RF termination

Abstract

The present invention is directed to an RF termination device that includes a substrate having a first meandered transmission line disposed on a first surface thereof. The meandered first transmission line has a predetermined first transmission line length and a characteristic impedance substantially equal to twice the predetermined system impedance. One end of the first meandered transmission line is configured as an open circuit. A second meandered transmission line is disposed on the first major surface adjacent the first meandered transmission line. The meandered second transmission line has a predetermined second transmission line length and a characteristic impedance substantially equal to twice the predetermined system impedance. One end of the second meandered transmission line is coupled to the other end of the first transmission line and the other end is coupled to ground.

Claims

1. An RF termination device for use in a system characterized by a predetermined system impedance, the device comprising: a substrate including a first major surface and a second major surface, a ground plane being disposed on the second major surface; an input port disposed on the first major surface; a first meandered transmission line disposed on the first major surface, the meandered first transmission line having a first characteristic impedance corresponding to a predetermined first transmission line length to provide a predetermined attenuation amount, the first meandered transmission line having a first-first meandered transmission line end coupled to the input port and a second-first meandered transmission line end open circuited; and a second meandered transmission line disposed on the first major surface proximate the first meandered transmission line, the meandered second transmission line having a second characteristic impedance corresponding to a predetermined second transmission line length to provide the predetermined attenuation amount, the second meandered transmission line having a first-second meandered transmission line end coupled to the input port and a second-second meandered transmission line end coupled to the ground plane.

2. The device of claim 1, wherein the device is configured as a microstrip structure.

3. The device of claim 1, wherein the substrate is formed from a ceramic material.

4. The device of claim 3, wherein the ceramic material includes an AlN material.

5. The device of claim 1, wherein the input port is configured to divide an incident RF signal into a first RF signal and a second RF signal, the first RF signal being directed down the first meandered transmission line and the second RF signal being directed down the second meandered transmission line so that the device experiences a predetermined return loss.

6. The device of claim 5, wherein both the first RF signal and the second RF signal traverse each of the first meandered transmission line and the second meandered transmission line twice before recombining at the input port as a residual RF signal.

7. The device of claim 1, wherein the predetermined attenuation amount substantially corresponds to a return loss less that about 30 dB.

8. The device of claim 1, wherein the first characteristic impedance and the second characteristic impedance are substantially equal to twice the predetermined system impedance.

9. The device of claim 1, wherein the predetermined first transmission line length and predetermined second transmission line length are less than or equal to about thirty (30) inches.

10. An RF termination device for use in a system characterized by a predetermined system impedance, the device comprising: a substrate including a first major surface and a second major surface; a first meandered transmission line disposed on the first major surface, the meandered first transmission line having a predetermined first transmission line length and a characteristic impedance substantially equal to twice the predetermined system impedance, the first meandered transmission line having a first-first transmission line end portion and a second-first transmission line end portion configured as an open circuit; and a second meandered transmission line disposed on the first major surface adjacent the first meandered transmission line, the meandered second transmission line having a predetermined second transmission line length and a characteristic impedance substantially equal to twice the predetermined system impedance, the second meandered transmission line having a first-second transmission line end portion coupled to the first-first transmission line end portion and a second-second transmission line end portion coupled to a ground plane.

11. The device of claim 10, wherein the ground plane is disposed on the second major surface so that the device is configured as a microstrip structure.

12. The device of claim 10, further comprising an input port disposed on the first major surface, the input port being coupled to the first-second transmission line end portion and the first-first transmission line end portion.

13. The device of claim 12, wherein the input port is configured to divide an incident RF signal into a first RF signal and a second RF signal, the first RF signal being directed down the first meandered transmission line and the second RF signal being directed down the second meandered transmission line so that the device experiences a predetermined return loss.

14. The device of claim 13, wherein both the first RF signal and the second RF signal traverse each of the first meandered transmission line and the second meandered transmission line twice before recombining at the input port as a residual RF signal.

15. The device of claim 10, wherein the predetermined first transmission line length and the predetermined second transmission line length are a function of a predetermined attenuation amount and the characteristic impedance.

16. The device of claim 10, wherein the substrate is formed from a ceramic material.

17. The device of claim 14, wherein the ceramic material includes an AlN material.

18. A method of making an RF termination device for use in a system characterized by a predetermined system impedance, the method comprising: providing a substrate having a first major surface and a second major surface; forming a first meandered transmission line on the first major surface, the meandered first transmission line having a first characteristic impedance corresponding to a predetermined first transmission line length to provide a predetermined attenuation amount, the first meandered transmission line having a first-first transmission line end portion and a second-first transmission line end portion configured as an open circuit; and forming a second meandered transmission line on the first major surface, the meandered second transmission line having a second characteristic impedance corresponding to a predetermined second transmission line length to provide the predetermined attenuation amount, the second meandered transmission line having a first-second transmission line end portion coupled to the first-first transmission line end portion and a second-second transmission line end portion coupled to a ground plane.

19. The method of claim 18, wherein the ground plane is disposed on the second major surface so that the device is configured as a microstrip structure.

20. The method of claim 18, wherein the substrate is formed from a ceramic material.

21. The method of claim 20, wherein the ceramic material includes an AlN material.

22. The method of claim 18, wherein the second meandered transmission line is disposed adjacent and parallel to the first meandered transmission line.

23. The method of claim 18, further comprising the step of forming an input port on the first major surface, the input port being coupled to the first-second transmission line end portion and the first-first transmission line end portion.

24. The method of claim 18, wherein the predetermined first transmission line length and the predetermined second transmission line length are a function of the predetermined attenuation amount and the characteristic impedance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention.

(2) FIG. 1 is a block diagram of an RF device connected to a termination;

(3) FIG. 2 is a diagrammatic depiction of an RF device connected to a conventional termination element;

(4) FIG. 3 is a detail schematic diagram of the conventional termination element depicted in FIG. 2;

(5) FIG. 4 is a schematic diagram of a termination element in accordance with the present invention;

(6) FIG. 5A is a diagrammatic depiction of a trace layout of the termination element depicted in FIG. 4;

(7) FIG. 5B is a detail view of the trace shown in the termination element depicted in FIG. 5A;

(8) FIG. 5C is a cross-sectional view of the termination element depicted in FIG. 5A;

(9) FIG. 6A is an isometric view of a termination element part in accordance with the present invention; and

(10) FIG. 6B is an isometric view of the termination element part depicted in FIG. 6A on a flange element.

DETAILED DESCRIPTION

(11) Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the RF termination element of the present invention is shown in FIG. 4, and is designated generally throughout by reference numeral 10.

(12) As embodied herein, and depicted in FIG. 4, a schematic diagram of a termination element 10 in accordance with the present invention is disclosed. The termination device 10 includes two equal length transmission lines 12, 14 that are connected at the input port 16.

(13) Each transmission line 12, 14 features a characteristic impedance Zo that is substantially equal to twice the system impedance Zs (i.e., Zo=2Zs) in order to match the port of the system impedance (Zs). In one embodiment the system impedance Zs is 50 Ohm; thus, the characteristic impedances of the two equal-length transmission lines (12, 14) is substantially equal to 100 Ohm. The end of the transmission line 12 is left open, whereas the end of the transmission line 14 is shorted to ground.

(14) Because the two parallel transmission lines 12, 14 present an impedance that is matched to the system impedance (i.e., Zs=Zo/2), when an RF device initially presents an incident RF signal at the input port 16, there is no reflection back toward the device (see, e.g., RF device 1 at FIG. 1). Instead, the incident RF wave is evenly divided into two RF signals so that half of the RF energy propagates along transmission line 12 while the remaining half of the RF energy propagates down transmission line 14. Each RF signal is converted into thermal energy as it propagates, and it slowly decays due to the thermal losses. Once the RF signals reach the end of their respective transmission lines, both waves are totally reflected due to the boundary condition. Since transmission line 12 is open circuited, the reflected RF signal remains substantially in phase (because the reflection coefficient of an open termination is 1); on the other hand, the reflected signal that propagates down transmission line 14 is substantially 180 out-of-phase (since the reflection coefficient of a short termination is 1). Accordingly, when the reflected waves superimpose at the input 16, they substantially cancel each other out (because the reflected waves are of equal magnitude and 180 degrees out of phase). As a result, the termination device 10 substantially does not direct any reflected energy back into the system (characterized by system impedance Zs). If the afore described cancelation is perfect, the reflected waves propagate across the input 16 and continue their journey along the other line. (If the cancelation is imperfect, the wave will propagate outside the device as reflected energy). When these signals again reach the end their respective lines, they are reflected again so that an additional phase difference of 180 is introduced so that the reflected waves are substantially in-phase. When these reflected signals again superimpose at input port 16, the residual energy exits the device as reflected energy. However, those skilled in the art will appreciate that one-half of an incident RF signal propagates a total distance equal to four times of physical line length L. Accordingly, any superimposed signal that propagates out of the input port 16 is attenuated to a negligible level with a suitable line length (L) so that any desired (low) return loss is readily achievable by the present invention.

(15) When one compares the termination element 10 shown in FIG. 4 with the conventional line termination 1 depicted in FIG. 3, the advantages of the present invention become apparent. For example, as noted above, the present invention includes two parallel transmission lines 12, 14 that present an impedance that is matched to the system impedance (i.e., Zs=Zo/2). The transmission line 12 is open circuited and the transmission line 14 is shorted so that each half of an incident RF signal propagates a total distance that is equal to four times of physical line length L. With respect to the conventional design, the characteristic impedance of the transmission line is Zo=Zs and the end of the transmission line is either open or short. An incident RF signal will only travel a distance equal to two times the physical line length. If one assumes that the present invention and the conventional device have the same attenuation per unit length, the line length requirement of the present invention is one-half that of the convention device (FIG. 3). Since the linewidth of a high impedance (2*Zs) transmission line is smaller than the linewidth of a low impedance (Zs) transmission line, the device of FIG. 4 can be realized in a much smaller volume that the conventional device depicted in FIG. 3.

(16) Accordingly, the termination device of the present invention features a termination device that is greatly reduced vis vis the conventional part depicted in FIG. 3. More importantly, the size reduction described herein allows the lossy line termination device 10 (of FIG. 4) to be manufactured as microstrip structure so that standard thick film processes can be employed. For all of the aforementioned reasons, the termination device 10 of the present invention is much more cost effective than the conventional part depicted in FIG. 3.

(17) Referring to FIG. 5A, a diagrammatic depiction of a trace layout for the termination element 10 depicted in FIG. 4 is disclosed. The trace for transmission line 12 is disposed on the left hand side of the substrate 20; again, the end portion of transmission line 12 is open-circuited. The trace for transmission line 14 is disposed on the left hand side of the substrate 20. The transmission line 14 includes a relatively short lead 14-3 that is connected to ground by an edge-wrapped plating 15-1 that provides connectivity to a bottom ground plane 15. Transmission line 12 and transmission line 14 are joined at the termination input 16 at the center of the substrate 18. In one embodiment of the present invention, the traces (12, 14) and the substrate 18 are implemented by a resistive paste to a 60 mil AlN substrate, respectively. Once the resistive paste is applied to the AlN substrate, the structure is fired for curing. In another embodiment, the resistive paste may be implemented by a resistive paste (e.g., TR9200) from Tanaka Kikinzoku Group (TKI) or an equivalent material. The characteristic impedance of all conductive materials can be measured in Ohms/square. (A lossy transmission line can be modeled as a large number of identical segments; each segment being characterized by an impedance measured in Ohms/square. Each segment is characterized by a segment resistance that is a function of the Ohms/square impedance. The overall attenuation provided by the traces is thus a function of the trace length and the characteristic impedance).

(18) Referring to FIG. 5B, a detail view of the trace 14 shown in the termination element 10 depicted in FIG. 5A is disclosed. In order to implement a 100 Ohm microstrip (2*Zs), the traces have about a 9 mil linewidth 14-1 and a 0.7 mil thickness. The characteristic impedance of the conductive material is about 0.1 Ohm/square. To be specific, both of the traces (12, 14) have a 9 mil linewidth and are each about thirty (30) inches long to achieve a 30 dB return loss at 0.5 GHz.

(19) Turning to FIG. 5C, a cross-sectional view of the termination element 10 depicted in FIG. 5A is disclosed. Again the thickness 18-1 of the AlN substrate is about 60 mil. As noted above, the relatively short lead 14-3 is connected to the ground plane 15 by an edge-wrapped plating 15-1 that provides connectivity between the lead 14-3 and the bottom ground plane 15.

(20) Referring to FIG. 6A, an isometric view of an RF termination part 10 in accordance with the present invention is disclosed. The encapsulated part 10 includes a lead 20 that is soldered to pad 16-1, which coupled to the input port 16. The termination part 10 has a footprint that is less than about one square inches (1 sq. in.). As shown in FIG. 6B, an RF assembly 100 includes the termination product 10 disposed on a flange 30. The flange 30 is employed as a heat sink. Thus, the I.sup.2R losses described above are conducted through AlN substrate 60 to the heat sink flange 30 and dissipated. As before, the termination device 10 (depicted in FIGS. 5A-6B) features a 100 Ohm characteristic impedance, a 9 mil linewidth, and a transmission line length of about thirty (30) inches to achieve a 30 dB return loss at 0.5 GHz. Those skilled in the art will appreciate that the footprint of the present invention represents a size reduction greater than 50%. Moreover, by using a thicker ceramic substrate than what is employed in the conventional stripline devices, the risk of device cracking is greatly reduced.

(21) While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. There is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto; inventive embodiments may be practiced otherwise than as specifically described and claimed.

(22) All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

(23) All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

(24) The use of the terms a and an and the and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context.

(25) As used herein in the specification and in the claims, the phrase at least one, in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase at least one refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, at least one of A and B (or, equivalently, at least one of A or B, or, equivalently at least one of A and/or B) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

(26) It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

(27) Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as about and substantially, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.

(28) The recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.

(29) All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate embodiments of the invention and does not impose a limitation on the scope of the invention unless otherwise claimed.

(30) No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

(31) In the claims, as well as in the specification above, all transitional phrases such as comprising, including, carrying, having, containing, involving, holding, composed of, and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases consisting of and consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.