SBIR-STTR Award

Full advantage of digital adaptive processing for phased arrays can only be achieved if the mutual coupling between elements and between the elements and near-field scatters is taken into account. Compact and conformal arrays will have increased mutual coupling effects when compared to planar arrays (increased element blockage). This effort will develop an integrated electromagnetic and super-resolution analysis capability that will support the design of compact conformal arrays, including those with highly directive elements. This capability must simultaneously address (1) scattering from electrically large structure of conductors and high electrical constant materials, (2) near-field interactions and (3) radiation transient effects. In addressing these goals, the capability must be both accurate and efficient. The method-of-moments (MOM) codes that we are proposing (WIPL-D, parallelized WIPL-D) will provide the greatest capability in terms of modeling electrically large structures and accuracy of modeling. These will be integrated with adaptive/super-resolution signal processing to meet the requirement of high-resolution spatial enhancement. Our signal processing approach (uniform linear virtual array, direct data domain) will address highly non-stationary and transient interference environments. Issues for maintaining efficiency and accuracy in wideband radar and communication systems will be identified. A combination of MOM and marching-in-time (MOT) will be analyzed for efficient modeling of wideband scattering

Multi-mission systems of the future will require antenna systems with increased aperture size to meet the challenging communications and surveillance requirements. This will include performance in severe interference situations. Planar arrays mounted on either the side, top or bottom of current airframes are impractical, if not aerodynamically unstable. Consequently, the Navy is investing in new RF technologies to support the development of compact conformal apertures and is investigating approaches for mounting/integrating them into a variety of conventional, and future air vehicles including E2C with a circular array, Multi-Mission Maritime Aircraft (MMA), UAV’s and mini-UAV’s. To meet mission objectives, the communication and surveillance systems are expected to rely on space-time adaptive processing (STAP) and super-resolution techniques to achieve the accuracy, resolution and interference suppression performance required. These conformal array systems, however, will face unique signal processing challenges. Many simplifying assumptions made by planar array processing approaches will be violated by conformal aperture designs. As demonstrated by our Phase I results, direction of arrival estimation and point-source interference rejection using compact conformal arrays requires the integration of electromagnetic analysis and adaptive processing (super-resolution, spatial adaptivity). Ongoing work in other programs has shown that a similar integrated approach is required for the rejection of continuous interference (clutter). This other work combines electromagnetic analysis and STAP. In Phase II, we will develop a full capability combined approach to achieve: (1) accurate signal direction-of-arrival (DOA) estimation, (2) parameter estimation for the desired signals, (3)undesired signal rejection, and (4) clutter and multipath rejection. We will focus our effort on specific conformal arrays of greatest interest to the Navy. Specifically we will develop this full capability integrated algorithm for circular conformal arrays that can be employed in Hawkeye-type systems, and non-conventional conformal arrays for future manned and unmanned airborne surveillance and communication systems.

Benefit:
The simulation, design and analysis capabilities developed under this effort have the potential to support a number of future airborne and space-based surveillance efforts. Airborne platforms (both manned and unmanned) have limited space where planar arrays can be mounted. The limited array size can adversely impact system performance, Previous and ongoing studies at military research organizations have shown that larger conformal arrays can be mounted on the many of these same aircraft. These conformal array radar concepts can provide significant improvements in performance if appropriate super-resolution and STAP algorithm techniques are applied to handle conformal array effects. Many programs that can benefit from the conformal array designs include: Hawkeye, Multimission Maritime Aircraft, UAV’s, and multimission helicopters. Non-radar applications also appear possible. Both space based and airborne communication systems employ conformal arrays. Interference rejection by these conformal array communication systems requires similar spatially adaptive processing. Simulation and analysis tools and conformal STAP algorithm techniques developed for airborne radars can be applied, with some modifications, to these systems.

Keywords:
STAP, conformal array, Smart Antenna, Adaptive Array, Compact Array, DOA estimation, Mutual Coupling, Clutter Suppression