Showing papers in "IEEE Microwave and Wireless Components Letters in 2020"

Orbital Angular Momentum Multiplexing in Highly Reverberant Environments

Abstract: Previous studies on orbital angular momentum (OAM) communication mainly considered line-of-sight (LOS) environments. In this letter, however, it is found that OAM communication with high-order modulation can be achieved in highly reverberant environments by combining the OAM multiplexing with a spatial equalizer. The OAM multiplexing exhibits comparable performance of the conventional multiple-input–multiple-output (MIMO) system.

Multiband Ambient RF Energy Harvesting for Autonomous IoT Devices

Abstract: This letter presents a novel multiband rectenna for the ambient wireless energy harvesting of an autonomous internet of thing (IoT) sensor. A bow-tie antenna with slits is proposed to obtain four frequency bands at 840 MHz, 1.86, 2.1, and 2.45 GHz, respectively. Furthermore, a multiband rectifying circuit combined of four single ring-loop rectifiers is designed with high conversion efficiency. Finally, a power management circuit with storing and converting the harvested voltage is proposed for smoothing dc output voltage. The energy harvester can be used in practical wireless sensor applications.

A Compact High-Efficiency Broadband Rectifier With a Wide Dynamic Range of Input Power for Energy Harvesting

Abstract: In this letter, a compact high-efficiency broadband microwave rectifier with an extended range of input power is proposed for energy harvesting. In the proposed structure, a novel broadband impedance-matching network is employed to reach high radio frequency (RF) to dc conversion efficiency. The reduction in mismatching loss over a wide bandwidth and input power range is achieved by impedance transformation from three segments of microstrip lines, which leads to a compact design to realize broadband impedance matching. A theoretical analysis and simulations of the proposed rectifier are presented. For validation, a broadband rectifier operating between 2.1 and 3.3 GHz is implemented and tested. The proposed rectifier shows a bandwidth of 44.4% for efficiency over 70% at an input power of 14 dBm. The measured efficiency remains above 50% from 2 to 3.3 GHz with an input power from 4 to 16 dBm. Moreover, the proposed rectifier has a compact size of 31 mm $\times18$ mm.

An Efficient Hybrid Sampling Method for Neural Network-Based Microwave Component Modeling and Optimization

Abstract: In this letter, we propose an efficient hybrid sampling method for microwave component modeling and optimization. The sampling method adaptively chooses samples from global and local samples to form a data set. The local samples are obtained using a greedy-like sampling method to exploit potential optimal solutions. The global samples are chosen using random sampling with minimum distance rejection to ensure the uniformity of the samples in the design space. The obtained data set is used to establish a surrogate model using the artificial neural networks (ANNs), and the optimal design parameters are obtained by optimizing the ANN model. A bandstop microstrip filter is taken as an example to verify the performance of the sampling method. The results show that the ANN model based on the proposed method achieves better modeling performance and yields better optimal design than the ANN model based on conventional sampling methods.

Compact-Balanced BPF and Filtering Crossover With Intrinsic Common-Mode Suppression Using Single-Layered SIW Cavity

Abstract: In this letter, compact-balanced bandpass filter (BPF) and filtering crossover are proposed with intrinsic common-mode (CM) suppression by using a single-layered substrate-integrated waveguide (SIW) cavity. The SIW cavity with low profile is TEn0m mode resonator, which has only one nonzero electric field component. Hence, it is also a natural frequency selection device of the differential signal. Meanwhile, the CM signal cannot excite the cavity due to the characteristics of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). For the design of the balanced SIW BPF, the differential-mode (DM) equivalent half circuit is a single-ended SIW filter with height halved. Furthermore, the microstrip differential transition structure is designed to excite the SIW cavity and has little conversion between DM and CM. On this basis, a compact SIW-balanced filtering crossover is proposed using the degenerate modes TE102 and TE201. Finally, compact third-order SIW-balanced BPF and filtering crossover are designed and fabricated, and the measured results show good agreement with the simulated ones.

Compact and Wide Stopband Substrate Integrated Waveguide Bandpass Filter Using Mixed Quarter- and One-Eighth Modes Cavities

Abstract: This letter presents the design of mixed quarter- and one-eighth modes substrate integrated waveguide (SIW) bandpass filter (BPF). The transmission zeros (TZs) of the proposed SIW BPF can provide wide stopband response and high selectivity characteristics by using different mode SIW cavities. For validation, two- and three-stage SIW BPFs with Chebyshev response were designed at a center frequency ( $f_{0}$ ) of 8 GHz. The measured results are consistent with the simulations. For two-stage BPF, the insertion loss smaller than 0.9 dB is measured within the passband of 0.65 GHz (7.75–8.4 GHz). The return loss higher than 19.7 dB is measured within the same passband. The spurious is produced at around 18 GHz ( $ ). The stopbands are attenuated more than 17.31 dB from the dc to 5.68 GHz ( $0.71f_{0}$ ) and from 9.28 GHz ( $1.16f_{0}$ ) to 16.67 GHz ( $2.08f_{0}$ ). The TZs are produced at 10 GHz and around 18 GHz due to a small cross-coupling between source/load and the interaction of the higher resonant modes of cavities, respectively. For three-stage BPF, the $\vert S_{21}\vert $ and $\vert S_{11}\vert $ smaller than −1.3 dB and −18 dB are measured within the passband of 7.57–8.45 GHz fractional bandwidth (FBW = 11%), respectively. The TZs are produced at 1.102, 1.9, and $2.39f_{0}$ and provide higher selectivity and attenuation compared to two-stage BPF.

Holey Glide-Symmetric Filters for 5G at Millimeter-Wave Frequencies

Abstract: A fully metallic glide-symmetric waveguide filter with transmission in $Ka$ -band and attenuation at its second harmonic is proposed. The filter is low-loss and cost-effective for high frequencies, and it can be easily integrated with an antenna. Glide symmetry and the possibility of breaking this symmetry provide an additional degree of freedom for passband and stopband control. A new kind of 2-D glide symmetry, referred to as braided glide symmetry, is presented, showing an increased attenuation per unit cell.

An Ultrahigh Sensitivity Microwave Sensor for Microfluidic Applications

Abstract: This work shows an ultrahigh sensitivity microwave sensor for microfluidic applications. The proposed sensor is made of a microstrip line loaded with a complementary split-ring resonator (CSRR). The meander slot is adopted in the CSRR to achieve high field confinement and is therefore covered with a polydimethylsiloxane (PDMS) microfluidic channel to enable strong interaction between the field and the liquid sample. The complex permittivity of the liquid sample can be retrieved by the variations in the resonant frequency and peak attenuation. The proposed design requires a very small liquid volume of $\sim 0.5~\mu \text{L}$ while offering a high sensitivity. A prototype is fabricated and tested, with a good agreement achieved between the extracted values and the reference data.

A Compact Ka -Band 4-bit Phase Shifter With Low Group Delay Deviation

Abstract: This letter presents a compact $Ka$ -band 4-bit switch-type phase shifter with low group delay deviation (GDD) using 28-nm CMOS technology. A magnetically coupled all-pass network (APN) configuration is employed to achieve both equal and flat group delay characteristics versus frequency at each phase state. The measured rms phase error is 1.2°, and the gain error is 1.1 dB at 33 GHz. The average measured insertion loss is 12.8 dB at 33 GHz, and the input and output return losses are both lower than −10 dB from 29 to 37 GHz. The fabricated phase shifter has a compact size of 0.08 mm2 excluding pads, low GDD of ±4 ps, and rms group delay error of $Ka$ -band phase shifter has the lowest GDD per bandwidth (GDD/BW) compared with other reported passive phase shifters.

Attention-Based Deep Neural Network Behavioral Model for Wideband Wireless Power Amplifiers

Abstract: The behavior models based on artificial neural networks (ANNs) have been widely used in the wideband power amplifier (PA). However, the selected terms of the input signal significantly affect the complexity of the ANNs. In this letter, a method using an attention-based deep neural network (DNN) is proposed to reduce the number of selected input terms for PA modeling. This method first selects the input terms with large contributions to PA modeling offline using the DNN with an attention mechanism. Then, the selected input items are injected into the DNN to build the PA model online. Experimental results show that the proposed method requiring only 1/3 of the input items can achieve good modeling performance with low complexity.

Single-Layer Dual-Band Balanced Substrate- Integrated Waveguide Filtering Power Divider for 5G Millimeter-Wave Applications

Abstract: A single-layer substrate-integrated waveguide (SIW) filtering power divider (FPD) with fully differential operation at 28 and 39 GHz is proposed in this letter. This FPD consists of three SIW cavities where the differential and common modes of each cavity were properly designed to form three-pole dual passbands, facilitate deployment of isolation resistors, and introduce transmission zeros while attaining high in-band common-mode rejection. To improve the output return loss and isolation in dual bands, a novel and simple approach to find the proper location of isolation resistors is presented. At operating frequencies, the measured differential-mode input or output return loss, minimum insertion loss, isolation, and common-mode suppression are >14.1 dB, 14.9 dB, and >30.3 dB, respectively. The amplitude and phase imbalances between outputs are < 0.48 dB and <4.2°, respectively.

Wideband Tunable Modified Split Ring Resonator Structure Using Liquid Metal and 3-D Printing

Abstract: Microwave split ring resonators (SRRs) are limited in modern designs to give a fixed resonant response based on their dimensions and material makeup. By designing an adjustable liquid metal component integrated in a highly coupled modified SRR, a frequency-tunable resonator structure was developed. The liquid metal integrated resonators were simulated to show that by varying the amount of liquid metal introduced to the system, the resonant frequency was continuously adjusted from 3.4 to 2.3 GHz, with a consistent resonant amplitude and quality factor of −22 dB and 75, respectively. The frequency-configurable sensor was fabricated with simple 3-D printing methods and inexpensive materials to control the liquid metal, resulting in a compact device with frequency tunability from 3.4 to 2.35 GHz. The fabricated resonator sensor had a resonant amplitude and quality factor of −24 dB and 70, respectively – with less than 10% variation along the entire frequency tuning process. Experimental analysis of the sensor showed continuous variation as the volume of liquid metal was increased within the straight channel, with a consistent resonant frequency sensitivity to liquid metal of 375 MHz/cm. The device enables measurement of a microwave frequency spectrum with user-desired resolution.

An Optimization Algorithm in Ultrawideband Bandpass Wilkinson Power Divider for Controllable Equal-Ripple Level

Abstract: In this letter, an ultrawideband (UWB) bandpass Wilkinson power divider (WPD) is introduced. By using filter synthesis theory and proposed optimization algorithm, all the S-parameters (S 11 , S 21 = S 31 , S 22 = S 33 and S 32 ) of the proposed topology could provide an equal-ripple response, and their equal-ripple level and bandwidth can be controlled, respectively. For verification purposes, a prototype UWB WPD has been simulated, fabricated, and measured. The measured and simulated results are matched reasonably well.

Ka-Band Coplanar Magic-T Based on Gap Waveguide Technology

Abstract: A coplanar Magic-T is proposed based on a combination of ridge and E -plane groove gap waveguides for Ka-band applications. All four ports of the proposed Magic-T are coplanar. The impedance bandwidth of the proposed Magic-T is about 43% covering the whole Ka-band from 26 to 40 GHz. The Magic-T isolation is better than 40 dB in the whole bandwidth while its insertion loss is about 0.25 dB.

Design of a Broadband High-Efficiency Hybrid Class-EFJ Power Amplifier

Abstract: This letter proposes a novel broadband, high-efficiency power amplifier (PA). The high-efficiency characteristics of Class-EF PAs and the large bandwidth advantages of Class-J PAs are effectively combined in the proposed PA. By theoretically analyzing the impedances of traditional Class-EF PAs and class-J PAs, we can consider the possibility of combining these two types of PAs. The conditions that need to be met are derived. In order to verify the effectiveness of the proposed method, a high-efficiency wideband Class-EFJ PA is designed and fabricated by using CGH40010F GaN HEMT. The measurement results demonstrate that the Class-EFJ PA has saturated output power of 40.5–42.7 dBm in 1.2–3.6 GHz. Drain efficiency of 63%–73% was achieved over the same frequency band. The Adjacent Channel Leakage Ratio (ACLR) was also better than −31.2 dBc at an average output power of 35.6 dBm.

A CSRR-Loaded Planar Sensor for Simultaneously Measuring Permittivity and Permeability

Abstract: This letter proposes a microwave planar sensor for the characterization of magnetodielectric materials. The sensor is designed by loading microstrip lines with complementary split-ring resonators (CSRRs). Two patches are connected to the microstrip lines to couple with the CSRRs, and a pair of 50- $\Omega $ resistors are in series with the lines to provide a notch. The designed sensor can extract the permittivity and permeability of the magnetodielectric materials simultaneously. A prototype of the designed sensor is fabricated and measured for validation of characterizing the magnetodielectric materials.

A Temperature-Compensated High-Resolution Microwave Sensor Using Artificial Neural Network

Abstract: In this study, a loss-compensated microwave (MW) planar sensor is used to characterize fluids at ~1 GHz. The environmental temperature is shown to adversely impact the recorded resonance frequency of the MW sensor, leading to data mixing. This issue is resolved using a feedforward artificial neural network with two hidden layers. Various concentrations of methanol in water (0%-100% with 10% increments) are measured at temperatures ranging between 22 °C and 60 °C. This smart sensor system exhibits a strong ability to discriminate the correct data regardless of erroneous interfering factors up to 92%.

Design and Evaluation of a Compact Harmonic Transponder for Insect Tracking

Abstract: Passive harmonic transponders are used in applications where weight and size restrictions are prohibitive to the use of active radio transmitters, e.g., for insect tracking. A typical harmonic transponder tag consists of a wire dipole antenna and a Schottky diode with a parallel inductance. Despite the simplicity in tag circuit, designing lightweight, compact, and efficient harmonic tags are challenging. In this letter, we describe a design that combines the reliability of a printed circuit with the simplicity and small mass of a wire dipole antenna. We study the interplay of individual system parameters and show that optimizing the tag antenna together with the tuning inductance provides further opportunities for tag miniaturization.

Broadband RF-to-DC Rectifier With Uncomplicated Matching Network

Abstract: A novel broadband RF-to-DC rectifier using an uncomplicated matching approach is proposed and tested. The proposed rectifier is based on a voltage doubler-type configuration and broadband matching is achieved by simply adding two inductors in series with each of the diodes, canceling out the large capacitance inherent in the diodes as well as producing resonances over a wide bandwidth. This uncomplicated matching network allows for a smaller circuit footprint while providing a wide bandwidth. The proposed rectifier is validated via simulation and measurement. The results demonstrate that a rectification efficiency of more than 50% is maintained over a bandwidth of approximately 83% (0.54–1.3 GHz) at 5-dBm input power, with the maximum rectification efficiency of 80% at 10-dBm input power.

Inverse Modeling for Filters Using a Regularized Deep Neural Network Approach

Abstract: Extracting coupling matrix from given ${S}$ -parameters can be viewed as an inverse problem for microwave filters, which is of importance for filter design and tuning. In this letter, a regularized deep belief network (R-DBN) is proposed to handle this inverse modeling problem. The training of an R-DBN consists of two steps. First, in unsupervised training, to accommodate the characteristics of input data, this model is constructed with a series of traditional restricted Boltzmann machines (RBMs), which are equipped with a continuous version of transfer function for continuous data processing. In addition, this training can provide suitable weights and bias for the following step. Second, in supervised training, Bayesian regularization is employed to increase modeling ability and prevent overfitting. Two experiments with different simulation environments are illustrated, and the calibration results show high accuracy and robustness in a more intelligent way using this method.

Differential Microwave Resonator Sensor Reveals Glucose-Dependent Growth Profile of E. coli on Solid Agar

Abstract: This letter presents a practical application of a differential microstrip microwave sensor for label-free and real-time monitoring of Escherichia coli ( E. coli ) growth under different nutritional conditions on solid agar media. Two planar microstrip ring resonators coupled with a one-port power divider form the core of the sensing system. The sensing resonator operates at 1.509 GHz with an amplitude of −10.21 dB and the reference resonator operates at 1.798 GHz with an amplitude of −11.75 dB. The growth profile of E. coli at each glucose concentration in Luria-Bertani (LB) agar was derived by measuring the resonant amplitude variations ( $\Delta {A}$ ) and is further supported by microscopic images. A complete inhibition of growth was observed at 10% glucose concentration. This research expands the application of microwave sensors to investigate the effect of nutritional parameters on bacterial growth.

Modeling of Mutual Inductance Between Two Misalignment Planar Coils in Wireless Power Transfer

Abstract: Mutual inductance is an important parameter for the design and optimization of the wireless power transfer (WPT) system. In this letter, a compact analytical model for mutual inductance of two coupled planar coil is proposed. The model is derived from Neumann’s integral of constant current-carrying filament with a Taylor expansion approach. It can predict mutual inductance at various lateral and angular misalignments. The analytical results show a good agreement with the 3-D electromagnetic simulation results, and the maximum error for the mutual inductance remains less than 15.1%. An experimental setup has been built, and the results reveal the proposed model can predict the mutual coupling rapidly and effectively.

Neural-Network-Based Digital Predistortion for Active Antenna Arrays Under Load Modulation

Abstract: In this letter, we propose an efficient solution to linearize mmWave active antenna array transmitters that suffer from beam-dependent load modulation. We consider a dense neural network that is capable of modeling the correlation between the nonlinear distortion characteristics among different beams. This allows providing consistently good linearization regardless of the beamforming direction, thus avoiding the necessity of executing continuous digital predistortion parameter learning. The proposed solution is validated, conforming to 5G new radio transmit signal quality requirements, with extensive over-the-air RF measurements utilizing a state-of-the-art 64-element active antenna array operating at 28-GHz carrier frequency.

A Broadband High-Efficiency RF Rectifier for Ambient RF Energy Harvesting

Abstract: In this letter, a compact broadband high-efficiency RF rectifier is presented for ambient RF energy harvesting (EH). A novel impedance matching network with an additional quarter-wavelength short-circuited stub was designed to achieve broadband impedance matching. After the branch was added, the parallel resonance point on track $S_{11}$ did not move, and the remaining points were compressed. The measurement results show that the proposed topology could realize a broadband high-efficiency rectifier for ambient RF EH, and the measured results were basically consistent with the simulation results. The measured efficiency is as high as 71.5% for an input power level of 8 dBm. A 1–2.4 GHz wide frequency band with an efficiency above 50% is achieved for an input power level of 5 dBm with a terminal load of 1.6 $\text{k}\Omega $ . Moreover, the circuit had wide dynamic input power characteristics, whose measured values remained above 50% with an input power of 3–14 dBm.

A Compact Frequency-Reconfigurable Rat-Race Coupler

Abstract: A compact rat-race coupler with tunable frequency is presented. The frequency-reconfigurable operation is achieved by attaching the frequency-reconfigurable matching network (MN) to each port of the four-port network. The MN composed of a shunt tunable capacitor transforms the port equivalent impedance of the four-port network to the port impedance across the entire frequency-tuning range. Closed-form design equations are derived. For demonstration, a compact frequency-reconfigurable 3-dB rat-race coupler is designed and measured. The measured results agree well with simulated ones. The measured frequency tuning range is from 1.0 to 2.96 GHz, with the >20-dB return loss and >35 dB isolation. As compared with state of the arts, the proposed coupler exhibits wide frequency tuning range with smaller size and fewer tuning elements.

A Wide Dynamic Range Rectifier Array Based on Automatic Input Power Distribution Technique

Abstract: In this letter, a microwave rectifier array using an automatic input power distribution technique (AIPDT) is proposed to achieve high conversion efficiency over a wide dynamic input power range. The rectifier array employs two rectifier cells operating at low- and high-power levels, respectively, and utilizes AIPDT to distribute the RF input power between them according to the input power level. In this way, a high RF-dc power conversion efficiency (PCE) and a low reflection coefficient over a wide input power range are achieved. For validation, the proposed rectifier array at 2.4 GHz was designed, fabricated, and characterized. The experimental results show that the PCE maintains over 50% when the input power ranges from 2.2 to 26.5 dBm, and the input power range for PCE >30% is from −7 to 30 dBm. Besides, the reflection coefficient remains less than −10 dB over a 40-dB dynamic range (−10 to 30 dBm).

Wide-Angle Impedance Matching Using Glide-Symmetric Metasurfaces

Abstract: This letter demonstrates that glide symmetry can be used to match the impedance of highly dense dielectric profiles in wide angle and broad bandwidth. Using glide-symmetric metasurfaces permits tuning the magnetic properties of materials, so high values of permittivity can be matched to free space in wideband. This matching is achieved without disturbing the performance of the device, since the refractive index remains fixed. The performance of the proposed matching method is validated through measurements for normal incidence. For oblique incidence, a hyperbolic dielectric lens is matched with glide-symmetric structures in simulations. These simulations demonstrate a smooth transmission of the fields, manifesting a well-matched profile of the lens.

A Voltage-Controlled Ring Oscillator With VCO-Gain Variation Compensation

Abstract: A voltage-controlled oscillator (VCO) with VCO-gain ( $K_{\mathrm {VCO}}$ ) variation compensation is proposed to reduce $K_{\mathrm {VCO}}$ variation in a current-mode logic (CML) ring oscillator by introducing a cross-coupled pair with capacitive degeneration that mitigates the nonlinearity of $K_{\mathrm {VCO}}$ . Designed and fabricated in a standard 0.18- $\mu \text{m}$ CMOS process, the proposed VCO can be tuned from 1.78 to 2.53 GHz, with the VCO gain variation less than 14.01%, while occupying a core area of $0.185\times0.081$ mm2 and consuming 20 mA including the bias circuitry, from a 1.8-V supply voltage. The phase noise is measured to be −92.68 dBc/Hz at 1 MHz offset and −114.97 dBc/Hz at 10 MHz offset from the high-band carrier frequency, respectively.

A 27-42-GHz low phase error 5-Bit passive phase shifter in 65-nm CMOS technology

Abstract: A 27-42-GHz 5-bit passive switching phase shifter is presented using 65-nm CMOS technology for the fifth generation (5G) applications. In the 180° phase shift bit, a reflection-type-based biphase modulator topology is developed to achieve good phase shifting performance over a wide bandwidth. The measured insertion loss (IL) of all 32 states is 12.4 ± 1.2 dB at 39 GHz and 11.4 ± 2.3 dB at 28 GHz with zero dc power. The phase shifter demonstrates an ultralow root mean square (rms) phase error of 0.7° and a low rms amplitude error of 0.8 dB at 37 GHz with an inherent digital phase-control mechanism. The rms phase error is less than 3.8° and the rms amplitude error is less than 2.1 dB from 27 to 42 GHz.

A Broadband and High-Efficiency Compact Transition From Microstrip Line to Spoof Surface Plasmon Polaritons

Abstract: Spoof surface plasmon polaritons (SSPPs) have been considered as a new-type surface wave transmission line (TL) because of its single line feature. However, it cannot be directly fed by the measured system because the transmission mode of SSPP TLs is totally different from the traditional TLs like microstrip lines. Also, the existing solutions require complicated structures and a big area on the circuit space to complete the transition between the two different propagation modes. Here, we propose an ultracompact and simple transition from the microstrip line to the SSPP single-conductor TL, consisting of a very short section of gradient corrugations and a specially designed flaring ground etched on the bottom side of the SSPP TL. Numerical simulations show a good agreement with the experimental results, showing high transmission efficiency for the proposed transition in a broad relative bandwidth from 4.5 to 11.5 GHz. Moreover, this SSPP feeding prototype is easy to migrate to other single-conductor SSPP devices.