Direction of Arrival (DOA) Estimation Using Electrically Small Tuned Dipole Antennas

We present a methodology for the direction of arrival (DOA) estimation using the induced voltages that are measured at the loads connected to electrically small tuned dipole antenna arrays illuminated by the signal of interest (SOI). The matrix pencil method is applied directly to the induced voltages to estimate the DOA of the various signals. Using electrically small tuned antennas can be advantageous as they can be placed in close proximity of each other saving the real estate and, thus, making it possible to deploy phased arrays on small footprints. When dealing with closely spaced tuned electrically small antennas, it is necessary to use a transformation matrix to compensate for the strong mutual coupling that may exist between the antenna elements. The transformation matrix converts the voltages that are induced at the loads corresponding to the feed point of the array operating in the presence of mutual coupling and other near field scatterers to an equivalent set of voltages that will be induced by the same incident wave in an uniform linear virtual array (ULVA) consisting of omnidirectional isotropic point radiators equally spaced and operating in free space. For any given incident field, the open circuit voltage developed across the feed-point of the small dipole will always be less than the open circuit voltage developed across the feed-point of the half-wavelength dipole. The difference is in the voltage developed across the loads connected to the dipole's feed-point. With the small dipole antenna, the voltage developed across the load impedance will be orders of magnitude greater than the voltage developed across the load connected to the half-wavelength dipole, even though the power captured by any conjugately matched antenna is approximately the same irrespective of their lengths. Three different scenarios are presented to illustrate the methodology. First, we consider resonant dipole elements spaced half wavelength apart, electrically small tuned antenna elements spaced half wavelength apart and electrically small tuned antenna elements placed in close proximity of each other to reduce the footprint without affecting the performance of the phased array. In addition, we consider the possibility of DOA estimation using a combination of different type of electrically small antennas both uniformly and nonuniformly spaced. Numerical examples are presented to illustrate the principles of this methodology.