GPS System Segments - Understanding GPS: Principles and Applications - page 104

Antenna

I/O

Control
display unit

Receiver Processor

Regulated dc power

Power
supply

Figure 3.23 Principal GPS receiver components.

3.4.1.1 Antenna
Satellite signals are received via the antenna, which is right-hand circularly polarized
(RHCP) and provides near hemispherical coverage. Typical coverage is 160° with
gain variations from about 2.5 dBic at zenith to near unity at an elevation angle of
15°. (The RHCP antenna unity gain also can be expressed as 0 dBic = 0 dB with
respect to an isotropic circularly polarized antenna.) Below 15°, the gain is usually
negative. An example antenna pattern is shown in Figure 3.24. This pattern was pro-

0

345

15

330 30

RHCP

315 45

300 60

LHCP

285

75

270

90

Gain (dBic)

255

105

240

120

225

135

210

150

195

165

180

Figure 3.24 Example of RHCP hemispherical antenna pattern.