Title:
HIGH-STABILITY ELECTROMAGNETIC RESONATOR
United States Patent 3633104
Abstract:
A metal disc is deposited on a quartz substrate to reduce the effective linear thermal coefficient of expansion of the disc, and air is contained between the quartz substrate and a ground plane to reduce the effective dielectric constant thermal coefficient to make an electromagnetic resonator which is stable in frequency with temperature.
US Patent References:
WIDE FREQUENCY BAND CIRCULATOR
Konishi - December 1970 - 3544920
Temperature compensated microwave cavity
McCoubrey - May 1962 - 3034078
REENTRANT CAVITY TYPE CIRCULATOR
Konishi - March 1970 - 3504303
PULSED DOPPLER RADAR SYSTEMS
Warren et al. - July 1969 - 3454946
WIDE FREQUENCY BAND CIRCULATOR
Konishi - December 1970 - 3544920
Temperature compensated microwave cavity
McCoubrey - May 1962 - 3034078
REENTRANT CAVITY TYPE CIRCULATOR
Konishi - March 1970 - 3504303
PULSED DOPPLER RADAR SYSTEMS
Warren et al. - July 1969 - 3454946
Inventors:
Gray, Douglas A. (Portola Valley, CA)
Heinz, William W. (Palo Alto, CA)
Heinz, William W. (Palo Alto, CA)
Application Number:
05/061225
Publication Date:
01/04/1972
Filing Date:
08/05/1970
View Patent Images:
Export Citation:
Assignee:
Hewlett-Packard Company (Palo Alto, CA)
Primary Class:
Other Classes:
333/229, 455/119, 455/91, 331/115
International Classes:
G01S7/03; H01P7/08; H04B1/38
Field of Search:
325/484,485,104,105,15,24,18 330/45,56,143 331/115,17G,175,176 333/83T 315/5.23
Primary Examiner:
Safourek, Benedict V.
Assistant Examiner:
Mayer, Albert J.
Claims:
1. An electromagnetic resonator comprising:
2. An electromagnetic resonator as in claim 1 wherein the second metallic layer is adjacent to the second dielectric layer and the first dielectric
3. An electromagnetic resonator as in claim 1 wherein the second metallic layer is adjacent to the first dielectric layer and the second dielectric
4. An electromagnetic resonator as in claim 2 wherein the first dielectric layer is quartz, the second dielectric layer is air and the first metallic
5. An electromagnetic resonator as in claim 4 including strip line means to
6. An electromagnetic resonator as in claim 2 wherein the electromagnetic resonator is part of a microwave transceiver, the electromagnetic resonator being connected to a negative resistance device and a directional coupler, the directional coupler being connected to a circulator, a detector being connected to the directional coupler through a band-pass filter, and output means being connected to the detector.
2. An electromagnetic resonator as in claim 1 wherein the second metallic layer is adjacent to the second dielectric layer and the first dielectric
3. An electromagnetic resonator as in claim 1 wherein the second metallic layer is adjacent to the first dielectric layer and the second dielectric
4. An electromagnetic resonator as in claim 2 wherein the first dielectric layer is quartz, the second dielectric layer is air and the first metallic
5. An electromagnetic resonator as in claim 4 including strip line means to
6. An electromagnetic resonator as in claim 2 wherein the electromagnetic resonator is part of a microwave transceiver, the electromagnetic resonator being connected to a negative resistance device and a directional coupler, the directional coupler being connected to a circulator, a detector being connected to the directional coupler through a band-pass filter, and output means being connected to the detector.
Description:
SUMMARY OF THE INVENTION
An electromagnetic resonator may be constructed by placing a conductor parallel to and insulated from a ground plane. If that conductor is in the shape of a disc, the resonant frequency of the structure is determined by the radius of the disc and the dielectric constant of the material between the disc and the ground plane. Changes in temperature can cause changes in the resonant frequency of the structure by affecting the radius of the disc or the dielectric constant of the material between the disc and the ground plane. If the metal disc is bonded to a dielectric substrate with a lower linear thermal coefficient of expansion, then the effective linear thermal coefficient of expansion of the disc is that of the dielectric substrate. Thus, changes in resonant frequency due to changes in the radius of the disc can be reduced. The thermal stability of the dielectric between the disc and the ground plane can be improved by placing between the substrate and the ground plane another dielectric which has a dielectric constant with either a lower thermal coefficient or one of opposite polarity. By reducing temperature effects on the radius of the disc and the dielectric constant of the dielectric, the frequency stability of the resonator is improved.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a sectional perspective view of the preferred embodiment of an electromagnetic resonator according to this invention.
FIGS. 2-4 show sectional views of alternative embodiments of an electromagnetic resonator according to this invention.
FIG. 5 shows an electromagnetic resonator, such as that of FIG. 1, in a doppler radar.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in FIG. 1 an electromagnetic resonator 10 is comprised of a metal layer or disc 12 bonded to a dielectric layer or substrate 14 mounted on a metal layer or block 16. Metal block 16 has a recess 17 directly below disc 12 for a dielectric layer 18 of, for example, air. The bottom of recess 17 forms a ground plane 20. Recess 17 is sufficiently larger in diameter than disc 12 that all the electric field lines from disc 12 are essentially perpendicular to ground plane 20. Strip lines 22 deposited on substrate 14 are used to couple signals in and out of resonator 10. Gaps 24 act as coupling capacitors between strip lines 22 and disc 12.
If, for example, gold is used for disc 12 and it is vacuum deposited on a quartz substrate 14, then the linear thermal coefficient of expansion of disc 12 will change from 14 parts per million per centigrade degree (p.p.m./C.°) to 0.5 p.p.m./C.°. Thus, changes in resonant frequency due to changes in the radius of disc 12 can be greatly reduced.
The thermal stability of the dielectric between disc 12 and ground plane 20 can also be improved by placing another dielectric 18 having a dielectric coefficient with either a lower thermal coefficient or one of opposite polarity (such as air) between quartz substrate 14 and ground plane 20. A thermal coefficient which increases with increasing temperature is said to have a positive polarity and one which decreases with increasing temperature is said to have a negative polarity. If a dielectric with a positive dielectric constant thermal coefficient is combined with one having a negative thermal coefficient the resultant combination can be made to have a zero thermal coefficient by selecting the necessary thickness of each dielectric. Reduction of the effective dielectric constant thermal coefficient can also be achieved by placing a dielectric 18 between substrate 14 and ground plane 20 which has a smaller dielectric thermal coefficient than substrate 14, though of the same polarity. For example, the dielectric constant thermal coefficient of quartz is +28 p.p.m./C.° and that of air is essentially 0. By using an air layer with a thickness approximately equal to the thickness of substrate 14 for dielectric 18 the effective thermal coefficient of the total dielectric between disc 12 and ground plane 20 can be reduced to about 6 p.p.m./C.°. A 10 gigaHertz resonator has been built using the above-mentioned materials and the following dimensions are given for illustrative purposes. Disc 12 is 0.5 mil thick by 400 mils in diameter, substrate 14 is 25 mils thick and recess 17 is 25 mils deep by 600 mils in diameter. Gaps 24 may be between 10 and 60 mils wide depending upon the impedance of the circuit they are coupling into.
FIGS. 2, 3 and 4 illustrate alternative embodiments of the electromagnetic resonator. As shown in FIG. 2, dielectric 18 may also be placed above disc 12 to achieve the desired results. FIGS. 3 and 4 show triplate rather than strip line configurations with the alternative placements of dielectrics 14 and 18 as were shown for the strip line embodiments in FIGS. 1 and 2. Transmission lines for coupling signals into and out of the electromagnetic resonator are omitted in FIGS. 2, 3 and 4 for the purposes of illustration.
FIG. 5 shows the use of a high stability electromagnetic resonator 10 in a doppler radar 30 including a negative resistance device 32, such as a Gunn diode, Impatt diode or tunnel diode, to excite the electromagnetic resonator at its resonant frequency. Electromagnetic resonator 10 is connected to a directional coupler 34 which in turn is connected to one port of a circulator 36. The second port of circulator 36 is connected to antenna 38 and the third port of circulator 36 is connected through directional coupler 34 to band-pass filter 42. Band-pass filter 42 is connected to detector 44 which in turn is connected to display 46. Antenna 38 radiates a microwave signal 48. If signal 48 strikes a moving object 40, part of the signal will be reflected by the moving object and will return to antenna 38 as signal 50. Signal 50 will be offset in frequency (i.e., doppler shifted) from signal 48 by an amount proportional to the velocity of moving object 40 and will then pass through circulator 36 into directional coupler 34. In directional coupler 34 a part of the signal from resonator 10, at the same frequency as signal 48, is combined with doppler shifted signal 50 and the resultant two-tone signal passes through band-pass filter 42 and is mixed in detector 44. The output of detector 44 is the frequency difference between signals 48 and 50. This frequency difference may be employed for driving display 46 to indicate the velocity of moving object 40, or to serve as an alarm indicating the presence of a moving object. The high stability electromagnetic resonator ensures that the frequency of one doppler radar set will not drift into the frequency range of another and cause erroneous readings, and it ensures a high degree of accuracy in the measurement of velocity.
An electromagnetic resonator may be constructed by placing a conductor parallel to and insulated from a ground plane. If that conductor is in the shape of a disc, the resonant frequency of the structure is determined by the radius of the disc and the dielectric constant of the material between the disc and the ground plane. Changes in temperature can cause changes in the resonant frequency of the structure by affecting the radius of the disc or the dielectric constant of the material between the disc and the ground plane. If the metal disc is bonded to a dielectric substrate with a lower linear thermal coefficient of expansion, then the effective linear thermal coefficient of expansion of the disc is that of the dielectric substrate. Thus, changes in resonant frequency due to changes in the radius of the disc can be reduced. The thermal stability of the dielectric between the disc and the ground plane can be improved by placing between the substrate and the ground plane another dielectric which has a dielectric constant with either a lower thermal coefficient or one of opposite polarity. By reducing temperature effects on the radius of the disc and the dielectric constant of the dielectric, the frequency stability of the resonator is improved.
DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a sectional perspective view of the preferred embodiment of an electromagnetic resonator according to this invention.
FIGS. 2-4 show sectional views of alternative embodiments of an electromagnetic resonator according to this invention.
FIG. 5 shows an electromagnetic resonator, such as that of FIG. 1, in a doppler radar.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in FIG. 1 an electromagnetic resonator 10 is comprised of a metal layer or disc 12 bonded to a dielectric layer or substrate 14 mounted on a metal layer or block 16. Metal block 16 has a recess 17 directly below disc 12 for a dielectric layer 18 of, for example, air. The bottom of recess 17 forms a ground plane 20. Recess 17 is sufficiently larger in diameter than disc 12 that all the electric field lines from disc 12 are essentially perpendicular to ground plane 20. Strip lines 22 deposited on substrate 14 are used to couple signals in and out of resonator 10. Gaps 24 act as coupling capacitors between strip lines 22 and disc 12.
If, for example, gold is used for disc 12 and it is vacuum deposited on a quartz substrate 14, then the linear thermal coefficient of expansion of disc 12 will change from 14 parts per million per centigrade degree (p.p.m./C.°) to 0.5 p.p.m./C.°. Thus, changes in resonant frequency due to changes in the radius of disc 12 can be greatly reduced.
The thermal stability of the dielectric between disc 12 and ground plane 20 can also be improved by placing another dielectric 18 having a dielectric coefficient with either a lower thermal coefficient or one of opposite polarity (such as air) between quartz substrate 14 and ground plane 20. A thermal coefficient which increases with increasing temperature is said to have a positive polarity and one which decreases with increasing temperature is said to have a negative polarity. If a dielectric with a positive dielectric constant thermal coefficient is combined with one having a negative thermal coefficient the resultant combination can be made to have a zero thermal coefficient by selecting the necessary thickness of each dielectric. Reduction of the effective dielectric constant thermal coefficient can also be achieved by placing a dielectric 18 between substrate 14 and ground plane 20 which has a smaller dielectric thermal coefficient than substrate 14, though of the same polarity. For example, the dielectric constant thermal coefficient of quartz is +28 p.p.m./C.° and that of air is essentially 0. By using an air layer with a thickness approximately equal to the thickness of substrate 14 for dielectric 18 the effective thermal coefficient of the total dielectric between disc 12 and ground plane 20 can be reduced to about 6 p.p.m./C.°. A 10 gigaHertz resonator has been built using the above-mentioned materials and the following dimensions are given for illustrative purposes. Disc 12 is 0.5 mil thick by 400 mils in diameter, substrate 14 is 25 mils thick and recess 17 is 25 mils deep by 600 mils in diameter. Gaps 24 may be between 10 and 60 mils wide depending upon the impedance of the circuit they are coupling into.
FIGS. 2, 3 and 4 illustrate alternative embodiments of the electromagnetic resonator. As shown in FIG. 2, dielectric 18 may also be placed above disc 12 to achieve the desired results. FIGS. 3 and 4 show triplate rather than strip line configurations with the alternative placements of dielectrics 14 and 18 as were shown for the strip line embodiments in FIGS. 1 and 2. Transmission lines for coupling signals into and out of the electromagnetic resonator are omitted in FIGS. 2, 3 and 4 for the purposes of illustration.
FIG. 5 shows the use of a high stability electromagnetic resonator 10 in a doppler radar 30 including a negative resistance device 32, such as a Gunn diode, Impatt diode or tunnel diode, to excite the electromagnetic resonator at its resonant frequency. Electromagnetic resonator 10 is connected to a directional coupler 34 which in turn is connected to one port of a circulator 36. The second port of circulator 36 is connected to antenna 38 and the third port of circulator 36 is connected through directional coupler 34 to band-pass filter 42. Band-pass filter 42 is connected to detector 44 which in turn is connected to display 46. Antenna 38 radiates a microwave signal 48. If signal 48 strikes a moving object 40, part of the signal will be reflected by the moving object and will return to antenna 38 as signal 50. Signal 50 will be offset in frequency (i.e., doppler shifted) from signal 48 by an amount proportional to the velocity of moving object 40 and will then pass through circulator 36 into directional coupler 34. In directional coupler 34 a part of the signal from resonator 10, at the same frequency as signal 48, is combined with doppler shifted signal 50 and the resultant two-tone signal passes through band-pass filter 42 and is mixed in detector 44. The output of detector 44 is the frequency difference between signals 48 and 50. This frequency difference may be employed for driving display 46 to indicate the velocity of moving object 40, or to serve as an alarm indicating the presence of a moving object. The high stability electromagnetic resonator ensures that the frequency of one doppler radar set will not drift into the frequency range of another and cause erroneous readings, and it ensures a high degree of accuracy in the measurement of velocity.