QRC submits this proposal in response to SBIR AF98-286 for a Plane Wave generator. The plane wave generator is required to generate a free space RF wave installed in the Benefield Anechoic Facility (BAF) to evaluate the various electromagnetic systems installed on the aircraft systems such as the B1B, F16, and C17. The generator must cover a wide frequency band in order to test the many different radiating systems on aircraft today. In addition, the generator requires polarization agility, so the polarization of the system on the aircraft and the generator match. The generator input power must be at least 100W and should be capable of detecting any desired signal. This generator must be mobile enough to place at various locations within the chamber or even removed when not in use. Beam steering allows the generator to cover a wider range of the chamber without the generator. The generator must have a low RCS, so scattering does not interfere with any test. A coporate feed is proposed. Amplitude and phase control of the signals allows the array to place the desired plane wave at various angles and distances within the chamber. Design variables of the array include the number of elements, phase and amplitude weighting at the elements, and location of the elements. This design does not preclude aperiodic array designs. We propose designing a planar phased array that can steer and focus the plane wave via phase and amplitude weighting of the signals at the elements. Our appoach uses a genetic algorithm to optimize the antenna design. Genetic algorithms are computer algorithms that optimize complex problems by modeling natural selection and genetics. These algorithms are superior to conventional methods because they can optimize a large number of parameters over a very complex output. One important characteristic of the plane wave is the depth of field or quiet zone. Although not listed as one of the technical requirements, the depth of field may prove to be an important design parameter and can be calculated easily using the proposed computer model. The depth of field is a parameter that can be modified by appropriate phase and amplitude tapers on the array.
Benefits: The requirements for this chamber are extensive and stringent. A much lower cost version of this adaptive plane wave generator could be implemented much more cheaply for most other chambers. These developments would be particularly attractive for small chambers where the far field criterion severly limits the size of test objects and results in a new generation of anechoic chamber design.
