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Improvement in ellipticity bandwidth with a diagonal slotted diamond shaped microstrip patch antenna is analyzed in this paper. The antenna is electro-magnetically fed using two orthogonally oriented dumbbell shaped apertures fed by a 3dB 90° hybrid for dual polarization operation. The radiating element is a 45° rotated square patch (aspect ratio a/b = 1.015) forming a diamond. The antenna is designed to transmit and receive the two differently circularly polarized wide band signals simultaneously with a single antenna. It is observed that by cutting an electrically small rectangular slot along one of the diagonal of the square patch significantly improves the ellipticity bandwidth without altering its impedance bandwidth. The current distribution of the patch remains unaltered and hence the radiation pattern is also not affected. The use of a thick, low cost dielectric foam yields further improvement in bandwidth. A 2:1 impedance bandwidth of 26.5% and 3 dB axial ratio bandwidth of 20.4% has been achieved in simulation with the above geometry. An improvement of 5% in impedance bandwidth and 9% in ellipticity bandwidth is obtained over a patch of similar geometry with conventional rectangular shaped apertures. When compared to a non-slotted patch with dumbbell apertures the improvement in axial ratio bandwidth is of the order of 5% while the impedance bandwidth remains unaltered. The use of dielectric foam makes the antenna light weight and low cost. The above features make it an ideal element for wide band application as required for personal, mobile satellite and wireless communication systems.