MICROWAVE OSCILLATOR

Abstract: The microwave oscillator (40) comprises a substrate (44) made of a material having a high dielectric constant which is mounted on a bottom wall (42a) of a hermetically sealed metal chassis (42), while carrying thereon a microwave active ele­ ment chip (46) and a dielectric resonator (48). A threaded hole (76) extends throughout the bottom wall (42a) of the chassis (42) from the outside to the inside in alignment with the posi­ tion of the dielectric resonator (48) on the substrate (44). A metal screw (78) is engaged in the threaded hole (76) from out­ side the chassis (42). The screw (78) may be turned to vary the distance between it and the dielectric resonator (48) to adjust the oscillation frequency. The oscillator (40) insures reliability of the microwave active element chip (46) installed therein, and the oscillation frequency can be adjusted easily and accurately even after hermetic isolation.

Description: MICROWAVE OSCILLATOR BACKGROUND OF THE INVENTION The present invention relates to a microwave oscillator and, more particularly, to a dielectric-controlled type integrated oscillator which is furnished with a semiconductor active element chip and stabilized in oscillation frequency by a dielectric. resonator. In a dielectric-controlled integrated oscillator of the typedescribed, it is a usual practice to mount a substrate made of a material having a high dielectric constant on a bottom wall inside ametal chassis of a housing, and a semiconductor active element chip and a dielectric resonator on the substrate, the active element chip and dielectric resonator being electromagnetically coupled to each other. The top of the housing is closed by a cover plate to complete a single oscillator package. Generally, the semicondutor active element chip in use has to be protected from the atmospheric air (particularly moisture) by hermetically sealing the oscillator package Such is usually implemented by soldering or otherwise sealingly connecting the metal chassis to the cover plate after the installation of the substrate, active element chip and the like in the chassis. A problem encountered with the above-described type of prior art oscillator is that when the oscillator in the sealed package has undergone a change in oscillation frequency due to aging, particularly temperature variation or the like, it is practically impossible to adjust the oscillation frequency. Additionally, it is difficult, if not impossible, to set up a desired frequency while absorbing frequency deviation due to dimensional tolerance of the oscillator before the sealed confinement. As discussed above, the prior art dielectric-controlIed type integrated oscillator has failed to reconcile two major requirements to each other, L e. hermetic or air-tight sealing and frequency adjustment SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a dielectric-controlled integrated oscillator which is equipped with a semiconductor active element chip and stabilized in oscillation frequency by a dielectric resonator. It is another object of the present invention to provide a dielectric-controlled integrated oscillator in which a semiconductor active element chip is hermeticallY confined in an oscillator package to improve the reliability of operation. It is another object of the present invention to provide a dielectric-controlled integrated oscillator which allows its oscillation frequency to be adjusted with ease and accuracy not only before the hermetic confinement of the semiconductor chip in the oscillator package but also after the hermetic confinement It is another object of the present -invention to provide a generally improved dielectric-controlled integrated oscillator. A microwave oscillator having a semiconductor active element chip for ocillation and stabilizing an oscillation frequency thereof by use of a dielectric resonator of the present invention comprises a housing having an internal space which is defined by a plurality of walls and kept in a hermetically sealed condition, a substrate having a high dielectric constant mounted on a surface of predetermined one of the walls inside the housing, the substrate carrying the active element chip and the dielectric resonator magnetically coupled with the active element chip in predetermined positions on a surface thereof, and oscillation frequency adjusting means for adjusting the oscillation frequency arranged in the arousing with a predetermined positional relationship to the dielectric resonator. In accordance with the present invention, a substrate made of a material having a high dielectric constant is mounted on a bottom internal surface of a hermetically sealed metal package, while carrying thereon a mirowave active element chip and a dielectric resonator. A threaded hole extends throughout the bottom wall of the package from the outside to the inside in alignment with the position of the dielectric resonator on the substrate. A metal screw -is# engaged in the threaded -hole from ouside the package. The screw may be turned to vary the distance between it and the dielectric resonator to adjust the oscillation frequency. The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawing. BRIEF DESCRIPTION OF THE DRAWING Fig. 1A is a plan view of an internal structure of a prior art dielectric-controlled integrated oscillator viewed from the above; Fig. 1B is a section along line A-A' of Fig. IA and viewed in a direction indicated by an arrow; Fig. 2 is a fragmentary sectional side elevation of a modification to the prior art oscillator shown in Figs. 1A and IB; Fig. 3A is a plan view of an internal structure of a dielectriccontrolled integrated oscillator embodying the present invention viewed from above; Fig. 3B is a sectional side elevation along line B-B' of Fig. 3A and viewed in a direction indicated by an arrow; Fig. 3C is a bottom view showing the back of a substrate having a high dielectric constant which is included in the oscillator of Figs. 3A and 3B; ; Fig. 3D is an equivalent circuit of the substrate included in the oscillator of Figs. 3A-3C; and Figs. 4 and 5 are views representative of a relationship between an oscillation frequency of the oscillator shown in Figs. 3A-3D and a position of a screw adapted for frequency adjustment. DESCRLPTION OF THE PREFERRED EMBODIMENT While the microwave oscillator of the present invention is susceptible of numerous physical embodiments, dependw upon the environment and requirements of use, a substantial ntlmber of the herein shown and described embodiments have been made, tested and used, and all have performed in an eminently satisfactory manner. To facilitate understanding of the present invention, a brief reference will be made to prior art oscillators of the type concerned, shown in Figs. 1A and 1B and Fig. 2 Fig. I is a plan view of an internal arrangement of a prior art oscillator 10 viewed from the above, while Fig. 113 is a section along line A-A' of Fig. 1k The oscillator 10 includes a metal chassis 12 and a substrate 14 mounted on a bottom wall of the chassis 12. The substrate 14 is made of alumina ceramic or like material having a higit dielectric constant Carried on the substrate 14 are a semiconductor active element chip 16, a dielectric resonator 18, a pattert 20 for electromagnetically coupling the chip 16 and resonator 18, a pattern 22 for leading out an output, and a pattern 24 for blazing the chip 16. A terminal 26 for picking up an oscillation oFut and terminals 28 and 30 for applying DC bias to the chip 16 stend out from the metal chassis 12. The top of the metal chassis 12 is closed by a metal cover plate 32 as shown in Fig. 1S In the prior art oscillator construction described above1 the semiconductor active element chip 16 comprises a GaAs PET chip a gate electrode of which is connected to the pattern 20 and a drain electrode, to ground. To protect the chip 16 from the atmospheric air, the chassis 12 and cover plate 32 are sealingly connected together as by soldering. As previously described, the oscillation frequency of such a prior art oscillator cannot be adjusted when fluctuated after the oscillator per se is hermetically sealed. Also. a difficulty is experienced in setting up a necessary frequency before the hermetic sealing operation. In light of this, frequency adjustm#t may be implemented by, as shown in Fig. 2, forming a tapped through hole 34 in the cover plate 32 and fitting a metal screw 36 for frequency adjustment in the tapped hole 34. However, the tapped hole 34 in the cover plate 32 inevitably effects the sealed oscillator configuration to allow the semiconductor active element chip 16 to contact the atmospheric a*, resulting in a significant fall of the reliability of operation. A preferred embodiment of the present invention which. is ft from the drawbacks inherent in the prior art ocillators will now be described in detail. Fig. 3A is a plan view of an internal structure of a dielectriccontrolled integrated oscillator 40 in accordance with the present invention viewed from above, while Fig. 3B is a sectional side elevation along line B-B' of Fig. 3A and viewed in a direction indicated by an arrow. In these drawing, a substrate 44 made of alumina ceramic or like material having a high dielectric constant is laid on a bottom wall 42a of a metal chassis 42. Carried on the surface of the substrate 44 are a semiconductor active element chb 46, which comprises an FET or the like, a dielectric resonator 48, a pattern 50 for magnetically coupling the chip 46 and the resonator 48, and a pattern 52 for leading out an output. The coupling pattern 50 is connected at one end to a gate of the chip 46 and at the other end to ground via a chip resistor 54 and a chip capacitor 56. A pattern 58 extends out from the junction between the chip resistor 54 and the chip capacitor 56 so as to apply gate bias to the chip 46. Source bias is applied to a source of the chip 46 via a pattern 60. Further, the chip 46 is connected to ground via a pattern 62. As shown in Fig. 3C, a ground pattern 66 is formed on the entire back surface of the substrate 44 except for a limited area 64 which aligns in position with the dielectric resonator 48, which is mounted on the other surface of the substrate 44. The substrate 44 constructed in the manner described is represented by an equivalent circuit in Fig. 3D. As shown in Fig. 3A, the metal chassis 42 carries therewitli a terminal 68 for picking up an oscillation output, a gate bias suppb terminal 70 connecting to the pattern 58, and a source bias supply terminal 72 connecting to the pattern 60. As shown in Fig. 3B, the top of the metal chassis 42 is closed by a metal cover plate 74 and soldered or otherwise sealingly connected thereto. As shown in Fig. 3B, a bottom wall 42a of the metal chassis 42 of the oscillator in accordance with the present invention is formed somewhat thicker than the other wallsv A tapped through hole 76 is formed in an intermediate portion of the thicker bottom wall 42a corresponding to the specific area 64 of the back of the substrate 44 which lacks the ground pattern, that is, aligning with the dielectric resonator 48. The tapped hole 76 receives therein a metal or dielectric screw 78 adapted for frequency adjustment In this construction, part of an electromagnetic field developed by the dielectric resonator 48 leaks into the tapped hole 76, so that the oscillation frequency is adjustable by changing the position of the metal screw 78 in the tapped hole 76, i. e. depth of the tapped hole 76. Referring to Figs. 4 and 5, a relationship between a position of the frequency adjusting screw 7 a and an oscillation frequency is shown. In Fig. 4, let it be assumed that the metal chassis 42 has a depth A which is 8 mm, the cover plate 74 has a thickness B which is 5 mm and -a length C which is 19 mm, the screw 78 has a diameter D which is 5. 5 mm, the dielectric resonator 48 has a diameter E which is equal to the diameter D, i. e. 5. 5 mm, and a height F which is 2. 2 mm, the substrate 44 has a thickness G which is 0. 635 mm, the bottom wall of 42a of the metal chassis 42 has a thickness H which is common to the thickness B, i. e. 5 mm, the distance between the bottom wall 42a and the engaged portion of the screw 78, 1. e. position of the screw 78, is A, and the oscillation center frequency fO is 11. O GHz. Then, a relation holds between the position A(mm) of the frequency adjusting screw 78 and the oscillation frequency Af (MHz) as represented by a curve in Fig. 5. In the embodiment described above, ckiect;omagnetic shield is maintained by the metal chassis 42 and screw 78 substantially eliminating the fear that the no-load Q of the dielectric resonator should be lowered by radiator loss. Also, the various elements housed in the oscillator are hermetically confined therein by the metal chassis 42, cover plate 74 and substrate 44 and, therefore, the semicondutor active element chip 46 is free from the influence of the atmospheric air. In summary, it will be seen that the present invention provides a microwave oscillator which not only insures reliability of a semiconductor chip installed therein by sealingly isolating it from the atmospheric #air, but also allows its oscillation frequency to be adjusted with ease and accuracy by a simple arrangement even after the hermetic isolation. Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.

Claims: Patent Claims 1. A microwave oscillator having a semiconductor active element chip for oscillation and stabilizing an oscillation frequency thereof by use of a dielectric resonator, comprising: a housing having an internal space which is defined by a plurality of walls and kept in a hermetically sealed condition; a substrate having a high dielectric constant mounted on a surface of#redetermined one of the walls inside said housing, said substrate carrying the active element chip and the dielectric resonator magnetically coupled with the active element chip in predetermined positions on a surface thereof; and oscillation frequency adjusting means arranged in the housing with a predetermined positional relationship to the dielectric resonator for adjusting the oscillation frequency. 2. A microwave oscillator as claimed in claim 1, in which the oscillation frequency adjusting means is arranged in said predetermined one of the walls, the substrate constituting part of said predetermined one of the walls to maintain the internal space of the housing hermetically sealed. 3. A microwave oscillator as claimed in claim I or 2, in idh the oscillation frequency adjusting means comprises a threaded through hole extending in said predetermined one of the walls from outside the housing to inside and in a position which corresponds to a position of the dielectric resonator on the substrate, said through hole being closed by the substrate from inside the housing, and a screw received in said threaded hole, whereby the screw is turned to vary a distance between the screw and the dielectric resonator and, thereby, the oscillation frequency. 4. A microwave oscillator as claimed in claim 3, in which the walls of the housing and the screw are made of metal. 5. A microwave oscillator as claimed in claim 3, in which the screw is made of a dielectric. 6. A microwave oscillator as claimed in any of claims 1 to 5, in ¯icih said predetemined is is a bottom wall.

Inventors: MIZUMURA, MOTOO, WADA, KENZO
Applicants: NEC CORPORATION
Application year: 1984
Main classification: H01P1
IPC codes: H01P1, H03B9, H03B1, H03B5