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(11) | EP 0 551 618 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | System of "siamese" filter couples for microwave combination network |
| (57) In the system of band-pass filter pairs for networks combining microwave signals
from N transmitters, each filter pair is now formed of two cavities which are each
open on a wall thereof and are disposed on the opposite sides of a central plate consisting
of a nucleus and of two major walls each forming the missing cavity wall. |
[0001] The present invention relates to systems of couples of filters, f.i. band pass filters for networks of combination of radio frequency (microwave) signals, each filter of a couple consisting of a resonant cavity made of a box-like body having a polygonal form.
[0002] More particularly the invention refers to couples of microwave pass band filters so shaped to minimize the encumbrance of a combination network consisting of several couples of filters tuned on different frequencies.
[0003] Advantageously the filter couples are justapposed and interconnected at least two by two in a simple and efficient manner.
Prior Art
[0004] As known a combination network is intended to combine more signals generated f.i. from more transmitters working in the mocrowave field typically comprised between hundreds of Megahertz and some Gigahertz.
[0005] Just to refer to a recent embodiment of the basic stations for radio-mobile transmitter network the problem arises of combining on a single antenna the signals generated by a plurality of transmitters TX₁, TX₂...TXN. The combination circuit must take minimum possible encumbrance.
[0006] In fig. 1 the equivalent scheme of a circuit utilizing conventional technics for the solution of the above problem is shown.
[0007] Filters F₁, F₂...FN are coupled by mutual inductance M₁...Mn to a line L formed of N pieces S₁-Sn each having a length of /2, where corresponds to the central frequency of the working band. The line pieces Si are a part of the filters Fi and are connected to each other by means of N-1 connectors C₁, C₂...CN-1.
[0008] A suitable embodiment of the filter F₁ is described in the Applicant's Italian patent application No. 22559 filed on December 28, 1990 corresponding to Europ. Pat. Appln. 0492303.
[0009] In the scheme of fig. 1, the length of the connecting line amounts to the product of the wave half length /2 and the filter number i.e. X/2 N. /2.
[0010] From this derive poor electric characteristics due to the line length and a bad mechanical disposition of the filters which cannot be parts of a compact structure.
[0011] A more convenient solution is represented by a combining circuit of N filters formed of N/2 filter couples. The equivalent scheme is shown in fig. 2.
[0012] Each line L portion which also in this case is long half wave length of the central frequency of the working band, is subdivided in two semi-pieces SP₁-SP₂, SP₃-SP₄...SPn-₁SPn which are in parallel to each other and show double characteristical impedance. A filter Fi is coupled to each one of said semi-pieces, f.i. F₁ is coupled to SP₁ which is in parallel to SP₂ associated to filter F₂.
[0013] The total length of line L' which connects the filter couples Fi-₁-Fi to the antenna is now halved with consequent improvement of the elctric characteristics.
[0014] The filter number remains however equal to that of fig. 1 with the advantage that couples of filters (F₁, F₂, F₃, F₄ etc) face a commun line tract.
Summary of the Invention
[0015] A first object of the present invention is a system of composite filters consisting of at least a couple of filters combined as "siamese twins", each composite filter being advantageously obtained by the simply justapposing at least two elementar filters which are substantially and specularly identical to each other and each coincident with a filter normally used alone.
[0016] An other object of the invention is a filter couple which allows to drastically reduce the encumbrance and to obtain optimal electric characteristics.
[0017] A further object of the invention is to provide a particularly compact and efficient whole or set of at least two filter couples.
[0018] These and other objects are obtained, according to the invention, with a system consisting of at least one pair or couple of filters (f.i. band pass) for networks combining signals coming from N transmitters (TXi) each of which is coupled to a cammon line (L) directed to an antenna, each filter consisting of a resonant cavity formed of preferably polygonal walls and comprising input and output connectors and an electro-magnetic coupling organ, charaterized in that each pair or couple is formed of two cavities which are open at least on one portion thereof and are disposed on one side and on the other side of a central plate consisting of a nucleus and of two major external faces, each face forming the cavity open wall, said nucleus housing internally the control means of said electro-magnetic coupling organ.
[0019] According to the more remarkable feature of the invention, to each pair or couple of open cavities is associated a single plate which closes the two cavities and inserts in each one of them at least a dielectric resonator element.
[0020] According to an other advantageous feature of the invention, the electro-magnetic coupling organ formed of a curved lamina is disposed externally to each major face at a distance which is regulated through screws placed within a niche or recess made in the nucleus.
[0021] The plate thichness is advantageously regulated in a way to contribute to the obtainement of a /2 distance between connectors.
[0022] Preferably the cavities have a trapezoidal shape, the walls of each cavity taken away and associated to the plate are the bottom walls to which are to be associated the supports and the dielectric elements penetrated by the controllable tuning dielectrics.
[0023] In a particularly simple and advantageous embodiment of the invention, the two filters of each couple are combined as "Siamese twins".
[0024] The different features and advantages of the invention will better appear from the following description of the preferred but not limitative embodiment shown in the accompanying drawings in which:
- figure 2 is the equivalent scheme of the simplest system of filters combined two by two;
- figure 3 is an overall top view of the couple of filters assembled on the coupling plate according to the invention;
- figure 4 is a schematic and partial cross-sectional view of fig.3 taken along line X-X;
- figures 5 and 6 are views from the front and rear side respectively of the core of the invention, i.e. the central plate, to the major faces of which are associated the stationary dielectric parts, said plate being extracted from the cavities of the two filters;
- figure 7 is a view of a partial cross-section taken along line A-A of fig. 5 and shows one major face of the plate;
- figure 8 is a view of the filter (F₁) end remote from the central coupling plate, the motor and relevant accessories being desplaced, and
- figure 9 is a lateral view of an ensemble of superposed drawers in which at least two filter couples are just-apposed according to the invention.
[0025] For the sake of clarity in the description and drawing reference is made to the simplest case of two by two coupled filters, it is however obvious that the coupled filters can be more than two f.i. four. In fig. 2 F₁,F₂...FN indicate again the filters, TX₁...TXN the relevant transmitters, C₁...CN-1/2 the connectors and M₁...MN the coupling inductances of the filters F₁ to the line L'.
[0026] Instead of and in the place of each piece line Si of fig. 1 a small plate P₁...PN is inserted which has internally two semi-pieces SP₁-SP₂...SPN-₁-SPN in parallel. The odd filters are disposed all together on one side of line L' and the even filters on the other side, a semi-piece SPi of fig. 2 corresponding to a piece Si of fig. 1. Each semi-piece has a length still equal to a half wave length (corresponding to the central frequency of the working band).
[0027] The invention concerns in particular a system to couple the pairs of filters F₁-F₂...FN-₁-FN in such a way as to be possible to use elementary filters identical to the filters currently used alone, and to bring about modules of pairs of filters assembled with particularly efficient means of tuning control.
[0028] In the figures from 3 to 8 the two filters f.i. F₁ and F₂ are united, on their (truncated or trapezoidal) bottoms F0₁, F0₂, to a central plate PIA(1) at the ends of which the output connectors CU₁, CU₂ are disposed.
[0029] On the ends E₁, E₂ of filters F₁, F₂ remote from the plate PIA are placed the input connectors Ci₁,Ci₂. In the figures, CU₂ is hidden by the ring nut G of the male connector. In the cross-section of fig. 4 (partial cross-section of fig.3 taken along line X-X) the numeral reference 1 designates the cavity or support of filter F₂, in which penetrates the prolongation 19 of the input connector Ci₂ and is mounted the dielectric system placed on the base Ba.
[0030] This dielectric system comprises three elements, in particular the central female body DF in which enters the male dielectric body DM which can be moved (displaced) manually or preferably authomatically by a motor M provided with a command box Co which is fed by the electric current to operate the motor and by the tuning regulating signals trough the conductors 20. Accordingly the extension of the penetration of the male body into the female body can be controlled.
[0031] In prior patent Applications Applicant has described tuning systems with dielectric resonators as well systems to combine several high frequency signals.
[0032] In particular in the above mentioned Italian application No. 22559 A/90 (European Patent Application 91121336.1/0492303) a system is described to combine signals from filters having resonant cavities of tapered (trapezoidal or bottle-like) shape which allow a justapposition of minimum encumbrance because the tapered head (or bottle neck) of a filter is inserted between the wider portions of the preceding and successive filters.
[0033] Accordingly each filter pair is formed of two filters overturned of 180° and laterally approached, i.e. with the wall of one closed filter in contact with the lateral wall of the other filter.
[0034] Preferably the cavity houses a tuning dielectric system the coupling of which is regulated by means of an electric tele-controlled motor.
[0035] Advantageously the tuning dielectric system is that described in the Italian Patent Application No. 22557 A/90 (Europ. Pat. Appln. 0492304) while the system to select the motor control signal is that according to the Italian Pat. Appln. No. 22558 A/90 (Eur. Pat. Appln. 0492302).
[0036] The specifications of these two prior Applications can be considered as incorporated in this description.
[0037] Going back to fig. 3, the system according to the present invention comprises pairs of identical filters f.i. F₁ and F₂, specularly disposed on one side and on the other side of the central plate PIA.
[0038] Characteristically the bottom walls F0₁ and F0₂ of the cavity forming envelope (f.i. 1 in fig. 4) of filters F₁ and F₂ are now absent; as, it can be seen from fig.4, the body or box-like chamber 1 of each filter F₁, F₂ is open at the end opposite to the end E₁, E₂ respectively where the motors M₁, M₂ and input connectors Ci₁, Ci₂ are disposed. Accordingly the most remarkable feature of this invention is to be seen in the fact that the central plate PIA (represented alone and on an enlarged scale in the front view of fig.6 and in the relevant partially cross-sectioned rear-end view of fig .5) comprises a central nucleus NU showing a niche (recess) Nc, and two major faces PM₁, and PM₂. At the ends of NU are disposed the male connector 2 (Cu) provided with ring nut G, and the female connector 3C₁.
[0039] On each face PM₁, PM₂ is disposed the organ of electro-magnetic coupling R₁, R₂ between connectors 2 and 3; as it can be seen from fig.7, (a view partially cross-sectioned along line A-A on fig.3), said organ is preferably an arcuated lamina R₂ which has a length l₃ and is fixed on the two internal extensions PRO, PRO' of each connector.
[0040] The distance or height "h" of each small lamina R₁, R₂ from the relevant face PM₁, PM₂ of the plate PIA is controlled with the aid of isolating screws 10 acting through the protrusion 100 on said lamina R₁, R₂ which are secured (f.i. by means of screws) to spacers T6 connected on their turn, to the internal conductors PRO of the screw provided connectors 6.
[0041] Characteristically, as the distance between said connectors is determined by the length l₃ of R₁, R₂ (fig.7), by the penetration l₁, l'₁ of the internal conductor of each connector, and by the length 1₂, l'₂ of the T-shaped element T6 and must be equal to /2, it is advantageously acted on the thickness of the plate PIA i.e. on the length l₂ of said element T6, so as to have the sum of l₁+l₂+l₃ be equal to /2.
[0042] Since the figures 5,6 and 7 showing the plate PIA with the relevant dielectric female element DF carried by supports BA are to be imagined as exploded views of fig. 3, it can be understood that the filter pairs according to the invention are of the "Siamese twins" type.
[0043] Fig. 8 is a view of the internal part of a filter, f.i. F₂, seen in the direction of arrow C of fig.3.
[0044] A further advantage of the filter (F₁+F₂) pairs according to the invention is that said pairs beside being advantageous singularly i.e. when they are formed by two open cavities and by a single plate combined as single Siamese twins, they become even more advantageous when same pairs are combined two by two with further encumbrance reduction and electric characteristics improvements.
[0045] Indeed the pairs formed by F₁ and F₂ through the plate PIA₁, and F₃, F₄ through f.i. the plate PIA₂ are perfectly justapposable and are connected to each other by means of the output connector Cu (1,2) of F₁, F₂ which is engaged through the ring nut G, with unput connector Ci (3,4) of the pair or couple F₃,F₄.
[0046] Further significant advantages of the filters combined as Siamese twins according to the invention are obtained in their combinations f.i. of four, six etc. pairs disposed in box-like drawers or sub-racks in an extremely efficient manner to the end of reducing encumbrances and losses and improving the electric characteristics. Fig.9 shows three drawers CAS₁ (the central one with two pairs F₁-F₂, F₃-F₄, on the central line leading to the antenna An filter and connector) and CAS₂ and CAS₃ each containing three pairs of filters (F₅-F₆, F₇-F₈, and F₉-F₁₀ in CAS₂) and (F₁₁-F₁₂, F₁₃-F₁₄ and F₁₅-F₁₆ in CAS₃). The two drawers or sub-racks CAS₂ and CAS₃ each with three pairs are placed on one side and on the other side of the central drawer CAS₁ comprising only two pairs. The common outputs U₅-₁₀ of the filters in CAS₂ and U₁₁-₁₆ of the filters in CAS₃ are parallel connected to the common line of outputs U₁-₄ of CAS₁.
[0047] The line groups 29, 21, 22 and 23 each consisting of three lines as well as the line groups 24,25 of two lines indicate schematically the inputs to the filters CAS₂, CAS₃ while Ca indicate the open connectors.
[0048] Summarizing the invention provides a system to form pairs (couples) of filters with two open cavities and only one plate which, being placed centrally to the two open cavities, shows two walls to close said cavities and at least one dielectic resonator element projecting from said closing walls. In other words, it is as if on a single central plate were transferred: one wall of each cavity filter and the stationary portion of the dielectric resonator of each filter. Since these two resonator elements project from one and the other side of the plate, after assembling, the plate forming a single integral body does not only close externally the two open cavities but moreover inserts threin the "viscera" (bowels) as Siamese twins.
1. System of pairs (couples) of band-pass filters for networks combining radio-frequency
(microwave) signals, in particular for networks combining signals from N transmitters
(TXi) which, each through its own filter (Fi) is coupled to a common line (L') directed
to an antenna, each pair filter having a resonant cavity formed of polygonal walls
and containing at least one dielectric resonator and comprising input and output connectors
as well as an electro-magnetic coupling organ, characterized in that each pair or
couple is formed of two cavities which are open at least on one portion thereof and
are disposed on one side and on the other side of a central plate consisting of a
nucleus and of two major walls, said nucleus housing internally the central means
of said electro-magnetic coupling organ.
2. System according to claim 1, characterized in that a single plate forming an integral
unique body carries dielectric resonator elements for two cavities.
3. System according to claim 2, characterized in that the plate having two major faces
to close two open cavities and complementary dielectric resonators is inserted between
and within said cavities as a common portion typical of Siamese twins.
4. System of filter pairs according to claim 1, charaterized in that an electro-magnetic
coupling organ formed of a curved lamina is disposed externally to each major face
at a distance which is regulated through screws placed within a niche or recess made
in the nucleus.
5. System of filter couples according to claim 1, 2 or 3, characterized in that the plate
thickness is regulated and utilized to obtain a distance of /2 between the input connector
and the output connector.
6. System of pair filter according to at least one of the preceding claims, characterized
in that each cavity houses a dielectric resonator male element which is (tele)-controlled
to assume a controllable penetration in a dielectric resonator female element, this
last female element being secured to the plate major face through a dielectric support.
7. System of two filter pairs according to at least one of the preceding claims, characterizd
in that the pairs are approached in justapposition to each other, the male output
connector of the plate of a pair engaging the female input connector placed on the
plate of the other pair.
8. System of N pairs (N-2) of filters according to at least one of the preceding claims,
consisting of K drawers or sub-racks each comprising at least two filter pairs, K-1
drawers containing more than two filter couples and being connected to a common drawer
containing beside at least a filter pair, also an antenna single filter.