Impedance Transformer Research Articles

Design of Tri‐Band Doherty Power Amplifier Using Phase and Impedance Constrained Optimization

ABSTRACTTo realize the wideband and efficient operation of Doherty power amplifier (DPA) in multi‐band mode, this paper proposes a tri‐band DPA design method based on phase and impedance‐constrained optimization. First, the phases required for impedance transformation networks across multi‐band are determined based on the impedance required when the DPA operates at back‐off power (BOP) and saturation. Then, the impedance judgment method using multiple impedance constraint circles was employed to determine the optimal load impedances. Finally, the phase and impedance constraints at multiple frequencies were used to optimize the carrier and peaking output matching networks. For verification, a tri‐band DPA operating at 1.25−1.35, 1.9−2.1, and 2.75−2.85 GHz was designed and fabricated. Measured results show that, for the above three frequency bands, the drain efficiencies (DEs) at saturation reach 59.0%−61.7%, 59.5%−64.2%, and 52.4%−59.8% with corresponding output power exceeding 43 dBm. For 6 dB BOP, the DEs are 46.1%−54.2%, 50.4%−55.2%, and 44.8%−51.9%. Moreover, good linearity can be achieved after linearization for 20 MHz modulated signals.

Mathematical modeling development and synthesis of tapered transmission line resonators and filters

Abstract Tapered transmission line resonators can be used to achieve specific frequency responses and enhance the performance of microwave devices and impedance transformers. To develop a mathematical model (transfer function) of such a wideband resonator will facilitate the construction of an equivalent circuit and the synthesis of resonators of this type. This study discusses the system modeling of tapered transmission line (TTL) resonators using the singularity expansion method (SEM). The transfer function is analytically established for two types of wideband TTL resonators: exponential tapered transmission lines (ETTL) and linear tapered transmission lines (LTTL). The analytical transfer function is derived for the general tapered ratio (k/β). The physical poles of the structures are identified using the pole-energy matrix pencil (MP) approach. The transfer function expression is then utilized to develop an accurate equivalent lumped-element circuit for the TTL resonator. This study’s simplified approach for estimating the transfer function and associated poles and zeros from the S-parameters is the main contribution, whereas it is known that the transfer function becomes complicated for wideband frequency response. A direct synthesis approach is presented to develop two-stage and four-stage ultra-wideband (UWB) bandpass filters. The agreement between the frequency response data and the derived transfer function of the system model of the synthesized TTL filters demonstrates the reliability of the presented method. The proposed system modeling and synthesis methodology can be applied to more sophisticated filter TTL architectures.

Design of a Novel 16‐Way Short Pulse Power Divider Based on Transmission Line Transformer

ABSTRACTThis article presents a 16‐way short pulse power divider (PD) with the same input and output impedance based on the transmission line transformer (TLT) principle. Different from the traditional multi‐channel PD composed of impedance tapered transmission lines and PDs in parallel structure, the novel 16‐way PD is cascaded by multi‐stages of series‐parallel structure, which avoids the process of impedance transformer and improves the compactness of the device, as well as the transmission efficiency. It was composed of four stages of the novel series‐parallel constructure converted from coaxial waveguide to microstrip line. And to control the energy dissipation, a unified ground of the output ports was built, and the short‐ended metal shell was loaded between every stage. This 16‐way PD was fabricated and measured. The measured return loss of the PD is less than −16 dB from 440 MHz to 6 GHz, and less than −10 dB from 270 MHz to 6 GHz. The measured peak gain is more than 0.83 when input by a Gaussian pulse with tFWHM = 250 ps (FWHM: full‐width half maximum).

Four-element LC-baluns for power matching arbitrary impedances

Abstract Six four-element balun topologies are introduced that enable complex impedance matching in addition to common-mode rejection. Design equations for these topologies are presented. Three of these networks are universal, while the other three are capable of performing only specific impedance transformations. Examples of these networks were designed and fabricated along with a traditional lattice balun network for an operating frequency of 300 MHz. These networks were verified through extensive electromagnetic simulations and by measuring the fabricated networks. The fabricated novel network examples were able to achieve common-mode rejection ratios above 20 dB, power wave reflection coefficients below −20 dB, and insertion losses of approximately 0.1 dB; these results were similar to or better than the performance of the fabricated traditional lattice balun. The design example networks also provided power matching and low insertion loss over a greater bandwidth compared to the fabricated traditional network. These networks will allow for the footprints of lumped-element balun circuitry to be reduced, which is particularly useful in integrated circuit design. These topologies are also expected to further increase radio-frequency (RF) circuit design flexibility by offering more alternative realizations.

Thermo-mechanical analysis on reflection characteristics of deformed coupling system of a helix traveling wave tube

This paper proposes a fast ANSYS Multiphysics-based system coupling approach to study the impact of structural deformation on the reflection coefficient (S11) of the helix travelling wave tube (TWT) output coupling system at varying output powers. The system, comprising a coaxial stepped impedance transformer, a coaxial-to-rectangular waveguide with a door-knob transition, and a double-mitered bend waveguide, is analysed under 200 W and 250 W RF power in the X-band. The analysis shows that S11 improves at lower frequencies (−17.43 dB to −17.58 dB) and deteriorates at higher frequencies (−10.62 dB to −10.53 dB) due to structural deformation. Thermal simulation results were validated experimentally using infrared thermographic imaging.

Analytical Modeling of Short-Circuit Impedance of Square Foil Winding Phase-Shifting Transformer Based on Planar Energy Density Equivalence Method

Analytical Modeling of Short-Circuit Impedance of Square Foil Winding Phase-Shifting Transformer Based on Planar Energy Density Equivalence Method

A 5 mW 28 nm CMOS Low-Noise Amplifier with Transformer-Based Electrostatic Discharge Protection for 60 GHz Applications

This paper presents a low-power 60 GHz low-noise amplifier (LNA) designed for Gbit/s applications using 28 nm CMOS technology. The LNA exploits a single-stage pseudo-differential architecture with integrated input transformer for both electrostatic discharge (ESD) protection and simultaneous noise/impedance matching. An effective power-constrained design strategy is adopted to pursue the lowest current consumption at the minimum noise figure (NF), with the best tradeoff between gain and frequency bandwidth. The LNA, which has been designed to drive an on–off keying (OOK) demodulator, is operated at a supply voltage as low as 0.9 V and achieves a voltage gain of about 21 dB with a 3 dB bandwidth of 2 GHz around 60 GHz. Thanks to the proper impedance transformation at the 60 GHz input, the amplifier exhibits an NF of 6.3 dB, also including the input transformer loss with a very low power consumption of about 5 mW. The adoption of a single-stage topology also allows an excellent input 1 dB compression point (IP1dB) of −4.7 dBm. The input transformer guarantees up to 2 kV human body model (HBM) ESD protection.

Normal‐mode planar meander‐line antenna array with bidirectional broadside radiation pattern

AbstractIn this letter, a normal‐mode planar bidirectional broadside antenna array with the merits of high gain, broadband, low aerodynamic drag, and high assembly robustness is proposed. First, the bidirectional antenna array is implemented based on a novel design strategy. The expected radiation field generated by currents along the same direction is superimposed while the unexpected radiation field is offset due to the out‐of‐phase currents, achieving a normal‐mode high‐gain bidirectional pattern. Then, the bidirectional antenna array is designed with two metallic meander lines, featuring low aerodynamic drag and cost‐efficiency. Moreover, a simple feed structure using an impedance transformer parallel strip line is adopted for a wide bandwidth. Besides, the bidirectional antenna array exhibits a stable impedance when the array scale increases. The stable impedance is also observed when the antenna array is bent to different angles, ensuring ease of installation and high assembly robustness. To validate the design strategy, a prototype with an aperture length of 5.8λ at 2.4 GHz is fabricated. The proposed antenna array is designed to operate from 2.2 to 2.6 GHz, with a maximum gain of 13 dBi around the center of frequency, which can be a promising candidate in long and narrow communication scenarios.

Design of interline hybrid continuous trans-impedance turns ratio controlled tuning power filter: New approach to suppress harmonics in energy system

Harmonic distortion (HRD) is a major issue in power and energy systems due to its effect on output, power factor and performance of entire system. Interline hybrid continuous network impedance (IL-hCONTI) tuned filter is proposed to suppress the harmonic distortion in a inter tied i.e. integrated energy system. In a proposed method, effective transformer impedance i.e. trans-impedance is utilized rather than using entire grid impedance power system. Transformer impedance control (Tf-ZPC) in the power network under testing is possess the reactive voltage drop at point of common coupling (PoC). Transformer impedance is proportional to the turns ratio and the concern voltage change and it is imposed by the proposed tuned filter. Tuned filter is designed with the Tf-ZPC along with filter circuit impedance to control the harmonic currents and PoC voltage profile. Proposed hybrid filter design utilizes the both instantaneous capacitor voltage and inductive capacitor filter (LCF) voltage component to suppress harmonic component. Hence improved power factor of energy system is assured using proposed technique. Proposed IL-hCONTI tuned filter is tested over a strong grid conditions, as well as weak grid conditions for linear, non-linear loading.

A flexible tri‐band impedance transformer for frequency‐dependent complex impedances with simple structure

AbstractThis paper proposes a simple tri‐band impedance transformer for frequency‐dependent complex impedances. The proposed transformer is a cascade of a π‐model transformer, three series transmission lines, and a tri‐band susceptance stub network, the structure is simple, and the matching sequence of the three frequencies can be changed. All parameters of the design can be obtained from the derived analytical formulas, and the process of the design is elaborated. Two design examples demonstrate the proposed design method, and a prototype is fabricated for verification. Good agreement between the simulated results and measured results is obtained. Compared with the existing works, the transformer features a simple structure, offering flexibility to match frequency‐dependent complex impedances, and a simple method. Additionally, it features a very short total electrical length and wider bandwidth. Therefore, the proposed transformer is suitable for the tri‐band active circuits and wireless communication systems.

An epsilon‐near‐zero circuit based on half‐mode SIW with enhanced integrability for applications of narrowband large group delay

AbstractThe tunneling effect of an epsilon‐near‐zero (ENZ) is exploited to fulfill a narrowband large group delay by using a compact half‐mode substrate integrated waveguide structure built on thin substrate. The ENZ channel possesses a finite input impedance at the tunneling frequency point, and the finite input impedance can be matched to the final I/O port simply by a quarter wavelength impedance transformer. Thus, the enhanced integrability is realized in a planar form in the proposed circuit comparing to the conventional waveguide ENZ channel. Meanwhile, in the real ENZ channel, the effective impedance is observed to be close to 50 Ω, so that the ENZ can be connected with 50 Ω microstrip directly, which has been experimentally validated. The final measured net group delay is 1.36 ns at 3.08 GHz with 3.6 dB insertion loss, and the proposed method provides an alternative for the group delay engineering.

A circularly polarized graphene based wideband 1 × 2 array antenna for terahertz spectrum applications

A graphene-based 1 × 2 array antenna with circular polarization for terahertz applications is prescribed in this article. Initially, a novel concept of a folded quarter wave impedance transformer is utilized in the design process of a single element for minimizing the overall antenna size. The opposite corners of the patches have been truncated and structural modifications are performed with the insertion of four flower-shaped slots along with an additional circular slot for achieving a much-improved reflection coefficient and better impedance bandwidth. It also shows a much wider 3 dB axial ratio bandwidth, confirming circular polarization due to the suggested modifications in its geometry. Then, an array antenna has been formed to provide better gain. The configured patches are fed by a magic-T power divider to attain the required impedance matching. The results of the CP antenna array have been analyzed using the HFSS and CST simulators. The propounded 1 × 2 array antenna shows circular polarization with a 3 dB AR bandwidth of 205 GHz (2.345–2.55 THz) and wide spectral coverage of 210 GHz (2.345 − 2.555 THz) along with a maximum gain of 8.65 dB and 99.8 % radiation efficiency with a total size of 53.5 × 102 × 1.56 μm3. It could be utilized for high-speed data transmission, material characterization, terahertz spectroscopy, terahertz imaging, etc. applications.

Analysis, design, and optimization based on genetic algorithms of a highly efficient dual-band rectenna system for radiofrequency energy-harvesting applications

This paper gives an enhanced Rectenna design that operates at dual-band [2.45 and 5.8] GHz in the ISM (Industrial, Scientific, and Medical) band and is printed on an FR4-Epoxy substrate. This Rectenna design includes two proposed sub-designs for the receiving antenna and rectifier circuit based on the microstrip technology. The first sub-design concerns the microstrip patch antenna (MPA) described by its radiating element as a pentagonal, its ground being affected by a defective ground structure technique, and its polarization manner as circular polarization. This MPA design is analyzed, designed, optimized using genetic algorithms (GAs), simulated under CST MWS (i.e., computer simulation technology microwave studio), and confirmed by another software named HFSS (high-frequency structure simulator). The second sub-design concerns the microstrip rectifier circuit (MRC) that contains an input matching network based on a coupled-line impedance transformer strategy to achieve good adaptation between MPA and MRC, voltage doubler converter using an SMS7630 Schottky diode thanks to its high sensitivity, microstrip interdigital capacitor to mitigate the intrinsic losses due to the lumped elements, harmonic rejection filter based on a stepped-impedance low-pass filter to reject the unwanted harmonics generated by the non-linear behavior of SMS7630, and the resistive load that models the consumption of the system to be fed. This MRC is analyzed, designed, optimized using GAs, and simulated under ADS (Advanced Design System). The effectiveness of the proposed MPA is proven in terms of gain equals 3.06 dBi and 4.683 dBi at 2.45 GHz and 5.8 GHz respectively, and efficiency equals 95.13 % and 96.552 % at 2.45 GHz and 5.8 GHz respectively. The proposed MRC is effective in terms of efficiency at a lower input power value of about 97.18 % and 67.93 % at 2.45 GHz and 5.8 GHz respectively.

Bandwidth Extension of the Doherty Power Amplifier Using the Impedance Distribution and Control Circuit for the Post-Matching Network

Owing to the high impedance transformation ratio, the Doherty power amplifier (DPA) with a large output power back-off generally has bandwidth limitations. This study proposes an asymmetric DPA with an impedance distribution and control circuit (IDCC) at the post-matching network to improve the bandwidth. The IDCC, based on a resonance circuit and a series transmission line, distributes and controls the load impedance according to the frequency so that the bandwidth of the DPA can be extended. To verify the proposed IDCC, an asymmetric DPA was designed using GaN HEMT with a power capacity of 6 W and 10 W for the carrier and peaking amplifiers, respectively. The implemented DPA was evaluated for the broad frequency band between 3.3 GHz and 3.8 GHz using a 5G new radio (NR) signal with a bandwidth of 100 MHz and a peak-to-average power ratio of 7.8 dB. A drain efficiency between 43.2% and 50.7% and an adjacent channel leakage power ratio between –23.4 dBc and –27.3 dBc were achieved at an average power level that ranged between 33.5 dBm and 34.3 dBm.

Optimized gap positions for improved leakage impedance in dry-type transformer design

The power and distribution transformers must be properly designed to operate in a variety of conditions and manufactured following all applicable international standards to provide a reliable energy supply to consumers. The transformer can fail if it is improperly designed, and it cannot withstand the short-circuit condition if the short-circuit current is not calculated properly. Short-circuit current can be easily calculated by evaluating the leakage impedance. Customers can also demand the transformer companies to increase or decrease the leakage impedance. This paper evaluates the effect of the gap's position in the four different sections of the high voltage winding on the leakage impedance of the two-winding transformer and proposes effective design options for minimizing the leakage impedance. The accuracy of the finite element models was also investigated using an experimental laboratory transformer model specially designed for optimizing the leakage impedance. The experimental and finite element methods results show that the leakage impedance can be changed to the desired value and limits and easily assessed by the finite element analysis technique. The results indicate that even with the same use of the winding and core material, there was a considerable difference in the leakage impedance for each of the conditions.

Dual‐band bandpass‐filtering high‐efficiency power amplifier with second harmonic suppression

AbstractThis study proposes a dual‐band bandpass‐filtering high‐efficiency power amplifier based on dual‐function dual‐band impedance control network (DBICN) and a dual‐band bandpass‐filtering impedance transformer (DBBFIT). The dual‐function DBICN is exploited to transform the optimal fundamental complex load impedance to real one, and control the second harmonic load impedances of two bands to the high‐efficiency region in the Smith chart. Besides, two transmission zeros are constructed at dual‐band second harmonics to enhance harmonic suppression. Meanwhile, an easy‐to‐design DBBFIT is proposed by utilizing filter theory to realize real‐to‐real impedance transformation, and all design parameters can be obtained by simple closed‐form analytical equations. For validation, a prototype is designed, fabricated, and measured. The measured results indicate the drain efficiencies are 61.6% and 58.3% at 1.78 and 2.42 GHz with saturation output power of 40.8 and 39.6 dBm, respectively. Moreover, the second harmonic suppressions of the two bands are 40.1 and 47.1 dBc, respectively.

Broadband ridge waveguide to rectangular waveguide transition design in D‐band

AbstractThis article presents a D‐band (110–170 GHz) double ridge waveguide (WG) to standard rectangular WG transition with an E‐bend near the WG end. The transition incorporates metal ridge steps as impedance transformers, resulting in a compact total size of 3.53 mm × 1.95 mm × 1 mm. Fabricated using micro metal additive manufacturing with copper in a monolithic back‐to‐back configuration, the transition demonstrates a bandwidth of 50% (105–175 GHz) with an average insertion loss of 0.72 dB and return loss better than 15 dB, respectively. Measurement results align closely with simulation expectations, with deviations attributed to fabrication and assembly errors.

Study on the Design of Valve Base Insulation and Power Supply Transformer for High-Voltage DC Circuit Breaker

Abstract High-voltage DC circuit breaker is a key piece of equipment to building DC power grids. DC circuit breakers need to support and isolate from high voltage to ground through valve-based equipment and use valve-based power supply transformer to continuously supply energy to high potential components, the electrical performance of these two equipment determines whether DC circuit breakers and DC networks can be operated safely and reliably. For this reason, this paper carries out the research on the insulation capability of the valve base and the performance of the power supply transformer, such as the design and simulation of electric and thermal fields, as well as the test program. Firstly, the insulation design and simulation study of the valve base as a whole is carried out, and the design optimization of the equipotential scheme of the top homogeneous tubular bus, diagonal pull insulator and hydroelectric pole is completed. Secondly, the design and simulation verification of the thermal field distribution of the energy-supply transformer, the overvoltage between the ends of the output windings and the optimization scheme, and the short-circuit impedance were carried out. Finally, the insulation performance of the valve base, the temperature rise of the energy supply transformer, the overvoltage simulation of the output winding and the short-circuit characteristics were tested. The results show that: after optimization, the maximum field strength of the homogenizer is 2.3kV/mm, and the overall maximum field strength of the valve base is 2.61 kV/mm on the diagonal insulator, and there is no pressure difference between the water circuit and the fittings using the three-pin vertically distributed hydropower electrode scheme; the temperature rise of the supply transformer in the simulation and the actual measurement is 27K and less than 30K; by means of the parallel connection of the MOV, the overvoltage of the output winding of the power supply transformer under voltage impulse is effectively reduced to -1.8kV; the measured short-circuit impedance of the power supply transformer is 69.5%. The optimized design of DC circuit breaker valve base and power supply transformer can operate safely, and effectively support the construction of DC circuit breaker and DC power network.

Design of Reconfigurable Impedance Transformer and Its Application to Medium Voltage XLPE Power Cable With Joint in TV White Space

Design of Reconfigurable Impedance Transformer and Its Application to Medium Voltage XLPE Power Cable With Joint in TV White Space

A Broadband PA With Complementary Matching to Get High Impedance Transformation Ratio of 125 With 60% Bandwidth on Two-Layer HBT Process

A Broadband PA With Complementary Matching to Get High Impedance Transformation Ratio of 125 With 60% Bandwidth on Two-Layer HBT Process