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This paper demonstrates the design of an 800-MHz solar-powered active wireless beacon composed of an antenna and an integrated oscillator on a low-cost paper substrate. Inkjet printing is used to fabricate the conductive circuit traces and the folded slot antenna, while the oscillator circuit is designed using off-the-shelf components mounted on the paper substrate. Flexible, low-cost, amorphous silicon (a-Si) solar cells are placed on top of the slot ground and provide autonomous operation of the active circuit eliminating the use of a battery. A prototype is built and characterized in terms of phase noise, radiation patterns, and the effect of solar irradiance. Such low-cost flexible circuits can find significant applications as beacon generator circuits for real-time identification and position purposes, wearable biomonitoring as well as solar-to-wireless power transfer topologies. The measured phase noise is -\116 dBc/\Hz at 1-MHz offset, while drain current is 4 mA and supply voltage is 1.8 V. [ABSTRACT FROM AUTHOR]

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]

This paper proposes a new design methodology of dual-band stripline circulator for wireless communications applications. As far as the monoband classic circulator is based on coupling the counter-rotating fundamental modes, the operating principle of dual-band phenomenon is based on studying both fundamental and upper resonant modes within ferrite disks. Electromagnetic (EM) simulations have shown that two categories of dual-band operation could be obtained: simple (unidirectional) and left-handed /right-handed (LH–RH) circulators. The application dedicated to these two original concepts will be discussed, and simulation results will be ensured by the measurement of two prototypes in order to validate the methodology’s reliability. [ABSTRACT FROM AUTHOR]

This paper presents a new miniaturized ultra-wideband (UWB) multilayer balanced bandpass filter (BPF) using the liquid-crystal polymer technology. The design is based on the use of two baluns and uses the transversal signal-interference concept for the realization of differential-mode (DM) passband and common-mode (CM) stopband. The broadside coupled stripline structure is adopted in this paper to realize UWB performances and pure TEM mode. The fabricated prototype is self-packaged, light in weight, and cost effective with a small footprint. The demonstrated balanced BPF achieves the excellent DM and CM responses within the entire bandwidth, centered at 6.85 GHz. The simulation and measurement results show good agreement. [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, a novel complementary split-ring resonator (CSRR)-based sensor for full characterization of magneto-dielectric materials is proposed. In general, the operation of microwave resonance-based sensor hinges on the shift in the resonance frequency and the change in the quality factor of the loaded structure. However, both the electric permittivity and the magnetic permeability of the material under test (MUT) have similar effect on the response of the sensor that makes the simultaneous determination of the permittivity and permeability challenging. To remove this difficulty, the main idea behind this paper is to localize the highest intensity of the electric and magnetic fields in two separate zones. By the analysis of the measured resonance frequency and quality factor, the real and imaginary parts of the electric permittivity and the magnetic permeability of the MUT can be determined. Although the characterization of the permittivity and permeability of materials using split-ring resonator and CSRR-based sensors has been widely used, to the best of our knowledge, the full characterization of magneto-dielectric materials using a single sensor has not yet been reported in this paper. As a proof of concept, the sensor was fabricated and used to measure the permittivity and permeability of several materials. Strong agreement between the extracted values and the reference data was achieved. [ABSTRACT FROM AUTHOR]

In this paper, a novel type of dynamically tunable attenuator based on graphene is proposed. This type of attenuator is composed of one or two graphene sandwich structures (GSSs) and a microstrip line. The GSSs are spread on the substrate of microstrip line near the signal strip along the direction of propagation to dissipate electromagnetic field. By the application of biased voltage, the surface impedance of graphene can be tuned, and consequently, the insertion loss of microstrip line can also be adjusted while the return loss maintains relatively low level. A transverse equivalent network and a closed form of attenuation of each attenuator are also proposed, which can be utilized to analyze the performance of attenuator with different critical parameters of graphene in detail. According to the analysis, there is a maximum value of the attenuation as the surface impedance of graphene rises from 0 to $3000~\Omega /\Box $. As an example, a prototype of each tunable microstrip line attenuator operating at gigahertz frequencies is fabricated and measured. The fabricated attenuator present favorable attenuation ranges from 3 to 15 dB, at the operating frequency from 9 to 40 GHz, and with a stable wideband attenuation corresponding to bias voltage changing from 0 to 4.0 V. [ABSTRACT FROM AUTHOR]

This Mini-Special Issue of this Transactions includes 6 expanded papers from the fifth IEEE MTT-S International Wireless Symposium (IEEE IWS’2018) held in Chengdu, Sichuan, China, May 6–10, 2018. [ABSTRACT FROM AUTHOR]

This paper presents a technique capable to ameliorating the impairment caused by radio channel multipath, in the estimation of the wireless communications direction of arrival (DoA). This feature is enabled by a space division multiple access approach supported by a DoA technique based on the combination of the estimates achieved at both 2.45 and 5.2 GHz. The DoA estimation relies on a comparison between the real-time received signal strength indicator and the predicted signal level distribution, which can be estimated and stored without the need of lengthy offline measurement. The experimental setup adopted for the technique validation involves an active interferer, by which arbitrary multipath levels can be implemented. An equivalent reflection coefficient signal-to-interference ratio is defined as the ratio of the unperturbed signal and the induced coherent isofrequency interferer signal, compatible with the two-ray model of the multipath impairment. The proposed technique exploits a dual-band frequency planning, and because of the combined use of the data at the two frequencies, a mean error of 2.6° is observed within a domain ranging from 0.5 to 4 m, for the entire 360° angle in the reference anechoic scenario. The 90th percentile of the cumulative error distribution is 5.4°. In the presence of a strong coherent interferer, compatible with a total reflection from the walls, the mean error is 4.9°, while the 90th percentile of the cumulative error distribution is 10.5°. In the presence of the strongest coherent interferer signal available, which is more severe than the worst case of total reflection, the mean error is 7.1°, while the 90th percentile of the cumulative error distribution is 15.1°. [ABSTRACT FROM PUBLISHER]

This paper presents a CMOS transceiver IC for a single-antenna frequency-modulated continuous wave (FMCW) radar. Since transmitter (Tx) leakage is critical in a single antenna radar with CMOS technology, a comprehensive leakage canceling technique is proposed. It is able to cancel all the leakages caused by antenna reflection, asymmetry of a balanced structure, and lossy substrate without additional power or area. Even-order harmonic leakages from the power amplifier (PA) are also reduced by an even-harmonic filter, which is implemented simply by removing the real ground from the symmetrical point of the PA output transformer. Matching networks are simplified by using a modified coupler structure. A low-noise combining amplifier is used to make the combining circuit compact. As a result, the transceiver achieves the output power of −1.6 dBm, the phase noise of −105.44 dBc/Hz at 1MHz offset, the receiver (Rx) gain of 15.3 dB, and the noise figure of 11.6 dB. Tx leakages are canceled so that the isolation between Tx and Rx is 47.3 dB. The chip consumes 74.1 mA from a 1.5-V power supply. Despite the high integration level, the chip area including pads is 1.7 mm $\times $ 0.9 mm. A {K} -band FMCW radar module with a single antenna is implemented with this chip. [ABSTRACT FROM PUBLISHER]

These instructions give guidelines for preparing papers for this publication. Presents information for authors publishing in this journal. [ABSTRACT FROM AUTHOR]

In this paper, the surface-wave modal analysis of the transverse strip-grated dielectric-coated metal rod is done by using the asymptotic strip boundary conditions (ASBC) along with classical vector potentials in the cylindrical coordinate system. The yielded solvable system of linear equations is then cast into a homogeneous matrix equation, from which the characteristic equation as well as field distributions in explicit functional forms may be obtained. Modal dispersion diagrams and field distributions generated by this method are compared and validated with those simulated by an independent commercial full wave solver. The time cost by the ASBC method is also compared with that of the simulation software, upon which the vast superiority in speed of the proposed technique over the benchmark tool is demonstrated, but yet preserving high accuracy. Parametric studies that portray the variations of dispersion properties with various geometric attributes are carried out. Comparisons with its counterpart transverse corrugated rod are also carried out, and studies of dielectric losses are presented as well. A prototype was fabricated and measured, the experimental results of which concur well with theoretical expectations. [ABSTRACT FROM AUTHOR]

A novel diplexer-based fully passive transponder is presented in this paper, which targets sub-6-GHz 5G-compatible internet-of-things applications. To alleviate the antenna design restrictions of traditional transponder with two separate antennas, a new architecture has been proposed with the introduction of a diplexer, which allows transponder to simply employ a dual-band antenna. In this paper, a dual-band circularly polarized omnidirectional spiral slot antenna, with enhanced bandwidth and gain performance, is designed as the transponder Tx/Rx antenna. Besides the new architecture, a diode selection criterion is proposed as well. Analytical models are derived, showing relationships between the diode’s SPICE parameters and the conversion efficiency or conversion loss (CL) of such diode-based transponders. With help of the analysis, transponder designers can easily identify diodes to implement transponders with better performance. Under the guidance of the criterion, low-barrier diode SMS7630 is chosen for verification. Measured CL results of the transponder circuitry part show a noticeable improvement over the state-of-the-art works. The complete prototype was tested with radar’s transmitting power of 25 dBm, and it presents a maximum read-out distance up to 7 m when the operating fundamental frequency is 3.5 GHz. [ABSTRACT FROM AUTHOR]

This paper presents the first experimental assessment of a highly integrated dual-band dual-polarized antenna tile designed for synthetic aperture radar (SAR) digital beamforming (DBF) satellite applications. The demonstrator described in this paper is the first comprehensive experimental validation of an RF module providing the X-band and Ka-band (9.6- and 35.75-GHz) operation with custom downconversion stages. All the antennas, transitions, and downconversion chips are integrated in the same antenna tile fabricated using a customized 15-layer high density interconnect process. The designed tile goes to the limits of the proposed technology and for the high trace density and for the size of the vertical transitions. The proposed results represent the state of the art in terms of compactness for a DBF SAR RF module even though the demonstrator was manufactured with a standard low-cost technology. The experimental assessment proves the validity of the proposed manufacturing and integration approaches showing a substantial agreement between the performance of the individual blocks and of the integrated system. [ABSTRACT FROM AUTHOR]

In this paper, a novel triplexer using the substrate-integrated suspended line technology is proposed. Two matching circuits are designed to connect the three filter channels for the triplexer construction. The used bandpass filters are composed of a low-pass filter and a high-pass filter, and they have advantages of high controllability and low insertion loss. For the proposed triplexer, two adjacent filter channels compose a duplexer. Based on the design consideration, the triplexer can be extended to a multiplexer. The proposed design is further improved by using a patterned suspended substrate for loss reduction. The triplexer achieves good isolations among the three ports and low insertion losses of 1.4/1.3/0.8 dB for the three channels of 0.8, 2.5, and 5.8 GHz, respectively. [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]

Recently, microwave imaging under random field illuminations has attracted many interests. This paper theoretically analyzes and experimentally implements a qualitative microwave radar imaging system suitable for 2-D object. It can be customized on the demands of the desired object size and imaging resolution. Based on random illuminations generated by a minimum number of antenna elements, an analytical equation can be used to reconstruct the image of the object in near real time. The simple-structured and cost-effective imaging system can be implemented in microwave, millimeter-wave, and even sub-THz frequency bands, having promising potentials for various microwave imaging applications. [ABSTRACT FROM AUTHOR]

This paper describes the novel design concept of a wideband noncircular choke flange for connecting two contactless waveguide joints with the variable air gap. Resonant enhancement of transmission loss is observed in the experiment as well as the numerical simulation in Ansys HFSS software when a 2-D standing wave is excited in the narrow air gap. The shape of the choke groove is designed in such a way that ensures standing waves cannot be excited in the frequency band of interest, even considering possible linear and rotational misalignments between the connecting joints during practical operation, thereby making the design very robust. The eigenmode analysis is performed to decompose the mixed excitation mode into the fundamental and higher order modes, and for the case of misalignment, revealing why the electric field changes the direction of rotation above and below the resonant frequency. Experimental measurement results of the fabricated egg-choke flange showed that the transmission loss is less than 0.1 dB in the 2.5-GHz bandwidth from 8.5 to 11 GHz with possible misalignment which validates the design. Other choke shapes are possible following the same design methodology with different scaling parameters depending on the desired frequency band of the user application. [ABSTRACT FROM AUTHOR]

This paper presents the design and measurement of an interpolation-based low noise and variable gain cell (IBA-cell) in the 60-GHz band, using a 40-nm CMOS technology. The interpolation-based gain cell is designed for an innovative analog beamforming front end, where the array pattern is not only controlled in the phase domain, but also wins the flexibility in the magnitude domain. The circuit specifications are first derived for the application at 60 GHz. Techniques to combine low noise figure (NF) with variable gain tuning are presented focusing on the NF and linearity (IIP3) on the example of a 60-GHz low noise amplifier and variable gain amplifier. Subsequently, the design and measurement of the whole gain cell (IBA-cell) integrated into a single chip are reported with the technique of a cross-coupled feedback loop to reduce the phase variations over the gain tuning states and enhance the variations of IIP3. The IBA-cell achieves 15.8-dB maximum gain and 6.5-dB NF at 57 GHz with the gain tuning range from −2 to 15.8 dB and IIP3 varying from −11.3 to −16 dBm over the gain control range. The IBA-cell consumes a dc power of maximum 54 mA from 1.1 V. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method for designing a dual-channel balanced filter and a dual-channel balun filter based on the quad-mode dielectric resonator (DR) for the first time. By sharing one common quad-mode DR, two balanced filters or two balun filters are integrated as one single-cavity configuration, featuring compact size and high integration. A cylindrical DR with two short ends is investigated to construct the quad-mode DR. By properly arranging input and output feeding probes, two modes of the DR are only excited by the feeding probes of one channel and the other two modes are excited by that of the other channel. Accordingly, signals cannot be transmitted between the two channels, resulting in high isolation. Moreover, the required out-of-phase characteristics of the balanced and balun filters can be obtained by the inherent electromagnetic field properties of the DR without adding additional circuits, featuring a simple structure. For demonstration, a dual-channel balanced filter and a dual-channel balun filter are designed and fabricated, showing excellent balanced or balun filter performance of each channel as well as high isolation between the two channels. As compared to the other reported DR balanced and balun filters, the proposed designs exhibit a significant size reduction, which are attractive in wireless systems. [ABSTRACT FROM AUTHOR]

This paper proposes a smart wireless power transmission method, based on a two-step procedure, exploiting real-time beaming of time-modulated arrays. The sideband radiation phenomenon, which is usually a drawback of these radiating systems, is favorably used for intentional wireless power transfer (WPT): in a first step to precisely localize the tag to be powered and in the second one to perform directive WPT. The approach is first theoretically discussed, then the numerical procedure, which integrates full-wave analysis of the antenna array with nonlinear simulation of the modulated nonlinear feeding network, is used to validate the principle of operation and to include nonlinearities and electromagnetic couplings affecting the whole system performance. The procedure allows a flexible design of the time-modulated-array-based WPT system, taking into account the impact of different array elements layout and spacing on localization and power transmission performance. Experiment of the first step is carried out in a real indoor environment at 2.45 GHz: a TI MSP430 drives a Schottky-diode-based network to provide proper modulated RF excitations of the array elements. Measurements show that the system is able to select tags to be energized randomly distributed in a 100^\circ-scanning range. [ABSTRACT FROM PUBLISHER]

Carbon nanotubes (CNTs) have been researched extensively for gas-sensing applications due to their unique electrical, chemical, and structural properties. Single-walled carbon nanotubes (SWNTs) have been predominantly used due to their superior electrical conductivity and higher sensitivity relative to multiwalled CNTs. This paper presents the design and characterization of a novel planar sensor fabricated on paper substrate to detect small concentrations of ammonia gas, using the shift in resonance frequency of a patch antenna as the discriminator. We have investigated three main design issues in depth. First, functionalization of the SWNTs with a polymer is studied in order to enhance the gas detection sensitivity. Second, a thin film of the functionalized SWNT is characterized to create a surface impedance model for the explanation and prediction of the resonance shift due to different gas concentrations. Finally, as a proof of concept, functionalized SWNTs are integrated into a patch antenna design and the return loss is measured in a closed-system environment to show high sensitivity for low concentrations of ammonia gas. The proposed antenna-based wireless gas sensor can be utilized in several applications, given its small form factor, light weight, and little to no power requirements. [ABSTRACT FROM AUTHOR]

In this paper, a highly integrated frequency-modulated continuous-wave (FMCW) radar system with a single-antenna interface for range sensing is proposed. In this paper, a circulator structure was developed and used in the radar system with the single-antenna interface. This structure capitalizes on frequency orthogonality to separate transmitted and received signals; thus, the isolation can be improved by using integrated filters to further suppress transmitter leakage. Without an additional back-end leakage cancellation mechanism and antenna tuner, the single-antenna FMCW radar system can be devised. The proposed system is composed of a radar transceiver, a frequency synthesizer, an analog signal processor, and an AD converter; the system is fabricated using a 65-nm CMOS technology, occupies a chip area of 1.9 mm2, and consumes 147-mW dc power under a 1.2-V power supply. The implemented front-end circuit can provide an output power of 10.5 dBm with power efficiency of 30%, over 1-GHz impedance matching, an insertion loss of 2 dB, a maximum noise figure of 16.8 dB (including the following IF amplifier), $P_{1\,\text {dB}}$ of 2 dBm, and IIP3 of 7 dBm. A wireless measurement process proved that the system can provide a 37-cm range resolution over a 50-m range for a $20 \times 20$ cm2 copper plate. Finally, an FMCW radar front-end board and a digital signal processing board were implemented for data analysis, thus completing the FMCW radar sensor unit. The proposed system can be utilized for multiple applications including 1-D object tracking, 2-D localization, and 3-D object tracking. [ABSTRACT FROM AUTHOR]

This paper presents a flexible 2.45-GHz wireless power harvesting wristband that generates a net dc output from a −24.3-dBm RF input. This is the lowest reported system sensitivity for systems comprising a rectenna and impedance-matching power management. A complete system has been implemented comprising: a fabric antenna, a rectifier on rigid substrate, a contactless electrical connection between rigid and flexible subsystems, and power electronics impedance matching. Various fabric and flexible materials are electrically characterized at 2.45 GHz using the two-line and the T-resonator methods. Selected materials are used to design an all-textile antenna, which demonstrates a radiation efficiency above 62% on a phantom irrespective of location, and a stable radiation pattern. The rectifier, designed on a rigid substrate, shows a best-in-class efficiency of 33.6% at −20 dBm. A reliable, efficient, and wideband contactless connection between the fabric antenna and the rectifier is created using broadside-coupled microstrip lines, with an insertion loss below 1 dB from 1.8 to over 10 GHz. A self-powered boost converter with a quiescent current of 150 nA matches the rectenna output with a matching efficiency above 95%. The maximum end-to-end efficiency is 28.7% at −7 dBm. The wristband harvester demonstrates net positive energy harvesting from −24.3 dBm, a 7.3-dB improvement on the state of the art. [ABSTRACT FROM PUBLISHER]

This paper presents the design of microstrip-ridge gap waveguide using via-holes in printed circuit boards, a solution for high-frequency circuits. The study includes how to define the numerical ports, pin sensitivity, losses, and also a comparison with performance of normal microstrip lines and inverted microstrip lines. The results are produced using commercially available electromagnetic simulators. A WR-15 to microstrip-ridge gap waveguide transition was also designed. The results are verified with measurements on microstrip-ridge gap waveguides with WR15 transitions at both ends. [ABSTRACT FROM AUTHOR]

We report a 30-GHz impulse radiator chip for high-resolution 3-D radar imaging. In this paper, an asymmetrical topology in the cross-coupled pulsed VCO is introduced to minimize timing jitter of radiated impulses to 178 fs, which enables highly efficient spatial combining. The coherent combining over the air has been performed with two widely spaced impulse radiators. The shortest full-width-at-half-maximum pulsewidth of 60 ps is recorded. 3-D images of various metallic objects and dielectric objects are produced using a custom-designed synthetic array imaging system. A depth resolution of 9 mm and a lateral resolution of 8 mm at a range of 10 cm have been achieved. The impulse radiator was implemented in a 130-nm SiGe BiCMOS process technology with an area of 2.85 mm2 and an average power consumption of 106 mW. [ABSTRACT FROM PUBLISHER]

Silicon-based millimeter-wave (mm-wave) phased-array technologies are enabling directional wireless data communications at Gb/s speeds. In this paper, we review and discuss the challenges of implementing a multichip phased-array antenna module for mm-wave applications using organic buildup substrate technology. A prototype test vehicle has been fabricated and studied to evaluate the antenna and interconnect performance, dielectric properties, package substrate warpage conditions at different temperatures, chip- and board-level joint process reliability, and thermal management feasibility for cooling. Based on the learning from the test vehicle, an organic-based multilayered phased-array antenna package for 28-GHz mm-wave radio access applications is implemented. The package incorporates 64 dual-polarized antenna elements and features an air cavity common to all antennas. Direct probing measurements on a single-antenna element of the package show over 3 GHz of bandwidth and 3-dBi gain at 28 GHz. A phased-array transceiver module has been developed with the package; the module includes four SiGe BiCMOS ICs attached using flip-chip assembly. Module-level measurements in the TX mode show a 35-dB near-ideal output power increase for 64-element power combining; 64-element radiation pattern measurements are reported with a steering range of ± 50° without tapering in off-boresight directions, and 64-element radiation pattern measurements with tapering show achievement of a sidelobe level lower than −20 dB. The transceiver modules achieved 20.64-Gb/s throughput with 256 QAM and 800-MHz bandwidth in direct over-the-air link measurement results. [ABSTRACT FROM AUTHOR]

In this paper, a noninvasive quantum imaging method of the near-field (NF) distribution of patch antenna was proposed by using a diamond containing nitrogen-vacancy (NV) centers. We applied AM/FM pulse modulation technique combined with optical detection magnetic resonance to measure the microwave magnetic field of a patch antenna. A full reconstruction formulation of the magnetic field vector, including the amplitude and phase, is proposed by measuring both the left and right circular polarizations along the four NV axes. Furthermore, we proposed a novelty method to reconstruct the surface current distribution imaging of patch antenna by using an integral equation based on magnetic field. The proposed quantum imaging method can directly measure the NF distribution of real antenna. Compared with HFSS simulation, the microwave imaging experiment is sensitive to actual manufacturing details such as the metal cross section due to etching and dielectric layers such as solder masks and shows the microwave field distribution of the real antenna. A nanoscale diamond probe enables nanoscale high-resolution imaging. The proposed method is expected to have applications in diagnosis on monolithic microwave integrated-circuits chip, antenna characterization, and the field mode imaging of nanoscale semiconductor radio frequency devices. [ABSTRACT FROM AUTHOR]

This paper presents a novel design method of rat-race couplers with tunable frequency. The port equivalent impedances of a reciprocity four-port network being matched and isolated are derived by employing the even–odd mode analyses. A frequency-reconfigurable matching network (MN) transforming the port equivalent impedances to normalized unit resistance is first designed, and then the frequency-reconfigurable couplers are constructed by attaching the MN to each port of the four-port network. Based on the proposed method, two frequency-tunable rat-race couplers with power-dividing ratios of 1:1 and 2:1 are designed and measured. The measurements agree well with simulations. The measured center frequencies of the couplers with power-dividing ratios of 1:1 and 2:1 are tuned from 840 to 2480 and 840 to 2410 MHz, respectively, with a return loss of better than 15 dB and isolation of better than 20 dB. [ABSTRACT FROM AUTHOR]

This paper reports precision measurements of the electromagnetic permittivity of five highly refractive, single-crystal materials, SrTiO3, KTaO3, rutile TiO2, LiTaO3, and LiNbO3, using a single, well-controlled, frequency-scalable procedure over the frequency ranges 25–110 and 140–220 GHz. Real permittivity values were highly consistent for different samples measured across multiple frequency bands. For SrTiO3, KTaO3, and TiO2, real permittivities were more consistent with lower frequency values than typically reported in the millimeter-wave region of the spectrum. Real permittivities of LiTaO3 and LiNbO3 agreed with most reported data. The intrinsic dielectric loss of SrTiO3, KTaO3, and the extraordinary axis of rutile TiO2 was also characterized over the ranges 25–110 and 140–220 GHz, and intrinsic loss per unit frequency was found to be consistent with values measured at other frequencies by dielectric resonators and quasi-optical techniques. [ABSTRACT FROM AUTHOR]

Additive manufacturing technology has enabled the manufacturing of complex structures, especially those with intricate internal features. This paper proposes a method for building complex-structured millimeter-wave waveguides using a strategy that combines digital light processing 3-D printing technology, a curved corner design, an off-axis print angle of 45°, and a robust postmetallization process. To demonstrate the capability of this combined-strategy method, a traditional magic tee prototype and an adapted inherently matched magic tee prototype are fabricated for use in the W-band. The measured performance of the fabricated inherently matched magic tee demonstrates return loss better than 13.5 dB, isolation coefficients higher than 15.7 dB, insertion losses smaller than 1.3 dB, and a magnitude imbalance of less than 1.3 dB across 80–105 GHz. The 3-D printed magic tee has a comparable performance to a W-band CNC-machined magic tee but weighs 77.5% less than the metallic one. [ABSTRACT FROM AUTHOR]

In this paper, the design of a cavity crossover with three intersecting channels is presented. The three fundamental modes of a cavity resonator, namely, TE011, TE101, and TM110 modes, are adopted to resonate at each of three channels, respectively. Due to the modal orthogonality of these fundamental modes, high isolation among three channels can be achieved. Two kinds of crossovers, for narrowband and broadband applications, are presented. For the narrowband case, the proposed crossover resonates at 2.91 GHz with the fractional bandwidth of 1.4%. For the broadband case, the proposed crossover resonates at 3 GHz with the fractional bandwidth of 24%. The isolations of both designs reach more than 50 dB. For a proof of concept, the broadband example of the cavity crossover structures is fabricated and measured. A good agreement between the simulated and the measured results verifies the accuracy of the proposed design methodology. [ABSTRACT FROM AUTHOR]

A time-division duplex (TDD) transmit/receive (T/R) millimeter-wave (mm-wave) front-end comprises a power amplifier (PA), a low-noise amplifier (LNA), an antenna switch, and appropriate passive matching and combining networks. In this paper, a synthesis methodology is proposed that minimizes the overall losses by combining the PA output and the LNA input matching networks together with the T/R switch into one network. The technique improves mm-wave transceiver performance in terms of PA efficiency and LNA noise figure. The proposed T/R combiner can achieve high linearity and can handle large PA output voltage swings. The architecture can be implemented in any process which provides high integration capability. A Ka-band implementation is demonstrated using 45 nm CMOS silicon-on-insulator that includes a high power, four-stack-based PA and an inductively source-degenerated cascode-based LNA. Within the front-end, the PA achieves saturated output power of 23.6 dBm with peak power added efficiency of 28%, while the LNA achieves NF of 3.2 dB. The overall chip area is 0.54 mm2, including pads. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of methods for improving homogeneity inside various dielectric phantoms situated in a 10.5-T human-sized magnetic resonance imaging. The transmit ${B} _{1}$ (${B} _{1}^{+}$) field is excited with a quadrature-fed circular patch probe and a 12-element capacitively loaded microstrip array. Both simulations and measurements show improved homogeneity in a cylindrical water phantom, an inhomogeneous phantom (pineapple), and a NIST standard phantom. The simulations are performed using a full-wave finite-difference time-domain solver (Sim4Life) in order to find the ${B} _{1}^{+}$ field distribution and compared to the gradient-recalled echo image and efficiency result. For additional field uniformity, the wall electromagnetic boundary conditions are modified with a passive quadrifilar helix. Finally, these methods are applied in simulation to head imaging of an anatomically correct human body model (Duke, IT’IS Virtual Population) showing improved homogeneity and specific absorption rate for various excitations. [ABSTRACT FROM AUTHOR]

This paper presents a multi-input-multi-output (MIMO) range migration algorithm (RMA) with range compensation for near-field millimeter-wave imaging. The proposed algorithm is derived based on the effective phase center principle and scalar diffraction theory. Compared with the original MIMO RMA, the propagation loss is compensated better, and the reconstructed image quality is improved significantly. In the process of image reconstruction, a multistatic array topology is transformed to a monostatic array, and the round-trip propagation is converted into unidirectional optical field propagation. The efficiency of the proposed algorithm is analyzed theoretically, and demonstrated experimentally. Numerical simulations and experimental results show that the propagation loss in range is properly compensated by the proposed algorithm. [ABSTRACT FROM AUTHOR]

This paper proposes and describes in detail a new approach to the design of very compact active microwave compressors capable of providing rectangular pulses of up to 100 ns. The approach consists in using a storage cavity, which comprises linear waveguide sections connected by tees such that the cavity geometry can be 2-D or 3-D or can be variable to allow direct space-saving integration of a compressor into a microwave source. Also presented are the scattering matrix data on uniform wave propagation along the storage cavity with little reflection and on conditions necessary for such uniformity. The S-band experiments demonstrate the capability of storage cavities with two and three parallel waveguide sections of about 1 m long to produce rectangular pulses of duration 5, 15, and 25 ns with a power gain and output power of about 16 dB, 80 MW; 15 dB, 60 MW; and 13 dB, 40 MW, respectively. Our estimates suggest that 12 waveguide sections can provide a rectangular pulse of 100 ns with a power gain 10 dB. [ABSTRACT FROM AUTHOR]

This paper presents a broadband three-stage Doherty power amplifier (DPA) using impedance compensation for bandwidth extension. Different from the conventional design, an impedance-compensating load combiner is proposed to broaden the bandwidth of the three-stage DPA by employing the output impedances of the peaking amplifiers. Considering the load impedance of the peaking branch as an independent design variable, the Doherty load modulations are analyzed in theory, pointing out the optimized solution for the load combiner. To achieve the impedance compensation, the peaking output matching networks are deliberately designed with the dual-impedance matching topology. Experimental results show that a three-stage DPA is realized from 1.6 to 2.6 GHz (48% fractional bandwidth) with a measured efficiency of 50%–53% at 9.5-dB back-off and a saturated output power around 45.5 dBm. When stimulated by the 20- and 40-MHz modulated signals at an average output power of around 36.5 dBm, the proposed DPA can achieve the adjacent channel leakage ratio of −50 dBc over the whole frequency band after linearization, with an average efficiency of higher than 50%. [ABSTRACT FROM AUTHOR]

This paper presents a type of bandpass filter (BPF)-integrated single-pole double-throw (SPDT) switch using common shorted stepped-impedance resonator technique. The BPF-integrated ON-state with reverse-biased p-i-n diodes can be synthesized by classical coupled-resonator filter design theory, and the OFF-state with forward-biased p-i-n diodes is detuned which exhibits high OFF-state suppression (OSS). The transmission zeros due to the direct coupled feed, the cross-couplings and the cancelling effect of mixed electric and magnetic coupling are produced to improve the ON-state passband selectivity significantly. As examples, the third-order/fourth-order BPF-integrated SPDT switches at center frequency $f_{0} = 1$ GHz with ripple bandwidth of 110/100 MHz are designed, which show low insertion losses of 1.08/1.58 dB, sharp skirts, high roll-off rate of sidebands, high OSSs of 40.9/40.1 dB as well as high port-to-port isolation of 57.4/47.8 dB. Then, the switched 50- $\Omega $ matching circuits are in series with two output ports of above BPF-integrated SPDT switches, resulting in the absorptive OFF-state. The fabricated third-order/fourth-order BPF-integrated SPDT switches with absorptive OFF-state have the matched return losses of 30/28.2 dB, and their OSSs and port-to-port isolations are also improved. [ABSTRACT FROM AUTHOR]

This paper discusses the design of a batteryless wirelessly powered ultra-wideband (UWB) system-on-a-chip (SoC) tag for area-and-volume-constrained localization applications such as insect tracking. Key challenges for wirelessly powered operation at 10-m range include the design of high-sensitivity rectifiers and low-voltage high-efficiency UWB transmitters (TX). An antenna-rectifier co-design methodology is presented for sensitivity optimization under area constraints. A 300-nA power management unit (PMU) and low-voltage (0.8-V) UWB TX increases tag operating range by ensuring high rectifier sensitivity under loaded conditions and reducing required rectifier output voltage. The rectifier, PMU, and UWB TX are integrated in 65-nm CMOS, and the rectifier demonstrates state-of-the-art -\30.7–dBm sensitivity for 1-V output voltage with only 1.3 \cm^2 antenna area, representing a 2.3\,\times improvement in sensitivity over previously published work, at 2.6\,\times higher frequency with 9\,\times smaller antenna area, translating into a 50% longer range at the same frequency. The 0.8-V UWB TX consumes 64 pJ/pulse at 28-MHz pulse repetition rate and achieves 2.4 GHz -\10-dB bandwidth. Wireless measurements demonstrate sub-10-cm range resolution at ranges exceeding 10~m. Tag measurements in typical office environments demonstrate 20-m-range RF-energy harvesting with 36-dBm effective-isotropic radiated power in the 2.4-GHz ISM band. [ABSTRACT FROM PUBLISHER]

This paper presents a millimeter-wave tunable hybrid-transformer-based duplexer concept with dual-antenna configuration. By using orthogonal sequentially-rotated linearly-polarized antennas and the hybrid-transformer-based duplexer, the transmitter and receiver duplexes the two antennas with orthogonal circular-polarized signals. An on-chip tuning technique using magnetic coupling is introduced to improve the isolation of the duplexer in case of impedance imbalances. An alternative duplexer with a similar principle using an on-board rat-race coupler is also proposed and designed for comparison. In order to demonstrate the isolation with practical antenna connections, prototypes have been developed to integrate the on-chip duplexer and the rat-race coupler with on-board aperture-coupled microstrip antennas with sequential rotation technique. Measurement results demonstrate the orthogonal circular polarizations for the receiver and transmitter modes on both prototypes. The achieved isolation by the on-chip tunable duplexer is better than 50 dB between 30.2 and 31.2 GHz, while the achieved isolation by the rat-race version is about 20 dB in the same bandwidth. [ABSTRACT FROM AUTHOR]

A novel compact printable dual-polarized (DP) chipless radio-frequency identification (RFID) tag is presented along with its real-world implementation challenges. First, the DP tag with simulation and measurement results is presented, where ‘U’ shaped slot resonators are re-used in both vertical (V) and horizontal (H) polarizations to double the encoding capacity within a fixed bandwidth. Next, slot-length variation encoding technique is added to reduce the tag size by 50%. After that, a 16-bit proof of concept DP tag is developed that achieved 16.6 bits/cm^2 data density, which is the highest among the reported works. Next, a step-by-step guideline is presented to overcome the real-world challenges for implementing printable chipless RFID tags, which starts with a detail study on the effect of ink conductivity, and permittivity and loss tangent of the substrate on the tag performance. Then, a quick approximate substrate characterization technique is presented, which is verified by measurement of thermal printed patch tags. Finally, tag printing procedure on paper using a thermal printer is briefed, which is followed by a discussion on some printing inaccuracies and their plausible solutions. All these analysis will build a firm understanding and practical insight on implementing the proposed promising conductive ink printed chipless RFID tag for identification, authentication and sensing. [ABSTRACT FROM PUBLISHER]

Coupled electromagnetic resonances have various important applications in microwave engineering. Among them, the newly discovered electromagnetically induced transparency (EIT) has attracted much interest. In this paper, we explore the use of configurable electrically induced transparency to construct a microwave “diffractive medium” whose air-like optimally matched transparency and metal-like optimally reflective opacity can be conveniently switched by a binary dc voltage. Different from EITs based on closely coupled resonances, we use decoupled electrically induced resonances to achieve a low-loss transparency along with an optimal impedance matching with air. Satisfying the condition of a lossless perfectly matched layer, such transparency and opacity can be obtained in a wide range of incident angles. We validate our approach by experimentally demonstrating two electrically controlled steering antennas based on diffractive grating effect, both with thin planar apertures and binary digital control circuits. The proposed approach can be extended to higher frequencies, achieving configurable diffractive devices at millimeter-wave and terahertz frequencies. [ABSTRACT FROM PUBLISHER]

This paper addresses the challenge of increasing the sensitivity of wireless powering approaches to achieve targeted output voltage for wirelessly-powered sensors with the compact area. The design exploits a bootstrapping approach where the rectifier first stage and the antenna are reused to increase the rectifier output voltage following an initial charging phase. Area-constrained rectifier–antenna co-optimization results in a compact high- $Q~2.4$ -GHz antenna with 1.2-cm2 area which is then used in two topologies [cross-coupled (CC) and cross-coupled pMOS (CP)] based on the proposed bootstrapping concept. Both topologies increase the rectifier output voltage with no additional off-chip inductors or capacitors. The CC/CP topologies and the associated logic are integrated into a 65-nm CMOS with the IC occupying 1.1 mm2 of the area. The CC topology achieves input sensitivity of −34.5 dBm for 1.6-V output voltage with $R_{\mathrm{ LOAD}}$ of 1.8 $\text{M}\Omega $ , while the CP topology achieves −26.5-dBm input sensitivity with the 2.5-V output voltage and $R_{\mathrm{ LOAD}}$ of 250 $\text{k}\Omega $. These results confirm more than $2\times $ longer distance for wirelessly powering sensors compared to state of the art, with only 1.2 cm2 of the rectifier–antenna area. [ABSTRACT FROM AUTHOR]

Modern and future transmitter architectures are being driven toward multi-input multi-output (MIMO) transceivers, which make use of several radio frequency (RF) power amplifiers (PAs) to drive an antenna array. When moving to high integration scenarios, as is expected for fifth-generation communications, the isolation between the array and the PAs is often removed. Since the array elements are electromagnetically coupled, the waves fed to the antennas are also driving the output ports of the PAs. This effect creates an apparent variable load at the output of each PA, depending on the operation of the transmitter. In this system, the behavior of each PA cannot be fully described solely as a function of its input, as it will change according to the coupled signal. To predict and understand the behavior of these MIMO systems, simulation becomes a powerful tool. These simulators should be able to reproduce the main figures of merit (FoMs) of the transmitter, namely, output power, distortion, and efficiency. In this paper, we show how a recently proposed dc behavior model and an RF signal behavior model can be used in simulation setups to predict the MIMO transmitter FoMs of interest. [ABSTRACT FROM PUBLISHER]

The increasing data transmit rates per user (download speeds of about 1 Gb/s in 4G and 20 Gb/s in 5G), paired with the increasing number of users (people or devices) in mobile communications, require the continuous extension of the wireless network capacity. The demand for additional and higher usage of the available frequency spectrum is the driving force for the frequency spectrum adaptation at microwaves and millimeter waves and the implementation of new 3GPP cellular standards. These standards include multiband operation, carrier aggregation, and multi-input multi-output air interfaces. [ABSTRACT FROM PUBLISHER]

This paper presents the design and fabrication of low loss, weight, and cost prototypes in groove gap waveguide technology at Ka-band, manufactured with a metallized 3-D printing technique. A wide analysis of loss mechanisms and printing imperfections has been conducted, as well as the effect of temperature on structural deformations. Metallized 3-D printed and CNC machined prototypes have been compared and characterized with simulations and measurements at a band from 28 to 30 GHz. The average measured losses for metallized plastic prototypes are 1.4 dB/m. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a technique for comprehensive analysis of nonlinear and dynamic characteristics of multi-antenna transmitters (TXs). The analysis technique is enabled by the development of a Volterra series-based dual-input model for power amplifiers (PAs), which is capable of considering the joint effects of PA nonlinearity, antenna crosstalk, and mismatch for wideband modulated signals. By combining multiple instances of the PA model with linear dynamic antenna simulations, we develop the analysis technique. The proposed method allows the prediction of the output signal of every antenna in an arbitrarily sized TX array, as well as the total far-field radiated wave of the TX for any input signal with low computational effort. A 2.12-GHz four-element TX demonstrator based on GaAs PAs is implemented to verify simulation results with measurements. The proposed technique is a powerful tool to study hardware characteristics as, for example, the effects of antenna design and element spacing. It can be used in cases where experiments are not feasible, and thus aid the development of next generation wireless systems. [ABSTRACT FROM PUBLISHER]

This paper presents a simple structure for the realization of an $N$ -way reconfigurable power divider. With this N$ -way reconfigurable power divider, N$ different transmission modes with states can be realized by the use of only 3N-1$ p-i-n diodes. In each transmission mode, the input port and transmission ports are all matched and high isolations between transmission ports are obtained. To realize matching performances under different transmission modes, a reconfigurable multiple-impedance transformer network (RMITN) is introduced at the input port of the proposed divider. With the parameters of N-1$ p-i-n diodes under different bias conditions, N (port impedance) by RMITN, where load impedances can be real or complex impedances. In addition, no lumped elements, such as dc blocking capacitors, are required in the proposed reconfigurable divider. For verification, a 5-GHz four-way reconfigurable power divider is designed and fabricated. Four different kinds of transmission modes (four-path mode, three-path mode, two-path mode, and single-path mode) with 15 states are realized by the prototype. The measured transmission losses at 5 GHz in the four-path, three-path, two-path, and single-path modes are less than 0.78, 1.32, 1.9, and 1.74 dB, respectively; while in those modes, the isolations between different ports are higher than 30.2, 31.5, 24, and 27.4 dB, respectively. [ABSTRACT FROM PUBLISHER]

Monolithic integration of synthetic aperture radar (SAR) transceiver with small size, lightweight, and low power consumption is suitable for uploading to a compact unmanned aerial vehicle (UAV) for SAR imaging. This paper presents a monolithic frequency-modulated continuous-wave (FMCW) SAR transceiver that works at Ku-band and centers at 15 GHz. Techniques to address the special requirements of UAV SAR are proposed. A digital-tunable mixed-signal-mode FMCW chirp synthesizer is designed to be power efficient, to provide a tunable chirp rate, and to enable digital minimization of the root-mean-square (RMS) frequency errors. A saturated driver-amplifier-power-amplifier chain and an input-load peak-staggering low-noise amplifier are implemented to nullify the ripple effects so that the degradations of imaging performances can be prevented. Moreover, a 12th order active-RC bandpass filter is used to suppress the intermediate frequency interferences of both ground reflections and antenna leakage. A binary-weighted programmable gain amplifier and a successive approximation analog-to-digital converter are also integrated into the chip. Fabricated using a 65-nm complementary metal-oxide-semiconductor technology, the prototype demonstrates 1.48-GHz chirp bandwidth and <186-kHz rms frequency errors in a programmable modulation period from 1.18 to 10 ms. The transmitter and receiver RF front end attains 1.1- and 0.51-dB ripples, respectively. The function of the FMCW SAR transceiver is validated through the delay line and near-field ranging tests. The SAR imaging experiment with a distance of around 110 m is successfully carried out using the chip prototype and a range migration algorithm. At 1.2-V supply, the transceiver chip consumes 259.4 mW. [ABSTRACT FROM PUBLISHER]

When an antenna vibrates, it induces phase noise on the signals that it transmits and receives. This noise source is significant for microwave and millimeter-wave systems operating in high-vibration environments that require low phase noise at small frequency offsets. The purpose of this paper is to derive equations to compute phase noise from vibration parameters and to validate the equations with measurements. It is shown that the induced phase noise varies as fv^{-4} , where fv is the frequency of vibration. The results are then compared to the phase noise induced on an oscillator by vibration to determine the oscillator g sensitivity such that the oscillator and antenna phase noise contributions are equal. For state-of-the-art low-g-sensitivity oscillators, the phase noise contribution of the antenna can dominate at vibrational frequencies up to several kilohertz. The vibrational phase noise sensitivity of the antenna is also larger than the reported vibrational sensitivity of coaxial cables up to at least 1000-Hz vibrational frequencies and bandpass filters up to 300–1000-Hz vibrational frequencies depending on the filter quality factor. [ABSTRACT FROM PUBLISHER]