JPH0325042B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement of a magic T circuit composed of a microstrip line and a slot line. A conventional MIC magic T circuit is shown in a plan view in FIG. That is, the dielectric substrate 15
A microstrip line 11 and microstrip lines 12a, 12b branched from one end of this line 11 are provided on the surface of the substrate 15, and a cavity 14 is formed at the intersection of the lines 11, 12a, 12b on the back side of this substrate 15. A slot line 13 having the same structure is provided so as to be orthogonal to the microstrip lines 12a and 12b. In the figure, 1, 2, 3, 4 are each line 1
1, 12a, 12b, and 13 are input/output terminals.
Figure 2 shows terminal 4 to terminal 2 of Magic T in Figure 1.
3 shows an equivalent circuit of FIG. 2. In the figure, point P is the slot line 13 and the microstrip line 12.
31 is the equivalent circuit of the slot line 13,
32a and 32b are microstrip lines 12
In the equivalent circuit of a and 12b, 33 indicates the equivalent impedance Z of the cavity 14. In this configuration, the impedance of the slot line 31 is Z _S , the microstrip line 32a,
If the impedance of 32b is Z ₀ , the transformation ratio n
is practically equal to 1, so the matching condition for the circuit is as follows. Z _S =2Z ₀ /(1+2Z ₀ /Z) Here, if the impedance Z of the cavity 14 is ideally infinite, that is, if the slot line 13 is completely opened at point P in FIG. 2, then Z _S = = 2Z ₀ , and wideband matching can be realized that is limited only by the frequency characteristics of the characteristic impedance Z _S of the slot line. However, since a cavity in which Z is infinite cannot be realized, the matching range shown in FIG. 3 is limited by the frequency characteristics of Z. Therefore, in order to obtain a magic T circuit with a wider band, it is necessary that the cavity impedance Z is as high as possible. Incidentally, since the impedance of the slot line 13 or the cavity 14 shown in FIG. 2 is proportional to the width of the slot, it is desirable that the cavity 14 be as large as possible. In other words, by doing this, the slot line 13 is given a more complete open state at the point P, and the signal input from the terminal 4 is sent to the terminals 2 and 3 in reverse phase, thereby achieving a wide band and efficiency. It can be converted. 4 shows a plan view of a parallel T branch from terminal 1 to terminals 2 and 3 in the magic T shown in FIG. In this figure, since the lines 11, 12a, and 12b are microstrip lines, the back side must be a perfect conductor, and under this condition, the signal input from terminal 1 is transferred to terminals 2 and 3. Efficient conversion in the same phase. In this way, the conventional magic T shown in FIG.
It is constructed as a superimposed circuit of FIG. 2 and FIG. 4. Therefore, in order to efficiently convert signals from terminal 4 to terminals 2 and 3, it is necessary to make cavity 14 sufficiently large to provide a more complete open state to slot line 13. In addition, in order to distribute signals from terminal 1 to terminals 2 and 3, the cavity 14 is made as small as possible to sufficiently reduce disturbances in the electromagnetic field of the microstrip line, minimizing deterioration of VSWR and isolation characteristics. It is necessary to keep it within limits. In this way, conflicting conditions are required for the cavity 14 due to the selection of input/output terminals, and the conventional Magic T does not necessarily have good characteristics. Further, in order to open one end of the slot line 13, the same effect can be obtained by using a short-circuit line with a length of λ/4N or an open line with a length of λ/2N in place of the cavity 14. was an unavoidable drawback. An object of the present invention is to eliminate such drawbacks and provide a magic T circuit with better characteristics. The structure of the present invention includes a first microstrip line, second and third microstrip lines branched from one end of this line, a cavity, λ/4N (N is a positive odd number, In the magic T circuit, the branched second and second The microstrip line 3 surrounds the open end of the slot line, is symmetrically separated without intersecting the open line, and is placed on the open line of the slot line at an equal distance from the front branch point. Open ends extending by a length of λ/2 from the middle or midway of each of the microstrip lines are arranged to protrude so as to face each other so as to be electrically coupled to the slot line. It is characterized by The present invention will be explained in detail below with reference to the drawings. FIG. 5 is a plan view of an embodiment of the present invention, in which the same components as in FIG. 1 are given the same numbers. In the figure, point P is the connection point between the slot line 13 and the microstrip lines 12c (11a), 12d (11b), and each microstrip line protrudes into the slot of the slot line 13 in a loop shape. and are electrically coupled here. Point Q is a branching point where the microstrip line 11 is branched into lines 11a and 11b. In this embodiment, the branch point P of the microstrip line 11 and the connection point Q of the slot line 13 are separated, and the microstrip line 12
It is characterized in that c, 12d and the slot line 13 are coupled in a loop shape. Moreover, the cavity 14 is
At the same time as providing a sufficient opening condition at point P,
The microstrip lines 11, 12a, 12b are arranged so as not to affect the branch point Q. The operation of this Magic T is explained as follows.
The signal input from terminal 4 of slot line 13 is transmitted to microstrip line 12c at point P.
(11a) and 12d (11b) are excited in opposite phases.
Therefore, signals of the same level and opposite phase are outputted to the terminals 2 and 3 through the microstrip lines 12c and 12d. On the other hand, the microstrip line 1a,
Since the signal excited at point 11b has an opposite phase at point Q, which is equidistant from point P, no signal is output to terminal 1. Therefore, isolation between terminals 1 and 4 is maintained. On the other hand, a signal input from terminal 1 is distributed to microstrip lines 11a (12c) and 11b (12d) at point Q in the same phase, and in-phase signals at the same level are outputted to terminals 2 and 3. At point P, microstrip lines 11a (12c),
If the coupling portion between slot line 11b (12d) and slot line 13 is sufficiently short compared to the wavelength, there will be almost no effect on the output signals to terminals 2 and 3. Also, at point P, of course, the microstrip line 11a (12
c) and 11b (12d) are excited in the same phase, so there is no output signal to terminal 4. As explained above, the magic T of the present invention connects the slot line 13 to the microstrip line 12.
Branch point P to c, 12d and microstrip line 11 to microstrip line 12c, 12
Since the branch point Q to d is separated, the cavity 14 can be configured to completely open the slot line without affecting the microstrip line, which is better than the conventional Magic T. It can be seen that the following characteristics can be obtained. FIG. 6 is a plan view of a second embodiment of the invention. In the figure, 12e and 12f constitute part of microstrip lines 11a and 11b branched at point Q, respectively. In the figure, a signal input from terminal 4 of slot line 13 excites microstrip lines 12e and 12f at point P in opposite phases. This signal is branched into microstrip lines 12c and 11a or microstrip lines 12d and 11b,
Since they are in opposite phases, they cancel each other out at point Q,
No output signal is output to terminal 1. Furthermore, point Q becomes an equivalent short point for the signal input from terminal 4, as described above. Therefore, if the microstrip lines 11a and 11b are selected to be λ/4, the lines 11a and 11b will be connected at the branch point between the microstrip lines 12e and 12c and 11a, or between the microstrip lines 12f and 11b and 12d. The microstrip lines 12e, 12c, and 1212f are in an open state and do not affect signal transmission.
If the characteristic impedances Z ₀ of and 12d are selected to be the same, signals of the same level and opposite phases are efficiently output to terminals 2 and 3. Next, the signal input from terminal 1 is synchronously branched at point Q, and is connected to microstrip line 1.
1a and 11b, and the tracks 12c and 12, respectively.
The in-phase signal is distributed to e, 12d and 12f. By the way, since the lines 12e and 12f are open at a point, by selecting their length as λ/2, lines 11a to 12c and 12e and line 11b to 1
At the branch point to 2f and 15d, lines 12e and 45f can be opened. Therefore, if the characteristic impedances Z ₀ of the lines 11a and 12c and 11b and 12d are made the same, signals of the same phase and level are efficiently output from the terminal 1 to the terminals 2 and 3. Moreover, at point P, since the lines 12e and 12f are in phase, there is no excitation to the slot line 13, and the terminal 4
Since there is no output signal at , the isolation characteristics of terminals 1 and 4 are maintained in conjunction with the above-mentioned factors. As explained above, in the embodiment shown in FIG. 6, the line lengths of the lines 11a and 11b are λ/4, the line lengths of the lines 12e and 12f are λ/2, and the lines 11a, 11b, 12c, 12d, 12e, The line impedance of line 12f is Z ₀ , and the line impedance of line 11 is Z ₀ /
2. By selecting the line impedance of the line 13 to be 2Z ₀ , a magic T with good matching over a wide band can be realized. However, since the lines 11a and 11b are open when viewed from the terminal 4 side, the line 11
By using a and 11b as λ/4 impedance transformers, the characteristic impedances of the slot line 13 and microstrip line 11 can be selected independently. For example, if the impedances of lines 11 and 13 are Z ₁₁ and Z ₁₃ respectively, lines 12e and 12c,
The lines 12f and 12d are required to have a characteristic impedance of Z ₁₃ /2 due to impedance matching conditions with the slot line 13. On the other hand, since the characteristic impedances of the two microstrip lines branched from the microstrip line 11 can be matched at 2Z ₁₁ , the line impedances of the lines 11a and 11b are shown in FIG.

By setting [Equation], matched signal transmission from terminal 1 to terminals 2 and 3 is performed. As explained above, in the present invention, the cavity 14 and the microstrip line 11a (12c),
11b (12d) do not intersect and the branch points P and Q are separated, so it not only has better characteristics than the conventional magic T, but also has a microstrip line as mentioned above. There is also the effect that the impedances of the slot line 11 and the slot line 13 can be selected independently, and a compact Magic T with wide band matching can be realized. In this embodiment, the open end of the slot line 13 is explained using the cavity 14, but the same structure can be constructed using a short-circuit line with a length of λ/4 or an open line with a length of λ/2. is clear. As explained above, by using this invention, characteristics such as distribution and isolation between each input and output terminal, VSWR, etc. are improved compared to the conventional Magic T, and the impedance of each input and output terminal can be freely selected. Because of its high degree of power, it can be applied to modems, double-balanced mixers, etc. with full effect.

[Brief explanation of drawings]

Figure 1 is a plan view of the conventional MIC Magic T circuit.
Figure 2 is a plan view of the series branch section of a conventional Magic T, Figure 3 is an equivalent circuit diagram of Figure 1, and Figure 4 is the equivalent circuit diagram of Figure 1.
FIG. 5 is a plan view of the first embodiment of the present invention, and FIG. 6 is a plan view of the second embodiment of the present invention. In the figure, 1, 2, 3, 4...input/output terminals, 11, 11
a, 11b, 12a, 12b, 12c, 12d,
12e, 12f...Microstrip line, 1
3...Slot track, 14...Slot cavity,
15...Dielectric substrate, 31...Equivalent circuit of slot line, 32a, 32b...Equivalent circuit of microstrip line, 33...Equivalent impedance of cavity, P...Equivalent circuit of microstrip line and slot line The intersection point Q is the branching point between the microstrip line and the microstrip line.

Claims (1)

[Claims] 1. A first microstrip line, second and third microstrip lines branched from one end of this line, a cavity, λ/4N (N is a positive odd number, In the magic T circuit, the branched second and second The microstrip line 3 surrounds the open end of the slot line, is separated symmetrically without intersecting the open line, and is placed on the open line of the slot line at an equal distance from the branch point. Open ends extending by a length of λ/2 from the middle or midway of each of the microstrip lines are arranged to protrude so as to face each other so as to be electrically coupled to the slot line. The magic T circuit is characterized by: