Design and optimization of CPW‐based composite right/left‐handed transmission line

This article presents a systematic design procedure of CPW‐based Composite Right/Left‐Handed Transmission Line (CRLH TL), including the initial design and optimization algorithm. A Graphical User Interface (GUI) is provided to help inexperienced users synthesize CRLH at any given transition frequency, without tedious tuning or iterative trial. An improved fitness function based on Genetic Algorithm (GA) is presented to reduce the return loss and diminish the bandgap. This design procedure is fast and available, and has been verified by both measurement and full‐wave simulation results. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Continuously varying coupled transmission lines applied to design band‐pass filters

This article presents a technique to analyze and optimize Continuously Varying Transmission Lines (CVTL's), used to design microwave band‐pass filters in planar technology. For millimeters waves, radiation losses can increase quickly, especially for sharp discontinuities in planar circuits. In this approach, rather than taking account of this effect in a full‐wave analysis, we generate structures without discontinuities. Moreover, the line shape is optimized to reduce spurious responses out of the band‐pass. For several filters, measurements are compared with simulation results. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 288–295, 2002.     

Modeling and synthesis of the interdigital/stub composite right/left‐handed artificial transmission line

An efficient design procedure, including both analysis and synthesis, is proposed for Composite Right/Left Handed (CRLH) interdigital/stub structures. Improved models are developed for both the interdigital capacitor and the shorted stub inductor including its ground via hole. Subsequent optimal formulas are recommended to model these components with their parasitic effects. The models and formulas are verified by both full‐wave and experimental results. A CAD program with a friendly GUI, available online, is provided and its operation is described in details. This program allows a very fast design of the CRLH structure, and its synthesis parameters are proven very accurate without any full‐wave optimization. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.     

One‐dimensional low‐profile slot‐loaded epsilon‐negative zeroth‐order antenna with improved radiation efficiency

A novel low‐profile slot‐loaded epsilon‐negative (ENG) transmission line (TL) is proposed for efficiency‐improved zeroth‐order resonant antennas. It is demonstrated that the quality factor of the ENG TL‐based zeroth‐order resonator can be remarkably reduced by enlarging the slot size, therefore, a highly efficient radiating resonator can be designed with higher gain at the zeroth‐order frequency. Two one‐dimensional zeroth‐order resonant antennas with identical unit cell size but different unit cell number are fabricated and measured, each of which can realize a monopole‐like radiation pattern at nearly the same frequency. A maximum gain of 1.96 dBi is generated for the electrically small two‐unit‐cell configuration together with an improved efficiency from 57.0% to 69.1%, while the compact four‐unit‐cell antenna can realize a maximum gain of 3.86 dBi with an improved efficiency from 71.0% to 82.4%. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Dual‐band rotary standing‐wave voltage‐controlled oscillator

In this article, a dual‐band rotary standing‐wave oscillator (RSWO) is introduced that generates sinusoidal signals by the formation of a standing wave on a ring (closed‐loop)‐distributed composite right/left‐handed (CRL) Inductor‐Capacitor (LC) transmission line network. The LC network consists of four unit cells of CRL LC resonator stacked in series, and two pairs of cross‐coupled transistors are used to compensate for the loss of LC resonator. Varactors are used as the control to switch on/off the high‐ or low‐frequency bands. In the fundamental mode, the RSWO operates at the high‐frequency band. In the harmonic mode, the oscillator provides low‐frequency band outputs. The dual‐band function exploits the multiple oscillation modes of the CRL RSWO. The proposed RSWO has been implemented with the Taiwan Semiconductor Manufacturing Company, Limited (TSMC) 0.18‐μm SiGe BiCMOS technology. It can generate differential signals in the high‐band frequency range of 6.73–8.60 GHz and in the low‐band frequency range of 3.68–3.73 GHz. The die area of the RSWO is 1.123 × 1.123 mm². © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:536–543, 2014.     

Microstrip dual‐band bandpass filters using parallel‐connected open‐loop ring resonators

This article proposes a microstrip dual‐band bandpass filter that uses parallel‐connected open‐loop ring resonators. Compared to many microstrip dual‐band filters, the advantages of using microstrip open‐loop ring resonators are easy calculation (half‐guided‐wavelength), easy fabrication (equal width for all 50‐Ω lines and without grounding holes), and direct connection to external feed lines (reducing insertion loss caused by gap couplings). Another advantage of the filter is an asymmetrical feed on the ring resonator that provides sharp rejections at its adjacent bands. The input and output matches of resonators to the external feed lines are derived using a simple transmission‐line theory. The results of the derivation provide a simple design rule for filter designers. Simulated and measured results are presented with good agreement. The filter has minimum insertion loss of 1.25 dB at 1.85 GHz and 1.6 dB at 2.33 GHz. The 3‐dB fractional bandwidths are 5.9% for the 1.9‐GHz bandpass filter and 4.7% for the 2.4‐GHz bandpass filter, respectively. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

Miniaturized wide‐band rat‐race coupler

New designs of wide‐band rat‐race couplers are proposed. The wide‐band operation is achieved with the use of the microstrip nonuniform transmission line sections for the branches of the conventional rat‐race coupler. The design formulas are developed using ABCD matrix and the even‐ and odd‐mode analysis. The theoretical analysis has been verified by measurements of the two manufactured wideband rat‐race couplers, one operate within 0.85–1.92 GHz and other within 1.55–3.55 GHz frequency range with the equal normalized characteristic impedance functions. For both fabricated couplers, the isolation parameter is better than 15 dB over a 77% relative bandwidth. Also, it is shown that the designed wide‐band rat‐race coupler can be realized in higher frequency bands with the fixed fractional bandwidth. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 23: 675–681, 2013.     

Study on the propagation properties of TM electromagnetic wave in Lossy left‐handed material based on CUDA‐implemented parallel

By using the method of Finite Difference Time Domain (FDTD) and the technology of Compute Unified Device Architecture (CUDA), the propagation characteristics of electromagnetic waves in Left‐Handed Materials (LHM) have been studied in this paper. The LHM slab was matched with the free space and the secondary focusing phenomenon of LHM was simulated. Compared with the serial FDTD program, our work showed that this method had a high accuracy. The phase compensation effect and the inverse Snell effect of LHM were also discussed by using the parallel FDTD method based on CUDA, which further proved that our results were consistent with the theoretical study. By comparing the calculation time of traditional FDTD program with that of the CUDA based parallel FDTD program, we conclude that the latter is more efficient than the former. This parallel method can be used as a more efficient way to study LHM.     

High‐rejection wide‐stopband lowpass filters using signal interference technique

A design of compact, sharp rejection microstrip lowpass filters (LPF) with wide‐stopband is presented by using signal interference technique. The filter parameters can be easily controlled by the characteristic impedances of the configuration. Explicit design equations with graphs are presented. To validate the theoretical prediction, two prototype LPFs are fabricated. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Broadband and low‐loss composite right/left‐handed transmission line based on broadside‐coupled lines

A novel composite right/left‐handed (CRLH) transmission line (TL) structure is proposed and investigated. This structure consists of a pair of broadside‐coupled lines and a shorted stub. First, its fundamental characteristics and the relation between its electrical parameters and bandwidth are studied utilizing the TL theory. Then, closed‐form design equations with flexible parameter selection are given. Finally, several microstrip implementations of the proposed structure are developed to verify our theoretical results. It is shown that the proposed structure can achieve a very wide left‐handed (LH) and right‐handed (RH) bandwidth with low insertion loss and low return loss.     

Dual‐wideband filtering power divider based on center‐fed three‐line coupled structure

In this article, a dual‐wideband filtering power divider is proposed by using a center‐fed three‐line coupled structure with three open stubs and two isolation resistors. The center‐fed three‐line coupled structure can generate two wide passbands separated by a transmission zero (TZ). The three open stubs can achieve four TZs around the two passbands, which is conducive to the frequency selectivity. Compared with the reported designs, the bandwidth is extended and the performance of isolation, insertion loss and circuit size can reach balance. The proposed design is implemented with size of 0.22 λ_g × 0.39 λ_g (λ_g is the guided wavelength at the center frequency of the lower passband) which exhibits the 3‐dB fractional bandwidths of 56.5%/24.27% and the insertion loss of 0.51/0.68 dB at the center frequency of two passband (f₁/ f₂) of 1.94/4.2 GHz, while the isolation at f₁/f₂ are higher than 22.5/20.1 dB.     

Band‐notched ultra‐wideband antennas using nonperiodic composite right/left‐handed resonators

This article investigates the characteristics of a single/double‐cell composite right/left‐handed (CRLH) resonator and its application on multiple band‐notched ultra‐wideband (UWB) antennas while suggesting an accurate design procedure. Periodicity assumption and calculating a dispersion diagram allow band‐notched frequencies to adequately predict prior to antenna design. Zeroth‐order resonance (ZOR) frequency due to the CRLH characteristics of a mushroom resonator and higher‐order resonance frequencies are predictable through the hypothetical dispersion diagram. To demonstrate this method, compact, printed, ultra‐wideband circular monopole antennas with four/five‐band notched characteristics using a single/double mushroom resonator are presented. The effects of mushroom cell size on ZOR and the other band notched resonant frequencies are also investigated. The numerical simulations show that the asymmetrical unit cell provides the capability to tune both ZOR and band notched frequencies. Comparison between the simulation and measurement results shows reasonable agreement.     

Coaxial‐fed high‐gain triple‐band zeroth‐order circularly polarized antenna using pseudo‐open termination and asymmetric unit cells

A coaxial‐fed tri‐band zeroth‐order resonance (ZOR) circularly polarized antenna with higher gains for all the excited ZORs is designed and analyzed in this paper. Epsilon negative transmission line (ENG TL) and pseudo‐open termination (P‐OT) unit cells with different series capacitances (C_S and C_S1 ) resonate shunt ZOR (f_sh ) and two series ZORs (f_se and f_se1 ), respectively. Asymmetric unit cell concept is applied to ENG‐TL and P‐OT unit cells to create vertical and horizontal components, and the 90° phase shift is provided by the ZOR, resulting in circular polarization (CP). Left‐hand CP (LHCP) is achieved by creating two 90° right bends to the extended stubs in ENG TL and P‐OT unit cells. Higher gains for all the excited ZORs are achieved by shifting the shorting pins of ENG TL and P‐OT unit cells far away from the center position. After fabrication, the measured resonances occur at 4.64 GHz (f_sh ), 4.04 GHz (f_se ), and 3.86 GHz (f_se1 ) with fractional bandwidths of 1.62%, 1.73%, and 1.6%, respectively. The measured LHCP peak gains are 4.05 dBic (f_sh ), 3.85 dBic (f_se ), and 3.94 dBic (f_se1 ). The average axial ratio obtained is less than 3‐dB in the 10‐dB fractional bandwidth of the proposed antenna.     

Novel compact dual‐narrow/wideband branch‐line couplers using T‐Shaped stepped‐impedance‐stub lines

This article presents a compact model to reduce the physical size and increase the frequency ratio between the second and first resonance frequencies of a dual‐function stepped‐impedance‐stub (SIS) line, which was subsequently employed in the realization of dual‐band branch‐line couplers. The proposed model comprises of a loaded spiral T‐shaped SIS that reduces the size of a conventional SIS line as well as improving its frequency ratio. The proposed model behaves exactly similar to the recently developed dual‐band resonators with the advantage of size reduction of ～35% as well as having a wide range of realizable frequency ratios between 1.4 and 3.7 compared to 1.7–2.7 and 1.8–2.3 for the conventional SIS and T‐shaped transmission‐lines, respectively. Dual‐narrowband and wideband branch‐line couplers were developed based on the spiral T‐shaped SIS lines. The dual‐wideband device's bandwidth was enhanced by 2.7% accompanied by a size reduction of 58.6% in comparison with the conventional dual‐wideband couplers operating at the same frequencies. The theoretical results were verified by measurement. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Closed‐form approach to design distributed matching networks for high‐frequency amplifiers

Based on the use of distributed lossless elements, a closed‐form synthesis for double‐frequency‐matching networks is introduced with an emphasis on the design of high‐frequency amplifiers. Three different circuit conditions are considered and design relationships are provided and discussed. Finally, the proposed approach, which uses the circle method, is successfully employed to design a Ka‐band (26–32 GHz) linear amplifier with gain equal to 8 dB and return loss greater than 10 dB for the considered band. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006.     

Broadband magic‐Ts with the use of coupled‐line directional couplers and left‐handed transmission line sections

The problem of broadband magic‐T realization with the use of coupled‐line directional couplers and left‐handed (LH) transmission‐line sections has been comprehensively investigated. Broadband amplitude characteristics of the proposed networks are ensured with the use of coupled‐line couplers, whereas the required phase characteristics have been achieved by the appropriate selection of right‐ and left‐handed transmission line sections. To analyze the properties of the proposed networks, a model of an ideal left‐handed transmission line has been utilized. The presented concept has been verified by two designs of broadband magic‐Ts operating in 2.5–3.5 GHz and 0.8–2.3 GHz, respectively. The obtained results proved that the proposed magic‐T networks allows one to obtain broadband amplitude and phase responses together with its compact structure. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:513–521, 2014.     

Analytical method for optimal design of RF dual‐band rat‐race couplers for arbitrary frequency ratios

This article presents an analytical method to design a hybrid structure dual‐band rat‐race coupler at microwave frequencies. The proposed structure uses six identical cells of which each is engineered to work as a quarter wavelength transmission line with proper characteristic impedance at two distinct frequencies having arbitrary frequency ratio. The performances of the π‐ and T‐cells are studied to assess their ability to provide the required electrical parameters for dual‐band operation. It is demonstrated that the single‐section π‐topology can only lead to a suboptimal design for a dual‐band rat‐race cell at two nonharmonic frequencies. In contrast, the proposed double‐section π‐cell structure allows achieving an optimal dual‐band cell design. A dual‐band rat‐race coupler designed at 2.14 and 3.6 GHz has been simulated and fabricated in hybrid microstrip technology. Measurement results agree well with analytically based simulation results, which demonstrate the effectiveness of the proposed structure for dual‐band operation. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22: 690–700, 2012.     

Analysis of frequency‐selective impedance loading of transmission lines for dual‐band couplers

This article proposes an analytical design methodology for dual‐band hybrid couplers and baluns structures for any arbitrary frequency ratio using a stub‐loaded transmission line. An analysis of changing the impedance behavior of the stub, is carried out for the two bands of operation, which along with a dispersive analysis, emphasizes certain conditions where the existing methodology is not applicable. In addition, an extra degree of freedom has been included to increase the solutions for a given frequency ratio, thus providing greater flexibility and feasibility of the proposed structure. The design methodology is experimentally validated with the design and fabrication of dual‐band branch‐line and rat‐race couplers for various commercial frequency bands. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2011.     

Nonuniform reflect‐array antennas

A center‐fed reflect‐array antenna with nonuniform substrate as a reflecting surface is proposed. To design and analyze this kind of antennas, a simple method based on an equivalent circuit model is introduced. Using this method a low cross‐polarization of about ?21 dB below the main beam peak and wide 3‐dB gain bandwidth of 19.5% are obtained at X‐band frequency. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Asymmetric dual‐band linear‐to‐circular converter by bi‐layered chiral metamaterial

In this article, we present a dual‐band linear‐to‐circular transparent converter by bi‐layered chiral metamaterial (CMM) with an inverted “G” array in microwave region. The proposed metasurface consists of three layers which are the upper layer of the metasurface with a periodic regular metallic inverted “G” and wire array, the dielectric layer, and the bottom layer operating as chiral symmetric structure of the upper. The simulation results show that the transmitted right‐circular polarized wave with the axial ratio of 3 dB or less is in the range of 8.6‐10.9 GHz and the left‐circular polarized wave is within 18.1‐22.5 GHz when y‐polarized forward wave is normally incident. Specifically, the polarization conversion transmission can be maintained at over 85% at angle of incidence up to 40°. Therefore, the proposed CMM device is useful for the development of the integrated polarization manipulation devices.