User Manual

Interfacing and Controlling the RIM 801D Antenna integration: Positioning the antenna 27
RIM 801D OEM Radio Modem – Integrator’s Guide
Antenna efficiency
The optimal antenna radiation efficiency is produced by a monopole. The
best antenna length is the length of the wavelength, λ. Where f is the radio
frequency being used, λ=c/f ≈ 3x10
8
/f(metres).
Antenna lengths of λ/2, λ/4 or λ/8 also work well and usually result in a
relatively well matched antenna. λ/2 or λ/4 can be electrically “shortened”
by adding load matching elements to control the antenna match. However,
this shortening will reduce the antenna efficiency and therefore the effective
radiated power.
RIM recommends the use of an experienced antenna provider in order to
realize the highest gain possible. A well-designed antenna solution will
maximize efficiency, coverage area, and battery life.
Positioning the antenna
Proper positioning of the antenna will maximize the gain provided by the
antenna. In determining the “proper position,” the designer must carefully
consider the environment in which the device will be used. There is no
single “correct answer,” as embedded systems can vary significantly.
Incorporating the antenna is an integral part of a successful design.
The DataTAC network is based on vertically polarized radio-frequency
transmission. Therefore, the antenna should ideally be oriented so that it
provides vertical polarisation. This is achieved by positioning the antenna
vertically upward when the RIM 801D is in use. In small, hand-held
devices, it may be convenient to design the unit in such a way that the
antenna folds out of the way when not in use.
The antenna should be located as far from the active electronics of the
computing device as possible. Metal construction in the case of the
computing device and its internal components may attenuate the signal in
certain directions. This is not desirable, as it would reduce the sensitivity
and transmit performance of the radio modem.
If the computing device is designed to sit on a surface, then the antenna
should be as far from the bottom of the device as possible. This will reduce
RF reflections whenever the device is placed on a metal surface.