| ||STATEMENT OF INTENT: Improve Radar
|| Objective: ||Develop a thin (low-profile) wide-band phased array element for use in low-band VHF foliage penetrating radar applications.
|| Description: ||Foliage penetrating radars (FOPEN) use both VHF and UHF frequencies to achieve full functionality of detecting and identifying various target types hiding under various concealment and deception covers such as foliage canopies, camouflage nets, or inside light structures. The antennae used for the UHF band are well developed and suitable for use on both manned and large unmanned aircraft. The frequencies used for the VHF band (25-88 MHz) currently dictate the use of an array of log-periodic monopoles trailing the wings of the aircraft carrying the FOPEN. While these antennae deliver the gain and suppress the back lobe at a sufficient level, they are large, forcing a permanent installation on the aircraft, which then becomes missionized, and degrading the endurance of large UAVs. Presently, the best known wide-band array elements are 3-dimensional elements, [1-3], which use the dimension normal to the aperture plane to achieve the bandwidth. These elements usually have a depth of roughly 0.2 wavelengths, the wavelength at the low end of the frequency band, which becomes impractical for applications in the VHF region. Thin, planar, 2-dimensional elements  offer a simplified geometry and potentially simplified manufacturing and flush, conformal mounting. The challenge at present is how such antennae can be developed that provide a high rejection of the back lobe while being scaled to the low-band VHF region. Such performance is essential to the function of a VHF SAR radar. Given that such an element can be developed, it then needs to be designed to be able to be placed on the skin (metal or composite) of the aircraft fuselage.
The development of novel planar phased-array elements with low profile and wide bandwidth (25-88 MHz) is the objective of this research effort.
|| ||PHASE I: Phased array modeled as large periodic structure with only a single unit cell needing analyzed. Conceive novel array element designs with high front to back ratio and good bandwidth potential, and evaluate their preliminary performance using numerical analysis. A final tech report to be delivered.
|| || ||PHASE II: This phase would include detailed and complete numerical modeling of the element including its feed, the building of an experimental array with a representative number of elements, and measurement of its performance as an antenna, and a technical report and proof of concept antenna sub array will be delivered.
|| ||DUAL USE COMMERCIALIZATION: Military application: Arrays with this low-profile element would enable the use of the low-band VHF FOPEN function on UAVs. Commercial application: If an appliqué version could be developed, this technology would enable instant addition of low-band VHF capability without disturbing a commercial aircraft certification for use by civilian agencies.
|| References: ||1. H. Holter, T-H Chio, D. Schaubert: Elimination of Impedance Anomalies in Single- and Dual-Polarized End-Fire Tapered Slot Phased Arrays. IEEE Trans AP, Jan. 2000
2. D. McGrath: Numerical Analysis of TEM Horn Arrays. Sensor and Simulation Notes, No. 420, AFRL, Albuquerque, May, 1998.
3. J.J. Lee, S. Livingstone, R. Koenig: A Low-Profile Wide-Band (5:1) Dual-Pol Array. IEEE Antennas and Wireless Propagation Letter, Vol. 2, p. 46, 2003
4. B. Munk et al: A Low-Profile Broadband Phased Array Antenna. IEEE S-AP Int¡¦l Symp., Columbus, Ohio, June 2003
|Keywords: ||broadband, antenna, phased-array, element|