design method for the single-fed microstrip
antenna with switchable LP is first investigated. For a CP ringslot-coupled
microstrip antenna, there are two means to transform
into LP radiations, in which one is changing the length of
the open stub [6] and the other is using an open-ring slot instead
of the ring slot [7]. In addition, the directions of the LPs
obtained from the two means are different and they can be designed
to be orthogonal each other. These previous results give
a design method to realize the polarization switching between
two orthogonal LP modes. Furthermore, the two orthogonal LP
modes can be respectively converted to the RHCP and LHCP
modes when a perturbation segment, such as a cross slot [9] and
a protruded stub [10], is introduced into the radiating patch of
the microstrip antenna. Consequently, a reconfigurable antenna
with the polarization switching among the dual orthogonal LP
and two CP modes can be achieved by controlling the electric
characteristic of the perturbation segment. For the design of the
microstrip antenna with the quadri-polarization switching, we
construct a prototype and the number of the required diodes is
three, which is significantly less than that of the reported design.
Both the measured and simulated results for the constructed prototype
are presented