Patent Application
20070281421
The fundamental formula for a capacitor having 2 planar parallel electrodes/plates separated by a dielectric material is:
C=0.0885εA/d (1);
where C is the capacitance in picofarads (pF);
∈is the dielectric constant;
A is the area common to both electrodes in, for example, centimeters; and
d is the distance or spacing between the electrodes in, for example, centimeters.
In practice, the dielectric constant c is determined by the material between the electrodes of the capacitor. Many common dielectric materials used in capacitors designed for lower frequency operations exhibit a significant change in dielectric constant ε as well as higher losses as the frequency increases. That is, the value of the dielectric constant ε is a function of frequency. At low frequencies, having a dielectric material with a high dielectric constant ε produces greater capacitance for the size of the component. At higher frequencies, the internal equivalent series resistance (ESR) and lead inductance losses also increase as frequencies increases and degrades the quality of the capacitive component.
Air has a dielectric constant of 1 which is substantially frequency invariant. Thus, as the frequency of the signal through the capacitor increases, the capacitor exhibits substantially the same capacitance without any significant increases in ESR losses. However, lowering the dielectric constant ε to 1 reduces the capacitance value obtainable for a capacitor of a given size. Alternatively, capacitances in the range of 0.5-100 pF can be achieved using a gas dielectric or a vacuum dielectric at millimeter wavelengths.
As an example, typical capacitors for use in the millimeter wave frequency range may have a common electrode surface area A and spacing d as shown in TABLE 1.
The top line of TABLE 1 shows spacing between electrodes of 3, 5, 6, 8 and 10 microns. For the given spacing between electrodes and with an air dielectric, the capacitor electrode size is also shown in TABLE 1. For instance, square capacitor structures between 1×1 mm and 5×5 mm are shown with values of capacitance from 0.89 pF −73.73 pF, respectively.
Referring now to
As shown in
As
With the first electrode 11 and second electrode 12 bonded together, an additional epoxy cover 17 may be formed over the second electrode 12 and extending around the periphery of the first electrode 11. As shown in
As shown in exemplary embodiment of
As
With the first electrode 11 and second electrode 12 bonded together, an additional epoxy cover 17 may be formed over the second electrode 12 and extending around the periphery of the first electrode 11. As shown in
As shown in exemplary embodiment of
In addition, those skilled in the art will recognize that in accordance with U.S. Pat. No. 6,775,124 (i.e., '124 patent), the entire contents of which are incorporated by reference, the above-discussed device and method can provide a vacuum capacitor where a vacuum can be drawn between the space d and area A common to first electrode 11 and second electrode 12 forming a vacuum capacitor with the present invention discussed above. Alternatively, in accordance with the '124 patent, the above-discussed device and method can provide a gas capacitor where a gas can be inserted within the space d area A common to first electrode 11 and second electrode 12. The alternative embodiments of an air, vacuum or gas vacuum capacitor for the present invention are selected to supply an appropriate dielectric constant ε and capacitance value C that provides the required performance in accordance with a desired application.
Beyond capacitors, additional components can be implemented with the device and methods of the present invention discussed above. For example, with regard to transmission lines, the present invention can be used to implement parallel strips/striplines components with electrodes having an air, gas or vacuum dielectric between the electrodes. As discussed above, since an air dielectric in particular has no practical limitations with respect to RF losses, these transmission line devices may be developed well into the upper GHz frequency spectrum. Thus, the present invention can also be used to provide low loss transmission lines well into the high GHz frequency range.
Another application of the present invention is the implementation of transmission stripline impedance matching transformers. For example, the present invention can be used to implement a λ/4 transmission line requiring an impedance Zm, That is, a transmission line can be implemented with the device and methods of the present invention that can be used as an impedance transformer to match Zin to Zout. A λ/4 transmission line impedance matching transformer has been implemented in prototype form with the device and methods of the present invention. Yet another application of the above-discussed invention is a microwave low pass filter. In particular, the planar stripline electrodes discussed above can be used as microwave low pass filters with air or vacuum dielectrics between the parallel electrodes.
In addition, to the transmission line applications discussed above, yet another application for the present invention is the implementation of a ring circulator. In particular, a ring circulator is a ring transmission line directional coupler that can be used to sample RF signals that are traveling in different directions inside the ring. A 1.5λ microwave, 3 dB Hybrid Ring Circulator has been implemented in prototype form using the device and methods of the present invention. The ring circulator is a very useful component for a variety of applications including, but not limited to: signal power splitting; signal combining; and signal mixers.
As yet another example of an application of the present invention, low values of inductors (i.e., 0.1 nH to 0.9 nH) can be produced with the device and methods discussed above. In particular, a λ/8 length transmission line with a short circuit at the far end will resemble an inductor at an open ened. The equivalent or virtual inductance of the λ/8 length transmission line at a wavelength (λo)/frequency (fo) of interest is given by the following formula:
L=Z
o/(2*π*fo) (2)
where the inductance is L; the characteristic impedance is Zo; and the frequency of interest is fo From equation (2), the virtual value of the λ/8 transmission line inductance is a function of the actual line characteristic impedance Zo. That is, by controlling the characteristic line impedance Zo, with the device and methods of the present invention, one can arrive at a desired low inductance value.
As a practical example of the above, if the target low inductance L is 0.2 nH at a frequency of interest fo of 3 GHz, by using equation (2), the required λ/8 line impedance required create the characteristic line impedance Zo would be 3.77 ohms. The final inductor, with a characteristic impedance Zo of only 3.77 ohms, must have a very stable characteristics and not be affected by the circuit surroundings. The device and methods of the present invention provides these characteristics at a wide range of RF frequencies.
As a practical example of the above, if the target low inductance L is 0.2 nH at a frequency of interest fo of 3 GHz, by using equation (2), the required λ/8 line impedance required create the characteristic line impedance Zo would be 3.77 ohms. The final inductor, with a characteristic impedance Zo of only 3.77 ohms, must have a very stable characteristics and not be affected by the circuit surroundings. The device and methods of the present invention provides these characteristics at a wide range of RF frequencies.
The foregoing description of the invention illustrates and describes the present invention. Additionally, the disclosure shows and describes only the preferred embodiments of the invention in the context of an air, gas or vacuum capacitor and method for making an air, gas or vacuum capacitor, but, as mentioned above, it is to be understood that the invention is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, commensurate with the above teachings and/or the skill or knowledge of the relevant art. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention. Accordingly, the description is not intended to limit the invention to the form or application disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments.
