Advantages of non-uniform linear arrays based on COTS elements in passive radar applications

One of the advantages associated to the use of passive radars is the lower development and maintenance costs with respect to active ones, mainly related to the absence of a dedicated transmitter and to the possibility of using COTS components. In this paper, a study of the advantages of using Non Uniform Linear Arrays (NULAs) for the design of the antenna system for a passive radar exploiting DVB-T signals is carried out, considering as a basic requirement the use of commercial antennas. Commercial solutions are not designed for being used as single radiating elements in array configurations, so directivity and physical sizes are not the most desirable for array design. In Spain, the use of horizontal polarization includes additional constraints to inter-element distances, and usually gives rise to grating lobes. NULAs designed using optimization techniques for maximizing directivity and controlling side lobes levels are analyzed and compared to Uniform Linear ones (ULAs), proving the better performance of the NULA based spatial filtering. For a selected commercial antenna, performances of NULAs and ULAs are compared as a function of the number of elements, showing a better improvement as the number of elements increases. For completing the study, the single radiating element is redesigned for reducing the physical size maintaining the radiation properties, although the cost associated to this new design is clearly higher than the first one. Results show that NULAs with smaller elements give a better performance in terms of Side Lobe Level (SLL).