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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 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]

This paper presents an in-depth, systematic study of the impact of input and output harmonics in the design of high-efficiency power amplifiers (PAs). The study evaluates the performance of harmonically tuned amplifiers, tackling concurrently both input and output harmonics. The proposed theory starts with deriving an altered input voltage waveform under the impact of input nonlinearity. Intrinsic drain voltage and drain current components are formulated as a function of the conduction angle $\alpha $ considering both source and load terminations. Output power and drain efficiency are then computed as a function of input nonlinearity, $\alpha $ , and output loading conditions. The derived formulations allow to investigate the design sensitivity to input nonlinearity and its impact on fundamental design space. The impact of source harmonics is evaluated using harmonic source pull under different output loading conditions. Thereafter, PA design and implementation has been carried out using NXP 1.95 mm die to confirm the distinctive behavior of class GF and GF−1 amplifiers with respect to the input harmonic terminations. For practical validation, four different design cases with different second harmonic source impedances are investigated. At 2.6 GHz, drain efficiencies ranging between 76% and 83% were exhibited depending on the source and load harmonic tuning for each design case. Measurement results confirm the theoretical findings reported in this paper. [ABSTRACT FROM PUBLISHER]

In this paper, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the noninfinity output impedances of peaking stage. Specifically, the carrier PA of the designed DPA operates in a continuous class-J mode when the peaking PA is in the OFF-state, where the output impedance of the peaking PA has some influences on the carrier PA. When the peaking transistor is in the OFF-state, the load impedance variation of the carrier transistor versus noninfinity peaking impedance is presented in this contribution. The proposed method surmounts the back-off drain efficiency deterioration of DPAs at two side working bands through elaborately processing the noninfinity peaking impedance. This paper also presents a method to derive the required OFF-state output impedance of the peaking stage by the carrier PA in a symmetrical broadband DPA. A broadband CM-DPA working over 1.6–2.7 GHz (bandwidth of 51%) is designed and fabricated for interpreting our theories. The simulated load trajectory of the carrier transistor is in line with the design space of continuous class-J mode. Under continuous wave excitation, experimental results show the drain efficiencies of 46.5%–63.5% at 6-dB output back-off power levels and 56%–75.3% at peaking power levels. The maximum output power of this DPA is 43.8–45.2 dBm with a gain of 9.4–11.5 dB across the whole working band. Furthermore, a 20-MHz LTE modulated signal with a peak-to-average power ratio of 7.4 dB is also applied to the fabricated CM-DPA at 2.2 GHz. At an average output power of 37.5 dBm, measurement results show the adjacent channel power ratios of −30.2 and −50.1 dBc before and after digital predistortion, respectively. [ABSTRACT FROM PUBLISHER]

This paper presents a broadband poly-harmonic behavioral model for microwave mixers operating in the linear regime. It is extracted from large-signal vector measurements and predicts the response with respect to an arbitrary local oscillator (LO) phase. The model is capable of estimating the performance of the converted signals and the main mixing products for an intermediate frequency that spans within an a priori defined bandwidth. This paper gives a detailed model analytical treatment along with a discussion of its properties and the description of the characterization method. The model validation is achieved by the characterization of a subharmonic mixer implemented in the hybrid technology that operates with a 2.229-GHz LO, an intermediate frequency bandwidth of 732–754 MHz, and a corresponding radio frequency bandwidth of 5.191–5.211 GHz. Independent experimental validation is achieved by an image rejection mixer composed of two nominally identical mixers, individually characterized by the proposed technique. Validation is concluded with experimental data, demonstrating the model’s capability to deal with a phase-modulated LO signal. [ABSTRACT FROM PUBLISHER]

This paper presents a mechanically assisted microwave drill (MWD) capable of drilling 26-cm-deep 12-mm-diameter holes in concrete. This record significantly extends the inherent $\lambda $ /4-depth capability (~1.5 cm at 2.45 GHz) of the basic MWD scheme. Compared with conventional mechanical drills, this MWD is characterized by a relatively silent and vibration-free operation, but its drilling speed is yet slower than 1 cm/min. This paper reviews the fundamental MWD mechanism (utilizing localized microwave heating and thermal-runaway instability), and extends it for deeper holes by also using the coaxial applicator as a slowly rotating hollow reamer to remove the debris. The MWD prototype is introduced, including its adaptive impedance matching and remote-operation features, and its experimental results are presented. Theoretical and practical MWD aspects are discussed, and potential developments are indicated (e.g., for faster drilling and iron-rebar cutting). The present MWD performance can be useful for specific applications which critically require silent drilling operations in concrete. [ABSTRACT FROM PUBLISHER]

This paper presents a rotatable cyclic Vernier digital-to-time converter (DTC) with 1.8 ps timing resolution on an 80 ns time scale. The proposed DTC features high timing resolution, and can be utilized in beam-steering arrays, which is infeasible for ordinary Vernier DTCs. The proposed DTC was implemented within a passive time-equivalent direct-sampling ultra-wideband impulse-radio radar system and was fabricated in 65 nm CMOS technology. This radar system is capable of quantizing direct-sampled impulse waveforms to provide full degrees of freedom for backend digital signal processing. The measured differential nonlinearity/integral nonlinearity of the DTC was +4.6/−3 and 12.4/−9.4 where the LSB was 1.8 ps, and the total power consumption was 133 mW. Also, a new method for localization between wireless sensor nodes of equivalent-time direct-sampling radar is presented in this paper; this method can theoretically achieve resolution as high as that of regular radar. [ABSTRACT FROM PUBLISHER]

This paper proposes a new approach for inductive wireless power transfer (IWPT) tag-to-reader communication. A new technique to achieve transmitter/receiver (Tx/Rx) frequency separation is demonstrated. A two-tone Tx is adopted at the reader, and the third-order intermodulation (IM3) frequency generated by the tag rectifier nonlinearity is used as the Rx carrier, which is modulated by a baseband signal sent by the tag. The uplink signal at the IM3 frequency can be picked up by the reader coil. The IWPT impedance matching networks for both the reader and the tag coil can be reused efficiently, since the IM3 frequency at 5.06 GHz is close to the Tx fundamental frequencies at 4.94 and 5 GHz. Due to the Tx/Rx frequency separation, the Tx-to-Rx leakage at the Rx frequency can be suppressed by external filters to improve the Rx signal-to-noise ratio (SNR). The proposed technique is implemented within a 5-GHz IWPT system, and a tiny CMOS tag with a coil size of only 0.01 mm2 is used. This paper also implements conventional direct and intermediate frequency-based backscattering uplinks for comparison, and the proposed IM3 uplink is able to improve the Rx SNR by more than 20 dB. The achieved uplink data rate (100 kb/s) is also higher than the published work (20 kb/s) that adopted the conventional backscattering method. [ABSTRACT FROM AUTHOR]

This paper describes the modeling, analysis, and design of a complete (dc-to-dc) inductive wireless power transfer (WPT) system for industrial moving applications. The system operates at 6.78 MHz and delivers up to 150 W to a load moving along a linear path, providing a quasi-constant dc output voltage and maintaining a zero voltage switching operation, regardless of position and load, without any retuning or feedback. The inductive link consists of an array of stationary transmitting coils and a moving receiving coil whose length is optimized to achieve a constant coupling coefficient along the path. Each Tx coil is individually driven by a constant amplitude and phase sinusoidal current that is generated from a GaN-based coupled load-independent Class EF inverter. Two adjacent transmitters are activated at a given time depending on the receiver’s position; this effectively creates a virtual series connection between the two transmitting coils. The Rx coil is connected to a passive Class E rectifier that is designed to maintain a constant dc output voltage independent of its load and position. Extensive experimental results are presented to show the performance over different loading conditions and positions. A peak dc-to-dc efficiency of 80% is achieved at 100 W of dc output power and a dc output voltage variation of less than 5% is measured over a load range from 30 to $500~\Omega $ . The work in this paper is foreseen as a design solution for a high-efficient, maintenance-free, and reliable WPT system for powering sliders and mass movers in industrial automation plants. [ABSTRACT FROM PUBLISHER]

This paper presents several V-band (50–75 GHz) WR-15 and W-band (75–110 GHz) WR-10 waveguide components fabricated using both direct metal laser sintering in aluminum, nickel-chromium, maraging steel (MS), and copper alloys and stereolithography in copper-coated plastic. Printing resolution is analyzed with respect to feature creation. The RF performance and surface roughness are measured, and the loss due to surface roughness quantified. The measured loss for WR-10 at 92.5-GHz ranges from 5.5 dB/m for the copper-plated plastic waveguides to 36.9 dB/m for the nickel alloy and for WR-15 at 62.5-GHz ranges from 11.0 dB/m for the aluminum alloy to 14.4 dB/m for the MS alloy. From a loss budget study, it is found that standard models do not accurately predict loss due to surface roughness for rough surfaces where the height variation is much larger than skin depth $\delta$ . It is also found that for internally complex printing, the MS alloy versions maintain the closest structure to designed components and expected RF performance. This paper presents the current state-of-the-art in available additive-manufactured waveguide components at V- and W-bands. [ABSTRACT FROM PUBLISHER]

Self-tracking receivers have been suggested for satellite and mobile communication applications. In this paper, we propose and demonstrate an array receiver (Rx) architecture based on phase-locked loops. The system is capable of automatically tracking a moving source and providing direction-of-arrival (DOA) estimates calculated from array signal phase differences. After deriving the system transfer functions, we show a digital implementation of the receiver and experimentally prove its phase detection capability. In combination with an eight-element linear array and analog front ends, we build a hybrid receiver and demonstrate its DOA estimation performance in static and dynamic outdoor setups. This paper gives the details about theoretic principles, implementation concept, and realization of the proposed receiver. We demonstrate DOA errors below 4° and show the reproducibility of the results. Using dynamic experiments, we verify the tracking ability of the system, which makes it applicable to retrodirective antennas. [ABSTRACT FROM PUBLISHER]

A high data capacity chipless radio frequency identification (chipless-RFID) system, useful for security and authentication applications, is presented in this paper. Reading is based on the near-field coupling between the tag, a chain of identical split-ring resonators (SRRs) printed on a (typically flexible) dielectric substrate (e.g., liquid crystal polymer, plastic, and paper), and the reader. Encoding is achieved by the presence or absence of SRRs at predefined (equidistant) positions in the chain, and tag identification (ID) is based on sequential bit reading. Namely, the tag must be longitudinally displaced, at short distance, over the reader, a microstrip line loaded with an SRR and fed by a harmonic signal. By this means, the harmonic signal is amplitude modulated, and the (ID) code is contained in the envelope function, which can be obtained by means of an envelope detector. With this system, tag reading requires proximity with the reader, but this is not an issue in many applications within the domain of security and authentication (e.g., secure paper for corporate documents and certificates). Several circularly shaped 40-bit encoders (implemented in a commercial microwave substrate), and the corresponding reader, are designed and fabricated as proof-of-concept demonstrators. Strategies for programming the tags and a first proof-of-concept chipless-RFID tag fabricated on plastic substrate through inkjet printing are included in this paper. [ABSTRACT FROM PUBLISHER]

This paper presents an octave-bandwidth load modulated balanced amplifier (LMBA) that operates directly on a single modulated RF input. The architecture is based on the recently proposed LMBA technique, in which a control signal applied at the output isolation port of a balanced amplifier is used to modulate the apparent load impedance of the two devices comprising the balanced amplifier. In our approach, the injected control signal is used both as an active match and to dynamically load modulate the main devices to provide efficiency enhancement at back-off, thus extending the dynamic range compared to the original LMBA formulation. In this paper, we introduce a phase-compensation technique through which the active matching and load modulation tracks the frequency-dependent optimal loading trajectory of a packaged device. The result is a load-modulation power amplifier architecture able to perform an active, modulated match over an octave bandwidth. The technique is demonstrated over 1.8–3.8 GHz using packaged devices and an off-the-shelf hybrid coupler. The proof-of-concept octave RF-input LMBA has a peak CW output power of 44 dBm, with power added efficiency (PAE) over the 1.8–3.8 GHz operating frequency range of 37%–59% at peak power and 29%–45% at 6-dB output backoff. The RF-input nature of this architecture enables straightforward measurement with modulated signals; a W-CDMA signal at 3.8 GHz with 9-dB (measured) peak to average power ratio is demonstrated with adjacent channel leakage ratio of −30 dBc and average PAE of 18% for a 31-dBm average output power (2-dB backoff). [ABSTRACT FROM PUBLISHER]

The demand on mobile electronics to continue to shrink in size while increasing in efficiency drives the demand on the internal passive components to do the same. Power amplifiers require inductors with small form factors, high quality factors ( Q\texts ), and high operating frequency in the single-digit gigahertz range. This paper explores the use of magnetic materials to satisfy the demands of power amplifier inductor applications. This paper then discusses the optimization choices regarding material selection, device design, and fabrication methodology. The inductors achieved here present the best performance to date for an integrated magnetic core inductor at high frequencies with a 1-nH inductance and peak $Q$ value of four at about 3 GHz. Such compact inductors show potential for efficiently meeting the need of mobile electronics in the future. [ABSTRACT FROM AUTHOR]

Novel 2-D gray-scale inkjet printed microstrip line (MSL) terminations are presented in this paper. The proposed open-end type MSL termination is constructed of a lossy trace printed on paper and placed on a typical dielectric substrate with background. Optimal design guidelines are also discussed for attaining best absorption band given ink resistivity and termination size. Both fixed width and tapered width lines are presented, experimentally showing high absorption levels over a wide bandwidth. These simple to fabricate structures may find applications in scenarios where low-cost wideband planar terminations are needed. [ABSTRACT FROM AUTHOR]

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]

This paper proposes a novel design approach for a filtering antenna, which contains an array of 4 by 2 waveguide aperture radiation elements. Coupling matrix theory is introduced in this paper to synthesize the multiple coupled-resonators circuit. Unequal amplitude excitation is applied to the 4 \times 2 elements so as to obtain a low sidelobe level. To demonstrate the concept, an X-band antenna array is designed and fabricated using a three-layer waveguide structure. Measured results show that the filtering antenna array can achieve a gain of more than 15.58 dBi and a radiation efficiency of higher than 90% over the passband (9.91–10.1 GHz). The sidelobe level is −18.3 dB in the {H} -plane and −21.1 dB in the {E}$ -plane. [ABSTRACT FROM AUTHOR]

This paper addresses the estimation and compensation of I/Q imbalance, one of the most prominent impairments found in wideband zero-intermediate frequency transceivers (TRxs). The I/Q imbalance encountered in this kind of TRx comprises not only frequency-selective gain and phase imbalance but also delay imbalance. Unless appropriate compensation is applied, the I/Q imbalance significantly degrades the performance of a communication system. This paper presents a novel compensation technique for transmitter I/Q imbalance based on built-in-self-calibration, a low cost and robust compensation technique that enables manufacturing as well as in-field calibration with low computational complexity. The method's performance is evaluated in a TRx with 64-quadratic-amplitude modulation and 2 GHz of bandwidth implemented with real hardware. The measurements show that the proposed technique achieves an image rejection ratio greater than 35 dB in the entire 2 GHz bandwidth and an error vector magnitude lower than 3%. [ABSTRACT FROM AUTHOR]

This paper addresses the estimation and compensation of I/Q imbalance, one of the most prominent impairments found in wideband zero-intermediate frequency transceivers (TRxs). The I/Q imbalance encountered in this kind of TRx comprises not only frequency-selective gain and phase imbalance but also delay imbalance. Unless appropriate compensation is applied, the I/Q imbalance significantly degrades the performance of a communication system. This paper presents a novel compensation technique for transmitter I/Q imbalance based on built-in-self-calibration, a low cost and robust compensation technique that enables manufacturing as well as in-field calibration with low computational complexity. The method’s performance is evaluated in a TRx with 64-quadratic-amplitude modulation and 2 GHz of bandwidth implemented with real hardware. The measurements show that the proposed technique achieves an image rejection ratio greater than 35 dB in the entire 2 GHz bandwidth and an error vector magnitude lower than 3%. [ABSTRACT FROM PUBLISHER]

Free-electron lasers are used to generate laser radiation using an accelerated electron beam. In this paper, an electrostatic accelerator was used with a thermionic cathode. Lasing pulses of the order of tens of microseconds were generated by passing the current pulses through a wiggler and resonator combination. The change in lasing power as a result of postsaturation variation of the energy of the electron beam during the lasing period is presented in this paper in the form of experimental measurements and simulations. In the experiments, the initial electron beam energy was ~1.4 MeV and the current was 1.13 A, whilst the lasing frequency was always close to 102 GHz. It is shown that postsaturation, positively ramping the beam energy increases the radiation extraction efficiency by around 50%. Whilst a falling beam energy results in a reduction in extraction efficiency. [ABSTRACT FROM PUBLISHER]

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 presents a digital beamforming (DBF) synthetic aperture radar (SAR) for future spaceborne earth observation systems. The objective of the DBF-SAR system is to achieve a low cost, lightweight, low-power consumption, and dual-band (X/Ka) dual-polarized module for the next-generation spaceborne SAR system in Europe. The architectures and modules of the proposed DBF-SAR system are designed according to a realistic mission scenario, which is compatible with the future small/microsatellites platforms. This system fills an important gap in the conception of the future DBF-SAR, facilitating a high level of integration and complexity reduction. The proposed system is considered not only the first demonstrator of a receive-only spaceborne DBF system, but also the first X/Ka-band dual-polarized SAR system with shared aperture. This paper presents a description of the proposed instrument hardware and first experimental validations. The concept and design of the DBF multistatic SAR system are discussed and presented first, followed by the design of subsystems such as DBF networks, microwave integrated circuit, and antennas. Simulated and measured results of the subsystems are presented, demonstrating that the proposed SAR instrument architecture is well-suited for the future SAR applications. [ABSTRACT FROM PUBLISHER]

This paper presents the first wirelessly synchronized multichip array (WSMA) in 65-nm CMOS. The proposed architecture makes use of a central wireless signal to synchronize an mm-wave array, eliminating the need for connecting wires between the array elements. Wireless injection locking of a single chip is successfully demonstrated, and a 3-dB linewidth of 400 Hz at a carrier frequency of 50 GHz is achieved (stability ratio of 8 ppb). In addition, a two-element WSMA with an array aperture greater than 20 wavelengths is demonstrated using the proposed transceiver architecture. The reported transceiver includes a receiving on-chip antenna, a low-noise amplifier, an injection-locked voltage-controlled oscillator, a buffer amplifier, an in-phase/quadrature generator, a phase shifter, a power amplifier, and a transmitting on-chip antenna. The chip is fabricated in a 65-nm CMOS process and occupies an area of 1.7 mm $\times 3.8$ mm. This paper sets the foundation for increasing the array aperture through wireless injection locking, extending traditional array systems into the high-resolution, narrow-beamwidth regime. [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]

This paper reports on the analysis of a radio frequency microelectromechanical systems (RF-MEMS) tuned cavity oscillator on $X$ -band based on a GaN-HEMT monolithic microwave integrated circuit reflection amplifier. The RF-MEMS-switches are mounted on a low-loss printed circuit board (PCB) intruded in an aluminum cavity that is coupled to a microstrip line connected to the reflection amplifier. This paper investigates the influence of the number of switches as well as their positions with respect to phase noise and tuning range. Vertical and horizontal positions of the switches are varied with target on optimum trade-off between phase noise and total tuning range. For a three-row MEMS-configuration at 1-mm depth from the end cavity wall, a tuning range of 4.9% is measured. The center frequencies are ranging from 9.84 to 10.33 GHz with measured phase noise of −140 to −129 dBc/Hz at 100-kHz offset. A similar three-row MEMS setup at 2.5-mm depth provides a tuning range of 12.3% with measured phase noise of −133 to −123 dBc/Hz at 100-kHz offset. [ABSTRACT FROM AUTHOR]

Microdispensing of thick-film conductive paste has been demonstrated as a viable approach for manufacturing microwave planar transmission lines. However, the performance and upper frequency range of these lines is limited by the cross-sectional shape and electrical conductivity of the printed paste, as well as the achievable minimum feature size which is typically around 100~\mu \textm . In this paper, a picosecond Nd:YAG laser is used to machine slots in a 20–25- \mu \textm -thick layer of silver paste (Dupont CB028) that is microdispensed on a Rogers RT5870 substrate, producing coplanar waveguide (CPW) transmission lines with 16– 20~\mu \textm -wide slots. It is shown that the laser solidifies an about 2- \mu \textm -wide region of the edges of the slots, thus significantly increasing the effective conductivity of the film and improving the attenuation constant of the lines. The extracted attenuation constant at 20 GHz for laser machined CB028 is 0.74 dB/cm. CPW resonators and filters show that the effective conductivity is in the range from 10 to 30 MS/m, which represents a $100\times $ improvement when compared to the values obtained with the exclusive use of microdispensing. This paper demonstrates that a hybrid approach of additive manufacturing and laser machining enables the fabrication of higher frequency circuits (up to at least 40 GHz) with improved performance. [ABSTRACT FROM AUTHOR]

In this paper, a radar demonstrator system with real-time capability operating at W -band is presented. It operates at 90–100 GHz and provides 3-D information about the illuminated scene. The system uses frequency modulated continuous wave signals to extract range information whereupon long-range applications are aimed at. It consists of a sparse array of 22 transmitting and 22 receiving antennas and makes use of the multiple input multiple output (MIMO) principle. A back-propagation algorithm provides cross-range information. With the help of simulations and a simulated annealing algorithm, the geometry of the sparse array is optimized to meet application requirements using the available hardware. In this paper, the demonstrator system is described and the imaging theory is shortly reviewed. Measurements are presented to verify simulation results as well as 3-D imaging and long-range capability. [ABSTRACT FROM AUTHOR]

This paper proposes a linear and efficient transmitter prototype based on pulsed load modulation (PLM) power amplifier (PA). The proposed transmitter setup utilizes the complex delta–sigma (DS) modulation as a signal processing technique instead of the envelope DS modulation for higher linearity performance. Using the complex DS modulation technique reduces the in-band quantization noise significantly at the output of the modulator and consequently, enhances the linearity of the transmitter. To validate the proposed technique, the linearity and efficiency performance of the complex DS modulator (CDSM)-based transmitter are compared with the performance of its envelope DS modulator (EDSM) counterpart in measurement. For this paper, an efficient and linear PLM PA is designed and fabricated using GaAs E-pHEMT transistors. For a Long-Term Evolution (LTE) uplink standard signal with 3-MHz bandwidth and 7-dB peak-to-average power ratio, the CDSM-based transmitter achieves the drain efficiency and power added efficiency of 46% and 42%, respectively, at an average output power of 25.1 dBm. The comparison measurement study of EDSM-based transmitter and the CDSM-based transmitter with the LTE uplink signal shows about 11-dB improvement in the signal-to-noise and distortion ratio of the output signal. The measurement results for LTE signals were able to pass the spectral requirements defined by the standard without applying predistortion techniques. [ABSTRACT FROM AUTHOR]

This paper considers a method for accelerating finite-element simulations of electromagnetic problems on a workstation using graphics processing units (GPUs). The focus is on finite-element formulations using higher order elements and tetrahedral meshes that lead to sparse matrices too large to be dealt with on a typical workstation using direct methods. We discuss the problem of rapid matrix generation and assembly, as well as accelerating preconditioned iterative solvers in the context of limited on-board GPU memory, and we show how to mitigate some of these problems using multiple GPUs. We propose a new fast data-distribution technique for multi-GPU platforms that allows optimal splitting of finite-element method (FEM) matrices between graphics accelerators. The technique draws upon the graph partitioning approach used in nonoverlapping domain-decomposition methods and provides information that drives the FEM matrix-generation and assembly process in such a way that it produces data structures for each GPU; this not only ensures load balancing and minimizes communication between GPUs, but also reflects the hierarchy of the basis functions. The concepts proposed in this paper are illustrated with examples involving sparse matrices of up to 13.9 million rows and over a billion nonzero elements. [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]

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]

The effect of the output impedance of peaking power amplifier (PA) on Doherty PAs (DPAs) is analyzed in this paper. In the design procedure of DPAs, the ideal case is that the output impedance of auxiliary PA is infinite at output power back-off (OPBO) level. However, it is almost impossible to realize this perfect condition in broadband DPAs. Therefore, when the output impedance of peaking path deviates from infinity, some potential effects on DPAs must be produced. In this paper, these effects are explained at the internal plane of transistors. The conclusion is that, at different normalized frequencies, there are different optimal impedance regions for the output impedance of peaking stage. This means that the noninfinite output impedances of peaking stage can enhance the performances of broadband DPAs so long as they are elaborately processed. A 1.65–2.7-GHz (48% bandwidth) broadband DPA is designed considering the effects of peaking PA. The experimental results show that this DPA obtains a drain efficiency of 41%–59.6% at 6-dB OPBO levels and a drain efficiency of 55.8%–72.2% at saturation power levels. The maximum output power across the entire operating band is 43.1–45.2 dBm with a gain of 9.0–10.2 dB. Furthermore, the designed DPA achieves an adjacent channel leakage ratio of −45.8 dBc with an output power of 36.1 dBm at 2.0 GHz after digital predistortion when it is excited by 5-MHz WCDMA signal with a peaking-to-average power ratio of 8.6 dB. [ABSTRACT FROM PUBLISHER]

A miniaturized millimeter-wave substrate integrated waveguide (SIW) in IBM 130-nm digital CMOS process is presented in this paper. The footprint of the interconnect is reduced compared with previous works using the folding technique. A current-loop transition structure is proposed in this paper that is built inside the SIW interconnect and excites its TE10 mode with minimal area overhead. A simulation-based comparison of T-FSIW and other planar transmission line structures reveals that the T-FSIW interconnect shows a much higher resonant quality factor. A prototype waveguide is designed and fabricated to operate with a cutoff frequency of 175 GHz. Furthermore, the current-loop excitation is optimized for the frequency range of 180–220 GHz. Simulation and experimental data are used to confirm the proposed interconnect approach. [ABSTRACT FROM PUBLISHER]

This paper presents a rigorous scattering model of an infinite slit on a dielectric-loaded parallel-plate waveguide with an oblique incident TEM wave. The dyadic Green’s functions of an equivalent line source are derived first and then applied to solve the scattered fields in terms of reflection, transmission, and radiation. Special treatment with PEC/PMC symmetry is employed for fast and accurate calculation. The proposed model was carefully validated by the full-wave simulator with excellent agreement. Some interesting scattering phenomena are found and emphasized, as they are crucial in explaining the special features of slit-based planar structures. In this paper, we demonstrate the presented model for the analysis and physical explanation of unique features found in a slitted substrate integrated waveguide, grounded coplanar waveguide, and grounded coplanar stripline. The proposed model provides a simple and effective approach for the design of potential slit-based planar circuits and antennas based on the presented structures in this paper. [ABSTRACT FROM PUBLISHER]

Spectral signature barcodes functional at the $S$ frequency band are presented in this paper. The barcodes are implemented by loading a coplanar waveguide transmission line by means of multiple S-shaped split ring resonators (S-SRRs), each one tuned to a different frequency. The main particularity of this paper is the fact that more than two logic states (i.e., three or four, depending on the implementation) are assigned to each resonant element. By this means, the total number of bits of the barcode (for a given number of resonators) is increased, as compared with previous approaches based on two logic states per resonator. This multistate functionality is achieved by rotating the S-SRRs. Such rotation modulates the line-to-resonator coupling intensity, and consequently the notch depth at the S-SRR fundamental resonance. Therefore, by considering three or four fixed rotation angles (or orientations) between the line axis and the S-SRR (for the tri- and four-state multiresonator barcodes, respectively), intermediate levels between the maximum and minimum attenuation are achieved. This multistate strategy only exploits a single frequency per resonant element (the fundamental one). Therefore, the data capacity per bandwidth are improved as compared with two-state-based barcodes or to multistate barcodes that use two frequencies per resonant element. As illustrative examples, two different four-state multiresonator barcodes with eight S-SRRs (providing 4^{8}= 65.536 different codes, or 16 bits) and with nine S-SRRs (equivalent to 18 bits), occupying a spectral bandwidth of 1 GHz and less than 6.75 and 8.2 cm2, respectively, are designed, fabricated, and characterized. [ABSTRACT FROM AUTHOR]

In this paper, the resonant cavity problem with anisotropic fully conducting media, complex geometrical structure and perfect electric conductor walls is investigated. We solve this problem based on the finite element method (FEM) with tangential and linear normal (CT/LN) element and standard linear element. An effective numerical method is proposed by us such that it is free of nonphysical modes. After the FEM discretization, we need to solve a quadratic algebraic eigenvalue problem with a linear constraint condition. In order to overcome this difficulty in the field of numerical algebra, we change this algebraic eigenvalue problem into a generalized eigenvalue problem by introducing an auxiliary zero eigenvector. Moreover, when the permittivity and conductivity are two constants, both the eigenmodes of infinite algebraic multiplicity and all the nonphysical modes are also removed by linearization method. Several numerical experiments show that computational method in this paper can suppress all the spurious modes. [ABSTRACT FROM PUBLISHER]

The article lists several members of the periodical who reviewed papers during 2011 including F. Ellinger, A. Kucharski, and D. Blackham.

The article calls for papers related to microwave theory for the periodical.

With the integrated radar technology being increasingly common in the automotive segment, it becomes even more cost-effective in other applications as well. Taking into account its price and robustness, radar sensors can be considered as a potential replacement for laser interferometry which is being widely used for accurate contactless sensing. In this paper we describe a phase evaluation algorithm for highly accurate distance measurements using linear frequency modulated continuous wave (FMCW) radar systems, considering hardware dependent effects i.e. frequency responses of the signal paths. In several investigations we show that this novel algorithm is significantly more robust against disturbing radar targets or micro vibrations than typical techniques. Distance measurements were carried out using an 80 GHz wideband FMCW radar sensor on a maximum measurement range of 5.2 m with a movable radar target. For free space measurements the unambiguous measurement accuracy was improved to $\pm 4.5~\mu \text{m}$ , using phase evaluation techniques in a non-ideal environment over the entire measurement range, which was previously around $\pm 120~\mu \text{m}$ with frequency evaluation techniques. Due to its robustness and accuracy, the proposed algorithm is well suited for harsh industrial environments such as real time positioning of machine tools. [ABSTRACT FROM AUTHOR]

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 proposes a single-input single-output (SISO) digital predistortion (DPD) model for linearizing millimeter-wave (mm-wave) RF beamforming arrays. It starts with a dual-input power amplifier (PA) model that accounts for steering angle-dependent load modulation effects. This dual-input model is then transformed into a SISO model under the assumption of weak PA nonlinearity and RF beamforming architecture. The underlying coefficients of the SISO array model incorporate the beamforming weights, antenna cross-coupling, channel coefficients, and any possible phase-shifter gain variation with phase shift setting. An over-the-air (OTA) measurement setup is finally developed to validate the capacity of a SISO DPD model to linearize two different arrays-under-test with 4 and 64 elements and radiating mm-wave modulated signals with 320- and 800-MHz bandwidth. Although, in principle, the DPD coefficients should be retrained for each steering angle, experimental results have shown that the same set of coefficients can be used over a wide range of steering angles, and only a few sets of trained DPD coefficients are sufficient to minimize the distortion in a mm-wave RF beamforming array across a 120° steering range. [ABSTRACT FROM AUTHOR]

Millimeter-wave imaging systems are increasingly used in human screening at checkpoints, in linear or multi-input multi-output (MIMO) array modes. Rather than pressing intrinsic system requirements to improve image quality, it seems more economical to appeal to some specific approaches, for example, super-resolution (SR) techniques. In this paper, as a variation of SR, coherence factor (CF) is incorporated in the framework of the range migration algorithm (RMA), termed CF-RMA for short. As a critical part of CF, the double integral in the wavenumber domain is approximated by a single integral in the sense of the point-matching method, resulting in a particular formulation to carry on another independent RMA program. Being computationally efficient, the proposed method is shown to be effective in suppressing sidelobes and background noise. The resolution (as gauged by the width of the main lobe of the point spread function) is enhanced as well. A structural similarity (SSIM) index is employed to quantify the image quality enhancement with respect to state-of-the-art SR approaches. In terms of computation load, the new approach is shown to be much more efficient than state-of-the-art SR approaches. [ABSTRACT FROM AUTHOR]

In this paper, a fully integrated silicon-germanium (SiGe)-based compact high-resolution frequency-modulated continuous-wave (FMCW) radar sensor working in a frequency range from 198 to 250 GHz is presented. The wide modulation bandwidth of 52 GHz enables a range resolution better than 3 mm combined with a measurement accuracy in the micrometer regime. Together with a low power consumption of approximately 3.5 W, a high-focusing Teflon lens antenna, and a compact and robust housing, the presented radar system is capable of satisfying the needs of several novel measuring tasks. A compensated measurement accuracy of down to −0.5–0.4 $\mu \text{m}$ is achieved, which is demonstrated by distance measurements using a laser interferometer reference. Additionally, a calibration technique is shown enabling multi-target measurements reaching to the theoretical limit of the range resolution. As the fundamental feedthrough of common frequency doubler architectures cause false targets in the range profile, a dielectric fundamental frequency filter is presented as well, filtering the fundamental feedthrough signal and thus removing the false target, improving the unambiguousness of the presented radar sensor. [ABSTRACT FROM AUTHOR]

In this paper, a 2-D beamforming phased array using a novel 2-D Nolen matrix network is presented. The Nolen matrix is a novel antenna feeding network composed of only couplers with dedicated coupling ratios and phase shifters. It does not require crossover and load termination compared to other networks based on Butler and Blass matrix. To be specific, the closed-form equations are derived first for uniplanar single $3 \times 3$ Nolen matrix, which is composed of three couplers and three phase delay lines. Most importantly, it is found that the proposed Nolen matrix can employ couplers with arbitrary phase differences to achieve relatively flexible progressive phase delays across the radiating elements, presenting a high degree of freedom on circuit topology and beamforming performance. Then, a 2-D antenna feeding network is designed by stacking and cascading six $3 \times 3$ Nolen matrices, and a 2-D patch antenna array is integrated with the proposed feeding network to generate nine radiation beams with unique directions on azimuth and elevation planes, realizing the 2-D beamforming function. To verify the proposed design concept, a prototype of 2-D beamforming phased array operating at 5.8 GHz is designed, fabricated, and measured, and the experimental results agree well with simulation and theoretical analysis. [ABSTRACT FROM AUTHOR]

Digital modulations such as orthogonal frequency-division multiplexing (OFDM) have received increasing interest for radar. However, the required fast analog-to-digital (AD) and digital-to-analog (DA) converters providing the necessary bandwidth have not been feasible for automotive applications so far. In this paper, the first highly integrated, fully coherent OFDM radar capable of multiple-input multiple-output (MIMO) and stepped-carrier OFDM for automotive applications is presented. The stepped-carrier OFDM approach is adopted to reduce AD/DA requirements using an analog local oscillator (LO) frequency step generator. The capability to generate frequency steps with a duration of a few microseconds required for automotive applications is demonstrated. Calibration steps that are required with the new architecture are discussed and measurements are done to validate the functionality of the system. Also, possibilities for adaptive reconfiguration of the radar sensor in the presence of ambiguities are demonstrated. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel frequency-domain reading method for the chipless radio frequency identification (RFID) tags. It is based on a single scalar measurement of transmission coefficient magnitude between two antennas by the presence of a tag. The method enables to reliably read the chipless RFID tags based on a dipole resonator array, which is backed by a limited ground plane, in a real environment outside the anechoic chamber. Moreover, it suits simple, yet not necessarily well impedance matched, reader antennas represented by an open end of the rectangular waveguide. The method was verified experimentally in the frequency band of 7–11 GHz. [ABSTRACT FROM AUTHOR]

Some equivalent circuits of two-port lossy devices are discussed in this paper. The main advantage of the proposed circuits is that they are obtained with two positive resistances, while other classic circuits could also contain negative resistances, as it happens in the presence of lines in lossy waveguide device. The proposed circuits are two: the first simplifies the identification of the reactive part of the device kernel (“classic” circuit), while the second simplifies the resistive part (“compact” circuit). The key of the identification is the presence of two input–output lines with proper lengths that permit to realize the first or the second simplification. Both circuits are able to identify correctly any lossy two-port waveguide device and can help the designer in the analysis of the effect of the losses due to the components of the device. The “compact” circuit seems to have more promising developments in the design of filters/multiplexers. [ABSTRACT FROM AUTHOR]

This paper introduces a new computational framework to derive electromagnetic field derivatives with respect to multiple design parameters up to any order with the finite-difference time-domain (FDTD) technique. Specifically, only one FDTD simulation is needed to compute the first-order field derivatives with respect to $N$ parameters, while two FDTD simulations are needed to compute the field derivatives with respect to one parameter up to any order. The field derivatives with respect to $N$ parameters up to any order are computed with $(N+1)$ FDTD runs. In addition to its efficiency, this framework is based on a subtractive cancellation error-free approach, providing guaranteed accuracy toward the computation of field derivatives up to any order. With high-order field derivatives available, sensitivity analysis, parametric modeling, and uncertainty quantification can be accurately performed. [ABSTRACT FROM AUTHOR]

This paper introduces a transmission line model analysis for dielectric-loaded self-resonant structures (SRSs). Equivalent circuit models, besides their fast computational time, usually offer some insights into the underlying physics of the electromagnetic structures, hence simplifying and improving the design and optimization criteria of these structures. A systematic approach for deriving impedance expressions of SRS on and within multi-layer dielectric media is presented. The process of extracting equivalent circuit parameters from impedance expressions is explained. The trends of equivalent circuit parameters are studied with different dielectric medium properties and various angles of incidence for an SRS with multiple resonant states highlighting the effect of changing the physical and electrical dimensions on the equivalent circuit parameters. The transmission line model responses are compared to full-wave simulation results, and model accuracy is assessed using the mean absolute error criteria. Furthermore, a new simplified method for calculating the forward transmission coefficient of an SRS within multi-layer media is proposed. This expression offers fundamental insights into the factors contributing to the $S_{21}$ response. Finally, experimental measurements for SRS embedded in a multi-layer dielectric media inside a waveguide is conducted and compared to the equivalent model with very good agreement. [ABSTRACT FROM AUTHOR]

Wideband and low-noise tunable oscillators at microwave frequencies are crucial within microwave frequency synthesizers and key to high-end measurement systems based on electromagnetic sensing in the microwave range as well as in the terahertz (THz) and sub-THz range. This paper presents a novel, wideband, and low-noise differential yttrium iron garnet (YIG) tuned oscillator. It is based on a SiGe monolithic microwave integrated circuit and a transmission-type YIG resonator. The integrated circuit contains a fully differential amplifier as a part of the oscillator core. The resonator was realized by two orthogonal, crossed pad-to-pad bonds and an YIG sphere, which is positioned between those bonds and the integrated circuit. To design and optimize the oscillator, an equivalent circuit modeling the resonator was developed. Concerning the tuning range and the phase noise, the results of the circuit simulations are in good agreement with the measurements. Two oscillators with different lengths of the inductive load transmission line were realized. First, the oscillator with a short transmission line offers very high-oscillation frequencies with a tuning range from 32.0 to 48.2 GHz. It exhibits an excellent phase noise of less than −119dBc/Hz at an offset frequency of 100kHz for oscillation frequencies up to 42GHz. Second, the oscillator with a longer transmission line length offers a tuning range from 19.1 to 41.4 GHz. This configuration exhibits an excellent phase noise of less than −120dBc/Hz at an offset frequency of 100 kHz for oscillation frequencies up to 38GHz. [ABSTRACT FROM AUTHOR]