An electromagnetic band‐gap (EBG) structure which combines a tapered surface structure and a tapered defected ground structure is proposed in this article. “I”‐typed EBG units with different size and center distance are etched on the microstrip line on the upper layer of the substrate. Without sacrificing the bandwidth, a feasible method is proposed to implement miniaturization by reducing the second half of the tapered EBG, which is concluded by analyzing the relations between the working frequency and tapered periodic structure. By using HFSS simulation tool, the proposed structure possesses a wide stop‐band of 23.72 GHz (1.88–29.20 GHz). Particularly, the actual size characteristic is only about 40 × 20 × 0.6 mm3. Meanwhile, the proposed structure is fabricated and measured. And the experimental results basically agree well with the simulated results, which indicate that the proposed EBG is promising for designing high performance band‐stop filters and associated antennas with width bandwidth and small size.