JPH0151086B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a microwave amplifier using a strip line.

[Technical background of the invention and its problems]

Normally, amplifiers for ultra-high frequencies such as microwaves are made by etching a conductor such as a copper plate bonded to a dielectric substrate to form a circuit pattern mainly consisting of strip lines, and attaching semiconductor elements to this. In addition, it is realized by a so-called microwave integrated circuit.

FIG. 1 is a top view showing an example of the structure of a conventional microwave amplifier, in which current is supplied to the amplifier circuit section mainly composed of a strip line 3 and a semiconductor element 4 on a dielectric substrate 1, and the semiconductor element 4. A bias circuit 5 is installed for this purpose. Board 1
is housed in a metal case 6, and input/output connectors 7, 8 and bias supply terminals 9 are attached to the side wall of the case 6. If the high frequency current flowing through the strip line 3 leaks into the bias circuit 5, it will cause loss in the amplifier circuit section and deteriorate the characteristics.
It is constructed by combining strip lines with a length of one-quarter wavelength (λ/4).

In a strip line, a high frequency signal is sandwiched between a metal conductor on a dielectric substrate and a ground conductor on the bottom surface of the substrate, and propagates in a so-called stripline mode. However, as shown in FIG. 3, some of the electric lines of force 10 coming out of the strip line 3 on the dielectric substrate 1 do not take a path through the substrate 1 and end at the ground conductor 2 on the bottom surface of the substrate 1. It radiates into the space above. Although electromagnetic waves leak onto the dielectric substrate 1 in this way, generally the dielectric substrate 1 of the amplifier
is surrounded by a metal case 6 consisting of a metal side wall 6a and a top plate 6b as shown in the figure.
This metal case 6 appears as a waveguide to electromagnetic waves. For this reason, in addition to the stripline mode, a so-called waveguide mode occurs in the propagation case 6.

Electromagnetic waves in the stripline mode do not propagate to the next stage unless the stripline 3 on the dielectric substrate 1 is coupled directly or through a large capacitance, but when propagation occurs in the waveguide mode, the electromagnetic waves are transferred to the substrate 1. You will be able to fly over them without any problems. This causes coupling between the output and input of the amplifier, reducing so-called reverse isolation. The amplifier used as a preamplifier of a microwave receiver has a
Since good reverse isolation characteristics are required, the occurrence of waveguide modes on the substrate 1 of the amplifier is a serious problem. Further, feedback of the signal from the output to the input deteriorates the frequency characteristics of the amplifier, and if the amount of feedback is large, it causes oscillation.

For these reasons, it is necessary to suppress the generation of waveguide modes on the amplifier circuit. For this purpose, it is most effective to utilize the cut-off phenomenon of the waveguide. In other words, in a waveguide with a rectangular cross section, electromagnetic waves with a frequency lower than the frequency at which the width of the waveguide in the direction perpendicular to the direction of the electric field is 1/2 of the free space wavelength will not pass through the waveguide. Take advantage of the fact that it cannot pass through. In FIG. 3, the width of the metal case 6, that is, the opposing side walls 6
The cutoff frequency is determined by the interval A between a,
Propagation of electromagnetic waves with frequencies lower than this frequency can be suppressed. Therefore, by selecting the cutoff frequency to be higher than the amplification frequency band of the amplifier, it is possible to prevent the input and output of the amplifier from being coupled in the waveguide mode.

However, as the frequency at which amplifiers are used tends to increase, it has become necessary to reduce the width A of the amplifier case in order to suppress the waveguide mode. For example, in a 12 GHz amplifier, the width A needs to be 9 mm or less. However, since it is difficult to reduce the size of the bias circuit 5 shown in FIG. 2, it has become difficult to fit the dielectric substrate 1 into a case 6 having a width that can suppress the waveguide mode. In high-frequency amplifiers, we were forced to give up on using the cutoff phenomenon to suppress waveguide modes.

[Purpose of the invention]

The present invention eliminates the drawbacks of the prior art described above, and aims to provide a microwave amplifier having a structure that allows easy suppression of waveguide modes even at high frequencies.

[Summary of the invention]

In order to achieve the above object, the present invention has a foot portion connected to the ground conductor on the bottom surface of the substrate so that the spatial width of the high frequency circuit portion is 1/2 or less of the free space wavelength in the amplification frequency band. By placing a conductive shield plate on the dielectric substrate, the board is divided into two parts, and one side contains the amplifier circuit section including the strip line and semiconductor elements, and the other section contains other circuit sections, such as the bias circuit section. It is characterized by the placement of

〔Effect of the invention〕

According to the present invention, the cutoff frequency is determined by the distance between the shield plate and the side wall of the metal case on the amplifier circuit side due to the presence of the conductor shield plate, so even if the operating frequency of the amplifier becomes high, the bias The waveguide mode can be suppressed without being influenced by the size of other circuit parts such as circuits. In addition, since the feet of the shield plate are directly grounded to the ground conductor on the bottom surface of the dielectric substrate, these feet can be used as a through-hole ground. It is possible to touch the ground at a distance. When a Teflon substrate is used as the dielectric substrate, it is not easy to make through-holes by plating, so it is extremely useful to be able to use the legs of the shield plate as a through-hole ground.

[Embodiments of the invention]

FIG. 4 is a sectional view showing an outline of an embodiment of the present invention, and FIG. 5 is a perspective view.

In the figure, a dielectric substrate 11 is divided by a conductor shield plate 20 into a portion where an amplifier circuit including a strip line 13 is formed and a portion where a bias circuit 15 is formed. Shield plate 20
passes through the dielectric substrate 11, and the substrate 11 is divided into the above two parts also in terms of high frequency.
A high frequency current flows through the strip line 13, and in the structure shown in the figure, the cutoff frequency is determined by the distance B between the shield plate 20 and the side wall 16a of the metal case 16. Amplify this interval B and increase the frequency band to 12G
In the case of Hz, if the wavelength is set to 1/2 or less of the free interval wavelength of this frequency band, for example, 9 mm or less, generation of a waveguide mode can be prevented and isolation between input and output can be obtained. In the conventional amplifier shown in FIG. 3, the cutoff frequency is determined by the width A of the entire metal case 6 including the amplifier circuit section and the bias circuit section, whereas B is the width of only the amplifier circuit section. As an amplifier, it has a much higher cutoff frequency and can easily suppress waveguide modes.

Furthermore, since the amplifier circuit section and the bias circuit section are separated by the shield plate 20, the width C of the bias circuit section does not affect the waveguide mode suppression of the amplifier. There are no more restrictions. Therefore, as shown in FIG. 5, it is possible to place large components such as the variable resistor 25 on the dielectric substrate 11.

In a microwave amplifier, it is necessary to apply an optimal bias voltage to each semiconductor element in order to make the semiconductor element exhibit its maximum performance, and for this purpose a variable resistor (potentiometer) is essential. However, due to the large size of these components, it has been difficult to place them on dielectric substrates until now.
Therefore, a variable resistor (potentiometer) must be placed in the power supply circuit, and the output voltage of the power supply circuit can be adjusted to an odd value, such as 2.3 volts or 1.4 volts, depending on the individual amplifier. The need arose. On the manufacturing line, the power supply used to check the characteristics of an amplifier as a unit is often not the same as the power supply actually used when the amplifier is incorporated into equipment, and the variable resistor (potentiometer) If the amplifier is not installed on a dielectric substrate, there is an inconvenience in that the power supply voltage must be adjusted every time the power supply is connected to the amplifier.

In this regard, in this embodiment, since the variable resistor 25 is incorporated on the amplifier board, it is possible to make the variable resistor 25 variable with respect to the voltage obtained as the output of an IC-based three-terminal regulator, such as 5.0 volts. If the resistor 25 is adjusted, the voltage applied to the power supply terminal 19 may always be constant, and there is no need to readjust the voltage after changing the power supply. To connect the strip line 13 of the amplifier circuit section and the bias circuit 15, as shown in FIG. 5, a tunnel 21 is provided under the shield plate 20, and a wiring pattern is placed on the dielectric substrate 11 in this part. I am going by. If the width of the tunnel 21 is small, the shielding effect of the shield plate 20 will not be reduced at all.

In microwave amplifiers, the semiconductor elements used have a very large gain at low frequencies, so it is necessary to provide a bypass capacitor in the bias circuit to suppress the gain. being done. That is, in order to ground the bypass chip capacitor 24 at the shortest distance, the ground conductor 12 on the bottom surface of the dielectric substrate 11 is
The legs 22 of the shield plate 20 and the board 1 are in contact with
A conductor land 23 on the top of the chip capacitor 24 is connected to the land. In this case, the leg 22 of the shield plate 20 functions as a through-hole ground, allowing the bypass chip capacitor 24 to be grounded at the shortest distance.

As described above, in the present invention, by erecting a shield plate on the dielectric substrate to separate the amplifier circuit section from other circuit sections such as the bias circuit section, the waveguide mode can be suppressed. , it becomes possible to incorporate a complex and large-shaped bias circuit section and the like together with an amplifier circuit section on one substrate.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of an example of a conventional microwave amplifier, Figure 2 is a detailed view of the bias circuit in Figure 1, and Figure 3 is a direction perpendicular to the input/output direction of the amplifier in Figure 1. FIG. 4 is a cross-sectional view schematically showing a microwave amplifier according to an embodiment of the present invention, and FIG. 5 is a perspective view of the same embodiment. 11... Dielectric substrate, 12... Ground conductor, 13
... Strip line, 14 ... Semiconductor element, 15
...Bias circuit section, 16...Metal case, 18
...Output connector, 19...Power supply terminal, 20
...Conductor shield plate, 21...Tunnel, 22...
...foot part, 23...conductor land, 24...chip capacitor for bypass, 25...variable resistor.

Claims (1)

[Claims] 1. A microwave amplifier configured using a strip line and an amplifying element formed on the other side of a dielectric substrate having a ground conductor on one side, at least a high frequency wave including the strip line and the amplifying element. A conductor shield provided between the circuit section and another circuit section in contact with the ground conductor so that the spatial width of the high frequency circuit section is 1/2 or less of the free space wavelength in the amplification frequency band. A microwave amplifier characterized by comprising means. 2. Claim 1, wherein the other circuit section includes a bias circuit for the amplification element.
Microwave amplifier as described in section.