Choke Ring Research Articles

SIGNAL DISTORTION IN HIGH PRECISION GPS SURVEYS

The aim of this paper is to show that GPS signal distortions can significantly influence the accuracy of the results of a GPS survey. Signal distortions may occur if the satellite signals propagate through a diffuse obstacle such as a bush and the distorted carrier phases arrive at the GPS antenna. As a result errors in the horizontal position of up to 2 cm and in the vertical position of up to 5 cm can occur. The results of several experiments will be shown. Different GPS choke ring antennas and receivers as well as different GPS processing software packages were used in order to prove that this effect is hardware and software independent. The signal distortion was evident in all experiments. The detailed investigation of the double difference phase data allowed the removal of the affected data which subsequently yielded the correct GPS results.

SIGNAL DISTORTION IN HIGH PRECISION GPS SURVEYS

The aim of this paper is to show that GPS signal distortions can significantly influence the accuracy of the results of a GPS survey. Signal distortions may occur if the satellite signals propagate through a diffuse obstacle such as a bush and the distorted carrier phases arrive at the GPS antenna. As a result errors in the horizontal position of up to 2 cm and in the vertical position of up to 5 cm can occur. The results of several experiments will be shown. Different GPS choke ring antennas and receivers as well as different GPS processing software packages were used in order to prove that this effect is hardware and software independent. The signal distortion was evident in all experiments. The detailed investigation of the double difference phase data allowed the removal of the affected data which subsequently yielded the correct GPS results.

GPS surveying with 1 mm precision using corrections for atmospheric slant path delay

Multipath and atmospheric effects can limit GPS surveying precision. We surveyed a 43 km baseline using large diameter choke ring antennas to reduce multipath and pointed radiometer and barometric data to correct for atmospheric slant delay. Based on 11 daily solutions, atmospheric slant delay corrections improved vertical precision to 1.2 mm rms and horizontal precision to sub‐mm. Applications for high precision GPS surveying include deformation monitoring associated with earthquake and volcanic processes, subsidence, isostasy, and sea level measurements; monitoring of atmospheric water vapor for climate and global change research, and to improve the resolution of synthetic aperture radar; calibration of satellite altimeters; and precise satellite orbit determination.

Sensing integrated water vapor along GPS ray paths

We demonstrate sensing of integrated slant‐path water vapor (SWV) along ray paths between Global Positioning System (GPS) satellites and receivers. We use double differencing to remove GPS receiver and satellite clock errors and 85‐cm diameter choke ring antennas to reduce ground‐reflected multipath. We compare more than 17,000 GPS and pointed radiometer double difference observations above 20° elevation and find 1.3 mm rms agreement. Potential applications for SWV data include local and regional weather modeling and prediction, correction for slant wet delay effects in GPS surveying and orbit determination, and synthetic aperture radar (SAR) imaging. The method is viable during all weather conditions.

Modeling radiation with an efficient hybrid finite-element integral-equation waveguide mode-matching technique

A method is presented to model electromagnetic radiation, combining the finite-element technique in the penetrating portion of a three-dimensional (3-D) radiating structure with an integral equation on the outer surface of the computational domain, and with a waveguide mode-matching technique on a cross section of the feeding waveguide. The antenna can be of general shape, provided a portion of the surrounding medium up to a surface of revolution is chosen as part of the computational domain. This truncation scheme and the accurate source representation are more general than those existing in the literature for radiation modeling. An open-ended waveguide and a waveguide with a choke ring are analyzed and their radiation patterns are obtained and compared with available measurements.