In this paper we address the problem of target's range migration in passive bistatic radar exploiting long coherent integration times with fairly wideband signals of opportunity. We resort to the well-known Keystone Transform (KT) to compensate for the range walk effect and to take advantage of a higher coherent integration gain against targets with non-negligible radial velocity. Specifically, an efficient implementation of the KT is proposed, based on Lagrange polynomial interpolation, in order to reduce the computational load of the method that mostly depends on the required slow-time interpolation stage. The analysis conducted against simulated data shows that the conceived approach allows to achieve theoretical performance while further reducing the KT complexity with respect to alternative solutions based on cardinal sine functions or Chirp-Z Transforms. Moreover, the application against experimental data sets collected by a DVB-T based passive radar proves the practical effectiveness of the proposed algorithm and highlights its suitability for real-time air traffic surveillance applications.

In this paper, we consider the possibility of extending the coherent processing interval (CPI) as a way to improve target detection capability in passive radars for maritime surveillance applications. Despite the low velocity of the considered targets, range walk effects could limit the performance of the system when long CPIs are considered. To overcome these limitations while keeping the computational load controlled, we resort to a suboptimal implementation of the Keystone Transform (KT), based on Lagrange polynomial interpolation, recently presented by the authors and successfully applied against aerial targets. Following those promising results, we extend the proposed approach to a coastal surveillance scenario. In the considered case, since longer CPI values are used, the proposed strategy appears to be even more attractive with respect to a conventional KT implementation based on the Chirp-Z Transform interpolation. In fact, comparable detection performance are obtained with a remarkable computational load saving. In detail, the effectiveness of the proposed approach is demonstrated against experimental data provided by Leonardo S.p.A., using a DVB-T based passive radar.