Wave transmission lines and networks – Plural channel systems – Nonreciprocal gyromagnetic type
Reexamination Certificate
2001-12-07
2003-01-07
Bettendorf, Justin P. (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Nonreciprocal gyromagnetic type
C333S024200
Reexamination Certificate
active
06504445
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable
REFERENCE TO A MICROFICHE APPENDIX
Not applicable
BACKGROUND OF THE INVENTION
The present invention relates generally to the microwave ferrite devices, and particularly to the design of ferrite circulators/isolators that provide the suppression of intermodulation distortion (IMD), include coplanar mounting portion, and allow the application of pick-and-place technology both in production and installation. More specifically, the present invention relates to the structure of circulator/isolator operating above the ferromagnetic resonance. It includes the shape of the central conductor, the housing and installation base, and the assembly procedure for the entire structure.
Increasing demands for high signal power and bandwidth capacity in modern communication networks imposes stronger limitations to the allowed level of IMD. In many cases the typical level of IMD~−75 dBc measured in the existing high power circulators is not sufficient for providing the required inter-channel isolation. The suppression of IMD decreases the interference between the adjacent communication channels and leads to the higher quality of operation. Therefore, the development of a circulator/isolator that is capable of handling high input power while maintaining a low signal distortion is of crucial importance.
The major contributor to IMD in microwave ferrite devices, such as circulators/isolators, is the non-linear phenomenon of ferromagnetic resonance. The closer is the frequency of ferromagnetic resonance (FMR) to the operation range the larger will be the signal distortion. Another contributor to the IMD is a non-uniform design. This means that the more portions of different conducting materials are used in the design, the worse is a device in terms of IMD. Therefore, the efficient suppression of IMD may be achieved by using the similar conducting materials in the signal path and by providing the design allowing the operation of circulator/isolator with high FMR frequency offset.
The operation above the ferromagnetic resonance is realized when the biasing magnetic field sets the frequency of magnetic resonance above the operation range. The magnetized ferrite produces the rotation of the field that creates the circulation action used in the non-reciprocal ferrite devices, such as circulators/isolators. The amount of rotation depends on the anisotropic splitting factor k/&mgr;, where &mgr; and k denote the diagonal and off-diagonal components of the ferrite relative permeability tensor. The typical variation of anisotropic splitting factor with frequency is shown for two values of the external biasing magnetic field, H
1
and H
2
(H
1
<H
2
). Denoting the range of circulator operation as f
oper
, and the frequencies of ferromagnetic resonance corresponding to the biasing fields H
1
and H
2
as f
1
and f
2
respectively, we get the equation:
f
ri
=&ggr;H
i
, (
i
=1,2)
where &ggr;=2.8 MHz/Oe is the gyromagnetic ratio.
The major contributor to IMD in ferrite devices is the non-linear response of circulator to the external RF field, which follows from the fundamental non-linearity of the magnetic moment motion. This non-linear term is inversely proportional to the spacing factor, |f
r
2
−f
oper
2
|
−1
. One can see that the efficient suppression of IMD can be achieved by increasing the frequency offset, f
r
−f
oper
, or, otherwise, by incrementing the biasing field from H
1
to H
2
. However, the field enhancement shifts the whole curve toward higher frequencies and at the given operation frequency band reduces the splitting factor from its nominal value that produces 30-degree turn of the standing wave pattern. In the conventional center conductor designs the input quarter-wave transformer arms are usually used for impedance matching purposes, and the open-end stub resonators including some of the central area—to get the specific frequency characteristics. However, the shape of the open stub resonators intended for enhanced magnetic field operation is not defined.
Rapid expansion of communication networks and base stations sharply increased demands for the low cost circulators/isolators intended for high power applications. This application presumes the design that allows the attachment of circulators/isolators to the customer's system, usually a printed circuit board (PCB) using surface mount technology. In order to ensure the reliable electrical contact with the customer's system and to use effectively the pick-and-place technology, the connecting leads and the mounting base of a circulator/isolator have to be rigid and flat (usually the overall flatness of the mounting base should be within 4 mils).
With all of the above-mentioned features, the circulator/isolator should be inexpensive. Keeping the cost as low as possible in the large-scale production implies the usage of simple mechanical design that is compatible with automated pick-and-place assembling and mounting technology.
Thus, both electrical and mechanical portion of the design should be suitable for application of pick-and-place method both in assembling and at installation, and should provide high reliability, low IMD and the low cost. In order to enable the use of surface mount technology it is very important to maintain the coplanarity between all contacting surfaces that include both the ground plane and the ports.
The surface mount circulators/isolators are already known (see, for example, U.S. Pat. No. 6,011,449). The known devices include a housing having flat bottom and circumferential side portions with openings. Electrical conductors of a central junction extend from the openings onto substantially rigid supports. The conductors are positioned above the supports and are electrically connected to contacts, which are secured in and go down through apertures formed in the supports. Each contact is isolated from the support by a dielectric material. The output end of the contacts and the bottom surface of the housing have to be kept coplanar. However, it is difficult to provide tight tolerance coplanarity in such design because all contacts are made by different constructive parts of the structure.
Relatively simple structure of circulators/isolators, that includes an inexpensive sheet metal housing bent to shape (no machining) is also known (see, for example, U.S. Pat. No. 3,621,476). In this structure the required pressure on the ferrite-center conductor-magnet component stack over the operating temperature range is applied by a pressure plate made of a silicon rubber that is disposed inside the housing. This pressure plate is “an extra part” that increases the size of the device and diminishes the magnetic flux. In some other known structures the pressure is applied by using a cover with a concave surface. But because of such surface's high rigidity the concave does not perform satisfactory as a spring element, especially in the small devices, and tends to crack ferrites under an excessive pressure with the temperature variation.
The center conductor in known devices is usually shaped to match the circulator's impedance to that of a transmission line. The tuning elements comprise of the quarter-wave transformer arms as well as of the open-end tuning stub resonators symmetrically situated between the arms (see, for example, U.S. Pat. No. 3,673,518). Impedance matching provides a smooth passage of microwave energy between the corresponding circulator ports. The experiments have demonstrated that the shaping of the center conductor is also important for achieving the low IMD level.
Accordingly, the objective of the present invention is an inexpensive high power circulator/isolator structure with improved IMD and temperature performance, having a simple sheet metal housing and coplanar mountain surface, and allowing the utilization of automated assembling and installation technique.
BRIEF SUMMARY OF THE INVENTION
In acc
Bettendorf Justin P.
Renaissance Electronics Corporation
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