MICROWAVE DIELECTRIC MATERIAL

Abstract: A laminate construction for use in microwave electronics, such as for circuit boards or antennas, has expensive dielectric material having a low dissipation factor (Df < 0.005 at 1 GHz), such as PTFE/glass or Gore-ply3, only in the upper 200 mu m and less expensive dielectric material having a higher dissipation factor (Df > 0.005 at 1 GHz), such as FR-4, cyanate ester, BT/epoxy, polyimide thermount or polyimide, in the underlying 400 mu m of the dielectric material, thereby reducing cost while maintaining the same performance as regards low energy loss and consistency of the dielectric constant over the temperature and frequency range of use.

Description: Microwave Dielectric Material TECHNICAL FIELD OF THE INVENTION The present invention relates to laminate constructions containing dielectric material for use in microwave electronics. They can be used for microwave applications in inter alia component carriers such as circuit boards and in microwave antennas. The invention also relates to a method of manufacturing such new dielectric laminate constructions. RELATED ART In such dielectrics it is important that there not be excessive variations in the dielectric constant (D^) over the temperature and frequency ranges of use. It is also important that the dissipation factor (tan δ) should be low, so that there will be a minimum energy loss (heat). This has been achieved previously by arranging a di- electric layer to support a microstrip conducting layer thereon. In order to achieve the just described desired effects, a dielectric material layer is applied which has the desired properties. The dielectric materials used in these designs can have a thickness of ca. 600 μm and dielectric materials having the desired or required properties can increase the cost of the board significantly In the GSM mobile radio systems, for example, an antenna having a large amount of material is used, which can be veiy expensive if high quality dielectric material must be used. SUMMARY OF THE INVENTION In accordance with the foregoing background discussion, an object of this invention is to provide a dielectric microwave electronic component carrier or a dielectric microwave antenna, which is less expensive than hitherto known component carriers or antennas but which provide the same high quality properties as regards low total dissipation factor, that it to say essentially low heat generation and low variation in the dielectric constant. This is especially desirable in antennas using significant amounts of materials, such as those used in the new GSM 1.8 system. Tests on which the present invention is based have shown that for a frequency of 1 GHz only the top 200 μm of the board need be of top quality as regards its dissipation constant and the remaining underlying portion can be of lesser quality thus reduc- ing the total cost of the laminate. Another object of the present invention is to provide a method of manufacturing such a component carrier or antenna. BRIEF DESCRIPTION OF THE DRAWINGS The figure shows schematically a composite microwave board. DETAILED DESCRIPTION OF EMBODIMENTS The figure shows one embodiment of the invention which is a composite microwave board. To a ground plane 1 there is applied a lower layer 2 of a less expensive dielectric material which in this case is an FR-4 material. It is also possible within the scope of the invention to use other materials having a dissipation factor at 1 GHz which is greater than 0.005 such as cyanate ester, BT/epoxy, polyimide thermount, or polyimide. To this lower layer 2 there is applied an upper layer 3 of a higher quality material such as PTFE/glass or Gore-ply®. This upper layer 3 has a dissipation factor D f at 1 GHz which is less than 0.005. The dissipation factor D f is used as a measure of the energy lost (heat) in relation to energy stored at a certain microwave frequency (in this case 1 GHz). This dissipation factor can be expressed as tanδ where δ is the angle formed by the vector components ε' and ε" where ε' is a real component corresponding to the energy stored and ε" is an imaginaiy component corresponding to the dissipated energy, called the loss factor. In a vector diagram z and ε" are represented as 90° out of phase and therefore the ratio between them can be represented as tan δ where δ is the angle formed by the two vectors. In the method according to the invention, a lower layer 2 of less expensive dielectric material having a high dissipation factor (D f >0.005) is applied to an earth plane. This lower layer may have a thickness of 400 μm of a total dielectric thickness of 600 μm. An upper layer 3 (ca. 200 μm ) of a more expensive dielectric material (D f O.005) is then applied onto the lower layer 2. A conductor layer 4 is then ap- plied to the upper layer 3. ElectiOnic components may be mounted on the conductor layer 4.

Claims: CLAIMS 1. Laminate construction for microwave electronics applications, comprising: at least one earth plane (1), a lower layer (2) of dielectric material having a dissipation factor D at 1 GHz of greater than 0.005, applied to said earth plane, an upper layer (3) of dielectiic material having a dissipation factor D at 1 GHz of less than 0.005 applied to said lower layer, a conductor layer (4) possibly including electi'onic components mounted on said up per layer. 2. Laminate construction according to Claim 1, wherein the upper layer (3) of dielectric material is approximately 200 μm thick. 3. Laminate construction according to Claim 1 or 2, wherein said laminate construction is a circuit board. 4. Laminate construction according to Claim 1 or 2, wherein said laminate construction is an antenna. 5. Method of manufacturing a laminate construction as defined in one of the preceding claims, comprising the following steps: 1. applying onto an earth plane (1) a lower layer (2) of dielectric material having a dissipation factor D at 1 GHz of greater than 0.005, 2. thereafter applying onto said lower layer (2) an upper layer (3) of dielectric material having a dissipation factor D f at 1 GHz of less than 0.005 applied to said lower layer (2), 3. thereafter applying a conductor layer (4) onto said upper layer (3).

Inventors: BERGSTEDT LEIF, BERGSTEDT, LEIF
Applicants: TELEFONAKTIEBOLAGER L M ERICSS, TELEFONAKTIEBOLAGER L M ERICSSON (PUBL)
Application year: 1999
Main classification: H01P3
IPC codes: H01P3, H01Q1, H01Q9, H05K1