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Multiarm slotline stubs have been used to increase the bandwidth of slotline open circuits in transitions between microstrip and slotline and between coplanar waveguide and slotline. The model used in prior papers is a series connection of the short-circuit terminated stubs, resulting in an increase in the input impedance by a factor of $N$ , where $N$ is the number of stubs. In this paper, it is shown that this model cannot be applied for slotline with finite width metal planes or coplanar stripline (CPS), because it does not account for higher order modes that are necessarily excited on the multiarm structure. This paper presents a physical explanation and model that accounts for the higher order modes on the structure and explains how the multiarm finite width slotline/CPS stub structure increases the bandwidth of the transitions between slotline and other transmission lines. With the correct model presented in this paper, it is expected that improved slotline or CPS circuits can be developed. [ABSTRACT FROM AUTHOR]

This paper presents a new spiral inductor based on substrate integrated suspended line (SISL) technology. SISL is a new type of transmission line, which has many merits, such as low loss, low dispersion, and self-packaging. New series of spiral inductors based on this advanced SISL platform is proposed and modeled in this paper. SISL to microstrip transition is designed for the measurement of the SISL inductor, and an open-short deembedding method is introduced for the accurate extraction of inductor network parameters. A $\pi$ equivalent circuit model is applied for modeling of the SISL inductor and new double-sided SISL (DSISL) inductor, and the accurate empirical expression of inductance L$ , peak quality factor Q_{\mathrm {max}} , and self-resonance frequency are given. The typical relative error of each expression is less than 8%. Finally, a new DSISL inductor with patterned substrate is proposed, which can significantly improve the quality factor up to 40%. Simulation and measurement results show good agreement. [ABSTRACT FROM PUBLISHER]

An accurate physical model for GaN high-electron-mobility-transistors (HEMTs) device is imperative and crucial for circuit design and technology optimization. In this paper, a scalable large-signal surface-potential (SP) model of AlGaN/GaN HEMTs is presented. The drain current model is capable of accurately modeling the self-heating effect and trapping effect. The self-heating effect is modeled by embedding temperature increment into free-carrier mobility model, and the trapping effect is modeled by introducing an indirect variable effective gate voltage V\mathrm {gseff} . Moreover, the scaling and multiharmonic characteristics of the SP model are studied for the first time. The geometry-dependent thermal resistance R\mathrm {ths} is identified by the electrothermal finite-element method simulations, which is scalable with the gate width W and power dissipations P\mathrm {diss} of the device. Single-tone on-wafer load–pull measurements at operating frequency 8 GHz is carried out for verification purpose. Accurate predictions of the static (dc) $I\!-\!V$ , pulsed-gate-and-drain $I\!-\!V$ , S-parameters up to 40 GHz and large-signal harmonic performance (the fundamental, second- and third-harmonics output power, and power-added efficiency) for the devices with different gate peripheries have been achieved by the proposed model. The results of this paper can pave the way for the full application of the physical-based model in circuits design. [ABSTRACT FROM PUBLISHER]

This paper presents a frequency- and bandwidth-tunable bandstop filter using substrate-integrated wave- guide (SIW) resonators. For designing such a filter, this paper also presents a tunable coupling structure between a microstrip line and an SIW resonator for obtaining the bandwidth tuning capability. The coupling structure has two coupling slots between the microstrip line and the resonator, and the phase shift between the two slots determines the overall external coupling value of the resonator. This external coupling value can be controlled by making use of a phase shifter, which in turn makes it possible to adjust the bandwidth of a bandstop filter. A thorough mathematical analysis is shown using the equivalent circuit model of the presented coupling structure, and it has been verified by measuring an SIW resonator containing the presented structure. The presented tunable coupling structure has also been applied to a design of bandstop filter that can be tuned from 2.8 to 3.4 GHz. The measured results at 3.1 GHz show that the bandwidth can be tuned from 0 (all-pass) to 96 MHz reaching the attenuation level of 44 dB. [ABSTRACT FROM PUBLISHER]

Frequency-dependent coupling (FDC) emerges as a new method to introduce the finite-position transmission zeros (TZs) in the synthesis and design of filtering networks. In this paper, several fundamental building blocks with FDCs are introduced and studied. The higher order filters with many TZs can be constructed by cascading these fundamental building blocks. As compared with the conventional coupled-resonator filters with only constant couplings, the inclusion of FDCs can potentially create more TZs with the same coupling topology. It is also shown that to realize the same TZs, a filter can be realized in a simplified structure with less cross-couplings by using FDCs. In this paper, one complete filter design procedure is illustrated, including the steps of the circuit model synthesis by the method introduced in this paper, physical dimensioning of the filter by the electromagnetic simulation and measurement of the fabricated filter. The measurement results are in very good agreement with the theoretical predictions, which validates the modular design strategy for filters with FDCs. [ABSTRACT FROM AUTHOR]

In this paper, we propose a compact topology for high-frequency bandpass filters using coaxial cavities embedded in a bed of nails, including a complete design procedure combining equivalent circuit models and full-wave simulators. The resonance generated around a shortened cylindrical nail of the bed hosting structure is used as the basic element of the proposed filter, which is fed through groove gap waveguides. For design purposes, an equivalent circuit model of the considered resonance is first obtained, and then the coupling levels between resonators are recovered with the distance between adjacent shortened nails. In order to validate the proposed structure and its design procedure, a filter prototype with a bandpass response (centered at 30 GHz and with relative bandwidth of 1.7%) has been designed, manufactured, and measured. Good experimental results, in terms of insertion losses (with a minimum value of 1.6 dB) and return losses (greater than 16.6 dB in the whole passband), have been achieved. [ABSTRACT FROM AUTHOR]

This paper presents geometrical-based wideband circuit models for different configurations of loaded slotline and loaded coplanar waveguide (CPW). It investigates, first, the strip-loaded slotline and then extends the developed model to strip and split-ring resonator (SRR)-loaded CPW. The proposed models successfully describe the behavior of several structures of interest in the literature and provide new insights on the design procedure. They operate over the entire frequency range if higher order modes are not generated without the need for fitting parameters. This paper also presents three applications, of which the design relies on the proposed modeling methodology. They are a third order maximally flat low-pass filter with 1.4-GHz cutoff frequency, a 3-GHz slow wave structure with a slow wave factor larger than 2 in the linear range of the dispersion relation, and a balanced composite right-/left-handed SRR-loaded CPW with 100% (2.31–7.1 GHz) fractional bandwidth. Experimental results, which are in a very good agreement with the electromagnetic simulations, confirm the proposed theory. [ABSTRACT FROM AUTHOR]

In this paper, we propose a compact, lightweight, and easy-to-fabricate Hilbert curve-based metasurface resonator that can effectively increase the sensitivity (radio frequency (RF) field intensity) and penetration depth of an RF coil for 7-T magnetic resonance imaging scanner. A circuit model is proposed to accurately calculate the resonance frequency of Hilbert curve resonators of different orders. A single element of a transverse electromagnetic (EM) coil was used for this paper. The increase in the field sensitivity introduced by the proposed metasurface to an RF coil was successfully demonstrated through simulations and experiments. The EM field produced by the RF coil is redistributed due to the presence of the proposed metasurface. The key feature of the proposed structure is its significant increase in the penetration depth of magnetic fields into the imaging volume. An enhancement of the magnetic field by more than four times was observed at 13.5 cm away from the coil experimentally. Flexibility for matching the coil integrated with the proposed surface is shown. [ABSTRACT FROM AUTHOR]

This paper presents an analysis and design technique for an RF-input load modulated balanced amplifier (LMBA) with Doherty-like efficiency enhancement characteristics. The LMBA is a recently introduced power amplifier (PA) architecture in which a control signal is injected into the isolation port of the output coupler of a balanced amplifier. This control signal modulates the apparent load impedance of the two main devices. In the RF-input LMBA presented in this paper, the control signal is generated from the single-modulated RF input using a class-C control amplifier, producing an overall Doherty-like response. A complete theoretical analysis of the RF-input LMBA is presented, by assuming generalized networks for the output combiner and input splitter which are then solved in terms of transistor parameters and boundary conditions for high efficiency. Based on this analysis, a generalized design technique is presented. The LMBA is, thereby, shown to have advantages over the Doherty PA, including the device periphery scaling between the main and control devices for a given back-off range. The design technique is demonstrated at 2.4 GHz using packaged GaN devices. The prototype has a peak CW output power of 45.6 dBm, with a power-added efficiency of 60% at peak power and 50% at 6-dB output back-off, including the power dissipated by the control PA. A long-term evolution signal at 2.4 GHz with a 7.5-dB peak-to-average power ratio is demonstrated with an unlinearized ACLR of −27 dBc and an average drain efficiency of 47% for a 38-dBm average output power. [ABSTRACT FROM AUTHOR]

In this paper, we present the performance and imaging results of an integrated single-chip CMOS-microelectromechanical systems (MEMS) scanning microwave microscope (SMM). A systematic analysis for sensitivity improvement is described in detail. We first explain why it is important to have high sensitivity for this type of microscope and then propose a systematic method to analyze and design the entire structure for better sensitivity. For this, accurate lumped models are derived for each section of the system and comparisons are made between different designs. Furthermore, a new concept based on the quality factor of the individual sections is described to give the designer a tool to improve the sensitivity of individual sections without the need to simulate or model the entire system. A high-sensitivity measurement system is also explained. Finally some measurement results are presented. While the analysis presented in this paper is for CMOS-MEMS SMM, it is applicable to any type of SMM. [ABSTRACT FROM AUTHOR]

This paper presents a novel technique for suppressing cable noise currents, the quadruplet-resonator-based ferrite-free choke (QR-based FFC), to eliminate the gigahertz (GHz) electromagnetic interference caused by noise currents flowing on the cable shielding. This problem is difficult to handle with conventional ferrite materials since their permeabilities dramatically degrade when the operating frequency goes up to several GHz. In this paper, with the aid of QR surrounding on the cable shielding, the FFC forms bandstop responses against the noise currents. The corresponding equivalent lumped circuit model is proposed and investigated. Furthermore, the synthesis procedure is established using microwave filter theory. The QR-based FFC can achieve a high-level current suppression at the desired frequency band. This technology is experimentally verified: a given design example is demonstrated at the operating center frequency of 2.57 GHz. The frequency range of 3-dB current suppression is measured from 2.47 to 2.75 GHz (FBW = 10.8%), where the highest suppression level is up to 36 dB. The FFC-added cable also demonstrates a good result in the reduction of far-field radiation, where the reduction level of radiation peak gain is measured as 7 dB compared with that of a bare cable. [ABSTRACT FROM AUTHOR]

This paper presents a low noise figure (NF) and high gain super-regenerative receiver (SRR) with coupled networks for portable millimeter-wave (mm-wave) imaging systems. Compared with the previous SRR designs, this paper presents a novel SRR structure comprising of two oscillators coupled by a serial resonator, which consists of the inductors and capacitors. Due to the coupled oscillators, the gain of the SRR is significantly improved and the NF of the SRR structure is reduced by 3 dB simultaneously. These benefits lead to a high-sensitivity SRR at mm-wave frequency. The circuit is realized in 65-nm CMOS process with a core area of 0.06 mm2. Measured results show that the receiver can detect −84-dBm minimum input power with 541-MHz integration bandwidth (BW). It has a noise-equivalent-power of 0.615 fW/(Hz), a NF of 7.52 dB, a BW of 3.5 GHz, and a power consumption of 8.1 mW. With frequency calibration procedure, these performances show the proposed chip meets portable imaging system requirement. [ABSTRACT FROM AUTHOR]

The nonlinearities and memory effects of power amplifiers (PAs) can be compensated by multistage cascaded digital predistortion with low complexity. Compared with full multistage models, sparse multistage models may have the same linearization performances while their complexities are even lower. However, the choice of the model structure is very difficult, especially for the sparse models. For instance, if there are $(K+1)(L+1)$ full models, then $2^{K+L-2}$ different corresponding sparse models exist. An algorithm with the optimal search space definition is proposed in this paper to search for the optimal cascaded sparse model structure. The search criterion represents tradeoff between the modeling accuracy and identification complexity with a weight coefficient. A method to determine the value of the weight coefficient is proposed in this paper. The sparse model solution found by the proposed algorithm is evaluated with a three-way Doherty PA using a long term evolution-advanced signal. It is also compared with the solution of full model structure search. [ABSTRACT FROM AUTHOR]

In this paper, an analytical coupling matrix extraction scheme is proposed for parallel-connected dual-passband coupled-resonator filters for the first time. Model-based vector fitting technique is adopted to fit the measured responses of the dual-passband filter (DPBF) with a set of rational functions, from which a transversal coupling matrix can be constructed. A novel coupling matrix transformation strategy is developed to transform the transversal coupling matrix to the one corresponding to the topology of a parallel-connected DPBF. A practical filter is used as a test example to demonstrate the extraction procedure. In diagnosing the coupling matrix of the test filter, two kinds of ambiguity problems are discussed in detail and are solved by a perturbation technique. This paper provides a general theoretic framework for computer-aided tuning of a parallel-connected dual-passband or multiple-passband filter. [ABSTRACT FROM PUBLISHER]

Products of passive intermodulation (PIM) generated by weak nonlinearities of passive circuits subjected to relatively high transmit power of multicarrier signals may cause strong interference in emerging broadband and multiradio communication systems. This paper presents a new approach to a characterization of distributed nonlinearities in printed circuits fabricated on commercial grade microwave laminate materials. An efficient procedure for PIM characterization has been devised using the commercial RF-CAD software. The phenomenological model has been developed to take into account concurrent distributed nonlinearities of printed transmission lines and to evaluate PIM products of arbitrary order. It has been observed for the first time that the sources of nonlinearity in typical microstrip circuits may have highly uneven distributions which require a different means for PIM characterization and modeling. The proposed methodology has been validated by accurate predictions of the PIM response of complex circuit layouts. The results of this paper pave the way to a holistic approach to the design of planar microwave circuits and devices under given linearity constraints. [ABSTRACT FROM PUBLISHER]

This paper presents a balanced frequency doubler with 6.5-dBm peak output power at 204 GHz in 130-nm SiGe BiCMOS technology ( fT/f\max =210 /250 GHz). To convert the single-ended input signal to a differential signal for balanced operation, an on-chip transformer-based balun is employed. Detailed design procedure and compensation techniques to lower the imbalance at the output ports, based on mixed mode S parameters are proposed and verified analytically and through electromagnetic simulations. The use of optimized harmonic reflectors at the input port results in a 2-dBm increase in output power without sacrificing the bandwidth of interest. The measured conversion loss of the frequency doubler is 9 dB with 6-dBm input power at 204-GHz output. The measured peak output power is 6.5 dBm with an on-chip power amplifier stage. The 3-dB output power bandwidth is measured to be wider than 50 GHz (170–220 GHz). The total chip area of the doubler is 0.09 mm2 and the dc power consumption is 90 mW from a 1.8-V supply, which corresponds to a 5% collector efficiency. [ABSTRACT FROM PUBLISHER]

This paper aims to effectively integrate a GaN amplifier into a high-efficiency active-antenna design. In this paper, the antenna is designed for a GaN high-electron-mobility-transistor (HEMT) impedances calculated by a load–pull simulation with a GaN nonlinear model, which contributes to a lossless design and prevents power-added-efficiency (PAE) reduction by active-antenna integration. The antenna impedance is selected to reduce the impedance-transform ratio with the GaN HEMT. In addition, the active antenna includes a second-harmonic-tuning circuit for high efficiency. The active antenna comprises antenna- and amplifier-circuit layers piled onto a Peltier unit, which has a high affinity with this cooling systems. The antenna and amplifier circuits are designed on low- and high-dielectric substrates, respectively, enabling the amplifier to be downsized and the antenna gain to be increased. Each layer is connected by a through-hole. First, the single-stage amplifier is fabricated with a maximum output power of 37.95 dBm and a maximum PAE of 62.94%. Next, the GaN active antenna is fabricated with a maximum effective isotropically radiated power of 44.61 dBm and a maximum antenna gain of 23.99 dBi. The assumed amplifier large-signal characteristics of the active antenna agree with those of the single-stage amplifier. Therefore, the amplifier and the antenna are integrated without loss. [ABSTRACT FROM AUTHOR]

Wireless power transfer (WPT) systems working at several megahertz (MHz) are widely considered as a promising solution for a mid-range transfer of a medium amount of power. The soft-switching-based Class E power amplifier (PA) and rectifier are known to be suitable for high-frequency applications, which may potentially improve the performance of the MHz WPT systems. Meanwhile, the efficiency and output power of the Class E PA are sensitive to its loading condition, particularly when there is variation in the relative position of the coupling coils, namely a changed mutual inductance between the coils. Thus the purpose of this paper is to propose and discuss circuit and design improvements that maintain a high efficiency and output power of the MHz WPT systems over a wide range of mutual inductance, when the Class E PA and the Class E rectifier are employed. Besides, the suppression of the harmonic contents, i.e., the electromagnetic interference problem, is also considered in the circuit design. Both the simulation and experimental results show that the newly added and optimally designed $\pi $ matching network obviously improves the drops of the efficiency and output power of the Class E PA and the overall WPT system when the mutual inductance varies. The reduction of the total harmonic distortion in the input voltage of the coupling coils is also significant, from the original 52.9% to 9.6%. The circuit and design improvements discussed in this paper could serve as a general and practical solution for building high-performance MHz WPT systems. [ABSTRACT FROM PUBLISHER]

This paper proposes the use of the coplanar waveguide (CPW) odd mode, also known as the parasitic slotline mode, as a design parameter. It presents a novel equivalent circuit model for the CPW cross-junction, where each CPW has two modes: the even mode, which is the conventional CPW mode also known as the coplanar mode, and the odd mode. The model is simple, intuitive, and physical-based. It can be used in different combinations including the case of slotline cross-junction. The model paves the way to design novel air-bridge free CPW applications. Among them, two are presented in this paper: CPW-to-slotline transition (balun) and Wilkinson power divider. For both applications, closed form expressions for the operating point are derived. Results are verified by EM simulations. An air-bridge free CPW power divider that combines both applications is fabricated and characterized. Simulations and measurements are in a very good agreement. [ABSTRACT FROM PUBLISHER]

In this paper, compact time-domain (TD) models featuring materials with frequency-dependent electromagnetic (EM) properties are derived. The considered frequency-dependent material models include multiterm Debye and Lorentz models for the electric permittivity and the magnetic permeability and a multiterm Drude model for the electric conductivity. The TD models are based on finite-element systems in the frequency domain (FD). To render the model compact and computationally efficient, the dimension of the FD system is compressed with the help of projection-based model-order reduction. In contrast to older approaches, the TD transformation is performed on the FD model itself rather than on the transfer function. The result is a state-space representation, which may either be solved by custom time integrators or imported into commercial circuit simulators. The advantages of the new approach include provable passivity of the FD model, provable causality of the TD model, and the ability to reconstruct the transient EM fields. [ABSTRACT FROM AUTHOR]

In this paper, a novel matching circuit design method utilizing a genetic algorithm (GA) and the measured S-parameters of randomly moved coil configurations is discussed. Through the detailed comparison of different matching circuit topologies, the superiority of active matching circuits is clearly demonstrated, and potentially there is 21.4% improvement in the wireless power transfer efficiency by using a four-cell active matching circuit, which can create 16 different impedance values. Also, the matching circuit design simulation can be further simplified by choosing a much smaller subset of representative impedance values for the utilized time-changing coil configuration through the employment of $k$ -means clustering and use only these values for the derivation of the optimal matching circuit. This heuristic approach could drastically reduce the time for the matching circuit design simulation, especially for matching circuit topologies with a larger number of cells. [ABSTRACT FROM PUBLISHER]

An enhanced full-wave method based on circuit analysis is presented in this paper, where the whole set of modes TEmnp and TMmnp are taken into account. The modeling of a split cylinder resonator is done with two circuit networks of one and three ports, characterized by their generalized admittance matrix, which is computed making use of the mode matching method. The improved full-wave circuit method has been applied to the accurate determination of dielectric properties of materials. The proposed method has been validated through comparisons with other published models and also with measurements. [ABSTRACT FROM PUBLISHER]

This paper is focused on the synthesis of capacitively loaded coupled lines for the design of bandpass filters with compact size and spurious suppression. The filters consist of cascaded pairs of coupled lines periodically loaded with patch capacitors. The loading capacitances provide a slow-wave effect to the coupled lines useful for filter miniaturization, whereas periodicity introduces bandgaps that can be controlled in order to achieve spurious suppression. Filter design is achieved following an automated process based on aggressive space mapping (ASM) optimization. The two reported examples, a third-order filter with central frequency f0 = 1.0 GHz, 8% fractional bandwidth, and 0.1-dB ripple level and a fifth-order filter with central frequency f0 = 1.8 GHz, 8% fractional bandwidth, and 0.1-dB ripple level, demonstrate the potential of the proposed ASM-based design approach, as well as the effectiveness of the loading capacitances to reduce filter size and reject the spurious bands. Significant size reduction in both filters is achieved, whereas the out-of-band rejection is better than 30 and 45 dB in the third-order and fifth-order filters, respectively, up to at least 4f0 . [ABSTRACT FROM PUBLISHER]

Transmitters based on nonlinear radio-frequency (RF) modulators and switched-mode power amplifiers are systems that, at least theoretically, can provide high linearity and energy-efficient generation of RF signals at the same time. However, the nonlinear memory-affected behavior remains an issue hindering practical applications. This paper shows that it is possible to model the nonlinear memory of such circuits based on time-domain observations and how to use this information in computationally efficient time-domain RF circuit models. In contrast to other works, this model covers the full bandwidth of the active device (dc–10 GHz) and it uses hierarchical data structuring to adaptively find a compact model without prior knowledge of the circuit’s memory depth. The data for this work were gained from a laboratory setup, designed to be used as an LTE transmitter for a signal bandwidth of 20 MHz at a fixed center frequency of 2.5 GHz. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel and unified synthesis approach and design procedure for microwave filters with extracted pole and nonresonating node (NRN) technique. By introducing a general circuit topology, the traditional extracted pole and NRN filters can be unified to a general prototype. With the new design process, the exact mapping relationship between the electromagnetic (EM) model of the pole producing element and the circuit model can be achieved. All the physical dimensions of the filter structure can be obtained by a fully analytical approach. No full EM optimization or adjustment is needed in the filter design. A three pole TE \mathrm { {101}} mode waveguide filter with one finite transmission zero is designed to illustrate the new procedure. In addition, a seven-pole TE \mathrm { {011}} mode filter with four finite transmission zeros covering all three possible types of arrangements is designed and fabricated to demonstrate the versatility of the proposed method. The simulated and measured results verified the efficiency and the accuracy of the proposed design method. [ABSTRACT FROM AUTHOR]

This paper presents a generalized geometrical equivalent circuit model for a strip-loaded coplanar waveguide (CPW) that carries the even and odd modes simultaneously. The proposed model enables the analysis, sets the design requirements, and defines the constraints of the realization of an air-bridge free all CPW Wilkinson power divider (WPD). To overcome these constraints, this paper proposes two implementations. The first one engineers the dispersion relation of the odd mode to provide a slow-wave factor that compensates the difference in the electrical lengths with the even mode, while the second implementation deploys the floating strips as electrical air-bridges. The proposed power dividers are designed to operate at 2.4 GHz. Measurements, which are in good agreement with the EM simulations, confirm the theoretical predictions. [ABSTRACT FROM AUTHOR]

The demand and relevance of efficient analog fault diagnosis methods for modern RF and microwave-integrated circuits increase with the growing need and complexity of analog and mixed-signal circuitry. The well-established digital fault diagnosis methods are insufficient for analog circuitry due to the intrinsic complexity in analog faults and their corresponding identification process. In this paper, we present an artificial neural network (ANN) modeling approach to efficiently emulate the injection of analog faults in RF circuits. The resulting metamodel is used for fault identification by applying an optimization-based process using a constrained parameter extraction formulation. A generalized neural modeling formulation to include auxiliary measurements in the circuit is proposed. This generalized formulation significantly increases the uniqueness of the faults identification process. The proposed methodology is illustrated by two faulty analog circuits: a CMOS RF voltage amplifier and a reconfigurable bandpass microstrip filter. [ABSTRACT FROM AUTHOR]

A class of self-isolated harmonic oscillator (SIHO) with a feedback-loop structure is able to significantly reduce the pulling effect without involving extra circuit complexity such as a buffer amplifier. In the first part of this paper, the operation principle of the SIHO is theoretically studied through equivalent circuit models and X-parameter techniques. Closed-form expressions are derived to represent the respective linear and nonlinear equivalent impedances of SIHO subnetworks perturbed by varied load and injected signals. A conventional feedback-loop oscillator structure delivering the fundamental tone is used for comparative study. Such a modeling technique reveals the physical principle and behavior parameters that have an impact on the pulling effect. The experimental verification of the SIHO operation principle and modeling is presented as the second part of this paper. To this end, a harmonic measurement and design system is proposed and implemented for the design of an exemplary SIHO, which delivers a 4-GHz signal with 16.6-dBm power, 28% dc-RF efficiency, and −136.5-dBc/Hz phase noise at 1-MHz offset. The design process does not rely on circuit simulation software packages or a prior knowledge of the large-signal model of transistors, thus demonstrating the concept of a model-free nonlinear circuit design automation based on the experimental optimization. The SIHO circuit model is validated with the measured X-parameters of its nonlinear subnetwork. [ABSTRACT FROM AUTHOR]

This paper presents an injection-locked 65-nm CMOS circuit that upconverts and power amplifies baseband signals to RF. The circuit delivers an RF output power of 28.7 dBm, with a power gain and maximum power added efficiency (PAE) of 20.6 dB and 68.1%, respectively. Both AM–AM-conversion and AM–PM-conversion are low, less than 1 dB and 1°, respectively, resulting in an EVM of 4.7% for Long Term Evolution (LTE) and 4.1% for WCDMA signals. The circuit provides an average output power of 20.3 dBm for LTE, with a PAE of 44.1%, and for WCDMA, the average output power is 23.8 dBm with a PAE of 55.6%. Supply modulation improves power back-off efficiency and the voltage range is from 540 mV to 3 V. The spectral mask for LTE signals has a worst case ACLR of 33.2 dBc using predistortion. For WCDMA signals, ACLR1 is 39.9 dBc and ACLR2 is 47.2 dBc, both values worst case and using baseband predistortion. This performance is achieved by introducing a cross-coupled cascode topology, and supporting theory and simulations are presented. The startup loop-gain and small-signal equivalents are derived, a power dissipation analysis is performed, and the injection circuit is analyzed to investigate the AM–PM behavior. Analysis and simulations show that, compared to conventional cascode amplifiers, PAE is improved by 24% (15% points). The circuit is implemented in an STM 65-nm CMOS process and occupies an area of $1.0 \times 0.53$ mm2. [ABSTRACT FROM AUTHOR]

This paper presents, to the best of the authors’ knowledge, the first realizations of the Gysel-type power combiner/divider in ridge waveguide technology with two different configurations. Gysel combiners exhibit wider bandwidths than traditional combiners, while offering compact designs when implemented in ridge waveguide, compared with traditional waveguide combiners. In addition, Gysel combiners provide relaxed requirements on the power handling capability of the terminating loads in the case of fault conditions, which may result from imbalance between different inputs. The ridge waveguide designs offer better power handling capabilities, especially in comparison with planar designs. These advantages are shown with two different realizations, in top–bottom and side-by-side configurations, exhibiting very wide bandwidths while occupying very compact volumes. These two designs have been simulated, fabricated, and tested. Excellent test results have been obtained, confirming the validity of the concept. [ABSTRACT FROM AUTHOR]

This paper presents the design of a capacitive wireless power transfer system for operation in fresh water. This paper clarifies two particular points. One is the behavior of $k$ and kQ product for the frequency; $k$ means coupling coefficient in the coupler and kQ product means the product of $k$ and $Q$ -factor in the coupler. The other is the design method of the general capacitive coupler under fresh water. First, $k$ is derived from the equivalent circuit of the coupler, and it is elucidated that $k$ and kQ product are dependent on the frequency. The pivotal elements that improve kQ product are also found. Next, it is then clarified that the design parameters at maximum kQ product have the maximum available efficiency and we clarify the applicable condition for our design method. We achieved an efficiency of 91.3% at a transfer distance of 20 mm via experimentation. Finally, it is demonstrated that power is wirelessly transferred to the Lux sensor module using our coupler implemented on the charging station and that measured data are also wirelessly transferred to it. [ABSTRACT FROM AUTHOR]

This paper describes a method for characterizing mixer noise in terms of several noise parameters. A measurement method for extracting the noise parameters is proposed and verified with simulations of a mixer and measurements of two mixers. Direct measurements of single-sideband noise figures are accurately represented by the measured noise parameters, which fully characterize the noise figure of the mixers for all harmonic impedance loading conditions. Over 606 measurements, the maximum error between the measured and modeled noise factors was less than 0.12 dB. This is the first paper that proposes and verifies a method of mixer noise parameter measurements. [ABSTRACT FROM PUBLISHER]

In this paper, a new concept of matrix-inversion-less derived physically expressive circuit method of model order reduction for large-scale high-speed/microwave circuit problems is proposed. It is the first model that is derived based on the mesh information of partial element equivalent circuit modeling. This new proposed method absorbs insignificant nodes and parallel branches while retaining the physical meaning of all the inductive and capacitive elements. This method does not involve any matrix inversions or decompositions and its computational overhead is dominated by outer products that can be simply accelerated by the massive GPU acceleration technique. The resultant order-reduced circuit is very useful for not only speeding up the analysis of a large-scale high-speed/microwave circuit but also interpreting the physical insight of the circuit layout from the circuit domain point of view. Three numerical examples are given, demonstrating the versatility, scalability, accuracy, and simplicity of the method. [ABSTRACT FROM PUBLISHER]

In this paper, a nonintrusive polynomial chaos (PC) approach for the fast multidimensional uncertainty quantification of microwave/RF networks is presented. The key feature of this paper is the development of a linear regression methodology based on sparse D-optimal design of experiments to accurately evaluate the PC coefficients of the network responses. A greedy search algorithm to identify the sparse set of D-optimal design of experiments from within a multidimensional random space has been presented. Additional numerical approaches to further accelerate the search algorithm for high-dimensional random spaces have also been developed. [ABSTRACT FROM PUBLISHER]

This paper presents a multifunctional reconfigurable frequency-selective surface (FSS) based on liquid-metal-filled microchannels engraved in an elastomeric substrate. The proposed FSS comprises two layers of periodic meandered patterns encased within the opposite sides of a dielectric, where the layers are arranged in orthogonal polarization with independent control of reconfigurability. The novelty of the design lies in its switching characteristic between four different working states (dual-polarized all pass, single-polarized low pass, single-polarized bandpass, and dual-polarized bandpass) with the injection of a liquid metal in the top and bottom microchannels. Moreover, the design exhibits miniaturization performance during one of the states (exhibiting dual-polarized bandpass response at 1.58 GHz) corresponding to the unit cell dimensions of $0.052\lambda _{0} \times 0.052\lambda _{0}$. The equivalent circuit models and parametric variations are extensively analyzed for understanding the design principles. Because any liquid-metal-based reconfigurable FSS structure has not been reported earlier, a detailed description of the fabrication and measurement procedure are presented in this paper. The experimental validation of the fabricated prototype also confirms the potential use of microfluidic technology-based reconfigurable structures in future. [ABSTRACT FROM AUTHOR]

The general coupling matrix representation of bandpass filter (BPF) circuits is a widely used technique that has simplified the analysis and optimization of complex microwave filters. In this paper, we demonstrate a novel application of the general coupling matrix for modeling wireless power-transfer (WPT) systems based on the BPF model of magnetically coupled resonators. Compared to other methods of WPT analysis, our model simplifies accommodation of complex loads and provides direct expressions for impedance matching (IM) in WPT systems. Using this tool, we achieve optimal IM for two resonator systems with a complex load, thus achieving the greatest possible power-transfer efficiency (PTE). Furthermore, our model reveals additional design constraints for optimizing PTE in coupled resonator systems exhibiting low quality factor and small interresonator coupling. Overall, this paper introduces a new, versatile framework for the analysis and optimization of coupled resonator WPT systems. Experimental results are presented, verifying the optimal IM design process. [ABSTRACT FROM PUBLISHER]

This paper investigates the back-gating effects due to traps, and presents a new nonlinear trap modeling approach suitable for gallium nitride (GaN) high electron mobility transistors (HEMTs). It is shown that the traps have nonidentical influence on the channel compared with the gate. The potential due to trapped electrons in the buffer and the gate–source voltage need to be differentiated to model their respective influence on conductivity of the 2-D electron gas. Hence, the back-gating potential due to traps cannot be included in the transistor model by directly offsetting the gate–source voltage. A new modulation factor is therefore introduced to create an effective back-gating potential, and thereby improve the modeling of trapping effects. The proposed nonlinear trap model is shown to accurately predict the trapping behavior for a large voltage operating region. A detailed procedure is presented to derive the model parameters from basic device measurements. The model is experimentally validated and shown to accurately predict dc-, pulsed-IV, and large-signal waveform performance for a commercial GaN HEMT. [ABSTRACT FROM PUBLISHER]

In this paper, a new systematic technique to design manifold-coupled multiplexers in waveguide technology is proposed. The new technique uses generalized low-order electromagnetic (EM) distributed models, which constitute a half-way point between the fast, but imprecise, analytical models, and the more accurate, but costly, full-wave EM models. The method can be applied to contiguous and noncontiguous channel multiplexers, in both E-plane or H-plane configurations. This paper covers the complete design procedure for manifold multiplexers, starting from the required specifications and finishing with the physical dimensions. After explaining the general design technique for multiplexers with channel filters based on transmission-line resonators, the method is specialized for the design of classic multiplexers with circular-waveguide dual-mode filters. As a further application example, the same methodology is also used for the design of a nonconventional tuningless wideband multiplexer with a new type of rectangular waveguide filters. This paper is concluded with a comparison between simulation and measurements for the wideband multiplexer. Excellent agreement between measurements and simulations are demonstrated, thereby validating the complete design procedure. [ABSTRACT FROM AUTHOR]

A microwave Doherty power amplifier (DPA) consists of a carrier amplifier (CA), a peaking amplifier (PA), and an impedance inverting network. In this paper, a novel DPA topology with neither the impedance inverting network nor offset lines is proposed. This topology enables the enhancement of amplifier bandwidth and achieves a more compact amplifier size. To remove the impedance inverting network and to realize high efficiency at large back-off power level, the output-matching network of the CA is designed to realize high performance both at a low signal power level in the off-state of the PA and at the saturated signal power level. A 1.9-GHz series-connected load Doherty power amplifier without an impedance inverting network is designed and fabricated using GaN HEMTs. The amplifier achieves a power-added efficiency (PAE) of 50% under a 6-dB output back-off from a 34-dBm saturated output power with a PAE of 59%. A maximum PAE higher than 44% is obtained over a frequency range of 1.63–1.98 GHz. [ABSTRACT FROM AUTHOR]

This paper presents a new method to track the optimal efficiency of a magnetic resonance (MR)-wireless power transfer (WPT) system for biomedical capsule endoscopy. Recently, capsule endoscopy technology has been developed and emerged as an alternative to small bowel endoscopy, gastroscopy, and colonoscopy, all of which cause discomfort to patients because of their relatively large-diameter and flexible cables. However, commercialized capsule endoscopy still suffers from limited battery capacity. This paper presents a theory for tracking the optimal efficiency of an MR-WPT system, along with its experimental verification. An MR-WPT system with a 9-mm-diameter receiver is implemented, which is small enough to fit in the current capsule endoscope. The proposed system improves the efficiency despite variations in the distance, angle, and axial misalignment, with maximum increases of 2.45, 4.69, and 1.48 dB, respectively. Penetrative transfer through biological tissue is demonstrated with a low degradation in efficiency of 0.390 dB. The proposed system was found to have a very low specific absorption rate of 1.74 W/kg, which demonstrated that it is safe to use in the human body. [ABSTRACT FROM PUBLISHER]

This paper presents two different types of high-power gallium–nitride (GaN) phase shifters designed for X-band (8–12 GHz), but offering good performance over a much wider band. The first is a 22.5^\circ switched-filter phase shifter, which has much wider bandwidth than is typically found with this configuration, while maintaining low insertion loss (<2 dB), good return loss (>11.15 dB), and an amplitude imbalance of less than 1.03 dB across X-band. The 1-dB compression point was higher than laboratory equipment was able to measure (>38 dBm) and the phase shifter monolithic microwave integrated circuit exhibited an input-referred third-order intercept point (IIP3) of 46.2 dBm. The second phase shifter is a novel design, which promises wide bandwidth (in our case, limited by the single-pole double-throw switch we have also designed), but which achieves decent insertion loss (5 dB), good return loss (better than 11 dB), and very low phase variation (1^\circ) across X-band, also with 22.5^\circ phase shift. It offers a 1-dB compression point of 30.1 dBm and an IIP3 of 46.3 dBm. The components for a 45^\circ differential phase shift using the same structure were also fabricated and verified with measurements. The high-power phase shifters have been fabricated in a 0.5-\mu\ m GaN HEMT process and were designed using an accurate customized switch field-effect transistor model. [ABSTRACT FROM PUBLISHER]

High-order compensation provides more design freedom for inductive power transfer systems and can help improve output voltage/current controllability. This paper develops a simplified decomposition and synthesis method for high-order-compensated inductive power transfer systems. It can achieve load-independent (LI) output under coupling variation, and easily fulfill the various charging requirements, such as constant voltage or constant current. The coupling independent resonance is ensured by using the induced source model, and the whole resonant tank is effectively decomposed as three parts. The power transfer characteristics are discussed for each part, and the requirements for LI output and zero phase angle (ZPA) operation are combined to generate the compensation candidates for both sides. Two families of topologies are synthesized for four kinds of conversions, i.e., voltage to voltage, voltage to current, current to voltage, and current to current. Meanwhile, the proposed method dramatically simplifies the evaluation for the influence of the coil equivalent series resistors on the transfer function and efficiency. These resistor-caused effects are quite different for two families of topologies. Finally, a 6.78-MHz system with 10-W output is designed to verify the difference between two-family topologies. [ABSTRACT FROM AUTHOR]

This paper is devoted to theoretical and practical issues concerning computer-aided tuning (CAT) of coupled-resonator diplexers with tapped wire T-junction. Special attentions are paid to the following aspects: 1) finding an appropriate circuit model to represent the tapped wire T-junction; 2) developing a legitimate transformation strategy to obtain the coupling matrix of the right form corresponding to the topology of the diplexer containing a tapped wire T-junction; and 3) proposing an adaptive CAT scheme that takes stray couplings into account in a dynamically optimized target coupling matrix. A conventional combline diplexer and a helical resonator diplexer are used as examples to demonstrate the circuit model extraction procedure and the adaptive CAT concept, showing the effectiveness and robustness of the proposed adaptive CAT method for practical applications. [ABSTRACT FROM PUBLISHER]

Multimode transceivers for the next generation of wireless devices require new and innovative frequency-agile microwave circuit designs to reduce their complexity, size, and cost. Intrinsically switchable frequency reconfigurable thin-film bulk acoustic resonators (FBARs) and filters that utilize these resonators are presented here for the very first time. Barium strontium titanate (BST) is a ferroelectric material that exhibits electric-field-induced piezoelectricity, which allows for the design of voltage controlled bulk acoustic wave devices. In this paper, a frequency reconfigurable resonator consisting of two series connected BST-based FBARs and a reconfigurable dual-band filter consisting of two 1.5 stage ladder-type bandpass filters are discussed. Their small size, simple design, and zero static power consumption make multifunctional ferroelectric thin-film devices attractive for use in adaptive and reconfigurable radios. [ABSTRACT FROM AUTHOR]

This paper first presents two types of wideband microstrip-to-microstrip equal ripple vertical transitions designed with the uniform and folded slotline structures, respectively. By solving the characteristic function with differential calculation, the condition for realizing the constant equal ripple frequency response but different bandwidths (BWs) for the proposed transition is determined with resorting to the characteristic impedances of the coupled open-circuited microstrip line and slotline. Then, a vertical transition with the uniform slotline is synthetically analyzed and designed with Chebyshev polynomial function and another similar vertical transition with the same in-band ripple level but different BWs is also comparatively presented. By modifying the normalized impedances of the proposed transition to make the theoretical result close to the simulated one with the initial normalized impedances, the transformer turns ratios of the microstrip-to-slotline intersection is exactly calculated by the impedance ratios between two corresponding sets of normalized impedances. Due to the degraded high-frequency performance caused by the radiation loss of the uniform slotline, two vertical transitions with the folded slotline structure are further analyzed and the related turn ratios are extracted with the proposed approach. To verify the effectiveness on the reduction of radiation loss for the folded slotline structure, a six-pole wideband bandpass filter is presented with high-frequency performance greatly improved. In final, wideband vertical transitions with different slotline structures and a six-pole wideband bandpass filter are synthetically designed, simulated, fabricated, and measured. [ABSTRACT FROM AUTHOR]

This paper describes the voltage doubler (VD) behavior of a 2.45-GHz VD-type rectenna. An important feature of the developed VD-type rectenna is the absence of the charge pump capacitor that is present in conventional VDs. Based on the circuit simulation and measurement results, the developed VD-type rectenna shows drastic improvement to the radio frequency-to-direct current (RF–dc) conversion efficiency in comparison with a half-wave rectifier (HWR)-type rectenna at output loads exceeding $100~\Omega $ . From the simulation, both the VD- and HWR-type rectennas show VD behavior, even without the charge pump capacitor. This behavior was found to be attributable to the electric charge stored in the junction and package capacitances of the Schottky barrier diode in the rectennas. Additionally, it was found that the improvement of the RF–dc conversion efficiency is caused by the voltage conservation in the series diode. This improvement is dependent on the microwave period and the electric discharge time constant. When the microwave period is comparable with the electric discharge time constant, the VD-type rectenna conserves a dc voltage even when the input microwave voltage is negative. These phenomena were observed by analyzing the voltage and current waveforms of the rectenna equivalent circuit obtained via circuit simulation. [ABSTRACT FROM AUTHOR]

Knowledge-based neural network modeling techniques using space-mapping concept have been demonstrated in the existing literature as efficient methods to overcome the accuracy limitations of empirical/equivalent circuit models when matching new electromagnetic data. For different modeling problems, the mapping structures can be different. In this paper, we propose a unified automated model generation algorithm that uses \boldsymbol l\mathbf {1} optimization to automatically determine the type and the topology of the mapping structure in a knowledge-based neural network model. By encompassing various types of mappings of the knowledge-based neural network model in the existing literature, we present a new unified model structure and derive new sensitivity formulas for the training of the unified model. The proposed \boldsymbol l\mathbf {1} formulation of modeling can force some weights of the mapping neural networks to zeros while leaving other weights as nonzeros. We utilize this feature to allow \boldsymbol l\mathbf {1} optimization to automatically determine which mapping is necessary and which mapping is unnecessary. Using the proposed \boldsymbol l\mathbf {1} optimization method, the mapping structure can be determined to address different needs of different modeling problems. The structure of the final knowledge-based model can be flexible combinations of some or all of linear mapping, nonlinear mapping, input mapping, frequency mapping, and output mapping. In this way, the proposed algorithm is more systematic and can further speed up the knowledge-based modeling process than existing knowledge-based modeling algorithms. The proposed method is illustrated by three microwave filter modeling examples. [ABSTRACT FROM PUBLISHER]

In this paper, we present a new dynamic-bias measurement setup and its application to the extraction of a nonlinear model for microwave field-effect transistors. The dynamic-bias technique has been recently proposed and relies on the use of low-frequency (LF) and high-frequency (HF) vector-calibrated measurements acquired, for instance, by means of a large-signal network analyzer. In this paper, we propose a new and alternative technique to perform the dynamic-bias measurements, based on relatively low-cost instrumentation commonly available in microwave laboratories. The new acquisition system is composed of a four-channel vector LF receiver (e.g., an oscilloscope) and a one-channel HF scalar receiver (e.g., a spectrum analyzer), which replace the eight-channel vector receiver. Moreover, the proposed architecture greatly simplifies the measurement setup and the calibration procedure. As a case study, a 0.25- \mu \textm GaN HEMT is considered. Dynamic-bias measurements, carried out by means of the proposed measurement setup, are used for the identification of a nonlinear model of this device. Finally, the model is fully validated through comparison with time-domain harmonic load–pull measurements carried out at 5 GHz. [ABSTRACT FROM PUBLISHER]

This paper presents a comparison of existing and novel behavioral models targeted at the outphasing power amplifier (PA) architecture. A comprehensive comparison of ten modeling strategies is presented in the results. Novel techniques for outphasing PAs, such as vector switched and dual path time series, are also presented for the first time. Investigation of such techniques was driven by the analysis of outphasing operation at minimum output powers, demonstrating the generation of frequency-dependent amplitude and phase deviations, which can be difficult to characterize. The increased robustness was achieved at the cost of additional complexity; for practical implementation, time series coefficient reduction techniques were also evaluated. The results of all modeling approaches are experimentally validated for the wideband operation of an NXP 19-W GaN digital outphasing amplifier module. Considering computational complexity and accuracy for system-level modeling across all presented options, a subset of existing and new models is identified as best suited for modeling outphasing PAs. [ABSTRACT FROM PUBLISHER]

In this paper, an approach to 1-to- 2^n ( n = 2, 3, 4,\ldots ) way microstrip balanced power divider is proposed for the first time. This approach is realized by one balanced-to-single-ended power divider, 2^{n-1} single-ended-to-balanced power dividers, and 2^{n-1}-2 single-ended power dividers. The function of differential-mode power dividing and common-mode suppression can be ensured by the balanced-to-single-ended and single-ended-to-balanced power dividers. The advantage of this approach is that it can reduce the circuit size effectively when comparing with the approach using all the balanced-to-balanced power dividers. The analysis of the balanced-to-single-ended power divider and the single-ended-to-balanced power divider is realized by combining the standard S -parameters, the mixed-mode S -parameters, and the odd- and even-mode equivalent circuits. To verify the theoretical prediction, three prototypes (one balanced-to-single-ended power divider, one single-ended-to-balanced power divider, and one 1-to-4 way balanced power divider) are fabricated and measured. The fabricated 1-to-4 way balanced power divider with the size of shows an insertion loss of 0.45 dB at 1.8 GHz, a fractional bandwidth for a 15-dB return loss of 29%, a 20-dB common-mode suppression of 74.6%, and a 20-dB differential-mode isolation ( \vert S\mathrm{ dd32}\vert and \vert S\mathrm{ dd42}\vert ) of 15.1% and 100%, respectively. [ABSTRACT FROM AUTHOR]