We propose a conductive shielded compact antenna hat, which can be utilized as a low loss passive RF repeater or coupler, to perform the RF compatibility testing of the aircraft, rocket, and launch vehicle using inverted‐F type antennas. Although the onboard antenna is very closely enclosed by the proposed antenna hat without RF absorbers, the resonance of the antenna itself is hardly affected compared to the free space radiation. The antenna hat which is fabricated for the S‐band inverted‐F antenna with the size of 74 × 13 × 16 mm3 has the small enclosure of 88 × 35 × 44 mm3, the return loss of 25.6 dB, the insertion loss of 0.3 dB, and the leakage loss of 52.5 dB at 2.25 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:220–223, 2015