Patent Application
20150334787
Typical microwave components and subsystems comprise metal, or at least metal-coated, enclosures that form cavities for mounting monolithic microwave integrated circuits (MMIC) chips and other components, which can include amplifiers. These enclosures include lids that physically protect the MMIC chips, wire-bonds, and other components from damage in manufacture and use and from the external environment. The lids also protect the components from interference caused by electromagnetic radiation from the electronics in the rest of the system and the operating environment.
Microwave circuits typically radiate energy, such as from interconnect tracks, bond wires, and/or the chips themselves. At certain frequencies, the energy can dominate the functionality and destroy performance of the chips. For example, radiated energy can couple into other parts of the circuit and can often cause unwanted or catastrophic behavior, such as resonance in the “cavity” that houses the MMIC chips. Resonances often cause amplifiers to oscillate, which can render a microwave module completely non-functional. The ease with which unwanted radiation “leaks” into and affects all parts of a system presents a substantial challenge. A typical approach to managing these problems is to package microwave chips with radiation-absorbent material, such as a thin sheet of radiation-absorbent material attached to an underside of a module's lid, or metal or dielectric posts located inside a module to suppress cavity resonances and stray radiation coupling.
Features and advantages of the invention will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate, by way of example, features of the invention; and, wherein:
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.
As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result.
As used herein, “adjacent” refers to the proximity of two structures or elements. Particularly, elements that are identified as being “adjacent” may be either abutting or connected. Such elements may also be near or close to each other without necessarily contacting each other. The exact degree of proximity may in some cases depend on the specific context.
An initial overview of technology embodiments is provided below and then specific technology embodiments are described in further detail later. This initial summary is intended to aid readers in understanding the technology more quickly but is not intended to identify key features or essential features of the technology nor is it intended to limit the scope of the claimed subject matter.
Although typical solutions for dealing with cavity resonance have been effective in some situations, these solutions may be almost completely ineffective in many other situations. For example, when the gain of a radio frequency (RF) emitting chain of amplifiers in a small space is high (i.e., between about 20 dB and about 30 dB) or very high (i.e., greater than about 30 dB), the typical metal lid with a layer of absorber is not likely to reduce feedback/resonances to a level that avoids oscillations, particularly in small cavities. Thus, there is a need for an effective solution that provides stability for high gain modules.
Accordingly, a microwave module lid is disclosed that suppresses feedback that leads to oscillatory conditions for high gain modules. In one aspect, the lid is effective for high gain modules that are confined in a small cavity. The microwave module lid can include an inner side operable to define, at least in part, a cavity configured to have an RF emitting component disposed therein. The microwave module lid can also include at least two dielectric layers proximate one another. Each layer can have a thickness, a dielectric constant, and a dielectric loss characteristic. In addition, the microwave module lid can include a metal backing layer proximate one of the dielectric layers to contain RF energy within the microwave module lid. The thicknesses, the dielectric constants, the dielectric loss characteristics, or combinations thereof of the at least two dielectric layers can be configured to minimize RF resonance in the cavity.
In another aspect, a microwave module is disclosed. The microwave module can include a substrate, a RF emitting component disposed on the substrate, and a lid coupled to the substrate. The lid can include an inner side operable with the substrate to define a cavity about the RF emitting component. The lid can also include at least two dielectric layers proximate one another. Each layer can have a thickness, a dielectric constant, and a dielectric loss characteristic. In addition, the lid can include a metal backing layer proximate one of the dielectric layers to contain RF energy within the lid. The thicknesses, the dielectric constants, the dielectric loss characteristics, or combinations thereof of the at least two dielectric layers can be configured to minimize RF resonance in the cavity.
One example of a microwave module 100 is illustrated in
It is common for the wire bonds 104 and/or circuit components 103 to emit “stray” RF radiation. Prior microwave modules typically use a metallic lid to shield and/or protect the circuit components 103 and the wire bonds 104. In this type of microwave module, instabilities due to microwave energy reflected back from the lid to the input of the device can create a feedback path that can cause the amplitude to oscillate. For example, a typical metallic lid can create resonances and feedback paths in the cavity that can cause problems for circuit components, such as causing amplifiers to oscillate and/or have ripple in their pass band characteristics. Resonances and feedback can be particularly prominent in a small cavity where space inside the cavity 107 has been minimized around the circuit components 103 and the wire bonds 104. Thus, the presence of the metallic lid can make it difficult to keep the microwave module stable when there is a lot of RF gain inside the module because only a small amount of feedback is needed to induce oscillations due to radiated RF energy looping back to the input of an amplifier.
To minimize or eliminate problems such as these that arise when using a lid, the lid 101 can include dielectric layers 110, 120 proximate one another to absorb RF energy. In addition, the lid 101 can include a metal backing layer 140 proximate the dielectric layer 110 to provide a reflecting plane and contain RF energy within the lid 101. In one aspect, the dielectric layers 110, 120 can define, at least in part, the inner side 106a of the lid 101. In another aspect, the metal backing layer 140 can define, at least in part, an outer side 106b of the lid 101. Each dielectric layer 110, 120 can have a thickness 111, 121, respectively, a dielectric constant 112, 122, respectively, and a dielectric loss characteristic 113, 123, respectively, which can be tuned or configured individually or in any combination to minimize RF resonance in the cavity 107. For example, the thickness 111, 121 of the dielectric layers 110, 120, respectively, can vary for tuning absorption to a desired frequency band (i.e., 15-18 GHz). The materials of the dielectric layers 110, 120 can be selected with appropriate dielectric constants 112, 122, and dielectric loss characteristics 113, 123. In one aspect, a dielectric constant can be selected for a particular frequency range. In some example lids, the thickness 111, 121 and the dielectric constant 112, 122 have been recognized as the dominant factors, with the dielectric loss characteristic 113, 123 contributing to a lesser degree. In such cases, the lid 101 can be configured with a multiple dielectric layer 110, 120 stack-up with the right properties for a given frequency band.
In one aspect, absorption of RF energy by one or more of the dielectric layers 110, 120 can be due to matched impedance for a particular frequency range. In another aspect, RF energy can be attenuated by one or more of the dielectric layers 110, 120, which can be “lossy” absorbers or absorbing dielectric materials. As RF energy is reflected by the metal backing layer 140 the energy cancels itself out to some degree. The result is a stack-up of dielectric layers 110, 120, working in unison, with a metal backing layer 140 that can provide a good match to a microwave signal in a particular frequency or operating band that may impinge on the lid 101, such that the microwave signal is absorbed into the lid 101 and not reflected back to the circuit components 103, thereby reducing or eliminating resonances in the cavity 107 of the microwave module 100. In one aspect, the metal backing layer 140 can also serve to shield components external to the module 100 from RF energy originating within the module 100.
A properly “tuned” lid 101 can therefore appear as if it is not there, in that the negative aspects of a typical metal lid with regard to resonances and feedbacks in the cavity 107 are eliminated or minimized. A microwave module lid in accordance with the present disclosure may be particularly useful when the gain of a microwave module's RF amplifiers is very high because, in this case, only a small amount of feedback is needed to induce oscillations due to radiated RF energy looping back to the input of an amplifier. The lid 101 can therefore provide much greater module stability by effectively absorbing substantially all stray RF energy instead of partially absorbing and/or attenuating radiated RF energy, as with prior absorber coated metal lids.
The dielectric layers 110, 120 can include an absorbing or “high loss” material (i.e., ECCOSORB®) and/or a “low loss” material (i.e., ECCOSTOCK®) comprising an elastomer, polymer, composite, ceramic, etc. The dielectric layers 110, 120 can be of any suitable form or configuration, such as a foam, epoxy, coating, powder, sheet, adhesive, etc. In a particular example, a dielectric layer 110, 120 can comprise a polyurethane or silicone sheet loaded with iron particles. Still other configurations, forms and materials are contemplated, as will be recognized by those skilled in the art, with those described herein not intending to be limiting in any way.
In one aspect, one or more of the dielectric layers 110, 120 can be configured to form a primary structural support for the lid 101. For example, dielectric layer 120 can form the structural basis for the lid 101, in that side walls 108a, 108b of the lid 101 extend from the dielectric layer 120 and include interface features 109a, 109b to facilitate coupling the lid 101 to the substrate 102. This coupling can be done to seal the lid 101 to the substrate 102, such as with a hermetic seal, if desired. In addition, the dielectric layer 120 can be configured to provide support for the dielectric layer 110 and the metal backing layer 140. For example, as illustrated in
Thus, as illustrated in
In accordance with one embodiment of the present invention, a method for facilitating minimizing RF resonance in a cavity of a microwave module is disclosed. The method can comprise obtaining a microwave module lid, the lid having at least two dielectric layers proximate one another, each layer having a thickness, a dielectric constant, and a dielectric loss characteristic, and a metal backing layer proximate one of the dielectric layers to contain RF energy within the lid. Additionally, the method can comprise facilitating coupling of the microwave module lid to a substrate on which an RF emitting component is disposed, the microwave module lid and the substrate defining a cavity about the RF emitting component, wherein the thicknesses, the dielectric constants, the dielectric loss characteristics, or combinations thereof of the at least two dielectric layers are configured to minimize RF resonance in the cavity. It is noted that no specific order is required in this method, though generally in one embodiment, these method steps can be carried out sequentially.
In one aspect, at least one of the dielectric layers can be configured to form a primary structural support for the microwave module lid and include an interface feature to facilitate coupling the microwave module lid to the substrate. In another aspect, the metal backing layer can be configured to form a primary structural support for the microwave module lid and include an interface feature to facilitate coupling the microwave module lid to the substrate.
It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.
While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
