Adjustable directional coupler
View Patent ↗A simple low-loss high-directivity wire coupler uses a wire over ground transmission airline structure and the center conductor of a folded low diameter coaxial cable ending in a wire loop sensor, which is inserted into the ground wall of the transmission line, branching into a coupled and an isolated port. The coupling factor is adjustable by laterally displacing the conductor of the transmission line in the area of the sensor without affecting the characteristic impedance. Directivity and residual reflection are maintained. Higher, capacitively induced, electrical current, because of the confined zone between signal conductor and ground wall, compares favorably with the antiphase magnetically induced current component in the wire loop sensor and leads to increased coupling and directivity over a frequency range up to at least 70 GHz.
1. An adjustable directional RF signal coupler having an input port, an output port, a coupled port, and an isolated port;
the adjustable directional RF signal coupler comprises:
a) a wire-over-ground transmission airline between the input and output ports, the wire-over-ground transmission airline comprising a metallic ground plate and a signal conductor joining the input and output ports, the signal conductor being parallel to the ground plate, and
b) a “U” shaped wire loop sensor having a bottom section and two branches, the two branches comprising a first branch and a second branch, the “U” shaped wire loop sensor being coupled electro-magnetically in a non-contacting relationship with the signal conductor, and
c) means for controlling a coupling factor between the input port and the coupled port;
wherein
the “U” shaped wire loop sensor is inserted in a perpendicular hole into the metallic ground plate and protrudes into an area between the ground plate and the signal conductor with the bottom section extending parallel to the signal conductor,
and wherein
each branch of the “U” shaped wire loop sensor extends into a center conductor of a coaxial cable, the first branch terminating into the coupled port and the second branch terminating into the isolated port;
and wherein
the means for controlling the coupling factor comprise:
a) a device with a low dielectric factor touching the signal conductor close to the bottom section of the “U” shaped wire loop and displacing the signal conductor parallel to the ground plate;
b) means for controlling a position of the low dielectric factor device;
and wherein
signal conductor deflection predominantly occurs near the “U” shaped wire loop sensor.
2. The adjustable directional signal coupler of claim 1 , wherein
the “U” shaped wire loop sensor is inserted in the metallic ground plate in a zone closest to the signal conductor.
3. The adjustable directional signal coupler of claim 1 , wherein
the signal conductor is cylindrical.
4. The adjustable directional signal coupler of claim 1 , wherein
a characteristic impedance of the wire over ground transmission airline is 50 Ohms.
5. The adjustable directional signal coupler of claim 1 , wherein
a deflection range of the signal conductor is at least as large as a diameter of the signal conductor.
6. The adjustable directional signal coupler of claim 5 , wherein
a maximum deflection range of the signal conductor does not exceed an elasticity range of the signal conductor.
7. The adjustable directional signal coupler of claim 1 , wherein
the means for controlling the position of the low dielectric factor device allows discrete repeatable settings.
8. The adjustable directional coupler of claim 7 , wherein the means for controlling the position of the low dielectric factor device comprises control by a remotely controlled stepper motor.