Antenna device and communication system comprising such an antenna device

Abstract

The invention relates to an antenna device (106) comprising: - a dipole (108A, 108B) designed to switch from guided propagation to free-space propagation of an electromagnetic wave, and vice versa; - a mast (114) which has a hollow section and to which the dipole (108A, 108B) is attached; - an internal line (402C) designed to conduct the electromagnetic wave via guided propagation, the internal line (402C) running in the mast (114); and - a rejection filter (414, 416) comprising an open line (418, 420) connected to the internal line (402C) located in the mast (114). The open line (418, 420) extends entirely in the mast (114) as a continuation of the internal line (402C), and no open line of the rejection filter extends in the mast (114) along the internal line (402C).

Description

Description TITLE: ANTENNA DEVICE AND COMMUNICATION SYSTEM COMPRISING SUCH ANTENNA DEVICE Technical field of the invention

[0001] The present invention relates to an antenna device and communication system comprising such an antenna device. Technological background

[0002] The international PCT application published under number WO 2023 117192 A1 describes an antenna device of the type comprising: a dipole designed to switch from guided propagation to radiated propagation of an electromagnetic wave, and vice versa; a mast which is hollow section and to which the dipole is fixed; an inner line designed to conduct the electromagnetic wave in guided propagation, the inner line running in the mast; and a rejecting filter comprising an open line connected to the inner line located in the mast.

[0003] For the purposes of the present invention, a notch filter, also called a band-stop filter or notch filter, is an electronic filter that prevents the passage of a specific range of frequencies while allowing others to pass through.

[0004] The open line is housed in an additional tube attached to the tubular mast, outside of it. However, the rejection filter, and therefore the additional tube, is sized for a wavelength corresponding to the dipole's operating frequency. Consequently, for a nearby higher-frequency array, the additional tube acts as a parasitic element, interfering with the high-frequency array. This is particularly problematic when the high-frequency array operates at approximately twice the dipole's operating frequencies. In the aforementioned publication, where the antenna system combines a low-frequency array and a high-frequency array in close proximity, this problem is especially evident.

[0005] It may therefore be desirable to provide an antenna device that overcomes at least some of the aforementioned problems and constraints. Summary of the invention

[0006] An antenna device of the aforementioned type is therefore proposed, characterized in that the open line extends entirely into the mast in line with the inner line, and in that no open line of rejecting filter extends into the mast along the inner line.

[0007] Thus, thanks to the invention, the presence of the reject filter does not entail the use of an additional tube which could constitute a parasitic element for another network.

[0008] Furthermore, the absence of an open line of rejection filter in the mast along the inner line avoids coupling between the inner line and the open line of the rejection filter, which could create an impedance mismatch.

[0009] The invention may further include one or more of the following optional features, in any technically feasible combination.

[0010] Optionally, the dipole is a low-frequency dipole designed to radiate in a low-frequency band, the antenna device further comprising at least one high-frequency dipole designed to radiate in a high-frequency band.

[0011] Optionally, the low-frequency band has a low-frequency center frequency and the high-frequency band has a high-frequency center frequency, and the high-frequency center frequency is at least 1.5 times higher than the low-frequency center frequency.

[0012] Optionally, the open line of the rejector filter and the mast form a coaxial line in which the mast forms a shield and the open line a center conductor.

[0013] Optionally, the antenna device also includes a low-pass filter attached to the mast, outside of the latter.

[0014] Optionally, the low-pass filter also includes an electrically conductive low-pass filter line.

[0015] Optionally, the low-pass filter line can also extend substantially parallel to the inner line.

[0016] Optionally, the antenna device also includes a low-pass filter tube attached to the mast, the low-pass filter line extending into the low-pass filter tube, the low-pass filter line and the low-pass filter tube forming a coaxial line in which the low-pass filter tube forms a shield and the low-pass filter line a center conductor.

[0017] Optionally, the low-pass filter line also includes a succession of conductive elements of different diameters and, for at least one of the conductive elements, a dielectric element interposed between this conductive element and the low-pass filter tube in the form of a sleeve extending at least over the entire length of the conductive element.

[0018] Optionally, the antenna device also includes an anti-slip system designed to limit slippage of the dielectric element relative to the low-pass filter line, at least in one direction along the low-pass filter line.

[0019] Optionally, the anti-slip system also includes an internal shoulder formed in the dielectric element against which the conductive element is butted.

[0020] Optionally, the anti-slip system also includes at least one internal compression seal between the dielectric element and the conductive element.

[0021] Optionally and independently, the dipole comprises two arms separated from each other by an inter-arm space and a foot fixing at least one of the two arms to the mast, the antenna device further comprises: - an end line connected to the inner line and extending into the foot; - an inter-arm conductor connected, on one side, to the end line and, on the other side, to the other arm, passing through the inter-arm space; and - a dielectric material extending around the inter-arm conductor in the inter-arm space.

[0022] A communication system is also proposed, comprising: an antenna device according to the invention; a low-frequency transmitter / receiver; and an external coaxial cable connecting the low-frequency transmitter / receiver to the dipole to exchange the guided propagation electromagnetic wave with the dipole through the external coaxial cable.

[0023] Optionally, the antenna device is according to the invention and further includes a pressurization device designed to supply pressurized air in the outer coaxial cable, and an internal space in the low-pass filter tube in which the low-pass filter line extends is in communication with the pressurized air, so as to be filled by the pressurized air. Brief description of the figures

[0024] The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings in which: Figure 1 is a highly schematic view of a communication system comprising an antenna device according to the invention. Figure 2 is a side view of a low-frequency dipole of a low-frequency array of the antenna device of Figure 1. Figure 3 is a side view of a high-frequency dipole from a high-frequency array of the antenna device shown in Figure 1. Figure 4 is a cross-sectional view illustrating conductor lines for the low-frequency network. Figure 5 is a cross-sectional view of a low-pass filter for the low-frequency network. Figure 6 is a front view of a dielectric element for holding a conductive line in a tube. Figure 7 is a cross-sectional view of a dielectric element holding a conductive element of the low-pass filter. Figure 8 schematically illustrates a pressurization system for a cable and a low-pass filter. Figure 9 is a cross-sectional view illustrating a pressurization barrier present at one end of the low-pass filter. Figure 10 shows a front view and a side view of an electrical washer for holding an electrical conductor in place within a hollow conductor. Figure 11 is an enlargement of Figure 1 showing an inter-arm conductor passing through an inter-arm gap separating two arms of a dipole; Figure 12 is a front view and a three-dimensional view of a dielectric washer placed in the inter-arm gap and into which the inter-arm conductor is inserted, and Figure 13 is a view similar to Figure 2 illustrating a local radome on the low-frequency dipole. Detailed description of the invention

[0025] A 100 communication system according to the invention will now be described.

[0026] Referring to Figure 1, the 100 communication system is designed to simultaneously transmit and / or receive two radio frequency signals from two distinct services. For example, one service is an FM (Frequency Modulation) broadcasting service and the other is a digital terrestrial radio (DAB) service.

[0027] The two services operate respectively in a first frequency band and a second frequency band, the latter being higher than the first. Thus, the first frequency band is called the low-frequency band (LF band), while the second frequency band is called the high-frequency band (HF band). Each of the LF and HF bands has a center frequency. For example, the center frequency of the HF band is approximately twice as high as the center frequency of the LF band, that is, for example, between 1.5 and 2.5 times the center frequency of the LF band, preferably between 1.8 and 2.2 times the center frequency of the LF band.

[0028] The low frequency (LF) band, for example, falls within the metric frequency range, i.e., between 30 and 300 MHz. For example, the center frequency of the LF band is an FM frequency (e.g., 88, 98, or 108 MHz). The high frequency (HF) band, for example, falls within the decimetric frequency range, i.e., between 300 and 3000 MHz. Alternatively, the center frequency of the high frequency (HF) band may be outside the decimetric frequency range, for example, a DAB frequency (e.g., 174, 200, or 225 MHz). However, in general, the LF band and the HF band do not necessarily belong to distinct frequency domains (i.e. metric, decimetric, etc.).

[0029] The communication system 100 thus includes an antenna device 106 intended for outdoor installation. The antenna device 106 comprises: for the first service, an LF 108 network of LF 108A-B dipoles and, for the second service, an HF 110 network of HF 110A-D dipoles.

[0030] Thus, the BF 108A-B dipoles and the HF 110A-D dipoles are close to each other. More precisely, each of the BF 108A-B dipoles is within 0.4XÀOHF and / or 0.2XÀOBF of at least one HF 110A-D dipole, and each of the HF 110A-D dipoles is within 0.4XÀOHF and / or 0.2XÀOBF of at least one BF 108A-B dipole, with ÀoBF=c / foBF and ÀoHF=c / foHF, where foBF is the center frequency of the BF band, foHF is the center frequency of the HF band, and c is the speed of light.

[0031] The antenna assembly 106 further includes a support 112 for the LF 108 array and the HF 110 array. In particular, the support 112 includes, for example, at least one mast 114 to which the LF 108A-B dipoles are attached and at least one mast 116, 118 to which the HF 110A-D dipoles are attached. The mast(s) 114, 116, 118 are each hollow in cross-section, for example oval, preferably circular, or rectangular, preferably square.

[0032] For example, as in the illustrated example, the BF 108A-B dipoles are all mounted on a single mast 114. Again, for example, as in the illustrated example, the BF 108A-B dipoles and the HF 110A-D dipoles are mounted on different masts 114 and 116, 118. Again, for example, as in the illustrated example, some of the HF 110A-B dipoles are mounted on a mast 116 and other HF 110C-D dipoles are mounted on another mast 118. Again, for example, as in the illustrated example, the mast(s) 116, 118 carrying the HF 110A-D dipoles are attached to the mast 114 carrying the BF 108A-B dipoles.

[0033] Masts 114, 116, and 118 extend in a direction D, which is intended to be vertical when the antenna device 106 is installed. In the figures, direction D is illustrated, once the antenna device 106 is installed, by a vertical arrow pointing from bottom to top.

[0034] The communication system 100 further includes an LF transmitter / receiver 122 and an HF transmitter / receiver 124 designed to exchange an LF electrical signal (i.e. a guided propagation LF electromagnetic wave) and an HF electrical signal (i.e. a guided propagation HF electromagnetic wave) respectively with LF dipoles and HF dipoles.

[0035] The communication system 100 may further include a radome 126 designed to protect the antenna device 106 from the elements. The radome 126 may be a global radome surrounding or overhanging the antenna device 106, as illustrated in Figure 1, or, as illustrated in Figure 13, a local radome 1302 provided for each dipole and surrounding at least part of the arms 202, 204 and the base(s) 206, 208 of the dipole. The local radome 1302 may, for example, comprise two dielectric half-shells. Such a local radome 1302 may be provided for each high-frequency and low-frequency dipole, as well as around the bases of the dipoles.

[0036] Referring to Figure 2, each of the BF 108A-B dipoles is designed to convert the BF electromagnetic wave from guided propagation to radiated propagation, and vice versa, depending on whether the electromagnetic wave is emitted or received. In particular, each of the BF 108A-B dipoles is designed to radiate in the BF band.

[0037] In particular, each of the BF 108A-B dipoles has two electrically conducting arms 202 and 204. Preferably, the arms 202 and 204 are identical, specifically of the same length and collinear. Thus, the two arms 202 and 204 have the same current density, so that the BF 108A-B dipole exhibits limited electromagnetic radiation instabilities.

[0038] Arms 202, 204 have a length between AOBF / 8 and AOBF / 2, WHERE A denotes the wavelength equal to AoBF=c / foBF.

[0039] Furthermore, each of the BF 108A-B dipoles has at least one foot 206, 208 to which at least one of the arms 202, 204 is attached. For example, as in the illustrated example, each of the BF 108A-B dipoles has two feet 206, 208 to which the arms 202, 204 are respectively attached. Alternatively, each of the BF 108A-B dipoles could have a single foot to which both arms 202, 204 would be attached. Each foot 206, 208 is thus, for example, attached to the mast 114.

[0040] With reference to Figure 3, each of the HF 110A-D dipoles is designed to perform a conversion between an HF electromagnetic wave in the HF band and the HF electrical signal from the HF 124 transmitter / receiver. In particular, each of the HF 110A-D dipoles is designed to radiate in the HF band.

[0041] In particular, each of the HF 110A-D dipoles comprises two electrically conducting arms 302 and 304. Preferably, the arms 302 and 304 are identical, specifically of the same length and collinear. Thus, the two arms 302 and 304 have the same current density, so that the HF 110A-D dipole exhibits limited electromagnetic radiation instabilities.

[0042] Arms 302, 304 have a length between A / 8 and A / 2, where A denotes the wavelength equal to the inverse of the center frequency of the HF band.

[0043] Furthermore, each of the HF 110A-D dipoles has at least one foot 306, 308 to which at least one of the arms 302, 304 is attached. For example, as in the illustrated example, each of the HF 110A-B dipoles has two feet 306, 308 to which the arms 302, 304 are respectively attached. Alternatively, each of the HF 110A-B dipoles could have a single foot to which both arms 302, 304 would be attached.

[0044] Each foot 306, 308 is fixed to the mast 116 or 118 depending on the HF dipole 110A-D.

[0045] With reference to Figure 4, the antenna device 106 further includes an electrically conductive inner line 402C running within the mast 114 and, for each of the BF 108A-B dipoles, an electrically conductive line, referred to as the end line 402A, 402B, extending in one of the legs (the leg 206 in Figure 4) of that BF 108A-B dipole, from the inner line 402C to one of the arms 202, 204 of that BF 108A-B dipole. More precisely, the inner line 402C is preferably straight and there is a bend between the inner line 402C and the end lines 402A-B.

[0046] Thus, the 402C inner line and the 114 mast and the 206 feet form a coaxial line, in which the 114 mast and the 206 feet form a shield.

[0047] The antenna device 106 further includes an electrically conductive connecting line 404, which is connected to the inner line 402C and which passes through the mast 114 so as to present an outer portion located outside the mast 114. Preferably, the antenna device 106 includes a connecting tube 406 fixed to the mast 114 and surrounding the outer portion of the connecting line 404. Thus, the connecting line 404 and the connecting tube 406 form a coaxial line, in which the connecting tube 406 forms a shield.

[0048] The antenna device 106 further includes a low-pass filter 408 located outside the mast 114 and fixed to the mast 114. The low-pass filter 408 is thus located close to the mast 114, for example less than O,O4XÀOBF from the mast 114.

[0049] The 408 low-pass filter is designed to reject the high-frequency band. Thus, the 408 low-pass filter is designed to apply an attenuation of at least 10 dB, preferably at least 25 dB, in the high-frequency band, and less than 1 dB, preferably less than 0.1 dB, in the low-frequency band.

[0050] The 408 low-pass filter can be of any order, this order being chosen to achieve the desired level of rejection.

[0051] The low-pass filter 408, for example, includes an electrically conductive line, called the low-pass filter line 410, which has a first end connected to the outer portion of the connecting line 404. In particular, the low-pass filter line 410 extends substantially parallel to the inner line 402C. Preferably, the low-pass filter 408 also includes an electrically conductive tube, called the low-pass filter tube 412, fixed to the mast 114, for example, as in the illustrated example, to the connecting tube 406, and through which the low-pass filter line 410 extends. The low-pass filter line 410 and the low-pass filter tube 412 form a coaxial line, in which the low-pass filter tube 412 forms a shield and the low-pass filter line forms a central conductor.

[0052] To connect the BF 108A-B dipoles to the BF 122 transmitter / receiver, the communication system 100 further includes an external coaxial cable BF 413 connecting a second end of the low-pass filter 408, in particular a second end of the low-pass filter line 410, to the BF 122 transmitter / receiver.

[0053] The antenna device 106 further includes at least one rejection filter 414, 416 designed to attenuate a frequency band, called the rejected frequency band, equal to or greater than the high-frequency band. For example, the rejection filter 414, 416 is designed to apply an attenuation of at least 3 dB in the rejected frequency band, and less than 3 dB outside the rejected frequency band.

[0054] Each reject filter 414, 416 is located in the mast 114 and connected to the inner line 402C. In this case, a first reject filter 414 is for example connected to a first end of the inner line 402C (in particular, at the elbow with the end line 402A extending into foot 206), in continuity with this inner line 402C, and a second reject filter 414 is for example connected to the second end of this inner line 402C (in particular, at the elbow with the end line 402B extending into foot 206), in continuity with the inner line 402C.

[0055] For example, each reject filter 414, 416 has an open line 418, 420 which is conductive and connected to the inner line 402C. The open line 418, 420 extends into the mast 114, so as to form with the latter a coaxial line, in which the mast 114 forms a shield and the open line 418 a central conductor.

[0056] It is desirable that the mast 114 maintain a virtually unchanged cross-section along its height, at least along each of the rejection filters 414 and 416. Integrating the rejection filters 414 and 416 directly into the mast 114 minimizes their impact on the radiation pattern of the HF array. This integration avoids the need for an additional tube outside the mast 114. Such an additional tube would be sized for a specific wavelength in the low-frequency band. However, since the high-frequency band is approximately twice the width of the low-frequency band, this sizing would correspond to twice a wavelength in the high-frequency band, or generally to a size larger than a wavelength in the high-frequency band, which would disrupt the high-frequency array. Thus, the integration of the reject filters 414, 416 into the mast 114 makes it possible to avoid this disturbance.

[0057] Referring to Figure 5, the low-pass filter line 410 comprises, for example, a series of conductive elements 410A-D of varying diameters, alternating between high and low impedance conductive elements. The number of conductive elements varies, for example, from 2 to 6, depending on the embodiment. The higher the number of conductive elements, the greater the rejection, but also the length of the low-pass filter 408 and its losses. Thus, in practice, the number of conductive elements 410A-D is chosen to establish a compromise.

[0058] The impedance of each 410A-D conductive element, for example, ranges from 10 Ω to 200 Ω, depending in particular on the average and peak power that the communication system 100 must withstand during operation. These values ​​allow for reasonable diameters for the 410A-D conductive elements, since the higher the impedance, the smaller the diameter, and vice versa. The thinner the 410 low-pass filter line, the lower its average power handling. Conversely, the thicker the low-pass line, the lower its peak voltage handling. Thus, the impedance values ​​are chosen to establish a compromise.

[0059] The conductive elements 410A-D have respective lengths along the low-pass filter line 410, for example, between Àg / 20 and Àg / 5, where Àg represents the guided wavelength associated with the center frequency of the HF band and an electrically insulating medium present between the conductive elements 410A-D and the low-pass filter tube 412.

[0060] In order to keep these conductive elements 410A-D in the low-pass filter tube 412, the low-pass filter 408 includes, for example, dielectric elements 502A-C interposed between at least some of the conductive elements 410A-D and the low-pass filter tube 412. The dielectric elements 502A-C are, for example, made of polytetrafluoroethylene and / or preferably have a relative permittivity less than 3 and a loss tangent preferably less than 0.001.

[0061] The 502A-C dielectric elements facilitate the placement of conductive elements in the 412 low-pass filter tube by limiting the risk of contact with the 412 low-pass filter tube.

[0062] For the small-diameter 410A and 410D electrically conductive elements, the 502A and 502C dielectric element can be in the form of a washer. Similar washer-shaped dielectric elements can also be used to hold the open lines 418 in place within the mast 114.

[0063] For large-diameter electrical conductive elements 410C, it is preferable for the dielectric element 502B to be in the form of a sleeve extending at least along the entire length of the conductive element 410C. The dielectric element 502B is, for example, made of polytetrafluoroethylene. Indeed, due to their large diameter, these electrical conductive elements 410C are located close to the low-pass filter tube 412. Thus, without the sleeve, in the event of a high peak voltage, there would be a risk of arcing (the formation of an electric arc) through the air separating them. Furthermore, mechanical vibrations could cause these electrically conductive elements 410C to come into contact with the low-pass filter tube 412. Therefore, the presence of the sleeve along its entire length, exhibiting a dielectric strength significantly greater than that of air, resolves these problems by limiting the risks of high-power arcing and contact with the low-pass filter tube 412.

[0064] With reference to Figure 6, the dielectric element 502A, 502C is, for example, particularly when the low-pass filter tube 412 has a circular cross-section, in the form of a washer split by a slot 602 passing through a hole 604 for the low-pass filter line 410. The washer is further trimmed into three equidistant areas to form three straight edges 606, 608, 610. To limit the risk of breakage of the washer during its placement on the low-pass filter line 410, the slot 602 is preferably terminated by a hole 612 with a diameter greater than the width of the slot 602.

[0065] Such a dielectric element can also be used to hold other conductive power lines in tubes, such as the 402C inner line in mast 114.

[0066] Such a washer offers, for example, one or more of the following advantages: Easier installation: The split and trimmed profile reduces the contact area with the inside of the tube, thus decreasing friction when inserting coaxial cables. This greatly simplifies the installation process, especially in long or narrow masts. Reduction of mechanical stresses: The split shape allows slight flexibility of the dielectric element, which can absorb small variations in internal diameter of the mast or movements due to vibrations, thus reducing the risk of mechanical stresses on the internal conductors. Improved cooling: The spaces created by the chamfering allow for better airflow around the conductors, which can contribute to better system cooling, particularly important for high-power applications. Reduction of parasitic capacitive effects: Reducing the contact area between the dielectric element and the mast can reduce parasitic capacitive effects, thus helping to maintain the desired electrical characteristics of the coaxial line. Adaptation to manufacturing tolerances: The split design allows some flexibility to adapt to slight variations in internal diameter of the mast, thus ensuring effective support of the internal conductors despite manufacturing tolerances.

[0067] With reference to Figure 7, the sleeve-shaped dielectric element 502B preferably includes anti-slip means relative to the low-pass filter line 410, at least in one direction along the latter.

[0068] The anti-slip means include, for example, an internal shoulder 702 against which the conductive element 410C is butted, to prevent the dielectric element 502B from sliding downwards when the antenna device 106 is installed.

[0069] Furthermore, the anti-slip means include, for example, at least one internal dielectric seal 704, 706 (two in the illustrated example) interposed under compression between the dielectric element 502B and the conductive element 410C to prevent slippage of the dielectric element 502B relative to the conductive element 410C. The internal seal 704, 706 is, for example, toroidal in shape. The internal seal 704, 706 is, for example, as in the illustrated example, inserted into an internal annular groove formed in the dielectric element 502B. The internal seal(s) 704, 706 prevent displacement of the dielectric element 502B along the low-pass filter line 410, in both directions, during transport of the antenna device 106, and downwards once the antenna device 106 is installed.

[0070] Referring to Figure 8, the outdoor coaxial cable 413 has an inner conductor 802 and a conductive sheath 804 surrounding the inner conductor 802 at a distance. Pressurized air 806 separates the conductive sheath 804 from the inner conductor. To maintain the conductive sheath 804 away from the inner conductor 802, the outdoor coaxial cable 413 includes, for example, a helical support (not shown) interposed between the inner conductor 802 and the conductive sheath 804. The pressurized air prevents the ingress of moisture and dust that could lead to misalignment, overheating, and arcing.

[0071] To establish the overpressure, the communication system 100 includes a pressurization device 808 to supply overpressure air 806, preferably dry, in the external coaxial cable 413.

[0072] The low-pass filter tube 412 has an internal space 810 containing the conductive elements 410A-D and the dielectric elements 502A-C. This internal space 810 is connected to the pressurized air 806, so that it is filled by the latter. Thus, the overpressure in the external coaxial cable 413 is minimally maintained along the entire length of the low-pass filter 408.

[0073] Preferably, the antenna device 106 further includes a pressurization barrier 812 between the low-pass filter 408 and the mast 114, so that the over-pressurized air 806 does not reach the mast 114. This prevents air leaks in the mast 114 which would require too frequent operation of the pressurization device 808.

[0074] With reference to Figure 9, the pressurization barrier 812 comprises, for example, a wall 902, for example made of polytetrafluoroethylene, interposed between the connecting conductor 404 and the connecting tube 406, as well as a first sealing gasket 904 between the connecting tube 406 and the wall 902, and a second sealing gasket 906 between the connecting conductor 404 and the wall 902.

[0075] Referring to Figure 10, in some embodiments, the washer-shaped dielectric element 502A, 502C has curved edges 1002, 1004, 1006 which are further chamfered to break the angle of attack. This facilitates mounting the washer onto the conductive elements 410A-D in the low-pass filter tube 412.

[0076] Referring to Figure 11, the antenna device 106 further includes an inter-arm conductor 1102 connected, on one side, to the end line 402A extending into the foot 206 to which the arm 202 is attached, and, on the other side, to the other arm 204. Thus, the end line 402A and the arm 204 are electrically connected to each other. For example, the inter-arm conductor 1102 is in the form of a threaded rod screwed into the end line 402A and into the arm 204.

[0077] The inter-arm conductor 1102 thus passes partly through an inter-arm space 1104 separating the two arms 202, 204 from each other. This inter-arm space 1104 naturally forms an inter-arm capacitance. Therefore, the invention also proposes introducing a dielectric material into the inter-arm space 1104, this dielectric material having a dielectric constant higher than that of air, so as to increase the value of the inter-arm capacitance. This improvement is independent of the other improvements described above. For example, the dielectric material is Teflon (registered trademark).

[0078] Preferably, the dielectric material extends from arm 202 to arm 204, i.e. is in contact with both arms 202, 204, so as to form a spacer keeping arms 202, 204 at a desired distance from each other.

[0079] The presence of the dielectric material also helps to limit the risk of arcing between the two arms 202, 204.

[0080] For example, one or more washers 1106, 1108 made of dielectric material are provided, having a central hole 1106T, 1108T into which the inter-arm conductor 1102 is inserted. When the washers 1106, 1108 are thick, they can then resemble a cylinder.

[0081] With reference to figure 12, each washer 1106, 1108 preferably has, in the central hole 1106T, 1108T, a shoulder 1202, 1204 for receiving a nut (not shown) used to lock the threaded rod forming the inter-arm conductor 1102.

[0082] Furthermore, each washer 1106, 1108 may also have a slot 1210, 1212 passing through the central hole 1106T, 1108T allowing the washer 1106, 1108 to be removable, in order to place and remove the washer 1106, 1108 on the inter-arm conductor 1102.

[0083] Furthermore, each washer 1106, 1108 may have one or more additional holes 1206, 1208 allowing adjustment of the quantity of material in each washer 1106, 1108 and thus achieve the desired inter-arm capacity value.

[0084] Adjusting the inter-arm capacitance value can compensate for a capacitive effect of the radome 126. Indeed, the radome generally exhibits low electromagnetic permittivity, resulting in a capacitive effect that is taken into account when dimensioning the antenna device 106. However, due to manufacturing tolerances of the radome, its capacitive effect may be less than predicted during the dimensioning of the antenna device 106. Thus, adding dielectric material to the inter-arm space 1104 between the arms, around the inter-arm conductor 1102, allows the capacitive effect of the radome to be compensated for to achieve the desired value.

[0085] In conclusion, it is clear that an antenna design such as the one described above allows for the provision of a rejection filter for a low-frequency array without introducing parasitic elements for other, higher-frequency arrays. In particular, the combined use of a rejection filter and a low-pass filter improves decoupling between the two arrays without degrading radiation at the frequencies used by the high-frequency array, thanks to the integration of the rejection filter within the tubular mast.

[0086] Thus, thanks to the decoupling achieved, it is easier to adapt the respective impedance of the low frequency and high frequency networks in their respective frequency bands.

[0087] Thus, each network can be more easily optimized to operate optimally within its own frequency band, without interference from the other network. This synergy between the low-pass filter and the notch filter allows for both strong decoupling and good radio performance for each network, while maintaining a compact and integrated structure.

[0088] It should also be noted that the invention is not limited to the embodiments described above. Indeed, it will be apparent to those skilled in the art that various modifications can be made to the embodiments described above, in light of the information just disclosed to them.

[0089] In the detailed presentation of the invention given above, the terms used shall not be interpreted as limiting the invention to the embodiments set forth in this description, but shall be interpreted as including all equivalents which can be foreseen by a person skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.

Claims

Demands [1] Antenna device (106) comprising: a dipole (108A, 108B) designed to transition from guided propagation to radiated propagation of an electromagnetic wave, and vice versa; a mast (114) which has a hollow section and to which the dipole (108A, 108B) is attached; an internal line (402C) designed to conduct the guided propagation electromagnetic wave, the internal line (402C) running in the mast (114); and a reject filter (414, 416) comprising an open line (418, 420) connected to the inner line (402C) located in the mast (114); characterized in that the open line (418, 420) extends entirely into the mast (114) in line with the inner line (402C), and in that no open line of reject filter extends into the mast (114) along the inner line (402C). [2] Antenna device (106) according to claim 1, wherein the dipole (108A, 108B) is a low frequency dipole designed to radiate in a low frequency band, the antenna device (106) further comprising at least one high frequency dipole (110A, 110B, 110C, 110D) designed to radiate in a high frequency band. [3] Antenna device (106) according to claim 2, wherein the low frequency band has a low frequency center frequency and the high frequency band has a high frequency center frequency, and wherein the high frequency center frequency is at least 1.5 times greater than the low frequency center frequency. [4] Antenna device (106) according to any one of claims 1 to 3, wherein the open line (418, 420) of the reject filter (414, 416) and the mast (114) form a coaxial line in which the mast (114) forms a shield and the open line (418, 420) a center conductor. [5] Antenna device (106) according to any one of claims 1 to 4, further comprising a low-pass filter (408) fixed to the mast (114), outside the latter. [6] Antenna device (106) according to claim 5, wherein the low-pass filter (408) comprises an electrically conductive low-pass filter line (410). [7] Antenna device (106) according to claim 5, wherein the low-pass filter line (410) extends substantially parallel to the inner line (402C). [8] Antenna device (106) according to claim 6 or 7, further comprising a low-pass filter tube (412) fixed to the mast (114), the low-pass filter line (410) extending into the low-pass filter tube (412), the low-pass filter line (410) and the low-pass filter tube (412) forming a coaxial line in which the low-pass filter tube (412) forms a shield and the low-pass filter line (410) a center conductor. [9] Antenna device (106) according to any one of claims 6 to 8, wherein the low-pass filter line (410) comprises a succession of conductive elements (410A-D) of different diameters and, for at least one (410C) of the conductive elements (410A-D), a dielectric element (502B) interposed between this conductive element (410C) and the low-pass filter tube (412) in the form of a sleeve extending at least over a whole length of the conductive element (410C). [10] Antenna device (106) according to claim 9, further comprising an anti-slip system designed to limit slippage of the dielectric element (502B) relative to the low-pass filter line (410), at least in one direction along the low-pass filter line (410). [11] Antenna device (106) according to claim 10, wherein the anti-slip system comprises an internal shoulder (702) formed in the dielectric element (502B) and against which the conductive element (410C) is abutted. [12] Antenna device (106) according to claim 10 or 11, wherein the anti-slip system comprises at least one internal seal (704, 706) interposed in compression between the dielectric element (502B) and the conductive element (410C). [13] Antenna device (106) according to any one of claims 1 to 12, wherein the dipole (108A, 108B) comprises two arms (202, 204) separated from each other by an inter-arm space (1104) and a base (206) fixing at least one of the two arms (202, 204) to the mast (114), further comprising: - an end line (402A)19 connected to the inner line (402C) and extending into the foot (206); - an inter-arm conductor (1102) connected, on one side, to the end line (402A) and, on the other side, to the other arm (204), passing through the inter-arm space (1104); and - a dielectric material (1106, 1108) extending around the inter-arm conductor (1102) in the inter-arm space (1104), the dielectric material (1106, 1108) comprising, for example, a washer or a cylinder, this washer or cylinder being able to have holes and / or being removable. [14] Communication system (100) comprising: an antenna device (106) according to any one of claims 1 to 13; a low-frequency transmitter / receiver (122); and an external coaxial cable (413) connecting the low frequency transmitter / receiver (122) to the dipole (108A, 108B) to exchange the guided propagation electromagnetic wave with the dipole (108A, 108B) through the external coaxial cable (413). [15] Communication system (100) according to claim 14, wherein the antenna device (106) is according to any one of claims 8 to 12, and further comprises a pressurization device (808) designed to supply pressurized air (806) in the external coaxial cable (413), and wherein an internal space (810) of the low-pass filter tube (412) in which the low-pass filter line (410) extends is in communication with the pressurized air (806), in order to be filled by the pressurized air.

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