Coupled Line Structure Research Articles

Design and Analysis of Microstrip Low Pass and Bandstop Filters

In this paper a simple approach of designing the microstrip low pass and bandstop filter is presented. The microstrip stub based low pass filter with 2.4 GHz and attenuation of more than 60 dB at 4 GHz frequency is designed. The bandstop filter is also designed with notch characteristics at 2.4 GHz frequency. The fractional bandwidth of designed filter is estimated to be 30% with 117 dB of attenuation is recorded at notch frequency of 2.4 GHz in SIR based bandstop filter topology. The bandstop filter is implemented using coupled line structure as well as step impedance resonator techniques. The filters are designed on Roger RC40003C substrate. The design and analysis of filter with its layout and EM simulation is accomplished using Agilent ADS software. These filters can be used in front end transceiver systems, antennas, and modern wireless communication systems.

Design of multi‐standard single/tri/quint‐wideband asymmetric stepped‐impedance resonator filters with adjustable TZs

This study presents an original asymmetric stepped-impedance resonator filter combined with meander coupled-line structures and enabling the realisation of finite transmission zeros (TZs) and the implementation of multi-band bandpass filters. The meander coupled sections (MCSs) tune the TZs and resonant frequencies: with higher-order spurious frequencies cancelled by the TZs, a single wideband with wide stopband from 1.18 to 1.84 GHz is possible. Furthermore, by positioning the finite TZs between the high-order spurious frequencies and adjusting the coupling strength between resonators, a quint-wideband filter can be realised, with centre frequencies of 1.19, 4.29, 5.43, 6.97, 9.9 GHz and fractional bandwidths of 31.9, 15.4, 15.8, 4.3, 39.2%, respectively. More importantly, two filters with single/quad-wideband performance can be realised by tuning the parameters of the MCS, and therefore they can be designed separately by using only one original structure. The triple-wideband filter is realised with the help of the asymmetric parallel uncoupled microstrip section. These filter structures enjoy the advantage of single/multi-band versatility, structure reusability and simplicity. The good in-band and out-of-band performance, low loss and simple structure of the proposed single/tri/quint-wideband filters make them very promising for applications in future multi-standard wireless communication.

Design of a wideband filtering power divider with good in‐band and out‐of‐band isolations

In this article, a wideband filtering power divider with good in-band and out-of-band isolations is designed based on a hybrid Wilkinson and Gysel structure. To achieve a good in-band response, two additional in-band transmission poles can be introduced by installing the coupled-line structures at each port. By mounting a stepped impedance open stub at the input port, two transmission zeros are generated near the passband to improve the passband skirt. Furthermore, the out-of-band rejection and isolation are achieved by the other two transmission zeros, which are produced by the open stub and the three coupled-line sections mentioned above. Additionally, a good in-band isolation is realized by the isolation resistor between output ports. For the demonstration, a wideband filtering power divider centered at 1.5 GHz with a 56% fractional bandwidth and 20-dB isolation is designed and fabricated. The simulated and measured results are in good agreement with each other.

Design and band coalition of dual band microstrip filter using DGS, coupled line structures and series inductive metallic vias

An approach to design compact dual band BPF and technique to unite the two bands into a single wide band is presented in this paper. The novelty of the filter stands on the application of series of metallic vias which are used to merge the bands obtained using coupled line circuits and DGS structure. The coupled line filter and the coupled line filter integrated with DGS shows passband resonance at 4.5 GHz and 5.1 GHz within the microwave frequency of operation. Series metallic vias are used to merge the passbands into a single wider passband of bandwidth 1.6 GHz (3.5–5.1 GHz). The filter configurations are fed using stepped-impedance open stub technique to reduce cross coupling between adjacent structures. Moreover effects of several salient filter parameters like gap between edge of the microstrip coupled line resonator and via series GV and gap between mid-point of the open ended feed line and via row GM are studied to achieve greater isolation at higher frequencies. All simulated designs are fabricated and experimentally studied to vindicate the practical performance of all filter configurations.

Crosstalk analysis of multi‐microstrip coupled lines using transmission line modeling

This article presents a new analytical method to predict crosstalk of a homogeneous terminated two microstrip coupled lines over a ground plane using transmission line theory. The derived formula is frequency and location dependent, which can be used to quickly estimate the crosstalk of a coupled line. Also, the effect of the geometrical parameters of the lines and load are included in the derived formula. Presented method can be used for the other types of coupled lines including lossy or lossless lines. To verify the accuracy of the introduced method, a few microstrip coupled line structures with different geometrical parameters are considered numerically and experimentally. The results of crosstalk based on the proposed analytical methods, simulation study using high frequency structure simulator and those obtained by measurements are reported and compared with each other. It is shown that our proposed method accurately estimates the amount of crosstalk for a two microstrip coupled lines.

Unconditionally Stable Multiple One-Dimensional ADI-FDTD Method for Coupled Transmission Lines

The unconditionally stable multiple one-dimensional alternating direction implicit finite-difference time-domain (M1-D ADI-FDTD) method for coupled transmission lines is presented. The differential equations for coupled transmission lines are formulated in compact matrix form. Proper $4 \times 4$ split matrices are introduced, which feature unconditional stability for the ADI procedures. These matrices also lead to update equations with the left-hand sides involving tridiagonal matrices that can be solved efficiently. The update equations of the M1-D ADI-FDTD method are given, which comprise one implicit and three explicit updates in each procedure. The analytical proof of unconditional stability is also provided based on the von Neumann method. The M1-D ADI-FDTD method allows quick simulation and visualization of electromagnetic fields everywhere along the coupled transmission lines. To demonstrate the usefulness of the M1-D ADI-FDTD method, various coupled line structures for filter and filtering antenna are analyzed using the method.

Design of filtering power divider with high frequency selectivity

AbstractA novel controllable wideband filtering power divider (FPD) with sharp roll‐off skirt and good isolation is presented in this article. By introducing a pair of coupled lines and several uniformed quarter‐wavelength microstrip lines to the power divider, a wide flat passband with good selectivity is achieved. A resistor is then arranged between the 2 coupled line structures to obtain good isolation. Even‐mode and odd‐mode approach is applied to deduce the design equations of the proposed FPD. The center frequency can be adjusted flexibly by simply controlling the length of the coupled lines and the other microstrip lines. Eventually, the proposed power divider centered at 2.3 GHz with a fractional bandwidth of 75% is fabricated and measured for verification. The measured minimum in‐band insertion loss is 0.3 dB, while the isolation is better than 20 dB. Good agreement is shown between the simulated and measured results.

A Coupled-Line Coupling Structure for the Design of Quasi-Elliptic Bandpass Filters

A coupled-line coupling structure is proposed for the design of quasi-elliptic bandpass filters (BPFs). The coupled-line structure functions as the input coupling structure for a BPF and introduces one pair of symmetrical transmission zeros at around the cutoff frequencies. Equivalent circuit models play an important role in the design of microwave filters. Accordingly, this paper undertakes a major effort to develop the equivalent circuit of the coupling structure. The equivalent circuit is in a form that can be readily used in combination with a given direct-coupled filter. The coupling structure can serve as a basic building block for the design of quasi-elliptic BPFs. As demonstrated by the theoretical and experimental treatment, the coupling structure can be used to transform a Chebyshev filter into a quasi-elliptic filter.

A Novel Wideband Filtering Power Divider With Embedding Three-Line Coupled Structures

This paper presents a novel wideband filtering power divider. Instead of the T-junction in the traditional power divider design, a three coupled-line structure is utilized to provide the equal power division to every outputs. Together with the quarter-wavelength coupled line in each way, a wideband filtering response can be obtained. In order to enhance the frequency selectivity, a pair of half-wavelength open stubs are loaded between the three-line coupled structure and parallel coupled lines to produce a pair of transmission zeros on both sides of the passband. To enhance the upper stopband rejection, two additional open stubs are installed at output ports. A new three-port equivalent network for the three-line coupled structure is proposed, and the circuit model for the filtering power divider can be developed for illustrating the working mechanism and the design process. Furthermore, the generalized Chebyshev function is applied to synthesize and analyze the whole structure systematically. For demonstration, a prototype of the wideband filtering power divider operating at 3 GHz is designed and fabricated. The measured results show a 16-dB bandwidth of 62%, an isolation better than 16.5 dB, and a 29-dB wide stopband from 4.39 to 7.73 GHz ( $1.1f_{0}$ ).

Design of Dual Band-Reject Filter based on Short-Circuited Parallel Coupled Lines Structure at S-Band

This paper presents a simple design of dual-band reject filter based on parallel coupled lines structure. Parallel coupled lines structure is a four-port network. A dual-band shunt resonator using this structure is obtained by short-circuiting two opposite ports to ground and connecting one of the two remaining ports to a transmission line in shunt. The fourth port is an open circuit. This modified parallel coupled lines structure has been connected with a high impedance transmission line to obtain the narrow dual band reject filter. Theoretical analysis has been performed in order to obtain the resonant frequencies. The numerical simulations have been performed and these results have been verified by the full-wave electromagnetic simulations for an S-band dual band reject filter with rejecting frequencies at 2.5 GHz and 3.5 GHz. The control over the band rejection frequencies is obtained by selecting the parameters of the parallel coupled lines in terms of gaps, widths, and lengths.

Absorptive Bandstop Filter With Prescribed Negative Group Delay and Bandwidth

An absorptive bandstop filter is proposed and synthesized with prescribed negative group delay (NGD) and negative group delay bandwidth (NBW). It is realized with resistor-loaded coupled-line structures where the NGD can be controlled by the Q-factors of resonators. The resistor of the first section is determined for impedance matching, also providing a negative delay. A prototype is developed, following the proposed design procedure, with NGD = −6.5 ns and NBW= 105 MHz obtained. The proposed method is experimentally validated by the good agreement between the synthesized and measured results.

Design of a dual‐band microstrip branch‐line balun using T‐shaped coupled lines

ABSTRACTThis article presents the development of a novel dual‐band branch line balun with design flexibility. The T‐shaped coupled line structure is constructed by two series short‐ended coupled lines and one open‐ended stub to obtain the dual‐band characteristics. The proposed dual‐band structure has the capability to design a conventional microstrip line with arbitrary impedances and electrical lengths at two different operating frequencies. In addition to this, different range of frequency ratios is obtained by varying the length of the stub. The required explicit design equations are derived analytically to compute the physical dimensions of the coupled lines and stub. Based on these equations, closely and widely spaced frequency bands useful for many wireless communication systems are devised. To prove better agility, three examples of dual‐band branch line baluns are designed. Finally, a prototype of dual‐band balun is demonstrated for GSM and WiMAX applications at 0.9 and 3.5 GHz, respectively. Good agreement is found between the theoretical predictions and experimental results. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1197–1202, 2017

Wideband Single-Ended and Differential Bandpass Filters Based on Terminated Coupled Line Structures

In this paper, a novel terminated coupled line structure (TCLS) is introduced, which is constructed by a coupled line section and four terminations loaded on it. Introducing different kinds of terminations, three types of bandpass filters (BPFs) based on TCLSs are proposed, theoretically analyzed, and fabricated, including two single-ended wideband BPFs with fractional bandwidths (FBWs) of 67% and 40% respectively, and a wideband differential BPF with 74% differential-mode FBW. These BPFs can achieve wide passband bandwidth, low in-band insertion loss, high passband selectivity, as well as deep stopband rejection performance simultaneously, benefited from the multiple transmission zeros and transmission poles obtained by the TCLSs. The practical design procedures of these BPFs are presented and explained. The agreement among theoretical predictions, EM-simulated, and measured results validates our proposed filter structures. Finally, the generalized multistage filter topology based on TCLSs is proposed to design high-order filters with better filtering performances.

Design of a microstrip dual-frequency diplexer using microstrip cells analysis and coupled lines components

In this paper, a microstrip diplexer composed of two similar resonators is designed. The proposed resonator is consisting of four microstrip cells, which are connected to a coupled lines structure. In order to select a suitable geometric structure, first, all cells are assumed as undefined structures where there is a lack of basic information about their geometry and dimensions. Then, an equivalent LC circuit of the coupled lines is introduced and analyzed to estimate the general structure of the resonator respect to a requested resonance frequency. The proposed diplexer is designed to operate at 2.36 and 4 GHz for wireless applications. The insertion losses (S21 and S31) are decreased significantly at the resonance frequencies, so that they are 0.2 and 0.4 dB at 2.36 and 4 GHz, respectively. The designed diplexer is fabricated and measured and the measurement results are in a good agreement with the simulations.

Wideband Balanced-to-Unbalanced Filtering Power Dividers Based on Coupled Lines

Three novel wideband balanced-to-unbalanced filtering power dividers based on coupled lines are proposed in this paper. Multifunctional power dividers can replace various cascaded single devices to decrease integration mismatching loss and circuit size. The wideband response can be easily realized by the coupled lines structures. To further improve the differential-mode passband selectivity, open/shorted coupled lines and half-wavelength open stubs are applied to introduce two transmission zeros near the passband, respectively. In addition, a resistor in the middle of two single-ended ports can be used to realize isolation between out ports. To verify the proposed concepts, three prototypes of wideband balanced-to-unbalanced filtering power dividers operating at 2 GHz are designed and fabricated with the 4-dB differential-mode bandwidths of 80.5%, 71.5%, and 80%. All the structures show good performances for differential-mode out-of-band suppression, common-mode suppression, and isolation.

A Novel Balanced-to-Unbalanced Complex Impedance-Transforming In-Phase Power Divider

In this paper, a simple and compact planar balanced-to-unbalanced in-phase power divider with arbitrary terminated impedances is proposed based on the coupled-line structure and a single grounded resistor. By using the even-/odd-mode analysis and the traditional transmission-line theory, the complete design procedure and analytical equations are obtained to achieve good performances for differential-mode transmission, common-mode suppression, phase difference, arbitrary terminated impedances, and isolation. For demonstration, two different prototypes with 50-to- $50~\Omega $ matching and complex impedance transformation are designed, fabricated, and measured. Good agreement can be observed between simulated and measured results.

A Coupling Matrix and Admittance Function Synthesis for Mixed Topology Filters

In this paper, a direct coupling matrix technique is presented for narrowband mixed topology filters that possess a series of extracted-pole sections. With respect to previous works, this technique exhibits distinct benefits due to its simplicity as all the coupling elements, of both cross-coupled and extracted-pole structures, can be obtained as an entity at one time. As the basis, a unique process is introduced to rebuild the couplings and admittance functions for an ${N}$ th-order cross-coupled low-pass prototype, from which a series of extracted-pole sections can be naturally generated with no more operations, thus deriving a mixed topology transversal array directly. To show the flexibility of this paper, a couple of examples, including fully canonical cases and fully extracted-pole cases (considered as a particular kind of mixed topology filters here), are demonstrated. Moreover, a miniaturized coupled line structure is proposed to properly construct filters of fully extracted poles, which provides a reasonable possibility to design compact planar mixed topology filters, in comparison with others in the literature. The simulated and measured results are in good agreement.

Dielectric Constant Measurement of Low Loss Materials Using NB BPF with Modified Slow Wave Resonator

Compact wide-stopband narrow bandpass filter using modified slow wave resonators is proposed. The basic filter consists of an open-stub, transmission line and coupled line. Using transmission line theory and coupled line structure, the new design methodology of a narrowband BPF is employed and resonant frequency has been clearly explained. Experimental results show that the designed filter has a fractional-bandwidth of 2 %, an insertion loss about 0.38 dB and return loss better than 30 dB. Spurious response suppression is achieved until 5f0. The overall physical size of this filter is only 23.9 mm × 10.2 mm or 0.41 źg × 0.175 źg, having a smaller size compared with conventional narrowband pass filters. The bandwidth of this filter has capability of changing with the coupled lines used in the middle of the proposed filter structure, having tunable resonance frequencies. Due to the narrow bandpass property, the proposed filter is used as a sensor to measure the dielectric constant of materials. The resonant characteristics of resonator vary with dielectric constant of the material. The proposed filter is designed, simulated and fabricated. The measured and simulated results are well complied with each other.

A 10:1 unequal gysel power divider/combiner

ABSTRACTThis article introduces a modified Gysel power divider, providing high power division ratios, alongside the advantage of high power handling. To overcome fabrication limitations of high characteristic impedance line, caused by the anticipated high power division ratio, a coupled line structure with two shorts is used. This proposed structure makes closed‐form equations available for design and leads to a simple microstrip fabrication. A 10:1 unequal Gysel power divider is presented and fabricated as a design example and a satisfactory agreement between measurements and simulation results is verified. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2689–2692, 2016

Wideband Four-Way Filtering Power Divider With Sharp Selectivity and Wide Stopband Using Looped Coupled-Line Structures

A compact wideband four-way filtering PD is presented. The structure of the proposed device includes a pair of looped coupled-line structures to provide the needed power division to four output ports. Moreover, a pair of short-ended coupled-line stubs is used to introduce multiple transmission poles and transmission zeros for a sharp cut-off of the passband and high upper-stopband rejection. A detailed design procedure is shown to determine the initial design parameters. A prototype is designed, simulated and measured experimentally. The measured results show 56.5% bandwidth centered at 1.5 GHz with more than 15 dB upper-stopband rejection up to 4.15 GHz, more than 13 dB in-band isolation, and 15 dB return loss at all output ports.