Baharak Mohajer-Iravani

Enhanced Bandwidth Artificial Magnetic Ground Plane for Low-Profile Antennas

In this letter, it is shown that using magneto-dielectric materials as substrate can increase the in-phase reflection bandwidth of electromagnetic bandgap (EBG) structures. To show this, a compact wideband EBG structure is designed and simulated. The numerical results show that this EBG has an in-phase reflection bandwidth of 70% which is several times greater than a conventional EBG resonating at the same frequency. Additionally, the new EBG surface has a smaller cell size, an important feature in the design of small antennas. As a demonstration of the effectiveness of the new structure, a low-profile unidirectional spiral antenna is designed to operate from 8 to 18 GHz. The improvement in the voltage standing wave ratio (VSWR) and gain of this antenna is presented while comparison is made to the case when using conventional EBG surface.

Suppression of EMI and Electromagnetic Noise in Packages Using Embedded Capacitance and Miniaturized Electromagnetic Bandgap Structures With High-k Dielectrics

A novel miniaturized simple planar electromagnetic bandgap (EBG) structure is proposed. The new structure mitigates different types of electromagnetic noise in packages. The design of the new EBG structure proposed here relies on the use of high-k dielectric material (epsivr >100), and consists of Meander lines and patches. The Meander lines serve to provide current continuity bridges between the capacitive patches. High-k dielectric material increases the capacitance of the patches substantially in comparison to commonly used material with much lower dielectric constant. Simulation results are provided to show that using the proposed EBG, it is possible to obtain a very wide stop band (~ 10 GHz) which covers the operating frequency of current processors and a wide range of the resonant frequencies of a typical package. The wideband is obtained using a unit cell of less than 2 mm.

Coupling reduction in enclosures and cavities using electromagnetic band gap structures

The physical mechanism behind electromagnetic interference (EMI) is the coupling of energy between different primary and secondary sources of radiation and components within the package or chassis. This coupling can be either through conduction or radiation. However, regardless of the coupling mechanism, surface currents are needed to support the electromagnetic fields that eventually cause radiation, which in turn, constitute the EMI in the victim component. Minimizing these surface currents is considered a fundamental and critical step in minimizing EMI. In this work, we address novel strategies to confine surface currents. Unlike the traditional use of lossy materials and absorbers, which can be costly and can suffer from considerable disadvantages including mechanical and thermal reliability leading to limited life time, we consider the use of electromagnetic band gap (EBG) structures. These structures are inherently suited for surface current suppression. Their design is straightforward, and they are inexpensive to implement and do not suffer from the limitation of the previous methods used for the type of EMI suppression previously described. The effectiveness of the EBG as an EMI suppresser will be demonstrated using numerical simulations and measurements.

Wideband Circuit Model for Planar EBG Structures

In this paper, we present a comprehensive equivalent circuit model to accurately characterize an important class of electromagnetic bandgap (EBG) structures over a wide range of frequencies. The model is developed based on a combination of lumped elements and transmission lines. The model presented here predicts with high degree of accuracy the dispersion diagram over a wide band of frequencies. Since the circuit model can be simulated using SPICE-like simulation tools, optimization of EBG structures to meet specific engineering criteria can be performed with high efficiency, thus saving significant computation time and memory resources. The model was validated by comparison to full-wave simulation results.

EMI Suppression in Microprocessor Packages using Miniaturized Electromagnetic Bandgap Structures with High-k Dielectrics

A novel miniaturized planar electromagnetic bandgap (EBG) structure is proposed for microprocessor packages. The design of the proposed EBG structure consisting of meander lines and patches are based on the use of high-k dielectric material with epsiv r ges 100. High-k dielectric material increases the effective capacitance of the EBG cell in comparison to commonly used materials with much lower dielectric constant. Simulation results are provided to show that using the proposed EBGs with periodicities less than 2 mm; it is possible to obtain a very wide stop-band (~10 GHz) in addition to more than 10 times in unit cell size reduction. This wide bandgap can cover the operating frequency of current processors and a wide range of the resonant frequencies of a typical package.

Electromagnetic noise mitigation in high-speed printed circuit boards and packaging using electromagnetic band gap structures

In this work, we discuss the novel concept of using metallo-dielectric electromagnetic bandgap (EBG) structures to address critical electromagnetic noise problems in high-speed circuits, packages and boards. Various design techniques for these structures, when embedded in a parallel metallic-plate structure, are presented and their efficacy and preciseness are compared. An accurate physics-based model for the unit cell of these surfaces is introduced and its accuracy is compared with simulations and measurements. It is shown that the behavior of the EBG structures in PCBs is like a low-impedance surface rather than a high-impedance surface. In particular, novel concepts presented in recent works are being used to show the validity of this observation and the effectiveness of the physics-based model to model the new concepts and applications. Finally, a new technique for the reduction of electromagnetic interference in packages using EBG structures is introduced and numerical simulations are used to show the mechanism of such interference reduction.

Ultra-wideband and compact novel combline filters

This paper presents a novel method of designing ultra-miniaturized cavity based combline filter integrable in PCB technology for EMI filtering. Each combline resonator is designed based on concepts of designing a unit cell of metamaterials. The other design steps follow the conventional design procedure of microwave filters. Choice of metamaterial unit cell leads to extreme size reduction and conventional design method results-in optimum number of resonators. A strong inter-cavity coupling value not realizable with conventional evanescent method is realized by TEM section. Therefore, the final structure is very compact and broadband. The design is realized using multilayer planar technology. A design example is provided where a dramatic reduction of the volume of filter by a factor of 7 is obtained.

Radiating emissions from the planar electromagnetic bandgap (EBG) structures

Electromagnetic bandgap (EBG) structures are considered as a viable solution for the problem of switching noise in printed circuit boards and packages. Less attention, however, has been given to whether or not the introduction of EBGs affect the EMI potential of the circuit to couple unwanted energy to neighboring layers or interconnects. In this paper, we show that the bandgap of EBG structures, as generated using the Brillouin diagram, does not necessarily correspond to the suppression bandwidth generated using S-parameters. In fact, we show that the slow modes which typically exist at the edges of the bandgap of periodic structures contribute to increased radiation, even within the suppression band obtained from the S-parameters. We validate this finding using numerical simulation. Based on this work, design guidelines for EBG structures can be drawn to insure not only suppression of switching noise but also minimization of EMI.

Analysis of tapped-in coupling between combline resonators applicable in wideband filter designs

In this work, the comprehensive analysis of coupling for combline resonators coupled through tapped-in TEM transmission line is presented. The analysis and discussions are based on developed equivalent circuit modeling the physical structure. The effects of lumped elements in this model on coupling value and resonant center frequency are studied. The results confirm the possibility to achieve a wide range of coupling varying from zero to unity. Strong coupling results in the dramatic increase of resonant center frequency. The measurement results for two-coupled planar resonators based on tapped-in coupling method verify the concepts. Therefore, this tapped-in coupling between resonators is an asset in designs of wideband filters. The developed circuit model is useful for early stages of design. The lumped elements are functions of physical design parameters hence the circuit model speeds up the realization process of finding the initial physical dimensions of resonators which satisfy the required coupling matrix and resonant center frequency. Following, full-wave analysis is performed for the final optimization of total filter structure.

A miniaturized ultra-wideband microstrip filter Using interdigital capacitive loading and interresonator tapped-in coupling

Design of miniaturized wideband filter in combline configuration using interresonator taps and interdigitally-coupled capacitive loading is described. The design is based on increasing the effective capacitance of the original quarter-wavelength combline resonator by engineering the loading interdigital capacitance at the open end of resonator, thus achieving the same resonant frequency by using a shorter physical length. The resonator structure is designed to confine the electric field in a smaller real estate to decrease losses and coupling interference with adjacent components. The filter is physically compact and has wide passband. An ultra-wideband UHF filter having bandwidth more than 20% is designed using full-wave solving software and fabricated in microstrip technology. Experimental results are in good agreement with the theoretical and simulated results.