation Distortion on Transmission Lines}, volume={59}, ISSN={["1557-9670"]}, DOI={10.1109/tmtt.2011.2106138}, abstractNote={A theoretical treatment of distributed electro-thermally induced intermodulation distortion is developed for microstrip transmission lines. The growth of passive intermodulation distortion (PIM) along the length of a line is derived accounting for both loss and electrical dispersion. PIM dependencies on width, length, thickness, and substrate parameters are analyzed leading to design guidelines for low distortion lines. Single metal silver transmission lines are fabricated on sapphire and fused-quartz substrates to isolate the electro-thermal effect and validate the model. Electro-thermal PIM is measured in a two-tone test with tone separation ranging from 4 Hz to 10 kHz.}, number={5}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Wilkerson, Jonathan R. and Lam, Peter G. and Gard, Kevin G. and Steer, Michael B.}, year={2011}, month={May}, pages={1190–1205} }
 @article{hu_lowry_gard_steer_2011, title={Non-linear radio frequency model identification using a hybrid genetic optimiser for minimal user intervention}, volume={5}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map.2010.0435}, abstractNote={An adaptive reduced-order procedure for developing grey-box models of radio frequency systems is presented. The stochastic model extraction combines a modified genetic algorithm and the Nelder–Mead simplex algorithm to present a user with a range of possible good models from which the user can use intuition to select the most physically realistic candidate. The procedure is ideal for identifying models given incomplete observations, noisy data and inexact model structure. This procedure replaces the commonly used human-in-the-loop ad hoc deterministic approach in which a skilled operator must guide model fitting. Being able to use an expanded range of model architectures beyond the Wiener and Hammerstein family, the stochastic approach, utilisation of incomplete observations and extraction of multiple distinct model candidates, enables the insight and intuition of a skilled operator to be used to advantage. The extraction of a multistage microwave amplifier exhibiting long-term memory effects is used as an example.}, number={15}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Hu, J. and Lowry, J. Q. and Gard, K. G. and Steer, M. B.}, year={2011}, month={Dec}, pages={1880–1890} }
 @article{wilkerson_gard_steer_2010, title={Automated Broadband High-Dynamic-Range Nonlinear Distortion Measurement System}, volume={58}, ISSN={["1557-9670"]}, DOI={10.1109/tmtt.2010.2045525}, abstractNote={This paper presents an intermodulation distortion measurement system based on automated feedforward cancellation that achieves 113 dB of broadband spurious-free dynamic range for discrete tone separations down to 100 Hz. For 1-Hz tone separation, the dynamic range is 106 dB, limited by carrier phase noise. A single-tone cancellation formula is developed requiring only the power of the probing signal and the power of the combined probe and cancellation signal so that the phase shift required for cancellation can be predicted. The technique is applied to a two-path feedforward cancellation system in a bridge configuration. The effects of reflected signals and of group delay on system performance is discussed. Spurious frequency content and interchannel coupling are analyzed with respect to system linearity. Feedforward cancellation and consideration of electromagnetic radiation coupling and reverse-wave isolation effects extends the dynamic range of spectrum and vector analyzers by at least 40 dB. Application of the technique to the measurement of correlated and uncorrelated nonlinear distortion of an amplified wideband code-division multiple-access signal is presented.}, number={5}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Wilkerson, Jonathan R. and Gard, Kevin G. and Steer, Michael B.}, year={2010}, month={May}, pages={1273–1282} }
 @article{li_hoover_gard_steer_2010, title={Behavioural modelling and impact analysis of physical impairments in quadrature modulators}, volume={4}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map.2009.0278}, abstractNote={Non-linear distortion and linear static errors (DC offset and gain/phase imbalance) are the major analogue impairments in microwave I/Q quadrature modulators. They can adversely impact the performance of the systems using them, especially for direct-conversion transceiver systems. The impacts of these impairments were investigated for three different modulator applications: double sideband modulation, zero intermediate frequency (IF) single sideband (SSB) orthogonal frequency-division multiplexing (OFDM) modulation and low-IF SSB OFDM modulation. A behavioural model for characterising the non-linear response and the linear static errors was developed. The non-linear characteristic of each input was modelled by a complex power series based on amplitude-to-amplitude modulation and amplitude-to-phase modulation measurements. The linear static errors were modelled as three static error terms added into the complex power series based on a four-DC-point vector network analyser measurement. The non-linear model was validated by measurements with three types of signals representing the three modulator applications.}, number={12}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Li, M. and Hoover, L. and Gard, K. G. and Steer, M. B.}, year={2010}, month={Dec}, pages={2144–2154} }
 @article{mazzaro_steer_gard_2010, title={Intermodulation distortion in narrowband amplifier circuits}, volume={4}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map.2009.0281}, abstractNote={The contribution of bandpass filter memory to intermodulation distortion in narrowband amplifier circuits is examined. A method for generating multisines from filtered switched tones is presented, and techniques for measuring an amplifier's IP3 and extracting a filter's passband using these multisines are developed. It is shown that amplified filtered pulses produce intermodulation distortion in frequency-hopping communication systems. In the experimental study, 465 and 900-MHz Chebyshev bandpass filters are considered.}, number={9}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Mazzaro, G. J. and Steer, M. B. and Gard, K. G.}, year={2010}, month={Sep}, pages={1149–1156} }
 @article{mazzaro_gard_steer_2010, title={Linear amplification by time-multiplexed spectrum}, volume={4}, ISSN={["1751-858X"]}, DOI={10.1049/iet-cds.2009.0263}, abstractNote={A new waveform processing technique for reducing intermodulation distortion (IMD) generated by an amplitude-modulated signal is presented. The technique eliminates amplifier-generated IMD by time-multiplexing portions of the signal spectrum prior to amplification. The input signal is described as a sum of sinusoidal signals. The peak-to-average ratio of the time-multiplexed amplifier input is lower than that of its non-multiplexed counterpart, but it contains spectral aliases at multiples of the switching frequency. Thus, the reduction in distortion of the desired amplified signal is achieved at the expense of momentarily widening the signal bandwidth. Following amplification, the desired signal is recovered using a bandpass filter which spreads the signal in time and narrows its bandwidth. An analytical expression for distortion reduction when amplifying two multiplexed carriers is developed along with measurements verifying the theory. Distortion reduction is demonstrated experimentally at 3.6 GHz for 2 20 multiplexed carriers, and linear recovery is demonstrated for four multiplexed carriers. The technique reduces third-order IMD by 8 22 dB in experimental measurements of three different amplifiers. The presented technique has the unique property of improving linearity without requiring feedback, feedforward cancellation or calibration.}, number={5}, journal={IET CIRCUITS DEVICES & SYSTEMS}, author={Mazzaro, G. J. and Gard, K. G. and Steer, M. B.}, year={2010}, month={Sep}, pages={392–402} }
 @article{domizioli_hughes_gard_lazzi_2010, title={Noise Correlation in Compact Diversity Receivers}, volume={58}, ISSN={["1558-0857"]}, DOI={10.1109/tcomm.2010.05.080601}, abstractNote={The impact of antenna mutual coupling on signal correlation in multi-antenna receivers has been studied in great detail. By contrast, there has been little work on how mutual coupling affects noise. In this paper we present a noise model for a diversity receiver that includes noise generated by the antennas, front-end amplifiers, and other receiver components. This model shows that noise in a compact diversity receiver may be spatially correlated. Expressions relating noise correlation to properties of the antennas and amplifiers are derived and its impact on the outage probability of an optimal diversity combiner is studied. Examples illustrating the relationship between mutual coupling and noise correlation demonstrate how different noise sources may impact performance in profoundly different ways.}, number={5}, journal={IEEE TRANSACTIONS ON COMMUNICATIONS}, author={Domizioli, Carlo P. and Hughes, Brian L. and Gard, Kevin G. and Lazzi, Gianluca}, year={2010}, month={May}, pages={1426–1436} }
 @article{ding_gard_2010, title={Tanh cascode cell amplifier - an arbitrary transfer characteristics amplifier}, volume={46}, number={22}, journal={Electronics Letters}, author={Ding, M. and Gard, K. G.}, year={2010}, pages={1495–1496} }
 @article{krishnamurthy_gard_2010, title={Time division multiplexing front-ends for multiantenna integrated wireless receivers}, volume={57}, number={6}, journal={IEEE Transactions on Circuits and Systems. I, Regular Papers}, author={Krishnamurthy, G. and Gard, K. G.}, year={2010}, pages={1231–1243} }
 @article{santos_carvalho_gard_2009, title={Characterization of SNDR Degradation in Nonlinear Wireless Transmitters}, volume={19}, ISSN={["1099-047X"]}, DOI={10.1002/mmce.20370}, abstractNote={This article presents a measurement strategy and a characterization bench for the evaluation of Signal to Noise and Distortion Ratio (SNDR) in nonlinear wireless systems when in presence of memory effects. This measurement proposal will be combined with a closed analysis of the nonlinear mechanisms appearing in communication systems presenting memory. The analysis of this memory mechanism, when the system is excited by complex modulated signals with different statistics, will be a useful tool for design engineers to evaluate the degradation of SNDR in nonlinear wireless systems. Finally, the proposed measurement approach will be applied to a CDMA communication system, by evaluating carefully the SNDR of that system. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.}, number={4}, journal={INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING}, author={Santos, Rui Estanqueiro and Carvalho, Nuno Borges and Gard, Kevin}, year={2009}, month={Jul}, pages={470–480} }
 @article{mazzaro_steer_gard_2009, title={Filter characterisation using one-port pulsed radio-frequency measurements}, volume={3}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map:20080111}, abstractNote={A method for extracting the loaded quality factor of the first resonator of a bandpass filter using one-port measurements is introduced. Properties of the quality factor are reviewed, and a time-domain approximation is used to estimate the loaded Q value from the decay rate of the filter's natural response. Narrowband 900 MHz Chebyshev filters are characterised.}, number={2}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Mazzaro, G. J. and Steer, M. B. and Gard, K. G.}, year={2009}, month={Mar}, pages={303–309} }
 @article{mazzaro_gard_steer_2009, title={Low Distortion Amplification of Multisine Signals Using a Time-Frequency Technique}, ISBN={["978-1-4244-2803-8"]}, ISSN={["0149-645X"]}, DOI={10.1109/mwsym.2009.5165843}, abstractNote={A novel time-frequency technique is presented for reducing intermodulation distortion when a multisine signal is applied to a nonlinear radio-frequency amplifier. A fast periodic switch is used to apply only one spectral tone at a time to the nonlinear amplifier. A bandpass filter following the amplifier removes switching spurious signals, leaving only the linearly amplified multisine signal at the output. The technique is used to linearize the response of a broadband amplifier with a four-tone uniform phase input signal centered at 465 MHz. The technique yields a 14 dB improvement in intermodulation distortion in comparison to the response of the original four-tone signal at the same output power.}, journal={2009 IEEE/MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM, VOLS 1-3}, author={Mazzaro, Gregory J. and Gard, Kevin G. and Steer, Michael B.}, year={2009}, pages={901–904} }
 @inproceedings{yelten_gard_2009, title={Theoretical analysis and characterization of the tunable matching networks in low noise amplifiers}, booktitle={2009 European Conference on Circuit Theory and Design, vols 1 and 2}, author={Yelten, M. B. and Gard, K. G.}, year={2009}, pages={890–893} }
 @article{wilkerson_gard_schuchinsky_steer_2008, title={Electro-Thermal Theory of Intermodulation Distortion in Lossy Microwave Components}, volume={56}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2008.2007084}, abstractNote={An analytic formulation of dynamic electro-thermally induced nonlinearity is developed for a general resistive element, yielding a self-heating circuit model based on a fractional derivative. The model explains the 10 dB/decade slope of the intermodulation products observed in two-tone testing. Two-tone testing at 400 MHz of attenuators, microwave chip terminations, and coaxial terminations is reported with tone spacing ranging from 1 to 100 Hz.}, number={12}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Wilkerson, Jonathan R. and Gard, Kevin G. and Schuchinsky, Alexander G. and Steer, Michael B.}, year={2008}, month={Dec}, pages={2717–2725} }
 @article{carvalho_remley_schreurs_gard_2008, title={Multisine signals for wireless system test and design}, volume={9}, ISSN={["1557-9581"]}, DOI={10.1109/MMM.2008.919938}, abstractNote={Multisine signals are used in the laboratory and in the field to provide a periodic, well-characterized waveform that can simulate complex modulated radio frequency (RF) signals. In the field of wireless telecommunications, multisines are often used to provide realistic test signals that have statistics similar to various types of digitally modulated signals. It is concluded that the multisine approach is well suited for evaluating a nonlinear system excited by real communication signals. Multisine signals enable to gather important information about the in-band distortion and to excite long-term memory effects by generating baseband components. They are periodic and straightforward to characterize, making them ideal for identifying both magnitude and phase distortion during test and verification. Using multisines to simulate standard wireless system excitations and figures of merit allows for very good laboratory nonlinear distortion measurement setups.}, number={3}, journal={IEEE MICROWAVE MAGAZINE}, author={Carvalho, Nuno B. and Remley, Kate A. and Schreurs, Dominique and Gard, Kevin G.}, year={2008}, month={Jun}, pages={122-+} }
 @article{domizioli_hughes_gard_lazzi_2008, title={Optimal Front-End Design for MIMO Receivers}, ISSN={["1930-529X"]}, DOI={10.1109/glocom.2008.ecp.717}, abstractNote={The effect of antenna mutual coupling on fading correlation in compact MIMO arrays has received considerable attention. By contrast, relatively little attention has been paid to the noise. In this paper we present a circuit model for a noisy MIMO receiver front-end that includes arbitrary coupling and noise correlation. The noise figure for two-port networks is extended to multiport networks, from which theorems for optimal front-end design are derived. Numerical results are presented which provide insight into receiver noise behavior in the presence of coupled antennas.}, journal={GLOBECOM 2008 - 2008 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE}, author={Domizioli, Carlo P. and Hughes, Brian L. and Gard, Kevin G. and Lazzi, Gianluca}, year={2008} }
 @article{mazzaro_steer_gard_walker_2008, title={Response of RF Networks to Transient Waveforms: Interference in Frequency-Hopped Communications}, volume={56}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2008.2007085}, abstractNote={The long-tail transient responses of a bandpass network to pulsed and switched-tone stimuli are examined and a time-domain closed-form expression of the envelope response is developed. It is shown that the long-tail response leads to interference in frequency-hopping communication systems. Interference, and in particular co-site interference, can result in any radar, communication, or RF sensor system becoming exposed to unintentional pulsed RF signals. In the experimental study, 900-MHz Chebyshev bandpass filters are considered.}, number={12}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Mazzaro, Gregory J. and Steer, Michael B. and Gard, Kevin G. and Walker, Aaron L.}, year={2008}, month={Dec}, pages={2808–2814} }
 @article{gharaibeh_gard_steer_2007, title={Estimation of co-channel nonlinear distortion and SNDR in wireless systems}, volume={1}, ISSN={["1751-8733"]}, DOI={10.1049/iet-map:20070034}, abstractNote={The effective signal-to-noise and distortion ratio (SNDR) at the output of a nonlinear amplifier is defined through the decomposition of the nonlinear output into correlated output and uncorrelated distortion. The analysis is based on the orthogonalisation of the nonlinear behavioual model that allows the accurate estimation of the effective in-band (or co-channel) distortion and hence determination of SNDR. Fundamental issues regarding the evaluation of the effective in-band distortion and its effect on digitally modulated signals are discussed. Simulations of in-band distortion and SNDR of WCDMA signals are verified experimentally using feed-forward cancelation.}, number={5}, journal={IET MICROWAVES ANTENNAS & PROPAGATION}, author={Gharaibeh, K. M. and Gard, K. G. and Steer, M. B.}, year={2007}, month={Oct}, pages={1078–1085} }
 @misc{gard_2007, title={Reality thinking in 'microwave bytes'}, volume={8}, number={2}, journal={IEEE Microwave Magazine}, author={Gard, K. G.}, year={2007}, pages={14} }
 @article{walker_steer_gard_2006, title={A vector intermodulation analyzer applied to behavioral modeling of nonlinear amplifiers with memory}, volume={54}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2006.872810}, abstractNote={A large signal vector intermodulation network analyzer with a dynamic range of 90 dB and phase resolution of better than 2/spl deg/ is reported. The analyzer is used in conjunction with a multislice behavioral model to characterize memory effects in three different RF power amplifiers: an MOSFET instrumentation amplifier, a multistage GaAs/silicon-based broadband microwave integrated-circuit amplifier, and an SiGe HBT monolithic-microwave integrated-circuit amplifier. The multislice behavioral model architecture builds on conventional single-tone AM-AM and AM-PM modeling extended to capture long-term memory effects that are characterized by asymmetric intermodulation distortion (IMD). Phase asymmetries of upper and lower IMD are captured. A systematic procedure for extracting the model is presented.}, number={5}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Walker, Aaron and Steer, Michael and Gard, Kevin G.}, year={2006}, month={May}, pages={1991–1999} }
 @article{jang_walker_gard_steer_2006, title={Capturing asymmetrical spectral regrowth in RF systems using a MultiSlice behavioral model and enhanced envelop transient analysis}, volume={16}, ISSN={["1099-047X"]}, DOI={10.1002/mmce.20160}, abstractNote={Nonlinear distortion in RF and microwave systems results in spectral regrowth of digitally modulated signals. The distortion above and below the main channel can be at different levels and this is attributed to baseband effects. This article presents a new multislice behavioral‐model architecture that captures this asymmetry and can be implemented in a variety of circuit simulators, including SPICE, harmonic balance (HB), envelope transient (ET), and system simulators. The work is experimentally validated using an HBT power amplifier at 2.5 GHz driven by a WCDMA signal. The model is used with envelope transient circuit simulation which is enhanced to accommodate an arbitrary baseband transfer function. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.}, number={4}, journal={INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING}, author={Jang, Wonhoon and Walker, Aaron and Gard, Kevin and Steer, Michael B.}, year={2006}, month={Jul}, pages={400–407} }
 @article{walker_steer_gard_2006, title={Capturing asymmetry in distortion of an RF system using a multislice behavioral model}, volume={16}, DOI={10.1109/LMWC.2006.0872114}, number={4}, journal={IEEE Microwave and Wireless Components Letters}, author={Walker, A. and Steer, M. and Gard, K.}, year={2006}, pages={212–214} }
 @article{nath_fathelbab_lam_ghosh_aygun_gard_maria_kingon_steer_2006, title={Discrete Barium Strontium Titanate (BST) thin-film interdigital varactors on alumina: Design, fabrication, characterization, and applications}, ISBN={["978-0-7803-9541-1"]}, ISSN={["2576-7216"]}, DOI={10.1109/mwsym.2006.249652}, abstractNote={Discrete barium strontium titanate (BST) thin-film capacitors in industry standard 0603 footprint are introduced and characterized. BST capacitors have a voltage-dependent permittivity, enabling BST thin-film capacitors to be used as tuning elements in frequency agile devices. The capacitance changed by 1.5:1 at 35 V (116 kV/cm) bias. The temperature dependence of the capacitance was measured to be less than plusmn 20 % from -100 degC to +100 degC. A 2nd-order tunable combline bandpass filter on FR4 substrate has been implemented using the discrete BST varactors. The filter showed a center frequency tuning of 22% from 2.14 GHz to 2.61 GHz upon application of 130 V (433 kV/cm) bias. The zero-bias insertion loss was 4.9 dB which decreased to 2.9 dB at the high bias state. The return loss was better than 11 dB over the tuning range. Nonlinear characterization of the filter using two-tone test and a digitally-modulated CDMA 2000 signal showed an IP3 of +32 dBm and an ACPR of better than -50 dBc up to 26 dBm of input power, respectively}, journal={2006 IEEE MTT-S INTERNATIONAL MICROWAVE SYMPOSIUM DIGEST, VOLS 1-5}, author={Nath, Jayesh and Fathelbab, Wael M. and Lam, Peter G. and Ghosh, Dipankar and Aygun, Seymen and Gard, Kevin G. and Maria, J. -P. and Kingon, Angus I. and Steer, Michael B.}, year={2006}, pages={552–555} }
 @article{gharaibeh_gard_steer_2006, title={In-band distortion of multisines}, volume={54}, ISSN={["1557-9670"]}, DOI={10.1109/tmtt.2006.879170}, abstractNote={Multisine signals are shown to be useful for estimating distortion of communication signals. In particular, a generalized approach for the evaluation of effective in-band distortion in a nonlinear amplifier using multisine excitation is presented. The output of the nonlinearity is represented as the sum of uncorrelated components by the transformation of a behavioral model. Simulated and measured results are presented for code-division multiple-access signals}, number={8}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Gharaibeh, Khaled M. and Gard, Kevin G. and Steer, Michael B.}, year={2006}, month={Aug}, pages={3227–3236} }
 @article{luniya_gard_steer_2006, title={Modeling nonlinear distortion of ultra wideband signals at X-band}, volume={16}, ISSN={["1558-1764"]}, DOI={10.1109/LMWC.2006.875588}, abstractNote={Nonlinear distortion in the adjacent channels of an X-band amplifier driven by an ultra-wideband digitally-modulated carrier is analyzed. Statistical properties of the input signal with a complex power series-based behavioral model of the amplifier are used to calculate the output power spectrum. Comparisons are made between measured and predicted adjacent channel power rejection for the X-band monolithic microwave integrated circuit.}, number={6}, journal={IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS}, author={Luniya, Sonali and Gard, Kevin G. and Steer, Michael B.}, year={2006}, month={Jun}, pages={381–383} }
 @article{gard_larson_steer_2005, title={The impact of RF front-end characteristics on the spectral regrowth of communications signals}, volume={53}, ISSN={["1557-9670"]}, DOI={10.1109/TMTT.2005.848801}, abstractNote={The nonlinear characteristic of an RF front-end results in in-band distortion and spectral regrowth of digitally modulated signals with distortion being dependent on the statistical variation of the signal. In this paper, the interaction of the nonlinear response with the signal is explored using a time-averaged autocorrelation analysis applied to several limiter-amplifier models having characteristics ranging from soft-to-hard amplitude limiting. The analysis is verified by comparing measured and predicted adjacent channel power rejection for a code-division multiple-access amplifier.}, number={6}, journal={IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES}, author={Gard, KG and Larson, LE and Steer, MB}, year={2005}, month={Jun}, pages={2179–2186} }