Different from the phased-array using the same carrier frequency for each transmit element, the frequency diverse\narray (FDA) uses a small frequency offset across the array elements to produce range-angle-dependent transmit\nbeampattern. FDA radar provides new application capabilities and potentials due to its range-dependent transmit\narray beampattern, but the FDA using linearly increasing frequency offsets will produce a range and angle coupled\ntransmit beampattern. In order to decouple the range-azimuth beampattern for FDA radar, this paper proposes a\nuniform linear array (ULA) FDA using Costas-sequence modulated frequency offsets to produce random-like energy\ndistribution in the transmit beampattern and thumbtack transmit-receive beampattern. In doing so, the range and\nangle of targets can be unambiguously estimated through matched filtering and subspace decomposition algorithms\nin the receiver signal processor. Moreover, random-like energy distributed beampattern can also be utilized for low\nprobability of intercept (LPI) radar applications. Numerical results show that the proposed scheme outperforms the\nstandard FDA in focusing the transmit energy, especially in the range dimension.
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