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Abstract Here, an ultra‐high gain quadratic boost DC–DC converter (UQBC) based on the conventional quadratic boost converter (CQBC) and a three‐winding coupled inductor (TWCI) has been proposed. It benefits from an extensive voltage gain range and low voltage stress on semiconductors. In addition, the converter requires a reasonable number of components. This structure is suitable for connecting renewable DC power sources like fuel cells to a DC‐bus in DC microgrids. Unlike CQBC, the produced conversion ratio has been improved to [1+n+m+d(1+n)]/(1−d)2 thanks to integrating a TWCI into CQBC. As a result, the proposed quadratic boost converter gives a better step‐up factor than previously presented quadratic boost converters (QBC). Meanwhile, the employed improvement method has not adversely affected some critical parameters like voltage stress on semiconductors or the input current ripple. This paper presents the mathematical analysis and operating principle of the proposed topology for both continuous and discontinuous current modes (CCM and DCM). Experimental results are represented to validate the converter theory and its performance. Results indicate that a high gain and efficiency have been obtained. Also, the voltage stress on the power switch is reduced by one‐fourth by choosing a proper duty cycle and winding coefficient.

Here, an ultra‐high gain quadratic boost DC–DC converter (UQBC) based on the conventional quadratic boost converter (CQBC) and a three‐winding coupled inductor (TWCI) has been proposed. It benefits from an extensive voltage gain range and low voltage stress on semiconductors. In addition, the converter requires a reasonable number of components. This structure is suitable for connecting renewable DC power sources like fuel cells to a DC‐bus in DC microgrids. Unlike CQBC, the produced conversion ratio has been improved to [1+n+m+d(1+n)]/(1−d)2 thanks to integrating a TWCI into CQBC. As a result, the proposed quadratic boost converter gives a better step‐up factor than previously presented quadratic boost converters (QBC). Meanwhile, the employed improvement method has not adversely affected some critical parameters like voltage stress on semiconductors or the input current ripple. This paper presents the mathematical analysis and operating principle of the proposed topology for both continuous and discontinuous current modes (CCM and DCM). Experimental results are represented to validate the converter theory and its performance. Results indicate that a high gain and efficiency have been obtained. Also, the voltage stress on the power switch is reduced by one‐fourth by choosing a proper duty cycle and winding coefficient. [ABSTRACT FROM AUTHOR]

Fast data-driven surrogate models can be employed as replacements of computationally demanding full-wave electromagnetic simulations to facilitate the microwave design procedures. Unfortunately, practical application of surrogate modelling is often hindered by the curse of dimensionality and/or considerable nonlinearity of the component characteristics. This paper proposes a simple yet reliable approach to cost-efficient modelling of miniaturized microwave components which adopts two fundamental mechanisms to improve the computational efficiency of setting up the surrogate. Firstly, the model domain is confined-using a set of pre-optimized reference designs-to the region of the parameter space containing high-quality designs with respect to the relevant performance figures. Secondly, the domain is spanned by the selected principal components of the reference set for dimensionality reduction. Consequently, the surrogate model, covering wide ranges of the device parameters and operating conditions, can be established using a fraction of training data samples required by conventional approaches, without compromising its predictive power. The proposed technique is illustrated using two miniaturized microstrip components: a rat-race coupler (RRC) and an impedance matching transformer. The following accuracies of the PCA-based surrogates have been obtained: 0.9% for RRC and 2.1% for the transformer (for 800 training data samples). [ABSTRACT FROM AUTHOR]

In this study, the authors will investigate the insertion loss (IL) of the broadband 8‐way power combiner used in their millimetre‐wave power amplifier (PA) design. By treating this combiner as impedance transformer under resistor‐capacitor (RC)‐loading condition, both the characteristic impedance and electrical length of the constituting metal lines can be obtained, where the much shorter line length suggests wider bandwidth and lower IL. However, proper loss analysis must take into account the multi‐reflection of voltage wave along these mismatched transmission lines, i.e. the use of the power attenuation expression e−2αL is just not accurate enough. With their derived equations, it shows that the IL of their proposed 8‐way combiner can be as low as 0.92 dB at 94 GHz, which is much smaller than the 1.5 dB for the conventional quarter‐wavelength combiner. Mathematics for the IL of the drain‐bias shunt stub and the output DC‐blocking capacitor has also been derived. As a demonstration, a 77–110 GHz 40 nm‐complementary metal–oxide–semiconductor PA made of cascode transistors is then designed that has more than 18 dB gain, and its OP1 dB is around 13 dBm across the whole frequency range. [ABSTRACT FROM AUTHOR]

A compact and wideband slot antenna backed by a square substrate integrated waveguide (SIW) cavity is presented. By exciting the dual-slotted SIW cavity with an offset coaxial feed, a transverse electric (TE)110 resonant mode along with two hybrid modes as combinations of TE110 and TE120 resonances can be generated within a close range. The triple resonances contribute to producing a wideband response while maintaining a compact antenna structure. An antenna prototype with a total size of 0.49λ0 × 0.49λ0 × 0.16λ0 is manufactured and experimentally tested. Measures results show that an operating band of about 33.0% is obtained. Meanwhile, it also exhibits stable unidirectional patterns and moderate gains over the whole band. [ABSTRACT FROM AUTHOR]

A kind of impedance transformer with high impedance ratio based on tapped coupled-resonator filter theory is proposed. Differently with the published ones, the proposed filtering transformer incrementally takes impedance property of the filter into consideration. Thus, the high impedance ratio can be achieved. By proper design of impedance and type of resonator, two prototypes with impedance ratios as high as 400:50 and 800:50 and 3-dB fractional bandwidths of 20.2 and 22.8% are realised. [ABSTRACT FROM AUTHOR]

In many planar antenna array designs, impedance transformers are required to interconnect the elements to ensure that their impedances are matched. However, impedance transformers take up space and reduce area utilisation. If each element is electrically small and able to function individually as an electrically small antenna (ESA), they can be combined into an array without using impedance transformers. In this study, a stubbed hexagonal shaped folded dipole ESA of one tenth of the wavelength is proposed and developed. This metamaterial inspired design of loading the folded dipole with split ring resonator overcomes the problem of fabricating ESA of one tenth of the wavelength using typical printed circuit board fabrication technologies for the 2.45 GHz band. To show the potential of using this ESA as a unit element for antenna array without using impedance transformers, a seven-element array is designed and fabricated. By optimising the element separation distance, and stub lengths, the ESA array shows good S(11) of less than −25 dB, and gain improvement of up to 12 dB compared with a single unit ESA.

In this Letter, a differentially fed impedance‐transforming directional coupler is considered. The utilisation of recently introduced unequal‐width differentially fed coupled conductors allows for setting independently terminating impedances for each of coupled lines as well as for coupling control in a chosen dielectric stack‐up. The theoretical analysis is confirmed by experimental verification, in which an impedance transforming 70–50 Ω 3 dB single‐section directional coupler has been designed and measured. [ABSTRACT FROM AUTHOR]

This study presents a novel dual-band antenna design methodology utilising a dual-frequency impedance transformer with defected ground structure (DGS). The proposed dual-frequency DGS impedance transformer generates a second resonant frequency from a conventional single-band antenna, resulting dual-band operation. Simulation studies illustrate that the adopted design achieves versatile configurations for arbitrary operating frequencies and diverse input impedance ranges in planar antenna structures. To experimentally verify the proposed design methodology, a dual-frequency DGS impedance transformer was implemented for a 2.4 GHz monopole antenna to obtain a 900/2400 MHz dual-band antenna. Measurement shows that the 10 dB return loss bandwidth in 900 MHz band is 34.4 MHz, whereas that in 2400 MHz band is wider than 530 MHz. Typical monopole radiation patterns are observed at both operating bands.

Tunable surface‐acoustic‐wave‐(SAW)‐based bandpass filters (BPFs) with flat in‐band group delay (τg) and variable passband bandwidth (BW) are reported. They are based on N hybrid acoustic‐wave‐lumped‐element‐resonator (AWLR) modules shaped by one lumped‐element resonator and K RF‐switched SAW resonators that are arranged in a Gaussian‐type source‐to‐load impedance‐inverter network. Fractional bandwidth (FBW) tuning is achieved by reconfiguring the number of SAW resonators within the AWLR modules. Major advantages of the proposed filter concept when compared to conventional SAW BPFs are as follows: (i) they do not depend on the electromechanical coupling coefficient (kt2) of the SAW resonators – FBW>kt2 can be realised –, (ii) they do not require lossy elements or SAW resonators with different frequencies, and (iii) they can be tuned. For experimental‐validation purposes, a 433.9 MHz two‐pole/four‐transmission‐zero prototype was built and measured. It exhibited flat‐in‐band‐τg passbands with discretely‐tunable BW between 0.18 and 0.45 MHz (i.e. 2.5:1 tuning ratio). [ABSTRACT FROM AUTHOR]

A wideband filtering impedance transformer (WFIT) based on transversal interaction concept is presented. The proposed WFIT has four reflection zeros in the passband to broaden the operating bandwidth. Moreover, two transmission zeros are generated to enhance the selectivity. For verification, a prototype is designed, simulated and measured. The measured results show that the proposed WFIT has about 60% bandwidth in terms of S11 larger than 20 dB and the rejection out‐of‐band is better than 30 dB. [ABSTRACT FROM AUTHOR]

A novel impedance transformer (IT), which transforms different terminations at multiple bands is reported. This transformer is especially suitable for extremely low and high impedances. By utilising the impedance buffer method and introducing ladder networks, this IT is generalised and is available to arbitrary number of bands theoretically. For verification, a quad‐band prototype is fabricated and measured. The results show good agreement with the design expectations. [ABSTRACT FROM AUTHOR]

The design of optimal electromagnetic compatibility filters for converters used in electrical networks requires the precise knowledge of input and output terminal impedances. For this reason, the knowledge of the network impedance, including all connected converters, is determined. This paper proposes a study of both the common mode (CM) and the differential mode (DM) impedances of modern embedded networks including cables and several converters. Using a dc network for illustration, we determine the impedance taking into account all operating states of a converter (online or offline operations). Without any restrictions, a theoretical model is developed to express the CM and DM impedances using a switching function and a Fourier series decomposition. An experimental validation has been carried out in a frequency range from a few Hertz up to 80 MHz. Our model has then been used in a simple network, so as to compute the network impedance. Measurements have confirmed the proposed model accuracy. [ABSTRACT FROM AUTHOR]

Compact unequal power dividers are suggested for high-power division ratios and arbitrary phase differences. The power dividers are classified into two parts: power-dividing and impedance-transforming parts and consist of the asymmetric impedance transformers of constant voltage-standing wave ratio (VSWR)-type transmission-line impedance transformers (CVTs) and constant conductance-type transmission-line impedance transformers (CCTs). Given the special properties of asymmetric impedance transformers, the arbitrary phase differences between two outputs may be obtained by controlling the impedance-transforming part. Compactness can be achieved by using the equivalent circuits of stepped-impedance modified T-types and LS1-types. A power divider with a power division ratio of 9 (9.542 dB) and total transmission line sections that are 181.1 ° long is fabricated to verify compactness and best frequency performance. Another power divider comprising two CVTs and two different CCTs is measured for 45 ° phase difference between two outputs. The measured results are in good agreement with the predicted findings. [ABSTRACT FROM AUTHOR]

Coupled inductors have been used with impedance-source networks, extended from the earlier Z-source network, to keep their shoot-through times short, while providing high-voltage gains. A commonly stated requirement for these networks is that their magnetic couplings must be strong or their leakage inductances must be small. This is often difficult to achieve in practice especially at high switching frequencies. It is therefore necessary to understand the effects that leakage inductances have on the performance of these converters. In this letter, we address these issues for the latest Y-source network, showing in particular that voltage spikes will appear across its switching devices in some, but not all, cases. Experimental results verifying the findings have been obtained and presented at the end of this letter. [ABSTRACT FROM AUTHOR]

To create an active phase‐gradient metasurface relying on variable inductance, an impedance converter is used to realise positive inductance values. By varying the inversion coefficient, a variation of the inductance can be achieved electronically. A prototype of the circuit is fabricated and tested. Different inductance values are obtained with respect to the inversion coefficient used. Such circuit can be readily applied to an LC resonant cell to control the phase responses. A potential application for beam steering is further numerically verified. [ABSTRACT FROM AUTHOR]

In this paper, ultra-wideband (UWB) Marchand baluns using substrate integrated coaxial line (SICL) technology are first proposed. SICL is a shielded planar coaxial line, which is very suitable for wideband and high-speed applications due to its broad unimodal operation band, low insertion loss, very small dispersion, and easy integration with other planar circuits. In order to achieve wider bandwidth and better VSWR performance of the SICL balun, a pair of quarter-wave impedance transformers are inserted into the balanced line. The impedance characteristics of the proposed SICL baluns are analyzed, and the parameters that determine the balun bandwidth are discussed. Then, curves of the balun resistance, reactance, and the SICL characteristic impedance are presented. According to these curves, the design parameters of the proposed SICL baluns can easily be determined. To verify these ideas, an UWB SICL single balun and an UWB SICL dual balun are designed, fabricated, and measured. Both full-wave simulated and measured results are presented, and good agreement between them is observed. The proposed SICL baluns have a simple structure and good performance, which are suitable for applications in UWB communication systems. [ABSTRACT FROM AUTHOR]

This paper presents, for the first time, the design and implementation of a dual-band branch-line coupler with unequal operating bandwidths. The control of bandwidths is accomplished by the use of dual-band quarter-wavelength impedance transformer with controllable phase slopes over the two designated frequency bands. The adjustment of phase slopes is attained by the proper selection of the circuit parameters of the transformer. For design purposes, closed-form expressions are derived for the determination of the electrical lengths and line impedances of the resulting coupler. For experimental verification, both simulated and measured results of dual-band couplers designed to operate at 1 and 2 GHz are shown. [ABSTRACT FROM AUTHOR]

A novel filtering push–pull power amplifier (PPPA), based on unbalanced‐to‐balanced impedance transformers, is presented for the first time. This novel impedance transformer can not only simplify the PPPA topology and miniaturise the overall circuit size, but also provide the bandpass filtering response and improve the second harmonic suppression performance. The proposed impedance transformers, which are constructed by two different C‐type line resonators, can provide good impedance matching performance under the odd‐mode excitation, while achieve high common mode suppression under the even‐mode excitation. Finally, a PPPA is designed and fabricated with the centre frequency of 2.45 GHz and bandwidth of 200 MHz for WLAN application. Moreover, detailed explanation and measured results are demonstrated for verification. [ABSTRACT FROM AUTHOR]

A small transformer consisting of two sections for real load impedances is proposed. The characteristic impedances and their electrical lengths for two sections are derived in closed form. From the newly derived design equations, once two real terminal loads are determined, the electrical lengths of two sections can be selected arbitrary, and then their characteristic impedances are calculated automatically. Furthermore, when electrical lengths for both sections are exchanged, the same S‐parameters can be derived, and this is called symmetry property in this Letter, and this property proved that: there are two different group design parameters with the same performance under the same conditions. In experiments, one circuit was fabricated. The experimental results showed good agreement with theoretical results. [ABSTRACT FROM AUTHOR]

The article discusses the application of the broadband impedance inverter in transmission line transformer. Filter designers often postulate imaginary impedance inverters, which use negative reactance elements. [ABSTRACT FROM PUBLISHER]

A semi-lumped balun transformer for UHF and ultrawideband (UWB) dipole antennas is presented in this paper. The proposed structure is based on two asymmetric filters that also transform the variable antenna impedance into the desired source impedance. These asymmetric filters make use of a binomial impedance transformer in each filter section. The asymmetric filters (one low pass filter, LPF, and other high pass filter, HPF) allow the balun bandwidth to be increased while the binomial transformer matches the variable balanced dipole impedance. In this way the ripple in the balun response due to the variation of the UWB dipole impedance is reduced. A balun for a UHF and UWB dipole antenna working from 220 to 820 MHz (bandwidth of 4:1) has been achieved with losses lower than 1 dB. These types of baluns are particularly useful in the low microwave frequency band. [ABSTRACT FROM PUBLISHER]

A compact unitraveling-carrier photodiode (UTC-PD) module with a WR-8 rectangular waveguide output port for operation in the F-band (90-140 GHz) has been developed. A resonating matching circuit integrated with a UTC-PD and a microstrip-line-to-rectangular-waveguide transformer are designed to have high output powers with a wide bandwidth covering the F-band. The module size and configuration are equivalent to those of conventional optoelectronic devices, which enables the use of standard assembly technology. The fabricated module exhibits a record millimeter-wave output power of 17 mW at 120 GHz for a bias voltage of -3 V. The 3-dB bandwidth is as wide as 55 GHz, which fully covers the F-band. An optical input stress test at a photocurrent of 10 mA performed to confirm the long-term stability of the module showed that the dark current stays below 1 μA for more than 4000 hours. [ABSTRACT FROM PUBLISHER]

A fully integrated power amplifier using a power cell switching technique, implemented in 65 nm CMOS technology is presented. The main objective of the proposed architecture is to significantly improve the efficiency at high power back‐off. To do so, distributed active transformers are used as the splitter, the combiner and the DC bias feed to partition the power requirements among the parallelised power cells. An individual cell can be dynamically turned ON/OFF according to the desired output power. At 2.5 GHz, the measured maximum output power is 28.2 dBm and the power‐added efficiency is improved for low level, +3.2 and +4.9% for 18 and 23.7 dBm, respectively. [ABSTRACT FROM AUTHOR]

A novel coupling configuration between an SIS mixer, an antenna, and a local oscillator has been numerically characterized for an integrated receiver operated in the sub-THz region. The configuration consists of two vertically stacked superconducting striplines, where the thickness of their common electrode t/sub 2/ is of the order of its magnetic penetration depth /spl lambda//sub 2/. It has been found that the coupling efficiency between the antenna and the mixer decreases with decrease of t/sub 2///spl lambda//sub 2/, while that between the mixer and the local oscillator has a local maximum. It is also shown that the coupling efficiencies increase with decrease of Q/sub A/, the Q-factor due to the tunneling loss in the mixer. For Q/sub A/=5.0 and 16, 75-85% of the available signal power and sufficient power from the local oscillator can be absorbed in the tunnel conductance of the mixer at 1 THz. This coupling efficiency is equal to or larger than that of a conventional planar coupler. [ABSTRACT FROM PUBLISHER]

A metamaterial based compact microstrip T-junction power divider working at 10GHz is proposed. The metamaterial unit cell consists of microstrip gaps and via holes whose behavior is equivalent to the combination of series capacitors and shunt inductors respectively, that is, a dual transmission line (high-pass) configuration. By adjusting the parameters of these structures, the characteristics of the Metamaterial-medium can be set to achieve a desired phase shift. To validate the design, a T-junction power divider is fabricated and measured. A 70% reduction of the length of the impedance transformer, without significant performance degradation, has been achieved [ABSTRACT FROM PUBLISHER]

A Wilkinson power divider operating not only at one frequency f0, but also at its first harmonic 2f0 is presented. This power divider consists of two branches of impedance transformer, each of which consists of two sections of 1/6-wave transmission-line with different characteristic impedance. The two outputs are connected through a resistor, an inductor, and a capacitor. All the features of a conventional Wilkinson power divider, such as an equal power split, impedance matching at all ports, and a good isolation between the two output ports, can be fulfilled at f0 and 2f0, simultaneously. [ABSTRACT FROM PUBLISHER]

Quarter-wavelength coplanar waveguide (λ/4-CPW) impedance transformers with low and high characteristic impedance are characterized via fullwave method of moments short-open calibration (MoM-SOC) approach and further utilized as alternative K- and J-inverter networks with enhanced coupling. Network parameters are obtained and compared with those of two traditional lumped-CPW elements, demonstrating tightened coupling behaviors. The two improved λ/4 CPW bandpass filters are then constructed and their performances are optimized via cascaded topology. Predicted results show us a few attractive features, i.e., wide passband and first-order harmonic suppression as confirmed by experiment. [ABSTRACT FROM PUBLISHER]

We derive a two-section dual-band impedance transformer that matches a resistive load at two arbitrary frequencies. The transformer is equivalent to a two-section Chebyshev transformer whose parameters have been adjusted to achieve reflectionless notches at the two desired frequencies. [ABSTRACT FROM PUBLISHER]

A novel substrate integrated waveguide to rectangular waveguide (RWG) transition for effective power transfer is proposed. The substrate taper is inserted into a conventional height‐stepped impedance transformer of the RWG region to improve transmission loss and bandwidth. The transition is designed to cover the entire K‐band (18–26 GHz), showing a return loss of 20 dB. A back‐to‐back transition has been fabricated to verify the proposed transition. The experimental results show good agreement with the analysis. The transmission loss of the stand‐alone transition is 0.22 dB at 21.7 GHz with a usable bandwidth of 36%. [ABSTRACT FROM AUTHOR]

The flexible design of decoupling and matching networks for coupled antennas is introduced. The network includes three parts: circuits for impedance transformation, an element for odd‐mode decoupling and conventional matching networks. It is found that all three parts are determined by one parameter of the ABCD matrix of the impedance transformation circuit. Thus a large variety of circuits with different element values can be used for decoupling which relaxes the practical design constraints. [ABSTRACT FROM AUTHOR]

The feasibility of an electrically small two-section transformer (total length one-third-wavelength at the fundamental) capable of achieving ideal impedance matching at a fundamental frequency and its first harmonic is demonstrated, analytically. To achieve this, the exact solution to the resulting transcendental transmission line equations for two sections is obtained with no restrictions. The parameters of the transformer are presented in explicit closed form and are exact. The results of this study are useful for a number of practical design problems, including dual-band antennas and RF circuits in general. [ABSTRACT FROM PUBLISHER]

The quarter-wave transformer transforms in one frequency f0 , but not its first harmonic 2f0. The transform in 2f 0 is needed in a dual-band operation of GSM and PCS. This requirement can be fulfilled in a two line-sections of 1/6 wavelengths each, adding to 1/3 wavelengths for the total transformer length in the lower band centering at f0 (fundamental), or 2/3 wavelengths in the upper band centering at 2f0 (1st harmonic). The 1/3-wave transformer is analytically inexact but effectively exact for engineering applications. For example, for impedance transforms of K = 4, the inexactness gives a reflection of |Γ| = 0.013 [ABSTRACT FROM PUBLISHER]