Fundamental Impedance Research Articles

A 50 W dual‐band high‐efficiency gallium nitride high electron mobility transistor power amplifier with three‐stage L‐type DC bias circuit at 1.8 and 2.6 GHz

AbstractA 50 W dual‐band high‐efficiency gallium nitride (GaN) high electron mobility transistor (HEMT) power amplifier with a three‐stage L‐type DC bias circuit capable of individually adjusting second‐harmonic impedances is proposed for 1.8 and 2.6 GHz frequencies. The output network of this power amplifier is composed of an output matching network comprising five‐stage transmission lines and a three‐stage L‐type DC bias circuit with three L‐type circuits and one transmission line. The one‐stage L‐type circuit comprises a series transmission line and a quarter‐wavelength open‐ended shunt stub. For the high‐efficiency performance of the power amplifier, the output matching network is matched to the optimum impedances of the fundamental frequencies, and the DC bias circuit optimizes the impedances individually at the second‐harmonic frequencies without affecting the matched fundamental frequency impedances in the output matching network. Measured results show that the proposed dual‐band GaN HEMT power amplifier achieved gains of 15.6 and 13.8 dB as well as maximum power‐added efficiencies of 70.5% and 66.3% with 47 dBm output power at 1.8 and 2.6 GHz, respectively.

Design of a C-Band High Efficiency Power Amplifier With Compact Harmonic Control Network

In this letter, the design of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$ </tex-math></inline-formula> -band high-efficiency power amplifier (PA) with a compact harmonic control network (HCN) is presented. Based on the device model, the optimal fundamental and second harmonic load impedance was obtained by load-pull simulation. Then a simply fundamental matching network (FMN) is realized using the simplified real frequency technique (SRFT). To improve efficiency, a compact HCN based on a predesigned FMN is proposed. Besides, the microstrip radial stub (MRS) is used instead of the microstrip open-circuited stub to reduce the loss. A high-efficiency PA working across 6.1–7.2 GHz is simulated and fabricated. Experimental results show that the fabricated PA delivers a saturated output power of 38.2–39.3 dBm with a drain efficiency (DE) of 43%–63.4% in the interested band.

Automatic Methodology for Wideband Power Amplifier Design

This letter presents an automatic power amplifier (PA) design methodology that uses a multidimensional search algorithm to find the best compromise between fundamental and harmonic impedance terminations for a specified bandwidth. In conventional design methodologies, PA designers need to preselect the optimum impedances, which normally follow non-Foster trajectories, and are thus impossible to achieve with passive matching networks (MNs) for a wide frequency range. Instead, the proposed automatic design method directly synthesizes the MNs to achieve the desired output power, efficiency, and gain performance, without forcing any impedance profiles. For that, load-pull data are interpolated using artificial neural networks and an algorithm based on the simplified real frequency technique is used to obtain the MNs. Finally, the method is validated with a single-ended PA implementation.

Design of bandwidth‐enhanced power amplifier based on class‐EF modes

AbstractThis article describes a methodology for designing broadband high‐efficiency GaN HEMT power amplifier (PA) which is suitable for base stations and modern wireless communication based on the Class‐EF mode. To achieve both efficiency enhancement and bandwidth extension for the PA, the load‐pull technique is employed to acquire the optimum impedance regions of the second harmonic. Especially, considering the influences of the harmonic control network on the accuracy of obtaining the fundamental impedance, the load‐pull technique is performed to obtain the optimal fundamental impedance again after the harmonic control circuit is determined. In addition, the theory of multiple frequencies matching is also employed to manipulate six desired fundamental frequency points concurrently. Based on the proposed theory, the Class‐EF PA prototype is designed and fabricated. The measurement results exhibits a drain efficiency (DE) of 60%–75% in the range of 2.1–3.6 GHz while having an output power of 38–40.5 dBm and gain of larger than 8 dB.

High-Efficiency Power Amplifier with a Multiharmonic Tuning Network

One high-efficiency power amplifier (PA) with a novel multiharmonic tuning (HT) network is presented. The second and third harmonic impedances are simultaneously controlled with a simple offset double-sided parallel strip line (DSPSL)-based output-matching network. Based on the above strategy, high PA efficiency can be achieved by mapping the fundamental and harmonic impedances to the optimum positions, while PA linearity can be improved through third harmonic suppression. The offset DSPSL is used to realize the transmission lines with extremely high impedance ratio in the multiharmonic trapping circuit. For demonstration, a PA using Cree CGH40010 GaN HEMT is designed with up to third harmonic control. The fabricated PA achieves peak power-added efficiency (PAE) and drain efficiency (DE) of 78.2% and 82.3%, respectively, while delivering 39.2-dBm output power at 1.8 GHz. Besides, the output third-order intercept point (OIP3) of the PA has an improvement of 3 dB.

Modified Class-F power amplifier design with fundamental frequency output impedance load

A modified Class-F power amplifier with medium output power at 433 MHz was designed, simulated and implemented in this paper. The design process used a load condition of 1) output impedance of the amplifier at the fundamental frequency, 2) short-circuit loads at the even harmonics and 3) open-circuit loads at the odd harmonics. By biasing the circuit to be a typical Class-F, the circuit yielded moderate efficiency as the load condition was different from the optimum one. By strongly biasing the circuit toward that of Class-A, the load condition approached the optimum, but the circuit still yielded moderate efficiency due to the low efficiency nature of a Class-A amplifier. By proper choice of the operating point in Class-AB, a prototype circuit, with 9 dBm input power, yielded a maximum PAE of 68.5% with output power 21.8 dBm. Furthermore, at 11 dBm input power, the prototype yielded a better PAE 79.6% with 23.2 dBm output power. Our design procedure did not need expensive load-pull equipment.

Design of a Dual-Band Power Amplifier Using a Simple Method

This letter presents a simple method to design dual-band high-efficiency power amplifiers (PAs). The dual-band coupler is exploited to design the output circuits of the PA. By proper selection of impedance conditions of terminal ports, the dual-band coupler can convert the fundamental impedance of transistor to the standard 50- $\Omega $ load at two frequencies. At the same time, the second harmonic impedance is also controlled without the need for additional tuning. For validation, a dual-band high-efficiency PA is designed and fabricated by using CGH40010F GaN HEMT. Measurements indicate that the designed PA can deliver saturated output power of 41.6 and 42.1 dBm at 1 and 2.3 GHz, respectively. Also, the obtained drain efficiency exceeds 72% at both frequencies.

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Unified analysis and output estimation for strong coupling contactless slipring system

Contactless slipring (CS) system utilizing inductive-power-transfer (IPT) technology is a good candidate for the traditional mechanical slipring assemblies. However, suffering from the high harmonic currents in strong coupling CS system, the output power will deviate from the theoretical values estimated by the fundamental harmonic approximation (FHA) and its extension method, i.e., E-FHA, in which the power are transferred by both the fundamental current and the high order harmonic currents. In order to achieve high precise output estimation, a unified analysis is proposed in this paper. Firstly, Fundamental-harmonic Double Resonance Phenomenon is revealed via impedance analysis, to address the nature of the high harmonic currents in strong coupling system. Then, a unified output current expression owning high precision is derived, followed by a unified fundamental load impedance. Discussions show that both the output and the fundamental load impedance of FHA, and E-FHA are all the special cases of the unified expressions proposed. FHA, and E-FHA are precise enough for the loose coupling system, whereas the proposed method is indispensable for the strong coupling system with k>0.4. Finally, simulations and experimental measurements of a 1.6kW CS system, as well as the comparative studies among FHA, E-FHA, and the proposed method, are presented, indicating that the proposed method are effective for high precise output estimation.

A Novel Suppression Method for Grounding Transformer Against Earth Current From Urban Rail Transit

Earth current generated by the operation of urban rail transit can enter into the neutral point of grounding transformer, which will result in the deterioration of transformer operation performance and cause electrical safety problems. In this article, the neutral current for 220 kV transformers has been measured in the real power system, the characteristics of dc and harmonic current are analyzed, and a novel suppression method for the dc and harmonic current simultaneously combining an active converter with a dc blocking capacitor is proposed, which solves not only the traditional dc bias problem but also the intrusion of the harmonic current from urban rail transit. The active converter is designed to compensate harmonic voltage to suppress harmonic current, and the capacitor provides blocking for the dc current. The protection scheme in case of the high fault current of the neutral point is presented. The improved control method is designed to control the neutral current and adjust the fundamental impedance for the requirements of relay protection. The effectiveness of the proposed method is verified by the digital simulations and the laboratory experiments based on the field working conditions, and the results demonstrate the satisfying performances.

A high‐efficiency design for 5‐W 2.4/5.8 GHz concurrent dual‐band class‐E power amplifier

AbstractIn this letter, a distributed element‐based load network is proposed for designing a high‐efficiency dual‐band (DB) 5‐W Class‐E power amplifier (PA), at two widely spaced frequencies of 2.4 and 5.8 GHz. This network consists of two different stages. The first stage deploys a flexible network configuration with crossed transmission lines (TLINs) to provide concurrent DB fundamental matching in a closed‐form derivation, which transforms the standard resistance of 50 Ω directly to the optimal complex impedances. By tolerating the combination of the up‐side and down‐side TLINs, the size of the overall circuit as well as the implementation complexity are reduced. The second stage uses a DB TLIN‐based resonator preceded by a series 50 Ω stub to control the harmonic impedances without altering the fundamental impedances, ensuring high efficiency at the fundamental frequencies. The measured prototype shows highest power added efficiency (PAE) of around 62.9% and 61.7% with output power of about 39 and 35 dBm at 2.45 and 5.76 GHz, respectively.

Beam gap transient analysis and mitigations in high-current storage rings for an electron-ion collider

The U.S. electron ion collider will utilize high current electron and ion storage rings with many bunches and large rf systems. Because of the dissimilarity of the two rings, the rf transients created by gaps or variations in the current distributions will be very different in the two rings. These transients cause a shift in the synchronous phase of the beams as a function of rf bucket position, can impact the luminosity through shifts in longitudinal position of the IP, will affect the performance of the rf and LLRF control loops, and may require significant rf power overhead to control. A machine design that uses superconducting crab cavities will also have sensitivity to gap transients and synchronous phase variations along the bunch train with variations in crab cavity voltage seen by each bunch, since the high $Q$ of the crab cavities precludes modulating them to compensate for the time of arrival shifts caused by the gap transients in the main rf systems. All these effects make the problem of managing gap transients crucial to the operation of the EIC. This work presents methods to study the dynamics of the rf and LLRF systems for these heavily beam loaded facilities. An illustrative machine design example is presented and used to investigate the expected magnitudes of the rf gap transients, and exploration of various possible remedies to match the gap transients in the two dissimilar EIC rings. In addition to the study of the power required and gap transients, this work also estimates longitudinal coupled-bunch instabilities due to the baseline cavity fundamental impedance. The work is motivated to emphasize the importance of tools and methods to estimate these effects as part of the early design phase of the Electron-Ion Collider or any high current storage ring design.

Accurate harmonic source identification using S-transform

This paper introduces the accurate identification of harmonic sources in the power distribution system using time-frequency distribution (TFD) analysis, which is S-transform. The S-transform is a very applicable method to represent signals parameters in time-frequency representation (TFR) such as TFR impedance ( Z TFR ) and the main advantages of S-transform it can provide better frequency resolution for low frequency components and also offers better time resolution for high-frequency components. The identification of multiple harmonic sources are based on the significant relationship of spectral impedances ( Z S ) that extracted from the Z TFR , consist of the fundamental impedance ( Z 1 ) and harmonic impedance ( Z h ). To verify the accuracy of the proposed method, MATLAB simulations carried out several unique cases on IEEE 4-bus test feeder cases. It is proven that the proposed method is superior, with 100% correct identification of harmonic source location. It is proven that the method is accurate, fast and cost-efficient to localize harmonic sources in the power distribution system.

Design of multioctave power amplifier using multi‐harmonic bilateral pull technique

AbstractIn this letter, the design, implementation and measurements of a multioctave bandwidth high‐efficiency GaN HEMT power amplifier (PA) based on a novel systematic design methodology are presented. To achieve bandwidth expansion while maintaining a high level of efficiency, the multi‐harmonic bilateral pull technique has been employed to acquire the optimum fundamental and second harmonic impedance regions. Especially, the impedance region of the second harmonic is analyzed to conclude that the second harmonic impedance can be expanded to a resistive‐reactive with complex load impedances. Therefore, multioctave bandwidth can be achieved by combining low‐pass lumped circuit (LC) matching network. For experimental verification, the wideband PA is achieved with a 10‐W GaN device. The measurement results manifest that the implemented PA has a drain efficiency (DE) of 54% to 71% and a saturated output power of 38.2 to 42.3 dBm for the entire intended frequency range between 0.5 to 3.1 GHz with a relative bandwidth of 144.4%, while providing a gain larger than 8.2 dB. Measurement results confirm the theoretical findings.

A novel independent harmonic tuned two‐port output network for efficiency enhanced RF power amplifiers

AbstractThis article introduces a simple two‐port harmonic tuned output network‐based design of RF Power Amplifiers. The proposed output network facilitates mutual independence between the fundamental, second, and third harmonic impedances, which thereby eases the tuning process. The proposed two‐port harmonic tuning network has been synthesized, fabricated, and measured separately to demonstrate the harmonic independence behavior. Thorough graphical and analytical deductions are provided for the design scheme. The proposed design strategy has been validated with a Cree 10 W GaN HEMT based fabricated prototype at 2.4 GHz. The measured results show an obtained drain efficiency up to 82.3% and a gain of &gt; 11.0 dB.

Fundamental grid impedance estimation using grid‐connected inverters: a comparison of two frequency‐based estimation techniques

With the continuous increase in distributed energy resources that are being integrated into the utility grid, it becomes necessary for inverters to estimate the grid impedance online to be used for several applications. Despite the fact that online grid impedance estimation techniques using grid-connected inverters gained more attention recently, no comprehensive study has been evaluating the performance of different estimation techniques under several grid conditions. This study proposes an extensive comparison to assess the accuracy of two online frequency-based grid impedance estimation techniques at the fundamental frequency. These two techniques are based on the 75 Hz frequency injection technique and pseudo-random binary sequence injection, respectively. Results from MATLAB/Simulink and PLECS RT Box present the advantages and disadvantages of these estimation techniques and the required trade-offs. This comparison study analyses the effects of disturbance magnitude and its injection time, the variation of grid impedance and non-ideal grid voltage. Furthermore, solutions are proposed to enhance the estimation accuracy of both techniques for non-ideal grid voltage containing inter-harmonics and sub-harmonics. The study concludes with recommendations regarding the best use of these two frequency-based grid impedance estimation techniques to suit a particular low voltage grid scenario.

A novel direct matching network synthesis technique and its application to broadbandclass‐Jpower amplifier

A novel direct matching network (MN) synthesis method improving the conventional simplified real frequency technique (SRFT) is presented in this article. By straightforwardly optimize the characteristic impedance (physical width) and electrical length (physical length) of each distributed element in a preselected configuration, the proposed method has one more degree of design freedom by comparison with the SRFT, and therefore increases design flexibility and matching effects. To demonstrate its effectiveness, a broadband class-J power amplifier (PA) is devised for which both the input and output MNs are realized using the proposed method. The simultaneous manipulation of fundamental and second harmonic impedances is successfully realized by defining a novel target function that indicates the degree of proximity for the realized impedances to the optimal transistor impedances. Comprehensive equations and complete design procedures of the new technique are given. The measured class-J PA implemented for verification achieves an output power of 39.2 to 42.3 dBm and power-added efficiency of 61.8% to 71.6% over the frequency range of 2.5 to 3.8 GHz using a 10-W GaN HEMT. A 20-MHz LTE-A signal is employed to validate the linearization capability of this class-J PA. An adjacent channel leakage ratio level around −43.8 dBc is achieved after utilizing digital predistortion technique.

Generalized Hybrid Continuous Mode for Designing Broadband Power Amplifiers

It has been widely validated that continuous working modes are powerful theories for designing broadband power amplifier (BPA). Theoretically, the conduction angle of all continuous-mode power amplifiers (PAs) is 180∘ (class-B-biased). However, in practice, these PAs are always biased in class-AB condition. Thus, continuous-mode PAs biased in class-AB condition should be researched. This paper generalizes the theory of hybrid continuous mode (HCM) for implementing broadband power amplifiers. The intrinsic drain current waveform of HCM biased above the pinch-off point (conduction angle is larger than 180∘) is first derived. Then, the impedance space of the generalized HCM (class-AB-biased) is explored and analyzed. The conclusion is that the generalized HCM possesses a shifted fundamental impedance space along with the enlargement of conduction angle. For validating the proposed theory, a broadband PA working over 1.6–3.0[Formula: see text]GHz is implemented. Experimental results indicate that the designed BPA achieves a saturation power of 40.3–42.7[Formula: see text]dBm and a drain efficiency of 64.3–74.4%.

Robust Power Sharing Control for Parallel Three-phase Inverters Against Voltage Measurement Errors

In islanded microgrids, distributed generations (DGs) have been increasingly employed through parallel voltage source inverters (VSIs). To fully utilize the VSI capacity and avoid overloading, the total load power is expected to be accurately shared among VSIs based on their power ratings. However, it is revealed that even small voltage measurement scaling errors may severely deteriorate the power sharing by injecting positive- and negative-sequence circulating currents. An explicit analysis indicates that this issue cannot be avoided if the conventional voltage-feedback control is adopted with an accurate fundamental voltage tracking ability. To solve this problem, a hybrid feedback and feedforward control is proposed, which makes the power sharing robust against voltage measurement errors. In specific, the feedforward control is utilized to enhance the unbalanced and reactive power sharing by reshaping the VSI fundamental output impedance. Meanwhile, the feedback-based impedance shaping control is also employed to improve the harmonic power sharing. As no communication and sensor error knowledge are required, the proposed control scheme provides a simple but effective solution for decentralized power sharing among parallel three-phase VSIs. Finally, both simulation and experimental results are provided for verification.

Co-Design of Second Harmonic-Tuned Power Amplifier and a Parallel-Coupled Stub Loaded Resonator

This brief presents a co-design of the second harmonic-tuned broadband power amplifier (PA) in cascade with a stub loaded parallel-coupled lines microstrip bandpass filter. These coupled microstrip lines are bilaterally connected with the shorted stub. Filter parameters are determined by an even-odd mode impedance analysis to ensure the high-selectivity and anti-interference bandpass response. Hence, a proper fundamental and second harmonic impedance matching is realized in the desired regions of the Smith chart. Moreover, an overall circuit size is significantly reduced with easy integration. For validation, the proposed structure is manufactured and tested for a commercial 10-W GaN transistor across 1.6-2.8 GHz (54.5%), with 49.1%-65% measured drain efficiency (DE) and 38-41 dBm of measured output power has been obtained. Also, when this PA-filter circuit is driven by a 5 MHz long term evolution signal with a peak to average power ratio of 8.2 dB, an adjacent channel leakage ratio of lower than -55 dBc is achieved.