Satellite communications system with the zero-db coupler

• US 5,274,839 A
• Filed: 02/12/1992
• Issued: 12/28/1993
• Est. Priority Date: 02/12/1992
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: General Electric Company
• Inventors: Praba, Krishna, Kularajah, Ratnarajah
• Primary Examiner(s): Lee, Benny T.
• Application Number:
  US07/834,587
• Time in Patent Office: 685 Days
• Field of Search: 333/109, 333/117, 333/113, 333/114, 455/12.1, 455/13.1, 455/13.3, 370/123, 370/75, 392/353
• US Class Current: 455/12.1
• CPC Class Codes: H01P 5/182 the waveguides being arranged in parallel

Abstract

A zero-dB hybrid or directional coupler includes a first through waveguide extending between first and third ports and a second through waveguide, parallel to the first waveguide, and extending between second and fourth ports. A plurality of branch waveguides extend between the first and second through waveguides, and are adjusted to couple signal from the first port only to the fourth port, and from the second port only to the third port (within in limits of systems isolation). Particular normalized branch line impedances provide best operation. A communication system especially adapted for use as a spacecraft uses a zero-dB coupler in a "planar" waveguide system to transpose or "crossover" the positions of two system ports, whereby the physical positions of the various ports are arranged in the same relation as their phase progression.

Claims

1. A zero-dB branch transmission-line directional coupler, comprising:

a first elongated main transmission line having one of a normalized impedance and a normalized admittance of unity at a particular frequency;

a second elongated main transmission line parallel with said first main transmission line, said second main transmission line also having one of an impedance and admittance, said one of said impedance and admittance of said second main transmission line being equal to a corresponding one of said impedance and admittance of said first main transmission line at said particular frequency;

a first branch transmission line extending between first locations along said first and second main transmission lines and forming first junctions therewith, said first branch transmission line having an electrical length of about one quarter wavelength at said particular frequency;

second and third branch transmission lines extending, parallel with said first branch transmission line, between second and third locations along said first and second main transmission lines and forming second and third junctions therewith, with said first junctions of said first branch transmission line being located on said first and second main transmission lines between said second and third junctions of said second and third branch transmission lines;

fourth and fifth branch transmission lines extending, parallel with said first branch transmission line, between fourth and fifth locations along said first and second main transmission lines and forming fourth and fifth junctions therewith, said fourth junctions of said fourth branch transmission line being located on said first and second main transmission lines between said first and second junctions of said first and second branch transmission lines, and said fifth junctions of said fifth branch transmission line being located on said first and second main transmission lines between said first and third junctions of said first and third branch transmission lines;

said first branch transmission line having said one of said normalized impedance and said normalized admittance of about 0.87 at said particular frequency;

said second and third branch transmission lines each having said one of said normalized impedance and said normalized admittance of about 0.35 at said particular frequency; and

said fourth and fifth branch transmission lines each having said one of said normalized impedance and said normalized admittance of about 0.74 at said particular frequency.

2. A coupler according to claim 1 wherein the spacing of said first branch transmission lines relative to each of said fourth and fifth branch transmission lines, respectively, is about one quarter wavelength at said particular frequency.

3. A coupler according to claim 1 wherein said transmission lines are hollow rectangular waveguides, and said junctions are series junctions.

4. A zero dB branch-line waveguide coupler, comprising:

a first elongated rectangular main waveguide including mutually parallel broad electrically conductive walls spaced apart by mutually parallel narrow electrically conductive walls, and defining a first axis of elongation, said first waveguide having a normalized impedance of unity at a particular frequency;

a second elongated rectangular main waveguide, parallel with said first, said second main waveguide including mutually parallel broad electrically conductive walls spaced apart by mutually parallel narrow electrically conductive walls, and defining a second axis of elongation, said second waveguide having an impedance equal to the impedance of said first waveguide at said particular frequency;

a first rectangular branch waveguide coupled to and extending between particular broad walls of said first and second main waveguides, said first branch waveguide defining a third axis, and having a length of about one quarter wavelength in the direction of said third axis, and a normalized impedance of about 0.87 at said particular frequency;

second and third rectangular branch waveguides coupled to and extending between said broad walls of said first and second main waveguides at locations on opposite sides of, and spaced from, said first branch waveguide, said second and third rectangular branch waveguides being mutually identical and defining fourth and firth axes, respectively, said second and third rectangular branch waveguides having a length of about one quarter wavelength in the direction of said third and fourth axes, respectively and each having a normalized impedance of about 0.35 at said particular frequency; and

fourth and fifth rectangular branch waveguides coupled to and extending between said particular broad walls of said first and second main waveguides at locations between said first and second, and about halfway between said first and third branch waveguides, respectively, said fourth and fifth branch waveguides being mutually identical and defining sixth and seventh axes, respectively, each of said fourth and fifth branch waveguides having a length of about one quarter wavelength and a normalized impedance of about 0.74 at said particular frequency.

5. A spacecraft communications system, comprising:

receive antenna means for receiving uplink signals;

receiving means coupled to said receive antenna means for receiving said uplink signals therefrom, for at least filtering said uplink signals to generate received signals;

demultiplexing means coupled to said receiving means for separating said received signals into a plurality of frequency channels;

amplifying means coupled to said demultiplexing means for amplifying the signals in at least two of said channels for forming amplified signals;

first and second multiplexing means coupled to said amplifying means for coupling signals in said two of said channels onto first and second different paths;

transmit antenna means including at least first, second and third input ports arranged at positions centered on a plane, for transmitting signals applied in a particular spatial phase relation to said first, second and third input ports of said transmit antenna means;

planar dual-mode coupling means coupled to said first and second paths for coupling said signals in said first and second paths together for forming signals to be transmitted, said dual-mode coupling means also including first, second and third output ports at which said signals to be transmitted appear, said first, second and third output ports arranged at positions centered on said plane with the phases of two adjacent ones of said first, second and third output ports reversed in said positions from said particular spatial phase relation; and

zero-dB coupling means, said zero-dB coupling means including;

a first elongated main transmission line having one of a normalized impedance and a normalized admittance of unity at a particular frequency, and defining first and second ports, a first port of which is coupled to one of said two adjacent ones of said first, second and third output ports of said dual-mode coupling means;

a second elongated main transmission line parallel with said first transmission line, said second main transmission line also having said one of an impedance and admittance, said one of said impedance and admittance of said second transmission line being equal to a corresponding one of said impedance and admittance of said first main transmission line at said particular frequency, and defining first and second ports;

a first branch transmission line extending between first locations along said first and second main transmission lines and forming first junctions therewith, said first branch transmission lines having a length of about one quarter wavelength at said particular frequency;

second and third branch transmission lines extending, parallel with said first branch transmission line, between second and third locations along said first and second main transmission lines and forming second and third junctions therewith, with said first branch transmission line located between said second and third branch transmission lines;

fourth and fifth branch transmission lines extending, parallel with said first branch transmission lines, between fourth and fifth locations along said first and second main transmission lines and forming fourth and fifth junctions therewith, said fourth branch transmission line being located between said first and second branch transmission lines, and said fifth branch transmission line being located between said first and third branch transmission lines;

said first branch transmission line having said one of said normalized impedance and normalized admittance of about 0.87 at said particular frequency;

said second and third branch transmission lines each having said one of said normalized impedance and normalized admittance of about 0.35 at said particular frequency; and

said fourth and fifth branch transmission lines each having said one of said normalized impedance, and normalized admittance of about 0.74 at said particular frequency.

6. A system as in claim 5, wherein said main and branch transmission lines are rectangular waveguides, and said junctions are series junctions.

7. A system as in claim 6, wherein said main and branch waveguides are in the form of a bipartite monolithic whole.