Abstract
Low loss high directivity signal couplers use one or two U-shaped wire loops inserted into a slot of a low loss transmission line; the low diameter coaxial cable ending in wire loop sensors, which are inserted into the slot of the transmission line lead to a coupled, an isolated and a divided port. High, capacitively induced, electrical current, because of the proximity between the signal conductor of the airline and the wire loop, compares favorably with the antiphase magnetically induced current component in the wire loop sensor and leads to increased coupling, division and directivity over a wide frequency range starting at a few hundred MHz and exceeding 18 GHz. The signal coupler-divider is used in hybrid load pull tuners with instantaneous vector signal measurement capability.
Claims
1. A directional RF signal coupler-divider comprising d) an input port, an output port, a coupled port, an isolated port and a divided port, e) a transmission airline with a slot, a signal conductor between the input and output ports, and f) two U shaped electro-magnetic wire loop sensors, a first wire loop sensor and a second wire loop sensor, said wire loop sensors having each a bottom section and two branches, a first branch and a second branch, said U shaped wire loop sensors being inserted into the slot of the airline and coupled contactless with the signal conductor; wherein the bottom sections of the U shaped wire loop sensors run parallel to the signal conductor, the second branch of the first wire loop sensor being joined with the first branch of the second wire loop sensor; and wherein the first branch of the first wire loop sensor leads to the coupled port, the second branch of the first wire loop sensor and the first branch of the second wire loop sensor are joined and form a common branch leading to the isolated port, and the second branch of the second wire loop sensor leads to the divided port, and wherein each branch extends into forming a center conductor of a coaxial cable terminating into a coaxial port.
2. The directional signal coupler-divider of claim 1, wherein the signal conductor is cylindrical.
3. The directional signal coupler-divider of claim 1, wherein a characteristic impedance of the transmission airline is 50 Ohms.
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 vector 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, magnetically induced and capacitively coupled currents inside the coupling loop of a wire coupler.
(5) FIG. 4 depicts prior art, definition of transmission, reflection, division and coupling RF parameters in a directional coupler.
(6) FIG. 5 depicts coupling, isolation, and division characteristics of the embodiment of the present invention.
(7) FIG. 6 depicts a detail of an embodiment of the signal coupler-divider in a hybrid load pull system (see ref. 8).
(8) FIG. 7 depicts an embodiment of the wideband signal coupler divider integrated in an impedance tuner housing.
(9) FIG. 8 depicts a common implementation and embodiment of the signal coupler-divider in a hybrid (active plus passive) vector load pull tuner system.
(10) FIGS. 9A through 9B depict a second embodiment of the signal coupler-divider using two adjacent U-shaped wire loops: FIG. 9A depicts the concept; FIG. 9B depicts coupling behavior from 0.4 to 4 GHz.
DETAILED DESCRIPTION OF THE INVENTION
(11) The directional signal coupler-divider uses a slotted low loss transmission airline or a slabline which is popular in air-based couplers (see ref. 5 and 6). The advantages offered by this method are twofold: a) it is mechanically simpler than a microstrip line (see ref. 3); b) it offers an in-situ embodiment of a divided port. The strong concentration of electric field in the zone between signal conductor and close-by wire loop (FIG. 3) leads to higher induced electric currents, in the wire loop sensor, which increases the coupled signal and decreases the isolated signal, thus increasing the coupling and directivity at the same time. If one branch is split, FIG. 4, adding a fifth port 5, the simple bi-directional signal coupler becomes a coupler-divider. The quantity describing this is called division D(2) as follows equations 1 and 2:
D(2)=S51+S52*S21*2/(12*S22)S51+S52*2{eq. 3}
If S51=0 then, as before, D(2)=S52*2.
(12) The coupling and isolation mechanism, first described in ref. 6 works as follows (FIG. 3): the RF signal current Is inside the signal conductor 30 creates a magnetic field H around it. This pulsing magnetic field H, 32 couples into the parallel running wire loop sensor 31-33 and creates a magnetically induced current I.sub.H which flows from branch 33 through the bottom of the U shaped loop 34 into branch 31. Since the bottom of the wire loop sensor runs parallel to the signal conductor 30 there is a capacitive coupling between the two. This capacitive coupling induces, capacitive current I.sub.E into either 50 Ohm terminated branches 31 and 33. These currents are proportional to the electric field in this region. Inside branch 33 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 branch 31 these currents run antiphase and subtract. The total signal power in the load to branch 33 is therefore |I.sub.E+I.sub.H|.sup.2*Zo and in branch 31 |I.sub.HI.sub.E|.sup.2*Zo. This creates both the forward coupling into branch 33 and the isolation in branch 31.
(13) 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 the difference I.sub.H-I.sub.E in branch 31 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.
(14) FIG. 5 shows wideband behavior of the simple coupler divider from a few hundred MHz up to 18 GHz and beyond. Directivity is, as expected between 10 and, mostly, 20 dB. The emphasized area 60 in FIG. 6 (see ref. 8) shows the embodiment of an application where the implementation of a coupler-divider, with inherently larger bandwidth, as shown in FIG. 4, saves an external power-divider/combiner. The coupler-divider samples signal for instantaneous wave measurement by the vector network analyzer and splits, at the same time, part of the signal into the active feedback loop.
(15) This double function of the coupler-divider is best demonstrated in FIG. 8: The outgoing signal 80 from the DUT is split by the coupler into branches 81 and 82; branch 82 is split into branch 88 and 89; branches 81 and 89 are fed into the ports of the VNA to measure instantaneously the power waves 80 and 83 and calculate the actual reflection factor <a>/<b> at the ports of the DUT, generated by the active feedback loop 88-87-86 including the coupler and the amplifier 87 in combination with the passive pre-matching passive tuner 85, which, in itself creates an added passive reflection 84.
(16) FIG. 9A depicts an alternative embodiment of the signal coupler-divider device; in this case the two wire loops are joined and have a common central branch, leading to originally used isolation port 4; port 5 is the second branch of the second wire loop and leads to the division port 5. Ports 1 and 2 are, as before, input and output ports of the slotted airline and port 3 is the original coupled port. The specific coupler has been designed to reach to low frequencies below 1 GHz, but the concept is valid for any frequency range and covers at least one frequency decade Fmax/Fmin=10, as shown in FIG. 9B.
(17) FIG. 7 is a view of an implementation of the signal coupler-divider as part of the passive tuner, showing that the test setup of FIG. 8 could be further simplified, if the coupler-divider were integrated inside the tuner housing.
(18) In conclusion the new coupler-divider embodiment is superior in coupling to alternative embodiments and superior in directivity. Obvious alternatives and modifications to the herein disclosed general concept of the use of a wire coupler with one spit branch for making a wideband coupling-dividing and high directivity wire coupler shall not impede in the validity of the invention.
