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

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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

 

 

 

 

 

 

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Multi-Frequency (RTK)

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High Multipath Rejection

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Gain

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Gain Roll-off (Low elevation gain)

 

 

 

 

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Axial Ratio

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Ultra-low PCO/PCV

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Low PCO/PCV

 

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L-band frequency
 (Correction Services) Narrow Bandwidth (interference rejection)

All of these metrics impact position accuracy! NovAtel Inc - Proprietary

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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) NovAtel Inc - Proprietary

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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 NovAtel Inc - Proprietary

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Measured C/No (dB-Hz)

Study #1 – Rooftop Survey

C/No is good but varies between antenna types NovAtel Inc - Proprietary

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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) NovAtel Inc - Proprietary

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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 NovAtel Inc - Proprietary

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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. NovAtel Inc - Proprietary

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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.