Miniaturized High Directivity Norman Window Directional Coupler

This paper presents a novel planar microstrip directional coupler design using a Norman window shape in the frequency range of 2 to 4 GHz. The Norman window acts as a resonator, enabling a miniaturized size for the coupler while still achieving high directivity and a wide bandwidth. The designed coupler offers a flat coupling ratio of 40 dB and a directivity of more than 25 dB, as demonstrated by simulations. Compared to conventional couplers, the coupling section size is significantly reduced by 80% to just 2 mm × 4.6 mm. These advantages make the proposed coupler a promising candidate for a wide range of applications in microwave and antenna technology.