Double-folded Monopole Antenna with Coaxial Cable

Previously, we proposed a small high-active-gain antenna called the double-folded monopole antenna with coaxial cable. This antenna consists of two 0.15-wavelength coaxial cables, each of which has one end that is short-circuited. The source is connected to the center conductor of one of the coaxial cables, and the center conductor of the other coaxial cable is grounded to the ground plane. Two coaxial cables are arranged in parallel and are perpendicular to the ground plane, thereby forming a parallel monopole antenna. Finally, the outer cylinders of each coaxial cable are connected by a short wire at the open end of the cables near the feed point. Although this antenna has a very small height, it has high active gain due to its high input impedance of approximately 50ohm. This antenna has a relatively simple structure and a complicated electrical operational principle. The present paper is the flrst report of the coaxial cable loaded monopole antenna of reduced size. Using this antenna, we describe the construction of the double-folded monopole antenna with a coaxial cable. Finally, we discuss the operational principle of the coaxial cable loaded monopole antenna with respect to the relationship between the resonant length of this antenna and the input impedance. It is hoped that the present paper will clarify the theory of the double-folded monopole antenna with coaxial cable.