Reactive phase shifter for bandwidth enhancement of microstrip reflectarray antennas

A popular method for creating required phase shifts for patches in a microstrip reflectarray uses open ended stubs attached to the patches. Uniform stubs are narrowband and hence limit the bandwidth of the array. In this paper, a novel method for designing broadband reactive phase shifters is proposed based on the method of least squares. A structure consisting of transmission lines and open-ended stubs is considered for the phase shifter. A least square error function is constructed for the required phase shift and the characteristic impedances and electrical lengths of transmission lines are obtained by its minimization. Then, the circuit is realized by microstrip lines to be attached to the microstrip patch. It is shown that this novel phase shifter creates the required phase shift in a broader bandwidth than those of uniform stub phase shifters.