Rat race circuit

Abstract

To provide a rat race circuit capable of matching a frequency with the best reflection characteristic, a frequency with the best transmission characteristic, and a frequency with the best isolation characteristic.SOLUTION: A rat race circuit 1 includes a first port P1, a second port P2, a third port P3 and a fourth port P4 provided in that order on a ring-shaped conductor line RC, and the length of the line R12 between the first port P1 and the second port P2, the length of the line R23 between the second port P2 and the third port P3, and the length of the line R34 between the third port P3 and the fourth port P4 are set to be longer than 1 / 4 wavelength by the amount of shift of the phase reference plane of the high-frequency current at the branch point between the conductor line RC and each of the ports P1 to P4, such that the reflection, transmission, and isolation characteristics of each of the ports P1 to P4 are optimal near a predetermined frequency.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a rat-race circuit used as a branch circuit in the microwave band and the like.

Background Art

[0002] A rat-race circuit is a high-frequency / microwave circuit composed of a microstrip circuit printed and wired on a dielectric substrate. As shown in FIG. 7, four ports P1 to P4 are provided, which are drawn out and wired at intervals of 1 / 4 wavelength, that is, at angular intervals of 60°, to a ring-shaped conductor line (ring-shaped line) RC with a circumference of 1.5 wavelengths (for example, see Patent Document 1). That is, when four ports P1 to P4 are provided at intervals of 1 / 4 wavelength with respect to the ring-shaped line RC having a circumference of 1.5 wavelengths, three lines R12, R23, and R34 with a length of 1 / 4 wavelength and one line R41 with a length of 3 / 4 wavelength are formed. Further, when the impedance of each port P1 to P4 is set to 50 Ω, the impedance of the ring-shaped line RC becomes 70.71 Ω, which is √2 times.

[0003] In such a rat-race circuit, when a high-frequency signal is input from the first port P1 at one end, it is output in half to the second port P2 adjacent thereto and the fourth port P4 skipping one port. Their amplitudes are the same, but the phases are different by 180°. At this time, no output is provided to the third port P3. Also, when a high-frequency signal is input from the third port P3, it is output in half to the second port P2 and the fourth port P4, and their amplitudes and phases are the same, and no output is provided to the first port P1.

[0004] Such operations and functions are reversible. When high-frequency signals with the same amplitude and in-phase are input from the second port P2 and the fourth port P4, a signal obtained by adding the signals input from the second port P2 and the fourth port P4 is output from the third port P3. At this time, no output is generated from the first port P1. Also, when high-frequency signals with the same amplitude and opposite phases (phase difference of 180°) are input from the second port P2 and the fourth port P4, a signal with an amplitude twice that obtained by adding the signals input from the second port P2 and the fourth port P4 is output from the first port P1. At this time, no output is generated from the third port P3. Such non-output characteristics are referred to as isolation characteristics.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in a conventional rat-race circuit, since the lengths of the lines R12, R23, and R34 between adjacent ports P1 to P4 are 1 / 4 wavelength, the present inventors have confirmed that there is a problem in that the frequency at which the reflection characteristics of each port P1 to P4 are optimal, the frequency at which the transmission characteristics are optimal, and the frequency at which the isolation characteristics are optimal do not match.

[0007] That is, when the center frequency to be used is 2.45 GHz, as shown in FIGS. 8 and 9, the frequency at which the reflection characteristics are optimal is located at a frequency higher than the center frequency. Here, in FIGS. 8 and 9, "S1,1" indicates the reflection characteristics (S parameter) of the first port P1, "S2,2" indicates the reflection characteristics of the second port P2, "S3,3" indicates the reflection characteristics of the third port P3, and "S4,4" indicates the reflection characteristics of the fourth port P4.

[0008] Also, when a high-frequency signal is input from the first port P1, the isolation characteristic that no output is produced from the third port P3 is optimal at approximately the center frequency, as shown in FIG. 10. On the other hand, when a high-frequency signal is input from the first port P1, the frequencies at which the transmission characteristics and transfer characteristics output from the second port P2 and the fourth port P4 are optimal are located at frequencies higher than the center frequency, as shown in FIG. 11. Here, in FIGS. 10 and 11, "S2,1" indicates the S parameter from the first port P1 to the second port P2, "S3,1" indicates the S parameter from the first port P1 to the third port P3, and "S4,1" indicates the S parameter from the first port P1 to the fourth port P4.

[0009] Therefore, an object of the present invention is to provide a rat-race circuit capable of matching (bringing closer) the frequency at which the reflection characteristic is optimal, the frequency at which the transmission characteristic is optimal, and the frequency at which the isolation characteristic is optimal.

Means for Solving the Problem

[0010] In order to solve the above problems, the invention according to claim 1 is a rat-race circuit in which a first port, a second port, a third port, and a fourth port are provided in order on a ring-shaped conductor line, and the phase reference plane of the high-frequency current at the branch portion between the conductor line and each port is shifted by an amount such that the reflection characteristic, the transmission characteristic, and the isolation characteristic of each port are optimal in the vicinity of a predetermined frequency. The lengths of the lines between the first port and the second port, between the second port and the third port, and between the third port and the fourth port are set to be longer than a quarter wavelength.

Effect of the Invention

[0011] According to the invention of claim 1, the lengths of the lines between the first port and the second port, between the second port and the third port, and between the third port and the fourth port are set to be longer than a quarter wavelength so that the reflection characteristics, transmission characteristics, and isolation characteristics of each port are optimized in the vicinity of a predetermined frequency (center frequency). Therefore, it is possible to make (bring closer) the frequency at which the reflection characteristics of each port are optimized, the frequency at which the transmission characteristics are optimized, and the frequency at which the isolation characteristics are optimized coincide.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

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Figure 7

Figure 8

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Figure 10

Figure 11

Embodiment for Carrying Out the Invention

[0013] Hereinafter, this invention will be described based on the illustrated embodiments.

[0014] FIG. 1 is a plan view showing a rat-race circuit 1 according to an embodiment of the present invention. This rat-race circuit 1 is a high-frequency circuit composed of a microstrip circuit printed and wired on a dielectric substrate, and has the same configuration as a conventional rat-race circuit except for the arrangement intervals of ports P1 to P4.

[0015] In the rat-race circuit 1, a first port P1, a second port P2, a third port P3, and a fourth port P4 are sequentially provided on a ring-shaped conductor line (ring-shaped line) RC. And, in the vicinity of a predetermined frequency, that is, in the vicinity of the center frequency to be used, the lengths of the line R12 between the first port P1 and the second port P2, the line R23 between the second port P2 and the third port P3, and the line R34 between the third port P3 and the fourth port P4 are set to be longer than 1 / 4 wavelength of the center frequency so that the reflection characteristics, transmission characteristics, and isolation characteristics of each of the ports P1 to P4 become optimal.

[0016] That is, the angular intervals between the first port P1 and the second port P2, between the second port P2 and the third port P3, and between the third port P3 and the fourth port P4, which are drawn out from the ring-shaped line RC, are set to be larger than the conventional 60° (in this embodiment, to 60.2°). Further, the length of the line R41 between the first port P1 and the fourth port P4 is set to the same 3 / 4 wavelength as in the prior art. Therefore, the total circumference length of the ring-shaped line RC is set to be longer than the conventional 1.5 wavelengths (the diameter φ1 of the ring-shaped line RC is set to be larger than the conventional diameter φ2).

[0017] Thus, setting the lengths of line R12, line R23, and line R34 to be longer than a quarter wavelength is because at the branching portion (root portion) where ports P1 to P4 branch off from the ring-shaped line RC, the phase reference plane of the high-frequency current is shifted from the center of the branching portion. That is, when forming a T-branch with a microstrip line, it is known that the phase reference plane of the high-frequency current propagating through the line is located at a position slightly shifted from the center of the intersection of the T-branch (the shifted positions d1 and d2), as shown in FIG. 2.

[0018] The amounts of shift d1 and d2 at this time are calculated by the following calculation formulas. That is, f: Frequency [GHz] t: Plate thickness [mm] ε eff : Effective dielectric constant Z1: Impedance of the main line Z2: Impedance of the branch line d1: Phase reference plane offset of the main line d2: Phase reference plane offset of the branch line Then,

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[0019] Such a deviation also occurs at the branch of the rat-race circuit 1. When the lengths of the line R12, the line R23, and the line R34 are set to 1 / 4 wavelength, the phases of the line R12, the line R23, and the line R34 do not match those of the 3 / 4 wavelength line R41. Therefore, the inventors of the present application considered that it is necessary to make the lengths of the line R12, the line R23, and the line R34 longer than 1 / 4 wavelength by the amount of deviation of this phase reference plane (in the case of a T-branch, twice the amount of deviation d1).

[0020] Therefore, based on (referring to) the deviation amount d1 in the T-branch of the microstrip line, the lengths of the line R12, the line R23, and the line R34 are set to be longer than 1 / 4 wavelength so that the reflection characteristics, transmission characteristics, and isolation characteristics of each port P1 to P4 are optimal in the vicinity of the center frequency.

[0021] Specifically, when the diameter φ1 of the ring-shaped line RC is 30 to 40 mm, it is set to be several tenths of a millimeter longer than 1 / 4 wavelength, and this extension amount is a value that is orders of magnitude larger than the thickness of the etching of the printed wiring (for example, 18 μm). Also, in this case, the diameter φ1 of the ring-shaped line RC is several tenths of a millimeter larger than the conventional diameter φ2 (FIG. 7). Note that the width D1 of the ring-shaped line RC and the widths D2 of each port P1 to P4 are the same as the conventional widths D3 and D4 (FIG. 7).

[0022] According to the rat-race circuit 1 having such a configuration, the length of the line R12 between the first port P1 and the second port P2, the length of the line R23 between the second port P2 and the third port P3, and the length of the line R34 between the third port P3 and the fourth port P4 are set to be longer than 1 / 4 wavelength so that the reflection characteristics, transmission characteristics, and isolation characteristics of each port P1 to P4 are optimal in the vicinity of a predetermined frequency (center frequency). Therefore, it is possible to make the frequency at which the reflection characteristics of each port P1 to P4 are optimal, the frequency at which the transmission characteristics are optimal, and the frequency at which the isolation characteristics are optimal coincide (approach), that is, to make them the center frequency.

[0023] Furthermore, the length of the line R41 between the first port P1 and the fourth port P4 is set to 3 / 4 wavelength. That is, since the total length of the ring-shaped line RC is set to be longer than 1.5 wavelengths, it becomes possible to set (bring closer) the center frequency at which the reflection characteristic, the transmission characteristic, and the isolation characteristic are optimal to a desired frequency.

[0024] Here, the calculated values of the frequency characteristics of this rat-race circuit 1 are shown in FIGS. 3 to 6. When the center frequency to be used is 2.45 GHz, as shown in FIGS. 3 and 4, it can be confirmed that the frequency at which the reflection characteristic is optimal is near the center frequency. Here, in FIGS. 3 and 4, "S1,1" indicates the reflection characteristic (S parameter) of the first port P1, "S2,2" indicates the reflection characteristic of the second port P2, "S3,3" indicates the reflection characteristic of the third port P3, and "S4,4" indicates the reflection characteristic of the fourth port P4.

[0025] Also, as shown in FIG. 5, the isolation characteristic in which no output is produced from the third port P3 when a high-frequency signal is input from the first port P1 is optimal at approximately the center frequency. Furthermore, as shown in FIG. 6, it can be confirmed that the frequency at which the transmission characteristics output from the second port P2 and the fourth port P4 are optimal when a high-frequency signal is input from the first port P1 is near the center frequency. Here, in FIGS. 5 and 6, "S2,1" indicates the S parameter from the first port P1 to the second port P2, "S3,1" indicates the S parameter from the first port P1 to the third port P3, and "S4,1" indicates the S parameter from the first port P1 to the fourth port P4.

[0026] In this way, it can be confirmed that, compared with the frequency characteristics of the conventional rat-race circuit (FIGS. 8 to 11), the frequencies at which the reflection characteristic, the transmission characteristic, and the isolation characteristic of this rat-race circuit 1 are optimal are near the center frequency, which is the same frequency.

[0027] The embodiments of the present invention have been described above. However, the specific configuration is not limited to the above embodiments, and even if there are design changes and the like within the scope not departing from the gist of the present invention, they are included in the present invention. For example, in the above embodiments, the case where the rat-race circuit 1 is configured by a microstrip has been described, but it may be configured by a waveguide or the like other than the microstrip. Also, although the case where the ports P1 to P4 are drawn out outside the ring-shaped line RC has been described, it can also be applied to the case where the ports P1 to P4 are drawn out inside the ring-shaped line RC.

Industrial Applicability

[0028] The rat-race circuit according to the present invention can be used in the fields of radar devices, direction detectors, satellite tracking antennas for mobile bodies, and various electronic application devices.

Explanation of Reference Numerals

[0029] 1 Rat-race circuit RC Ring-shaped conductor line (ring-shaped line) P1 First port P2 Second port P3 Third port P4 Fourth port R12 Line between the first port and the second port R23 Line between the second port and the third port R34 Line between the third port and the fourth port R41 Line between the first port and the fourth port

Claims

[Claim 1] A rat race circuit in which a first port, a second port, a third port and a fourth port are provided in this order on a ring-shaped conductor line, the length of the line between the first port and the second port, the length of the line between the second port and the third port, and the length of the line between the third port and the fourth port are set to be longer than ¼ wavelength by the amount of shift of the phase reference plane of the high frequency current at the branching portion between the conductor line and each of the ports so that the reflection characteristic, the transmission characteristic, and the isolation characteristic of each of the ports are optimized in the vicinity of a predetermined frequency; A rat race circuit characterized by:

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