JPS6216041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a circulator using striplines.

Non-reciprocal circuits using striplines include circulators, isolators, etc., but since an isolator is generally made by terminating one end of a circulator, the conventional technology will be explained here with respect to stripline circulators.

There are various types of stripline circulators, but when classified by the type of substrate used for the circuit, they can be divided into two types: those using ceramic substrates and those using ferrimagnetic substrates. Recently, due to advances in improved substrate manufacturing technology for ferrimagnetic materials, many stripline circulators using ferrimagnetic materials as substrates have been manufactured.

Figure 1 is a plan view of a conventional stripline circulator using this ferrimagnetic substrate;
The figure is a cross-sectional view taken along line X-X'. Reference number 1 is a ferrimagnetic substrate that functions as both a nonreciprocal element and a substrate, 10 is an internal conductor, 2 is a circular junction of the internal conductor 10, 3 and 4 are branch lines of the internal conductor 10, and 3 is an impedance. Impedance matching line with a length of 1/4 wavelength for matching, 4 is a transmission line, 6
5 is a ground conductor, and 5 is a magnet for applying magnetic bias perpendicularly to the ferrimagnetic material. Generally, the characteristic impedance of the stripline used in microwave circuits is selected to be 50Ω. Therefore, even in a circulator using a stripline,
The impedance of the connection point with the outside is generally determined to be 50Ω, depending on the characteristic impedance of the external line. The length of the 1/4 wavelength impedance matching line 3 is determined by the frequency used,
You cannot choose freely. Therefore, if the dimensions of the ferrite substrate are determined, it is necessary to provide a 50Ω transmission line 4 up to the connection point with the external circuit.

After metal is deposited on the ferrimagnetic substrate 1, only the surface thereof is etched, leaving the metal on the side facing the outer conductor 6 as is, to obtain the inner conductor 10. The structure will be further described in the case where YIG (yttrium iron garnet) is used as the ferrimagnetic substrate 1. First, if the thickness of the YIG substrate is 0.635 mm, which is the same as the ceramic substrate often used in general microwave integrated circuits, then the conductor width of the transmission line 4 with a characteristic impedance of 50Ω provided on the ferrimagnetic substrate 1 Since the dielectric constant ε of YIG is about 14, the
microwave engineer′s hand−book and buyer′s
When calculated using the graph on page 95 of "Guide", 1968, it is approximately 0.35 mm. When the stripline circulator shown in FIG. 1 is used in a microwave circuit, it is necessary to connect it to a coaxial plug or a board made of ceramic or Teflon glass fiber. When making this connection, since the conductor width of the line 4 is as narrow as 0.35 mm, electrical discontinuity occurs at the connection part, making it difficult to obtain stable electrical characteristics, and mechanically the strength of the connection part is weakened, making soldering extremely difficult. There are disadvantages such as difficulty in

The purpose of the present invention is to eliminate these drawbacks.
It is an object of the present invention to provide a stripline circulator having a wider conductor width at a connection part with an external circuit.

According to the present invention, an inner conductor is formed that has a junction, a branch line configured of an impedance matching line connected to the junction, and a transmission line connected between the impedance matching line and an external circuit. In a circulator consisting of a ground conductor and a magnet attached to a ferrimagnetic substrate, a capacitive line wider than the transmission line is installed on the surface of the ferrimagnetic substrate and at the connection end between the transmission line and the external circuit. A circulator is obtained, in which the length of the capacitive line is equal to or less than ⅛ wavelength of the operating frequency.

The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a plan view of a stripline circulator using a ferrite substrate according to the present invention. The line 7 is newly provided according to the present invention. This is a short line having a characteristic impedance lower than the characteristic impedance of 50Ω of the transmission line 14 provided at the connection end between the circulator and the external circuit. The length of this line 7 is desirably 1/8 wavelength or less so that the capacity is concentratedly added to the line. The thickness of board 1 is 0.635 mm (line 1
4 is approximately 0.35 mm), the conductor width and length of this line 7 are determined to be 0.6 mm or more and 0.8 mm or more, respectively, in order to facilitate electrical and mechanical connection with an external circuit. That is, the line 7 is formed on the surface of the substrate 1 at the connection end between the transmission line 14 and the external circuit, and is a capacitive line that is wider than the transmission line 14. Here, if only the structure of the connecting end of the conventional circulator as shown in Fig. 1 is changed,
Since the characteristics of the circulator change depending on the capacitance exhibited by the newly added line 7, it is necessary to slightly change the characteristic impedance and length of the impedance matching line 13 in advance. For example, if the length of the line 7 is slightly shorter than ⅛ wavelength, good impedance matching can be obtained by making the impedance slightly lower than in the case of FIG.

The present invention will be further explained using the Smith chart shown in FIG. In FIG. 4, point A is the impedance (normalized impedance: 50Ω) of the connection between the circular junction 12 and the impedance matching line 13, and the point
A' is the impedance obtained by normalizing the impedance at point A with the impedance of the matching line 13, locus A-B is the impedance due to the length of the matching line 13, and point B' is the connection between the matching line 13 and the transmission line 14. represents the impedance (normalized impedance: 50Ω). Next, depending on the length of the transmission line 14, the impedance of the connection between the lines 14 and 7 becomes point C. The above is an impedance diagram, but when this is converted into an admittance diagram, point C moves to point C'. Due to the capacitive line 7 added here, point C' is moved to point D and matched. Even if the external capacitive line 7 is added in this way, matching can be easily achieved by changing the length of the impedance matching line 13 and its impedance.

As described above, if the circuit according to the present invention is used,
It is easy to connect the circulator using a magnetic substrate with external circuits by soldering, etc., and at the same time, the stripline circulator has stable characteristics without deterioration of characteristics due to electrical discontinuity at the connection part. rate can be realized.

In the previous examples, ε = 14, and the thickness of the substrate
Although we have explained the case of 0.635 mm, if ε is larger or the thickness of the board is thinner, the conductor 14
Since the width of 0.35 mm is smaller than 0.35 mm, the application of the present invention will produce a greater effect.

Although the outline of the present invention has been described above regarding a circulator with three branch lines, it goes without saying that the present invention can also be applied to an isolator in which one terminal of the circulator is terminated, or a circulator having three or more branch lines.

[Brief explanation of the drawing]

Figure 1 is a plan view of a conventional stripline circulator, Figure 2 is its XX' cross-sectional view, and Figure 3
The figure is a plan view of the stripline circulator according to the present invention, and FIG. 4 is a Smith diagram for explaining the impedance matching state of the circulator according to the present invention. In the figure, 1...Ferimagnetic substrate, 2...Circular connection part, 3...
1/4 wavelength impedance matching line, 4... transmission line, 5... magnet, 6... ground conductor, 7... line added to the circulator according to the present invention.

Claims (1)

[Claims] 1 Ferrimagnetism in which an inner conductor is formed that has a junction, an impedance matching line connected to this junction, and a branch line consisting of a transmission line connected between this impedance matching line and an external circuit. In a circulator consisting of a body substrate, a ground conductor and a magnet attached to the ferrimagnetic substrate, a circulator having a width wider than the transmission line is provided on the surface of the ferrimagnetic substrate and at a connection end between the transmission line and the external circuit. What is claimed is: 1. A circulator characterized in that a capacitive line with a wide width is formed, and the length of the capacitive line is 1/8 wavelength or less of the operating frequency.