The effect of air-bridges on the mode suppression of asymmetrical CPW-fed slot antennas

Due to its uniplanar characteristic, the coplanar waveguide (CPW) is suitable for the design of monolithic microwave integrated circuits (MMICs). Nevertheless, the two dominant modes, CPW and coupled slotline (CSL) modes, of such a structure might cause some problems in the circuit performance. Because of the higher dispersive property of the CSL mode, the CPW mode is usually the only desired mode to propagate in this uniplanar structure. However, the CSL mode is still excited if there are asymmetrical discontinuities in the circuit. Therefore, the air-bridge is commonly used to suppress the unwanted CSL mode for asymmetrical CPW discontinuities. In the past only the CPW-fed symmetrical slot antennas were analyzed. There are no air-bridges needed in those structures. The present paper contributes to analyze the effect of air-bridges on the asymmetrical slot antennas by using the full-wave spectral domain approach.