fairfolio
Saved Projects

Brewster's Angle Effect on GPS Multipath

CSEF · 2005 Electricity & Electronics

Scott M. Elder · Chino Senior High School, Chino

Overview

Objectives/Goals Brewster's angle is typically associated with light. However, it also has an effect on GPS Radio Frequency (RF) signals. When a GPS navigation signal is reflected off a material, it will change from a right hand circular polarized to a left hand circular polarized signal at Brewster's angle. If the reflected signal reaches a GPS antenna, it can cancel out the real or direct GPS signal. This is called multipath and it can cause a position error in a GPS receiver. The problem is how to determine Brewster's angle at the GPS frequency and its effect on the GPS receiver. My hypothesis states "If I can create a controlled GPS multipath environment, then I can determine Brewster's angle and determine the effect on the Global Positioning System signals for different materials". Methods/Materials I first created a controlled multipath environment by mounting my GPS antenna on a board and pointed the antenna towards the WAAS POR Geostationary (GEO) satellite. This satellite supplies a GPS signal but is a GEO satellite so its orbital position to earth stays the same. Also, this signal is lower power than GPS signals so it will react more to multipath. I then used different surface materials to determine their effect on the GPS receiver operations. Results My board was the propagation environment and it was big enough to contain the first Fresnel zone from 10 degrees to 50 degrees with an antenna height of 4 inches. Placing the board in line with the POR signal created a controlled multipath environment and tilting the board at different angles resulted in different multipath signals being received by the GPS antenna. Conclusions/Discussion The multipath signal did result in a disruption of signal power as I increased the angle of the board. For each surface type tested there was a complete loss of signal at a specific angle. Although this angle was not Brewster's angle, it did correspond to Brewster's angle by subtracting 7 degrees. The 7 degree difference is attributed to the internal GPS processing techniques.

Summary statement

I determined Brewster's angle at the Global Positioning System (GPS) L1 frequency and what its multipath effect was on the GPS receiver operations.

Help received

Dad helped with the test fixture design.

Competition history

  • CSEF 2005 Electricity & Electronics · Entry S0703

Resources

Related projects

Closest projects by meaning, across every fair and year in the corpus.

Browse more like this

Source: California Science & Engineering Fair public projects

Save projects to your library

Sign in with Google to keep track of projects you find interesting, organized into folders. An account also raises your daily allowance for “Has this been done?”, and lets you create a key for the MCP server with a much higher limit than anonymous use. Browsing stays public.

Continue with Google