GPS World, February 2012
Fig 3 Straight pins structure with the imaginary impedance surface This see through image shows Topcons convex impedance ground plane that combines with its TA 5 full spectrum antenna element to create the new PN A5 GNSS antenna incorporates this new convex ground plane based on pin structures ADVERTORIAL Antenna Performance Characterization The following examples compare the performance of the PN A5 antenna with a CR4 antenna Topcon version of the original JPL Choke Ring design to demonstrate low elevation gain Improvement of the PN A5 antenna SNR for low elevation satellites allows a receiver to reliably track satellites to the horizon It should be noted the antenna gain at zenith for the PN A5 antenna is 2dB less compared to the CR4 This is in agreement with the main antenna directivity theorems based on the energy conservation law Namely an antenna with a wider pattern is to have less maximal gain Figs 6a 6b demonstrate this maximal gain with lessening of 2dB in SNR for directions close to zenith compared to the CR4 This does not lead to signal tracking difficulties as the already high SNR values near zenith Another important feature of the reference station antennas is phase center offset variations in vertical versus frequency of GNSS signal This is illustrated by Fig 7 It should be noted with the earlier CR4 JPL design there is a resonance close to the lowest GNSS frequency resulting in rapid phase center variations With Topcons improved CR G5 Choke Ring this resonance is shifted below the GNSS band Additionally Topcons PN A5 shows very smooth phase center offset variations due to the pin structure design versus the choke grooves Summary The CR G5 and the PN A5 are new Topcon full wave GNSS geodetic antennas The CR G5 uses a new Choke Ring design ground plane The PN A5 comprises a new convex impedance ground plane Both antennas use the new TA 5 broadband multi dipole antenna element Both antennas are suitable for all GNSS signals existing and those planned for the coming 10 15 years Fig 4 Multipath rejection by convex impedance structure Fig 6a Signal to noise ratio versus satellite elevation GPS CA code Fig 6b Signal to noise ratio versus satellite elevation GPS P code Fig 7 www gpsworld com February 2012 GPS World 33
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