JPH0325081B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a polarization demultiplexer that separates a pair of circular TE ₁₁ modes in which electric lines of force propagating in a circular waveguide are orthogonal with low loss and high separation. .

Prior Art First, in the present invention, a pair of circular TE ₁₁ mode waves (hereinafter referred to as V and H waves)
propagates from left to right in the drawing (hereinafter referred to as the positive propagation direction), and these two
Only the case of demultiplexing waves will be described, and the opposite case of combining two waves can be explained in the same manner, so the description will be omitted. Furthermore, in the drawings below, arrows marked V or H represent the direction of polarization (direction on the diameter of the electric field vector).

Conventionally, there have been types of V and H wave polarization splitters using circular waveguides as shown in FIGS. 6A and 6B and 7A and 7B.

In Figures 6A and B, one circular TE ₁₁ mode wave (V wave) is transmitted from the tube wall on the diameter parallel to the electric force line to the probe (metal probe) 1 while maintaining insulation from the tube wall. Insert an appropriate length into the waveguide 2, and parallel to the V-wave electric line of force from a starting point at a predetermined distance approximately equal to a quarter of the wavelength in the tube in the positive propagation direction from the probe 1. A plurality of straight thin metal rods 3 spanning both ends of the diameter are arranged at regular intervals on a diameter of Derive to.
The thickness of the straight metal thin rod 3 is made so thin that it exhibits only a negligible susceptance component to the other orthogonal mode wave, H wave. The light is transmitted through the rod 3 with almost no reflection and propagates to the right of the circular waveguide 2, where it is separated into V waves and H waves.

In this method, a plurality of thin metal rods 3 must be arranged at predetermined intervals in the propagation direction of the circular waveguide 2 in order to achieve a short-circuit state of the mode wave taken out from the probe 1, so it can be used as a polarization splitter. It had the disadvantage of being long in the propagation direction.

In addition, in Figures 7A and B, a pair of orthogonal circles
The end of the circular waveguide 4 that propagates the TE ₁₁ mode wave is short-circuited in the usual way by terminating it with a metal plate 5, and the H The H wave is led out of the circular waveguide 4 by inserting the probe 6 into the tube by an appropriate length from the tube wall on a diameter parallel to the wave's electric lines of force.
Furthermore, at a point where the propagation returns in the negative direction of the tube by approximately three-quarters of the wavelength from the short-circuit surface, the probe 7 is inserted into the tube from the tube wall on the diameter parallel to the electric line of force of the other mode wave, the V wave. The V wave is guided out of the circular waveguide 4 by inserting it by a certain length.

In this method, as shown in Fig. 8, when the circular waveguide 4 with short-circuited terminals is considered as a transmission line, the potential at each point in the propagation direction becomes like a curve c ₀ with respect to frequency ₀ . . However, points A and B are points at one-fourth and three-quarters of the internal wavelength from the terminal, respectively, with respect to frequency ₀ . For the frequency ₁ = ₀ + Δ, which is slightly away from ₀ , the curve becomes like c ₁ , and the potential difference ΔV ₁ (see Figure 3c) for the above two frequencies at point A is clearly the same as that at point B ΔV ₂ (see Figure 3c).
This means that at points A and B, the impedance difference at frequencies ₀ and ₁ when looking in the positive direction of propagation is more pronounced at point B than at point A, and probe 7 in FIG. 7 is more pronounced than probe 6. This also shows that it is difficult to achieve impedance matching over a wide range of frequencies.

As described above, the methods shown in FIGS. 7a and 7b also have the disadvantage that broadband matching of one probe is difficult.

In addition, in Figures 7a and 7b, d ₁ = d ₂ , that is, when a pair of orthogonal probes is placed at the same point in the propagation direction, the distance between the two probes is too close, and the inside of the pipe near the probe It can be experimentally confirmed that disturbances in the electromagnetic fields affect each other's probes, and the degree of separation between the two orthogonal mode waves deteriorates.

Problems to be Solved by the Invention As described above, in the conventional example shown in FIG. Because it is necessary to install the thin metal rod 3,
As a polarization splitter, it has the disadvantage that its dimensions are long in the propagation direction, and in the conventional example shown in Figure 7, it is difficult to match the impedance of one probe over a wide frequency band. It had drawbacks.

The present invention solves the problem that the dimensions are long in the propagation direction as in the first conventional example, and the difficulty in achieving impedance matching over a wide frequency band as in the second conventional example. This is an attempt to resolve the issue.

Means for Solving the Problems In the present invention, a pair of circular shapes whose electric lines of force are perpendicular to each other
For the TE ₁₁ mode, we installed a thin metal plate with extremely short dimensions in the propagation direction in the circular waveguide, which acts as a short circuit for one mode and acts as a transmitter for the other mode. Features.

Effects According to the present invention, by using the metal thin plate described above, it is possible to solve the first problem of the conventional method, which is that the length of the waveguide becomes longer in the propagation direction. In addition, approximately 4
By providing a probe at a distance of one-tenth of the inner wavelength, the mode wave reflected from the thin metal plate can be guided out of the waveguide from the probe, and two probes are used as shown in FIG. 6 of the conventional example. Even if
By placing the above metal thin plate between the two probes and at the end, the distance between each probe and the metal thin plate can be reduced to approximately 1/4 of the tube wavelength, allowing a wide range of frequencies for each mode wave. Impedance matching can be achieved throughout. Therefore, the second problem mentioned above can also be solved.

Embodiment Hereinafter, an embodiment of the present invention will be described in FIGS. 1 to 5.
This will be explained using figures.

First, the coordinate system of the circular waveguide 11 is shown in Fig. 2A and B.
In the cylindrical coordinate system (r, z), each coordinate component (E _r , E, E _z ) of the electric field vector E→ of the circular TE ₁₁ mode is expressed as follows.

E _r =jωμ1/rA・J ₁ (u′ ₁₁ /ar) ・sin・e ^-j 〓 ^z E=jωμu′ ₁₁ /aA・J′ ₁ (u′ ₁₁ /ar) ・cos・e ^-j 〓 ^z E _z =0 where a is the inner radius of the circular waveguide 11, u' ₁₁
is the first root of the linear function of the Betzel function J ₁ (x) (u′ ₁₁ >0), β is the propagation constant of the circular TE ₁₁ mode, and A is a constant proportional to the electric field strength. be.
Note that we are considering the case of a mode parallel to the radius vector when the electric field vector is =90°. Round
The electric field vector of the TE ₁₁ mode does not have a component E _z in the propagation direction of the circular waveguide 11, and the lines of electric force, which are the loci at each point of the electric field vector, have a shape as shown in FIG. 3A.

Now, at each point on the circular cross section in Figure 3A,
If the loci of vectors perpendicular to these lines of electric force are drawn, a group of curves as shown in FIG. 3B will be obtained. Although the explanation will be omitted here, the group of curves shown in FIG. 3B corresponds to the locus of the (r,) component (also referred to as transverse component) of the magnetic field vector of the circular TE ₁₁ mode.
FIG. 3C is a linear approximation of the curve group in FIG. 3B.

Next, as shown in FIG. 1, a thin metal plate 13 having a narrow band-shaped metal piece 12 that approximately corresponds to the locus of a vector perpendicular to the electric line of force of the circular TE ₁₁ mode, as shown in FIG. Consider a case where the circular waveguide 11 is inserted into a cross section perpendicular to the propagation direction. Figure 3D
In the case where the electric lines of force in the circular TE ₁₁ mode and the fine-diameter metal piece 12 of the thin metal plate 13 are approximately orthogonal, at each point of the metal piece 12 of the thin metal plate 13, the vector product n→×E→( (n is the normal vector to the metal piece 12 as shown in FIG. It is thought that it will never happen. (If n→×E→ has a certain finite value, it can be considered that a disturbance electromagnetic field is generated by the point source n→×E→ according to electromagnetic field theory). This means that
This means that the mode wave is transmitted through this thin metal plate 13 with almost no influence. On the other hand, for the other mode wave orthogonal to the mode wave, most of each metal piece 12 of the thin metal plate 13 in FIG. , the mode wave is almost in a short-circuit state. Therefore, this mode wave is almost completely reflected by the thin metal plate 13. This thin metal plate 13 basically functions as described above, but despite the small diameter of the metal piece 12, the susceptance of the metal part at the focusing part cannot be ignored, and it has a negative effect on the transmission mode wave. It exhibits inductive susceptance (see FIG. 3E), and it is necessary to add capacitive susceptance (see FIG. 3F) to cancel this. For this purpose, a portion of the strip metal piece 12 is arranged in a straight line to provide capacitance.

The thin metal plate 13 obtained as described above is shown, for example, in FIGS. 1B and 1C. An example of actually measuring the transmission and reflection characteristics of this thin metal plate 13 will be shown below. In a circular Al waveguide with an inner diameter of 15.8 mm, as shown in Figs. 4A and B and 5 A and B, a 0.2 mm thick brass metal is placed at one point on the propagation axis of the circular waveguide 11. The thin plate 13 was inserted perpendicularly to the propagation axis, and the reflection loss and transmission loss were actually measured in relation to the polarization direction and the orientation of the metal piece 12 as shown. However, the measurement frequency is a sweep signal of 11.7-12.7GHz. In the case of Fig. 4 A and B (when the circular TE ₁₁ mode wave passes through the thin metal plate 13), the maximum value of the return loss (return loss at the signal input end (left side of the drawing)) within the above frequency band is -25 dB, while in the case of Fig. 5 A and B (when the circular TE ₁₁ mode wave is reflected by the thin metal plate 13), the above frequency band of transmission loss (rate of leakage to the signal output end (right side of the drawing)) The maximum value within this range was -22 dB.

An embodiment of the present invention will be described below. As a polarization demultiplexer in a circular waveguide in which a pair of circular TE ₁₁ mode waves with orthogonal electric lines of force propagate, one of the demultiplexed mode waves is guided out of the waveguide by a probe, and the other mode is There are two types: a type in which the wave remains within the original circular waveguide, and a type in which both mode waves are separately led out of the waveguide using two props. In this embodiment, the latter type will be described. Embodiments of the former type are possible as well.

1A, B, and C are diagrams showing an embodiment of the present invention, in which a pair of circular TE ₁₁ mode waves whose electric lines of force are perpendicular to each other propagate to the right in the circular waveguide 11, and the propagation direction Probes 14 and 15 for guiding V and H mode waves out of the waveguide 11 at points A and B, respectively, are placed parallel to the electric lines of force of the V and H mode waves and on the diameter of the circular waveguide 11. The waveguide 11 is inserted from outside the waveguide 11 through the tube wall so that its central axis is at . However, in order to keep the probes 14 and 15 insulated from the tube wall,
Probe 1 with dielectric material 16, 17 such as Teflon
It is surrounded by metal rods numbered 4 and 15. moreover,
The aforementioned thin metal plates 13a and 13b are placed in a plane perpendicular to the central axis of the circular waveguide 11 at a point where the probes 14 and 15 have advanced in the positive direction of propagation by a distance approximately equal to one quarter of the wavelength in the tube. It is arranged.

With such a configuration, the above-mentioned thin metal plate 13
Due to the action of a and 13b and the action of probes 14 and 15, the H wave is split and output from the probe 14,
The probe 15 outputs a divided V wave. Note that the probes 14 and 15 and the dielectrics 16 and 17
The thickness, shape, length of insertion into the tube, and probe 1
The optimum distance between 4 and 15 and the metal thin plates 13a and 13b is determined so that impedance matching for each mode wave can be achieved, that is, a circular waveguide input, that is, a constant position when looking from the left side of the figure to the right side. The wave ratio is determined to be the minimum. However, probe 14,
It is assumed that the output terminal of No. 15 is terminated with a matched load, for example, 50 ohms.

Effects of the Invention As described above, according to the present invention, a circular TE _11- mode polarization splitter can be realized in which the length of the circular waveguide in the propagation direction can be extremely reduced and the impedance matching is good over a wide frequency band. Manufacturable. The thin metal sheet of the present invention is an aggregate of strip-shaped metal pieces with minute diameters as described above, but it also has the advantage of being able to be manufactured in large quantities with high precision through photo etching processing, etc., and has great industrial value. be.

[Brief explanation of drawings]

FIGS. 1A, B, and C are partial side sectional views of a circular TE ₁₁ mode polarization splitter according to an embodiment of the present invention, Y-
Y' sectional view,
D, E, F, FIGS. 4A, B, and 5A, B are diagrams for explaining the structure of the metal thin plate and its effects in the present invention, FIGS. 6A, B, and 7
Figures A and B are partial side cross-sectional views and front views of conventional polarization duplexers, respectively. Figure 8 is a characteristic diagram for explaining the action of the polarization duplexer in Figure 7, and Figures 9A, B is a partial side sectional view and a front view of another conventional polarization splitter having a slot. 11...Circular waveguide, 12...Metal piece, 13...
...Thin metal plate.

Claims (1)

[Claims] 1. A pair of circular waveguides in which a pair of circular _TE11 modes whose electric lines of force are orthogonal to each other propagate, at least one
A probe located on the tube wall on a diameter parallel to the electric field lines of the TE ₁₁ mode is provided, and approximately 1/4
It is located at a distance of the tube wavelength and in a plane perpendicular to the propagation direction, and has a short-circuiting effect on the above TE ₁₁ mode and a transmitting effect on the other TE ₁₁ mode,
and try to lead it out of the tube with a probe.
A thin metal plate made up of a plurality of narrow metal strips that are perpendicular or approximately perpendicular to the lines of electric force in modes other than the TE ₁₁ mode is provided, and in the metal thin plate, the tube wall of the circular waveguide is The strip-shaped metal pieces converge in the vicinity, and in order to cancel out the inductive component that the thin metal plate presents to the mode transmitted by the two converging parts, some of the strip-shaped metal pieces are arranged in a straight line to create a capacitive A polarization demultiplexer characterized by having: