An embedded broadband impedance matching technique for microstrip patch antennas

An impedance matching technique for enhanced bandwidth is presented for implementation in edge-fed and aperture-coupled microstrip patch antennas. An additional piece of transmission line is placed at the output (terminal plane) of the microstrip antenna and is used in conjunction with a series capacitor to obtain a second resonance. The series capacitor has to be chosen so that it cancels the inductive component that is introduced by the transmission line. Since a small capacitance is needed at W-band frequencies, fabrication can be kept simple by printing an interdigital capacitor in series with the line. To keep the area occupied by the antenna and the matching network small, an inset feed is used to control the input impedance. As result, a major portion of the transmission line is embedded in the patch structure itself and a very compact size is obtained. The simple and intuitive design, the compact size and the easy implementation and fabrication make the proposed method a good choice for many applications.