Coupled Microstrip Lines Research Articles

Broadband Determination of the Even- and Odd-Mode Propagation Constants of Coupled Lines Based on Two-Port Measurements

We describe a method for the broadband measurement of the even- and odd-mode propagation constants of symmetrical coupled transmission lines. The main advantage of the method, its simplicity, lies in the lack of need for four-port measurements. Only two-port measurements are required, and thus just a two-port vector network analyzer (VNA). The accuracy of the results can be increased at the cost of a higher number of measured coupled-line lengths. The new approach has been successfully applied for the determination of coupled microstrip lines in the 2- to 20-GHz frequency band in both simulated and experimental cases. A brief discussion about the repeatability of the microstrip launcher and the adverse effects of radiation is included.

A split-ring resonator probe for assessing subsurface wood defects.

The Microwave Nondestructive Testing (MNDT) method has been increasingly used for inspecting wood characteristics. In this work, a MNDT method is established for effective and accurate detection and analysis of wood subsurface structural defects. A microwave near-field probe loaded with a split-ring resonator is proposed to bring in strong electric field, which is directly attached to the trailing end of the coupled microstrip line. High-resolution, light weight, low-cost, and compactness are some of the advantages of the sensor. The designed sensor is used for detecting subsurface structural defects under the thin paint layer of wood. Here, S21 values are used to analyze the characteristics of wood. Different width and depth defects of wood samples with different moisture content levels were measured. The experimental results show that the maximum relative error between the actual widths and measured widths is less than 10%. The spatial resolution is approximately 0.42λ0 at a resonant frequency of 9 GHz. The results demonstrate that the designed probe can accurately trace defects in wood with different moisture content levels without striping the upper coating of the paint.

Design of Dual Band and Tri-band Bandpass Filter (BPF) with Improved Inter-band Isolation Using DGS Integrated Coupled Microstrip Lines Structures

A novel approach to design dual-band as well as a triple-band BPF with improved isolation is ventured in this paper. In dual-band filter, dual mode property of coupled line filters is utilized to obtain resonant frequencies at 2.4 GHz and 7.4 GHz suitable for WLAN and WiMAX application respectively. Additionally a rectangular-ring DGS element is introduced within the coupled line filter to obtain a separate mid-band resonance at 5.2 GHz. The frequency shifting property of the pass bands due to cross-coupling between the microstrip line resonators and the DGS element is mostly eliminated by implementing stepped impedance open stub (SIOS) technique. All filter configurations are fabricated, measured and compared with the simulated models to validate the practical effectiveness. Stop band isolation > 40 dB and insertion loss (IL) < 0.8 dB is attained in all the filter configurations.

Broadband Filtering Magnetoelectronic Dipole Antenna With Quasi-Elliptic Gain Response

A filtering magnetoelectronic dipole antenna (MEDA) with quasi-elliptic gain response and wide operating band is investigated. Different from the conventional MEDA, the antenna studied here is fed by fork-shaped microstrip line aperture-coupled excitation. The intrinsic radiation null of the MEDA at the lower passband edge is utilized, and a mathematical model is first put forward to demonstrate its working mechanism. Four driven stubs connected to the shorted walls of MEDA are used to excite the planar dipole arms. The parasitic inductor and the coupling capacitor introduced by driven stubs form an equivalent low-pass filter network, leading to a radiation null at higher frequency. Furthermore, a third radiation null is generated by introducing two quarter-wavelength U-shaped shorted stubs to improve the out-of-band suppression. Besides, due to the introduction of multiple coupling structure, including the fork-shaped microstrip line coupling slot and driven stubs, a wide operating band can be realized while maintaining a low profile of 0.15 wavelength. The experimental results show that an impedance bandwidth of 53.5% (2.95-5.1 GHz) is achieved and an out-of-band suppression level higher than 17.9 dB is obtained. What is more, an average gain of 8 dBi and good radiation patterns are realized over the whole operating band.

High coding capacity chipless radiofrequency identification tags

AbstractA novel tristate coupled line microstrip resonator is proposed for compact chipless radiofrequency identification tags. The proposed resonator can be reconfigured to present one of the three possible states: 00, 10, and 01, which denote no resonance, resonance at f1, and resonance at f2, respectively. The resonator can be designed with f1 and f2 at appropriate positions, reducing the required spectrum. A multiresonator prototype consisting of 14 elements of the proposed resonator is designed, analyzed, and experimentally characterized. This prototype is implemented on an RT Duroid 5880 substrate with a dielectric constant of 2.2 and a thickness of 0.78 mm. The prototype can be reconfigured for 314 codes. A test‐bench comprising six resonators and transmitting and receiving wideband antennas is established and used to experimentally characterize a prototype tag. The experimental results exhibit good agreement with the simulation.

Isolation Improvement of an Overlapped Two-element MIMO Antenna

An overlapped two-element antenna structure with excellent compactness is proposed. Extraordinarily strong mutual coupling is effectively mitigated by a decoupling network with simple coupled microstrip lines connected to the antennas in shunt. Simulation example and results are demonstrated. The isolation improvement is better than 8 dB (from about 2 dB to over 10 dB) in most of the Wi-Fi 2.4 GHz band. Four lumped components networks are utilized to maintain the good impedance matching before and after decoupling, and the return loss is higher than 7 dB over the band of interest. Remarkable decrease in envelope correlation coefficient (ECC) in most of the working band is achieved. All these performances prove the presented antenna structure and decoupling scheme a promising option for those mobile terminals and wireless communication devices which have high data rate and compact volumes.

Forward‐wave directional coupler based on slow‐wave coupled microstrip lines

This study presents the design of a forward-wave directional coupler based on slow-wave coupled microstrip lines realised in a multilayered printed circuit board technology. Thanks to the concept of slow-wave, a high difference between the even- and odd-mode phase velocities can be inherently achieved. Hence, by choosing adequate even- and odd-mode characteristic impedances close to 50 Ω, reduced-length forward couplers can be designed. As a proof of concept, a 0 dB forward coupler operating at 4.5 GHz is proposed. It exhibits a very high coupling of 0.56 dB at the centre frequency and a very large bandwidth of 43%, corresponding to 10 dB of isolation. A length miniaturisation of 84% is obtained as compared to the standard microstrip, leading to a total surface area of 0.132 λ g 2 , the smallest one reported so far.

Series-Fed Dual-Polarized Single-Layer Linear Patch Array With High Polarization Purity

In this letter, a novel dual-polarized 1 × 4 patch array using proximity feed technique is presented. The proposed single-layer antenna consists of four square patch elements, two short-terminated parallel coupled microstrip lines, and a rat-race incorporated in the feed network. The patches are placed at the inner space between the two parallel microstrip feedlines. Horizontal and vertical polarizations of the patch array are excited by the even and odd modes of the two microstrip lines, respectively. The rat-race structure is used to provide in-phase and 180° out-of-phase feeds for the two modes. A prototype operating at 3.5 GHz is fabricated and measured. The measured overlapping bandwidth of the two ports is 81 MHz, also with port isolation higher than 40 dB. Owing to the symmetry of the structure and balanced excitations, the measured cross polarizations are all below -29 dB in E- and H-planes.

Spurious Passband Suppression in Compact Microstrip Rat-Race Coupler Deploying Modified Split Rings and Coupled Microstrip Lines

This manuscript presents the design of a size reduced microstrip rat-race (RR) coupler with improved spurious passband suppression performance. The coupler operates at 0.95 GHz, corresponding to 5G applications (sub-1 GHz 5G applications). The combined effect of coupled microstrip lines, slant connected split ring structure and the ring shaped defects offer deep suppression of harmonic signals beyond the passband till 4 GHz. The proposed coupler also offers 47.2% size reduction compared to a conventional RR coupler model.

Crosstalk analysis of uniform and nonuniform lossy microstrip‐coupled transmission lines

In this article, an analytical method is presented to precisely estimate the crosstalk of uniform and nonuniform microstrip-coupled transmission lines (TLs) in frequency domain using modified transmission matrix. The obtained expression is quantitatively related in terms of the geometrical parameters of the coupled lines. A straightforward procedure is presented to obtain a closed form formula to accurately determine the crosstalk of a microstrip-coupled line. For a nonuniform structure, the TL is divided into a few series of uniform sections with a specific modified transmission matrix. The total modified transmission matrix is determined by multiplying the modified transmission matrix of different sections and then the crosstalk can be calculated using the total modified transmission matrix. Several structures are considered to confirm the validity of the presented method. It is shown that the obtained results are in a good agreement with those obtained by simulation and measurement.

Compact Wideband Differential Bandpass Filter Using Coupled Microstrip Lines and Capacitors

A compact wideband differential bandpass filter (BPF) is achieved by loading two pair of capacitors at different positions of the half-wavelength-coupled microstrip line. The capacitances and loaded positions of capacitors combining with the even–odd-mode impedance of the coupled microstrip line can produce and control the three differential-mode (DM) transmission poles (TPs), four DM transmission zeros (TZs), and three common-mode (CM) TZs. Comparing with the state-of-the-art wideband differential BPFs, the proposed design has the advantages of compact size and low insertion loss. A prototype with the size of 51 mm $\times 4$ mm ( $0.5\,\,\lambda _{ g} \times 0.04\,\,\lambda _{ g} $ , $\lambda _{ g} $ is the microstrip guided wavelength at the center frequency $f_{ 0 }$ ) is designed for demonstration, which exhibits the 3-dB fractional bandwidth of 105% centered at 1.8 GHz and the minimum insertion loss of 0.16 dB.

Four-State Coupled-Line Resonator for Chipless RFID Tags Application

A novel quad-state coupled-line microstrip resonator is proposed for compact chipless radio frequency identification (RFID) tags. The proposed resonator can be reconfigured to present one of four possible states: 00, 01, 10, and 11, representing, no resonance, resonance at f2, resonance at f1, and resonance at both f1 and f2, respectively. The frequency span between f2 and f1 can be easily controlled, thereby reducing the required spectrum. Moreover, the proposed technique allows the storage of a large amount of data in a compact size to reduce the cost per bit. A multi-resonator prototype consisting of six resonators is designed, analyzed, and experimentally characterized. This prototype is implemented on the RT Duroid 5880 substrate with a dielectric constant of 2.2, loss tangent of 0.0009, and thickness of 0.79 mm. The designed configuration can be reconfigured for 46 codes. Two complete the RFID tags, including the six resonators and two orthogonally polarized transmitting and receiving antennas, are implemented and tested. The first tag code is designed for all ones, 111111111111, and the second tag is designed as 101010101010 code. Experimental results show good agreement with the simulation.

Design and Measurement of a 1-bit Reconfigurable Transmitarray With Subwavelength H-Shaped Coupling Slot Elements

A novel 1-bit 256-element reconfigurable transmitarray antenna (RTA) at the Ku-band is presented. The element consists of two orthogonal H-shaped slots as receiving and transmitting structures, and the power transmission is realized by a coupling microstrip line in between. Two p-i-n diodes integrated on the coupling line can be electronically controlled to reverse the excitation directions, thus generating two states with 180° phase difference and low transmission loss. A subwavelength element spacing of $\lambda _{0}$ /3 is utilized to stabilize the element performance under oblique incidence. A transmitarray prototype with $16 \times 16$ elements and aperture size of $5.3\lambda _{0}\times 5.3\lambda _{0}$ at 12.5 GHz is fabricated and measured for the experimental verification. The measured results show that the maximum gain is 17.0 dBi with an aperture efficiency of 14.0%, and 2-D scanning beams within ±50° angular range are obtained. The 3-dB gain bandwidth of the broadside beam is 9.6%.

Suppression of mutual coupling in rectangular dielectric resonator antenna arrays using Epsilon-Negative metamaterials (ENG)

ABSTRACTA double slotted symmetrical split ring resonator with an inductive stub in its inner ring is presented as a Single Negative Electric (SNG) metamaterial to suppress mutual coupling between two E-plane coupled microstrip line fed rectangular dielectric resonator antenna (RDRA) array. The proposed SRR exhibits two resonant frequencies and wide stop-bands. The -10 dB bandwidth of S21 from 2022MHz to 2720 MHz and from 2187 MHz to 3839 MHz are obtained for the first structure, #1, and the second structure, #2, respectively. By introducing an ENG layer between the two RDRAs, the experimental reduction in mutual coupling is more than 23 dB with a small frequency shift (∼ 20 MHz), while the impedance matching is improved. The radiation efficiency and total efficiency are increased while the far-field pattern in the E-plane is not disturbed.

Generation of Stochastic Interconnect Responses via Gaussian Process Latent Variable Models

We introduce a novel generative model for stochastic device responses using limited available data. This model is oblivious to any varying design parameters or their distribution and only requires a small set of “training” responses. Using this model, new responses are efficiently generated whose distribution closely matches that of the real data, e.g., for use in Monte-Carlo-like analyses. The modeling methodology consists of a vector fitting step, where device responses are represented by a rational model, followed by the optimization of a Gaussian process latent variable model. Passivity is guaranteed by a posteriori discarding of nonpassive responses. The novel model is shown to considerably outperform a previous generative model, as evidenced by comparing accuracies of distribution estimation for the case of differential-to-common mode conversion in two coupled microstrip lines.

Equation-Based Solutions to Coupled, Asymmetrical, Lossy, and Nonuniform Microstrip Lines for Tab-Routing Applications

In this paper, analytical equation-based solutions are derived to allow quick and accurate calculations directly from the physical parameters of coupled, asymmetrical, lossy, and nonuniform microstrip lines with interdigital trapezoidal tabs incorporated, resulting in their corresponding scattering parameters. Capacitance and inductance matrices under a quasi-static condition are derived from the cross-sectional dimensions of asymmetrical coupled microstrip lines with unequal widths. They are converted into a frequency-dependent resistance–inductance–conductance–capacitance model, allowing complete equation-based solutions to their four-port Z-matrix, S-matrix, and ABCD-matrix. As an application example of tackling the complexity of transmission lines, the derived analytical method is applied to a transitional structure with linearly varying trace width in tabbed microstrip lines by the method of segmentation. In addition, a new concept of tab-coupling fringing capacitance is specifically introduced to compensate for underestimated mutual capacitance at tab positions, which will improve the accuracy of the proposed approach. Numerical modeling results from commercial simulation tools are compared for validation purposes. As a conclusion, the proposed method and its versatility are demonstrated with applications to practical high-speed and high-density printed circuit board designs, which renders itself effective and efficient in an optimization process.

Modeling a Planar Coupled Microstrip Lines using various Wavelets and Method of Moments

In this paper, we apply a several wavelets basis functions to the method of moments to modeling the parallel-coupled microstrip lines. The first set of equations is for the shielded microstrip line solved with moment’s method and wavelets. The Green’s function is obtained from the theory of images. The second set are for the parallel-coupled microstrip lines operating in the TEM mode or when the analysis can be based on quasi-static approximation, the properties of coupled lines can be determined from the self- and mutual inductances and capacitances for the lines. To demonstrate the effectiveness and accuracy of the proposed technique, numerical results of even- and odd-mode characteristic impedances, coupling coefficient, percentage sparsity achieved in the impedance matrix, the CPU Time to reverse impedance matrix, and error relative for Daubechies, Coiflets, Biorthogonal and Symlets wavelets are presented. Numerical results are in good agreement with those in previous publications.

Design of Microstrip Dual-Mode Impedance Transformers

new four-port component, dual-mode impedance transformer for wideband matching of two microstrip lines with equal characteristic impedance and a coupled microstrip line with general even- and odd-mode impedances, is proposed. Practical realization problems are discussed and a new dimension correction approach is derived. Two transformers between 50- $\Omega $ microstrips and microstrip coupled lines with even/odd impedances $100~\Omega /68~\Omega $ and $36~\Omega /27~\Omega $ , respectively, were built. The concept was experimentally verified at the frequency band 0.01–16 GHz.

Dual Band BPF Based on Parallel Coupled Lines Loaded by Open Stubs for Ku-Band Satellite Applications

This paper presents a dual band Band Pass Filter (BPF) operating at both the downlink and uplink frequency bands for Ku-band satellite applications. The commonly used frequency band in mobile communications satellites is the Ku-band. These mobile satellite systems help connect remote regions, vehicles, ships, people and aircraft to other parts of the world and/or other mobile or stationary communications units, in addition to serving as navigation systems. The structure of the proposed filter is based on parallel coupled microstrip lines and four sections are used. Tuning the two operational bands can be achieved using two open-circuited stubs at the first and last sections of the parallel coupled microstrip lines. The proposed filter is adjusted to operate at 12.54 GHz and 14.14 GHz for downlink and uplink bands, respectively. The proposed dual band BPF is fabricated, measured, and good agreement is obtained between simulated and measured results.

A novel band pass filter design and analysis using inductive via series

A novel approach to implement a compact dual band BPF and an efficient technique to conjoin the two bands into a single wide band (three transmission poles) is presented in this paper. This article also provides the information that with proper positioning of inductive metal vias it is possible to generate greater electromagnetic coupling at a particular frequency through guiding the EM waves in a proper scheme. In our proposed design a pair of inductive metallic via series is introduced to conjoin the passbands obtained from rectangular DGS structure and coupled microstrip line structure. Designed dual band BPF loaded with DGS and coupled microstrip line structure shows passband resonance at 4.5 GHz and 5.0 GHz respectively. Inductive metallic via series provides the flexibility to transform the dual band BPF into a wideband BPF of 1.6 GHz (3.5–5.1 GHz) bandwidth significantly, with generating another transmission pole at 4.25 GHz of the passband. Proposed filter configurations are fed using stepped discontinuous microstrip line to reduce the cross coupling between adjacent structures. All designs are fabricated and experimentally studied using R&S ZVL13 vector network analyzer to prove the practical performance of all filter configurations.