Monopole with inductive loading

This paper presents the results of a study undertaken to determine the electrical characteristics of a base-driven inductively loaded monopole, shorter than self-resonant length, oriented normal to an infinite perfectly conducting ground screen. The antenna may be tuned by a combination of two lumped coils of finiteQ. One is in series with the generator at the base; the other is in series with the antenna conductor some distance above the feed point. In some installations the use of two loading inductors may be a convenience in that this arrangement permits final tuning adjustments to be made at the base of the antenna. Sufficient information is available to permit determination of the reactance of the lossy loading coils to achieve resonance, the voltage rise across the coils, the impedance presented to the generator, and the antenna efficiency in the absence of antenna ohmic and ground system losses. Simple ancillary studies, as proposed by an illustrative example, permit decisions to be made regarding the merit of a particular inductively loaded monopole of small dimensions in terms of the operating wavelength-whether the application is for VLF transmission from a shore radio station, or for transmission from a moving motor vehicle at shorter wavelengths. An interesting by-product of the present analysis is a formula for the impedance of a monopole grounded at its base, and driven some distance above the earth plane.