This paper presents a novel design of a directional coupler using the substrate integrated double-strip coaxial line (SIDSCL). In contrast to the standard substrate integrated coaxial line (SICL) which has only one central signal strip, the proposed SIDSCL possesses double strips configuration that grants the SIDSCL a great circuit layout diversity and a lower transmission loss. The SIDSCL also inherits all the advantages of the SICL which include better phase linearity, low profile, low-frequency dispersion, zero cutoff frequency, and wider bandwidth. A sample 10-dB directional coupler is fabricated to verify the circuit design. Good agreements are observed between the measured and simulated data.