Microwave coupler with high isolation and high directivity

A microwave signal coupler for coupling a microwave signal loosely from a main microstrip transmission line to a coupled microstrip transmission line with high directivity, said coupling including:

• a ground plane;
• a dielectric substrate layer disposed over said ground plane;
• a section of each of said main and coupled microstrip transmission lines disposed on the exposed surface of said dielectric substrate layer adjacently aligned with a predetermined gap therebetween to form a coupling region, the length of said coupling region being substantially less than one-quarter wavelength of said microwave signal;
• a capacitive coupling element disposed within said coupling region across said main and coupled transmission line sections for supplementing the dielectric capacitive coupling of the gap therebetween to increase the directivity of said microwave signal coupling, said capacitive coupling element splitting the coupled transmission line section of the coupling region into two branches, said capacitive coupling element being physically adjustable in size to balance the electric and magnetic field microwave signal coupling components of one of said branches and to reduce the microwave power output thereof;
• and
• at least one of the microstrip transmission line coupling sections having a V-shaped notch removed from the width thereof on a side opposite said gap and in the proximity of said capacitive coupling element.