EP2549587A1

EP2549587A1 - Improvements of antennas, particularly log-periodic antennas

Info

Publication number: EP2549587A1
Application number: EP12174694A
Authority: EP
Inventors: Andrea Negretti
Original assignee: EMME ESSE SpA
Current assignee: EMME ESSE SpA
Priority date: 2011-07-21
Filing date: 2012-07-03
Publication date: 2013-01-23
Anticipated expiration: 2032-07-03
Also published as: ES2429506T3; EP2549587B1; ITBS20110102A1; SI2549587T1

Abstract

The invention relates to an antenna (1) for receiving/transmitting electromagnetic waves, particularly log-periodic antenna, comprising assembling members (2) which can be fastened to a supporting structure, a first cradle (3) and a second cradle (4) developing along a respective longitudinal axis from a respective rear end (3a, 4a), at which they are fastened to the assembling members, to a respective front end (3b, 4b), the cradles being mutually fastened so that the respective axes of longitudinal development lie on the same median plane (5). The antenna comprises a plurality of in-phase resonant dipoles (6) each comprising a first rod - shaped element (6a), fastened to said first cradle, and a second rod - shaped element (6b), fastened to said second cradle, extending in opposed half - spaces defined by said median plane (5). The antenna further comprises at least one in-phase opposition resonant dipole (7; 70) composed of a respective first rod - shaped element (7a) fastened to said first cradle and a respective second rod - shaped element (7b) fastened to said second cradle, the respective first and second rod - shaped elements of said at least one dipole (7; 70) facing towards the same direction relatively to the median plane (5).

Description

FIELD OF THE INVENTION

The present invention relates to a device for receiving/transmitting electromagnetic waves, in particular for receiving/transmitting radio-television frequency signals, from GSM, DCS, UMTS or WLAN, hereinafter denoted as "antenna".
The invention relates as well a method for receiving/transmitting electromagnetic waves through such an antenna.

STATE OF THE ART

Antennas are known, for example of the type shown in the document IT 1349635 in the name of the Applicant, used for receiving, transmitting or transceiving electromagnetic waves. Such antennas can consist in a couple of tubular elements, denoted as "cradles", developing longitudinally prevalently and arranged substantially parallel one to another. Typically at a rear end of such an antenna, corresponding to respective rear ends of the cradles, convenient fastening means to a supporting structure (for example a post) are arranged and at a front end of the antenna, corresponding to respective front ends of the cradles, the signal picked up by the antenna can be caught and carried, for example by means of a coaxial cable, towards a signal processing device.
Some known antennas, to pick up the electromagnetic waves, have a plurality of rod-shaped elements, denoted as "directors", variously constrained to the cradles and arranged crosswise to the longitudinal development of the cradles. The cradles can be parallel or not, for example they can converge towards the front end of the antenna. The directors can be orthogonal to the cradles or forward tilted in the same plane of the cradles, or yet they can lie on respective tilted planes with respect to the cradles.
The rod-shaped elements are distributed on cradles in such a way to form couples of rod-shaped elements denoted as "dipoles", where each dipole comprises a first rod-shaped element fastened to a cradle and a second rod-shaped element fastened to the other cradle and facing to opposite directions. The two rod-shaped elements of each dipole are typically arranged at the same respective distance from the front or rear end of the antenna. In particular, in the so called "log-periodic" or "logarithmic" antennas, a plurality of dipoles consisting in rod-shaped elements having preset lengths are present, typically but not exclusively decreasing from the rear end to the front end, and arranged at specific distances each one from the subsequent. Each dipole is structured to resonate at a determined frequency, that is to pick up respective electromagnetic waves, and to generate respective signals and transmit them to the two cradles. All signals generated by the dipoles, having different frequencies, are carried in the two cradles as a single signal and on the whole the antenna has a receiving band, that is a range of frequencies composing such a signal, substantially continuous and extending even beyond the proper frequencies of the end dipoles of the antenna itself.
Depending on the applications, the dipoles can be arranged along the cradles according to various layouts, in addition to the already mentioned logarithmic layout, with variable distances between a dipole and the subsequent one.
The Applicant found that current devices and methods for receiving and transmitting electromagnetic waves, in particular television signals, are not free from drawbacks and can be improved in different aspects.
In particular, it has been found that the known devices for receiving/transmitting electromagnetic waves pick up/ transmit a very extended and continuous frequency range and/or they are not able to accurately select the limits of such a range and/or they are not able to define an intermittent receiving/transmitting band. This results in the drawback, in use, by which the antenna can pick up/transmit unwanted, and intended to other transmissions, frequencies, which can generate interferences with the interest frequencies for which the antenna is used, particularly detrimental referring to the digital signals.

OBJECTS AND SUMMARY OF THE INVENTION

The above being stated, object of the present invention is to provide antennas, in particular log-periodic or logarithmic antennas, for receiving/transmitting electromagnetic waves able to compensate for one or more of the mentioned drawbacks.
More particularly, object of the present invention is to provide a log-periodic antenna which allows to receive/transmit electromagnetic waves, characterized by a well defined, restricted and repeatable band of frequencies that can be received/transmitted, as well as selectable and/or customizable.
A further object of the invention is to provide an antenna which allows an effective and contention - free reception/transmission of a signal having a determined frequency band, advantageously without substantially modifying structure and installation and use mode of the antenna.
One or more of these and other possible objects, which will be better evident from the following description, are obtained by a device and a method for receiving and transmitting electromagnetic waves having the technical specifications contained in one or more of the attached claims, each of which taken alone (without the corresponding dependencies) or in any combination with the other claims, as well as according to the following aspects and/or exemplary embodiments, variously matched, even with the afore said claims.
In one aspect the invention relates to an antenna comprising:

assembling members intended for being fastened to a supporting structure;
a first cradle and a second cradle having tubular shape and developing along a respective longitudinal axis from a respective rear end, at which they are fastened to said assembling members, to a respective front end, said first and second cradle being mutually fastened so that the respective longitudinal axes lie on the same median plane;
a plurality of in-phase resonant dipoles each comprising a first rod - shaped element extending from a side of the first cradle and a second rod- shaped element extending from the opposite side of the second cradle, said first and second rod - shaped elements lying in opposed half - spaces defined by said median plane;

Advantageously, the combination of the above mentioned characteristic techniques allows to obtain an antenna for receiving/transmitting electromagnetic waves having a determined band of frequencies that can be received/transmitted and characterized, at the same time, by a simple, rational structure which is easy and cost effective to produce. Consider in fact that, as it is known, the two elements of an electric dipole carry a positive wave and a negative wave respectively which, in the case for example of a log-periodic type antenna, run in the respective cradle up to add up at the front ends of the cradles, where typically the deriving signal is caught. Therefore, the two waves, one being positive and the other negative, are phase shifted of 180° one to another and, at the signal catch point, they are typically connected to the shield and core of a coaxial cable, respectively, which introduces a further phase shifting of 180° which allows the waves to add up in-phase.
This is the case of the afore said plurality of phase resonant dipoles, each of whom allows therefore to receive a determined frequency.
Conversely, as regard to the afore said at least one in-phase opposition resonant dipole, the fact that its rod-shaped elements are both on the same side with respect to the afore said median plane determines the in-phase passage of the respective waves in the two cradles resulting in, as a consequence of the phase shifting introduced during the signal catching step, the two waves of such a dipole being in-phase opposition and therefore generating a null resultant. This means that the determined frequency picked up by the in-phase opposition dipole is eliminated during the catching step, thus defining the band of frequency which can be received, to not interfere with frequencies intended to other transmitting/receiving devices.
In one aspect the antenna comprises a device for catching the signal from said first and second cradles, preferably located at the front ends of said first and second cradles, structured to put together the electromagnetic waves picked up by the dipoles in a single electrical signal and to carry such a signal towards a processing device.
Said at least one in-phase opposition resonant dipole may be placed at a distance from the rear ends of the cradles lower than the respective distance of each dipole of said plurality of in-phase resonant dipoles. In such a case the in-phase opposition resonant dipole is a first antenna dipole along the axes of longitudinal development of the cradles. Advantageously such an arrangement allows to select the lowest limit of the band of frequencies that can be received/transmitted, by "cutting off" the lower frequencies which therefore are not received/ sent through the cradles.
Or else, said at least one in-phase opposition resonant dipole may be placed at a distance from the rear ends of the cradles higher than the respective distance of each dipole of said plurality of in-phase resonant dipoles. In such a case the in-phase opposition resonant dipole is the last antenna dipole along the axes of longitudinal development of the cradles. Advantageously such an arrangement allows to select the highest limit of the band of frequencies that can be received/transmitted, by "cutting off" the higher frequencies which therefore are not received/ sent through the cradles.
Or else, said at least one in-phase opposition resonant dipole may be placed at an intermediate distance from the rear ends of the cradles relatively to the respective distance of at least two dipoles of said plurality of in-phase resonant dipoles. In such a case the in-phase opposition resonant dipole is interposed between the other antenna dipoles along the axes of longitudinal development of the cradles. Advantageously such a configuration allows to select a determined frequency, or frequencies range, intended to be excluded from the band of frequencies that can be received/transmitted.
According to another aspect the antenna can comprise a plurality of in-phase opposition resonant dipoles. As an example, then the antenna can comprise more in-phase opposition resonant dipoles at the front ends of the cradles and/ or the rear ends of the cradles and/ or in intermediate positions of the cradles.
It has been found how by selecting the position of a suited number of in-phase opposition resonant dipoles along the longitudinal development of the cradles, a determined receiving/transmitting band can be obtained for the antenna, which can be designed according to the application and type of picked up/transmitted signal and free from electromagnetic perturbations typical of the known antennas.
Further note how the technical solution of the present invention, in particular the arrangement of suited in-phase opposition resonant dipoles, can be integrated in already existing antennas and/or of known type as well, in order to provide them with a limited receiving/transmitting band and with the desired characteristics.
The invention also includes a telecommunication system comprising at least one antenna in accordance with the present invention and a processing device, for example a decoder for digital radio-television signals.
Another aspect of the present invention relates to a method for receiving electromagnetic waves comprising the steps of:

a) arranging a first and a second cradle having tubular shape and developing, according to a respective longitudinal axis, from a respective rear end to a respective front end, said first and second cradles being mutually fastened in overlapped positions in such a way that the respective axes of longitudinal development lie on the same median plane;
b) receiving, by means of a plurality of in-phase resonant dipoles assembled to said first and second cradles, a plurality of couples of in-phase electromagnetic waves, each in-phase resonant dipole comprising a first rod-shaped element fastened to said first cradle and a second rod-shaped element fastened to said second cradle, wherein said first and second rod-shaped elements lie in opposite half-spaces defined by said median plane;
c) receiving, by means of at least one in-phase opposition resonant dipole assembled to said first and second cradles, a couple of in-phase opposition electromagnetic waves, said at least one in-phase opposition resonant dipole comprising a first rod-shaped element fastened to said first cradle and a second rod-shaped element fastened to said second cradle, lying in a same half-space defined by said median plane;
d) carrying the electromagnetic waves received in step b) and c) to the first and second cradle;
e) catching the electromagnetic waves running on the first and second cradle to provide an overall output signal intended for a processing device.

The above described method advantageously allows to easily, rapidly and cost effectively receive electromagnetic waves, in particular digital radio-television signals.
In one aspect, such a method can be implemented by means of one or more devices for receiving electromagnetic waves in accordance with the present invention in its various aspects and/or claims.
In one aspect, in step c), the reception may happen by a plurality of in-phase opposition resonant dipoles, placed at the front or rear ends of the first and second cradle and/ or in one or more intermediate positions of the first and second cradle.
In a further aspect the present invention relates to an antenna comprising:

a receiving/ transmitting body structured to pick up electromagnetic waves and generate an electric signal;
a catching device operatively connected to said receiving body and structured to catch said electric signal from the receiving body and to provide an electric output signal intended for being sent to a processing device;

characterized in that

The Applicant believes that the above technical solution advantageously allows to select the receiving band desired for an electromagnetic waves receiving device, for example an antenna for digital radio-television signals. Such a solution is advantageously applicable to antennas not belonging to the cradle type as well.
In one aspect the in-frequency filter can be a high-pass filter, a low-pass filter or a band-pass filter, for example implemented by means of known technologies. This allows, respectively, to select the lowest frequency, the highest frequency (typically denoted as "cut off frequency"), or the end frequencies defining the range of frequencies which compose the frequency spectrum of the electric output signal (typically denoted as "bandwidth").
Preferably the in-frequency filter is wholly integrated in said catching device.
In particular, said in-frequency filter comprises an electronic circuit, for example a C-L circuit, that is a circuit comprising a capacitor and inductance arranged in series, where the circuit receives said input electrical signal and outputs said electric output signal.
In one aspect said catching device can be a "balun" device (from the English words "balanced-unbalanced"), known in the radio communication field and used for the impedance matching between the electric output signal from an antenna and the user device.
In one aspect the in-frequency filter, for example the afore said electronic circuit, is integrated in said balun device.
In a further aspect the present invention relates to a method for receiving electromagnetic waves comprising the steps of:

a) arranging a receiving body structured to pick up electromagnetic waves and generate an electric signal;
b) catching, by means of a catching device operatively connected to said receiving body, said electrical signal from the receiving body;
c) in-frequency filtering the electrical signal in such a way to generate an electric output signal comprising certain frequencies only;
d) providing said electric output signal intended to be sent to a processing device.

In one aspect the step c) is implemented by a high-pass filter, a low-pass filter or a band-pass filter, for example of the type of the above described aspects.
Preferably the in-frequency filter is fully integrated in the catching device, which realizes the steps b) and c) and/or d).
In one aspect the catching device of the steps b), c) and/or d) can be a "balun" device, as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages will be evident from the following description made with reference to the attached drawings, provided for illustration purposes only and thereby not limitative, wherein:

figures 1 and 2 show two perspective views of an antenna in accordance with the present invention seen from different angles;
figure 3 is a top plan view of the antenna of figure 1;
figure 4 shows an electrical scheme of a filter of an antenna in accordance with the present invention;
figure 5 is a schematic representation of a possible embodiment of the filter of figure 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the attached figures, an antenna according to the present invention is wholly denoted with the reference numeral 1. In general, the same reference numeral is used for the same elements, possibly also in their embodiment variations.
The antenna 1 comprises assembling elements 2, for example a bracket 2a, adapted to be fastened to a supporting structure, not shown and of known type (exemplarily a fixed post).
Further the antenna comprises a first cradle 3 and a second cradle 4 having tubular shape and developing along a respective longitudinal axis from a respective rear end 3a, 4a at which they are fastened to said assembling members, to a respective front end 3b, 4b; the first 3a and the second 4 cradle being mutually fastened so that the respective longitudinal axes lie on the same median plane 5. The antenna further comprises a plurality of in-phase resonant dipoles 6, each one consisting in a first rod-shaped element 6a fastened to the first cradle and a second rod-shaped element 6b fastened to the second cradle, such rod-shaped elements are oriented and lie in opposite half-spaces defined by the median plane 5. The antenna 1 further comprises at least one in-phase opposition resonant dipole 7 consisting in a respective first rod-shaped element 7a fastened to the first cradle and a second rod-shaped element 7b fastened to the second cradle, and both these rod-shaped elements 7a, 7b are facing towards the same direction and therefore lie in a same half-space between the two defined by the median plane 5.
The antenna 1 further comprises a device 10 for catching the signal from the first and second cradles, preferably located (figures 1-3) at the front ends 3b, 4b of the two cradles, structured to put together in a single electrical signal the electromagnetic waves picked up by the dipoles 6 and 7 and to carry such a signal towards an usual processing device (not shown). Exemplarily, the signal catching device can comprise a coaxial connector connected to the two cradles and wherefrom a coaxial cable intended to the processing device separates; the catching device can be for example of the type described in the patent IT 1349635 .
Preferably the respective first 6a and second 6b rod-shaped elements of each in-phase resonant dipole 6 and/or the respective first 7a and second 7b rod-shaped elements of the afore said at least one in-phase opposition resonant dipole 7 are fastened to the respective cradle substantially at a respective same distance from the rear ends 3a, 4a of the cradles. In other words, the two rod-shaped elements of a dipole lie on a same plane orthogonal to the cradles. Alternatively, the two rod-shaped elements of a dipole can lie on discrete planes orthogonal to the cradles and offset one to another.
Preferably, as exemplarily shown in the figures, the device 1 is an antenna of the log-periodic or logarithmic type.
Preferably, the first 3 and the second 4 cradles are substantially identical, for example obtained by cutting a tubular metal bar having determined thickness. Alternatively, the two cradles can have length differing from each other; for example, the rear end of the first cradle can extend beyond the rear end of the second cradle to provide a useful portion to realize specific anchorages to the supporting post.
Preferably the first cradle 3, the second cradle 4, and the in-phase resonant dipoles 6 and the afore said at least one in-phase opposition resonant dipole 7 are made in an electrically conductive material, preferably in aluminium or its alloys, steel (preferably stain-less or galvanized steel) or other metal material.
The rod-shaped elements of the dipoles can have a solid or hollow cross section and have various shapes. The rod-shaped elements can be constrained to the respective cradle for example by insertion in a respective hole in the cradle and subsequent welding, or by forced introduction into the respective hole, a manufacturing mode described in the patent IT 1355719 in the name of the Applicant.
As exemplarily shown in figure 1 and 2, the rod-shaped element is inserted in a hole of the cradle and it passes throughout the cradle itself, exiting from a hole aligned on the opposite side; in this case the element is forcedly inserted in both holes or it is welded next to them. Advantageously this allows to obtain a simple to use and mechanically stable fastening of the rod-shaped elements to the cradle, since relying on two discrete anchoring points. The cradles and dipoles, rather than by means of tubular elements and rod-shaped elements, can be equally implemented by printed circuits suitably shaped in such a way to recreate the above described cradle-dipole structure, as on the other hand is known in the field.
Note that the first cradle and the second cradle, associated with the assembling elements 2, are in direct contact one to another at their rear ends. Such a contact typically represents the only element of electrical continuity between the cradles and it is located outside of the plurality of dipoles, that is before the first dipole of the antenna. In addition, the antenna 1 can comprise one or more spacers 9, made in an electrically insulating material (exemplarily in a plastic material), interposed between the first and the second cradle. Such spacers 9 allow to keep the mutual position of the two cradles and to avoid them to contact beyond the first dipole and throughout their operative length, event which could result in a loss of the signal picked up by the antenna dipoles.
Preferably the respective first and second rod-shaped elements of an in-phase, or in-phase opposition, resonant dipole are both oriented substantially uniformly with respect to the median plane 5, preferably they are both orthogonal to the median plane.
Preferably the first and second rod-shaped elements of each dipole have a respective length, preferably the same length, typical of the dipole and defining a respective dipole frequency. Preferably the respective, in-phase or in-phase opposition resonant, dipole lengths of the antenna are decreasing from the rear ends to the front ends of the cradles. This way a determined range of frequencies can be picked up with continuity by means of subsequent dipoles.
Preferably the ratio of the respective length of the rod-shaped elements of a dipole and the respective length of the rod-shaped elements of the subsequent dipole is substantially constant. Preferably the ratio of the distance between two adjoining dipoles (also denoted as "pitch"), along the longitudinal axis of the cradles, and the distance between the two subsequent adjoining dipoles is substantially constant (thus realizing a logarithmic series of the dipoles along the cradles).
In a possible, not shown, embodiment the afore said in-phase opposition resonant dipole 7 is positioned at a distance from the rear ends of the cradles shorter that the distance of each dipole 6 of said plurality of in-phase resonant dipoles, that is to say it is the first dipole of the antenna starting from the rear ends of the cradles.
In another possible embodiment, the afore said in-phase opposition resonant dipole 7 is placed at an intermediate distance from the rear ends of the cradles relatively to the respective distance of at least two dipoles of said plurality of in-phase resonant dipoles 6, that is it is interposed between the other antenna dipoles along the longitudinal development of the cradles.
In another possible embodiment, the afore said in-phase opposition resonant dipole 7 is positioned at a distance from the rear ends of the cradles longer that the respective distance of each dipole of said plurality of in-phase resonant dipoles, that is to say it is the last dipole of the antenna starting from the rear ends of the cradles.
As shown in the figures 1-3, the antenna 1 can comprise a plurality of in-phase opposition resonant dipoles 7. Exemplarily, the antenna comprises more in-phase opposition resonant dipoles 70 at the front ends of the cradles and one in-phase opposition resonant dipole located at an intermediate position of the cradles. In general, the antenna can comprise more in-phase opposition resonant dipoles at the front ends of the cradles and/ or the rear ends of the cradles and/ or in intermediate positions of the cradles.
In still another embodiment of the present invention, the antenna comprises a receiving body structured to pick up electromagnetic waves and to generate an electrical signal, a catching device operatively connected to the receiving body and structured to catch up the afore said electrical signal from the receiving body and provide an electric output signal intended to be sent to a processing device. In this arrangement, the afore said catching device comprises an in-frequency filter (indicated in figure 4 and 5 with numeral 20) structured to filter the afore said electrical signal so that the afore said electric output signal comprises certain frequencies only.
Preferably, the in-frequency filter can be a high-pass filter, a low-pass filter or a band-pass filter, implemented by means of known technologies.
Exemplarily, the in-frequency filter can be designated to "cut off" the frequencies higher than 870 MHz and/or the frequencies lower than 470 MHz (in case of filter for the UHF band) or lower than 606 MHz (in case of filter for the fifth band).
Preferably the in-frequency filter is wholly integrated in the afore said catching device. Alternatively, the in-frequency filter can be a distinct component connected in series, downstream or upstream of the catching device.
Preferably the in-frequency filter comprises an electronic circuit, for example a C-L circuit (figure 4), that is a circuit comprising a capacitor and inductance arranged in series, wherein the circuit receives the afore said input electrical signal (indicated in figure with symbol V_in) and it outputs the afore said electrical output signal (indicated in figure with symbol V_Filtered).
Preferably the catching device can be a "balun" device, indicated with number 11 in figure 5; in such a case the filter circuit can be implemented directly on the electronic card inside the balun, for example by embedding capacitors and inductances in such a card. In fact one capacitor C can be implemented for example by overlapping two copper areas 21 and one inductance L can be implemented by creating a track 22 with suited shape and size on the card, as schematically shown in figure 5.
Preferably the antenna comprises assembling members bearing the receiving body and intended for being fastened to a supporting structure.
A person skilled of the art will be able to make various changes and variations to the devices and methods above described to satisfy contingent and specific requirements, on the other hand all contained in the protection scope of the invention.
The present invention can be advantageously applied, besides the afore said log-periodic antennas, to different types of antenna as well, for example Yagi antennas or dipole antennas.
Definitively, the inventive conception at the base of the invention can be equivalently applied to each kind of antenna, for example of the afore mentioned types having variously shaped and oriented cradles and variously tilted, oriented and spaced dipoles.

Claims

Antenna for receiving/ transmitting electromagnetic waves, particularly log-periodic antenna, comprising:
- assembling members (2) intended for being fastened to a supporting structure;

- a first cradle (3) and a second cradle (4) developing along a respective longitudinal axis from a respective rear end (3a, 4a), at which they are fastened to said assembling members, to a respective front end (3b, 4b), the first cradle and the second cradle being mutually fastened so that the respective axes of longitudinal development lie on the same median plane (5);

- a plurality of in-phase resonant dipoles (6) each comprising a first rod - shaped element (6a) fastened to said first cradle and a second rod - shaped element (6b) fastened to said second cradle, said first and second rod - shaped elements extending in opposed half - spaces defined by said median plane (5);
characterized by comprising at least one in-phase opposition resonant dipole (7; 70) composed of a respective first rod - shaped element (7a) fastened to said first cradle and a respective second rod - shaped element (7b) fastened to said second cradle, said respective first and second rod - shaped elements of said at least one dipole (7; 70) facing towards the same direction relatively to said median plane (5).
Antenna according to claim 1, wherein said at least one in-phase opposition resonant dipole (7) is placed at a distance from the rear ends (3a, 4a) of the cradles lower than the respective distance of each dipole of said plurality of in-phase resonant dipoles, proving to be the first antenna dipole along the axes of longitudinal development of the cradles.
Antenna according to claim 1, wherein said at least one in-phase opposition resonant dipole (7) is placed at an intermediate distance from the rear ends (3a, 4a) of the cradles relatively to the respective distance of at least two dipoles of said plurality of in-phase resonant dipoles (6), in that case proving to be interposed between the other antenna dipoles along the axes of longitudinal development of the cradles.
Antenna (1) according to claim 1, wherein said at least one in-phase opposition resonant dipole (7) is placed at a distance from the rear ends (3a, 4a) greater than the respective distance of each dipole of said plurality of in-phase resonant dipoles, in that case proving to be the last antenna dipole along the axes of longitudinal development of the cradles.
Antenna according to any one of the preceding claims comprising a plurality of said in-phase opposition resonant dipole (7), for example more in-phase opposition resonant dipoles at the front ends of the cradles and/ or the rear ends of the cradles and/ or in intermediate positions of the cradles.
Antenna according to any one of the preceding claims comprising a device (10) for catching signal from said first (3) and second (4) cradle, structured to put together electromagnetic waves picked up by dipoles (6, 7) in a single electric signal and to carry such a signal towards a processing device.
Antenna according to any one of the preceding claims, wherein the respective first and second rod - shaped elements of each in-phase resonant dipole and/ or the respective first and second rod - shaped elements of said at least one in-phase opposition resonant dipole are fastened to the respective cradle at substantially the same respective distance from the rear ends of said cradles, wherein the respective first and second rod - shaped elements of a dipole (6, 7) are facing substantially parallel one another and preferably orthogonally to said median plane (5), and wherein the first and second rod - shaped elements of each dipole have a respective length, preferably the same length, typical of the dipole and defining a respective dipole frequency.
Method for receiving electromagnetic waves by a television antenna, the method comprising the steps of:
a) arranging a first and a second cradle developing according to a respective longitudinal axis from a respective rear end to a respective front end and in such a way that the respective axes of longitudinal development lie on the same median plane;

b) arranging a plurality of in-phase resonant dipoles each one comprising a respective first rod - shaped element constrained to said first cradle and a respective second rod - shaped element constrained to said second cradle, the elements being faced to opposite directions;

c) arranging at least one in-phase opposition resonant dipole comprising a first rod - shaped element constrained to said first cradle and a second rod - shaped element constrained to said second cradle, the elements being faced to the same direction from the same side of the cradles;

d) receiving, by said plurality of in-phase resonant dipoles, a plurality of couples of in-phase electromagnetic waves and, by said at least one in-phase opposition resonant dipole, a couple of in-phase opposition electromagnetic waves;

e) carrying the electromagnetic waves received in step d) to the first and second cradle;

f) catching the electromagnetic waves running on the first and second cradle to provide an overall output signal intended for a processing device.
Method according to the preceding claim implemented by one or more antennas according to any one of the claims from 1 to 7.
Method according to claim 8 or 9 wherein, in step d), the reception may happen by a plurality of in-phase opposition resonant dipoles, placed at the front or rear ends of the first and second cradle and/ or in one or more intermediate positions of the first and second cradle.
Antenna for receiving/ transmitting electromagnetic waves comprising:
- a receiving body structured to pick up electromagnetic waves and generate an electric signal;

- a catching device operatively connected to said receiving body and structured to catch said electric signal from the receiving body and to provide an electric output signal intended for being sent to a processing device; characterized in that said catching device comprises an in-frequency filter (20) structured to filter said electric signal in such a way that said electric output signal comprises determined frequencies only.
Antenna according to preceding claim, wherein the in-frequency filter is a high-pass filter, a low-pass filter or a band-pass filter, said filter being able to be implemented by an electronic circuit comprising a capacitor (C) and an inductance (L) arranged in series, where the circuit receives said electric signal as input and provides said electric output signal as output.
Antenna (1) according to claim 11 or 12, wherein the in-frequency filter is completely integrated in said catching device or it is a distinct component connected in series, downstream or upstream of the catching device.
Antenna (1) according to any one of the claims from 11 to 13 wherein said catching device is a "balun" device (11) and said in-frequency filter (20) is integrated in said balun device.