Designs of square microstrip antennas backed by modified ground plane for circular polarised response

Circular polarised design with U-slot embedded on the patch is a reported configuration. For substrate thickness ≥0.07λg, it yields dual band response with a circular polarised characteristic only in the first band. This paper presents the advantages of embedding U-slot on the ground plane. Designs of square microstrip antenna backed by U-slot cut ground plane for circular polarised response are proposed. On total substrate thickness of 2.72 cm (0.072λcAR), antenna yields axial ratio bandwidth of 40 MHz (5.11%), which lies inside the reflection coefficient bandwidth of 188 MHz (22.24%). These values are improved ones against the design employing U-slot on the patch. A reduction in total substrate thickness is achieved either by using Bow-tie shape of the ground plane or by employing shorted microstrip line feed. Using U-slot cut Bow-tie shape ground plane, antenna yields axial ratio bandwidth of 42 MHz (5.38%), but on total substrate thickness of 2.12 cm (0.058λcAR), whereas using shorted microstrip line feed, antenna offers axial ratio bandwidth of 24 MHz (3.08%), on substrate thickness of 1.32 cm (0.039λcAR). In both reduced substrate designs, antenna offers more than 15% reflection coefficient bandwidth with a broadside radiation pattern and gain of more than 6 dBic. A methodology is presented that helps to realise similar design as per given wireless application. With the obtained antenna characteristics, proposed designs can find applications in GSM frequency bands.