|Nearfield Antennas Test Range|
The NFR at MEMCO is a combination Vertical Planar/ Cylindrical scanner with a six axis controller.The scanner has a physical scan area of 13'x 13' and is in an enclosed absorber lined test chamber that is approximately 24'x 22'x 20' (L x w x H). The scanner and data acquisition software were purchased from Orbit-FR and test chamber was designed and constructed by MEMCO. A custom Azimuth over Elevation positioner ( designed and manufactured for installation on military vehicles) was installed on precision slide rails to accommodate a variety of antenna geometries withvarying focal length. The Az/ El position is utilized by MEMCO to perfom cylindrical Nearfield pattern cuts for some of out earth station customers. The RF subsystem selectedby MEMCO for our NFR is the old reliable HP 8510 system. We chose this RF system because of the open architecture that allows us to sepratethe down converter from the receiver and synthesized signal generator. The down convertor is mounted inside the chamber on the scanner tower. This helps prevent the power loss issues associated with many NFR subsystems which have to use auxiliary amplifires because of long RF cable runs. It also allows for better measurment stability do to cable flexure since the X-Axis cable is now IF rather than RF. The only RF cable that is moving in our system is the Y-Axis cable installed in the vertical cable tray. To reduce inserstion loss ( increase dynamic range) and improve phase stability, MEMCO has installed waveguide runs ( WR 137, WR 75, WR 42, WR 28 with other sizes to be added in the future as rewuired) under the absorber floor for test frequencies above 5.7 GHz. A low loss, phase stable RF cable is installed under the floor for frequencies below 5.7 GHz where lost power and dynamic range are less of a problem.
MEMCO designed and implemented most of the test range features such as the air circulationsystem which helps maintain a uniform temperature distribution inside the enclosed test chamber.The test equipment room was also designed and built by MEMCO and is attach to the side of the test chamber with access to the chamber through a standard 36 wide door.The back wall of the test chamber was designed with a roll-out section ( on piano casters)that provides a 10' x 10' opening to install larger antenna structures (designed for 2.4m antenna access).MEMCO also designed the lighting system based on experimental testing of commercially availbale light fixtures to test for Heat generation, EMI considerations, life expectancy, and even light distribution ( LUX meter testing). Our chamber uses a total of 30 self-ballasting fluorescent flood light fixtures controlled by multiple light switches ( banks of 15 lights per switch). A video camera monitoring system is installed to allow for safety observation during antennatesting (just to make sure no physical crash takes place). No sprinkler systemwas installed in the chamber as MEMCO feels that these systems can often cause more harm than good.The absorber is coated with the standard flame resistant paint used by most absorber vendors. One advantage of being a small business is flexibility; and we simply address security and safety issues based on a case by case basis, dependant on the antenna system being tested and customer requirements ( for example the military has different concerns that an earth station vendor for the VSAT business). The final piece of the puzzle for NFR testing is the measurement hardware (test probes) utilized in conjunction with the type of test facility configuration. MEMCO has long provide high quality Dual-Polarized test probes through-out the antenna measurment industry, including NIST, SS/L, Lockheed Martin, NOrthrop Grumman, Space Systems/ Loral and a host of other antenna companies. This is an area that we have a distinct advantage; we can simply design and manufacture any custom waveguide test probe assembly as required for any specific antennameasurement program. MEMCO designed our Nearfield Range to be as flexible as possible in order to accommodate a wide variety of antenna testing needs including both earth station and satellite antennas. We are confident that our NFR is a high quality test facility with great flexibility to accommodate even the most challenging antenna test requirements.