GPS/GNSS Antenna Characterization GPS‐ABC Workshop V RTCA Washington, DC October 14, 2016 Christopher Hegarty, The MITRE Corporation The National Transportation Systems Center U.S. Department of Transportation Office of Research and Technology Advancing transportation innovation for the public good John A. Volpe National Transportation Systems Center Overview One component of the Department of Transportation’s GPS Adjacent Band Compatibility Study is the characterization of GPS/GNSS receiver antennas Such characterization is needed to: . Compare radiated and conducted (wired) test results . Apply interference tolerance masks (ITMs) to use cases where adjacent band transmitters are seen by GPS/GNSS receiver antennas at any direction besides zenith (antenna boresight) This presentation summarizes characterization data obtained thus far: . Gain patterns for 14 external antennas o Right‐hand/left‐hand circular polarization (RHCP/LHCP), vertical (V), and horizontal (H) polarizations o 22 frequencies: 1475, 1490, 1495, 1505, 1520, 1530, 1535, 1540, 1545, 1550, 1555, 1575, 1595, 1615, 1620, 1625, 1630, 1635, 1640, 1645, 1660, and 1675 MHz . Approximate L1 RHCP relative gain patterns for 4 antennas integrated with receivers . Saturation measurements for the 14 external (all active) antennas . All antennas provided by the USG 2 Gain Pattern Measurement Approach External antennas . Measured in 30’ x 21’ x 15’ anechoic chamber at MITRE, Bedford, MA . Calibrated absolute patterns produced using Nearfield Systems Inc measurement system and software . Full azimuth/elevation patterns produced for RHCP, LHCP, V, and H polarizations at 22 frequencies Integrated antennas . Approximate relative RHCP gain patterns at L1 estimated using live‐sky GPS C/A‐code C/N0 measurements 3 External Antenna Gain Measurements* *Note: 1. Only RHCP results shown in this presentation as examples. LHCP, V, and H polarization gains were additionally measured. 2. When viewing gain vs frequency plots, please keep in mind that measurements were made on only the 22 frequencies listed earlier. 3. All external antennas measured were active, and measured gain is for the entire transducer (passive antenna element + active subassembly) 4 Antenna #1 (TIM) 45 50 40 40 30 35 20 30 10 25 0 20 Gain (dBic) Gain Gain (dBic) Gain -10 15 -20 10 -30 5 -40 -50 0 1450 1500 1550 1600 1650 1700 -200 -150 -100 -50 0 50 100 150 200 Frequency (MHz) Off-boresight angle (deg) RHCP Gain at L1 vs RHCP Gain at Boresight Off‐boresight Angle vs Frequency Peak RHCP gain = 41.5 dBic Directivity = 4.4 dBic Difference in RHCP gain between 90 and 5 deg = 4.6 dB 5 Antenna #2 (HPR) 40 40 35 30 30 20 25 10 20 0 15 -10 Gain (dBic) (dBic)Gain 10 -20 5 -30 0 -40 -5 -50 -200 -150 -100 -50 0 50 100 150 200 1450 1500 1550 1600 1650 1700 Off-boresight angle (deg) Frequency (MHz) RHCP Gain at L1 vs RHCP Gain at Boresight Off‐boresight Angle vs Frequency Peak RHCP gain = 37.2 dBic Directivity = 3.2 dBic Difference in RHCP gain between 90 and 5 deg = 3.3 dB 6 Antenna #3 (TIM) 40 40 35 20 30 0 25 -20 Gain (dBic) Gain (dBic) 20 -40 15 -60 10 -80 -200 -150 -100 -50 0 50 100 150 200 1450 1500 1550 1600 1650 1700 Off-boresight angle (deg) Frequency (MHz) RHCP Gain at L1 vs RHCP Gain at Boresight Off‐boresight Angle vs Frequency Peak RHCP gain = 38.0 dBic Directivity = 3.9 dBic Difference in RHCP gain between 90 and 5 deg = 4.1 dB 7 Antenna #4 (GLN) 20 20 15 15 10 5 10 0 5 -5 Gain (dBic)Gain (dBic)Gain -10 0 -15 -20 -5 -25 -10 -30 -200 -150 -100 -50 0 50 100 150 200 1450 1500 1550 1600 1650 1700 Off-boresight angle (deg) Frequency (MHz) RHCP Gain at L1 vs RHCP Gain at Boresight Off‐boresight Angle vs Frequency Peak RHCP gain = 19.0 dBic Directivity = 4.4 dBic Difference in RHCP gain between 90 and 5 deg = 4.4 dB 8 Antenna #5 (GLN) 25 30 20 20 10 15 0 10 -10 Gain (dBic) Gain (dBic) 5 -20 0 -30 -5 -40 -200 -150 -100 -50 0 50 100 150 200 1450 1500 1550 1600 1650 1700 Off-boresight angle (deg) Frequency (MHz) RHCP Gain at L1 vs RHCP Gain at Boresight Off‐boresight Angle vs Frequency Peak RHCP gain = 21.8 dBic Directivity = 4.4 dBic Difference in RHCP gain between 90 and 5 deg = 6.0 dB 9 Antenna #6 (HPR) 35 35 30 30 25 25 20 20 15 15 10 10 Gain (dBic) 5 (dBic) Gain 5 0 0 -5 -5 -10 -10 -15 -15 -200 -150 -100 -50 0 50 100 150 200 1450 1500 1550 1600 1650 1700 Off-boresight angle (deg) Frequency (MHz) RHCP Gain at L1 vs RHCP Gain at Boresight Off‐boresight Angle vs Frequency Peak RHCP gain = 32.5 dBic Directivity = 6.7 dBic Difference in RHCP gain between 90 and 5 deg = 11.6 dB 10 Antenna #7 (HPR) 40 40 30 30 20 20 10 10 Gain (dBic)Gain (dBic)Gain 0 0 -10 -10 -20 -20 -200 -150 -100 -50 0 50 100 150 200 1450 1500 1550 1600 1650 1700 Off-boresight angle (deg) Frequency (MHz) RHCP Gain at L1 vs RHCP Gain at Boresight Off‐boresight Angle vs Frequency Peak RHCP gain = 33.7 dBic Directivity = 7.8 dBic Difference in RHCP gain between 90 and 5 deg = 11.6 dB 11 Antenna #8 (TIM) 35 40 30 30 20 25 10 20 0 Gain (dBic) Gain (dBic) 15 -10 10 -20 5 -30 -200 -150 -100 -50 0 50 100 150 200 1450 1500 1550 1600 1650 1700 Off-boresight angle (deg) Frequency (MHz) RHCP Gain at L1 vs RHCP Gain at Boresight Off‐boresight Angle vs Frequency Peak RHCP gain = 32.8 dBic Directivity = 5.0 dBic Difference in RHCP gain between 90 and 5 deg = 8.4 dB 12 L1 RHCP Relative Gain Pattern Summary 0 -5 -10 -15 -20 -25 Relative Gain (dBic) Gain Relative -30 -35 -40 -150 -100 -50 0 50 100 150 Off-boresight angle (deg) Red lines correspond to 5 deg elevation angle on either side of antenna. 13 Boresight RHCP Frequency Selectivity Summary 0 -20 -40 -60 -80 Relative Attenuation (dB) Attenuation Relative -100 -120 1450 1500 1550 1600 1650 1700 Frequency (MHz) 14 Integrated Antenna Gain Measurements 15 N Antenna #9 (GLN) 13 10 27 28 8 PRN Elevation C/N0 30 W E (deg) (dB‐Hz) 16 7 1 36.9 43.5 11 17 1 7 71.2 47.4 9 9 4.7 32.4 S 11 60.8 41.0 0 16 8.8 36.2 -5 17 3.9 26.0 -10 28 26.7 39.8 -15 Relative Gain (dB) Gain Relative -20 -25 0 10 20 30 40 50 60 70 80 Elevation Angle (deg) 16 N Antenna #10 (GLN) 13 10 27 PRN Elevation C/N0 28 8 (deg) (dB‐Hz) 30 W E 16 1 36.9 42.1 7 11 7 71.2 47.5 17 1 8 59.1 47.0 9 S 9 4.7 31.3 0 10 1.8 25.3 -5 11 60.8 49.6 13 49.6 37.9 -10 17 3.9 30.7 -15 27 24.4 47.6 (dB) Gain Relative 28 26.7 42.6 -20 -25 30 57.3 44.4 0 10 20 30 40 50 60 70 80 Elevation Angle (deg) 17 N Antenna #11 (GLN) 13 10 27 28 PRN Elevation C/N0 8 30 (deg) (dB‐Hz) W E 16 7 1 36.9 41.9 11 8 59.1 45.4 17 1 9 4.7 26.9 9 S 10 1.8 31.9 0 11 60.8 44.9 -2 -4 13 9.0 35.8 -6 17 3.9 31.3 -8 -10 28 26.7 35.6 -12 Relative Gain (dB) Gain Relative 30 57.3 43.7 -14 -16 -18 -20 0 10 20 30 40 50 60 70 Elevation Angle (deg) 18 N Antenna #12 (HPR) 13 10 27 28 8 PRN Elevation C/N0 30 W E 16 (deg) (dB‐Hz) 7 1 36.9 47.2 11 17 1 7 71.2 52.0 9 8 59.1 51.3 S 0 9 4.7 37.8 -2 11 60.8 53.2 -4 13 9.0 39.0 -6 16 8.8 42.0 -8 -10 17 3.9 39.6 (dB) Gain Relative 27 24.4 45.8 -12 28 26.7 49.0 -14 -16 0 10 20 30 40 50 60 70 80 30 57.3 50.7 Elevation Angle (deg) 19 Saturation Measurements and Summary 20 Saturation Measurements For 14 external antennas, output vs input power measured for single tone at 22 frequencies (see example results below) Results are being processed to estimate small‐signal 1‐dB compression point vs frequency Processing will take into account 2:1 difference in compression between small‐signal and large‐signal gain* 1.540GHz 1.545 1.55 1.555 1.575 1.595 1.615 5 0 ‐5 ‐10 ‐15 (dBm) ‐20 ‐25 Level ‐30 Rx ‐35 ‐40 AUT ‐45 ‐50 ‐55 ‐60 ‐30 ‐25 ‐20 ‐15 ‐10 ‐50 5101520 Probe Tx Level (dBm) *See, e.g., Domino et al., “Polynomial Model of Blocker Effects…”, Applied 21 Microwave & Wireless, June 2001. Summary GPS/GNSS receiver antenna characterization is an important component of the Department of Transportation’s GPS Adjacent Band Compatibility Study 18 antennas have thus far been characterized .