GPS World, February 2018
ANTENNAS a b c The UIGD is a comprehensive metric to describe the DGD uniformity but needs accurate phase measurement over the entire bandwidth which may not be always easily obtainable As a matter of fact phase can be challenging to measure some indication of the areas most likely to deliver increased DGD can be found while considering gain patterns qualitatively providing an easier metric to compare different antennas In this case the Uniformity Indicator for Gain UIG can be used 3 The UIG expresses the maximum value over all elevation 30 GPS WORLD WWW GPSWORLD COM FEBRUARY 2018 b FIGURE 5 Measured 3D RHCP gain patterns at f 1575 MHz for a badly polarized COTS antenna b DLR dual feed antenna c DLR four feed antenna and azimuth angles of the standard deviation of the RHCP gain derivative over frequency in the band of interest therefore indicating the roughness of the antenna gain pattern in frequency and angle Such a metric does not relate totally with DGD behavior but serves as an easier metric of pattern uniformity The UIG for the one two and four feed antennas is respectively 685 57 and 03 REAL LIFE PERFORMANCE AND IMPACT ON ACCURACY To evaluate the performance of actual antennas three prototypes were measured in a Satimo Starlab anechoic chamber at the German Aerospace Center DLR The antennas under test were A badly polarized COTS active antenna having a FIGURE 4 Differential group delay versus elevation angle and frequency each color represents an azimuth value for a single feed antenna b dual feed antenna c four feed antenna a c
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