An antenna for a portable data terminal

A Portable Data Terminal has radiation requirements somewhat different from those of a traditional portable radio. A portable transmitter is normally required to radiate in the hands or on the belt of the user when the operator depresses the Push-To-Talk (PTT) switch. The radiation environment, the objects in the immediate vicinity of the radiator (say less than six inches distant) and the position of the radio with respect to such objects, is predictable. For example, the designer can expect that the radio case will be in the hand of the user, the antenna in front of the face of such person, and that there are a few feet of free space around the head of the user. The user of the radio can be expected to operate the transmitter in such conditions. This is not the case for a portable data terminal whose RF transmissions are controlled not by an operator but by interrogation by a base station. In these conditions, the terminal is required to radiate from inside a briefcase, on a table, on a metal slab, etc. In general, one can see that the terminal is expected to radiate from any position in the close vicinity of conducting or non-conducting surfaces. Traditional portable antennas, e.g., whips and helices, cannot satisfy the condition of radiating efficiently when placed close to and parallel to conducting surfaces.