Frequency-dependent Inductor Research Articles

Computer‐aideddesign methodology for inductive compensated microwaveclass‐Epower amplifier

This article presents a simulation-based analysis to first evaluate the impact of excessive transistor output capacitance on class-E power amplifiers and to second show how inductive compensation can be used to recover optimum class-E operating conditions. As a starting point, the finite-feed inductor in a parallel-circuit topology is replaced by a frequency-dependent inductor, which in turn can be substituted by a network composed of a series inductor and additional subharmonic resonators. This complex lumped-element network is then replaced by a generalized transmission line equivalent topology, suitable for microwaves. Calculation of the transmission line impedances and electrical lengths of the proposed generalized network is shown in detail and a design procedure for this modified class-E is provided. The analysis presented here is further extended by using a simplified large-signal model for the employed GaN HEMT device, which allows evaluating the effects of non-ideal switching as well as of capacitance voltage-dependency and feedback capacitance. The analysis is validated by simulation and design of a test board. Measurements of the test board showed a drain efficiency of 80.3%, power-added efficiency of 76.3% and output power of 40.1 dBm at 1.96 GHz, demonstrating the validity of the proposed approach.

Electrically Tunable Microwave Absorber Based on Discrete Plasma-Shells

This paper presents the feasibility of deploying a large-scale tunable absorber based on discrete plasma-shells. The proposed conductor-backed absorber is realized by integrating ceramic gas-encapsulating chambers (plasma-shells) and a closely coupled lossy resonant layer that also serves as a biasing electrode to sustain the plasma. Two topologies comprising lossy inductive or capacitive layers are investigated to realize tunable microwave absorbers. The plasma is sustained by a sinusoidal radio frequency (RF) voltage source coupled directly through the walls of the plasma-shells. These active frequency-selective absorbers are analyzed using a transmission line approach to provide the working principle and its frequency tuning capability. By varying the voltage of the sustainer, the plasma can be modeled as a lossy, variable, frequency-dependent inductor, providing a dynamic tuning response of the absorption spectral band. A prototype plasma-tuned absorber is fabricated and measured in a free space environment to validate the concept. A good agreement between the equivalent circuit model, full-wave electromagnetic simulation, and the measurement results is obtained.

Frequency-Dependent Resistance of Litz-Wire Square Solenoid Coils and Quality Factor Optimization for Wireless Power Transfer

In order to achieve the highest efficiency of wireless power transfer (WPT) systems, the quality factor of the resonant coil should be as high as possible. Due to the skin effect and the proximity effect, the coil resistance increases with the increase in the frequency. The highest quality factor exists for the optimal frequency together with the corresponding frequency-dependent inductor resistance. This paper employs the Biot–Savart law to calculate the magnetic field strength, which results in the proximity-effect resistance in single-layer litz-wire square solenoid coils without a magnetic core. A strand-number coefficient is introduced to reflect the influence of the strand number inside the wire bundle on the proximity-effect resistance. The coefficient is obtained through simple inductor resistance measurements for various numbers of litz-wire strands. The optimal frequency for the highest quality factor is derived based on the resistance evaluation. Several prototype coils were manufactured to verify the resistance analysis. Two $50\,\rm{cm}\times50\, {\rm cm}$ square coils were employed to construct a WPT prototype. The maximum dc–dc efficiency of this WPT was about 75% at 100-cm distance.

DESIGN AND INVESTIGATION OF BROADBAND MONOPOLE ANTENNA LOADED WITH NON-FOSTER CIRCUIT

The possibility of using non-Foster circuit to expand the bandwidth of a monopole antenna is investigated theoretically. Beginning with an inductor-loaded monopole antenna resonating at difierent frequencies by changing the value of the loaded inductor, we show that a frequency-dependent inductor is needed to enhance the bandwidth of the monopole antenna. The curve for the reactance of the frequency-dependent inductor versus frequency is fltted, which enlightens us to use a non-Foster reactive circuit to realize the frequency-dependent inductor. Based on the above studies, a monopole antenna loaded with a non-Foster circuit is presented. Simulated results demonstrate that the input reactance of the loaded antenna becomes stable and approaches zero, which favors the impedance matching and extends the bandwidth to a certain extent. Finally, a passive (Foster) matching circuit is designed to improve the bandwidth further. A 0.69-m monopole antenna with 2.0:1 VSWR in the frequency range 30{150MHz is designed and investigated.

A Monolithic CMOS 2368<tex>$pm$</tex>30 MHz Transformer Based<tex>$Q$</tex>-Enhanced Series-C Coupled Resonator Bandpass Filter

A three-pole 0.1 dB ripple Chebyshev series-C coupled resonator bandpass filter with transformer-based Q-enhancement is presented. This Q-enhancement technique compensates resonator loss and produces a flat passband response with low insertion loss. The compensation scheme uses frequency-dependent negative resistance to compensate frequency-dependent inductor losses, avoiding passband distortion, which is a problem with cross-coupled negative resistance circuits. Fabricated in 0.18 /spl mu/m CMOS, the measured filter center frequency is 2368 MHz with a 60 MHz (3 dB) bandwidth, including probe pad and connecting trace parasitic losses. The filter draws 5.84 mA at 1.5 V, and the die area is 1.5 mm/spl times/1.5 mm.

Lumped-element microstrip narrow bandpass tunable filter using varactor-loaded inductors

A model of tunable microwave narrowband lumped-element microstrip filters is developed, using varactor-loaded inductors to achieve frequency-dependent inductance. A bandwidth transformation technique is utilized, so that the bandwidth of the filters is determined by the inductance slope of frequency-dependent inductors dL/df. Large coupling capacitance with small element separations can still be applied to these tunable narrowband filters, hence maintaining their compactness. The centre frequency of the filters is tuned by varying the bias voltage of the varactors. The numerical results of a tunable 2-pole narrowband filter are presented. It has a bandwidth of 4 MHz with a tuning range of 90 MHz, from 0.92 GHz to 1.01 GHz, for a bias voltage from 0 V to 15 V, respectively. The varactor losses are also discussed and compared with experimental data.

Narrowband lumped-element microstrip filters using capacitively-loaded inductors

Coupling between microstrip resonators decreases very slowly as a function of the resonator separation. Therefore, it is difficult to realize narrowband filters (e.g., <0.1% fractional bandwidth) in reasonably sized microstrip form due to the very weak coupling values required. In this paper, we report a class of lumped-element filters that uses capacitively-loaded inductors to give frequency-dependent inductance values. A novel frequency transformation technique is used in the design process. Using this approach, filter bandwidth is determined by the inductance slope of frequency-dependent inductors, dL/d/spl omega/. Large coupling capacitance, thus small coupling element separations, can still be used in narrowband microstrip filters to keep the filter layout compact. We present a 5-pole, 0.27% bandwidth YBa/sub 2/Cu/sub 3/O/sub 7/ high-temperature superconducting thin film microstrip prototype filter at 900 MHz, which has 1.2 dB insertion loss and 20 dB return loss. It was designed with the coupling capacitors of a 1% bandwidth filter, and then transformed to a 0.27% fractional bandwidth using an appropriate inductance slope parameter, dL/d/spl omega/. Measurement showed good agreement with theory.