Improved Circularly Polarized Microstrip Antenna

Two modifications improve the performance of a circularly polarized microstrip-patch-array antenna described in U.S. Patent 5,661,994. Because the phase difference between the orthogonal sides in the original design was 135°, there was substantial cross-polarization and waste of power. One modification is a change in the layout of two microstrip transmission lines through which excitation is applied to two orthogonal sides of each microstrip patch, such that the phase difference between the sides becomes 90°, which is optimum for circular polarization. The other modification pertains to the use of a quarter-wave impedance transformer after a junction that sums the power of two elements of a two-element subarray. When combining these subarrays to form a four-element subarray, the use of a postjunction transformer dictated the use of a meandering transmission line to obtain the required phase shift between the subarrays. The second modification is the placement of an impedance transformer before the junction, such that a transformer is no longer needed after the junction and the meandering transmission line can be eliminated. Hence, the radiative, ohmic, and dielectric losses of the meandering transmission line are also eliminated and the design is simplified.