Showing papers by "Francisco Medina published in 2018"

Balanced Microwave Filters

Abstract: This book examines differential-mode, or balanced, microwave filters by discussing several implementations of practical realizations of these passive components. Topics covered include selective mode suppression, designs based on distributed and semi-lumped approaches, multilayer technologies, defect ground structures, coupled resonators, metamaterials, interference techniques, and substrate integrated waveguides, among others.

On the Computation of the Dispersion Diagram of Symmetric One-Dimensionally Periodic Structures

Abstract: A critical discussion on the computation of the dispersion diagram of electromagnetic guiding/radiating structures with one-dimensional periodicity using general-purpose electromagnetic simulation software is presented in this work. In these methods, full-wave simulations of finite sections of the periodic structure are combined with appropriate simplifying network models. In particular, we analyze the advantages and limitations of two different combined methods, with emphasis on the determination of their range of validity. Our discussion is complemented with several selected numerical examples in order to show the most relevant aspects that a potential user of these methods should be aware of. Special attention is paid to the relevant role played by the high-order coupling between adjacent unit cells and between the two halves of unit cells exhibiting reflection, inversion, and glide symmetries.

Unlocking Complexity Using the ECA: The Equivalent Circuit Model as An Efficient and Physically Insightful Tool for Microwave Engineering

Abstract: In the study of electromagnetic wave propagation and scattering, researchers have always faced the dichotomy of dealing directly with Maxwell's equations (and their complicated analytical/numerical solution methods) or trying to find a simplified model (usually in terms of an equivalent circuit) that can help provide some physical insight into the involved electromagnetic phenomena. The pursuit of analytical solutions for propagation, radiation, and scattering problems does not seem to be a task currently in much demand in microwave engineering, although it was only 20 years ago that many research papers on these topics included some sort of analytic derivations.

Balanced-to-Balanced Microstrip Diplexer Based on Magnetically Coupled Resonators

Abstract: Two balanced-to-balanced planar diplexers based on magnetically coupled microstrip resonators are proposed in this paper. For the first prototype, each channel/differential-output is composed of a second order single-band balanced bandpass filter based on open-loop resonators. For the second diplexer example, the filters composing the differential outputs are fourth order and are implemented by means of folded stepped-impedance resonators. The design procedure for the differential response is quite straightforward, since it is based on the use of the well-known external quality factor and coupling coefficients concepts. Common-mode is inherently rejected thanks to the benefits of magnetic coupling, which precludes common-mode transmission over a wide frequency range. The proposed structure also offers a high level of channel-to-channel isolation. To demonstrate the usefulness of the proposed idea, the two prototypes are simulated, fabricated, and measured. Good differential-mode and common-mode performance is observed in both examples. Simulations and measurements show good agreement.

Compact Balanced-to-Balanced Diplexer Based on Split-Ring Resonators Balanced Bandpass Filters

Abstract: A compact balanced-to-balanced diplexer composed of two balanced bandpass filters is proposed in this letter. The balanced filters are implemented using compact edge-coupled square split-ring resonators. The design methodology is based on the standard coupled-resonators filter synthesis procedure. First, each filter is independently designed. Then, they are connected to a common differential input port in order to achieve the desired diplexing operation, with the pertinent adjustments to take into account the loading effect of the second filter. Magnetic coupling inherently prevents common-mode transmission. An illustrative prototype example is provided with simulations and measurements to demonstrate the benefits of the proposed topology.

Resonant Modes of a Waveguide Iris Discontinuity: Interpretation in Terms of Canonical Circuits

Abstract: This paper presents an eigenproblem for computing the resonances of multiresonant irislike discontinuities in waveguides. The formulation of the eigenproblem is based on integral equation methods, and its solution provides the resonance frequencies (eigenvalues) and the associated resonant aperture field’s patterns (eigenvectors). These eigenvectors can be used as a basis for the expansion of the aperture fields at any frequency within the band of interest, thus leading to a significant reduction of the size of the method-of-moments admittance matrix. Moreover, under certain approximations, the orthogonality of the eigenvectors allows for the derivation of a Foster-like canonical equivalent circuit with capacitances and inductances that present a smooth frequency dependence. In order to obtain an equivalent Foster circuit with frequency-independent inductors and capacitors, a straightforward and simple iterative refinement is proposed. The circuit thus obtained accurately reproduces the response of the multiresonant irislike discontinuity over a wide frequency band.

Efficient Hybrid Full-Wave/Circuital Approach for Stacks of Frequency Selective Surfaces

Abstract: This letter shows an efficient hybrid method to study stacks of identical frequency selective surfaces (FSSs) separated by possibly different dielectrics. The method takes advantage of the ability of the equivalent circuit approach to create a $\Pi$ -network for a pair of coupled FSSs and combines it with full-wave simulations involving a single FSS. This way, the solution of the complete problem of $N$ stacked surfaces only involves full-wave simulations of a single periodic layer. Three scenarios have to be simulated where the surface is either standalone, or backed by perfect electric or perfect magnetic conductors. The proposed approach is validated through the analysis of several examples.

Metamaterial‐inspired balanced filters

Abstract: This chapter is focused on two different strategies for the design of balanced bandpass filters with common‐mode suppression, where the relevant aspect is the small size of the resulting devices. One of them is based on a combination of open split ring resonators (OSRRs) and open complementary split ring resonators (OCSRRs) and the other one is based on S‐shaped CSRRs (S‐CSRRs). The chapter shows that the combination of OSRRs and OCSRRs is useful to implement compact balanced filters with high common‐mode rejection ratio (CMRR) in the differential‐mode passband. The OSRR and OCSRR are open resonators that can be excited not only by external magnetic or electric fields but also by means of a current or voltage source. The chapter briefly reviews the topology of these resonant elements and justifies their small electrical size, and then details their application to the design of compact balanced filters.

WIDEBAND BALANCED FILTERS BASED ON MULTI‐SECTION MIRRORED STEPPED IMPEDANCE RESONATORS (SIRs)

Abstract: This chapter aims to study some implementations of wideband balanced bandpass filters based on multi‐section mirrored stepped impedance resonators (SIRs) and to provide guidelines for their design. Through the use of such resonant elements, it is possible to achieve wideband differential‐mode responses and an efficient common‐mode rejection by the selective introduction of transmission zeros for the common mode. The chapter also reports three filter examples, including an order‐5 and an order‐7 wideband filter, both based on 7‐section SIRs coupled through admittance inverters, and an order‐5 ultra‐wideband (UWB) balanced filter based on 5‐section SIRs and patch capacitors. In order to implement the balanced filters, the mirrored SIRs are alternated either with balanced quarter‐wavelength transmission‐line sections (acting as admittance inverters) or with series resonators (in balanced configuration) implemented by means of lumped elements (interdigital or patch capacitances and inductive strips).

Introduction to balanced transmission lines, circuits, and networks

Abstract: This chapter is an introduction to the topic of balanced lines, circuits, and networks. It deals with the fundamentals of differential‐mode transmission lines, including the main topologies and propagating modes. In differential transmission lines and circuits, the main contribution to noise is the so‐called common‐mode noise. Common‐mode noise is originated from electromagnetic radiation (through crosstalk or through an external source) and from the ground terminal. The chapter points out some main approaches for the implementation of balanced microwave filters with common‐mode noise suppression. The scattering parameters (S‐parameters), or scattering matrix (S‐matrix), are typically used for the characterization of microwave networks. These parameters give relative information of the amplitude and phase of the transmitted and reflected wave with reference to incident wave, at least in the small‐signal limit (linear regime). The chapter ends with the mixed‐mode S‐parameters, useful for the analysis and characterization of differential circuits, and their relation to the single‐mode S‐parameters.

Balanced power dividers/combiners

Abstract: This chapter discusses several kinds of balanced‐to‐balanced power divider/ combiner. As the key component in a balanced RF transceiver, the concept of balanced‐to‐balanced power divider/combiner is proposed, which divides the input differential‐mode power into several ways with good port isolation and common‐mode suppression. To extend the applications of balanced‐to‐balanced power dividers, the chapter designs a dual‐band balanced‐to‐balanced power divider. It introduces balanced‐to‐balanced Wilkinson power dividers implemented using microstrip technology. The desired performance of the balanced‐to‐balanced Gysel power divider has been implemented with the half‐mode substrate integrated waveguides (SIWs) ring structure, and a high power handling capability can be expected. The balanced‐to‐balanced power dividers are designed in Wilkinson and Gysel topologies and realized in microstrip line and half‐mode SIW. They are also designed with arbitrary power division ratio, bandpass filtering response, and dual‐band operation.

Physically-insightful equivalent circuit models for electromagnetic periodic structures

Abstract: In this presentation it will be discussed how to obtain analytical or quasi-analytical equivalent circuits to deal with periodic structures such as frequency selective surfaces and/or metasurfaces. Both the topology and the values of the involved elements of these circuits are obtained from a basic rationale to solve the corresponding integral equation. This procedure, besides providing a very efficient analysis/design tool, allows for a good physical insight into the operating mechanisms of the structure in contrast with the almost blind numerical scheme of commercial simulators.

Coupled‐resonator balanced bandpass filters with common‐mode suppression differential lines

Abstract: Coupled‐resonators are widely used for implementing narrowband bandpass filters, which are essential components for many RF/microwave applications. This chapter starts by designing a balanced single‐band bandpass filter based on conventional coupled resonators. Next, several types of common‐mode (CM) rejection stages (which are the basic unit cells of artificial differential lines with CM rejection) are cascaded with the basic filter to verify how effectively CM rejection is significantly improved without altering the differential‐mode (DM) response. The chapter demonstrates that differential lines providing CM rejection over a desired frequency band can be used to improve the response of balanced filters with poor CM performance. This has been done for both single‐band and dual‐band implementations. The LC‐loaded lines are intended to be applied to reject the CM transmission in a balanced dual‐band bandpass filter. The filter itself are implemented using two pairs of coupled resonators.

Circuit Modeling of Electromagnetically Induced Reflection by Multiple Slits on a Metallic Screen

Abstract: The study of classical analogues of electromagnetically induced transparency (EIT) or of its dual counterpart, electromagnetically induced reflection (EIR), has attracted the interest of many researchers in the field of optics and microwaves in recent years. Apart from the theoretical interest of the phenomenon, this effect has potential applications in practical systems demanding narrow band, slow light propagation and high non-linearity. The physical mechanism behind this phenomenon can be interpreted in terms of a coupled resonators system, which can be implemented by means of coupled resonant LC circuits. In this work we propose an extremely simple periodic electromagnetic system exhibiting EIR and a Foster-like circuit model involving uncoupled resonators accounting for the fundamental resonances of the electromagnetic structure. The specific unit cell treated in this contribution consists of three identical coupled slits made in a thin conducting plate. The features of the transmission band and the induced narrow transmission dips are easily explained in terms of the values of the parameters of the equivalent Foster-like circuit. Some rules for tailoring the location of the transmission dip and the bandwidth of the passband where the dip is located are given. The results obtained with the circuit model are validated by proper comparison with simulations carried out by using a commercial electromagnetic solver.

Circuit Models for Printed Multiresonant FSSs

Abstract: Frequency selective surfaces, the unit cell of which shows a multiresonant behavior, are analyzed in this work by means of an equivalent circuit approach. The derivation of the topology and the computation of thevalues of the elements in the equivalent circuits is achieved through the extension of a previous formulation developed by the authors for multiresonant discontinuities in hollow-pipe waveguides. This formulation results in the obtaining of canonical circuits formed by a series connectionof resonant LC tanks. The results provided by the circuit models for the scattering behavior of a frequency selective surface printed on a dielectric substrate are compared with those computed using a commercial electromagnetic simulator.

Narrowband coupled‐resonator balanced bandpass filters and diplexers

Abstract: Narrowband bandpass filters (BPFs) are key components in modern communication systems and other applications of wireless technologies. This chapter discusses balanced filter topologies where common‐mode (CM) is inherently rejected due to the geometric properties (including symmetry) of the proposed structures. It also discusses several examples of this kind of narrowband filter implementation strategy. Diplexers are also important components in modern dual‐band wireless communication systems. The chapter presents a brief discussion on some balanced diplexers made in microstrip technology. Balanced diplexers can be roughly classified into two categories: balun diplexers; and non‐balun diplexers. Balun diplexers are composed of a single‐ended input (output) and two balanced outputs (or a balanced input). On the other hand, a non‐balun diplexer is a genuine balanced diplexer in the sense that both input and output ports are balanced ports.

UWB AND NOTCHED‐BAND UWB DIFFERENTIAL FILTERS USING MULTILAYER AND DEFECTED GROUND STRUCTURES (DGSs)

Abstract: The development of ultra‐wideband (UWB) differential filters is an attractive topic in microwave circuit research because of the capacity of these filters for high data rate transmission, high immunity to environmental noise, and low electromagnetic interference (EMI). The mechanism of the multilayer microstrip‐to‐slotline transition (MST) and its applications in differential topology are analyzed, with the slotline defected ground structure (DGS) pattern etched in the ground. This chapter presents several typical types of UWB and notched‐band UWB differential filters based on the MST. It describes UWB differential filters based on the MST with a notched band and enhanced stopband. To achieve UWB differential filters based on the MST, many investigators have presented a variety of designs with satisfactory performance. In the chapter, the strip‐loaded slotline resonator is introduced and applied to differential filters with multimode operation. The employment of back‐to‐back microstrip resonators enables easy control of the resonant modes for constructing wideband differential filters.

Wideband and uwb balanced bandpass filters based on branch‐line topology

Abstract: The branch‐line‐like structure is one of the earliest works in the design of wideband differential‐mode bandpass filter with common‐mode suppression. This method has been still widely used because of its simple geometry, easy design rule, and compact size. In another method, a wideband bandpass differential‐mode filter with enhanced common‐mode rejection can be constituted by using the transversal signal interference technique. This design concept stems from the distributed active filter theory. In this chapter, a class of ultra‐wideband (UWB) balanced bandpass filters on microstrip line with good common‐mode suppression is designed and implemented. The so‐called signal interference technique on two parallel transmission lines of different electrical lengths and characteristic impedances is proposed to design a wideband stopband under common‐mode excitation. The chapter also presents a novel method to improve the filter selectivity performance of a wideband filter by stretching a traditional 90° branch‐line stub to 270° in two sides.

On the Computation of the Dispersion Diagram of Symmetric Periodic One-dimensional Structures

Abstract: A critical discussion on the computation of the dispersion diagram in periodic one-dimensional guiding structures is carried out. In particular, an analysis is presented of the pros and cons of combined methods that make use of full-wave simulations done with commercial software packages with further analytical post-processing based on simplifications brought by an equivalent circuit model of the structure. Some of the most common methods reported in the literature are reviewed and their advantanges and limitations highlighted. Our discussion is complemented with several selected numerical examples in order to discuss the most relevant aspects that a potential user of these methods should be aware of. Special attention is paid to the relevant role played by the high-order coupling between the two halves of a symmetric unit cell of the periodic structure.

Dual‐band balanced filters implemented in substrate integrated waveguide (siw) technology

Abstract: This chapter introduces two types of balanced filters with dual operation bands utilizing the potential substrate integrated waveguide (SIW) technology. For the first type of dual‐band balanced bandpass filters (BPF), it is constructed by utilizing the TE 101 and TE 102 modes, where the common‐mode (CM) signals are effectively suppressed by the balanced sections resonating at the TE 102 mode. As for the second type of dual‐band balanced BPF, it is designed by the adoption of TE 101 , TE 102 , TE201, and TE 202 modes, where the CM signals are effectively suppressed by the balanced sections resonating at the TE 102 and TE 202 modes. The chapter shows a typical SIW cavity configuration. It deals with a new dual‐band balanced filter using high‐order resonant modes in SIW cavities. Specifically, in the differential‐mode (DM) response, the first passband is derived by the dominant modes, while the second passband is obtained by employing the higher‐order modes in the SIW cavities.

Wideband balanced filters on slotline resonator with intrinsic common‐mode rejection

Abstract: This chapter proposes several novel wideband balanced bandpass filters (BPFs) with intrinsic common‐mode (CM) rejection. The hybrid microstrip‐slotline structure is used in the chapter in order to maintain the intrinsic CM rejection. A more generalized hybrid slotline multimode resonator (MMR) is also proposed by two kinds of transmission line, that is, microstrip line and slotline, and it is utilized to design an alternative wideband balanced BPF with intrinsic CM rejection. The chapter shows the three‐dimensional view and top view of the two proposed balanced BPFs on slotline MMR, respectively. In each filter, a slotline resonator is formed on the middle ground plane of a two‐layer substrate, and its multimode resonance is utilized to build up a wideband balanced BPF. Furthermore, the chapter explains working mechanisms and design methods of the wideband balanced filters, theoretically demonstrated and experimentally validated over a wide frequency range for both differential‐mode (DM) and CM frequency responses.