An Educational Antenna Measurement System
The AL-2000-EDC Educational Antenna Measurement System is a low cost, yet versatile, automated antenna measurement system that allows a variety of antenna measurements to be accomplished in a small facility for a variety of antennas. The system is configurable for all the research needs of universities, allowing for measurements to be accomplished in all the standard antenna measurement modes, including far field, planar near field, cylindrical near field and spherical near field.
As a result of its multimode measurement capability, the system can be used for characterization of antennas encompassing a wide variety of performance characteristics, including pencil-beam, fan-beam, omnidirectional, low sidelobe and high front-to-back ratio antennas. Applications for the system include antenna measurements related to wireless systems, automotive-based systems, satellites and aerospace.
The system is designed to be located in a space-limited test environment, such as a small laboratory or anechoic chamber. It is capable of rapid reconfiguration, both from a hardware and software standpoint. The measurement mode and hardware parameters are easily saved and recalled from test parameter files that contain all necessary setup and test information. Many of the required test setup parameters can be automatically calculated for the user when desired.
The system maintains the required accuracies for RF measurements from 700 MHz to 44 GHz (110 GHz with an extended system). It features a gain accuracy of ±0.25 dB and sidelobe accuracy of ±1.5 dB per 10 dB (to 30 dB down) at 10 GHz. Measurement time per polarization is 20 minutes. Beam pointing is 0.5° and maximum antenna size (±45° pattern) is 32" x 32". The basic system includes a low profile roll-over-azimuth positioner for antenna-under-test orientation, 3' ¥ 3' rigid box-frame high accuracy planar scanner, DC amplifier and cabling for control and feedback for all axes of motion, mounting hardware and RF probe. Also included are a data acquisition system (including personal computer and all necessary boards); software package for automated data acquisition, analysis and plotting for all measurement modes; and system documentation and manuals.
The system allows interface to standard RF equipment. This interface is accomplished through selectable device drivers that provide flexibility in reconfiguring the system for a variety of measurement applications as well as frequency ranges. The block diagram, shown in Figure 1 , illustrates the flexibility of measurement scenarios accommodated by the system.
Data acquisition and data analysis/plotting are implemented in separate packages to allow for off-line processing and data display. Both packages feature a graphical user interface implementation designed to allow for logical automated task definitions. Built-in contour and three-dimensional (3-D) plotting permit overviews and rapid visualization of both raw and processed data. A sample 3-D plot is shown in Figure 2 .
Automated tests can be executed in a user-defined order of multi-axis movements with the primary test axis scanned in either continuous or stepped motion. This flexibility allows the data collection sequence to be optimized for a given test application, minimizing required measurement time. All motions in the system are closed loop using encoder-based position feedback, thus providing confirmation of all requested data acquisition points. The system can be reconfigured rapidly for different measurement modes, thereby providing an extremely cost-effective investment for organizations, such as universities, where a single system can accommodate a wide variety of research projects and laboratory testing.