Broadband Focused Radar at Ground Penetrating Frequencies for Detecting Mines, Unexploded Ordnance, or Mobility Related Surface Layers

摘要

Report developed under SBlR Contract for topic Army 00-027 effort is to produce a fully mobile, broadband radar system with a focused planar beam over approximately 10 MHz to 1000 MHz for the detection of buried objects and the detection of frozen or thawed layers which effect mobility. The proposed antenna configuration consisted of a contra-wound helix, to cover the frequencies from 10 MHz to 100 MHz, and an array of contra-wound conical spirals, to cover the range from 100 MHz to 1000 MHz. A detailed near field analysis of the helix yielded the results that at lower frequencies the axial component of the electric field intensity (Ez) dominates the transverse components (Ex and Ey). The windings of a helix has a z component which gives rise to (Ez) component in the field. The z component also adds on the counter wound helix which makes this antenna solution unacceptable in the near field . It is clear that when the antenna aperture or elements are restricted to lie in a plane, then the zcomponents from symmetric current components will cancel at observation points near the axis. Structures that satisfy this condition are a planar aperture with a TEM aperture field and planar wires (spirals). The major disadvantage is the large size and weight (approximately 75 by 54 by 70 inches for a horn that operates down to 100 MHz). A planar dual linear polarization sinuous antenna is selected to provide the desired frequency coverage. The low frequency cut off is determined by the largest circumference (diameter = 50 inches for 50 MHz -12dBi). Larger diameters would provide lower frequency response. The radar is an Agilent network analyzer which is programmed to cover the frequency band su orted b a Dell com uter drivin two dis Ia 5.