In particular the invention refers to filters at least comprising:-a base body (box-like) in metalic material, generally open at its top;-resonant cavities dug-out in said body ;-resonatos projecting out of said cavity bottoms;-and means to control the tuning and possibly the inter-cavity coupling.

Prior Art The conventional filters are made of metal material (ferreous or not-ferreous) which associate to their important advantages also the inconvenience to demand complexe machine workings and to involve thereby total relevant costs etc.. For years it has been hoped to remedy to these drawbacks by adopting filters which do not have the handicap of those made of the more used metals, requiring final delicate machine workings.

In the US Patent N° 4, 431,977 it is suggested to make filters by forming a dielectric material block and by coating it with a conductive material layer (particularly barium-, titanium, zyrconium-oxide).

The filter results to be still heavy and expensive because of the several difficulties to make the couplings and the tuning means.

In the more recent US Patent N° 5,329,687 is described a method to manufacture filters of the"COMBLINE"type, comprising the steps consisting in:-moulding a body defined by a bottom and by a continuous side wall, which form n cavities and show n resonators integral with said bottom from which they project inwardly;-simultaneously mould al least a wall with a iris in each of said resonator couples;-metalizing the hollow body internal part including at least the bottom, the side wall, the surfaces of the resonators and of the iris forming wall;-applying a closure conductive cover;-and insert tuning threaded screws penetrating through the cover inside the filter body. The metalization comprises at least a copper first layer (having a thickness of at least 1 micron) and a silver second layer (having a thickness from 16 to 24 microns).

The method according to said US Patent N° 5,329,687 shows some merits togheter with several drawbacks among which we may limit ourself to mention that the filter body seems restricted to one filter type (combline), the filer body moulding is contemporaneous to that of all the resonators, the metalizing can be insufficient for very complex and sophisticated filters systems, etc.

Applicant's Italian Patent Application N°97A 000205 describes complex filters at material diversity, comprising a box-like plastic body in which are made a first major band pass filter with n resonant cavities and a second band pass filter, m of the n resonators associated to said cavities consisting of a material different from that of the box-like body and of the resonators integral with it. A machine working is always requested for these prior Art filters.

First object of the present invention is now a system which allows the elimination of the Prior Art inconveniences, in particular of the above mentioned drawbacks, and to obtain even complex structures of components, especially of filters and/or amplifier containers for high frequency signals, which request practically no machine working and, at a parity of encumbrance and of electric characteristics of the conventional components, have costs lowered of even up to 65%.

In one particularly advantageous and therefore preferred embodiment, the invention concerns a complex filter of the duplexer type.

These and other objects are reached with the system according to the invention, the more relevant characteristics of which are recited in the claim 1, the filters having more complex structure being contemplated in the successive claims.

As anticipated, the exigency to have complex components like filters, duplexer, triplexer, containers, supports etc. made of a metalic material different from the classic aluminium, derives from the heavy manufacture costs and the need to increase the performances of said conven- tional elements. Indeed the manufacture of the majority of said metallic components must be concluded with machine working operations which are money and time consuming to be carried out with the required very high precision.

According to the basic feature of the present invention, we have now succeeded in preparing components made of zinc alloys, in particular of the alloys commercially known as ZAMA alloys, which components besides showing optimal electric and encumbrance characteristics are surprisingly manufacturable at very low costs, mainly due to the elimination of said machine working operations.

The different feature and advantages of the invention will more clearly appear from the description of the embodiments shown in the accompa- nying drawings in which: Brief Description of the Drawings -figure 1 is a schematic top view of a first embodiment of a filter substantially made of zinc alloy with however at least a couple of aluminium resonators; -figures 2 and 3 are schematic partial cross-sections with planes having as traces lines B-B, respectively D-D in figure 1; -figure 4 is a top view (similar to that of fig. 1) of a second filter embodiment according to the invention having all the resonators of zinc alloy integral with the filter body; -figures 5 and 5'are cross-sections of the ZAMA resonators coupling the filter inside with an outdoor connector through pins passing a hole through the resonator base; -figure 6 is a front view of a coupling resonator of figures 5 and 5' during the induction soldering phase; -figure 7 is a top view of figure 6; -figure 8 is a frontal view of the screw system used to block a cover or cap of aluminium on a filter body of a Zn-alloys; and -figure 9 is a view, from the outside, of the screw-free bottom of a ZAMA filter.

Detailed Description of the Invention Even if it is possible for the illustration of the invention to refer to elementary components and filters, f. i., of the combline type, it has been preferred to represent in the main figures the most complex case of a duplexer filter which may include also a low band pass filter, couplers (f. i. of the forward and reflex types), special tuning screws etc..

In fig. 1 is shown a filter of n (in this case n=10) cavities from Cl to C10 having generally shapes and volumes different from those of the conventional cavities. Indeed the shape is preferably different from the circular and is, most preferably quadrangular, whereas the volume (V. ZAMA) is substantially larger than the volume (V. Al) of the conventional Al-cavities, said major volume V. ZAMA being at least 1.3-4 times said (V. Al) i. e. the new higher ZAMA cavity volume can be even four times the correspondent volume of the conventional cavities, f. i. of aluminium (Al).

The inter-cavity windows or irises are indicated with the letters A, B, C, D, E, F, G, H, I. The filter body CF has a thickness Se of the outer walls and a thichess Si of the internal walls. Since the new components according to the invention must be interchangeable with the conventional components, they must have the same encumbrance, i. e. outer dimensions strictly equal to those of the components made of classic material like, f. i., aluminium. As anticipated, the basic feature of the present invention consists in that the new components are made of zinc alloys, in particularly alloys containing up to 96% Zn, and other elements, such as aluminium, Cu, Mg, Fe, Cd, Pd, Sn, in particular the alloys ZA4, ZA4C1, ZAC3, ZA8C1, ZA11C1, ZA27C2 etc., generally known and simply indicated as ZAMA alloys.

These alloys are standardized in the UNI-norms f. i. the norm UNI 3717 reports the following compositions: ZAMAComposition Alloys Zn A1 Cu A1 Cu Mg Fe Cd Pd Sn max max max max % % % % % % % % % % ZA4 96 4 0 3.9. 3 0. 03 0. 03-0.06 0. 03 0. 003 0. 003 0.001 ZA4C1 95 4 1 3.9 e 4.3 0.75-'1.25 0.03^ 0.06 0.03 0.003 0. 003 0.001 _. ZA4C3 93 4 3 3.9 4.3 2.7-3.5 0.03 *0.06 0.03 0.003 0.003 0.001 In general said ZAMA alloys are considered a poor material showing mainly unreliable characteristics from the mechanical, electric and chemical view points; just to mention a handicap, it is at least partially corrosive. Up to to-day there was thus a prejudice against the zinc alloys, which has prevented their use in the manufacture of components, in particular of those with remarkable added value like the electric filters.

This prejudice is remained substantially insuperable in the time and has conditioned the development of new advantageous ZAMA formed articles even if (especially recently) have been realized ZAMA alloys substantially free from the heavy typical defects of the old conventional Zn alloys. Just to in- dicate an example, it has been ascertained that the most recent ZAMA alloys allow a good anchorage between the ZAMA filter body skeleton and a coating consisting of, f. i., silver, copper, nickel and the like; moreover with some adeguate measures it is possible to avoid the formation of bubbles and the detachements typical of the ZAMA alloy of the precedent generations.

By overcoming the atavic technical prejudice in particular against said last alloys, Applicant has decided to experiment in critical conditions the use of the last generation ZAMA alloys to manufacture high added value electric components especially filters and has surprisingly obtained results of big relevance both technical and economical.

It has been ascertained that the last generation ZAMA alloys are: moldable under vacuum in warm (at about 350°C) chambers with the aid of pistons and relevant accessories drowned (buried) in the alloy molten mass to form articles (f. i., filters) with outer thickness Se and inner thickness Si extremely reduced (lowered) over the most favourable bodies obtained with aluminium (Al). One of the most important parameters is that the thermal linear expansion is about 24.10 6 for Al and 27.10 6 for the ZAMA alloys, what means that the thermal characteristics remain substantially comparable whereby it can be stated that a ZAMA filter according to the invention has a behaviour, under thermal stresses, substantially equal to that of an Al filter and finally the filters made of ZAMA are interchangeable with the filters made of Al.

Moreover, as above anticipated, the ZAMA alloys lend themself to be formed with very thin thicknesses, for instance up to 0.4 mm whereas with Al it is not possible to go under 2 mm. This allows to compensate the heavy specific weight of the ZAMA alloys (of about 6.5 Kilo per cubic decimeter, 3 3 Kg/decm) over that of Al (of about 2.7 Kg/decm). We have surprisingly succeeded to realize ZAMA products which have weight, layout, housing, external size etc. substantially comparable with the same parameters of the similar Al bodies.

According to an advantageous feature of the invention, at a parity of layout, outer dimensions, cavity numbers etc. of multicavity filters, the size of the ZAMA resonant cavities is decidedly higher than that of Al whereby the electric characteristics of the cavity filters according to the invention are far better than those of the Al filters, as knowingly the higher the cavity volume the easier and more precise the relevant filter calibration, setting and tuning. Further in the walls in which there is a coupling iris, the cavities keep the same volume however where and when there is no iris, one can take profit in placing therein a screw imparting thus to the cavity, shapes which appear strange but have in any case a higher volume.

Other important advantages are obtained in the ZAMA forming in which strong savings of the 65% order, are surprisingly realized over the Al forming. Indeed as the ZAMA alloys can have wall thickness minimal over those of the Al walls, the moulding takes typically place under vacuum and in a hot room (at about 350°C) whereas the Al moulding requires very hot chambers of about 660°C and thrust and forcing organs of the liquid Al alloys of the order of 150-200 tons. When using ZAMA a vacuum takes advantageously place and thanks to this vacuum the presses can work in a wide range of thrust, f. i. from 50 to 800 tons.

The ZAMA moulds have a decidedly longer life (up to 15.000 strokes) than the Al moulds, especially because of the moulding lower temperatures.

The hammermen of generally small ZAMA articles obtain also consistent savings in the consumption of the basic material of the 10-20% order in favour of the ZAMA alloys.

Other advantages are obtained because of the possibility to mould now pressure feet or stems, attachements and supports (2,3,4,5 respectively 6,7,8,9,10 etc. in the figures) not only of adequate thickness but above all integral and contemporaneously moulded with the filter body. The attachements snap now in the relevant rack slots.

Fig. 2 shows on an enlarged scale the portions of walls 100, 101 and of knots 103,104,105 etc. in which the iris free walls as well as said nodes or branch points have the shapes indicated in 100'of two semi- ellipses SE1, SE2 which increase enormously the cavity volume in correspondence to the zone in which there are no controll screws. Figure 3 is the cross-section along line B-B of figure 1 and shows the resonator R3 in the cavity C3 and the separation wall P4 between C3 and C4. Advantageously the iris D can now be less wide and be in the superior part of the partition wall, at a parity of coupling.

In a first embodiment, in addition to the ZAMA resonators integral with the filter body, other resonators made of a non-ZAMA material f. i. of Al can be inserted in said body.

In the embodiment of figure 4 the coupling resonators R'A in cavity C10 to be coupled f. i. with the connector 10 of an antenna A (not shown) and the resonator RA to be coupled with the low pass filter FPB (fig. 3) are indicated as conventional resonators, f. i., in Al, which are fixed f. i. with screws or similar conventional means SR to the bottom 20 (fig. 3) of the filter body CF ; this dishomogeneity (two Al resonators not embedded in the presso-molten body CF of ZAMA) is due to the fact that such coupling resonators RA and RB have to be soldered to the pins Pa and Pb connecting said resonators to the respective connectors (not shown) to the antenna AN, respectively to the low pass filter PBF.

In the advantageous embodiment of fig. 4 also said two coupling resonators RA', RB'are also in ZAMA and are obtained integrally i. e. are embetted in the filter body CF together with all the other resonators from R1 to RIO. According to a feature of the invention and as shown in fig. 6 and 7 the pins PA and PB are welded to the respective resonators RA'and RB'by induction; thanks to the conductor hollow arms PZ1, PZ2 an outer power source IS surrounds with its curved terminal portions PC1, PC2 (cooled by internal liquid circulation), the outer surface of resonator RA'which is heated only in the zone of the hole H for the passage of the pin PA which, once the soldering limited zone of R'A has been sufficiently heated, is welded by a soldering ring SO to the outer coating f. i. in silver on the resonator. On the internal portion IP of pin PA penetrating through hole H the whole length of the resonator base BA, a series of soldedring drops SO' takes place because of the gas developpment in the interface between the outer surfaces of both pin PA and resonator hole passage H.

As it can be seen from figure 7, the curved arms PC1, PC2 surrounding the resonator R'A are at a slight distance from the resonator outer surface and cause therein induction currents which generate the heat to soften and solder the pin PA to the resonator RA'.

Moreover it has been found that the ZAMA whole body (CF + resonators) can be coated by using a first layer (8-12 p thick) of copper electrolytically (and not chemically) obtained on which is further applied a layer of electrolytic nickel (8-12 p thick) that is finally coated with a layer of silver. It is emphasized that the first two layers are to be made with electrolytically obtained metals, significantly copper and nickel on top of which is applied a silver layer.

A further advantage of the ZAMA alloys use is that the brackets, straps, supports, fixing elements attachements and the like (from 1 to 11 in figure 1) between complex filter components, in particular duplexers, triplexers and the like are also made of ZAMA and are integrally formed with the bodies of the components to be compacted in a stable way. This contributes not only to the production of compact integrated bodies but also to the avoidance of the difficult insertion of components in not homogeneous materials which render very delicate the connection operations.

As anticipated, figure 4 is the top view of the inside of a filter (duplexer) having all the resonators integral with the filter body, said resonators and filter body being molded all together in ZAMA alloy. In figure 4 the filter is imagined open i. e. its cover CO (figure 8) being absent. The intercavity couplings are realized with the aid of the irises or windows D, E, F, G, and also of the brigdes SC34 and SC8 on the walls P3 respectively P9. These bridges consist generally of a probe embetted in a block and as they are known per se they do not need here a long description.

Figure 9 is a view from the outside of the bottom wall external face BW. From this fig. 9 a further important advantage can be appreciated, as there are no screws to fix the resonators to said wall BW. Indeed just because of the moulding of all the resonators at the moment of the moulding of the filter body (without cover), there is no need of the screws fixing the resonators to the bottom wall BW. Advantageously several bottom closed holes f. i. SCF1, SCF2, SCF3, SCF4, SCF5 and SCF6 are escavaded in said wall BW to extract the molded Zn filter body from the mould.

Figure 8 shows an aluminium cover Co. Al fixed to a Zama filter body CF. Zn through a precharged screw V of carbon steel and a washer G which initially does not fully rest on the below surface SAl of the Al-cap ; to compensate the climatic elongation difference a test in a chamber (not shown) at temperature varying from-10 to + 70°C is carried out to precharge the elastic washer G with a torque Key of about 1.4 N/m (newton/meter). As the temperature increases the cap in aluminium Co. Al and the filter housing in Zama-alloy CF. Zn tend to detach (separate) from each other generating an upwardly trust UT whereby the washer G goes to seat fully on the cap surface. When the temperature decreases the inverse behaviour takes place.

Important is here to have ascertained that the thermal elongation difference between a ZAMA-filter body CF-Zn and a cap or cover CO of a metal different from Zn can be fully compensate with simple means, f. i. with the introduction of precharged washers between housing CF. Zn and cap.

The invention is susceptible of changes, modifications, substitutions and the like which, being obvious to the skilled persons, fall naturally within the scope and the spirit of following claims.