Electromagnetics
Working Papers
- Applying Computational Methods to Test Site and Antenna Design
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In this article, we apply the Method of Moments to the design a half wave dipole and a biconical antenna. We will also use it to derive the site attenuation model developed by Willmar Roberts for use by the Federal Communication Commission.
- Circuit Models Make Shield Design Simple
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Inadvertent magnetic and electric field coupling limits the dynamic range of amplifiers, lowers noise margins and creates unwanted noise. While every engineer knows that shielding can prevent coupling, for many shielding is a vaguely understood concept. Part of the reason is the way that shielding concepts are traditionally taught – physicist’s concept of fields and flux is usually used. It is possible however to explain shielding theory using more familiar circuit concepts.
- Computational Magic and the EMC Engineer
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In this article we apply the Method of Moments to a variety of EMC problems. It is an established technique for calculating emissions from structures such as antennas, but can be used to predict emissions from printed circuit boards and associated structures as well.
- Designing Log Periodic Antennas
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Log periodic arrays consist of a set of dipole antennas of varying sizes strung together and fed alternately through a common transmission line. These remarkable antennas exhibit relatively uniform input impedance, VSWR, and radiation characteristics over a wide range of frequencies. In this article, we describe how design these versatile antennas.
- EMI: Why Devices Radiate
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Many of the problems associated with emissions from electronic equipment can be explained using the concept of “lost flux.” Any circuit will produce magnetic flux. However some of this flux does not remain confined to the circuit but instead envelopes it. This lost flux creates a common mode voltage across the circuit causing attached conductors to radiate. In this article we explore the concept of lost flux and through a series of experiments, demonstrate how it is possible to design circuits to minimize unwanted radiation.
- Experiments in EMC: How Common Mode Currents Are Created
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In this article, we explore the physics behind the creation of unwanted common mode currents in digital devices, and describe experiments anyone can do to understand and study the phenomenon.
- How Anechoic Chambers Work
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A radio frequency “anechoic chamber” is a shielded room whose walls have been covered with a material that scatters or absorbs so much of the incident energy that it can simulate free space. Innovations such as the use of ferrite tiles have greatly enhanced performance of these chambers. Though anechoic chambers may seem to operate through a bit of black magic, analysis of how they work is really quite straightforward.
- Know the Theory Of Partial Inductance to Control Emissions
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The theory of partial inductance is a powerful tool for understanding why digital circuits radiate. In this article we explore the theory of partial inductance, and then apply it printed circuit board geometries. Using the theory, we can predict emissions from circuits and design strategies to mitigate them.
- Minimizing Ringing and Crosstalk
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In this article, we explore strategies to minimize ringing and crosstalk in both microstrip and stripline designs.
- On Chip Design for Better Noise Control
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ICs can be designed to produce fewer emissions without compromising performance. The key is using a driver whose current drive capability matches the load. Changing the impedance with load requirements lessens demand on the supply and helps avoid ground bounce.
- Rethinking the Role of Power and Return Planes
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Good noise control calls for using power and return planes in a configuration that provides for low RF impedance. In this article, we explore the feasibility of using ground and return planes not only to provide low impedance, but to provide shielding as well. Using the ground and return planes as a shield prevents flux from escaping and enveloping the entire circuit board. “Lost flux" is a primary cause of emissions from electronic circuits.
- Shiver Me Timers! Using Spread Spectrum Clock Generators
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A spread spectrum clock generator (SSCG) reduces EMI by modulating the clock frequency, thereby spreading radiated energy over a frequency range wider range than the bandwidth of the receiver used to measure emissions. This article explores the history of their development and how they can be used to lessen emissions without compromising performance.