Nonsinusoidal Electromagnetic Waves Research Articles

Hands-on activity using the amplitude and frequency of electromagnetic waves to demonstrate the principle of information transfer

Electromagnetic (EM) waves are indispensable in modern telecommunications. Despite their essential role in modern technology, EM waves are considered to be an abstract concept by many students. In this activity, an inexpensive two-coil system was constructed in a teaching laboratory and used to demonstrate information transfer by non-sinusoidal EM waves. Twenty secondary school students were invited to try out a hands-on activity developed based on this system. The participants were divided into teams, with some members in each team encoding and transmitting a message using EM signals followed by other members receiving the signal and decoding the message. The message was encoded using different frequencies and amplitudes of the sinusoidal components in the EM signal. In this outreach activity, a significant number of participants was found to hold the misconception that all EM waves are sinusoidal. After this hands-on activity, the number of participants holding this misconception decreased.

Antenna patterns of nonsinusoidal waves with the time variation of a Gaussian pulse II

The development of antenna theory for nonsinusoidal electromagnetic waves has been based on the idealized rectangular pulse. In practice, an antenna that is designed to operate in the mode of an electric hertzian dipole would radiate a pulse that best approximates a Gaussian one when the driving current consists of a linear transient. The principle of radiation of nonsinusoidal electromagnetic waves with the time variation of Gaussian pulses is discussed. The properties of the Gaussian pulse are presented, i.e., the autocorrelation function, energy spectral density, and spectrum. Antenna patterns, such as peak-amplitude pattern, peak-power pattern, energy pattern, and slope pattern are derived for a Gaussian pulse received (or radiated) by a linear array antenna. Computer plots of the derived antenna patterns are presented that show a considerable improvement in the angular resolution capability over that of the antenna patterns that have been derived for a rectangular pulse. >

Nonsinusoidal Waves in Cavity Resonators

It has been shown that nonsinusoidal waves can propagate dispersion-free in loss-free waveguides. This situation opens the possibility of nonsinusoidal waves existing distortion-free in cavity resonators. A general solution of Maxwell's equations for nonsinusoidal waves in rectangular cavity resonators is derived. For the special case of a square wave, the electric and magnetic field strengths as functions of time and space are analyzed in detail. The implication of this analysis is that square waves or other periodic nonsinusoidal waves with various periods T can be separated by cavity resonators just as sinusoidal waves with various periods T can be separated. This paper is part of an ongoing effort to advance the technology of antennas and associated circuits for nonsinusoidal electromagnetic waves.

Antennas for Nonsinusoidal Waves. I. Radiators

During the last years numerous applications of nonsinusoidal electromagnetic waves have been discussed in this TRANSACTIONS. The next step is the implementation of these applications. It is generally accepted that the antennas pose the greatest diMculty. In a series of papers on radiators, sensors, and arrays, we will investigate antennas, both theoretically and experimentally. Sufficient information is provided to permit anybody who is equiped for work with pulses of about I-ns duration to build simple radiators and sensors.

Low-Angle Tracking by Carrier-Free Radar

Multipath transmission is currently the most important limitation for the accuracy of low-elevation-angle radar. The use of properly polarized nonsinusoidal electromagnetic waves permits one to discriminate between the wave that propagated directly from the radar to the target and back, and all the other waves that propagated via the surface of the earth, either on the way to the target or on the way back (first-order multipath transmission). The effect works both over water, a good conductor, and over dry land, a good insulator. It appears that the error due to first-order multipath transmission can be essentially eliminated. As a fringe benefit, one avoids the enormous propagation losses incurred when pulses with a duration of about 1 ns are transmitted with the help of a sinusoidal carrier. (A similar polarity-reversal effect, that exists for circularly polarized sinusoidal waves, cannot be used for an all-weather radar because of the high absorption losses.)

Selective Reception of Periodic Electromagnetic Waves with General Time Variation

Several transmitters and receivers for periodic nonsinusoidal electromagnetic waves have been built during the last few years. Various applications of such waves, primarily in radar, have been recognized. The first practical equipment, an into-the-ground radar for construction surveying, has become commercially available. The efficient radiation of nonsinusoidal periodic waves has been discussed in the literature, but very little has been published on their selective reception. This paper describes the principle of selective receivers for periodic waves with general time variation, in analogy to the design of the usual receivers for waves with sinusoidal time variation.