Abstract: A miniaturization radio frequency (RF) interface design with low insertion loss and high port isolation is proposed in this paper. This RF interface works in X-band and adopts ball grid array (BGA) technology as interface of RF module system instead of traditional electrical connectors by transmitting the RF signal to the interface of RF module system through the transmission path and vertical transition embedded in substrate board. Feasibility analysis is introduced and critical parameters of this interface circuit are calculated with high frequency simulation software. A specialized test fixture is also designed and manufactured to obtain the electrical performance of the interface design. The test result shows that in frequency range of 8 GHz to 12 GHz, voltage static wave ratio (VSWR) of this RF transfer structure can reach the level below 1.2, the insertion loss can reach the level better than 0.1dB, and isolation between ports is less than -80 dB. An X-band T/R module is designed based on this interface technology and several samples are manufactured and measured which can satisfy the required electrical performance.