Content area
Abstract
To maximize data transfer rates and simultaneously reduce the required size of antenna structure, many communication systems operate at Radio Frequencies (RF). In wireless systems, the receive antenna intercepts a combination of direct path transmissions and signals reflected by objects in the vicinity of the antenna; the signal is affected by the surrounding environment. When characterizing antennas, it is important to illuminate the antenna under test (AUT) with a direct path plane wave (no reflections.) This allows characterization of the antenna itself without the effects of the surroundings. An anechoic (“Anti-echo”) chamber is used to minimize reflections from the sides, roof and ceiling.
Through C3RP grants, the positioner system has been upgraded from a single to a double axis scanning system. Labview software was developed to control the computer, network analyzer and controller through the general purpose interface bus (GPIB). There are four main software algorithms that allow the user to measure the magnitude and phase: “Stop and Go,” “Stop and Go Multiple,” “Continual Sweep” and “2-axis Stop and Go.” These programs were also written to enable two data acquisition methods: “Stop and Go” and “Continual Sweep.” The “Stop and Go” method commands the motor to stop its motion when taking data while the “Continual Sweep” method does not. The iv single axis “Stop and Go” algorithm also has the capability to provide a frequency sweep for each angular measurement. The user defines the start and stop angles, and frequency. The radiation pattern data can then be plotted either with Matlab programs or Excel after post processing. The plots represent the AUT radiation patterns, which indicate how well the antenna receives power at different angles. The measured patterns are compared against the previous system completed in 2004 and to two simulation packages (Ansoft HFSS and PCAAD 4.0) for the standard gain horns available in the antenna lab. The simulations were conducted at the start and stop frequencies of the horn’s bandwidth. The goals are to build a:
1. Reliable data acquisition tool capable of taking 2-Axis scans without failing.
2. System with at least three times faster data acquisition times compared to the previous system with no degradation in accuracy.
3. System with motor resolution of 1° or better.
4. Repeatable system with fluctuations of <0.2dB at the main lobe.
5. System cost less than $20,000.
6. System has GPIB communication capability for a reliable data link between the computer and instruments.
7. System that allows the user to define the start and stop frequencies and start and stop angles.
