This paper presents a cost effective and simple anti-jamming method for global positioning system (GPS) antennas in the GPS L1 (1.563-1.587 GHz) band. The proposed structure is composed of a metallic conical structure with a microstrip patch antenna, which is selected as the basic element. To overcome intentional jamming signals coming from low elevation angles, the structure is applied around the low profile patch antenna. It is found that the maximum anti-jamming performance is achieved when the lower diameter (l), height (h), and upper diameter (d) of the structure are 90, 190, and 380 mm, respectively. The experimental results show that the peak gain in the horizontal plane for the jamming signal decreases by about 6.2 dB from -6.16 to -12.36 dBic, while the peak gain in the vertical plane for the GPS signal increases by about 5.58 dB from 1.32 to 6.9 dBic. Moreover, it is shown that an improvement in the circular polarization (CP) characteristics is also obtained with the proposed structure. The measured fractional bandwidth is about 3.7% (1.561-1.62 GHz).
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