Design of broadband probe-fed plate antenna with stub

A suspended probe-fed plate antenna with a stub is proposed for broadband applications. The radiating plate, which acts as a typical radiator, is designed based on standard rules for designing conventional microstrip antennas. The plate is suspended above a ground plane at a height of around 0.07 lambda. Owing to the large spacing between the plate and ground plane, a coaxial probe is used to excite the plate instead of the microstrip line often employed on an electrically thin dielectric substrate. To compensate for the large input inductance stemming from the long probe, a conducting stub is used as a broadband impedance matching network. The stub is attached to one of the radiating edges of the plate and is coplanar with the plate. Using transmission-line theory, the stub can be designed to function as a transmission-line type transformer. This method is used to design a rectangular suspended probe-fed plate antenna. Experimental results show that this design is capable of achieving a VSWR = 2:1 impedance bandwidth of about 25%, relatively stable radiation patterns, and maximum gains of 6.8-8.9dBi across the bandwidth.