Analysis of a square microstrip antenna with an eccentric slot

A topic of interest is the development of compact microstrip antennas, or the equivalent problem of reducing the resonance frequency for a given size. A possible technique consists of increasing the electrical length by optimizing the shape of the patch. Previous work on compact antennas proposed and studied shape changes to the standard patch antenna. One such antenna is the square-ring shaped patch that has been recently analyzed by P. Bafrooei and L. Shafai (see IEEE Trans. Antennas Propagat., vol.47, p.1633-9, 1999). Its resonance frequency decreases with an increase of the inner side of the slot. However, at the same time the input impedance grows rapidly and it becomes difficult to feed the antenna with a 50 ohm coaxial line. A square microstrip antenna with an eccentric slot is introduced and studied. This antenna is a generalization of that of Bafrooei and Shafai, when considering the latter as a square patch with a centered slot. The simulations show that the resonance frequency of the proposed antenna is lower than the conventional square patch antenna. In addition, a 50 ohm feed point is found by properly placing the slot.