Integration of GPS with Other Sensors and Network Assistance - Understanding GPS: Principles and Applications - page 530

position, and using different hand grips). Antenna efficiencies in the 30% to 40%
range are typical, with attenuation profiles in the 5- to 15-dB range, depending on
orientation and use pattern. Figure 9.36 shows a photograph (courtesy of Motorola)
of an embedded inverted-L GPS antenna in a cellular handset—in this case, a
Motorola A835, in which the antenna is mounted on the upper end of the unit. The
element is made to snake around the phone's digital camera aperture. Note the SMA
connector on the side of the unit is strictly for test purposes on this engineering unit
and is not present in the final product. The top-end antenna placement is ideal for
the dialing position or while using embedded navigation features as the user must
look at the screen, forcing a sky view to the antenna. Antennas have been placed on
the back side and in the upper and lower portions of flip-style phones, each
presenting unique and challenging integration issues.
Depending on how the user holds the product in operation, it's possible for the
user's hand to completely cover the antenna, which tends to attenuate the signal fur-
ther and detune the antenna to even worse efficiency. The product styling team is
usually forced to make compromises as well simply to make room for the antenna,
and in a world where product styling is very important, these types of compromises
are difficult. As such, some cell phone types reuse the cellular communications whip
or stub antenna as a GPS antenna, coupling into the device with tuning elements but
compromising the pattern even more, as the circular polarization can be lost.

9.4.2.2 Characterizing Signal Attenuations
This section presents the results of a measurement campaign that was conducted to
statistically characterize L-band and GPS signal attenuation in various environ-
ments. Preprocessing of the raw, measured signal amplitude data was corrected to
remove the effect of the transmit antenna pattern as its angle to the receiver changed.

GPS antenna

Figure 9.36 GPS antenna embedded into cell phone. (Courtesy of Motorola.)