In this paper, new designs of slot elements and a new configuration for array antennas for synthetic aperture radar at L- and Ku-band are proposed. The L-band are cavity-backed crossed slots for dual-polarization, and for Ku-band, waveguide slot arrays for single-polarization are used. The height of the L-band cavity is reduced by adopting an “inverted T” configuration. Each of the crossed slots is fed by a pair of differential probes. The Ku-band slot array is fed by a coax probe although waveguide divider. An initial prototype array comprising 2×2 L-band elements interleaved with Ku-band arrays was fabricated and measured. The impedance bandwidth (VSWR<2) of the antenna are dramatically broadened to 22% at L-band and 8.6% at Ku-band. This element design is applicable for larger Shared-Aperture arrays.