Wireless Solution for an Antenna Characterization System

The Challenge: Develop an integrated solution for measuring and plotting VHF signal reception from a rotating test platform.  

The Solution: A combination of RS232, GPIB, wireless modems and computer based data acquisition controlled by a custom written LabVIEW application.

Introduction

Shakespeare Composites and Electronics is a world leader in fiberglass reinforced composites engineering, design and manufacturing.  Part of Shakespeare’s product line includes antennae used in marine applications and on military land vehicles.  The United States Military was concerned with the performance of mobile communication antennae being affected by the placement of the antenna and geometry of the vehicle the antennae are mounted on. The Antenna Characterization System (ACS) was designed and developed by Aegis Solutions to automate the testing of antennae performance.

System Requirements

Open field antenna testing is performed by mounting the antenna on a test vehicle mock-up located on a turntable and broadcasting a signal from the antenna at various frequencies as the platform rotates.  This broadcast signal is received by another antenna, located in a fixed position at some distance, and the amplitude of the received signal is recorded in relation to the position of the test vehicle.  As the turntable rotates, any deficiencies or weak spots in the transmission can be observed based on fluctuations in the amplitude of the received signal.  To conduct this testing, a wireless method of controlling the signal broadcast was necessary so that the turntable could rotate throughout the test.  Data containing the exact angular position of the turntable at any time was also necessary so that weak spots in the transmission field are located with certainty.

The Equipment Solution

The solution developed by Aegis Solutions implemented system control via a personal computer (PC) located in the test station, approximately 100 yards from the turntable.  The computer contains a National Instruments PCI-GPIB interface card and a 6024E DAQ board.  A Hewlett-Packard spectrum analyzer is connected to the stationary receiving antenna and sends amplitude data to the PC via the GPIB interface.  The DAQ card is used to acquire angular data from an encoder mounted to the shaft of the turntable.   In order to set the frequency and amplitude of the transmitting antenna, a signal generator, located on the turntable, is controlled by the PC via a set of wireless modems.  One modem is connected to the PC in the test station which sends the desired frequency and amplitude settings to the second modem.  An RS232 to GPIB converter is used to connect the second modem to the signal generator.

The Software Interface

A user-friendly software interface was written by Aegis Solutions using National Instruments LabVIEW Development Environment.  The software application included a fully customizable test setup over any range of supported signal frequencies and amplitudes, real time data display with linear and polar plots, logging data to the local computer hard drive, and printing and reviewing prior data.  All data collection can be monitored as tests are being performed, but, as an automated system, the operator is not required to be present at the test site after a test is started.

The Problem Solved

Aegis Solutions’ use of off-the-shelf instrumentation and custom written application specific software allowed for rapid development of a flexible ACS system, which exceeded the client’s expectations and provided improved testing capabilities for the Shakespeare Company.

ACS Data Acquisition Screen with Linear and Polar Plots