TECHNICAL FIELD

The present invention relates to the technical field of RF telecommunications. In particular, the invention relates to a compact wide-band "monopole indirect ground' antenna for radio transmission, particularly suitable to be mounted on vehicles or portable or transportable radio transmitter systems.

By way of example, the invention can be advantageously used by a vehicle, typically a military vehicle equipped with radio transmission system. The above mentioned case, although non to be considered limiting to the application of the invention, presents all the problems and needs that gave rise to the present disclosure. For this reason, the invention will be described in the following with particular reference to the above mentioned application without excluding others, as already said, for which its use and advantages are immediate and obvious.

BACKGROUND ART

As far as the illustrative application of the invention is concerned, it is known how important the use of solid, reliable and stable radio transmission or devices is in military field. Much of the success of a mission or campaign is credited to the perfect operation of the telecommunications in the action territory. Mobile radio transmission systems fit out suitably designed vehicles or are installed onboard of armoured cars, battle tanks, aircrafts, helicopters or boats, to guarantee the best cover of the territory. Other radio transmission systems, installed on non self-propelled structures, can be transported by road or by air, as required by the operative zone. TECHNICAL PROBLEM

Such systems are often designed to work even in a very broad range of frequencies, which generally varies from some tens to some hundreds of MHz. Monopole antennas are widely used for these frequency ranges, as they have relatively compact dimensions, small size and a fairly good general efficiency.

Although several antennas may be installed, which work in narrower frequency bands, the possibility of efficiently covering the whole frequency spectrum of operation with only one antenna is undeniably advantageous.

Technical solutions are known which are aimed at extending the frequency spectrum covered by one antenna in an efficient way.

In particular, the so-called "monopole" antennas are suited to such frequency spectrum extension, that is, lambda quarters (λ/4) resonant antennas that include a ground plane, used to recreate the "missing" arm of the corresponding half lambda dipole due to the known Image principle". Generally, in the case of narrowband monopole antennas, the radiating element is composed by a thin rod arranged vertically in the centre of a sunburst pattern (in the case of "indirect ground" version). In order to extend the bandwidth, according to known techniques, the radiating element can be formed with a hollow cylinder of conductive material.

In this case, the bandwidth usable by the antenna is a function of the cylinder diameter and is defined in accordance with known semi- empirical formulas.

For example, in order to obtain a usable band between about 30 MHz and about 1 GHz, necessary to cover most of needs of the military medium-short haul transmission systems, a 500 mm long cylindrical radiant element can be used, having the diameter of 90 mm. In order to make the antenna work in the range between 30 MHz and about 200 MHz an impedance converter, obtained in accordance to known techniques, must be interposed between the antenna and the transceiver.

A drawback of the above described configuration of a "monopole" antenna, when installed in a vehicle or a mobile system, derives from the fact that the shape of the rigid and cylindrical radiating element causes a strong air resistance and moreover, it can be easily hit and damaged by branches or other objects during off-road routes. The air resistance can become significant as the speed of the vehicle transporting the antenna increases, and generate variable mechanical stresses, which can weaken the antenna supports, or, in any case, require its different dimensioning.

OBJECTS OF THE INVENTION

The main object of the present invention is to propose a compact, so-called "monopole" antenna, capable of providing a bandwidth that is identical or similar to that of a monopole antenna with cylindrical tubular radiator of equal dimension, and still has a considerably lower aerodynamic coefficient.

Another object of the invention is to propose a compact antenna capable of working also with one or more failed components and thus having a high resistance to damage.

A further object is to propose a compact antenna which has a simple construction, limited cost and simple maintenance, and is also particularly solid.

SUMMARY OF THE INVENTION

These and other objects are wholly obtained by a compact wideband, so-called "monopole" antenna, comprising a support base, and a plurality of linear ground elements, mounted on the support base and extending radially therefrom, to form an electrical ground plane for the compact antenna.

The antenna further comprises a radiating element, mounted on the support base and extending in a direction substantially perpendicular to that of the linear ground elements.

The radiating element comprises a plurality of rods, each of which is secured to the support base at its proximal end; the rods are parallel to one another and their proximal ends lie on a circumference, so as to form as many generatrices of a cylinder.

BRIEF DESCRIPTION OF THE DRA WINGS

The characteristics of the invention will become evident from the following description of preferred embodiments of the compact wideband antenna, in accordance with the contents of the claims and with help of the enclosed figures, in which:

- Fig. 1 is a side view of the compact wide-band antenna proposed by the invention in a first embodiment;

- Fig. 2 is a top view of the compact wide-band antenna of Fig. 1 ;

- Fig. 3 is a perspective view of a second embodiment of the compact wide-band antenna proposed by the invention;

- Fig. 4 is an exploded side view of the compact antenna of Fig. 3.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

With reference to Figures 1 and 2, and to a first preferred, but not only embodiment of the invention, the reference number 100 indicates a compact transceiver "monopole" antenna as a whole, destined mainly to be installed on vehicles, such as land vehicles, helicopters or boats, especially for military use, or anyway, in fields where particular compactness, strength and reliability are required.

The compact antenna 100 comprises a support base 1 , formed by a tubular member having a circular section and suitable mechanical features. The base 1 is fit to contain thereinside fastening devices, mechanical and electrical fittings and other known devices, to allow fastening of the antenna 100 and the electrical connections necessary to make it work. These devices are not pertinent to the invention and therefore they will not be described in further detail.

The antenna 100 further comprises a plurality of linear ground elements 2, mounted on the lateral surface of the support base 1 at its proximal ends 2a, designed to form an electrical ground plane 3 for the antenna 100.

The linear elements 2 extend radially from the support base 1 , according to an approximately horizontal plane, or, in any case, perpendicular to the base 1 axis, and angularly equidistant. In particular, in the illustrated embodiment, there are 10 linear elements 2, however it is possible to vary their number depending on particular functional specifications required for the antenna 100. Moreover, the angle of the radial linear elements 2 with respect to the support base 1 is not crucial and can be defined in a different way with respect to the perpendicular angle to the base 1 axis, for example, greater than 90 degrees with respect thereto, like the configuration of the so-called "ground plane" antennas.

The antenna 100 further comprises a radiating element 5, mounted on an upper face 1 a of the support base 1 , which extends in a direction that is substantially perpendicular with respect to that of the linear elements 2. The radiating element 5 forms the active part of the antenna 100 and is aimed at being electrically connected to a transceiver device, not shown.

According to a fundamental feature of the invention, the radiating element 5 comprises a plurality of rods 50, each of which is fastened to the upper face 1 a of the support base 1 at its proximal end 51 . The rods

50 are parallel to one another, equidistant and have their proximal ends

51 generally lying on different points of a closed line. In particular, in the illustrated embodiment, the closed line is formed by a circumference, the rods 50 are perpendicular to the circumference and are arranged along as many generatrices of a straight cylinder, whose base is constituted by the circumference.

The compact antenna 1 further comprises a pair of spacer elements 6, constituted by as many plates, provided with holes, whose dimensions allow the rods 50 to slide therethrough with a minimum friction. The spacer elements 6 are introduced in the radiating element 5 with each rod 51 being introduced in a relative hole. One of the two spacer elements 6 is situated near the distal ends 52 of the rods 50, while the other spacer element is situated substantially midway of their length.

The so structured antenna 100 has the same bandwidth as a corresponding monopole wide-band, continuous cylinder antenna, which is a function of the diameter of the circumference on which the rods 50 are situated.

The configuration of the compact antenna 100 as described allows a imitation of the above mentioned monopole, continuous cylinder, indirect ground antenna, maintaining its performance and increasing its advantages, however without its drawbacks.

Like a known monopole, continuous cylinder antenna, the compact antenna 100 can be used in a frequency band between about 30 MHz and about 1 GHz, necessary to cover most of needs of the military medium-short haul transmission systems. The typical dimensions of the radiating element 5 for such uses include the rods 50 being about 500 mm long, with the aforementioned rods 50 arranged along a circumference having a diameter of about 90 mm. Also in this case, in order to make the antenna work in the range between 30 MHz and about 200 MHz, an impedance converter must be interposed between the antenna and the transceiver. The impedance converter is obtained in accordance to known techniques and thus it will not be described in detail.

In particular, the compact antenna 100 proposed by the invention provides a minimum aerodynamic drag, in any case much lower than the drag presented by a corresponding antenna provided with a continuous cylinder radiating element of comparable performance. This makes it also stronger and more reliable.

Furthermore, the so configured compact antenna 100 is capable of losing gradually its functionality due to breaking of its rods 50 constituting the radiating element 5, however maintaining partially the aforesaid functionality.

A second embodiment of the compact antenna 100, illustrated in Figures 1 and 2, includes also a reinforcement core 20, having an elongated conformation and obtained with electrically insulating material. The core 20 has a cylindrical conformation and is coaxially fastened to the support base 1 , parallel to the rods 50 of the radiating element 5.

The diameter of the core 20 is considerably smaller than that of the cylinder delimited by the rods 50, since it must fulfil its structural reinforcement function without prejudicing significantly the aerodynamic efficiency of the radiating element 5.

In particular (see Figure 4), the core 20 is formed by two tubular portions, a lower portion 20a and an upper portion 20b, respectively, which are substantially equal. Furthermore, a first spacer element 6a is provided, having fittings designed to snap fit in the tubular portions 20a, 20b, and a second spacer element 6b is provided, having only one fitting designed to snap fit at the opposite end of the upper tubular portion 20b.

In this way, the mechanical strength of the radiating element 5 is increased and most stresses received thereby can be relieved and absorbed by the reinforcement core 20.

It is understood that what has been described above, is illustrative and not limiting, therefore, possible variants of details, which could become necessary because of technical and/or functional reasons, are considered from now on within the same protective scope defined by the claims below.