An application of a narrow slot cut in the ground to improve multi-band operation of a small antenna

In general, small size multi-band antennas for hand held phones have to operate at low frequency bands below 1 GHz and at upper frequency bands, which are in the vicinity of 2 GHz and 5.5 GHz. When the desired number of resonances is generated in a small antenna, normally much effort must be spent to achieve the required bandwidth properties, usually expressed in terms of impedance match and radiation efficiency. To cope with this problem, we have investigated a modification which concerns the introduction of a slot cut in the ground plane supporting a small antenna. We investigate the effect of various shapes of slot cuts on the impedance properties and radiation pattern of a modified antenna. The use of suitable slots can significantly improve the return loss bandwidths. The introduction of a slot in the ground plane raises concerns about increasing radiation towards the user. We have observed that there is no preferred direction of the radiation propagating towards the. user for frequency bands below 1000 MHz when slots or cuts are inserted in the ground. For upper bands above 1000 MHz, the strongest radiation can occur towards the user, but such an effect is also observed in antennas with solid ground plates.