In this paper, a novel artificial magnetic conductor (AMC) reflector is proposed for gain stability enhancement of a low‐profile wideband bowtie antenna (operates at C‐band). Two AMC reflectors are investigated: the first one is based on a standard square patch cell while the second one is based on a novel cell geometry called modified cross shape (MCS). The two units' cell geometries are studied and optimized to achieve the desirable performances, namely; low‐profile, wide impedance bandwidth, and gain stability. The proposed antenna structure with 5 × 8 MCS unit cells is fabricated and measured. The results show a significant steady gain compared to similar work in the literature. The fabricated structure presents a low thickness of 0.084 λL (λL is the guided wavelength at the lowest frequency, i.e., 3.94 GHz) with 0.85 dB of gain variation over a wide impedance bandwidth of about 50% (3.94–6.61 GHz).