Investigation of ducts as a “radar pinhole” for detecting objects through a wall

There is a continuing interest in the through-the-wall capabilities of radar. It has been found that walls behave as a low-pass medium, and therefore through-the-wall radar has been restricted to frequencies in the low GHz range. Unfortunately at these lower frequencies the resolution of the radar system is sacrificed. This thesis investigates the possibility of using a duct as a means of detecting objects through a wall. Ducts have been extensively studied in the past; however there has been limited research of ducts with two open ends. In this thesis the difference between an open-ended duct and a duct with two open ends is investigated through measurement and simulation. For simulation an approximate method is used that treats the duct as a waveguide. It is found that a significant amount of power is transmitted through a duct with two open ends. It is then shown that an object can be detected through a wall by using a duct that has been inserted into the wall. Then the two-way insertion loss of a duct with two open ends is determined through measurement and simulation. It is shown that a duct behaves as a high-pass medium and can be used as a propagation channel through a wall. The insertion loss due to the duct and the insertion loss through a concrete wall are compared