EP1887648A1

EP1887648A1 - Microwave structure with housing

Info

Publication number: EP1887648A1
Application number: EP06300862A
Authority: EP
Inventors: Simon Neil Batchelor
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2006-08-08
Filing date: 2006-08-08
Publication date: 2008-02-13

Abstract

The invention relates to a microwave structure comprising a conductor strip arrangement (C) disposed on a substrate layer (2, 2'), the microwave structure is enclosed within a housing (1) comprising a top wall (T), a bottom wall (B) and side walls (W), the housing is made of at least two pieces (P1, P2, P3) which are assembled together and at least one piece of the housing is made of a plastic material, the walls surface in the interior (I) of the housing are plated with an electrical conductive material and the substrate layer (2, 2') is embedded in one of the plastic housing assembly pieces (P1, P2, P3) or is an integral part of one of the plastic assembly pieces (P1, P2, P3).

Description

The present invention relates generally to the field of microwave constructions, and more particularly to microwave printed transmission line structures enclosed within a housing.
Today's microwave designers rely on many tools to help create effective circuits and systems. A number of different transmission lines are generally used for microwave integrated circuits e.g. micro strip lines and strip lines, each type having its advantages with respect to the others. Suspended substrate line technology is also among the principal transmission media used in the microwave and millimetre-wave bands. Most of the micro strip components, such as power dividers, filters, directional couplers and multiplexers are manufactured in suspended substrate line form. Covering the basic micro strip configuration with metal top and side plates leads to a shielded micro strip structure within a housing. The main purposes of the housing or package are to provide mechanical strength, electromagnetic shielding and also protection of the micro strip structure from moisture, humidity, dust and other outside agents.
Known from US patent 5,281,934 is for example a printed microwave multiplexer implemented in the form of a micro strip or suspended substrate multiplexer.

Figure 1 of said document shows a plan view of the micro strip multiplexer and
Figure 2 shows the multiplexer arrangement 20 including a first top housing member 22, a bottom housing member 24 and a substrate 26 disposed between said housing members. When assembled together, the substrate 26 is secured between the top and bottom housing members such that the circuit elements 26a, 26b and 26c lie within the corresponding recessed areas. The housing members 22 and 24 are preferably manufactured from aluminium.

Also known from US Patent 5,801,605 is a microwave structure implemented with the aid of micro strip and/or suspended substrate technology. In figure 7 of said document a number of metallic strips 46, 50 are shown disposed on a suspended substrate 48, such as a printed circuit board (PCB) and enclosed within a housing 12 constructed of an electrically conductive material such as copper. The PCB has a dielectric constant greater than the air of the internal environment above and below the substrate 48. Figure 9 shows the filter in the form of microstrip construction, the substrate 56 being supported on the bottom wall 18 of the housing 12.
A problem with the known shielded microwave structures of the prior art is that the substrate has to be manually mounted and secured on the housing metal structure e.g. by way of screws or clamp devices. Further the prior art housing and/or the substrate need to be provided with a support element or structure so that the substrate can be suspended. These disadvantages greatly increase the assembly time and manufacturing costs of the structure.
It is the object of the present invention to provide a microwave structure with housing which is easier and cheaper to manufacture.
The object is achieved according to the invention by a microwave structure according to claim 1 and a method for manufacturing a microwave structure according to claims 8 or 9.
The main idea behind the invention is to make the housing of the microwave structure of a plastic material and embed the microwave structure substrate in the housing piece or manufacture the substrate as an integral part of the plastic housing.
In accordance with the present invention, the housing comprises at least two pieces, which are assembled together, and the substrate layer of the microwave structure is embedded in one of said housing plastic pieces or is manufactured as an integral part of one of said plastic pieces. The substrate can be embedded in a housing assembly piece for example during the injection moulding process of said piece or be made as an integral part of one housing assembly piece when said piece is moulded. The interior walls of the housing are covered of an electrical conductive material in order to provide shielding and a ground conductor for the microwave structure.
The microwave structure of the invention can be implemented as a microstrip construction in which the substrate is located directly on a metal or metal-plated plastic wall in the interior space of the housing or as a suspended substrate structure in which the substrate is located within the housing so that there is a gap between the substrate and the walls of the housing above and below that substrate layer.
Also according to another embodiments of the invention, the suspended substrate microwave structure is mirrored in both sides of the substrate layer so that the signal does not propagate in the plastic substrate, thus reducing signal loss.
The microwave structure disclosed herein has the advantage that it can be manufactured without human intervention since there is no need to mount and secure the substrate layer of the microwave structure to the housing as part of a different or extra assembly step. Manufacturing effort and assembly time are therefore reduced. Also advantageous is the fact that when the substrate layer is manufactured as part of the housing, the metal conductors can be printed directly on said plastic substrate and there is no need to use PCB substrate structures. Furthermore, component count and material costs are also advantageously reduced.
Other advantageous configurations of the invention emerge from the following description and the drawings.
The invention is now explained with the aid of the embodiment examples of Figures 1 to 8.
Fig. 1 shows a cross sectional view of the microwave structure enclosed within a housing according to a first generalization of the invention.
Fig. 2 is a cross sectional view of the microwave structure enclosed within a housing according to a second generalization of the invention.
Fig. 3 shows a cross sectional view of the microwave structure enclosed within a housing according to a first embodiment example of the invention.
Fig. 4 is a cross sectional view of a microwave structure enclosed within a housing according to a second embodiment example of the invention.
Fig. 5 shows a cross sectional view of a microwave structure enclosed within a housing according to a third embodiment example of the invention.
Fig. 6 shows a cross sectional view of a microwave structure enclosed within a housing according to a fourth embodiment example of the invention.
Fig. 7 is a cross sectional view of a microwave structure enclosed within a housing according to a third generalization of the invention.
Fig. 8 is a cross sectional view of the microwave structure enclosed within the housing according to a fourth generalization of the invention.
Figure 1 shows a first simplified embodiment of a microwave structure according to the invention comprising a number of printed conductor strips C disposed on a substrate layer 2 and said microwave structure being enclosed within a housing 1 comprising a top wall T, a bottom wall B and four side walls W (two of them not shown in the figure). The structure of the housing 1 can be imagined as a box.
According to the invention the housing 1 and the substrate layer 2 are made of plastic, and the substrate 2 constitutes the same piece and is implemented in the same production step, e.g. by injection moulding, of one piece of the housing 1.
In subsequent production processes the conductor strips C are disposed on the substrate layer 2 and the surface of the walls in the interior I of the housing which do not constitute the substrate layer 2 are plated with an electrically conductive material. The space in the interior I of the housing above and below the substrate layer 2 is filled with air but could be filled with another kind of dielectric.
The substrate 2 is a plastic layer moulded with one housing piece that is not plated and acts as a dielectric for the conductor strips C. The dielectric constant of the substrate 2 is greater than the dielectric constant of the element filling the interior space I. While the substrate layer 2 is made of the same material as one piece of the housing 1 it is also possible that in a subsequent production step the substrate layer 2 is treated with a suitable process, e.g. particle bombardment or chemical deposition, in order to increase its dielectric constant.
Figure 2 shows a second simplified embodiment of a microwave structure according to the invention comprising a number of printed conductor strips C disposed on a substrate layer 2' and said microwave structure being enclosed within a housing 1 comprising a top wall T, a bottom wall B and four side walls W (two of them not shown in the figure).
According to the second simplified embodiment of the invention, the housing 1 and the substrate layer 2' are different pieces or are made of different materials and the substrate piece is embedded in at least one part of the housing pieces. The housing 1 may be for example of plastic and the substrate 2' be a conventional PCB substrate which is embedded in one or more of the side walls W during the plastic injection moulding step of the manufacturing process.
In a subsequent production process the surface of the walls in the interior I of the housing, that is, the interior surface of the housing that does not constitute the substrate layer 2', are plated with an electrical conductive material. The space in the interior I of the housing above and below the substrate layer 2' is filled with air but could be filled with another kind of dielectric.
The substrate layer 2' (a conventional PCB substrate or any other kind of substrate) may already contain the conductor strips C disposed on it when embedded in one housing piece but it is also possible that only the pure dielectric material is embedded in the housing piece during the plastic injection moulding step of the housing and in a subsequent production process the conductor strips C be disposed on the substrate layer 2'. Again it is also possible that the substrate layer 2' is treated with a suitable process, e.g. particle bombardment or chemical deposition, in order to increase its dielectric constant.
It has to be noted that although Figures 1 and 2 show a suspended substrate microwave structure the person skilled in the art would also be able to derive that they are also valid for a micro strip implementation in which the substrate layer 2, 2' is not suspended within the housing 1, that is, the substrate layer 2, 2' being, or resting over, one of the walls T, B or W of the housing.
It has to be understood that the housing 1 of Figures 1 and 2 is not made of just one piece of plastic material, since there is a need for an opening in order to access the interior space I of the housing in order to plate the interior walls and/or place the conductor strips C on the substrate layer 2, 2'. The housing 1 may be made of at least two pieces of plastic material that are assembled together. The substrate layer 2 of Figure 1 may be then part of one of the at least two pieces of the housing and the substrate layer 2' of Figure 2 may be then embedded in one of the at least two pieces of the housing constituents. Figures 3 to 6 show embodiment examples of how the housing 1 of the microwave structure of Figure 1 and 2 may be constructed.
Figure 3 shows an embodiment example of the of a microwave structure according to the invention comprising a number of printed conductor strips C disposed on a substrate layer 2' and said microwave structure being enclosed within a housing 1 comprising a top wall lid T, a bottom wall lid B and four side walls chassis W (two walls not shown in the figure).
According to the invention the housing 1 may be made of more than one piece. A first piece P1 comprises a four side walls chassis W, a second piece P2 comprises a top wall lid T and a third piece P3 comprises a bottom wall lid B. All the pieces P1, P2, P3 are assembled together to form the housing 1. The top and the bottom wall lid T, B may be made of metal or be also plastic moulded as the side walls chassis W and then plated at least in the surface facing the interior I of the housing. The side walls chassis W is adapted to receive the top and the bottom wall lid T, B and there is also provided a sealing mechanism (not shown) so that the lids and the chassis seal down fully and correctly. The sealing mechanism shall be designed in such a way that it provides very good metal-to-metal contact in order to avoid the generation of passive intermodulation within the microwave structure. Such sealing mechanism may include, for example, screws, glue or heat bonding techniques. It is also possible that the first piece P1 or side walls chassis W is made of more than one piece and the side walls being also assembled as independent pieces of the housing.
The substrate layer 2' is embedded in the first housing piece P1 according to the example of Figure 2 e.g. during the injection moulding process of the first piece P1. Now the independent substrate layer 2' is located in the housing directly over the bottom wall B in the form of a micro strip construction, but it is understood that the substrate layer can be located directly over and parallel to any of the interior surfaces of the walls T, W, B of the housing 1.
Figure 4 shows another embodiment example of the of a microwave structure according to the invention comprising a number of printed conductor strips C disposed on a substrate layer 2 and said microwave structure being enclosed within a housing 1 comprising a top wall lid T, a bottom wall B and four side walls W (two walls not shown in the figure).
According to the invention and similar to the construction shown in Figure 3, the housing 1 is made of more than one piece. A first piece P1 comprises three side walls W, a bottom wall B and a substrate layer 2, a second piece P2 comprises a top wall lid T and a third piece P3 comprises one side wall W. All the pieces P1, P2, P3 are assembled together to form a microwave structure shown in Figure 1. The top wall lid T may be made of metal or be also plastic moulded as the side walls chassis W and then plated at least in the surface facing the interior I of the housing.
The substrate layer 2 is an integral part of the first housing piece P1 created during the injection moulding process of the first piece P1.
It is also possible that the first piece P1 and the second piece P2 are moulded together forming only one piece, and thus only two pieces of the housing shall be assembled together as shown in Figure 5. Figure 5 shows the alternative in which a side wall W1 is moulded together with the substrate layer 2 as one piece P2.
Finally, Figure 6 shows still another assembly alternative in which the substrate layer 2 is moulded together with the side walls chassis W as one piece P1.
From the examples of Figures 3 to 6 it shall be understood that other combinations of pieces that shall be assembled together are possible and that said pieces might comprise other wall elements as the ones shown in the examples. Preferably, the microwave structure according to the invention comprises as few pieces as possible that shall be assembled. It has also to be understood that only some of the pieces of the housing, and at least the one comprising the substrate layers 2, 2', shall be made of plastic and the other pieces can be made of another material such as metal.
Figure 7 shows a third simplified embodiment of a microwave structure according to the invention comprising a number of printed conductor strips C and C' disposed on a suspended substrate layer 2 and said microwave structure being enclosed within a housing 1 comprising a top wall T, a bottom wall B and four side walls W (two of them not shown in the figure).
According to this embodiment of the invention, the printed conductor strips C and C' are disposed in opposite sides of a suspended substrate layer 2 in a mirrored manner. Due to the fact that the suspended substrate microwave structure is mirrored the signal does not propagate in the plastic substrate, thus reducing the signal loss due to losses caused by the signal propagating in the plastic substrate.
Although Figure 7 only shows a simplified structure of the housing 1 it is understood that the housing 1 and the substrate layer 2 can be implemented according to the examples shown in figures 3 to 6. The substrate layer may be an integral part of one piece of the housing 1 as explained in the examples of figures 1, 4, 5 and 6 or be an independent element that is embedded in one piece of the housing 1 as explained in the examples of figures 2 and 3.
Figure 8 shows a fourth simplified embodiment of a microwave structure according to the invention comprising a number of printed conductor strips C and C' disposed on a suspended substrate layer 2 and said microwave structure being enclosed within a housing 1 comprising a top wall T, a bottom wall B and four side walls W (two of them not shown in the figure).
According to this embodiment of the invention, at least one of the housing walls T, B or W comprises a wall projection TW, BW extending to the interior space I of the housing 1. These wall projections TW, BW provide electrical isolation between branches of the microwave structure. Although explained for a suspended substrate microwave arrangement, it is understood that said projecting walls could also be applied to a microwave structure in micro strip form as shown in Figure 3.

Claims

A microwave structure comprising a conductor strip arrangement (C) disposed on a substrate layer (2, 2'), said microwave structure being enclosed within a housing (1) comprising a top wall (T), a bottom wall (B) and side walls (W), the housing made of at least two pieces (P1, P2, P3) which are assembled together,
characterized in that
at least one of the housing assembly pieces is made of a plastic material;
the walls surface in the interior (I) of the housing are plated with an electrical conductive material; and
the substrate layer (2, 2') is embedded in one of the housing plastic assembly pieces (P1, P2, P3) or is an integral part of one of said plastic assembly pieces (P1, P2, P3).
The microwave structure of claim 1 wherein the substrate layer (2, 2') is suspended within the housing (1) so that there is a gap between the substrate and the walls of the housing above and below that substrate layer.
The microwave structure of claim 2 wherein the substrate layer (2, 2') further comprises a second conductor strip arrangement (C') disposed on the surface opposite to the first conductor strip arrangement (C), the second conductor arrangement being the mirror image of the first conductor arrangement.
The microwave structure of claim 1 wherein the substrate layer (2') is embedded in one of the housing assembly pieces (P1) during the plastic injection moulding step of the manufacturing process for that piece.
The microwave structure of claim 1 implemented in a micro strip construction in which the substrate is disposed directly on a metal or metal-plated plastic wall in the interior of the housing.
The microwave structure of claim 1 wherein at least one of the housing walls comprises a wall projection (TW, BW) extending to the interior (I) of the housing in order to provide electrical isolation between branches of the microwave structure.
Transceiver equipment or base station comprising a microwave structure according to claim 1.
A method for manufacturing a microwave structure, the microwave structure comprising a conductor strip arrangement (C) disposed on a substrate layer (2, 2') and said microwave structure being enclosed within a housing (1) comprising a top wall (T), a bottom wall (B) and side walls (W), the housing made of at least two pieces (P1, P2, P3), characterized by
moulding at least one of the housing pieces in plastic material;
moulding at least one plastic piece of the housing so that it comprises or contains a part of the substrate layer (2, 2');
providing the conductor strip arrangement (C) on the substrate layer (2, 2');
covering the walls surface in the interior (I) of the housing which are not plated with an electrical conductive material; and
assembling the pieces of the housing.
A method for manufacturing a microwave structure, the microwave structure comprising a conductor strip arrangement (C) disposed on a substrate layer (2') and said microwave structure being enclosed within a housing (1) comprising a top wall (T), a bottom wall (B) and side walls (W), the housing made of at least two pieces (P1, P2, P3), characterized by
moulding at least one of the housing pieces in plastic material;
moulding at least one plastic piece of the housing so that it contains a part of the substrate layer (2') with the conductor strip arrangement (C);
covering the walls surface in the interior (I) of the housing which are not plated with an electrical conductive material; and
assembling the pieces of the housing.
The method for manufacturing a microwave structure according to claims 8 or 9 wherein the substrate layer (2, 2') is located within the housing (1) so that there is a gap between the substrate and the walls of the housing above and below that substrate layer or is located directly on a metal or metal-plated plastic wall in the interior of the housing.