Unbalanced Antenna Research Articles

Performance of balance-fed antenna system for handsets in the vicinity of a human head or hand

The effectiveness of using balanced antenna systems for handsets to reduce degradation of antenna gain due to the body effect is discussed. Analyses, both theoretical and experimental, show much lower influence of the body effect on antenna performance so that degradation of gain at the talk position would be reduced by means of the balanced antenna structure as compared with an unbalanced antenna structure. An antenna model using a loop element placed on a rectangular ground plane and fed with balanced line is taken as an example. Current distributions on the ground plane as well as on the antenna element, and radiation patterns with and without human head and hand models, are studied for both balanced and unbalanced antenna structures. The effectiveness of the balanced structure is evidenced by the reduction of current flow on the ground plane and small variation in the radiation patterns in the balanced-antenna systems as compared with the unbalanced structure. Calculated and experiment results agree well.

Measurement of field strength and calibration of antennas at low frequencies

The electric component of the strength of an electromagnetic field at low frequencies (30 Hz-300 kHz) is measured by means of electrically short antennas. Geometrically balanced dipole antennas have gained the widest use. A characteristic of short dipole antennas at low frequencies is an increase in their electric unbalance. As is shown in [I], an electrically unbalanced antenna will respond not only to the field strength E but also to its potential r relative to ground. Therefore, the reading of a field-strength meter (FSM) from such an antenna will be determined by the expression