Equivalent Transmission Line Model Research Articles

Dual-Band Reflection-Type Circular Polarizers Based on Anisotropic Impedance Surfaces

A new method for constructing dual-band linear to circular polarization (CP) converter is introduced based on anisotropic impedance surfaces. An air gap is used between the substrate and ground plane to control the operating frequency of the surface without changing the substrate thickness. Required susceptance of the surface to produce CP is calculated using the equivalent transmission line model. The surface consists of small-size patches inside slotted large patches to construct a circular polarizer with two frequency bands: 1.9–2.3 GHz and 7.9–8.3 GHz. Sizes of the patches are obtained using analytical formulas. In addition, it is indicated that the permitted beamwidth of the incident wave can be increased by reducing the propagation angle ${{\theta}}$ . The circular polarizer with reduced ${{\theta }}$ has 52% and 9.8% bandwidths for less than 3 dB axial ratio with ${{{\theta }}_{{\bf max}}} = 39^\circ $ and ${{{\theta }}_{{\min}}} = 25^\circ $ . Finally, comparison between LHCP and RHCP radiation patterns of an antenna with the proposed circular polarizer indicates more than 10 dB difference throughout the main lobe.

Achromatic polarization manipulation by dispersion management of anisotropic meta-mirror with dual-metasurface.

A dual-metasurface-based reflective device ("meta-mirror") has been proposed for broadband polarization manipulation, which is composed of orthogonal metallic cut-wire arrays separated from a grounded plane with different distances. The reflective phases of orthogonally linearly-polarized components can be independently adjusted by changing the dimensions of the cut-wire pairs. Benefiting from the fully released dispersion management ability in both dimensions, achromatic (i.e., ultra-broadband) polarization manipulation can be achieved. The suggested approach has been numerically verified in both microwave and optical band. Moreover, experimental characterization in microwave regime has demonstrated the broadband polarization manipulation ability within 5 - 30 GHz. The underlying physical mechanism of dispersion engineering was explained in general equivalent circuit theory and transmission line model.

Analysis and Characterization of a Wide-Angle Impedance Matching Metasurface for Dipole Phased Arrays

The effects of mutual coupling impact the performance of phased arrays as the beam is scanned off broadside. Wide-angle impedance matching (WAIM) alleviates this problem from a transmission-line impedance matching viewpoint, increasing the useable scan range of the array. Traditionally, a dielectric slab is placed at some distance above the array, resulting in a match at some given angle off broadside. We propose a simpler and more effective solution, replacing the dielectric slab with an ultra-thin metasurface composed of a sheet of split-ring resonators (SRRs) to improve the scanning characteristics of a dipole phased array. It is shown that the presence of the metasurface results in significant improvements in multiple scan planes. A generalized equivalent transmission-line model is introduced for the classical WAIM configuration and adapted for the metasurface. A quasi-analytical model based on the equivalent transmission-line model and the extracted scattering parameters of the metasurface properly predicts the scan range of the full structure, and allows for an accelerated design process.

Analysis on bandwidth enhancement of compact probe‐fed patch antenna with equivalent transmission line model

In this paper, a comprehensive study of miniaturised broadband microstrip patch antennas for ultra-wideband applications is presented. At first, design and analysis of a compact wideband basic antenna which is composed of a folded-patch feed, a symmetric E-shaped edge, a U-shaped-slot patch and shorting pins are studied and investigated. The measured −10 dB impedance bandwidth of the proposed basic antenna is about 92% in the frequency range 3.94–10.65 GHz. To explicitly demonstrate the mechanism of the bandwidth enhancement method, the equivalent transmission line model of the basic antenna is exhibited. This model contributes the effect of different parts used in the basic antenna structure in order to predict the broadband behaviour of it. Moreover, with the use of a V-shaped slot instead of the U-shaped slot on the patch, an improved antenna with a wider bandwidth in order to cover the frequency range from 4 to 14.4 GHz is obtained. This improved design introduces comparatively a simpler structure with considerable size reduction and an enhancement of 21% in impedance bandwidth compared with the basic antenna. Experimental investigations and detailed simulations based on the parametric study are performed to describe and optimise the broadband performance of the proposed designs.

Multiway wideband power dividers

In this article, we propose a new design methodology to broaden the bandwidth of a multiway Bagley power divider BPD. Single-frequency matching uniform quarter-wave-length microstrip lines in the conventional design are replaced with impedance-varying transmission lines of broadband matching characteristics. The equivalent transmission line model is used for profiling impedance variations, which are governed by a truncated Fourier series. Such variations are determined by finding the optimum series coefficients that result in a wideband matching nature. The proposed technique leads to flexible spectrum allocation and matching level. Furthermore, the resulting structures are compact and planar. First, analytical results of three 3-way BPDs of different fractional bandwidths are presented and discussed to validate the proposed approach. Then, two examples of 3- and 5-way BPDs with bandwidths of 4-10 GHz and 5-9 GHz, respectively, are simulated, fabricated, and measured. Simulated and measured results are in a good agreement, with input port matching of below -15 dB and -12.5 dB for the 3- and 5-way dividers, respectively, over the bands of interest. The obtained transmission parameters of the 3- and 5-way dividers are -4.77±1 dB and -7±1 dB, respectively, over the design bands. The proposed wideband dividers find many applications in microwave front-end circuitry, especially in only-transmitting antenna subsystems, such as broad- and multicast communication links. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:730-738, 2015.

Compact dual-band bandpass filter using asymmetric stepped impedance stub loaded multimode resonator

This paper presents, a dual-band bandpass filter using asymmetric stepped impedance stub loaded open loop resonator (OLR) for WLAN and WiMAX application. The outer OLR is realized to operate at lower passband of 2.45 GHz which is directly coupled to input and output ports whereas the asymmetric stepped impedance stub that loads the outer resonator contributes to 3.5 GHz passband. The introduction of asymmetric stepped impedance stub provides further control of improving the upper passband edge selectivity of second passband and in shifting the spurious modes away from second band thereby contributing to the wide upper stopband. The insertion loss is within 1.5 dB for each passband with 10 dB passband bandwidth of 250 MHz at both bands. A stopband up to 10 GHz is also obtained. A prototype is developed and the s-parameters obtained from electromagnetic simulation, equivalent transmission line model and measurement are in close agreement. The overall dimension of the filter is 25.45 × 15.89 mm2 which renders it a compact size.

Transmission upper limit of band-pass double-layer FSS and method of transmission performance improvement

The transmission upper limit of a double-layer frequency selective surface (FSS) with two infinitely thin metal arrays is presented based on the study of the general equivalent transmission line model of a double-layer FSS. Results of theoretical analyses, numerical simulations and experiments show that this transmission upper limit is independent of the array and the element, which indicates that it is impossible to achieve a transmission upper limit higher than this one under a given incident and dielectric-supporting condition by the design of the periodic array. Both the applicable condition and the possible application of the transmission upper limit are discussed. The results show that the transmission upper limit not only has a good reachability, but also provides a key to effectively improve the transmission performance of a double-layer FSS or more complex frequency selective structures.

A New Implementation of UWB CRLH Based Antennas for Wireless Communications

In this article, a novel ultra wideband (UWB) small antennas based on the composite right/left-handed transmission lines structures are proposed. The antennas are presented with best in size, bandwidth and radiation patterns. Their physical size and the operational frequency depend on the unit cell size and the equivalent transmission line model parameters of the CRLH-TL. To realize characteristics of first proposed model, Q-shaped gaps printed into rectangular radiation patches are used. The antenna based on composite right/left-handed transmission lines is composed of two unit cells, each of which occupies only 10.8 × 8.6 mm and covers the 2.7–9.3 GHz bandwidth for VSWR < 2. The peak gain and radiation efficiency, are 5.78 dBi and 42.1% 9.3 GHz, respectively. Moreover, the second designed antenna has the same size and enhancement bandwidth, gain and radiation efficiency than the first proposed antenna with similar design procedure. It is constructed of the printed Q-shaped four unit cells. The length, width and height are 21.6, 8.6 and 1.6 mm, respectively, and it covers 4.1–11.7 GHz bandwidth for VSWR < 2 having highest gain (7.18 dBi) and radiation efficiency (92.69%) at 4.1 GHz.

Slit-Surface Disturbance Lattice EBG Structure for Simultaneously Switching Noise Suppression in High-Speed Data Acquisition System

Simultaneous switching noise (SSN) is verified as a serious impact on the quality of power distribution and accuracy of the data acquisition system in the mixed signal circuits by modeling and simulating the single-stage output buffer at the driver side. To reduce SSN, a board-level slit-surface disturbance lattice electromagnetic bandgap structure is proposed. The corresponding 1-D equivalent transmission line model is established and lower and upper bound cutoff frequencies of the bandgap are derived. Suitable test boards are fabricated and measured to demonstrate the accuracy of the design concept. The measured SSN reduced to 65% and the signal jitter is decreased by 75% comparing with the solid power/ground plane, which proves that the isolation between the analog and the digital signals can be enhanced to improve the quality of power distribution, and provides a new method to improve precision for data acquisition and transmission in power monitoring system. The results show that the simulated, modeled, and measured results are consistent.

Design of Microwave Patch Hybrid Couplers with Arbitrary Power Ratio and Impedance Transformation

A miniaturized patch hybrid coupler with arbitrary power ratio and impedance transformation is proposed and designed by loading a pair of asymmetric cross slots on a squared patch resonator. To obtain the arbitrary power ratio and impedance transformation, the rectangular size of stepped slot ends should be well designed to be asymmetry and thus to obtain the different inductive loadings along two current paths. Theoretically, the equivalent transmission line model is first developed to understand the physical relationship between the patch and traditional branch-line hybrids. The matching/isolation and power ratio conditions are then derived at center frequency. By following a detailed design guideline, a prototype of the hybrid with 1:2 power ratio and 1:1.3 impedance transformation is designed and fabricated at 4.2 GHz. The measured results show a good agreement with simulated results, where the measured -10 dB impedance bandwidth achieves 18% and the bandwidth of 90°±6° phase difference is about 35% in a frequency range from 3.5 GHz to 5 GHz.

High frequency characterization of graphene nanoribbon interconnects

Interconnects and nanoscale transmission lines are critical components in the design of nanoelectronic systems. In this letter, we study the high frequency characteristics of chemical vapor deposition (CVD) graphene nanoribbon (GNR) interconnects and radio frequency propagation in GNRs embedded in a coplanar waveguide structure up to 20 GHz. An equivalent transmission line model is proposed to characterize the GNRs in high frequency regime. The strong agreement between fitting circuit parameters and measured data suggests that our model can be used in the design of nanoscale circuits in which GNRs are used to interconnect elements in the circuits. The fabricated GNRs show fairly constant characteristic impedance at high frequencies which could be useful for radio frequency interconnect applications. Our study provides an insight into microwave behavior of GNRs for developing high speed graphene devices.

Numerical Modeling for Excitation and Coupling Transmission of Near Field Around the Metal Drilling Pipe in Lossy Formation

The wireless transmission of the logging signal by using metal drill pipe as a dipole antenna with an extremely asymmetric feeding is one of the potential techniques for logging (or measurement) while drilling (LWD, or MWD) and has drawn a lot of attention in recent decades. In this paper, a precise numerical model based on numerical mode matching (NMM) theory has been built for solving the very low-frequency radiation of the asymmetrical feeding dipole antenna in the layered background medium. First of all, the feeding gap of the antenna has been equalized as a magnetic current loop, and NMM numerical solutions have been applied to expand the field excited by the equivalent source, and then, the characteristics of input impedance and the near field radiated by the dipole have been calculated based on the field solutions. Furthermore, the results have been compared with the corresponding results of the “method of moments” and the “equivalent transmission line model,” respectively. The inference of the relevant parameters, such as the asymmetry of the feeding, the working frequency, the conductivity of the formation, the size of the insulating gap, the size of the casing, etc., on the transmission performance of the signal of electromagnetic MWD (EM-MWD) system has been discussed. In addition, the method for receiving the LWD signal transmitted to the ground is also evaluated, and an adaptive impedance matching scheme in transmitting terminal is proposed based on the numerical analysis in this paper.

Compact bandpass filter with improved upper stopband

A compact bandpass filter (BPF) with a wide upper stopband using a short-circuited microstrip coupled-line hairpin resonator is presented. The equivalent transmission-line circuit model is developed to analyse the performances of the proposed filter. The feeding lines are capacitively coupled to the resonator at the point which divides the fingers of the hairpin into two segments at a ratio of 1:2. As a result, the first harmonic appears at the frequency which is five times the fundamental frequency. In the final design with a grounding via hole, three transmission zeros are generated to improve the skirt effect. Therefore, a compact BPF with a wide upper stopband could be achieved. Finally, the proposed filter is fabricated to verify the design principles, and the measured results agree well with the predicted ones.

Delay uncertainty in MLGNR interconnects under process induced variations of width, doping, dielectric thickness and mean free path

This paper analyzes the delay performance of multi-layered graphene nanoribbon (MLGNR) interconnect under process induced variations. An equivalent multi-conductor transmission line (MTL) model driven by CMOS gate is employed for the analysis. The propagation delay is analyzed for different interconnect lengths and widths by taking into account the variations in width, dielectric thickness, dielectric constant, interlayer distance and doping concentration of MLGNR. Encouragingly, it is observed that the average deviation in delay is below 3 % for all process induced parameter variations except for the mean free path.

Introducing the new wideband small plate antennas with engraved voids to form new geometries based on CRLH MTM-TLs for wireless applications

In this paper, four new wideband small antennas based on the composite right/left-handed transmission line (CRLH-TL) structures are designed, tooled, and made. The proposed antennas are introduced with best in size, bandwidth, and radiation patterns. The physical size and the operational frequency of the antennas depend on size of the unit cells and the equivalent transmission line model parameters of the CRLH-TLs, including series inductance, series capacitance, shunt inductance, and shunt capacitance. To define characteristics of the antennas, the engraved J- and I-formed voids on the radiation patches are used. The physical sizes of the CRLH antennas are 0.45λ0 × 0.175λ0 × 0.02λ0, 0.428λ0 × 0.179λ0 × 0.041λ0, 0. 564λ0 × 0.175λ0 × 0.02λ0, and 0.556λ0 × 0.179λ0 × 0.041λ0 in terms of free-space wavelengths at the 7.5, 7.7, 7.5, and 7.7 GHz, respectively. These metamaterial antennas can be used for frequency bands from 7.5–16.8 GHz, 7.7–18.6 GHz, 7.25–17.8 GHz, and 7.8–19.85 GHz for VSWR < 2, which correspond to 74.4, 82.88, 84.23, and 87.16% practical bandwidths, respectively. Also, the ranges of the measured gains and radiation efficiencies of the recommended antennas are 0.1 dBi < G < 2.1 dBi and 20% < eff < 44.3%, and 0.8 dBi < G < 2.35 dBi and 23% < eff < 48.2%, for J-shaped antennas, whereas 0.1.15 dBi < G < 3.11 dBi and 30.24% < eff < 58.6%, and 1.2 dBi < G < 3.4 dBi and 32.4% < eff < 68.1% for I-shaped antennas, respectively.

Dispersion effects in Fakir's bed of nails metamaterial waveguides

The propagation characteristics of electromagnetic waves in waveguides implemented using the “Fakir's bed of nails” are investigated both analytically and numerically. The classical metal walls of a parallel-plate waveguide are replaced by a Fakir's bed of nails metamaterial having arbitrary pin lengths on both walls; treated as a homogenized effective spatially dispersive dielectric. A modal analysis of the electromagnetic fields is presented for the first time, and dispersion expressions for the propagating modes are derived analytically and independently validated with full-wave numerical simulations. An equivalent transmission line model is also given, and similarities with the classical metal-dielectric-metal structure commonly used in optics are discussed.

Single- and dual-band leaky wave antennas using an electromagnetic band gap structure

We propose new and practical design methods of a low-profile and high-gain leaky wave antenna (LWA). Based on a required dispersion relationship, we suggest appropriate equivalent transmission line models representing a unit cell of the LWA, which determines a specific frequency of maximum radiation together with optimal circuit values essential for maximum gain at a boresight direction. According to the equivalent model approach, we can design overall structure of the high-gain LWA very easily and accurately. In addition, we also propose a novel way of deriving dual-band resonance from a simple single-band-resonating LWA by means of an electromagnetic band gap (EBG) structure. In order to make the LWA resonate at two different frequencies, we intentionally introduce a propagation stop band into an existing one pass band by inserting an EBG structure. By doing so, we can obtain two new specific conditions resulting in maximum radiation toward a boresight direction at the two resonant frequencies locating on both sides of the inserted stop band. All experimental results show good agreement with theoretical predictions, which proves the validity and effectiveness of our approaches.

A Comprehensive Investigation of a Common-Mode Filter for Gigahertz Differential Signals Using Quarter-Wavelength Resonators

This paper presents a comprehensive investigation on an inexpensive and wideband common-mode noise suppression filter that uses a quarter-wavelength resonator. An equivalent transmission line model is also used to evaluate the effectiveness of the proposed structure in a common-mode filter (CMF). Moreover, more important parameters, such as coupling coefficients are presented to investigate the characteristics of CMF unit. The performance of CMF is then characterized using two coupling coefficients between two differential traces and between differential traces and a quarter-wavelength resonator. A simple design approach is also presented for a wideband CMF. Numerical results demonstrate that CMF with three different lengths of quarter-wavelength resonators have rejection bands of 3.94-8.74 GHz and 3.53-10.1 GHz at cutoff frequencies of -20 dB and -10 dB, respectively Time-domain common-mode noise is decreased by approximately 60%. Moreover, analyses of differential insertion loss and group delay indicate that the differential signals maintain sufficient signal integrity when the wideband CMF is used in single- and two-pair differential interconnects. Finally, CMF is validated by an eye diagram and by measurements of time/frequency-domain common-mode noise and I/O cable common-mode current.

Design of thin infrared quarter-wave and half-wave plates using antenna-array sheets

A thin quarter-wave plate and a half-wave plate are designed based on multiple antenna-array sheets (AAS). For transmission through cascaded antenna-array sheets, an equivalent transmission-line model is used. The interspacing dielectric is modeled as a transmission line with each AAS treated as a loaded shunt admittance. By utilizing this transmission-line model to treat the plates as a differential phase shifter between two orthogonal polarizations, a quarter-wave plate can be designed with two AAS and a half-wave plate can be designed with three AAS. Both wave plates can achieve high transmission with the desired 90° and 180° phase difference between two orthogonal polarizations.

Measurements of Medium-Frequency Propagation Characteristics of a Transmission Line in an Underground Coal Mine

In underground coal mines, medium frequency (MF) communication systems couple their signals to metal infrastructures such as ac power cables and wire-based telephone lines, which guide the signals to propagate for a long distance. To better understand the propagation characteristics of MF signals, an easy-to-use measurement method was recently developed at the National Institute for Occupational Safety and Health. The method will be introduced along with an equivalent transmission line model for a long metallic infrastructure in underground coal mines. The model serves as the fundamental driver for the method development. Propagation measurements on a twisted pair of telephone lines in an underground mine were made using this method. The measurements confirmed the low MF signal attenuation rate and the dependence of the propagation characteristics of the line on the electrical properties of surrounding coal and rock as theoretical studies predicted.