High directivity signal coupler

Abstract

Low loss high directivity wire couplers use a transmission airline structure and a low diameter coaxial cable ending in a wire loop sensor, which is inserted into an elliptically formed conical opening of the ground wall of the transmission line and protrudes into its cavity leading into a coupled and an isolated port. Lower, capacitively induced, electrical currents, because of the protruding ground edges of the conical or recessed openings, compared with the unperturbed antiphase magnetically induced currents, lead to controlled higher directivity in a frequency range up to at least 170 GHz.

Claims

1. A high directivity bi-directional RF signal coupler having an input port, an output port, a coupled port, and an isolated port, comprising: a) a coaxial airline between the input and output ports, comprising an external metallic mantle and a center signal conductor traversing the coaxial airline and linking the input and output ports of the coaxial airline, and b) an electro-magnetic “U” shaped coupling sensor having two branches and a concave bottom segment, being inserted into a conical hole into the external metallic mantle and coupled in a contactless manner with the center signal conductor, said conical hole having a wide opening and a narrow opening, wherein the narrow opening of the conical hole faces the center signal conductor, and wherein the “U” shaped coupling sensor samples RF energy flowing forward and reverse inside the coaxial airline.

2. A high directivity bi-directional RF signal coupler having an input port, an output port, a coupled port, and an isolated port, comprising: a) a coaxial airline between the input and output ports comprising: an external metallic mantle and a center signal conductor traversing the coaxial airline and linking the input and output ports of the coaxial airline, and b) an electro-magnetic “U” shaped coupling sensor having two branches and a concave bottom segment, being inserted into a recessed perpendicular hole in the external metallic mantle and coupled in a contactless manner with the center signal conductor, said recessed hole having a wide opening and a narrow opening, wherein; the narrow opening of the recessed perpendicular hole in the external metallic mantle faces the center signal conductor of the coaxial airline, and wherein; the “U” shaped coupling sensor samples RF energy flowing forward and reverse inside the coaxial airline.

3. A high directivity bi-directional RF signal coupler having an input port, an output port, a coupled port, and an isolated port, comprising: a) a coaxial airline between the input and output ports comprising: an external metallic mantle and a center signal conductor traversing the coaxial airline between the input and output ports, and b) an electro-magnetic “U” shaped coupling sensor being inserted into a perpendicular hole in the external metallic mantle of the coaxial airline and coupled in a contactless manner with the center signal conductor and having two branches and a concave bottom segment, wherein; the two branches of the “U” shaped coupling sensor are coaxial cables with a center conductor, dielectric filling and conductive outer shell and terminate into either the coupled or the isolated port, and wherein; the coaxial cables are stripped by removing the conductive outer shells and the dielectric fillings slanted by 45 degrees to expose a portion of the center conductor of the coaxial cables which forms the bottom segment of the electro-magnetic “U” shaped coupling sensor.

4. The high directivity bi-directional RF signal coupler of claim 1, wherein; a characteristic impedance of the coaxial airline is 50 Ohms.

5. The high directivity bi-directional RF signal coupler of claim 1 or 2 or 3, wherein; the bottom section of the “U” shaped electro-magnetic sensor runs parallel to the center conductor of the coaxial airline.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention and its mode of operation will be more clearly understood from the following detailed description when read with the appended drawings in which:

(2) FIG. 1 depicts prior art a Load pull test setup for measuring power contours and real time incident and reflected waves and load reflection factor of a DUT, using bi-directional coupler and network analyzer.

(3) FIG. 2 depicts prior art, signal coupler of type “wave-probe”.

(4) FIG. 3 depicts prior art, a voltage-current coupler of type I-V-probe.

(5) FIG. 4 depicts prior art, magnetically induced and capacitively coupled currents inside the coupling loop of a wire coupler of type wave-probe.

(6) FIG. 5 depicts a first embodiment of the high directivity signal coupler, using a conical hole.

(7) FIG. 6 depicts a second embodiment of the high directivity signal coupler using slanted sensor coaxial cables.

(8) FIG. 7 depicts prior art, definition of transmission, reflection and coupling RF parameters in a directional coupler.

(9) FIG. 8 depicts a third embodiment of the high directivity signal coupler, using a recessed opening.

(10) FIG. 9 depicts coupling and directivity data of the signal coupler of the first embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(11) The high directivity bi-directional coupler in this embodiment uses a low loss cylindrical coaxial transmission airline, which is popular in RF technology. The signal coupling and isolation mechanism, first described in ref 6, works as follows (FIG. 4): the RF signal current Is inside the signal conductor 40 creates a magnetic field H around it 42. This magnetic field H 42 couples into the parallel to the center conductor 40 running bottom section of the wire loop sensor 41, 43 and creates a magnetically induced current I.sub.H which flows from branch 43 through the bottom of the “U” shaped loop 44 into branch 41. Since the bottom of the wire loop sensor runs parallel to the signal conductor 40 there is also a capacitive coupling between the two. This capacitive coupling induces capacitive current I.sub.E into the branches 41 and 43. These capacitive currents are proportional to the electric field in this region. Inside the coupled branch 43 the magnetically induced current I.sub.H and the electric one I.sub.E add yielding a total current |I.sub.H+I.sub.E|. Inside the isolated branch 41 these currents run antiphase and subtract |I.sub.H−I.sub.E|. The total signal power in the load terminating branch 43 is therefore |I.sub.E+I.sub.H|.sup.2*Zo and in the load terminating branch 41 |I.sub.H−I.sub.E|.sup.2*Zo. This creates both the forward coupling into branch 43 and the isolation in branch 41.

(12) Since the predominant coupling mechanism is magnetic, I.sub.H is always larger than I.sub.E. Or, if we can increase I.sub.E and decrease I.sub.H, the difference I.sub.H-I.sub.E in isolated branch 41 tends towards zero. This increases isolation and directivity. At the same time, it also increases I.sub.H+I.sub.E; this increases forward coupling. The objective is therefore to increase I.sub.E and/or decrease I.sub.H.

(13) A prior art wire loop sensor, also known as wave-probe (FIG. 2, see ref. 6) is placed in free space above the center conductor of a slabline in the region of low electric and moderate magnetic field shows low coupling and low directivity, compared with a coaxial structure where both the electric and magnetic fields are homogenous and stronger. A prior art I-V probe of FIG. 3 (see ref. 6), where the electric field antenna and the magnetic loop are placed separated in the same slabline structure and shows even poorer directivity and has failed in real time applications.

(14) FIGS. 5, 6 and 8 show a number of embodiments allowing different electric versus magnetic field distributions with the objective of higher directivity compared with classic signal coupler designs: All herein presented embodiments use openings with a narrow iris towards the cavity of the airline. In the embodiment of FIG. 5 the electro-magnetic wire sensor 56 is inserted into a vertical hole 57, which has a conically shaped bottom section 50, which deforms the electric and magnetic field lines E and H. A reduced portion of the magnetic field 55 penetrates through the iris and induces a reduced current I.sub.H (FIG. 4) whereas the electric current I.sub.E (FIG. 4) is created only by the portion E.sub.C of the electric field. The modified ratio between I.sub.H and I.sub.E promotes the higher directivity as shown in FIG. 9.

(15) In the embodiment of FIG. 8 the iris is created by a simple recess 87 of the hole 82 in the airline body 83, in which the wire loop 86 penetrates and couples with the center conductor 85, the effect is similar to the embodiment of FIG. 5 with similar directivity 80, 81 behavior. It has been found, in both cases that the ratio of the iris diameter to the diameter of the hole creates a resonant behavior 90 of very high directivity, as shown in FIG. 9, that can be shifted by this ratio. In short, the ratio “coupled 91 to leaked” (|I.sub.H+I.sub.E|.sup.2/|I.sub.H−I.sub.E|.sup.2) signal power, determining the coupler directivity, is manipulated by the form and dimensions of the opening 50 as well as the degree of penetration of the sensor conductor 58 into the electro-magnetic field zone of the airline cavity.

(16) FIG. 6 depicts a third possible embodiment, which does not necessitate a special forming of the opening 61 of the mantle 60 into the cavity of the airline: the coaxial cables 66, 64, 65 are denuded slanted 63 under an angle of approximately 45 degrees and bent together to form an approximately 90 degrees corner angle with an exposed section of the center conductor 62 that forms the sensor conductor. The proximity of the coaxial mantle conductor and the easily adjustable penetration of the conductor 62 controlling the degree of electromagnetic coupling allow for the previously discussed directivity tuning. The penetration alone, affects coupling and directivity (reverse coupling) to a similar degree, though; it is the shape of the iris in FIGS. 5 and 8 which have an independent influence. The embodiment of FIG. 6 bears a potential problem if higher coupling and associated penetration is chosen, because the protruding coaxial cables into the cavity create higher residual reflection.

(17) The protrusion of the sensor conductor into the high field area of the cavity of the airline (FIGS. 5, 6 and 8) may disturb the signal propagation and is, in any case, a reason of concern regarding the residual return and insertion loss of the coupler and must be taken into consideration.

(18) In conclusion the new high directivity signal coupler embodiments shown are superior in coupling versus directivity ratio to prior art alternative embodiments. It also offers the benefit of “tuning” i.e., the shaping of the opening into the airline cavity towards an extremely high directivity without affecting the forward coupling capacity. Obvious alternatives and modifications to the herein disclosed general concept of using the shape of the opening into the airline cavity to optimize the directivity of the signal coupler shall not impede in the validity of the invention.