A monopulse antenna array is designed by using a novel element combining wideband linearly tapered slot antennas (LTSA) with an interleaved, closely-spaced, travelling wave slotted waveguide array (TWSWA) similar to [1-3]. To decrease the deteriorating coupling between sum and difference rows in previous studies for monopulse operation, adjacent rows of interleaved arrays are designed to have the same amplitude distribution but different propagation constants. So, interleaved arrays generate two simultaneous sum beams with distinct but close squint angles. Dual array elements are represented by Sport networks. A 40-by-infinite array operating in 13% sidelobe bandwidth in C-band with 30-dB Taylor amplitude distribution is synthesized by the method proposed in . The array is verified by full-wave simulations in HFSS.