Input Admittance Research Articles

Design and Implementation of a Printed Circuit Model for a Wideband Circularly Polarized Bow-Tie Antenna

A crossed bow-tie antenna design for S- and C-Band (2.44–7.62 GHz) with a peak gain of 7.29 dBi is presented to achieve wideband radiation efficiency greater than 90% and circular polarization with a single feed point. The polarization of the antenna is modeled by the input admittance of crossed bow-ties, and the model predictions are validated by experiments. A wideband matching network is designed to be tightly integrated with the antenna and produce a 103% impedance bandwidth. The matching network is decomposed into an equivalent circuit model, and an analysis is presented to demonstrate the principles of the matching network design. A prototype of the optimized antenna design is fabricated and measured to validate the analysis.

Admittance stability model and equivalent circuit analysis of three‐phase AC systems in different coordinate systems

AbstractIn recent years, with a large number of distributed energy sources connected to the grid, the distribution network has shown a clear trend towards the use of power electronics. As a power conversion interface, the stability of the converter's interaction with the grid has received considerable attention. Adequate admittance (impedance) modeling of the three‐phase grid‐connected converter is a prerequisite for analyzing the stability and resonance characteristics of the grid‐connected system. Understanding the internal mechanisms and proposing effective solutions are crucial to enable power systems to effectively cope with the impact of power electronics. Therefore, by studying the admittance equivalence relationship and equivalent circuit of three‐phase AC systems in various coordinate systems, this paper focuses on solving the non‐uniqueness problem of impedance admittance modeling of three‐phase converter system. It is proposed that the input admittance of the three‐phase asymmetrical system in the dq and fb rotating coordinate systems is a 2‐order matrix and equivalent. The input admittance of the three‐phase unbalanced system in the αβ and “12” static coordinate systems is a 4‐order matrix and equivalent. From both theoretical analysis and simulation verification, it is shown that the number of eigenvalues of the three‐phase asymmetrical system in the stationary coordinate system is twice that in the rotating coordinate system, and the overall damping of the system is improved. The control strategy based on the stationary coordinate system will make the system more stable. The second contribution of this paper is to establish the equivalent circuit of the three‐phase symmetric converter system by the node admittance matrix and extend it to the multi‐machine system to explain the system instability mechanism by the circuit resonance mechanism. Finally, the frequency coupling phenomenon is studied for the three‐phase asymmetrical converter system, and it is explained that it cannot establish an equivalent circuit similar to the three‐phase symmetrical converter system.

A super-compact wideband bandpass filter using capacitor-loaded coupled lines

Abstract A wideband bandpass filter (BPF) using capacitor-loaded coupled lines is proposed with super-compact circuit size and very simple structure. By loading three lumped capacitors in parallel to three same pairs of coupled lines, three transmission poles and four transmission zeros can be achieved and they can be calculated by input admittance derivation. To verify the design, a wideband BPF prototype with center frequency at 1.34 GHz is fabricated, whose measured 3-dB fractional bandwidth is 98.5 % (0.68–2 GHz), in-band insertion loss is less than 0.5 dB, return loss is greater than 17.5 dB, and circuit size is only 0.24 λ g × 0.02 λ g (λ g: guided wavelength at the center frequency).

Corrections to “Input Admittance, Directivity, and Quality Factor of Biconical Antenna of Arbitrary Cone Angle”

Corrections to “Input Admittance, Directivity, and Quality Factor of Biconical Antenna of Arbitrary Cone Angle”

Transmission line bandpass filters with multiple attenuation poles and small number of resonators

This article considers an alternative way to generate attenuation poles (AP) in bandpass filter (BPF) with parallel type resonators and admittance inverters. It consists in using special transmission line resonators, in which one or two antiresonant frequencies ωp1, ωp2 are placed next to the main resonant frequency ω0. These frequencies ωp1, ωp2 are the poles of the input admittance Y(jω). Four new resonators are synthesized in the article. Two resonators generate one AP, and other two resonators generate two APs located near the passband of the BPFs. If we use mixed couplings between proposed adjacent resonators in BPF, then the total number of APs will become quite large. This is because each mixed coupling adds one AP. N-order BPF without cross coupling can has (3 N – 1) APs. The increased number of APs improves the BPF selectivity, including the one-sided one. With APs, the filter can provide increased attenuation in certain frequency bands and effectively suppress unwanted signals. A microstrip second order BPF with center frequency f0 = 1 GHz and bandwidth BW = 70 MHz, which has five APs, is designed. It is compared with third order BPFs with two APs.

A new tunable bandstop filter square-ring resonator using varactor diodes.

This work presents the development of a bandstop filter with a tunable response. Varactor diodes are used as control elements. Studies and investigations demonstrate the influence of the variable capacitance on the input admittance and on the S-parameters frequency responses of the proposed square-ring resonator geometry. The design of the square-ring resonator is based on mathematical modeling of ideal transmission lines, considering parameters of characteristic admittance and electrical length for odd and even excitation modes. Based on S-parameters in ports, an equivalent circuit model of the resonator geometry is presented. The corresponding results are compared with numerical simulations. Comparative analyses are presented in order to guide the process of optimizing the physical dimensions of the layout. A prototype with dimension 0.0272 [Formula: see text] was designed, fabricated, and tested. As a measured result, a filter with two rejection bands was obtained, the first at 0.6-1.15 GHz and the second at 1.71-2.28 GHz, with 63.0 and 29.0% tuning range, respectively. In comparison with bandstop filters from the literature, the proposed reconfigurable filter presents a larger tuning range for the first band, sufficient inband rejection levels for several applications, and reduced physical dimensions. The proposed configuration is an attractive reconfigurable filtering device for use in modern communication systems operating below 3.0 GHz.

Virtual Admittance Feedforward Compensation and Phase Correction for Average-Current-Mode-Controlled Totem-Pole PFC Converters

This paper explores a current distortion problem in totem-pole bridgeless power factor correction (PFC) converters with average current mode (ACM) control. With in-depth modeling for the current and voltage loops, it was found that the current distortion is caused by the limited current loop bandwidth and input filter capacitor. These factors lead to the presence of a susceptance component in the input admittance, which degrades the power factor (PF) and total harmonic distortion (THD) of the PFC converter. To solve this problem, this paper proposes virtual admittance feedforward compensation (VAFC) and phase correction methods to adjust the input admittance to pure conductance. The VAFC can generate virtual admittance that compensates for susceptance components in the input admittance, while phase correction can generate an equivalent current source that offsets the current in input capacitors. Furthermore, a phase lock loop (PLL) is introduced to realize the VAFC, which reduces the feedforward interference caused by input voltage sampling noise. Finally, an experimental prototype was built to verify the effectiveness of the proposed strategies. According to the test results, the proposed compensation strategy improves the PF by 1.23%, while reducing the THD by 2.52% and achieving a peak efficiency of 98.69%.

Ultra-broadband absorber based on multilayered graphene

We propose an absorber with ultra-broadband and independent polarization. The bandwidth of the absorber is widened by increasing the number of layers of patterned graphene and also decreased the sensitivity of structure on incident wave polarization. Full wave simulation is demonstrated from 5 GHz to 197 GHz (extraordinary relative bandwidth 190%) the absorption is obtained above 90%. The equivalent circuit model is used for obtaining the input admittance of the proposed absorber. By adjusting the input admittance in a wide frequency range, matching is obtained. The destructive interference and multiple resonances approach is used in designing the absorber. The polarization effect of incident waves on absorption and bandwidth is studied. The parametric study is accomplished by analyzing the absorber’s performance and optimizing the structure.

Circuit Modeling and Parameter Extracting of a Filtering Series-Fed Antenna

This article presents a new method to model and extracts the equivalent circuit of a filtering series-fed antenna. The series-fed antenna usually suffers from spurious mode radiation excited by its long feeding line. The radiation strongly interferes with the antenna performance at the adjacent operating frequency bands. The filtering antenna technique is a potential method to solve this problem. However, there are rare reports about how to characterize a filtering series-fed antenna using the circuit model. To address this issue, a kind of series-fed antenna is investigated in this work. The antenna resonance characteristic is analyzed, and its equivalent circuit is constructed accordingly. By using the circuit transformation method and mathematical proof of this circuit, the series-fed antenna is proven to be equivalent to a second-order bandpass filter circuit. Then, as the antenna input admittance is approximated by the polynomials, the extraction method can be used to calculate the filter parameters. With these extracted filter parameters, the filtering series-fed antenna can be easily designed. Moreover, a notch circuit is introduced to further suppress the spurious mode radiations. For demonstration, a filtering series-fed array antenna with three elements is designed at the V2X band. The simulation and measurement results validate the proposed filtering circuit model and extraction method.

Impedance-Based Aggregation of Paralleled Power Factor Correction Converters in Data Centers

Existing aggregation methods for large-scale data center power systems often overlook disparities in power supply units, leading to reduced accuracy in the small signal dynamics of aggregated model. To fill this gap, this article develops an impedance-based aggregation method for paralleled power factor correction (PFC) converters with heterogeneities in power levels, conduction modes, and line impedances. The closed-loop input admittances of PFC converters operating in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) are presented first. The parametric scaling is then derived to aggregate multiple PFC converters at different power levels and operation modes, including the CCM, DCM, and mixed conduction mode, at the rack level. Furthermore, the aggregation rule and criteria for paralleled PFC converters with unequal line impedances is developed to provide a reduced-order dynamic model for adjacent server racks. The proposed parameter scaling and aggregation method allow efficient interaction analysis and stability assessment for data center power systems. The accuracy and robustness of the impedance-based aggregation are finally validated by simulations and experimental tests.

Low-Frequency Passivity-Based Analysis and Damping of Power-Synchronization Controlled Grid-Forming Inverter

This article presents a passivity-based analysis and damping method for the low-frequency dynamics of grid-forming (GFM) control. A closed-form analytical solution to the positive realness of control input admittance is developed, which reveals the inherent nonpassive property of GFM control. This feature gives rise to the risk of instability, especially in connection with a nearby nonpassive GFM inverter, which may induce undesired control interactions. It is further revealed that the passivity index is determined by a low-frequency resonance around 10 Hz in the dq -frame, and this resonance can be better dampened, therefore, with enhanced passivity index, by using a virtual reactance (VRA) than using a virtual resistance (VRS). Finally, the theoretical findings are verified by the experimental results.

Experimental demonstration of a spatiotemporally modulated sound diffusing metasurfaces

Spatiotemporal modulation of material properties has been studied across physics in an effort to control propagating waves. Using a semi-analytical approach, we have recently shown that the performance of a conventional sound diffuser can be significantly improved through spatiotemporal modulation of its surface admittance [Kang et al., Appl. Phys. Lett. 121, 181703 (2022)]. The improved performance is a result of energy in scattered sound at the incident wave frequency plus and minus harmonics of the modulation frequency of the temporal modulation of the input admittance. The additional frequencies of reflected sound increase the diversity of propagating diffraction modes and therefore increased angular distribution of scattered energy. This work presents the design of a sound diffuser element to implement the spatiotemporal modulation. The rigid bottom of a straight-tube diffuser well is replaced by a piezo disc shunted by a negative impedance converter (NIC), in which a capacitance can be controlled by varying a resistor value in the NIC. We present impedance tube measurements that show the presence of modulation harmonics in the reflected wave for single-frequency incident wave caused by a modulation of an acoustic admittance, and the diffusion performance measured in the anechoic chamber is compared with the non-modulated case.

Comparative Study of Three SAW Configurations for Temperature Sensing

This paper demonstrates three SAW configurations' electrical and mechanical behaviors: a one-port resonator, a two-port resonator, and a delay line that works as temperature sensors of around 440 MHz characteristic frequencies. We investigate the sensitivity of the sensors for temperatures up to 200 °C. A linear behavior of the frequency shift versus temperature is observed; the resulting sensitivity of the sensors is evaluated at 22.74 ppm/°C for the one-port resonator, 23.17 for the two-port resonator, and 3.83 ns/°C for the delay line structure. The electromechanical coupling coefficient (k2) is 0.492 % for the delay line, 0.489 % for the one-port resonator, and 0.55% for the two-port resonator. The quality factor QFactor calculated from Y11 electrical input admittance is 2858 for the one-port resonator, 2977 for the delay line, and 2903 for the two-port resonator. The optimized piezoelectric layer thickness value, for the one port resonator, is hAlN=1.5µm.

Investigation of resonant tank topologies performance in wireless power transfer applications

ABSTRACT Wireless power transfer (WPT) has been developed as a suitable candidate for energy transfer in various applications, recently. Resonant tank is the main passive part of such systems and various topologies are introduced to improve WPT systems performance. Characteristics of these topologies definitely affect system overall performance. Therefore, each topology’s specification and performance indexes should be evaluated and compared to choose a suitable one for a required application. In this paper, the characteristics and behaviour of voltage gain, input admittance and efficiency of well-known compensation topologies are thoroughly investigated for the first time. By calculating the voltage gain sensitivity, some analysis are performed on typical compensation including SS, SP, LCL-S, LCL-P, LCC-S, LCC-P and double-sided LCC under key parameter variations such as load resistance, switching frequency and coupling coefficient. In addition, by introducing a new formula for efficiency, the effect of resonant tank elements on efficiency is studied analytically which has not been performed before. In order to evaluate the theoretical analysis, the performance of all compensation topologies is investigated in MATLAB environment. By employing prototype SS and SP compensated inductive power transfer (IPT) test-bed system, some experimental verification are performed and the results confirm the analytical and numerical simulation findings.

2D scalar wave modelling of apodized RF BAW resonators for transverse mode analysis

This paper proposes the use of a two-dimensional scalar wave model for fast analysis of apodized AlN-based radio frequency bulk acoustic wave devices. First, the working principle and model setup is introduced. Only one particular Lamb mode (S1−) is considered, and its behavior is modeled by a simple scalar wave equation looking from the top surface. Multiple layers are added to the side boundaries so that mode conversion to other modes is treated as leakage to surroundings. The wavenumber of field distribution for each resonance mode is calculated, and then its excitation coefficient, quality factor, and resonance frequency are derived. The device input admittance is calculated by applying derived parameters to the equivalent circuit. A series of oval-shaped AlN-based film bulk acoustic resonator devices are simulated and compared with experimental results. The theoretical results agreed well with the experimental ones, and accuracy and effectiveness of the present analysis are verified.

Q Factor-Based Electrically Small Antenna Radiation Efficiency Measurement Using the Wheeler Cap

In this letter, a small antenna radiation efficiency measurement method is presented. The method utilizes the antenna quality factor, where it is a modification of the original Q factor method, amended by the loss Q factor of the antenna instead of the radiation Q factor. The method is verified for two kinds of antennas: the first is designed to operate at 868 MHz having a series resonance input impedance, and a second at 433 MHz having a parallel resonance input impedance. The method shows very high accuracy and prevent errors that may occur when using the conventional Wheeler cap method if the stored energy is not treated explicitly, which is considering the same imaginary part of the input impedance or input admittance for series resonance or parallel resonance, respectively.

The Power Transformer Winding Input Admittance and Frequency Response

The frequency response analysis is increasingly more widely used to estimate the electrical and mechanical condition of power transformer windings. The frequency response measurement procedure has been prescribed in the existing international and national standards. However, the interpretation of measurement results still remains a subject of discussion. Various approaches have been used to interpret the results, including an analysis of transformer windings’ complex impedances and admittances obtained by calculations from frequency responses. To improve the frequency response interpretation, the article presents an analysis of power transformer winding input and output currents and admittances based on simplified equivalent circuits. Qualitative and quantitative results are presented, which show that the admittances obtained from measured frequency responses differ essentially from the true input admittances of the windings. The main factors causing the differences between these winding admittances are considered. It is shown that despite the existing differences, the current through the neutral and the winding admittance determined from the measured frequency response can also be used in practice to determine the power transformer winding natural oscillation frequencies.

Accurate High-Frequency Modeling of the Input Admittance of PWM Grid-Connected VSCs

This article addresses high-frequency admittance modeling of current-controlled voltage source converters (VSCs). Recent studies have shown that harmonic instability may also occur at frequencies above the Nyquist frequency. To form an accurate multiple-frequency model in this frequency range, sidebands that originate from modulation and sampling must be examined. In this article, an accurate small-signal model is developed taking into account an adequate digital pulsewidth modulator (DPWM) representation, which allows to predict dependence of the frequency response on the steady-state dc (SS-dc) operating point. It is shown that when center-pulse sampling is implemented, pulsewidth modulation sidebands do not create additional loops leaving only sampling sidebands to be considered. Using the same approach as for SS-dc operation, a model that accurately represents admittance measurements during sinusoidal ac (S-ac) operation is developed. Its basis is a novel DPWM model suitable for S-ac regime, which allows to predict dependence of the VSC’s input admittance on the grid voltage magnitude. Experimental and simulated admittance measurements, performed on a single-phase two-level VSC during various SS-dc and S-ac regimes, match with the proposed models up to twice the sampling frequency.

A Multigap Loop Antenna With Phased Excitation in a Magnetoplasma

Electrodynamic characteristics of a multigap loop antenna immersed in a homogeneous magnetoplasma are studied using the integral equation method. The antenna has the form of a perfectly conducting, infinitesimally thin, narrow strip coiled into a ring with its axis parallel to an external static magnetic field. The antenna current is excited by appropriately phased external voltages applied across the gaps of the strip. A closed-form solution for the current distribution of the antenna is obtained, and the elements of its input admittance matrix are found. Based on this solution, conditions are determined under which such an antenna with phased excitation is capable of selectively exciting waves with given azimuthal indices in the surrounding magnetoplasma.

Filtering T-Type Switch With Flexible Signal Routing Reconfigurability for Crossover-/Adjacent-Channel Applications

In this letter, a filtering T-type switch is proposed for the first time, which exhibits signal routing reconfigurability for crossover-channel (State 1) and adjacent-channel (State 2 or 3) applications. The circuit consists of four T-shaped feeding lines, eight short-ended half-wavelength resonators, and a ring resonator. The p-i-n diodes are loaded to the resonators for switching ON and OFF the signal channels. When the diode is turned off, the channel is switched ON and intrinsic filtering responses are integrated by the coupled resonators. When the diode is turned on, the input admittance of the resonator is tuned to infinite for switching OFF the channel. In addition, the second harmonic is suppressed by the feeding structure. For verification, the circuit is implemented. The measured results exhibit good bandpass responses with high out-of-band suppression and high isolation in each state.