Enhanced Machine Controller-based Antenna Range is intended to help setup an automated antenna measurement capability.
Version: 0.1Enhanced Machine Controller-based Antenna Range (EMCAR) is a set of codes and documentation intended to assist the interested party in setting up an automated antenna measurement capability (i.e. Antenna Range) using non-specialized hardware and free soft
Operating System: Linux
This measurement capability may be of interest to antenna experimenters, science and engineering educators, researchers, amateur radio operators, Wi-Fi antenna enthusiasts, and others. The EMCAR system can be implemented without spending a lot of money. As such, the system serves to establish a fundamental capability for the measurement of antenna radiation patterns--rather than to push the state-of-the-art in antenna measurements. We'll save that for the next release!
The system is based on the EMC2 motion controller to take advantage of the excellent work done by its development team. EMC2 provides a real-time motion control solution that achieves a high degree of mechanical position accuracy and precision; the performance may be further enhanced using backlash compensation, if required.
The EMC2 system enables interfacing to several types of motor control circuits from industrial CNC machine tool motor drives to small homebrew motor controls. These motor controls may include a closed-loop servo motors with encoder feedback, as described herein, or open-loop stepper motor systems. Since the EMC2 system is used in production CNC machining applications, its accuracy and reliability are proven and thus suitable for use in the antenna measurement application where these characteristics are required.
The EMC2 application is programmed for CNC operations through the G-Code language, this open standard is documented in RS274. One feature of EMC's G-Code interpreter is it enables calls to external programs via M-word commands; this interface is employed in the EMCAR application for the initialization and subsequent access to an external RF measurement subsystem. This forms the heart of the EMCAR system.
Combining the proven EMC2 application with a custom RF measurement application yields all the computer controls needed for measurement of antennas in a variety of coordinate systems. Each mechanical axis may defined as either linear or rotational; so, planar or polar measurements of antenna data are possible. The development EMCAR system is directed toward traditional far-field antenna measurements. This introductory implementation employs a single-axis rotational system (i.e. an Azimuth-Only system).
The measurement sequence is programmed using the native language, G-Code, and the measured antenna data are stored in the user's own format. Since the G-Code offers complete flexibility in motion control, the user is in complete control of their measurement sequence. The possibility of measuring on irregular grids, using variable measurement increments, or measurements made through a trajectory, are thus enabled. Mechanical repeatability of an established measurement sequence (I.e. a G-Code program) is also assured--similar, in as much as one might expect a CNC-machined part to be made accurately, time after time.
The initial EMCAR development system employs a client/server model using TCP/IP socket programming, enabling the system to be potentially spread over a network. The benefit of this will be the ability to employ wireless data connections between the computer running the EMC2 (motion control) application and the RF measurement subsystem and computer, if needed. (There should be no problem meeting the far-field criteria for antenna measurements.) This is an improvement over traditional systems that required massive cabling between measurement components, both in terms of ease of use and in materials costs. Remote display of the EMCAR application may be made using normal X-Windows protocols over the network.
All this flexibility does come at some cost, however. Presently, the system requires stopping at each measurement point while the measurement data are triggered and recorded. Perhaps, with some help from the gurus of EMC2 and the HAL, the measurements can be made "on-the-fly" in the future? In any case, the EMCAR system offers an elegant and simple means of programming an antenna measurement acquisition for making automated measurements of antenna radiation data.
The EMCAR system features a real-time display of the measured data, thus providing feedback on the progress and results of the measurement. This feature is implemented using gnuplot under program control.
The hope is that this project will find use in both the amateur and professional arenas of antenna development. The cost of entry for this system is low, thus enabling private individuals, small businesses, educators, and poorly funded research organizations to focus on RF and microwave equipment, rather than motion control and antenna data presentation software.
Of course, there is still a place for the full-up, turnkey, antenna measurement solutions that are offered by our favorite vendors--they will provide product support, and added-value services with their product solutions. But, the EMCAR solution is about doing more with less, doing it yourself, and learning something along the way. So, enjoy!
A more in-depth description of the system, complete with references, a working measurement configuration, and measured data are described in the following pages. Finally, a request is made for the participation of "real" computer programmer to enhance or re-write the codes used in this initial project to make the application more robust, maintainable, and upgradeable for future enhancements.