A microstrip-fed ultra-wideband slot antenna

Ultra-wideband (UWB) antennas have gained great interest since the US Federal Communication Commssion (FCC) released the generic admission for UWB in the frequency band between 3.1 GHz-10.6 GHz in 2002. In Europe a similar regulation standard with a reduced bandwidth (6 GHz-8.5 GHz) is available. Due to the inherent wide bandwidth, communication systems with a high data rate and high resolution imaging systems are possible making this technology attractive for many different applications. Printed UWB antennas are preferred because they lead to compact and low-cost front-ends. Electrically thick dipole antennas with circular and more complex shapes are suitable candidates for a broadband operation. Slot antennas with a complementary shape to such dipole shapes have the same radiation characteristics according to Babinet´s principle; only the H- and E-field components are interchanged. An UWB antenna is realized in such a manner, whereas the antenna is fed by a coaxial cable soldered directly to each side of the slot center. In this publication a similar antenna is presented with a leaf-shaped slot and a microstrip feeding. Due to the planar feeding structure a robust antenna structure is achieved and single- ended active and planar circuits can be easily integrated with the antenna. The radiation of this antenna type results from the current of a wire loop and is inductive. Therefore, the H-field is dominant in the near field of the antenna. This is advantageous for integrated systems as coupling due to electrical fields in the near field are less probable.