Adaptive antenna structures

ABSTRACT:Unwanted RFI is a growing concern due to the ever expanding RF world around us. Not only are the number of RFI sources increasing, so too is the frequency usage across the RF spectrum. As a result, RF systems, like the AFSCN, are expected to become more susceptible to disruptions in coverage and service. Additionally, these systems must maintain a small RF footprint and not contribute to the problem either.Two approaches are proposed to rectify the situation. The first solution employs an RF absorber to minimize AFSCN antenna sidelobe levels, and hence, block unwanted stray signals. The second solution utilizes a feed having agile, variable beamwidth to improve satellite search time and link, with minimal RFI on transmission and reception. Both solutions are retrofits to the existing AFSCN antenna, and as such, are cost effective.The proposed program uses detailed theoretical RF models to define the properties, shape, and location of the RF absorber, as well as the illumination characteristics required of the feed for variable AFSCN antenna beamwidth. Novel low profile, structural, absorber and agile, reconfigurable RF surface technologies, will be designed, fabricated and tested to demonstrate their performance and feasibility as applied to the AFSCN antenna.BENEFIT:RF absorber technologies are important, cost effective enablers well beyond just reflector antenna RFI mitigation. In fact, RF absorber technologies are currently employed by a wide assortment of applications and platforms. Unfortunately, their applicability is often limited by their extreme thickness and lack of structural integrity. Thus, the development of an absorber that is conformal, low profile, structural, and lightweight, is especially attractive in many instances. The frequency selective nature of this technology is quite suitable for highly populated and diverse RF environments because performance can be specially tailored to accommodate requirements. Of course the ability to customize their performance in a retrofit-able package presents an affordable option to costly RF system upgrades.Reconfigurable surfaces can also support applications beyond just reflector feed augmentation. In fact they can be used to retrofit a variety of antennas already in existence. As such, the technology can provide very affordable alternatives to replacing entire antenna systems. Their reconfigurable nature not only offers variable beamforming capability, but also wider operational RF bandwidths. Additionally, because reconfigurable surfaces are essentially filters, they can be employed as EMI shields. Additionally, reconfigurable surfaces are not only limited to solving EMI issues. In particular they can be used to improve the radar signature of an RF system as well. Generally, where past solutions have been static, as is the case with traditional FSS approaches, reconfigurable RF surfaces provide a dynamically adaptable solution that can accommodate a wide range of RF requirements with improved RF performance.