page_title: J-pole antenna
section_title: Gain and radiation pattern
hierarchical_section_title: J-pole antenna / Characteristics / Gain and radiation pattern
context_page_description: The J-pole antenna, more properly known as the J antenna, was first invented by Hans Beggerow in 1909 for use in Zeppelin airships. Trailed behind the airship, it consisted of a single element, one half wavelength long radiator with a quarter wave parallel feedline tuning stub. This concept evolved to the J configuration by 1936 attaining the name J Antenna by 1943. When the radiating half-wave section is mounted horizontally, at right-angles to the quarter-wave matching stub, the variation is typically called a "Zepp" antenna.
context_section_description: Primarily a dipole, the J-pole antenna exhibits a mostly circular pattern in the H plane with an average free-space gain near 2.2 dBi (0.1 dBd).  Measurements and simulation confirm the quarter-wave stub modifies the circular H-plane pattern shape increasing the gain slightly on the side of the J stub element and reducing the gain slightly on the side opposite the J stub element. At right angles to the J-stub, the gain is closer to the overall average: about 2.2 dBi (0.1 dBd). The slight increase over a dipole's 2.15 dBi (0 dBd) gain represents the small contribution to the pattern made by the current imbalance on the matching section. The pattern in the E plane reveals a slight elevation of the pattern in the direction of the J element while the pattern opposite the J element is mostly broadside.  The net effect of the perturbation caused by quarter-wave stub is an H-plane approximate gain from 1.5 to 2.6 dBi (-0.6 dBd to 0.5 dBd).
caption: E-plane gain measurements of J antenna with respect to reference dipole.