Gain and Radiation Resistance
If mounted above a perfect ground plane, a quarter wave whip has a gain twice (3 dB greater than) that of a half wave dipole, or 5.19 dBi, and a radiation resistance of 36.8 ohms. However without a ground plane the gain is reduced and the radiation resistance increased. Whips mounted on vehicles use the metal skin of the vehicle as a ground plane. In hand-held devices usually no explicit ground plane is provided, and the ground side of the antenna's feed line is just connected to the ground on the device's circuit board. Therefore the radio itself, and possibly the user's hand, serves as a rudimentary ground plane. Since these are no larger than the size of the antenna itself, the combination of whip and radio often functions more as an asymmetrical dipole antenna than as a monopole. In stationary whip antennas, a "ground plane" consisting of several rods a quarter-wavelength long radiating horizontally from the base of the whip is often used. This type of antenna is called a ground plane antenna.
Read more about this topic: Whip Antenna
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