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This paper presents a new extended high-efficiency-range Doherty power amplifier (DPA) with a main and only a single auxiliary amplifier. In order to extend the output high-efficiency range with a high-efficiency level, asymmetrical cells are employed as the main and auxiliary amplifiers in class-F and class-C complex combining load (CCL) methodology, respectively. To verify the proposed methodology, a DPA with 12-dB output back-off (OBO) is designed and fabricated for wideband code division multiple access (WCDMA) applications. Large-signal continuous-wave measurement results show the power gain of about 11 dB with a drain efficiency of 59.9% at 12 dB of OBO. A two-tone test exhibits a third-order intermodulation distortion (IMD) of lower than − 2 1 dBc. Modulated wave measurements show over 55% of average drain efficiency and an adjacent channel leakage power ratio (ACLR) of lower than − 2 7. 5 dBc at an output power level of 31.5 dBm. [ABSTRACT FROM AUTHOR]

In this letter, high-selective bandpass filters, in the printed ridge gap waveguide technology, are presented. The filters are designed to perform 4.68% fractional bandwidth at center frequency $f_{0}$ = 24.78 GHz. In the proposed filters, to obtain high selectivity, a cross-coupling between the nonadjacent resonators and also a coupling between the input and output ports to create an extra pair of transmission zeros in the transfer function of the filters are used. Finally, the filters are fabricated, and their scattering parameters are measured to verify the simulation results. [ABSTRACT FROM AUTHOR]

In this paper, the design theory of an 8 GHz oscillator with a new structure of active dielectric resonator (DR) is presented. The new structure emphasizes on phase noise reduction by using only one active device. The proposed structure uses additional feedback from transistor to resonator in order to increase the quality factor. Measurement results report that phase noise is reduced to −145.19 dBc/Hz at 100 kHz offset frequency which represents 12 dB improvement compared with oscillators with passive DR. Also, in comparison with conventional active resonator oscillators, noise source of the second amplifier which makes spurious oscillation is removed. The size and power consumption are reduced due to the use of a single transistor. This structure has the lowest phase noise in comparison with other DR oscillators. In order to implement the proposed oscillator, a circuit including amplifier, resonator, coupler, and phase shifter is designed and realized. [ABSTRACT FROM AUTHOR]

In this study, the implicit Crank–Nicolson finite-difference time-domain (CN-FDTD) method is applied to discretize the governing telegrapher's equations of a composite right-/left-handed (CRLH) coupled-line coupler. The unconditionally stable CN-FDTD is compared with the conventional leap-frog (LF) FDTD method. The results obtained from the CN-FDTD scheme show up to 10 times increase in the temporal step size, reflecting in a dramatic decrease in processing time; in addition to having a good agreement with the LF method and the measurements. [ABSTRACT FROM AUTHOR]

A dual‐gate aluminium gallium arsenide (GaAs)/GaAs pseudomorphic high electron mobility transistor is analysed based on the distributed modelling approach, wherein the transistor is considered as an active multi‐conductor transmission line. Discretisation of the governing matrix Telegrapher's equation is carried out using the implicit Crank–Nicolson‐finite‐difference time‐domain (CN‐FDTD) method. The results obtained from the proposed method are compared with the results of the conventional leap‐frog (LF) FDTD scheme. It is observed that the unconditionally stable CN method is in good agreement with the LF method even by increasing the time step size by the factor of 5000, leading to a dramatic decrease in the central processing unit time. [ABSTRACT FROM AUTHOR]

An explicit finite difference time domain method is proposed for modelling of composite right-/left-handed active multiconductor transmission lines in time domain. For the first time, the concept of active composite right-/left-handed transmission lines is considered in field effect transistor (FET) modelling. In this work, based on the distributed model, the FET is considered as an active multiconductor transmission line in the mm/wave frequency range. In this modelling technique, the FET is divided into 2 different parts, the active part, represents the intrinsic equivalent circuit of the transistor, while the passive part symbolizes the device electrodes. The finite-difference time-domain scheme is proposed for the analysis, and the results of this technique are compared with the ones obtained from simulations. Furthermore, the stability issue is investigated and the sufficient condition for stability is derived. [ABSTRACT FROM AUTHOR]

This paper has proposed a new pre-processing stage algorithm to enhance the overall performance of current simplification algorithms in analog circuits. This pre-process stage takes place after the calculation of symbolic transfer function and before the main core of the simplification algorithm. The detailed stages of this pre-process are completely independent of the main simplification and symbolic transfer function algorithm. As such, the pre-process algorithm can be easily added to any simplification algorithm to improve the total simplification performance. The use of this command, which is based on the stack decision method, helps the pre-process algorithm to obtain a high-process speed. Based on the CPU time simulation results for a transfer function with 139 terms, it is expected to have a total CPU time in the simplification of a 9820 term of about 28 to 30 seconds pulse and 1.2 to 4.9 seconds for the pre-process algorithm. Finally, a total method, which involves the combination of this pre-process algorithm with the main simplification algorithm is proposed in, and a CPU time of about 30 to 35 seconds is needed for simplifying a huge transfer function with 9820 terms. The addition of extra pre-process algorithm to the main simplification algorithm will reduce the total CPU time of simulation from 820 to 35 seconds, indicating a reduction of 95% in the total needed simulation time. [ABSTRACT FROM AUTHOR]

The Crank-Nicolson finite-difference timedomain (CN-FDTD) method is used for the linear analysis of a field-effect transistor (FET) based on the distributed model, wherein the FET is considered as an active multiconductor transmission line (AMCTL). The telegrapher's equations governing the AMCTL are derived and discretized by the CN-FDTD method. The results are compared with measurements and the leapfrog (LF)-FDTD method. Unconditional stability of the CN scheme is investigated. Agreement with measured results is preserved in an acceptable level even by increasing the time step-size by a factor of 1500 to that of the LF-FDTD method. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we have investigated plasma column excited by surface-waves using monopole plasma antenna. Since the plasma frequency has an important role in conductivity of the plasma column and antenna radiation characteristics, determining the distribution electron density and plasma frequency in the inhomogeneous plasma column axis is particularly important. For this purpose, the plasma column is modelled by fluid equations for high-frequency discharges. Because of significant advantages such as high power handling capability at 2.45 GHz, the surfaguide launcher is chosen from the other conventional launchers to propagate the surface wave along plasma column. The surfaguide is experimentally excited an argon gas-filled tube at a pressure of 0.2 torr as a surface-wave plasma source. In this work, because of safety considerations about high power radiation, plasma frequency measurements was impractical using conventional methods. Therefore, a new system is designed consists of a solid-state VCO, amplifier, circulator, attenuator and two double-ridged horn antennas. The plasma frequency is obtained close to 5.7 GHz, which is consistent with theoretical concepts. © 2017 The Authors. Microwave and Optical Technology Letters. Microwave Opt Technol Lett 59:806-811, 2017 [ABSTRACT FROM AUTHOR]

The aim of this paper is to demonstrate the application of Unequally Spaced Arrays (USAs) in decreasing side lobe level (SLL) in linear arrays. As well known, solving of a nonlinear equation is needed in USA antenna pattern synthesis. In this paper, an improved algorithm for USA antenna pattern synthesis is presented. This method is based on converting the array factor into a triangular system of equations capable to be solved using a recursive algorithm. This method has more accuracy and speed than reported similar analytical methods based on simulation results, which leads to lower SLL and simulation time. In addition, an improvement of 3dB beamwidth in comparison with uniform spaced array can be observed. [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a novel reflective phase shifter based on wideband multi-section 3-dB hybrid coupler in slot-coupled structure. By terminating coupled and transmission ports of coupler with rectangular microstrip loads, reflective phase shifter is achieved. It designed on multilayer Rogers RO4003C substrate. The configuration consists of elliptically shaped transmission line and the combination of rectangular and elliptical shaped slots on the ground plane. To improve characteristics of the designed coupler especially in lower frequency band, multi-section transmission line and altering shape of the slot on ground is proposed. By etching extra rectangular slots on the ground plane the overall size reduction is achieved. Measurement results of the proposed coupler demonstrate coupling of 3 ± 0.7 dB with 90° ± 0.6 phase shift over 1-6 GHz (143%). The novel reflective phase shifter based on the designed coupler provides phase deviation less than 0.7° on 1.2-4.8 GHz (120%). The obtained return loss is better than 10 dB as well as insertion loss is less than 1.2 dB at the frequency band of interest. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:567-573, 2017 [ABSTRACT FROM AUTHOR]

The Crank–Nicolson (CN) version of the finite-difference time-domain (FDTD) method is applied to the analysis of multiconductor transmission lines (MCTLs). Stability and dispersion issues are investigated for different cases, including single and multiconductor lossless and lossy lines. It is shown that for MCTLs, stability of the CN-FDTD method is conditioned by the structure of coupling matrices. Sufficient conditions for unconditional stability are derived. Four practical problems are analyzed using the CN-FDTD method and the results are compared to measurements and Leap-Frog method. For the first three cases, it is observed that using the CN method, the Courant number can be increased by the factor of 50 with good agreement with measurement results. [ABSTRACT FROM PUBLISHER]

An analytic design guide to design a three-stage cascade CMOS operational amplifier compensated by AC boosting frequency compensation (ACBC) method is presented in this paper. The procedure allows electrical parameters such as gain bandwidth (GBW) product or phase margin to be related to the value of circuit elements such as aspect ratio or biasing currents of transistors. The presented design guide is suited for pencil-and-paper design and yields accurate performance without unnecessary circuit constraint introduction. Simulation results using TSMC 0.18 µm CMOS process verifies accuracy and robustness of proposed procedure. Various load capacitors and circuit conditions are simulated and, based on obtained results, the presented design guide is comprehensive and efficient since it leads us from frequency response parameters to aspect ratio of MOSFETs. [ABSTRACT FROM PUBLISHER]

In this paper, a novel compact T-shape defected ground structure (DGS) is proposed in order to reduce the mutual coupling between elements in a microstrip antenna array structure. The proposed DGS has considerable advantages compared to an H-shaped DGS. As is known, DGS insertion is a common problem in microstrip antenna array structures. However, the proposed T-shaped structure is more compact so it could be suitable for a compact microstrip array antenna. The T-shaped DGS is about 24% more compact than the H-shaped one. However, the most important novelty of our work is reducing mutual coupling both in the E-plane and the H-plane, which previously was discussed just in the E-plane. Finally, we have considered the disturbing effect of mutual coupling on the side lobe level (SLL) of unequally spaced arrays; using these results, a T-shaped DGS has been implemented in an 8-element unequally spaced array antenna in order to reduce its SLL. [ABSTRACT FROM AUTHOR]

In the millimeter-wave frequency range, electromagnetic effects can significantly influence a device behavior. As the core of modern communication systems, active devices such as field-effect transistors require up-to-date models to accurately integrate such effects, especially in terms of noise performance because most of communication systems operate in noisy environments. Based on the active coupled line concept, a novel approach for efficient noise performance modeling of millimeter-wave field-effect transistors is proposed. This distributed model considers the effect of wave propagation along the device electrodes, which can significantly affect the noise performance, especially in the millimeter-wave range. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]