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In CPW-fed slot-coupled microstrip antennas, several shapes of the excitation slot have already been proposed in the open literature: inductively coupled slot, capacitively coupled slot and coupled slot-loop. Among these coupling mechanisms, the impedance matching of the inductively coupled and slot-loop coupled antennas are much more sensitive to the slot dimension. Thus, these cases of antennas are not easy matching of impedance. In this article, we present the method of improving the impedance matching for slot-loop coupled microstrip antennas. We will introduce a tuning-stub on CPW feedline. By adjusting the length of the tuning-stub, the impedance matching of this slot-loop coupled microstrip antenna can be obtained easily. In some applications for wireless system, an antenna with omnidirectional radiation pattern in a horizontal plane is required. An omnidirectional pattern can be obtained by cutting the widths of the substrate and ground plane as narrow as that of the patch. This is due to the increase of the diffracted fields from the edges of the smaller size ground plane.