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Drought has been proved to be an important climatic factor affecting carbon (C) and nitrogen (N) cycles in terrestrial ecosystems. Despite this general understanding, relatively few studies have been conducted on the effects of drought on dissolved organic carbon (DOC) in soil in different ecosystems. To investigate whether the effects of drought on soil DOC varied in different ecosystems, and whether the difference increased with drought intensity (DI) and drought duration (DD), we conducted a meta-analysis synthesizing responses of DOC to droughts (or precipitation reduction experiments) in two main natural ecosystems: forests and grasslands. The data was gathered from 43 recent publications (457 samples of data at 34 sites) about the drought experiments across the globe. On average, drought reduced the DOC content of forest soils by 9.24%, and this effect escalated with increase in DI and mean annual temperature (MAT). In contrast, the DOC content of grassland soils was not significantly affected by drought. Overall, the effects of drought on soil DOC depend on ecosystem type (ET), mean annual precipitation (MAP), MAT and DI, and their interactions. [ABSTRACT FROM AUTHOR]

Wire bonding is widely used in various radio frequency (RF) devices and is one of the common forms of signal interconnection. In this article, a new geometric model with related physical parameters is used to describe various actual types of the bondwire, and the corresponding calculation method for the total length of the bondwire is obtained. Consequently, a new equivalent circuit modeling method of the single‐bondwire can be developed and the accuracy of model has been improved. On this basis, using the concept of partial inductance, the modeling method of double‐bondwire is proposed, which can be applied to asymmetric double‐bondwire modeling. The model of bondwire obtained by this modeling method is applied to the design of PA, and the special electrical properties of the bondwire are used to verify a novel harmonic control method, which second and third harmonics could be controlled. The results show that in the Sub‐6G, the proposed bondwire model has good accuracy, and its performance is close to the measured results. The designed PA combined with harmonic control network has good performance, achieving drain efficiency of 62.6%–70% and output power of 40–41.5 dBm at 3.2–3.8 GHz. It is proved that the proposed bonding line modeling method can be applied to the design of high‐efficient PA. [ABSTRACT FROM AUTHOR]

With the increasing demand for large signal bandwidth in communication systems, the complexity of the behavioral model of power amplifier (PA) will also increase. In this paper, a modified weighted magnitude‐selective model based on magnitude‐selective affine (MSA) function based model and weighted memory polynomial model is proposed to ensure low complexity and good modeling performance under broadband signal excitation. This model is constructed by using the power‐dependent weighted function instead of the sum of multiple MSA functions in MSA. It can not only be used to solve the nonlinearity of PA excited by large bandwidth signal but also reducing the model coefficients without affecting the modeling performance makes the digital predistortion of large bandwidth signals more simple and effective. In this paper, a 100 MHz broadband signal is used for simulation and experiment on a wideband PA. The results show that for the same performance the WMA model required approximately 80% less coefficients. [ABSTRACT FROM AUTHOR]

To cope with the degradation of digital predistortion when bandwidth changes, a bandwidth adaptive behavioral model with dynamic structures for radio frequency (RF) power amplifiers (PAs) is proposed in this article. By applying the nonlinear post‐compensation technology, PA's nonlinearity is decomposed and analyzed. Short‐time Fourier transform and transfer functions are adopted to study the influence of bandwidth variation on the linear memory effect. Based on PA's memory effect analysis, a bandwidth adaptive model with dynamic structures and a coefficient update scheme with low complexity are proposed. Experiments carried on PAs show that the proposed model achieves similar linearization performance as other conventional models. Simultaneously, the proposed model has fewer coefficients and a reduction in the coefficient update of at least 50%. [ABSTRACT FROM AUTHOR]

This paper intensely studies the impact of the input nonlinearity caused by the transistor's feedback on the hybrid continuous class‐F power amplifier. The research extends the influence of input harmonics on class‐F power amplifiers to a more general form. Through waveform engineering, the impact of feedback is analyzed. By analyzing the change in cutoff angle caused by input nonlinearity, the change of the drain voltage and current waveforms of the hybrid continuous class‐F power amplifier can be obtained. The new drain voltage and current waveforms obtained from the analysis redefine the design space of source impedance and load impedance for the hybrid continuous class‐F power amplifier. By designing the corresponding input and output matching network, the second harmonic is suppressed, and finally, the hybrid continuous class‐F power amplifier achieves a high‐efficiency state. The research reveals that input harmonics also play an essential role in the design process of power amplifiers. A comparative experiment is designed to verify the theory. Simultaneously, a 1.6–2.8 GHz broadband hybrid continuous class‐F power amplifier is designed using this theory, with a saturation efficiency of more than 61.2% and a saturation power of more than 40.4 dBm. [ABSTRACT FROM AUTHOR]

In this article, a design method for a tri‐band power amplifier (PA) with dynamic drain bias voltage is presented. Continuous operation modes are used to expand the impedance design space. In the input and output matching networks, harmonic control circuits are set up to improve efficiency. The load harmonic impedances are obtained by continuous theory. Bias network and harmonic short circuit are used in the input matching network to control harmonics and obtain stop‐band. Dynamic drain bias enables the PA to adapt to different emission environments. With input and output harmonic control technology, a 0.9, 1.5, and 2.1 GHz GaN PA is designed to achieve high efficiency in different modes. The measured efficiencies of the fabricated PA at all three bands are more than 58.6%. At 1.5 GHz, when driven with a 20 MHz LTE signal with a 7 dB peak‐to‐average power ratio, by applying digital pre‐distortion, the PA prototype maintains an adjacent channel power ratio of better than −48.7 dBc. [ABSTRACT FROM AUTHOR]

This paper presents a broadband linearizer based on equivalent power‐dependent impedance function (PDIF) of diode and load match network (LMN). A method to measure the PDIF is proposed, then the broadband LMN can be synthesized by using the PDIF and the transfer characteristic of the amplifier to realize a broadband linearizer. To verify the proposed method, a linearizer for a 100 W traveling wave tube amplifier (TWTA) is designed and measured from 29 to 31 GHz. By using the linearizer, the output 1‐dB compression point (OP1dB) has increased by more than 1.2 dB, and phase error has reduced by more than 16.9°. Then a two‐tone signal with 100 MHz spacing is used for test, the results show that 12.2 to 14.6 dB suppression of third‐order intermodulation distortion (IMD3) is achieved over the working frequency range without bias tuning. [ABSTRACT FROM AUTHOR]

In this article, based on a dual-input configuration (DIC), a method for implementing ultrawideband or multiband load-modulated Doherty power amplifiers (DPAs) is proposed. The proposed DIC possesses two Doherty operating modes with respect to the working frequency. Each subamplifier of the DIC plays a changeable role versus frequency, changing from carrier to peaking or changing from peaking to carrier. A dual-input DPA working over 0.7–3 GHz (a relative bandwidth of 124%) is constructed for validating the proposed theory. Under continuous-wave signal excitation, experimental results illustrate that the fabricated power amplifier achieves a 6-dB back-off efficiency of over 40% across 0.7–3 GHz. The maximum output power of the fabricated DPA changes from 42.2 to 44.7 dBm across the whole working band. Meanwhile, a 20-MHz wideband modulated signal with a peak-to-average ratio of 6.04 dB is utilized to stimulate the fabricated DPA at 0.9, 1.8, 2.4, and 2.8 GHz. After digital predistortion, the measured adjacent channel leakage ratios are less than $-$ 50 dBc at four experimental frequency points. [ABSTRACT FROM AUTHOR]

In this paper, the design of a wideband monolithic microwave integrated circuit (MMIC) low-noise amplifier (LNA) fabricated in 0.13- μ m GaAs pHEMT process is presented. A simple T-type input matching network (IMN) and a source feedback structure are employed to achieve low noise figure (NF). The MMIC LNA, which operates across 12–18 GHz, can be used for satellite applications. Experimental results show an NF around 1.5 dB in 12–17.5 GHz and a minimum NF of 1.21 dB at 16.5 GHz. In addition, a flat small-signal gain of 2 2 ± 0. 5 dB is achieved at 13.5–17.5 GHz. The input return loss is lower than − 1 0 dB at 12–14.5 GHz and the output return loss is lower than − 1 0 dB at 12–17 GHz. The power consumed is lower than 0.3 W and the P 1 dB (1-dB compression point) output power is around 13 dBm. [ABSTRACT FROM AUTHOR]

In this article, a novel method to design broadband linear power amplifier (BL‐PA) is presented. By adding the image parts for harmonics and intermodulation products (HIMPs), a suboptimal solution of efficiency and linearity in continuous frequencies can be achieved at a broadband to improve the efficiency and linearity performance of the BL‐PA. For verification, a BL‐PA operating 3.2‐3.8GHz is designed and the performances are assessed in multi modes. [ABSTRACT FROM AUTHOR]

In this article, the generating mechanisms of nonlinear distortion of the dual-input Doherty power amplifier (DIDPA) are discussed, and based on this, an adaptive signal separation algorithm (ASSA) is proposed to improve the nonlinearity of DIDPA. The main idea of the ASSA is to minimize the mismatch between the signal separation functions and the intended operation, which is considered to be the leading cause of nonlinearity in DIDPA. The signal separation functions are used to determine the power ratio and phase difference between the main and the auxiliary amplifier. Moreover, in order to maximize the drain efficiency, an efficiency dictionary which is derived from the static measured results is employed during the ASSA. The performance of the ASSA is validated experimentally on a gallium nitride (GaN)-based DIDPA. The measured results show that with the help of the ASSA, the adjacent channel power ratio and normalized mean square error of output signal can be improved significantly without sacrificing efficiency. In order to further demonstrate the validity of the ASSA, the digital predistortion results of the DIDPAs with and without ASSA are compared with two kinds of behavioral models and two kinds of modulation signals. [ABSTRACT FROM AUTHOR]

This letter proposes a method to further improve the efficiency of power amplifiers (PAs). A thermoelectric generator is used to harvest the thermal energy produced by the PA and transform it into electric energy. Then, the efficiency of the PA can be improved by feeding the obtained electric energy to the drain power supply via a dc–dc converter. For verification, a 10-W 3.2–3.8-GHz class-F PA for base station applications is built; the generated temperature distribution and the process of energy conversion are evaluated. Cost-effective commercial chips are applied to harvest, transform, convert, and feedback the energies to the drain supply. The measurement results demonstrate an improvement of ${1.1\%}$ drain efficiency at the peak output. [ABSTRACT FROM AUTHOR]

This paper introduces a methodology for implementing multi-band Doherty power amplifiers. Traditionally, a 90∘ impedance inverter line is required in Doherty architecture. In this contribution, a generalized impedance inverter line is utilized to construct multi-band Doherty power amplifiers. A tri-band Doherty power amplifier operating at 1.15, 1.85 and 2.55 GHz is designed to validate the proposed method. Measurement results show the fabricated Doherty power amplifier achieves 6 dB output back-off drain efficiencies of 62.3%, 49.3% and 50.5% at 1.15, 1.85 and 2.55 GHz, respectively. The peaking output power of the fabricated tri-band Doherty power amplifier is 43.2, 43.7 and 43.8 dBm with drain efficiencies of 64.5%, 62.2% and 64.5% at three working frequency points, respectively. Furthermore, when the designed Doherty power amplifier is driven by a 20 MHz wideband LTE signal with peak-to-average-power ratio of 6.4 dB, adjacent channel power ratios of − 29.4 and − 57.1 dBc are achieved before and after digital pre-distortion at 1.85 GHz. [ABSTRACT FROM AUTHOR]

This paper analyses the impacts of the harmonic-tuned hybrid continuous modes (HTHCMs) approach on the back-off efficiency of Doherty power amplifiers (DPAs). Based on the HTHCMs strategy, formulations are derived for designing the impedance inverting network (IIN) and impedance transforming network (ITN) in the DPA. Via the proposed approach, multiple impedance solutions for realizing broadband DPAs with substantial output back-off efficiency recovery is made possible. The potentiality of the design method is demonstrated by the realized prototype working from 1.4 to 2.45 GHz. Test results have shown over 50% drain efficiency at 6 dB back-off power. [ABSTRACT FROM AUTHOR]

To achieve high efficiency, an optimised method of the series–parallel form (SPF) hybrid envelope tracking power supply based on hysteresis current control is proposed in this Letter. The SPF hybrid power modulator is constituted by one linear regulator and two switched‐mode converters which include one multilevel converter and one buck converter. Based upon the equivalent average current slew rate matching theory and accurate power loss model analysed in this Letter, the voltage distribution of the multilevel converter is optimised. For verification, a prototype is fabricated aiming for tracking the 10‐MHz LTE envelope signal with the efficiency of 83%, 26.9 W average output power, and 67.6 W maximum output power. [ABSTRACT FROM AUTHOR]

This paper proposes bandwidth and efficiency improvements of symmetrical Doherty power amplifiers (SDPAs) using continuous harmonic-tuned Class-J mode (CHTCJM). By this approach, the effects of the CHTCJM on the impedance inverter network and post-matching network in SDPAs are reanalysed using formulated mathematical equations. In this way, to recover and further improve the bandwidth and efficiency performances in the conventional SDPA. The term recovery as proposed in this context is to redefine, reanalyse, retrieve and further enhance the output-power-back-off efficiency and bandwidth performances lost in the conventional SDPAs using an alternative theoretical methodology based on the CHTCJM. Based on the findings, the proposed technique can substantially recover and enhance the bandwidth and efficiency of SDPAs at the desired output-power-back-off level. According to the measurement results, the fabricated SDPA model operates within 1.45–2.45 GHz frequency band with more than 50% peak drain efficiency at 6 dB output-power-back-off. Furthermore, more than 60% drain efficiency, 12 dB gain and 43 dBm output power are delivered at saturation. Using digital predistortion with a 20-MHz long-term evolution signal in testing the linearity of the implemented SDPA, the SDPA's adjacent channel leakage ratio is less than −45 dBc at an average output power of 36 dBm. [ABSTRACT FROM AUTHOR]

A broadband low-noise amplifier (LNA) using 0.13 μ m GaAs HEMT technology for Ku-band applications is presented in this paper. By introducing an improved self-bias architecture, the LNA is achieved with low noise figure (NF) and high power gain. Compared with traditional LNA, self-bias architecture can reduce DC supplies to single one, and the improved architecture proposed here also takes part in source matching to reduce the complexity matching networks for broadband applications. To verify, an LNA operating over 12–18-GHz bandwidth is fabricated. The measurement results, for all the 72 chips on the wafer, and their average values are in great accordance with the simulation results, with 25.5–27.5-dB power gain, 1.1–1.8-dB NF, 15–17.5-dBm output power at P 1 dB and with a chip size of 2 mm ∗ 1.5 mm. [ABSTRACT FROM AUTHOR]

A method enabling the codesign of a high-efficiency power amplifier (PA) and a ring-resonator microstrip bandpass filter is proposed in this paper. Even–odd-mode analysis and a series of continuous modes (SCMs) are combined to realize broadband or multiband impedance matching as well as the suppression of undesired signals. The proposed codesign method can achieve both broadband and multiband frequency responses, and the designed component is relatively easy to analyze and fabricate due to its microstrip structure. For verification, a broadband and triband PA-filter components are designed and fabricated separately. The first component operates across 0.8–3.2 GHz (120%) with 39.7–42.9-dBm maximum output power and 57%–74% drain efficiency (DE). The second component, which has three passbands, covers several commercial frequencies with a measured output power of 39.6–41.3 dBm and DE from 62% to 68%. When these two components are driven by a 20-MHz long-term evolution signal with a peak-to-average power ratio of 6.2 dB, adjacent channel leakage ratios from −26.4 to −33.8 dBc and from −29.4 to −33.1 dBc are measured, respectively. [ABSTRACT FROM AUTHOR]

In this paper, a broadband continuous-mode Doherty power amplifier (CM-DPA) is realized taking advantage of the noninfinity output impedances of peaking stage. Specifically, the carrier PA of the designed DPA operates in a continuous class-J mode when the peaking PA is in the OFF-state, where the output impedance of the peaking PA has some influences on the carrier PA. When the peaking transistor is in the OFF-state, the load impedance variation of the carrier transistor versus noninfinity peaking impedance is presented in this contribution. The proposed method surmounts the back-off drain efficiency deterioration of DPAs at two side working bands through elaborately processing the noninfinity peaking impedance. This paper also presents a method to derive the required OFF-state output impedance of the peaking stage by the carrier PA in a symmetrical broadband DPA. A broadband CM-DPA working over 1.6–2.7 GHz (bandwidth of 51%) is designed and fabricated for interpreting our theories. The simulated load trajectory of the carrier transistor is in line with the design space of continuous class-J mode. Under continuous wave excitation, experimental results show the drain efficiencies of 46.5%–63.5% at 6-dB output back-off power levels and 56%–75.3% at peaking power levels. The maximum output power of this DPA is 43.8–45.2 dBm with a gain of 9.4–11.5 dB across the whole working band. Furthermore, a 20-MHz LTE modulated signal with a peak-to-average power ratio of 7.4 dB is also applied to the fabricated CM-DPA at 2.2 GHz. At an average output power of 37.5 dBm, measurement results show the adjacent channel power ratios of −30.2 and −50.1 dBc before and after digital predistortion, respectively. [ABSTRACT FROM PUBLISHER]

In this paper, an extended Chebyshev function is proposed to adapt the matching condition of the power amplifier (PA) by introducing a new factor. A set of impedance functions can be directly calculated along with the variation of a new variable, and the first element extracted from the functions is distributed in a wide range. In addition, the impedance function whose first element is the closest to the output capacitance of the transistor can be easily read out and selected as the original matching network. The fundamental impedance of the selected function will be reached a good matching state, and the impedances out of band will be on the edge of Smith chart. To achieve better performances, the real frequency technique is applied to adjust the harmonic impedances preventing it from falling into the low-efficiency region. Two PAs with a relative bandwidth of 34% and 75% are implemented to validate the proposed approach. [ABSTRACT FROM PUBLISHER]

In this article, a novel design method of multiband bandpass filters (BPFs) which have flexibly tunable center frequencies is presented by using T-shaped stub-loaded step-impedance resonators (SLSIRs)' multimode characteristics. By controlling the impedance ratios and the length ratios of the T-shaped open stubs, the center frequencies of a multiband BPF can be decided. To verify the effectiveness of the proposed method, a 1.34/2.2/3.3/4.5 GHz quad-band filter using split-ring based on SLSIRs is designed, fabricated, and measured. The proposed filter is composed of a pair of tri-section T-shaped open stubs transmission lines, which form a folded split-ring. By controlling the impedance ratios, the length ratios of the open stubs and the width of the gap of the folded split resonance loop, the quad-band center frequencies are flexibly tunable. Owing to the 0° feed structure, seven transmission zeros can be realized near the pass-band for enhancing the selectivity. The measured results show good agreement with the theory and the EM simulation. [ABSTRACT FROM AUTHOR]

The effect of the output impedance of peaking power amplifier (PA) on Doherty PAs (DPAs) is analyzed in this paper. In the design procedure of DPAs, the ideal case is that the output impedance of auxiliary PA is infinite at output power back-off (OPBO) level. However, it is almost impossible to realize this perfect condition in broadband DPAs. Therefore, when the output impedance of peaking path deviates from infinity, some potential effects on DPAs must be produced. In this paper, these effects are explained at the internal plane of transistors. The conclusion is that, at different normalized frequencies, there are different optimal impedance regions for the output impedance of peaking stage. This means that the noninfinite output impedances of peaking stage can enhance the performances of broadband DPAs so long as they are elaborately processed. A 1.65–2.7-GHz (48% bandwidth) broadband DPA is designed considering the effects of peaking PA. The experimental results show that this DPA obtains a drain efficiency of 41%–59.6% at 6-dB OPBO levels and a drain efficiency of 55.8%–72.2% at saturation power levels. The maximum output power across the entire operating band is 43.1–45.2 dBm with a gain of 9.0–10.2 dB. Furthermore, the designed DPA achieves an adjacent channel leakage ratio of −45.8 dBc with an output power of 36.1 dBm at 2.0 GHz after digital predistortion when it is excited by 5-MHz WCDMA signal with a peaking-to-average power ratio of 8.6 dB. [ABSTRACT FROM PUBLISHER]

In this study, a methodology is proposed for extending the high‐efficiency power range (HEPR) of symmetrical Doherty power amplifiers (DPAs). This method takes advantage of the output impedance of peaking stage. Traditional symmetrical DPAs maintain high efficiency over a 6 dB power range with an assumption of the output impedance of peaking stage being infinity. This study reveals that the HEPR can be further enhanced by tuning the output impedance of peaking stage away from infinity and changing the phase delay of the impedance inverter after carrier power amplifier. A 2.2–2.3 GHz symmetrical DPA with an HEPR of 9 dB is fabricated to validate our theory. The experimental results possess drain efficiencies of 45.3–49.5% at 9 dB output power back‐off level and 62.9–71% at peaking power level over 2.2–2.3 GHz. The maximum output power of the fabricated DPA is 45 dBm with a gain of 11.6–13.5 dB across 2.2–2.3 GHz. [ABSTRACT FROM AUTHOR]

ABSTRACT In this letter, an architecture is presented to solve problems of classical concurrent dual-band Doherty power amplifiers (DPAs) and its design procedure is given. It is a codesign of two single-band DPAs and four filters. Two of filters at the output port are used for impedance transformation, harmonic components suppressing and signal isolating, while the another two split concurrent dual-band signals at the input port. In this way, intermodulation components of the two bands can be effectively suppressed and each band can achieve a good performance as single-band one's. This design concept is demonstrated through implementing of a practical dual-band DPA operating at 1.8 and 2.5 GHz. Measurement results show that efficiencies are 65.0 and 56.3% at the 6 dB output power back-off for concurrent application. The intermodulation components and harmonic components are lower than −40 dB except second harmonic component at 1.8 GHz (−32 dB). © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:530-533, 2017 [ABSTRACT FROM AUTHOR]

This paper presents a modified Doherty configuration with extended bandwidth. The narrow band feature of the conventional Doherty amplifier is discussed in the view of the broadband matching. To extend the bandwidth, the post-matching architecture is employed in the proposed design. Meanwhile, broadband low-order impedance inverters are adopted to replace the quarter-wavelength transmission lines. Low-pass filter topologies are used to realize both the post matching network and the impedance inverters. A modified Doherty Power amplifier was designed and fabricated based on commercial GaN HEMT devices to validate the broadband characteristics of this configuration. The 6-dB backoff efficiencies of 47%–57% are obtained from 1.7 to 2.6 GHz (41.9% fractional bandwidth) and the measured maximum output power ranges from 44.9 to 46.3 dBm in the designed band. In particular, more than 40% efficiencies are measured at 10-dB backoff throughout the operation band. [ABSTRACT FROM PUBLISHER]

A 0.4–2.3 GHz broadband power amplifier (PA) extended continuous class-F design technology is proposed in this paper. Traditional continuous class-F PA performs in high-efficiency only in one octave bandwidth. With the increasing development of wireless communication, the PA is in demand to cover the mainstream communication standards’ working frequencies from 0.4 GHz to 2.2 GHz. In order to achieve this objective, the bandwidths of class-F and continuous class-F PA are analysed and discussed by Fourier series. Also, two criteria, which could reduce the continuous class-F PA’s implementation complexity, are presented and explained to investigate the overlapping area of the transistor’s current and voltage waveforms. The proposed PA design technology is based on the continuous class-F design method and divides the bandwidth into two parts: the first part covers the bandwidth from 1.3 GHz to 2.3 GHz, where the impedances are designed by the continuous class-F method; the other part covers the bandwidth from 0.4 GHz to 1.3 GHz, where the impedance to guarantee PA to be in high-efficiency over this bandwidth is selected and controlled. The improved particle swarm optimisation is employed for realising the multi-impedances of output and input network. A PA based on a commercial 10 W GaN high electron mobility transistor is designed and fabricated to verify the proposed design method. The simulation and measurement results show that the proposed PA could deliver 40–76% power added efficiency and more than 11 dB power gain with more than 40 dBm output power over the bandwidth from 0.4–2.3 GHz. [ABSTRACT FROM PUBLISHER]

A modified triangular loop resonator with an open‐circuited stepped‐impedance stub, which can generate two closely spaced passbands at 5.2 and 5.8 GHz, is analysed. For verification, the triangular loop resonators along with stub‐loaded resonators (SLRs) are then employed to design a compact 2.4/3.5/5.2/5.8‐GHz quad‐band bandpass filter (BPF) for wireless local area networks as well as worldwide interoperability for microwave access applications. Each of the four centre frequencies in the proposed quad‐band BPF is able to be controlled due to the design freedom. [ABSTRACT FROM AUTHOR]

A general matching method is presented in this paper for broadband power amplifier (PA) design. A novel cost function is proposed for the real frequency technique (RFT), which could straightforwardly describe PA optimal impedance along with frequency change. The new function is also developed to design a broadband transformer for the PA output matching network (MN). Based on Richard transformation, a commensurate transmission line is deployed so that the PA matching could be convenient expressed by a real positive function. More important is that the function could be directly implemented with a distributed MN through synthesis theory. Therefore, this method is practical for computer-aided design and has less calculation amount with new function for the RFT. To verify the method, a step-by-step design of a broadband PA is given. For large signals, power gain is 14.2–16.8 dB across 0.9–2.8 GHz, while output power is around 39.5 dBm. The maximum power-added efficiency is from 52.2% to 85.1%. [ABSTRACT FROM AUTHOR]

A design of controllable power limiter (CPL) using parallel reverse polarities Schotty diode is introduced. The main characteristic of the proposed PL are controllable, be difference with traditional PLs, the turning point is controllable and depend on the applied bias voltages on the diodes. For verification, a CPL using symmetry structure, with two controllable bias voltages, operating range from 1.9 to 2.7 GHz is fabricated. The measured results proved the feasibility of design, with <3 dB small signal insertion loss during the whole bandwidth the PL can limit output power at the level under 12 dBm while the large input power ranges over 30 dBm. [ABSTRACT FROM AUTHOR]

In this paper, the spectral regrowth issues of the separated broadband signals' magnitude and phase components have been analyzed using stochastic theory for polar transmitters. The analysis shows that limited bandwidth of the low-pass envelope reconstruction filter in the ΔΣ supply modulator can affect the transmitting signals' fidelity of the polar transmitter, which can be measured by the system specifications of error vector magnitude (EVM) and adjacent channel power ratio (ACPR). The relations between the cut-off frequency of the filter and the specifications of EVM and ACPR have been derived to determine the minimum required filter bandwidth. The relations are verified by simulation examples of wideband WCDMA and WLAN 802.11a signals. In the time-domain, the limited bandwidth of the low-pass filter is verified to be responsible for the quasi-memory effects observed in the input envelope amplitude to output envelope amplitude (AM-AM) relation of the ΔΣ supply modulator. Through numerical examples, the effects of inaccurate pulsewidth caused by non-zero transistor's rise and fall time have been found to be one of the factors causing nonlinear AM-AM relation of supply modulators. The ΔΣ envelope modulator restrained by limited envelope bandwidth and inaccurate pulsewidth can be characterized as a nonlinear system with memory, which is modeled by ARMAX Hammerstein systems in this paper. The validity of this model is verified by a simulation example of a WCDMA supply modulator. [ABSTRACT FROM AUTHOR]

A parallel LβCα tank circuit with an α-order capacitor and a β-order inductor is proposed in this paper, where α and β are positive real numbers. The impedance of the parallel LβCα tank circuit, which could perform as a pure real, pure imaginary or short impedance, is discussed in detail, followed by the phase response analysis in α - β plane. The results show that the parallel LβCα tank circuit could act as a constant phase element. The resonance frequency analysis demonstrates that there exists more than one resonance frequency. And the time domain response expression of the proposed LβCα tank circuit is given by applying the inverse Laplace transform. The dual transformation relationship between the series and parallel LβCα tank circuit is summarized at last. [ABSTRACT FROM AUTHOR]

Digital Predistorter is a cost-effective solution to compensate for the nonlinear distortions appearing in the RF power amplifiers (PAs). The indirect learning scheme is widely implemented because of its flexibility to eliminate the requirement for building a closed-loop real time system, which dramatically reduces the complexity for measurement setup. However, such scheme is sensitive to the measurement noise that may cause biasing in the coefficients estimation. To minimize the influence of measurement noise and simultaneously enable the open-loop implementation, we propose a predistortion technique that first model the PA and then generates predistorted signal iteratively through a feedback configured structure to avoid using the noisy signal when performing the inverse model estimation. Unlike the indirect learning which estimates the postinverse of the PA, our predistortion is based on the preinverse of the PA. Both simulations and measurements show that utilizing the proposed predistortion can obtain adjacent channel power ratio (ACPR) improvement in wideband code division multiple access (WCDMA) signal test compared with the conventional memory polynomial predistortion based on indirect learning. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011. [ABSTRACT FROM AUTHOR]

A power amplifier (PA) output matching network (OMN) based on the ring structure network is proposed to design multi‐octave wide band PA. The characteristics of ring structure and micro‐strip are analysed. For verification, validate the proposed structure, a multi‐octave wide band PA operating ranges 0.5−4.4 GHz over three octaves is fabricated and measured, with the minimum power added efficiency over 48%, output power (Pout) over about 40 dBm and 9.5−11.5 dB power gain are achieved during the operating frequency band. Comparison with reported over octave PAs are given. [ABSTRACT FROM AUTHOR]

The above article contains errors in (27), (29), and (30). The correct forms of are as follows: [ABSTRACT FROM AUTHOR]

A novel approach to achieve high‐efficiency dual‐band power amplifier (PA) is presented. Owing to the contradictions among the control of harmonics, most reported dual‐band or multi‐band PAs are intentionally avoiding the case when the higher‐frequency band overlaps the second harmonics of the lower‐frequency band, especially when fhigher=2flower. By introducing lower‐frequency feedback technique a method is proposed, make a compromise between high‐efficiency and power gain fluctuant, high‐efficiency dual‐band PA at the above condition can be achieved. To verify, a dual‐band PA operating at 1.7 and 3.4 GHz is fabricated and measured. The peak output powers of the dual‐band are 40.1 and 40.7 dBm with small signal gains 25 and 17 dB, and the drain efficiency at the peak output power reached 80.2 and 78.5%, respectively. [ABSTRACT FROM AUTHOR]

An under-sampling digital predistortion based on a multi-tone mixing feedback technique (MTM-DPD) is presented in this article. In contrast to the under-sampling digital predistortion (DPD) based on conventional receivers, the proposed method could simultaneously reduce the sampling rate and acquisition bandwidth using a multi-tone mixing (MTM)-based feedback channel. The MTM-DPD is implemented with an evolved direct learning architecture, where the coefficients of a predistorter are estimated based on the aliased feedback signal, preprocessed input signal, and preprocessed kernels of the DPD model. To preprocess the input signal and kernels, the behavioral model of the MTM-based feedback channel and its corresponding identification algorithm are analyzed in detailed. Experimental results show that for a gallium nitride (GaN)-based power amplifier (PA) with 40-MHz input, under the excitation of a 17 tone LO signal with frequency interval 7.68 MHz, the MTM-DPD with sampling rate 15.36 MSPS and acquisition bandwidth 15.36 MHz could improve the adjacent channel power ratio (ACPR) from −30.1 to −46.5 dBc and the error vector magnitude (EVM) from 9.13% to 1.76%. Compared with the conventional full sampling DPD (FS-DPD), the MTM-DPD could reduce the cost of analog-to-digital converters (ADCs) in feedback channel significantly while maintaining satisfactory linearization performance. [ABSTRACT FROM AUTHOR]

A dynamic deviation memory polynomial (DDMP) model for digital predistortion is proposed to compensate the non‐linear distortion of the power amplifier. It is based on the memory polynomial model and dynamic deviation reduction‐based Volterra (DDRV) model. Compared to the DDRV model, the proposed model shows better modelling accuracy under the same complexity. The effectiveness of the DDMP model has been verified by simulation and experiment results. [ABSTRACT FROM AUTHOR]

In this article, a dynamic dual‐band baseband equivalent Volterra (DDBE) model is proposed to compensate the nonlinear distortions of the concurrent dual‐band power amplifier (PA). The DDBE model is obtained by improving the discretized dual‐band baseband equivalent Volterra model which can describe the output characteristics of concurrent dual‐band PA completely in theory but is lack of practicability. Three simplification rules are proposed in the article, and the relevance between in‐band intermodulation and in‐band cross modulation is employed to simplify the establishment complexity of the model. Then the dynamic kernels are categorized into three groups, and based on this, DDBE models with different level dynamical kernels are derived. In addition, draw on the experience of single‐band PA behavioral model, even‐order kernels are introduced into DDBE models. Digital predistortion performances of a wideband PA, which works in concurrent dual‐band mode, are evaluated to verify the feasibility and advantages of the proposed model. [ABSTRACT FROM AUTHOR]

A semi‐analytic method is presented for dual‐band power amplifier design. A commensurate transmission line is applied to reduce the number of independent variables in a given topology so that the optimisation algorithm would be more robust to handle it. At the same time, it could be described as a rational function. To pursue a good performance at the two bands, continuous mode is also considered for controlling the harmonics. The impedance of the lower band is controlled up to the third harmonic, while that of the upper band is up to the second harmonic. The efficiency of the dual band is, respectively, 69.4 and 70.7%, and the corresponding output power is 41.7 and 41.5 dBm at 2.4 and 3.45 GHz, respectively. [ABSTRACT FROM AUTHOR]

A 1.7/2.6 GHz high‐efficiency concurrent dual‐band power amplifier (DBPA) with a dual‐band harmonic wave controlled transformer is demonstrated. The proposed dual‐band transformer, which transfers the fundamental and the second harmonic impedances of each frequency, is directly transmission line implemented with the help of an optimisation algorithm. The measurement results show that the proposed DBPA has performances of 70 and 64% power added efficiency with an 11 dB gain and a 41 dBm output power at 1.7 and 2.6 GHz, respectively. Its average drain efficiency is more than 42% and the adjacent channel leakage ratios are lower than −46 dBc at both frequencies with the digital predistortion adjustment for a 5 MHz WCDMA signal input. [ABSTRACT FROM AUTHOR]

Modulated wideband converter is a multi-branch compressed sampling structure in which each branch aliases the sparse input spectrum into a narrow band by mixing a pseudo-random local oscillator (LO) bit sequence. Based on the low-pass sampling sequences of the narrow bands and the sensing matrix which defines the weights of aliasing, the input signal can be recovered by compressed sensing reconstructing algorithms. Because the distortion in the hardware implementation is ignored, the calculated sensing matrix, which is obtained by directly expanding the Fourier values of the LO sequences, cannot lead a satisfactory signal reconstruction. To solve this problem, this paper proposed the concept of relative sensing matrix and considered these distortions as a part of the sensing matrix. To measure the relative sensing matrix, this paper also designs a triggering-based measurement system excited by wideband modulated signals. The system is synchronized by the trigger which controls the restart of input signals, LO sequences, and ADCs. Compared with the classical sinusoidal signals measurement system, the wideband modulated signals are more accessible to be synchronized by the trigger for their identifiable envelope header. A dual-carrier 5 MHz signal is injected to the receiver at a signal noise ratio of 37 dB, with the measured sensing matrix; the two baseband signals are reconstructed with the normalized mean-squared error (NMSE) reaching − 21.05 dB and − 19.72 dB, respectively. This result is much better than the baseband signals reconstructed by the calculated sensing matrix which only have the NMSE of − 7.47 dB and − 6.70 dB. [ABSTRACT FROM AUTHOR]

It is well known that accurate estimation of the loop delay between the input and output feedback signals is the key to behavioral modeling and digital predistortion of power amplifier. Nevertheless, most of the traditional loop‐delay compensation algorithms have the disadvantage of high computational complexity. For the purpose of solving this problem, a loop‐delay estimation algorithm based on sliding window has been proposed in this paper, where the first derivative characteristic of the signal is employed to evaluate the correlation between the input and output feedback signals. The simulation and experiment are carried out with different bandwidth signals in this paper. The results show that the proposed algorithm and the traditional cross‐correlation‐based method could align the input and output feedback signals successfully. But in terms of resource consumption, the proposed algorithm could reduce the multiplier nearly by 100% and the adder by approximately 93.2%. [ABSTRACT FROM AUTHOR]

An optimal balance between high efficiency and high linearity is one of the main performance metrics of modern base stations to handle the deep compression of the power amplifier (PA) module. In principle, the plethora of amplitude‐to‐amplitude (AM‐AM) and amplitude‐to‐phase (AM‐PM) distortions are issues worth exploring. Therefore, this paper presents a linearized harmonic‐tuned PA that operates at 2.4 GHz. The presented PA utilizes a compact input matching network (IMN) and output MN (OMN) with shunt‐connected tunable resonant circuits augmented by the stabilization network, whose presence greatly reduces the transistor parasitics and high‐order effects. Hence, a joint embodiment of each other gives optimal fundamental impedance matching alongside harmonic terminations and precise AM/PM waveform properties. The measurement results have shown that the fabricated PA exhibits peak saturated output power of 40.9 dBm and peak drain efficiency (DE) of 67%. In addition, the AM‐AM and AM‐PM curves under continuous‐wave excitation yield a gain flatness of 0.5 dB over a 37.5 dBm power range and ±3.5° phase distortion, respectively, when the input power level is swept up to the saturation level of 40 dBm. When driven with a 5 MHz 64‐QAM OFDM signal and 6.9 dB power back‐off, the manufactured PA meets the adjacent channel leakage ratio specification of −30 dBc at an average output power of 34.5 dBm. [ABSTRACT FROM AUTHOR]

Classical analysis of high-efficiency power amplifiers (PA) is usually based on ideal voltage and current waveforms limited to optimal states. A transistor's nonlinear I-V curves are not usually taken into consideration because of their complexity. With a computer-aided calculation tool developed herein, a direct waveform determination method involving nonlinear I-V curves is realized. Using this approach and simplified I-V curves, a PA's extended theoretical performance from the back-off region to saturation can be investigated. If using practical dc I-V curves, this method can also give good performance analysis results even at microwave frequency. Numerical examples of different PA settings are given to verify this method. Nonlinear calculations, harmonic balance simulations, and measurements of a class-E PA operating at 3 GHz are shown with consistent results to prove this waveform determination method. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a new approach of designing high Q surface acoustic wave (SAW) resonators as an inductive element in the matching network for W-CDMA power amplifiers (PAs). Spiral inductors based on CMOS/BiCMOS technologies presently possess relatively low Q (typically <10) and occupy a considerably large area. In order to break through the limitations of the spiral inductors, the authors attempt to apply higher Q and wideband SAW resonators employing Cu-grating/15°YX-LiNbO3-substrate structure to the matching network for improved PA performance. An analysis was made on SAW resonators in detail, and an SAW resonator having a very small capacitance ratio of 3.28 and moderate Q of 147.8 was developed. After discussing the frequency dependence of the effective inductances, SAW resonators, which are used to be as inductive elements in the matching networks of PAs, were designed and fabricated. The PA including the matching circuit was simulated using the characteristics of the fabricated SAW resonators. The result showed that with better shape factor and good out-of-rejection, the SAW resonators definitely work as an inductive element and could replace widely used spiral inductors. [Copyright &y& Elsevier]

A self-coupled resonator consisting of asymmetrical parallel-coupled microstrip transmission lines is proposed to design wide stopband dual-band bandpass filters. Due to the even-to-odd-mode analysis limitation to asymmetrical structure, a multiport analysis method is developed and applied to analyze the proposed self-coupled resonator and dual-band filter. According to the analysis, the proposed self-coupled resonator features a small frequency ratio of the second to the first resonances and controllable spurious responses, and its transmission zeros (TZs) are placed close to the position out-of-band spurs in order to achieve wide stopband. Moreover, a feed line consisting of tapped line loaded coupled line is investigated, resulting in flexible adjustment of the second passband external quality factor (${ \boldsymbol Q}_{ \boldsymbol e}$) with a minor influence on the first passband ${ \boldsymbol Q}_{ \boldsymbol e}$. A dual-band BPF prototype with a frequency ratio of 1.59 is proposed and validated. It is operated at 2.34 and 3.72 GHz with the insertion loss of 1.05 and 1.86 dB, respectively. A return loss better than 20 dB is achieved at both passbands. The out-of-band rejection is better than 30 dB within the frequency range from 4.19 to 11.24 GHz, and the harmonic suppression is 39.97 dB at 14.88 GHz and 61.41 dB at 18.6 GHz. The measured results verify the analytical method presented in this article well. [ABSTRACT FROM AUTHOR]

Active load modulation and harmonic injection can be used to boost the power amplifier's (PA) efficiency, but these techniques must add a fundamental external source or a harmonic generator. In this paper, a two‐way power amplifier architecture is introduced to extend high‐efficiency operation bandwidth by utilizing concurrent active load modulation with a waveform mapping method. Active load modulation is realized in between the two branches with the aid of independent input amplitude and phase control. Based on a calculated waveform database, high‐efficiency operations for both transistors from 1 to 4 GHz are designed in a self‐defined optimization platform considering waveform distance and input parameters. Finally, this PA is fabricated and measured to offer 41.6 to 45.0 dBm power, 8.2 to 11.7 dB gain, and 56% to 89% drain efficiency from 0.85 to 3.85 GHz. [ABSTRACT FROM AUTHOR]

In this article, a method for design automation high-efficiency power amplifiers (PAs) based on an optimization-oriented is proposed. The advantages of using particle swarm optimization to design PAs in electronic design automatic tools are analyzed, and then, simulated annealing is combined to form simulated annealing particle swarm optimization (SA-PSO). In this article, the perfectly inelastic collision used in conventional PSO is replaced by the perfectly elastic collision to improve the searching ability through reducing kinetic energy consumption. A stepped fitness function is defined to avoid the performance pit at a single-frequency point, and the concept “missing and returning” is introduced to solve the nonconvergence problem in simulation. Based on the improved SA-PSO algorithm, a broadband 10 W and a triband 6-W PA are designed. The broadband 10-W PA achieves an average drain efficiency (DE) of 62.5% and an output power of 41.2 dBm in the 0.8–3-GHz frequency band, respectively; the triband 6-W PA achieves an average of 57.4%/47.9%/47.3% DE and 37.7-/38.3-/37.4 dBm output power in 3.35–3.55-/5.75–5.95-/7.65–7.95-GHz frequency bands, respectively, while the gains of most stopbands reach less than 0 dB. With digital predistortion technology, the adjacent channel power ratio (ACPR) can reach less than −45 dBc. [ABSTRACT FROM AUTHOR]

In order to apply the traditional power amplifier’s (PA) waveform engineering in an RF-dc rectifier design, a piecewise ON-resistance transistor model is introduced into the derived equations. In this proposed analysis method, the connection between the drain voltage and current is built in order to make the theoretical waveforms easily applied to a practical rectifier design with optimized parameters of the best efficiency. Continuous class-F/inverse class-F and continuous class-B/J waveforms are evaluated with numerical examples in this work. Thus, the rectification performance with different classes and parameters can be compared. This study shows that a continuous class-F and a continuous class-B/J rectifier can barely offer higher than 52% and 70% efficiencies with precise on-duty ratio ($D$) of 0.5, respectively, except by reducing the conduction angle. However, a continuous inverse class-F shows the best rectification efficiency (easily higher than 85%) among all the studied cases for $D=0.5$. A self-driving inverse class-F design example with optimized parameters is given to verify the theoretical analysis and demonstrate the high-efficiency performance. The rectification efficiencies of 74.9% and 80.7% are measured for 11.2- and 6 W-input powers at 1.9 GHz, respectively. [ABSTRACT FROM AUTHOR]