JPH018002Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to improving the performance of a diode switch constructed of fine lines.

FIG. 1 shows an example of the structure of a diode switch constructed using a conventional finline.

A dielectric plate 2 is arranged approximately in the center of the wide surface of the waveguide 1 in parallel to the electric field, and a metal film 4 with a gap 3 provided along the radio wave propagation direction is adhered to the surface of the dielectric plate 2. There is. Further, diodes 5 are connected to the metal film 4 at predetermined intervals by bonding, soldering, etc. so as to bridge the gap.

The diode switch of the configuration example shown in FIG. 1 switches the polarity of the bias applied to the diode 5 in forward and reverse directions to cut off and pass radio waves propagating through the fin line.

That is, in the forward bias state, the impedance exhibited by the diode 5 becomes a low impedance, so that the microwave current flowing along the slit 3 is short-circuited and cut off, whereas in the reverse bias state, the diode 5 exhibits a high impedance. A passing state is obtained without affecting the microwave current.

Further, usually, a plurality of diodes 5 (two in the figure) are connected at predetermined intervals to improve isolation characteristics and reflection characteristics.

Incidentally, a diode switch configured with a finline is often used in a high frequency band because the diode 5 can be easily attached, it can be easily converted into a waveguide, and the loss is relatively low. However, as the frequency becomes higher, the impedance that the diode 5 presents to the microwave in the reverse bias state becomes lower. Therefore, there was a drawback that the reflection characteristics in the passing state of the switch deteriorated.

In this invention, in order to eliminate this drawback, on the surface opposite to the dielectric plate surface on the side where the diode is installed,
In addition, a metal film is coated at a position facing the diode mounting portion, and the diode and the metal film are caused to resonate in parallel to increase impedance and obtain good reflection characteristics in the switch.

FIG. 2 shows an embodiment of this invention.

Figure 2a is a perspective view, Figure 2b is a cross-sectional view at the BB' position in a plane perpendicular to the radio wave propagation direction in Figure 2a, and Figure 2c is a cross-sectional view along the radio wave propagation direction in Figure 2b. FIG. 3 is a cross-sectional view at the CC' position of the plane.

A metal film 4 having a slit 3 is adhered to one surface of the dielectric plate 2, and two diodes 5 are installed at a predetermined interval so as to bridge the slit 3. A strip conductor 6 made of a metal film is attached to the other surface of the dielectric plate 2 at a position opposite to the mounting position of the diode 5. This strip conductor 6 constitutes a microstrip line using the fine line metal film 4 as a ground conductor. An equivalent circuit with this microstrip line loaded in a fine line is shown in FIG. At this time, the susceptance B when looking at the microstrip line side from the connection between the fine line and the microstrip line is given by B=-jN ² ·2/Yom _tao (θm/2+Δθm) (1). Here, Yom is the characteristic admittance of the microstrip line, θm is the electrical length of the microstrip line, and Δθm is the equivalent electrical length increment due to line end capacitance Coc. Further, N is the transformation ratio of the transformer representing the coupled state.

The value of admittance B exhibited by this microstrip line is determined only by the line's characteristic admittance Yom and electrical length θm, and does not depend on its shape.
That is, it is determined by the width W and length l of the strip conductor and is not dependent on its shape.

The susceptance that this strip conductor 6 exhibits with respect to the fin line is determined by the millimeter wave W-band waveguide.
Measurements were conducted using a finline constructed by attaching a dielectric substrate to WRJ-900. The measured values and calculated values are shown in FIG. Here, the actual measured value is the strip conductor when the wavelength of the finline at the design frequency is λ, the spacing S of the slit 3 is normalized by the wavelength and is 0.016, and the width W of the strip conductor 6 is normalized by the wavelength and is 0.063. These are the results measured for the total length l.
Note that the thickness of the dielectric plate 2 is standardized by wavelength.
It is 0.037.

It can be seen from this figure that the strip conductor exhibits capacitance when l/λ is 0 to 0.35, and inductive when l/λ is 0.35 or more.

Next, the diode 5 connected to the fine line
The measured admittance values in the 92 to 98 GHz band are normalized by the characteristic impedance Yo of the finline and are shown in FIG. The diode 5 used is a beam lead type diode. A forward bias of 10 mA and a reverse bias of 10 V were applied. In forward bias, it shows a large inductive property, and in reverse bias, it shows a state in which a capacitive susceptance of about 1.5 as B/Yo is loaded in parallel to the line.

Therefore, if an inductive susceptance is connected in parallel to the narrow gap of the finline connected to this diode 5, the diode 5 exhibits even greater inductivity in the forward bias state, approaching a short-circuit state, and vice versa. In the bias state, it cancels out the capacitance of the diode 5, making it possible to bring the parallel loading susceptance close to zero. This is the case when an inductive susceptance equal to the capacitive susceptance of the diode is connected to 1.5, and from Fig. 4, l/λ
This can be achieved by setting 0.5.

Figure 6 shows the insertion loss and isometry at a fractional band of 6% in the W band when two diodes 5 are connected in a fine line at intervals of approximately 3/4λ and a strip conductor 6 is provided at a position facing the diodes 5. The actual measured values of ration and VSWR are shown.

In the W band, broadband characteristics of VSWR of 1.5 or less were obtained over a 6% fractional band, and high isolation of around 40 bB was obtained.

In this way, by providing the strip conductor 6 made of a metal film at a position facing the mounting portion of the diode 5 on the dielectric plate 2 constituting the fin line, and setting the length to a value indicating the inductive susceptance, The susceptance can be reduced by causing parallel resonance with the capacitive susceptance of the diode in the reverse bias state.

Therefore, the reflection characteristics of the fineline diode switch in the millimeter wave band are low over a wide band.
It has the effect of increasing VSWR.

Further, although FIG. 2 shows an example in which two diodes 5 are used, this invention is not limited to this, and is effective even when one or three or more diodes 5 are used. Due to the effect of the strip conductor 6, the diode 5 exhibits low susceptance in the reverse bias state and high susceptance in the forward bias state, so even when one diode is used, a switch with low reflection at the center frequency can be realized.

Further, as shown in FIG. 7, the position where the strip conductor 6 is arranged may be slightly shifted from the position facing the diode 5. A similar effect can be achieved if part of the metal film of the strip conductor 6 faces the diode 5.

In the finline diode switch according to this invention, by providing a strip conductor made of a metal film at a position approximately opposite to the dielectric plate on which the diode is mounted, good characteristics are obtained in the passing state of the switch, and good characteristics are obtained in the cut-off state of the switch. High isolation can be obtained.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing the structure of a conventional finline diode switch, Fig. 2 is a diagram showing the structure of a finline diode switch according to an embodiment of this invention, and Fig. 3 shows a strip loaded on the finline. The equivalent circuit diagram of the conductor. Figure 4 shows the measured value of susceptance in the W band of a strip conductor loaded on the finline. Figure 5 shows the admittance at 92 to 98 GHz with a diode connected in parallel to the finline. Figure 6 shows the measured values of the switch characteristics in the W band of the finline diode switch according to the present invention, in which two diodes are connected to the finline at 3/4 wavelength intervals. FIG. 7 is a diagram showing the structure of another embodiment of the finline diode switch according to this invention. In the figure, 1 is a waveguide, 2 is a dielectric plate, 3 is a slit,
4 is a metal film, 5 is a diode, and 6 is a strip conductor. In the drawings, the same or corresponding parts are designated by the same reference numerals.

Claims (1)

[Scope of utility model registration request] A dielectric plate is placed approximately in the center of the wide surface of the waveguide parallel to the electric field, and a metal film with a narrow gap along the radio wave propagation direction is coated on one side of the dielectric plate. A finline diode switch is provided with a diode mounted to bridge the gap and is equipped with a bias circuit for changing the bias state of the diode, which is formed on the surface of the dielectric plate facing the diode mounting portion, and 1. A finline diode switch comprising a metal film having a portion facing a diode mounting portion, and forming a strip conductor that resonates in parallel when the diode is in a reverse bias state.