Antenna Gain versus Height

This graph shows antenna gain for horizontal, vertical, and tilted orientation of a dipole for heights between 5 and 50 feet. Height is the highest point of the antenna, not its center. The tilted curve is for the tilt angle that maximizes gain. These are NEC results using the Sommerfeld-Norton ground model for average-quality earth. Modeled is a 98-MHz circularly polarized signal arriving at an elevation angle of 1° above the horizon. The gain reference is a circularly polarized isotropic antenna in free space.

The curves apply for any antenna when vertically displaced by its gain in dBd. In areas of low ground conductivity such as deserts or cities, the tilted and vertical responses will be lower than shown. In high-conductivity areas with elevated soil moisture, they will be higher. The curves are valid for flat ground with a single specular reflection. They do not apply for irregular terrain where reflection and diffraction at multiple points cause complex wave interference, although the general trend should hold.

Often unappreciated is that elevating an antenna may be the easiest and cheapest way to increase signal strength. For example, raising a dipole from 15 to 30 feet increases signal strength about 6 dB (5.6 dB if RG-6 feedline must be lengthened). This is similar to the gain a small Yagi would provide over the dipole with both antennas at 15 feet. Raising the Yagi to 21 feet would provide the same signal increase as stacking a pair horizontally at 15 feet.

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Updated March 27, 2008