Double-folded monopole antenna using parallel line or coaxial cable

Abstract

It has been shown that loading a certain reactance component at the feeding point of an antenna is useful in reducing antenna size. When a parallel transmission line with a short-circuited end is loaded onto a monopole antenna, we can obtain a small antenna called a parallel line loaded monopole antenna. However, a small antenna usually has low input resistance and low actual gain. The approach outlined is to increase the actual gain of the small loading antenna and utilise knowledge of a folded monopole antenna, which has a very high impedance value. A small folded monopole antenna called the double folded monopole antenna (DFMA) with high resistance and high actual gain can then be realised. An explanation of the operational principles of the DFMA is provided and the characteristics of small antenna design discussed. A coaxial cable is also used as the loading element for the loading antenna. It is proposed that a coaxial cable DFMA can be realised by replacing the parallel transmission line loading with coaxial cable transmission line loading. The advantage of the coaxial cable DFMA is that it has a small cross-sectional area, since the coaxial cable loading is embedded within the cylindrical antenna element. The results of actual testing of the coaxial cable DFMA are presented. All other results are provided by computer simulation using the method of moments, since the results are assumed to be similar to those recorded from practical experimentation.