Single patch designs of a microstrip antenna with a U-slot or a pair of rectangular slots (E-shape) provide a single band circularly polarized response, and hence they are not useful in frequency and polarization agile applications. In this paper, a modified design of a Ψ-shape microstrip antenna is proposed for dual band and dual sense circularly polarized response. Use of unequal length rectangular slots in the modified patch, optimizes the inter-spacing between the modified TM21 and TM22 resonant modes, surface current distributions and impedance levels at them to yield dual band circularly polarized response. An impedance bandwidth of 1992 MHz (37.05%) is obtained which completely covers the axial ratio bandwidth of 11.84 and 5.67%, in the two bands with frequency ratio of 1.3 in between them, thereby satisfying the requirements of frequency agile systems. Over the impedance and axial ratio bandwidth, the antenna exhibits nearly broadside radiation pattern with a gain of around 7 dBi. A design methodology based on the simple parametric formulation is presented, which helps in realizing a similar antenna in the specific frequency band. The proposed antenna can find applications in frequency and polarization agile systems where the signal loss due to the interference and jamming can be reduced.