LabVIEW-Based Antenna Measurements

Author(s):
Kevin Mescher - Virginia Tech University

Industry:
Telecommunications

Products:
LabVIEW

The Challenge:
Creating a state-of-the-art automated antenna measurement facility at Virginia Tech.

The Solution:
Using LabVIEW to provide a convenient way to accurately measure antenna performance.

Introduction
As a result of the growth in wireless communications, the design and testing of antennas takes on renewed importance. One of the important performance characteristics of antennas is their radiation pattern. These patterns are plotted to describe how power radiation varies with direction around the antenna.
While traditional antenna measurement systems employ analog devices and methods, movement toward digital systems is slowed by the cost of new instrumentation. As a compromise, many systems have replaced the analog data output with digital output, usually using a PC for data acquisition and data processing.

Multipath Distortion
A major difficulty encountered when trying to measure antenna patterns is a phenomenon called multipath distortion, in which unwanted reflections of the transmitted signal arrive at the antenna under test and interfere with the direct signal. The multipath distortion signal distorts the measured antenna pattern. Another characteristic of multipath distortion is that all the reflected signals arrive at the test antenna with a time delayed from the direct signal.

However, we can reduce multipath distortion effects by using a large, open outdoor test site for the antenna range or by taking measurements inside an anechoic chamber. An anechoic chamber has walls that absorb RF radiation, reducing the reflected signals. An outdoor test site usually requires a large open area, often several acres or more. Both outdoor ranges and anechoic chambers are expensive to build and operate.
The Virginia Tech antenna range is on the roof of a campus engineering building, which provides a secure open space. However, it also has objects that can create multipath distortion. We chose LabVIEW software for digital data collection and display control on the antenna range. We can apply LabVIEW signal-processing techniques to the pattern measurement data to reduce the range multipath distortion effects. To mitigate the multipath distortion effects, we used time-domain processing of the received signals.

Hardware Control Software
We wrote a LabVIEW-based program called Range Runner to handle all the hardware control for the Virginia Tech outdoor antenna range. It measures the antenna radiation pattern and provides pattern printouts via a laser printer. It also has the ability to perform automated time-domain processing, which filters reflected signals out of the measured pattern by giving the user full control over the processing.

We are completing a new anechoic chamber that uses modern digital instrumentation based on a vector network analyzer. In anticipation of the new chamber, we updated Range Runner to operate with the network analyzer. new version of the LabVIEW-based software is much faster – it can collect 36,180 data points in five minutes, a speed increase of about 30 times. With the new software, we can also calibrate the network analyzer, and take moretypes of measurements.

Results
Using LabVIEW, we have created a sophisticated, state-of-the-art, automated antenna measurement system. This system is equivalent to commercial software that can cost tens of thousands of dollars. LabVIEW made all this possible by providing a convenient way to control hardware, process the data, and provide a user-friendly interface for the program.

For more information, contact:
Dr. W.L. Stutzman

Director, Antenna Group

Virginia Tech University

627 Whittemore Hall

Blacksburg, VA 24061

Tel: (540) 231-6834.

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