A ground plane antenna is a very simple antenna. It is a quarter wave vertical radiator and four radials that simulate a ground for the radiator. It directly matches to 50 ohm coax and should show a VSWR of 1.5:1 or better at its center frequency.
The antenna has 0 dB gain and is non-directional, and it is useful for both scanner, CB, amateur FM and ATV use, and as a general purpose antenna. It is useful from HF through UHF, although it tends to be large below 30 MHz. While a ground plane cut for 439 mHz will have elements around 6.25 inches long, a ground plane cut for 28 MHz will have elements 8.5 feet long. The radiator (vertical portion) is equal in length to (234/F mhz) feet, and the radials (drooping elements) are made about 5% longer. These formulas are fairly accurate, but element diameter, proximity to other objects, and the presence of mounting hardware (brackets, pole, etc) will have an effect.
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