Fig. 4 Measured peak gain and axial ratio
Fig. 5 Measured axial ratio radiation pattern
Fig. 6 shows the measured radiation pattern of the proposed antenna at 1.575 GHz. In Fig. 6(a), the HPBW (Half Power Beam Width) of the X-Z plane is about 140° and that of the Y-Z is about 120° in Fig. 6(b). Because the antenna has a broad beamwidth about 120°, the antenna covers as many as satellites over the hemisphere. The front-to-back ratio is about 15dB, so the antenna rejects the unwanted signal from the bottom of the antenna and the device.
The implemented proposed antenna is shown in Fig. 7. A field test for the proposed antenna was conducted. Fig. 8 shows the locations of satellites which were observed at KAIST, in Daejeon, South Korea in September 15th 2007, 5:52 pm. The center point is the zenith of an observer and the outer circle indicates the horizon. The proposed antenna receives a signal from satellites 4, 2, 13, 17, 10, 12, 23, 5 which corresponds to C/N of 42 dB, 43 dB, 43 dB, 42 dB, 44 dB, 40 dB, 40 dB, 38 dB as you seen in Fig. 9. According to the field test, the radiation pattern coverage of the proposed antenna allows the GPS receiver to track satellites at very low elevation angles.
Fig. 6 Measured radiation pattern (a) X-Z plane (b) Y-Z plane
A new printed square quadrifilar helix antenna for GPS receiver has been presented and tested. The experimental results show that the input impedance is successfully increased by using an inverted-F antenna as a helix. Also, the proposed antenna has a good circularly polarized radiation performance. The proposed antenna can be used a promising candidate for many applications in GPS.