Evolution of Microwave Engineering: Maxwell's Legacy

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A Short History of Microwave Engineering:

  • Microwave engineering is often considered a fairly mature discipline because the fundamental concepts were developed more than 50 years ago, and probably because radar, the first major application of microwave technology, was intensively developed as far back as World War II. However, recent years have brought substantial and continuing developments in high-frequency solid-state devices, microwave integrated circuits, and computer-aided design techniques, and the ever-widening applications of RF and microwave technology to wireless communications, networking, sensing, and security have kept the field active and vibrant.

  • The foundations of modern electromagnetic theory were formulated in 1873 by James Clerk Maxwell, who hypothesized, solely from mathematical considerations, electromagnetic wave propagation and the idea that light was a form of electromagnetic energy. All of the practical applications of electromagnetic theory—radio, television, radar, cellular telephones, and wireless networking—owe their existence to the theoretical work of Maxwell.


  • Electric and magnetic phenomena at the macroscopic level are described by Maxwell’s equations, as published by Maxwell in 1873. Maxwell’s work was based on a large body of empirical and theoretical knowledge developed by Gauss, Ampere, Faraday, and others.

  • In RF and microwave engineering, then, one must often work with Maxwell’s equations and their solutions. It is in the nature of these equations that mathematical complexity arises since Maxwell’s equations involve vector differential or integral operations on vector field quantities, and these fields are functions of spatial coordinates.


are the simplest form of electromagnetic waves and so serve to illustrate a number of basic properties associated with wave propagation.


: Microwave components often act as distributed elements, where the phase of the voltage or current changes significantly over the physical extent of the device because the device dimensions are on the order of the electrical wavelength. At much lower frequencies the wavelength is large enough that there is insignificant phase variation across the dimensions of a component. The other extreme of frequency can be identified as optical engineering, in which the wavelength is much shorter than the dimensions of the component. In this case Maxwell’s equations can be simplified to the geometrical optics regime, and optical systems can be designed with the theory of geometrical optics. Such techniques are sometimes applicable to millimeter wave systems, where they are referred to as quasi-optical.

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