Topcon PN-A5 GNSS antenna
Part one of this series introduces the technicalities of antennas for GNSS reference stations in the context of GNSS spectrum expansion, and it provides details on Topcon’s PN-A5, including the basics of its unique design. Part two compares the antenna’s performance to a CR4 antenna, Topcon’s version of the original JPL choke ring design. Figure numbers continue from part one.
The PN-A5 antenna comprises a newly designed, full-spectrum GNSS antenna element. Figure 7 shows phase center offset in vertical versus frequency of the radio signal. (The results represented in the figure were obtained from anechoic chamber measurements. An offset for GPS L1 (1575MHz) is used as reference.) As demonstrated by this figure, the choke groove structure of the CR4 has resonance at approximately 1150MHz with rapid phase center variation near resonance. This is opposed to a phase center offset for the PN-A5 that is smooth versus frequency, with variations not exceeding 1cm over the entire GNSS band. This provides with consistent response for the different GNSS signals.