A Mainlobe Jamming Suppression Method for an FDA–MIMO Radar System with an Ultralarge Sparse Aperture

Conventional frequency diverse array (FDA) multiple-input multiple-output (MIMO) radar systems offer adjustable range-domain degrees of freedom (DOFs), enabling effective suppression of mainlobe deceptive jamming. However, their performance significantly degrades, especially in the presence of mainlobe suppressive jamming in electronic countermeasure scenarios. Inspired by distributed configurations, this paper investigates an FDA-MIMO radar system with an ultralarge sparse aperture (ULSA), achieved by deploying multiple auxiliary passive receiving antennas around the FDA-MIMO radar. This system retains the range-based DOFs provided by the FDA-MIMO radar while benefiting from the high angular resolution offered by the distributed configuration. Building on this, we propose a mainlobe jamming suppression method that combines the generalized inner product (GIP) with minimum variance distortionless response (MVDR) beamforming. This approach simultaneously mitigates both mainlobe deceptive and suppressive jamming within the joint range-angle domain. Simulations and measured data validate the effectiveness of the proposed system in suppressing mainlobe jamming. Comparative analysis with traditional FDA-MIMO and distributed MIMO radar systems demonstrates the superior performance of the proposed system.