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placed on a PCB like a standard circuit component are available, although these antennas suffer considerably in efficiency and should be used with caution. AT&T discourages the use of dielectric chip antennas on the AT&T network.

Printed antennas are strongly influenced by the PCB substrate material properties, namely the dielectric constant (DK) and loss tangent, often called dissipation factor (DF). The PCB substrate material will reduce the resonant length of the antenna which will result in a reduction of the usable bandwidth.

Additionally, the PCB substrate will introduce a loss mechanism and reduce the antenna efficiency. PCB substrate and plastic housing losses can substantially reduce embedded antenna efficiency and it is important to remember, as noted earlier in the efficiency discussion, that normally low-loss plastics can introduce significant loss when very close to and around an embedded antenna.

4.2 Antenna Type and Location

In this paper, the type of antenna discussed is limited to dipoles and monopoles (usually external antennas), the inverted-F (and its many variants), and the microstrip patch antenna. Other basic antenna elements, like the loop antenna and the slot antenna, have only limited applications, especially as embedded antennas. Detailed design information for each antenna type is beyond the scope of this paper but general design guidelines and common mistakes will be discussed.

While a properly designed external antenna will generally provide the best performance in almost all situations, today's product design constraints often completely eliminate the external antenna as an option. As such, external antenna implementation will be discussed from only one perspective - orientation. Simply put, the orientation of a dipole or monopole type external antenna must be generally perpendicular to the local ground plane of the wireless device. A dipole or monopole antenna that is positioned parallel to (and within about 30 mm of) the local RF ground plane, will have degraded return loss and compromised efficiency.

Antenna Fundamentals Technical Brief


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