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In this article, the design of a Pythagorean-tree shaped fractal microstrip antenna is investigated for RFID reader applications. The antenna consists of a fourth-order Pythagorean-tree shaped fractal, a feed-line matched to the radiator, and co-planar waveguide (CPW) line with the filleted ground plane. The monopole antenna provides a wider operational bandwidth from 4.22-7.52 GHz. The use of fractal geometry enhances the bandwidth of the microstrip antenna and reduces the metallic footprint size to a great extent. The simulated reflection coefficients are also validated with measured results. The simulated radiation characteristics demonstrate an omnidirectional pattern with the realized gain of 2.9 dBi at 5.8 GHz. The antenna with an overall dimension of 0.36λ×0.43λ×0.015λ (λ represents the wavelength at 5.8 GHz) covers the entire 5.8 GHz ISM band.