Antenna Performance Metrics for GNSS

Antennas for GNSS
Applications
Maged Shenouda
Date: February 19, 2015
Agenda
GNSS Constellations
Antenna Performance Metrics for GNSS
Antennas for GNSS Applications
Positioning Studies
Study 1 – Rooftop Survey
Study 2 – PPP Position Accuracy using L-band delivered
Corrections
Study 3 – ALIGN Heading Application
Summary
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GNSS Constellations
Constellation
Band
Operation Bands (MHz)
GPS
L1
1563 - 1587
L2
1215 - 1240
L5
1164 - 1188
L1
1593 - 1610
L2
1238 - 1254
L3
1190 – 1214
E1
1563 - 1587
E5a/b
1164 – 1188, 1195 - 1219
E6
1267 - 1291
B1
1560 - 1591
B2
1167 - 1217
L-Band
1525 - 1560
GLONASS
Galileo
BeiDou
Various
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Owner
Various GNSS
Bandwidths
drive Antenna
Bandwidth
Requirements
Broadband
antennas with
excellent GNSS
performance are
desired
New local GNSS
systems going
online: QZSS,
INRSS
-
Antenna Performance Metrics for GNSS
Parameter
Definition
Frequency
GNSS frequencies received
Phase Center Offset (PCO)
Antennas electrical center
Phase Centre Variation (PCV) Variation of PCO over azimuth
Multipath Rejection
Ability to reject GNSS reflections
Axial Ratio
How well antenna is Right Hand
Circularly Polarized (RHCP)
Polarization
Shape traced by E-field vector
Gain
Gain at zenith (90°) referenced to
isotropic antenna
Gain Roll-off
Gain reduction from zenith to
horizon
All of these metrics impact position accuracy!
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Key Antenna Parameters vs. Application
Survey
GIS
Reference Station
Aviation/
Aerial Survey
Marine
Construction/
Mining
Precision
Agriculture
Vehicle Tracking
Dock Operations
Unmanned Aircraft
Unmanned Vehicle
Timing
Application
Single Frequency
●
●
●
Multi-Frequency (RTK)
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
High Multipath Rejection
●
●
●
●
●
●
●
●
●
●
Gain
●
●
●
●
●
●
●
●
●
●
●
Gain Roll-off (Low elevation
gain)
●
●
Axial Ratio
●
●
●
●
●
●
●
●
●
●
Ultra-low PCO/PCV
●
●
Low PCO/PCV
●
●
●
●
●
●
L-band frequency
(Correction Services)
Narrow Bandwidth
(interference rejection)
All of these metrics impact position accuracy!
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●
● Antenna Performance Metrics for GNSS
Polarization describes shape drawn by E-field vector as a wave
propagates through space
RHCP: Right Hand Circular Polarized
LHCP: Left Hand Circular Polarized
RHCP Wave (Source:http://en.wikipedia.org/wiki/Circular_polarization)
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Antenna Performance Metrics for GNSS
What’s the most important parameter for a GNSS application?
»  Many in GNSS assume gain most important
»  Actually, it depends on the application
»  Examples:
•  Environment with heavy cover (such as forest) ! multipath rejection
and gain are most important
•  Precision Survey: PCO most important, gain still matters but not as
much
•  Mobile GPS: gain, PCO, PCV, etc. have less importance as accuracy
goal is +/- 5m
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Antennas For GNSS Applications
Antenna Type
Low-cost
single-feed
Patch
• Smaller Size; PCB Printed
• Narrowband, poor AR and MPR
• Poor low elevation tracking
Multiple-feed
Patch
Euclidean Spiral
(Pinwheel)
Helix
Choke Ring
AntiJamming
Typical Characteristics
• Small Size; PCB Printed
• Improved AR and MPR
• Improved low elevation tracking
• Supports all GNSS Bands
• Excellent gain at multiple frequencies
• Stable phase centers
• Good AR and MPR
• Highly circular polarized (good AR)
• Stable PCO, low gain roll-off
• Larger size needed for good gain
• Excellent gain, PCO, MPR
• Good low elevation tracking
• Large size and weight
• Array of several elements
• Contains electronics, firmware, and/or beam forming
to mitigate jamming sources
• High cost and design complexity
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Examples
Study #1 – Rooftop Survey
»  3 NovAtel FlexPak6 receivers
each connected to:
•  One GPS L1 only low cost
single-feed patch antenna
•  One GPS/GLONASS L1/L2
multiple-feed patch antenna
•  One Pinwheel L1/L2 Antenna
Purpose: Demonstrate how
antenna selection affects
position
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Study #1 – Rooftop Survey
Antenna Type
Gain
Gain Roll-off
PCO
PCV
Multipath Rejection
Axial Ratio
Pinwheel
Antenna
★ ★ ★ ★ ★
★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★ ★
GPS L1 Only
Single Feed
Patch
★ ★ ★ ★ ★
★
★
★
★
★ ★
★ ★
★ ★
★ ★
★ ★
GPS L1/L2/L5
Multi-feed
Patch
★ ★
Legend
★ ★ ★ = Excellent
★ ★ = Good
★= Fair
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Measured C/No (dB-Hz)
Study #1 – Rooftop Survey
C/No is good but varies between antenna
types
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Study #1 – Rooftop Survey
Trajectory Plots
Pinwheel
GPS L1 Patch
Pinwheel
• 
• 
Tight cluster of points
Additional bandwidth aids
solution
L1/L2/L5 Patch
GPS L1 single-feed Patch
• 
• 
• 
Largest distribution despite gain
rivaling Pinwheel
Only one band supported
Poor PCO, PCV, MPR, AR limit
accuracy of solution
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L1/L2/L5 multi-feed Patch
• 
• 
• 
Larger distribution of points Much lower gain than pinwheel
Roll-off, PCO, PCV, MPR aid
accuracy of solution
Study #2 – Position Accuracy with PPP Corrections
»  Study demonstrates how
choice of antenna can impact
Precise Point Position (PPP)
accuracy and convergence
time using corrections
delivered via L-band »  Pinwheel vs. Multi-feed patch
– Pinwheel yields reduced
position error and faster
convergence time
Antenna is an important
consideration
Horizontal Position Errors
(Clear Sky) using L-band correction service
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Study #3 – Heading Application
»  Use NovAtel ALIGN algorithm
to generate a GNSS based
heading solution
•  Used to determine heading on
moving and stationary vehicles
and structures
•  Uses a master and rover
antenna on same vehicle or
structure
•  Relative heading and pitch
computed with respect to a
master antenna and receiver
Study: Difference in heading
accuracy using different
antennas (Pinwheel vs. L1/L2
multi-feed patch)
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Rover
Antenn
a
Master
Antenna
Study #3 – Heading Application
»  Assess heading performance
using matched antenna types
on various baselines
200 cm
•  200 cm baseline
–  Typical for many heading
applications
20 cm
•  20 cm baseline
–  Approaching shortest baseline
possible with Pinwheel antenna
due to enclosure size
Purpose: Demonstrate how
antenna selection affects
position
Baseline distance between
Master and Rover antennas
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Study #3 – Heading Application
»  Test jig installed in an open sky area
•  Stationary for entire proof of concept test
»  Collected 6-8 hours of 1Hz ALIGN data
»  Heading error with a small patch antenna is 3X greater than when
using pinwheel technology
»  Choice of antenna in the application affects the heading error NovAtel Inc - Proprietary
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Summary
GNSS Antenna characterized by several metrics: gain, gain
roll-off, multipath rejection, axial ratio, bandwidth, PCO, PCV. Gain is not necessarily the most important metric.
Antenna selection has an impact on all GNSS applications to
varying degrees, needs to be carefully evaluated for a
particular application!
Survey, PPP positioning using L-band delivered corrections,
and Heading applications are shown to be impacted by
antenna selection.
A well-designed antenna is a critical part of a GNSS System.
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Centimeter Positioning with a Smartphone-Quality GNSS Antenna
Ken Pesyna, Todd Humphreys and Robert Heath
The University of Texas at Austin
Radiosense, LLC
Motivation
“I predict that by the GPS World dinner in 2020, carrierphase differential GNSS, will be cheap and pervasive. We’ll
have it on our cell phones and our tablets. There will be app
families devoted to decimeter- and centimeter-level
accuracy…This will be the commoditization of centimeterlevel GNSS.” –Todd Humphreys, GPS World Dinner 2012
Focus
Our focus has been on single-frequency
carrier-phase differential GPS/RTK
techniques. Why?
1. 
Our smartphones have single-frequency
antennas
2. 
As compared to PPP, CDGPS/RTK has
faster convergence times
3. 
Reference stations will eventually
proliferate, making dual-frequency less
important
4. 
Single-frequency Antennas are cheap!
$0.02 (smartphone) - $5 (low-quality
patch)
The Primary Challenge: Awful Antennas
Antenna
Axial Ratio
Polarization
Loss in Gain
compared to
Surveygrade
Survey-grade 1 dB @ 45°
RHCP
0 dB
High-quality
Patch
2 dB @ 45°
RHCP
0 – 0.5 dB
Low-quality
Patch
3 dB
(average)
RHCP
0.6 dB
Smartphonegrade
10+ dB
Linear
11 dB
Test Platform
Clock
Antenna
Front-end
Smartphone
GNSS
Chipset
Filter
LNA
Data
Storage
GRID SDR Outputs:
•  Phase/
pseudorange
measurements
•  Complex (I,Q)
accumulations
GRID
SDR
RTK
Engine
RTK Filter Outputs:
•  Cm-Accurate Position
• 
Phase Residuals
• 
Theoretical Integer Resolution
Success Bounds
• 
Empirical Integer Resolution
Success Rates
Gain Compared to a
Geodetic-Grade Antenna
(dB)
Gain Compared to a
Geodetic-Grade Antenna
(dB)
December 2014: Successful RTK positioning solution with a smartphone
Handheld RTK result with some signals passing through user’s body
GNSS “light painting” with a smartphone
Residuals Comparison
Standard Deviation:
3.4 mm
Residuals Comparison
Standard Deviation:
4.6 mm
Residuals Comparison
Standard Deviation:
5.5 mm
Residuals Comparison
Standard Deviation:
11.4 mm
Residuals Comparison
Standard Deviation:
8.6 mm
Time to ambiguity resolution
for static antennas
Time to ambiguity resolution
for static antennas
Overcoming multipath with more signals
A Mitigation Suited for Smartphones: Multipath
suppression via receiver motion (1 of 2)
Phase Residuals (No Motion)
Phase Residuals (Motion)
Residual Autocorrelation (No Motion)
Residual Autocorrelation (Motion)
A Mitigation Suited for Smartphones: Multipath
suppression via receiver motion (2 of 2)
radionavlab.ae.utexas.edu
13
The information contained herein is confidential and proprietary to Maxtena Inc.
4-02 L1/L2 Dual-Band
Antenna
Multiband Multifilar Antennas
•  High polarization purity
•  Very versatile design
•  Very compact
All dimensions are in mm.
The information contained herein is confidential and proprietary to Maxtena Inc.
Features
The M1227HCT-A2-SMA is Maxtena’s latest
high performance active rugged antenna
designed for L1/L2 GPS and GLONASS bands
for GNSS satellite applications. Features
•
•
•
•
•
•
•
•
•
•
L1/L2 GPS-GLONASS bands
Rugged IP-67 rating
Superior out-of-band rejection
50 V/m jamming resistant
Very low noise figure
SMA mount
Ground plane independent
GIS & RTK applications
Regulated voltage
Ultra light weight - 24 grams (typical)
All dimensions are in mm.
The information contained herein is confidential and proprietary to Maxtena Inc.
Applications (1)
Applications
•
•
•
•
•
•
•
•
•
•
Precision navigation
Precision timing
Military & security
Asset tracking
Oil & gas industries
Navigation devices
Mining equipment
LBS & M2M applications
Handheld devices
Law enforcement
The antenna is designed for
applications requiring greater accuracy
than what L1 only antennas can
provide. The information contained herein is confidential and proprietary to Maxtena Inc.
Applications (2)
Ideal for GIS & RTK
applications
•  L1/L2 high performances
•  Superior out-of-band
rejection
•  50 V/m jamming resistant
•  Very low noise figure
Ideal for UAV
applications
•  Ultra light weight
The information contained herein is confidential and proprietary to Maxtena Inc.
Out of Band Rejection
Superior out-of-band rejection
A built in dual-stage-LNA
and filtering offers up to
30dB gain (50 V/m
jamming resistant) for
GNSS applications that
utilize both GLONASS and
GPS.
The information contained herein is confidential and proprietary to Maxtena Inc.
90
80
70
60
50
40
30
20
10
0
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
Group Delay L1 GPS/
GLONASS
2.5 V
3 V
3.3 V
0
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
GHz
31.8 mm
1.215
1.217
1.219
1.221
1.223
1.225
1.227
1.229
1.231
1.233
1.235
1.237
1.239
1.241
1.243
1.245
1.247
1.249
1.560
1.563
1.566
1.569
1.572
1.575
1.578
1.581
1.584
1.587
1.590
1.593
1.596
1.599
1.602
1.605
1.608
Phase Center
Phase center is
located along axis
of symmetry of the
antenna
The information contained herein is confidential and proprietary to Maxtena Inc.
34.2 mm
Group Delay L2 GPS/GLONASS
120
100
80
60
2.5 V
40
3 V
20
3.3 V
Applications in Satellite M2M and
Voice
M1600HCT12-U.Fl
M1590HCT22-SMA
The information contained herein is confidential and proprietary to Maxtena Inc.
Applications in Satellite M2M and
Voice
M1600HCT12-U.Fl
M1590HCT22-SMA
The information contained herein is confidential and proprietary to Maxtena Inc.
The information contained herein is confidential and proprietary to Maxtena Inc.