Microwave Antenna and Waveguide Techniques before 1900

Between the years 1888, when Hertz first launched electromagnetic radiation in the radio spectrum, and 1900, when Marconi was successfully establishing communication by radio, the scientific investigators of the time turned their attention to microwaves. Later, when it was found that the longer waves were more suited to long-distance communication, interest in the microwaves waned. Between 1888 and 1900, however, microwave devices and techniques had a rich development anticipating much of present-day practice. This paper reviews the antennas and waveguides of the period, with some reference to the associated microwave techniques then developed. Apart from Hertz's dipole, with or without a plane reflector, the principal microwave antennas evolved were the cylindrical parabola, the dielectric lens, the waveguide cavity radiator, the radiating iris, and the electromagnetic horn. Among the waveguides produced were the round, square, and rectangular forms, the open end being used as a radiator. The experimental development of these hollow pipe radiators appears to have anticipated Rayleigh's theoretical paper on waveguides by a number of years, Lodge discovering the mode property experimentally in 1894. Many of the associated microwave components were of the "freespace" or quasi-optical type, rather than of the constrained or bounded type as common today, since the investigators between Hertz and Marconi were interested profoundly in the representation of optical phenomena at microwave frequencies. Hertz himself was the founder of "microwave optics," a classical subject being revived today.