High gains with highly efficient circularly polarized (CP) microstrip planar and conformal cylindrical patch antenna are designed for ISM band. Dumbbell shaped slot is incorporated at the centre of an irregular hexagonal radiator for the production of circular polarisation with high gain. The simulated results indicate impedance mismatch loss (S 11 ) bandwidth of 78.8 MHz and an axial ratio bandwidth (AR) of 10.3 MHz for planar patch. However the impedance mismatch loss bandwidth and AR

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... h comes out to be 46.2 MHz and 10.6 MHz for conformal cylindrical patch antenna respectively which shows that return loss bandwidth is dropped down by almost 42% for the case of conformal cylindrical antenna and axial ratio bandwidth remains almost similar. Axial Ratio beam-width for Phi = 0 degree are 83 degree and 61 degree for planar patch and conformal patch respectively. Consequently, the gain obtained in planar patch is 8.79 dBic with the efficiency of 96.33% and in the case of conformal patch, the gain comes out to be 4.16 dBic with an efficiency of 95 %.