A Low-profile Broadband Balun Fed Circular Patch Antenna

A low-profile broadband circular patch antenna that can excite TM
₁₁
and TM12 modes is proposed. The proposed antenna mainly consists of an annular slotted circular radiation patch, a metal ground, a set of shorting pins, and a vertical grounded balun feeding structure. One side of the vertical feeding substrate is slotted ground and the other side is a microstrip feeding line. A cross-shaped slot is introduced on the circular radiation patch, it improves the impedance matching of the antenna significantly. With a profile of 0.063 λ0 (λ0 is the center operating wavelength in the free space), the -10 dB impedance operating band is 3.49-5.5 GHz and the relative bandwidth is 44.7%.