JP2002057529A - Gun diode oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of characteristics variance or low efficiency in the work of assembly although a pill type package integrated with a messa type gun diode element is located inside a waveguide in the conventional gun diode oscillator utilizing a secondary higher harmonic mode. SOLUTION: A microstrip line 14 for oscillation part is formed on the upper surface of a dielectric substrate 31 of a prescribed width having a ground conductor 23 on the rear face thereof, a slot line 19 coupled with the microstrip line 14 in the manner of circuit in one terminal part is formed on the ground conductor, a surface-mounted gun diode 13 is packaged on the microstrip line 14 so that a substrate assembly can be provided. Then, this substrate assembly is inserted into a rectangular waveguide to comprise a fin line type output part, and the cutoff frequency of this fin line is set higher than the oscillation frequency of a basic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator using a Gunn diode in a microwave or millimeter wave band, and more particularly to a Gunn diode oscillator having improved second harmonic oscillation characteristics.

[0002]

2. Description of the Related Art Conventionally used Gunn diode oscillators include (1) a structure in which a Gunn diode element incorporated in a package is arranged in a waveguide,
(2) There is a type in which a surface mount gun diode is mounted on a planar circuit such as a microstrip line.

First, the conventional example (1) will be described. A gun diode element 50 formed in a mesa shape as shown in FIG. 8 is incorporated in a pill type package 57 as shown in FIG. 9, and this is arranged in a waveguide cavity (not shown). . In these figures, 51 is a semiconductor substrate, 52 is a contact layer, 53 is an active layer, 54 is a contact layer, 55 is a cathode layer, 56 is an anode layer,
58 is a radiator base, 59 is a cylinder, 60 is a gold ribbon, and 61 is a metal disk.

Ga or microwave or millimeter wave oscillators
As Gunn diode is Energy Relaxa of GaAs
Due to the limitation of the traction time, it is often configured in a second harmonic mode using a frequency twice the fundamental oscillation frequency. In the case of using the second harmonic, the output of the fundamental wave component is unnecessary and harmful and must be removed. However, if the structure arranged in the waveguide as described above is adopted, the frequency of the fundamental wave component is induced. If the cutoff frequency is equal to or lower than the cutoff frequency of the waveguide, the fundamental wave component is suppressed, and the main frequency spectrum of the oscillation output is only the second harmonic component. The cutoff frequency of the waveguide (inner dimension: long side a, short side: b) is given by c / 2a. Where c is the speed of light.

Next, the conventional example of the above (2) will be described. Japanese Patent Application No. 10-259006, which was a prior application of the applicant.
There is an oscillator using a Gunn diode having a planar structure (hereinafter referred to as a surface-mount Gunn diode) as disclosed in U.S. Pat. This oscillator is constructed by directly mounting a Gunn diode having the above structure on a substrate on which a microstrip line or a coplanar line is formed.

FIG. 1 is a cross-sectional view of an example of a surface-mounted gun diode, and FIGS. 2A and 2B are a plan view and a cross-sectional view showing a state where the gun diode of FIG. 1 is mounted on a planar circuit. is there. In FIG. 1, 1 is a semiconductor substrate, 2 is a first semiconductor layer, 3 is an active layer, and 4 is a second semiconductor layer.

A metal layer is formed on the second semiconductor layer 4, and each of the metal layers is partitioned by a cylindrical recess 10, and a plurality of (only two are shown) independent anode electrodes 5 are formed.
And a cathode electrode 6 (remaining portion) are formed. A bump (conductive projection) 8 is formed on each anode electrode 5, and a plurality of bumps (only two are shown) are formed on the cathode electrode 6. 9 are formed at the same height, and the surface except these bumps and the concave portion 10 are protected by the non-conductive film 11. On the back surface of the semiconductor substrate 1, a metal film 7 for ohmic connection is formed.

In FIG. 2, reference numeral 31 denotes a dielectric substrate, and reference numeral 33 denotes a back surface ground electrode. The microstrip line 14 including the signal electrode 15 and the two surface ground electrodes 16 is formed on the upper surface of the dielectric substrate 31, and each surface ground electrode 16 is connected to the rear surface ground electrode 33 by the via hole 12. .

The mounting of the gun diode 13 is performed by flipping the gun diode, placing the bumps 8 and the bumps 9 on the corresponding signal electrode 15 and surface ground electrode 16, and performing thermocompression bonding. When the planar circuit is formed of a coplanar line, the bumps are connected to the signal electrode 15 and the ground conductors 16 on both sides of the bump, respectively, and mounting is performed in the same manner as described above.

[0010]

The gun diode element having a mesa structure as shown in FIG. 8 usually uses a photoresist as a mask in order to form a mesa structure.
Although a method of performing chemical wet etching is used, since this etching proceeds simultaneously not only in the depth direction but also in the lateral direction, it is very difficult to control the electron traveling space (active layer), so that the gun diode It has the disadvantage that the device characteristics vary.

In the step of assembling the above-mentioned elements into the pill type package 57, the gun diode element 50 is
When bonding to No. 8, there is a problem that the bonding tool used obstructs the visual field, making it difficult to look directly, and the work efficiency is extremely poor. Furthermore, when the pill type package 57 is mounted on a microstrip line or the like on a flat substrate, there is also a mounting problem that parasitic inductance occurs due to the connection by the gold ribbon and characteristics vary.

A conventional Gunn diode oscillator in which a surface mount type Gunn diode is mounted on a microstrip line or a coplanar line has the advantage that the variation in characteristics can be reduced without causing such a problem. Even if it is designed to use the second harmonic of the Gunn diode element, its oscillation spectrum will include the fundamental wave together with the second harmonic component (oscillation frequency of the oscillator, hereinafter simply referred to as oscillation frequency). There is a problem that a fundamental wave component that is unnecessary as an oscillator output is also output, including a component (half the oscillation frequency).

An object of the present invention is to provide a Gunn diode oscillator which has solved the above-mentioned problems in manufacturing, characteristics, and mounting.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a Gunn diode oscillator according to the present invention, which comprises a dielectric substrate having a surface-mounted Gunn diode mounted thereon, and a metal housing the dielectric substrate. It is a Gunn diode oscillator comprising a housing and utilizing the oscillation output of the second harmonic, wherein the inside of the metal housing in which the dielectric substrate is housed is a rectangular waveguide, and the dielectric substrate has A slot line in which the oscillation output of the surface-mounted Gunn diode is electromagnetically coupled is formed to form a fin-line type output unit, and that a half of the oscillation frequency is equal to or lower than the cut-off frequency of the fin line. Features.

In the dielectric substrate, a signal electrode and two surface ground electrodes arranged so as to straddle the signal electrode are formed on the front surface by microstrip lines, respectively, and the back surface is connected to the surface ground electrode. A ground conductor also serving as a ground conductor of the microstrip line and the fin line,
The slot line formed by removing a part of the ground conductor is formed, and the surface-mounted Gunn diode is formed with one of an anode and a cathode connected to the signal electrode substantially at the center of the bottom surface, The other electrode connected to the surface ground electrode is formed on both sides of the electrode, and the oscillation output of the surface mount Gunn diode is electromagnetically coupled to the slot line via the signal electrode.

At this time, a stub composed of a microstrip line having a length L and having one end electromagnetically coupled to the signal electrode and the other end open is formed on the surface of the dielectric substrate. And the length L is suitable as a configuration determined so that the resonance frequency of the resonator becomes approximately half the oscillation frequency.

Alternatively, a coplanar line may be used instead of the microstrip line, and a signal electrode and two surface ground electrodes disposed so as to straddle the signal electrode on the surface of the dielectric substrate may be used as the coplanar line and the coplanar line, respectively. A configuration may be adopted in which the slot line is formed of a ground conductor, the ground conductor of the coplanar line also serves as the ground conductor of the fin line, and a part of the ground conductor is removed.

At this time, a stub composed of a coplanar line of length L having one end electromagnetically coupled to the signal electrode and the other end open is formed on the surface of the dielectric substrate, and the stub is used as a resonator. It is preferable that the length L is determined such that the resonance frequency of the resonator is substantially half of the oscillation frequency.

In each of the Gunn diode oscillators described above, a bias electrode defined by a conductor-removed portion is formed on one side of a ground conductor forming the slot line, and one electrode of the two-terminal element is connected to the ground electrode. The bias electrode is configured so that the other electrode can be connected to a part on the opposite side of the ground conductor.

In this case, different functions can be added by using the two-terminal element as a varactor diode or a PIN diode and mounting either of them on the slot line.

[0021]

FIG. 3 is a perspective view showing the inside of the structure of an embodiment of the present invention. A microstrip line 14 for an oscillating unit is formed on the front surface of the dielectric substrate 31, and a slot line 19 for an output unit is formed on the back surface of the substrate 31. Such a surface-mounted gun diode 13 is mounted in a form as shown in FIG.

The inside of the metal housing 20 is a waveguide, and the dielectric substrate 31 is mounted on the support base 18 also serving as a heat sink.
And is located at a substantially central position inside the metal housing 20. Although not shown, a short-circuit plate is provided at the left end of the metal housing 20, and a coupling portion for connection to an external waveguide is provided at the right end.

FIGS. 4A and 4B are pattern diagrams of line conductors formed on the front and back surfaces of the dielectric substrate 31, respectively. On the surface of the dielectric substrate 31, as shown in FIG. 4A, a signal electrode 15 for mounting a Gunn diode, a pair of surface ground electrodes 16 arranged so as to straddle the signal electrode 15, an open stub 17, and The microstrip line 14 including the bias pad 35 is formed. The output side end of the line 14 is arranged at a position where it is electromagnetically coupled to the slot line 19 formed on the back surface of the substrate.

As shown in FIG. 4B, a ground conductor 23 for a microstrip line is provided on the back surface of the dielectric substrate 31.
Are formed, and the ground conductor also serves as the ground conductor of the slot line 19.

The width of the dielectric substrate 31 is set in accordance with the width of the inner wall of the waveguide to be inserted. A strip-shaped conductor removal portion extending along the center line of the width is formed in the ground conductor 23, and the portion forms a slot line 19 for an output portion. The line 19 is formed at its terminal end so as to be high-frequency coupled to the output side end of the microstrip line 14 on the substrate surface.

The ground conductor 23 becomes a "fin" -shaped metal film by forming the slot line 19 as described above. The "fin" of such a metal film is inserted into a rectangular waveguide. Form a so-called "fin line" transmission line.

Here, the fin line will be described.
FIG. 5 shows a cross section of the most typical fin line. A dielectric in which a fin-shaped ground conductor 23 is formed in a central portion surrounded by a wall of a rectangular waveguide 40 (inner dimensions: long side a, short side b) so as to be parallel to the short side wall. A substrate 31 is mounted.

The main part of the electromagnetic wave propagates through the gap (gap dimension s) of the slot line 19, and in the main mode, the electric field is directed in a direction connecting the upper and lower metal films as shown in the figure. Therefore, the fin line transmission line has a good affinity for the waveguide, and is often used when dealing with a microwave or millimeter wave two-terminal device.

As understood from the above structure, the fin line transmission line does not have the TEM mode, and the main mode is the TE mode.
01 mode. Thus, this transmission line has a cutoff frequency and does not propagate at lower frequencies.

When the gap between the dielectric substrate and the slot line is at the center of the waveguide as shown, and the thickness of the dielectric substrate 31 is negligible, the cut-off frequency of the fin line transmission line is calculated by solving the following equation. Is required. jB / 2Yc-jcot (πa / λc) = 0, where λc is a cutoff wavelength to be obtained, Yc is a characteristic admittance of two parallel flat plate transmission lines having a unit width of width and a gap of b, and B is a characteristic admittance of slot line 19. The susceptance per unit length created by the gap, j is a constant.

This value is based on RECollin's "Foundation o
f According to Microwave Engineering ”, MacGraw-Hill, Inc.,

[0032]

(Equation 1)

However,

[0034]

(Equation 2)

Is as follows.

According to the present invention, the cut-off frequency is set higher than the fundamental wave oscillation frequency so that the fundamental wave oscillation frequency (half of the oscillation frequency) is lower than the cut-off frequency. Low)
Determine the specifications of the above structure.

Now, the bias pad 35 and the metal housing 20
When a voltage is applied between them, the open stub 17, signal electrode 15, gun diode 13, surface ground electrode 16, via hole 12, ground conductor 23, support base 18, metal housing 20
A current flows through the path, and an electromagnetic wave (microwave) is generated in the Gunn diode 13. The generated electromagnetic wave resonates in the open stub 17, passes through the microstrip line 14, and
It is coupled to the slot line 19 (fin line transmission line) on the back surface. Since the magnetic field of the TEM wave of the microstrip line and the magnetic field of the slot line 19 are similar, they can be easily coupled.

Although the electromagnetic wave propagates along the slot line 19, the fundamental wave component cannot propagate because it is lower than the cutoff frequency of the fin line, and only the component of the second harmonic or higher propagates.

Although the output ends of the metal housing 20 and the conductor lines are not shown, matching ends for coupling with the waveguide are provided at the ends of the slot lines 19 formed on the dielectric substrate 31. Is provided. For example, if the gap width of the slot line is
An alignment method is performed by forming a conductor pattern so as to gradually spread toward the output end and reach the metal housing wall at the end.

The embodiment shown in FIG. 3 is a case where the oscillation section of the Gunn diode is constituted by a microstrip line. However, as shown in FIG. 6, it can be constituted by using a coplanar line. The coplanar line 21 is formed by a coplanar ground conductor 22 formed on the upper surface of the dielectric substrate 31. In this case, the slot line 19 is also formed on the same surface by the coplanar ground conductor 22.

In the above-described embodiment of FIGS. 3 and 6,
The substrate 31 is placed at the center of the height inside the metal housing,
It is not always necessary, and it may be shifted from the center. In particular, in the case of the embodiment of FIG. 6, the configuration may be such that the substrate is directly attached to the bottom surface inside the metal housing. In this case, the cut-off frequency still exists, which is advantageous in that the mounting of the substrate is easy and the mounting is easy.

In the oscillator according to the present invention, it is preferable that a bias electrode defined by a conductor-removed portion is formed on the ground conductor. As a result, one electrode of the two-terminal element can be connected to the bias electrode, and the other electrode can be connected to the opposite part of the ground conductor. For example, as shown in FIG. The varactor diode 24 can be mounted to form a voltage controlled oscillator. The varactor diode 24 has the bias pad 25 formed on one ground conductor as one electrode and the opposite ground conductor as the other electrode. By applying a voltage to the bias pad 25, the impedance of the external circuit viewed from the Gunn diode changes, and the oscillation frequency changes accordingly.

Further, by mounting a PIN diode instead of the varactor diode, a pulse modulation oscillator can be obtained.

Further, the oscillator according to the present invention can determine the oscillation frequency by adjusting the length L of the open stub 17. This is an open stub 17
Work as a resonator, and the resonance frequency changes depending on the length L. The length L is a distance from the point where the electrode of the Gunn diode is connected to the open end, and is determined in advance by circuit simulation or the like so as to resonate at approximately half the oscillation frequency. However, even after the formation of the conductor pattern, the length can be adjusted by, for example, partially cutting off the open stub 17 or bonding a metal foil to the open stub 17 and the like to finally obtain a suitable length L. . In FIG. 4, the open stub 17 is formed to have a width different from that of the signal electrode 15, but the width is not limited to this and may be the same.

[0045]

As described above, the Gunn diode oscillator of the present invention is composed of a dielectric substrate on which a surface mount Gunn diode is mounted and a metal housing for accommodating the dielectric substrate. In addition, a rectangular waveguide is formed inside the metal housing, and a slot line is formed on the dielectric substrate to electromagnetically couple the oscillation output of the surface-mounted Gunn diode to form a fin-line output unit. It is possible to remove unnecessary fundamental wave components at the cutoff frequency of the fin line. Therefore, it is possible to realize a Gunn diode oscillator using second harmonics, which has a small variation in characteristics and high assembling work efficiency.

The oscillation output of the surface-mounted Gunn diode can be easily coupled to a slot line by using a microstrip line or a coplanar line, and an open stub opened at one end of a signal electrode with a length L is formed. This facilitates adjustment of the oscillation frequency.

Further, the Gunn diode oscillator of the present invention comprises:
By forming a bias electrode separated by a conductor removal part on the ground conductor forming the slot line, a two-terminal element can be mounted on the slot line, and different functions can be exhibited by selecting the two-terminal element. it can. Specifically, by mounting a varactor diode,
A voltage-controlled oscillator can be used, and a pulse modulation oscillator can be obtained by mounting a PIN diode.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a surface mount gun diode.

FIG. 2 is a plan view and a cross-sectional view showing a state where the Gunn diode is mounted.

FIG. 3 is a perspective view of one embodiment of the Gunn diode oscillator of the present invention.

FIG. 4 is a conductor pattern diagram of the upper surface and the lower surface of the substrate of the embodiment.

FIG. 5 is a sectional view for explaining a fin line transmission line.

FIG. 6 is a perspective view of another embodiment of the Gunn diode oscillator of the present invention.

FIG. 7 is an explanatory diagram in a case where a varactor diode is mounted on the Gunn diode oscillator of the present invention to form a voltage-controlled oscillator.

FIG. 8 is a sectional view of a gun diode having a mesa structure.

FIG. 9 is a cross-sectional view of a pill type package incorporating a mesa-type Gunn diode.

[Explanation of symbols]

1: semiconductor substrate, 2: first semiconductor layer, 3: active layer,
4: second semiconductor layer, 5: anode electrode, 6: cathode electrode, 7: metal film, 8: bump (anode), 9: bump (cathode), 10: concave portion, 11: non-conductive film, 1
2: via hole, 13: gun diode, 14: microstrip line, 15: signal electrode, 16: surface ground electrode, 17: open stub, 18: support base, 19: slot line, 20: metal housing, 21: Coplanar tracks,
22: Coplanar line ground conductor, 23: Microstrip line ground conductor, 24: Varactor diode, 25:
Bias pad, 31: dielectric substrate, 33: back surface ground electrode, 35: bias pad, 40: rectangular waveguide 50: mesa structure Gunn diode element, 51: semiconductor substrate, 5
2: contact layer, 53: active layer, 54: contact layer, 55: cathode layer, 56: anode layer, 57: pill type package, 58: heat dissipation base, 59: cylinder, 60: gold ribbon, 61: metal disk .

Claims (7)

[Claims] 1. A Gunn diode oscillator comprising a dielectric substrate on which a surface mount Gunn diode is mounted, and a metal housing for accommodating the dielectric substrate, and utilizing a second harmonic oscillation output, The inside of the metal housing in which the dielectric substrate is housed is a rectangular waveguide, and the dielectric substrate is formed with a slot line for electromagnetically coupling the oscillation output of the surface-mounted Gunn diode, and has a fin line type. Wherein the half of the oscillation frequency is equal to or lower than the cut-off frequency of the fin line. 2. The Gunn diode oscillator according to claim 1, wherein the dielectric substrate has a signal electrode on a surface thereof and two surface ground electrodes disposed so as to straddle the signal electrode, each of which is formed of a microstrip line. A ground conductor connected to the front ground electrode and also serving as a ground conductor for the microstrip line and the fin line, and the slot line formed by removing a part of the ground conductor are formed on the back surface, and the surface-mounted gun diode is formed. One of an anode and a cathode connected to the signal electrode is formed substantially at the center of the bottom surface, and the other electrode connected to the surface ground electrode is formed on both sides of the electrode. Wherein the oscillation output is electromagnetically coupled to the slot line via the signal electrode. 3. The Gunn diode oscillator according to claim 2, wherein a stub composed of a microstrip line having a length L, one end of which is electromagnetically coupled to the signal electrode and the other end of which is open, is provided on the surface of the dielectric substrate. A Gunn diode oscillator which is formed and uses the stub as a resonator, wherein the length L is determined such that the resonance frequency of the resonator is substantially half the oscillation frequency. 4. The Gunn diode oscillator according to claim 1, wherein said dielectric substrate includes a signal electrode on a surface thereof and two surface ground electrodes disposed so as to straddle said signal electrode, respectively. A ground conductor, the ground conductor also serving as the ground conductor of the fin line,
The slot line formed by removing a part of the ground conductor is formed, and the surface-mounted Gunn diode is formed with one of an anode and a cathode connected to the signal electrode substantially at the center of the bottom surface, The other electrode connected to the surface ground electrode is formed on both sides of the electrode, and the oscillation output of the surface mount gun diode is electromagnetically coupled to the slot line via the signal electrode. Oscillator. 5. The Gunn diode oscillator according to claim 4, wherein a stub formed of a coplanar line having a length L, one end of which is electromagnetically coupled to the signal electrode and the other end is open, is formed on the surface of the dielectric substrate. The stub works as a resonator, and the length L is determined so that the resonance frequency of the resonator is substantially half of the oscillation frequency. 6. The Gunn diode oscillator according to claim 1, wherein a bias electrode defined by a conductor-removed portion is formed on a portion of one side of the ground conductor forming the slot line, and one of the two-terminal elements is formed. A gun diode oscillator, wherein an electrode is connectable to the bias electrode, and the other electrode is connectable to a part on the opposite side of the ground conductor. 7. The gun diode oscillator according to claim 6, wherein said two-terminal element is a varactor diode or a PIN diode, and said varactor diode or PIN diode is mounted on said slot line. Oscillator.