LNA & Quadrifilar helix for GPS
- from a S53MV, Matjaz Vidmar, project -



Giorgio Brida (IZ1BTS), Giuseppe Vizio & Massimo Cravero (IK1XPD)

From VHF Communication 4/94, the Matjaz's project see also Charles C. Kilgus, Shaped-Conical Radiation Patternof the Backfire Quadrifilar Helix, IEEE Trans. Vol. Antennas and Propagation, May 1975, pp. 392-397; Charles C. Kilgus, Multi-element Fractional Turn Helices, IEEE Trans. on Antennas and Propagation, July 1968, pp. 499-500; Charles C. Kilgus, Resonant quadrifilar helix, IEEE Trans. on Antennas and Propagation, May 1969, pp.349-351; Charles C. Kilgus, Resonant quadrifilar helix design, Microwave Journal, December 1970, pp. 49-54; M. Walter Maxwell, W2DU, Reflections, Transmission Lines and Antennas, ARRL, 1990.

...and this is the reflection coefficient of the antenna close to 1575 MHz, the broadcasting frequency of GPS satellites.



The low noise amplifier has been described on VHF Communication 2/92



For details about components values and construction please see VHF Communication 2/92.
Here we report the gain and noise figure values measured on our prototype at +8 V and +12 V supply voltages.

Frequency [GHz]	Gain [dB]	Noise Figure [dB]	Gain [dB]	Noise Figure [dB]
	Supply Voltage + 12 V		Supply voltage + 8 V
1.100	21.55	1.52	24.39	1.35
1.125	21.67	1.48	24.56	1.31
1.150	21.50	1.42	24.44	1.26
1.175	22.49	1.36	25.35	1.20
1.200	22.29	1.28	25.22	1.13
1.225	22.71	1.20	25.63	1.04
1.250	22.96	1.08	25.89	0.94
1.275	23.22	0.97	26.15	0.84
1.300	23.41	0.87	26.42	0.74
1.325	24.10	0.76	27.05	0.63
1.350	23.99	0.64	27.03	0.51
1.375	24.62	0.54	27.63	0.44
1.400	24.72	0.44	27.78	0.34
1.425	24.94	0.36	28.04	0.28
1.450	25.36	0.31	28.43	0.23
1.475	25.34	0.28	28.40	0.24
1.500	25.80	0.31	28.72	0.27

On the web you my find some other pages devoted to this kind of antenna, see for example the QHA site;
for design software try this one...
Comments and helpul hints are welcome.

updated 6 april 2002