It is mandatory that the antenna system design includes protection means against troubles due to lightning: these shall not only prevent the direct damaging of elements installed on poles, trestles and in elevation in general, and therefore more subject to catch thunders, but also the propagation of over-currents along antenna down conductors and in general along radio frequency lines connecting the antenna to control or use equipment installed at ground level.

The performances requested to a lightning protection device are scope of international standards, in particular, ITU reference standards in the international environment are: ITU (K. 11, K 20, K21) while reference standards for the specific product are: IEC 61000-6-2, En 50 082-2, En 50121-4.

Of course, protection devices shall not negatively affect the performances of the system to protect. Protection devices satisfying this requirement avail of the different spectral distribution between the useful signal and the troubles and employ a line element in A/4 (where A is the wave length of the useful signal) between the line to be protected and the ground: as it is already known, an element in X/4 acts as open circuit for the signals having A wavelength, which are

reflected towards the line, and as short circuit for different wave length signals, discharged for instance to the ground.

The USA 5.844. 766 patent describes an example of a protection device of this type for antenna systems installed on a tower and suitable to enable the direct supply of components, installed they too on a tower, through a line connecting a base station to the antenna. The device is implemented through concentrated elements and includes: a directional coupler in series to the line to divert the low power supply direct current towards the components to supply; the element in A/4 separating the radio frequency useful signal from direct or low frequency signals ; two cylindrical capacitors in series between them and to the element in X/4, which form a low pass filter to separate and additionally filter the useful signal; and a gas discharger connected between the element in X/4 and the cylindrical capacitors and the ground.

Such a device shows some drawbacks: it has a complex and therefore expensive structure; considering the high number of components employed, the implementation with concentrated elements results bulky; the gas discharger allows a comparatively high residual of power; the presence of a directional coupler (equivalent to a capacitor from the electrical point of view) in addition to the element in A/4 makes insertion losses comparatively high.

Concerning cost and size aspects, we want to underline that some applications (e. g. some kinds of base stations of Pico-cell mobile telephone systems) require the protection of more ways leading to a common equipment contained in cubicles of standard size. A structure including a plurality of devices as those forming the object of the mentioned patent would result incompatible with the size of the cubicles and

have a non-affordable cost.

The USA 6.243. 247 patent describes a protection device realized with printed circuit technologies of the strip-line (strip-line) or micro-strip-line type. The device essentially consists of a capacitor structure implemented through two conductor tracks placed on two different plans and separated by a dielectric: one of these tracks (connected to the input where the lightning over current can occur) is joined to a track section in A/4 to discharge the over current to the ground.

The strip-line technology enables to implement a device of reduced size and low cost. However, also this already known device originates high insertion losses because, like the device of the previous patent, it is made, as for the electrical aspect of a capacitor in series to the line and the element in A/4 between the line and the ground.

Even considering applications in which it is not necessary to uncouple a direct voltage between input and output, employing the strip-line technology we cannot consider to use only the element in X/4 connected between the line and the ground, as it would be possible in theory : in fact, to have a high bandwidth, it should be necessary to realize said element with a conductor strip of reduced cross section, which is opposition to the need to dissipate high currents. On the other hand, the increase in the cross section of the strip necessary to obtain good performances would make the cost of the device equal to or even higher than that of a modest component device: therefore, we would have the already mentioned cost problems if the protection on more ways were implemented.

Summary of the Invention Scope of the invention is to supply a protection device, realized in printed circuit technology, in particular strip-

line, showing low insertion losses and good performance of dispersion to the ground of the power induced by the thunder without requiring an increase in the size and cost of the device. Therefore, the device well suits to the implementation of devices for the protection of more radio frequency ways connected to a common equipment.

Therefore, according to the invention a device is offered including at least a protection element connected to a line matching an input port and of a protected port and includes a first line element, which is an element in A/4, connecting the input port with the ground, in which said first line element forms part of a filter structure having high pass filter function, with closing to the ground, for the noises, and of band pass filter for radio frequency signals, and includes also a second and a third line element arranged between the input port of the noise and the insertion point of the first line element and between said point and the protected port, respectively, and having impedance adjustment functions., The invention, together with further objects and advantages. thereof that are considered to be novel, may be understood from the subjoined claims and appreciated with reference to the attached drawings, in which: Brief description of drawings - figure 1 is a plan view, at track plan level, of a device according to the invention for the protection of a plurality of radio frequency ways; -Figure 2 is a magnified scale plan view of one of the elements of the protection device; - Figures 3a, 3b are the block diagram and the electrical diagram of the element of fig. 2, respectively; -Figure 4 is a simplified prospect view of a preferred embodiment of the element of fig. 2, having a grounding

plan removed; - Figure 5 is a sectional view according to line V-V of fig. 2; and - Figure 6 is a diagram of an antenna system employing the device of fig. 1.

Description of the preferred embodiment of the invention with reference to figures 1 and 2, a device 1 is shown for the protection of a plurality of radio frequency ways, ending on a common equipment, against troubles consisting of direct high voltage instant over-current or however at low frequency, such as those due to lightning,.

The device 1 includes a plurality of separate protection elements 2a... 2n (eight in the example shown) each one associated to one of the lines to be protected. In the preferred embodiment of the invention each element 2 consists of conductor tracks realized on a printed circuit card 3. In particular, it is a device implemented in strip line technology (strip-line) that, as already known, foresees that conductor tracks are parallel to the card external surfaces forming two grounding planes, and are separated by the same through isolating layers.

Each one of the elements 2 is shown in detail in figure 2 and has, in plan, essentially T shape, in which both the wings 20,21 and the bar 22 of the T are sections of conductor track forming line elements in A/4 (see also figure 3a). Section 22 shows, at the end opposite to the wings 20, 21, metalized holes 23 for the electrical connection to the grounding plans 30 of card 3. In a conventional way, the track sections 20,21 have a terminal part 20A, 21A parallel to the bar 22, in order to reduce the space occupied on the circuit. Matching said terminal parts, metalized paths 24,25 are provided for the connection of the connectors for the lines incoming/outgoing from the protection device. The slots

4,5 separate these paths 24,25 from grounding plans 30, only one is represented in figure 2.

Profitably, the printed circuit card 3 is of the glass fiber type, like the one known with code FR4. Such a kind of printed circuit is not expensive and enables to assure the isolation of the single elements 2a... 2n in case of devices showing, as in fig. 1, a plurality of protection elements on the same card 3. In effect, said insulation is obtained through a plurality of metalized holes 6, preferably aligned, electrically connecting the grounding plans 30'and 30''and inserted in intermediate position among the elements 2.

The structure described is equivalent, from the electrical point of view to that represented in fig. 3b: the track sections 20,21 are equivalent to inductance and capacity in series and have impedance adjustment function, while the section 22, connected to the ground, is equivalent to inductance and capacity in parallel and has the actual function to suppress the noise availing of the different spectral distribution between noise and useful signal. The structure realizes a high pass filter with mass closing for the noise, and band pass filter for the radio frequency signal.

The filter structure described shows an insertion loss considerably lower than that of the devices of the known technique as mentioned above, because the capacitor (or the directional coupler) in series to the line is eliminated, requested to isolate input and output versus the direct one.

Moreover, this structure enables to make comparatively wide tracks, so to obtain a good dispersion of over currents due to the possible discharges without the need of high thickness, with consequent cost increase. In particular, this is due to the presence of impedance adjustment elements 20, 21, which enable to obtain a lower impedance at the interface

point with section 22.

As already said, the device 1 is realized according to printed circuit technology, in particular strip-line technology (strip-line). Said technology enables to easily implement devices in which each one of the elements 2 includes at least a couple of conductor sections 2', 2", each one having the structure shown in figures 1,2. The different sections 2', 2"are parallel between them and versus the grounding plans of the circuit and are separated by an insulating layer. This implementation is shown in figures 4, 5, where the same reference as figures 1 and 2 have been used, denoting it with apex or double apex, respectively, the homologue elements of the two sections. In the sectional view of fig. 5 it can also be noticed the insulating layer 32 between the two sections. Metalized holes 23 are steel foreseen, connecting sections 22', 22"between them and to the grounding plans 30', 30", and metalized paths 24,25 for the connectors, isolated from the grounding plans through slots 4"and 5".

Such an arrangement, with two or more sections in parallel, additionally helps the dispersion of high currents with thin tracks. In practice, the set of n sections in parallel assures, at equal width, performances essentially complying with those of a unique section with thickness n times higher.

The structure of figures 4 and 5 can be easily implemented through the manufacturing of two printed circuits with the surface tracks opposite to the grounding plan and bonding them with an isolating bonding agent.

'The tests made demonstrated that the described structure has performances well higher than the minimum performance required by the standards.

Figure 6 shows an antenna system for a base station of a mobile telephone system in which the protection is realized employing the invention. Provisions are made for one or more sets of antenna elements 100a, 100b.... 100n and 101x..., where each element shows a relevant connection line 102a... 102n, 103x... to the electronic equipment of the station, arranged in a cubicle 104. At the arrival point of lines 102,103... (e. g. of the upper face of the cabinet 104) a protection unit 105 is provided including, for each group of antenna elements, a device 1 like the one shown in fig.

1.

The many advantages and features of the present invention will be appreciated from the foregoing description of a preferred embodiment. It should be understood that the present invention is not limited thereto without departing from the scope thereof.

One of these modifications consists in positioning the protection elements matching the antenna elements 100, that is at the opposite end of the line compared to what shown in figure 6. Of course, protection elements can also be installed at each end of the lines.