Size reduction of microstrip-fed slot antenna by inductive and capacitive loading

Microstrip-fed slot antennas are useful in a broad range of applications due to their low profile, low cost, light weight, and ease of integration with other active components. Especially, there has been considerable interest in developing compact slot antennas for mobile communication systems. There are several techniques that can be used to reduce the size of slot antennas, including use of capacitive or inductive loading, increase of the electrical length, and change of antenna topology. However, the two reactive loading techniques have a little effect on size reduction, and the other techniques have a relatively small bandwidth. We present new slot antenna structures with capacitive loading and inductive loading simultaneously. One of designs has 52.9% size reduction of slot length compared to the conventional slot antenna and 2.8% impedance bandwidth, with the same radiation pattern as the conventional slot antenna. These antennas can be modified to a frequency tunable slot antenna by using a variable capacitor or a tunable capacitor.