Antennas for Mobile Units

Land Mobile Antennas Quarter-wave Antennas: The most common vehicle antennas utilize the car roof as one half of the antenna system. The antenna is a so-called ”monopoly on ground plane”. The basic type is a so-called quarter-wave ( ¼ λ) antenna. The fact that the antenna being close to 50 Ω is utilized when the whip has a length of approx. 1/4 wave length at the operating frequency. By lengthening the whip, the antenna gain will be increased. The gain will, however, again be reduced if the whip length is above 5/8 wave length.
Colinear Antennas: In case higher gain should be achieved, so-called ”colinear” antennas should be applied, for which more radiating elements are stacked and operate together, thus concentrating the radiation in the horizon. The optimum mounting site is in the centre of the car roof, at which the optimum omnidirectional characteristics are achieved.
Marine Antennas Marine antennas are in a way very similar to omnidirectional base station antennas except for the fact that usually intensified requirements as to mechanical sturdiness and corrosionresistance are made. Marine antennas are similar to omnidirectional base station antennas but with intensified requirements of sturdines Marine antennas are similar to omnidirectional base station antennas but with intensified requirements of sturdines Maritime communication is mainly taking place on medium wave, short wave and the maritime VHF bands.
Portable Antennas Quarter-wave Antennas: Like mobile antennas portable antennas are mostly ¼ wave ”monopoly” antennas, which utilize the chassis of the portable radio as ground plane, i.e. as one half of the antenna system. This usually results in insufficient ground plane as well as the fact that the radiation from the portable radios is mostly very badly defined owing to the presence of the hand or body, and in general a low efficiency for portable antenna systems should be taken into consideration, both because of disadjustment loss and loss owing to ”overturned” radiation.
Half-wave Antennas: If, however, antenna whips with a ½ wave length are applied together with an adaptation circuit the antenna being independent of the cabinet can be achieved. The antenna functions ”in itself” and a considerable improvement of 5 dB as average value can be achieved (compared to a ¼ wave antenna on the same device).
Nowadays air craft antennas are an integrated part of the fuselage