Among these designs the cases of a patch antenna using an equilateral triangular cavity ground a microstrip-line-fed antenna with two concentric annular slots a printed antenna with a quasi-self-complementary structure and a printed back-to-back folded planar are all capable of providing sufficient operating bandwidth accompanied with a special function of either high gain or omnidirectional pattern for 5.2=5.8 GHz WLAN application. However, the designation techniques and structure sizes
of these antennas are generally complicated or large