Technology - technical manual
The GardenBeam is a tri-band vertically polarized parasitic array that has been derived from a Yagi. Although a vertically oriented Yagi would perform well from low heights, it is not practical at frequencies below 50 MHz, as it must be mounted in front of the mast or tower, i.e. it must be mounted by the end of its boom.
The GardenBeam uses a set of vertical elements and a set of horizontal dipole elements, which are sized similarly to the elements of a Yagi. This results in a vertically polarized beam antenna that is well balanced and can be mounted at the center of its boom. This makes mounting on a rotator easy.
The antenna works well from modest heights. The minimum mounting height recommended is 3 meters (10 feet), as that puts the antenna above head (and eye) level. Performance improves only slightly when the antenna is mounted higher. The antenna is not totally independent of ground quality. Unlike with a ground mounted vertical, the effects of the ground immediately below the antenna are not large. Good quality ground will effect tuning some extent Poor quality ground, however, will not cause large losses and low efficiency. Ground in front of the antenna, however, just like with any vertical, will have a large effect on the far field gain.
Gain in dBi vs. height above Ground and soil quality.
GND: Poor .002 S and 12, Med .005 S and 13, Good .03 S and 20 (Diel Const)
The above table shows that there is almost no improvement when mounting the antenna higher. Indeed, over the good ground, the best performance is at 3 meters. Over salt-water, or up to 15 meters from the shore, the gain jumps to 10 dBi. This makes this antenna excellent for DXpedtions where the antenna can be mounted near the water. Indeed, not only does the GB eliminate the need for a tower, but from near the sea shore, it will perform better than almost any practical horizontal Yagi and tower combination.