Design of a CSRR based compact microstrip antenna for image rejection in RF down-converter based WLAN receivers

One major problem in mixer based RF down-converters and superheterodyne receivers is the presence of image frequencies. There have been a number of approaches, both in analog and digital domain, to address this issue. Of late, attempts have been made to integrate the image rejection filter with the antenna so that there is no chance of image frequencies being received. Complementary split ring resonators (CSRR) are planar metamaterial structures that can yield negative value of effective permittivity of a material. This property is utilized here to notch out two possible image frequencies in a compact rectangular patch antenna for WLAN application at 2.4 GHz. The antenna provides a suppression of about 15 dB at 1.4 GHz and that of about 21 dB at 3.9 GHz. The CSRR further helps in reducing the electrical size of the antenna by 14.3%.