Horn antenna element

Abstract

The application relates to a horn antenna element (100) comprising: a septum polarizer (110) configured to transform a linearly polarized input signal (102) into a circularly polarized output signal (104) at a common port (112); and a horn radiator (120) comprising: an input geometry formed as a quad-ridge waveguide (121) to receive the circularly polarized output signal (104) at the common port (112); and an aperture grid (124) to radiate a grid-based circularly polarized output signal (106), wherein the septum polarizer (110) is embedded in the quad-ridge waveguide (121) at the common port (112).

Description

TECHNICAL FIELD

[0001] The present application relates to a horn antenna element and to an airborne satellite communication system comprising such a horn antenna element. The horn antenna element is designed for simultaneously supporting dual-band operation and dual-circular polarization. In particular, the present application relates to a dual-band dual-circular polarization horn antenna comprising such a horn antenna element. BACKGROUND

[0002] In satellite communication, in particular on-the-move satellite communication systems, multimedia data is transmitted from a satellite network to a mobile vehicle such as an airplane, helicopter, ship or car. Antennas have to be mounted on the mobile vehicle. These antennas should be directional in order to track the desired satellite. In today's applications, the K-band (17.7 GHz - 20.2 GHz) or the Ka-band (27.5 GHz - 30.0 GHz) can be used for data transmission.

[0003] For efficient communication at high data rates, dual-band operation (i.e. dual-band operation in both the K-band and the Ka-band) and dual-circular polarization are required.

[0004] A currently available solution is the use of four-ridge micro-horns smaller than the wavelength at the highest frequency in an array combined with a hybrid coupler or a meander polarizer to achieve circular polarization. The disadvantage of the micro-horn technology is that it incorporates a stripline-based feed circuit which shows higher ohmic losses compared to a waveguide, thus reducing the array efficiency and key performance indicators such as G / T (gain over noise temperature). These micro-horn arrays are inherently linearly polarized and require additional external components such as a hybrid coupler or a meander polarizer for conversion between linear and circular polarization.

[0005] Other available solutions are the use of reflector or lens antennas fed by a single horn. These systems typically show lower efficiency compared to horn arrays due to amplitude taper, spill-over and feed blockage effects.

[0006] Available septum polarizers implemented in standard rectangular / square waveguide geometry only work in a much narrower frequency range.

[0007] According to US 2017 / 222310 A, a cover for an antenna for electromagnetic radiation of a specific wavelength comprises a layer with a uniform arrangement of honeycomb-like protrusions. When viewed from the upper or lower side of the layer, the layer within the protrusions is spaced apart from the layer outside the protrusions by a distance corresponding to approximately 1 / 4 of the wavelength of the antenna signal. The bottom side of the cover and thus of the layer is later mounted along the radiation direction of the antenna and in a spaced apart relationship to the antenna, thereby forming a radome for the antenna.

[0008] US 2016 / 072190 A1 relates to a radiating element comprising an antenna, which is separated from the antenna edge by a fold, and for an antenna system supporting bi-directional satellite communication operating in Ka, Ku or X band for mobile and aeronautical applications. SUMMARY

[0009] It is an object of the present application to provide techniques for reliable and efficient satellite communication, in particular for mobile satellite communication systems for transmitting multimedia data from a satellite network to a mobile vehicle such as an airplane, helicopter, ship or car.

[0010] In particular, it is an object of the present application to provide an efficient and reliable antenna element for such a satellite communication. The antenna element shall provide high data rates and reliable communication and dual band operation, in particular dual band operation in both K and Ka band. The antenna element shall also support dual circular polarization.

[0011] This object is achieved by the features of the independent claims of the present application. Further implementation forms are evident from the dependent claims, the description and the figures.

[0012] The basic idea of the present application is to apply a new design of a horn radiator element which supports simultaneously dual band operation (e.g. K / Ka band Rx 17.7 GHz - 20.2 GHz and Tx 27.5 GHz - 30.0 GHz) and dual circular polarization (left hand circular polarization - LHCP and right hand circular polarization - RHCP). The horn radiator element will be a unit cell of an arbitrarily sized high efficient horn array aperture antenna with an approximately circular contour. To achieve high antenna efficiency and low ohmic losses, a solution using waveguide technology is preferred. The antenna can be used as part of a mobile satellite communication system based on a multi-axis positioner, e.g. azimuth, elevation, skew, to permanently align the antenna to a given target satellite.

[0013] The concept for solving the above mentioned technical problem according to the present application is to combine dual band operation and dual circular polarization in a highly efficient way by combining multiple radio frequency (RF) design techniques into a new very compact horn radiator / OMT design as described in the following.

[0014] The horn element itself is designed as an oversized radiator, i.e. larger than one wavelength at the highest operating frequency, typically two wavelengths or more, using both a four-ridge waveguide input geometry to enable very wide band (dual band) operation, and a specially designed aperture grid to divide the single radiator into a virtual 2x2 element array. This grid significantly reduces the grating lobes in the antenna pattern which inherently occur due to the unit cell size exceeding one wavelength at the highest operating frequency.

[0015] For the Orthogonal Mode Converter (OMT), a septum polarizer embedded in a four-ridged waveguide at a common port is used. Using this method, the OMT performs two tasks: combining two orthogonal polarizations into a common waveguide, and simultaneously converting the linearly polarized TE1,0 mode into its corresponding circularly polarized LHCP / RHCP mode.

[0016] To describe the invention in detail, the following terms, abbreviations, and notations will be used:

[0017] OMT (Orthogonal Mode Transformer)

[0018] LHCP Left-handed circular polarization

[0019] RHCP right-hand circular polarization

[0020] RF (Radio Frequency)

[0021] The K-band frequency band between 17.7 GHz and 20.2 GHz

[0022] The Ka band between 27.5 GHz and 30.0 GHz

[0023] TE1,0 waveguide modes where the electric field is perpendicular to the propagation direction.

[0024] Another waveguide mode whose electric field is perpendicular to the propagation direction is TE0,1.

[0025] The septum polarizer described in this application is a linear-to-circular polarization converter. The septum polarizer consists of two rectangular waveguides (port 1 and port 2, see [link to application]) sandwiched together by a common wide wall (septum). Figure 5 As shown by reference numerals 501 and 502 in the attached figures, the common wide wall gradually decreases to zero height, thereby creating a square waveguide common port. It is assumed that RF power is applied to port 2 (…). Figure 5 As shown in Figure 502, the signal travels through the waveguide, and the horizontal E-field component begins to split into two orthogonal field components along the steps of the polarizer. At the end of the square output, one field component will be delayed by 90° relative to the other, and the two components will have the same amplitude. For an ideal septum polarizer horizontal field, the horizontal component of the E-field is equal to the vertical component of the E-field and has a 90-degree phase delay. Thus, right-hand circular polarization (RHCP) (clockwise rotation) is formed. The same reasoning applies to left-hand circular polarization (LHCP) at port 1.

[0026] A quadrature mode transformer (OMT) as described in this application is a waveguide assembly, often referred to as a polarization diplexer. A quadrature mode transformer is used to combine or separate two quadrature polarized microwave signal paths. One of the paths forms an uplink path or a downlink path, which is transmitted through the same waveguide as the received signal path. Such a device can be part of a satellite antenna feed or a terrestrial microwave radio feed. OMTs are often used with feed horns to isolate the quadrature polarizations of the signals and to transfer the transmit and receive signals to different ports.

[0027] A waveguide as described in this application is a structure that guides a wave, such as an electromagnetic wave, with minimal energy loss by restricting the transmission of energy in one direction.

[0028] A quad-ridge waveguide is a waveguide with ridges protruding from each sidewall into the center of the waveguide. The ridges of the top and bottom walls are parallel to the sidewalls of the waveguide. The ridges of the left and right sidewalls are parallel to the top and bottom walls of the waveguide. When compared to a regular rectangular waveguide, a ridge waveguide tends to have lower impedance and wider bandwidth in its fundamental mode. They also have lower cutoff frequencies and have lower power handling capability. Ridge waveguides can be used for impedance matching because they reduce the characteristic impedance of the waveguide. Ridge waveguides provide higher bandwidth compared to conventional waveguides.

[0029] Circular polarization of an electromagnetic wave according to the present application is a state of polarization in which at each point the electromagnetic field of the wave has a constant magnitude, but its direction rotates at a constant rate in a plane perpendicular to the direction of the wave. A circularly polarized wave can rotate in one of two possible senses: right-handed circular polarization (RHCP) in which the electric field vector rotates in the right-handed sense relative to the direction of propagation and left-handed circular polarization (LHCP) in which the vector rotates in the left-handed sense.

[0030] Linear polarization of an electromagnetic wave according to the present application is the restriction of the electric or magnetic vector to a given plane along the direction of propagation.

[0031] According to a first embodiment of the present application, a horn antenna element comprises: a septum polarizer configured to convert a linearly polarized input signal into a circularly polarized output signal at a common port; and a horn radiator comprising: an input geometry formed as a quad-ridge waveguide to receive the circularly polarized output signal at the common port; and an aperture grid to radiate a grid-based circularly polarized output signal, wherein the septum polarizer is embedded in the quad-ridge waveguide at the common port.

[0032] Such horn antenna elements provide higher efficiency and robust design advantages compared to existing micro-horn technology due to the polarizer embedded as part of the OMT. Furthermore, there are cost advantages compared to existing micro-horn technology due to the lack of stripline circuitry and the significantly larger waveguide structure that is easier and faster to machine.

[0033] The advantages compared to existing reflector-based solutions are high efficiency and configurability. Using an array enables optimization of the aperture illumination by individually exciting each array element with a specific amplitude / phase signal combination.

[0034] In an exemplary implementation of the horn antenna element, the four-ridge waveguide of the input geometry comprises four symmetrically formed ridges of equal size.

[0035] This provides the advantage that a high frequency range can be used for transmission and reception, such as the K-band frequency range and the Ka-band frequency range.

[0036] In an exemplary implementation of the horn antenna element, the aperture grid is formed as an array of four-ridge waveguides, for example as a 2x2 array of four-ridge waveguides.

[0037] This provides the advantage that four-ridge waveguides have lower impedance and wider bandwidth compared to regular rectangular waveguides. They can be used for impedance matching as they reduce the characteristic impedance of the waveguide. Four-ridge waveguides provide higher bandwidth compared to non-ridged waveguides.

[0038] In an exemplary implementation of the horn antenna element, the four-ridge waveguides of the aperture grid are symmetrically formed, each having the same cross-section.

[0039] This provides the advantage that an array of circularly polarized output signals with identical signal characteristics can be efficiently implemented when using a symmetrically formed aperture grid.

[0040] In an exemplary implementation of the horn antenna element, each four-ridge waveguide of the aperture grid comprises four ridges.

[0041] This provides the advantage that a high-quality circularly polarized signal with low axial ratio can be provided, forming a nearly perfect polarization circle.

[0042] The size of the ridges can be equal or different. The ridges can be symmetrically or asymmetrically formed.

[0043] In an exemplary implementation of the horn antenna element, the ridges of the four-ridge waveguide of the input geometry and the ridges of the array of four-ridge waveguides of the aperture grid are formed in a non-overlapping manner.

[0044] This provides the advantage that the circular polarized signal generated at the common port can be optimally mapped to the grid-based circular polarized signal to be radiated by the horn radiator.

[0045] In an exemplary implementation of the horn antenna element, the septum polarizer is configured to split an input TE1,0 mode of a linear polarized input signal into a mode combination of TE1,0 and TE0,1 with + / - 90 degree phase difference therebetween, resulting in a left-handed circular polarized LHCP signal or a right-handed circular polarized RHCP signal to be radiated by the horn radiator.

[0046] This provides the advantage that efficient communication with high data rates, dual band operation in both K- and Ka-band and dual circular polarization can be provided.

[0047] In an exemplary implementation of the horn antenna element, the horn antenna element comprises two single linear polarized ports configured to receive and / or transmit respective linear polarized components of a linear polarized input signal.

[0048] This provides the advantage that the two single linear polarized ports enable feeding two different signals, e.g. in downlink and uplink direction, in order to enable dual band operation in both K- and Ka-band.

[0049] In an exemplary implementation of the horn antenna element, the two single linear polarized ports are configured to receive and transmit simultaneously in the K-band frequency range and the Ka-band frequency range.

[0050] This provides the advantage that reliable and efficient satellite communication can be achieved. The antenna element provides high data rates, reliable communication and dual band operation in both K- and Ka-band and supports dual circular polarization.

[0051] In an exemplary implementation of the horn antenna element, the reflection coefficients of the two single linear polarized ports are below a predetermined threshold, in particular below -15 dB, and do not resonate in both K- and Ka-band.

[0052] This provides the advantage that high data rate communication can be achieved.

[0053] In an exemplary implementation of the horn antenna element, an axial ratio of the grid-based circular polarized output signal is below 1 dB in both K- and Ka-band.

[0054] This provides the advantage that cross talk between polarizations can be minimized.

[0055] In an exemplary implementation of the horn antenna element, the septum polarizer comprises a continuous ridge waveguide geometry from the two single linear polarization ports to the four-ridge waveguide of the horn radiator; and the septum polarizer is stepped to convert the linear polarization input signal into a circular polarization output signal.

[0056] This provides the advantage that the horn antenna element is easy to manufacture. In particular, the stepped structure can be manufactured at low cost by common machines.

[0057] In an exemplary implementation of the horn antenna element, the cross section of the four-ridge waveguide of the horn radiator corresponds to the cross section of the aperture grid of the horn radiator.

[0058] This provides the advantage that a circular polarization signal received at the common port can be efficiently mapped to a grid-based circular polarization signal to be radiated by the aperture grid of the horn radiator.

[0059] In an exemplary implementation of the horn antenna element, the geometry of the horn radiator is oversized with respect to the wavelength at the specified maximum operating frequency, in particular larger than the wavelength at one or more of the specified maximum operating frequencies.

[0060] This provides the advantage that an array of circular polarization signals at the maximum operating frequency can be provided for transmission and / or reception.

[0061] According to another embodiment of the present application, an airborne satellite communication system comprises a horn antenna element according to the first aspect; and a multi-axis positioner configured to permanently align the horn antenna element to a given target satellite.

[0062] This provides the advantage that the horn antenna element can be efficiently applied to airborne satellite communication.

[0063] According to the third aspect, the present application relates to a method of converting a linear polarization signal into a circular polarization signal by a horn antenna element, the horn antenna element comprising a septum polarizer configured to convert a linear polarization input signal into a circular polarization output signal at a common port; and a horn radiator comprising an input geometry formed as a four-ridge waveguide to receive the circular polarization output signal at the common port; and an aperture grid to radiate a grid-based circular polarization output signal, wherein the septum polarizer is embedded in the four-ridge waveguide at the common port. The method comprises receiving the linear polarization signal by the septum polarizer; converting the linear polarization input signal into the circular polarization output signal at the common port of the septum polarizer by the septum polarizer; receiving the circular polarization output signal at the common port by the horn radiator; and radiating the circular polarization output signal by the horn radiator through the grid as the grid-based circular polarization output signal.

[0064] Such a method offers the advantages of high efficiency and configurability compared to existing reflector-based solutions. The use of an array makes it possible to optimize the aperture illumination by individually exciting each array element with a specific amplitude / phase signal combination.

[0065] According to a fourth aspect, the application relates to a satellite communication method comprising aligning, by a multi-axis positioner of an airborne satellite communication system according to the second aspect, a horn antenna element according to the first aspect to a given target satellite. The alignment can be performed permanently. The airborne satellite communication system can comprise a processor configured to control the alignment of the horn antenna element.

[0066] According to a fifth aspect, the application relates to a computer program product comprising computer-executable code or computer-executable instructions that, when executed, cause at least one computer to perform the method according to the fourth aspect. Such a computer program product can comprise a non-transitory readable storage medium on which the program code is stored for use by a processor, the program code comprising instructions for performing the method as described above. BRIEF DESCRIPTION OF DRAWINGS

[0067] Further examples will be described with respect to the following figures, in which:

[0068] Figure 1 A schematic diagram 100 illustrating a horn antenna element 100 according to the present application is shown;

[0069] Figure 2 A schematic diagram illustrating an airborne satellite communication system 200 according to the present application is shown;

[0070] Figure 3 A front view 300 of an exemplary horn antenna element 100 according to the present application is shown;

[0071] Figure 4 A perspective view 400 of an exemplary horn antenna element 100 according to the present application is shown;

[0072] Figure 5 A 3-dimensional representation 500 of an exemplary horn antenna element 100 according to the present application is shown;

[0073] Figure 6 A back view 600 of an exemplary horn antenna element 100 according to the present application is shown;

[0074] Figure 7 A cut view 700 of an exemplary horn antenna element 100 according to the present application is shown;

[0075] Figure 8A cross-sectional side view 800 of an exemplary horn antenna element 100 according to the present application is shown;

[0076] Figure 9 A cross-sectional perspective view 900 of an exemplary horn antenna element 100 according to the present application is shown;

[0077] Figure 10 A cross-sectional front view 1000 of an exemplary horn antenna element 100 according to the present application is shown;

[0078] Figure 11 A performance plot illustrating S-parameters 1100 of an exemplary horn antenna element 100 according to the present application is shown; and

[0079] Figure 12 A performance plot illustrating axial ratio 1200 of an exemplary horn antenna element 100 according to the present application is shown. DETAILED DESCRIPTION

[0080] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific aspects in which the application can be practiced. It is understood that other aspects can be utilized and that structural or logical changes can be made without departing from the scope of the present application. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present application is defined by the appended claims.

[0081] It is to be understood that the comments made in connection with the described methods also apply to corresponding apparatus or systems configured to carry out the methods and vice versa. Further, it should be understood that the features of the various exemplary aspects described herein can be combined with each other, unless specifically noted otherwise.

[0082] Figure 1 A schematic diagram 100 illustrating a horn antenna element 100 according to the present application is shown.

[0083] The horn antenna element 100 comprises a septum polarizer 110 and a horn radiator 120. The septum polarizer 110 is configured to transform a linearly polarized input signal 102 into a circularly polarized output signal 104 at a common port 112. The horn radiator 120 comprises an input geometry formed as a four-ridge waveguide 121 to receive the circularly polarized output signal 104 at the common port 112. The horn radiator 120 further comprises an aperture grid 124 to radiate a grid-based circularly polarized output signal 106. The grid-based circularly polarized output signal 106 corresponds to the circularly polarized output signal 104 after passing through the aperture grid 124. The septum polarizer 110 is embedded in the four-ridge waveguide 121 at the common port 112.

[0084] Both the septum polarizer 110 and the horn radiator 120 can be embedded in the housing. Embedding the septum polarizer 110 in the quad-ridge waveguide 121 can provide a fixed arrangement of these two components in the horn antenna element 100 such that rotation or movement of the septum polarizer 110 relative to the horn radiator 120 is not possible. The horn antenna element 100 can be formed of a single material. It is also possible to produce the septum polarizer 110 and the horn radiator 120 separately and connect these two components, for example, by fusing, soldering, bonding, gluing, or the like.

[0085] The linearly polarized input signal 102 can be fed to the input port 111 of the horn antenna element through a feed network (not shown in Figure 1 ).

[0086] The quad-ridge waveguide 121 of the input geometry can comprise four symmetrically formed ridges 311a, 311b, 311c, 311d of equal size, for example, as shown in Figure 3 .

[0087] The aperture grid 124 can be formed as an array of quad-ridge waveguides 124a, 124b, 124c, 124d, for example, as shown in Figure 3 , for example, as a 2x2 array of quad-ridge waveguides 124a, 124b, 124c, 124d as shown in Figure 3 .

[0088] The quad-ridge waveguides 124a, 124b, 124c, 124d of the aperture grid 124 can be symmetrically formed such that each of the quad-ridge waveguides 124a, 124b, 124c, 124d has the same cross-section, for example, as shown in Figure 3 .

[0089] Each of the quad-ridge waveguides 124a, 124b, 124c, 124d of the aperture grid 124 can comprise four ridges 301a, 301b, 301c, 301d, for example, as shown in Figure 3 .

[0090] The ridges 311a, 311b, 311c, 311d of the quad-ridge waveguide 121 of the input geometry and the ridges 301a, 301b, 301c, 301d of the array of quad-ridge waveguides 124a, 124b, 124c, 124d of the aperture grid 124 can be formed in a non-overlapping manner, for example, as shown in Figure 3 .

[0091] The septum polarizer 110 can be configured to split the input TE1,0 mode of the linearly polarized input signal 102 into a combination of modes of TE1,0 (702) and TE0,1 (701) with + / - 90 degree phase difference therebetween, resulting in a left-handed circularly polarized LHCP signal 703 or a right-handed circularly polarized RHCP signal 704 to be radiated by the horn radiator 120, e.g., as shown in Figure 7 .

[0092] The horn antenna element 100 can include two single linear polarization ports 501, 502 configured to receive and / or transmit respective linear polarization components of the linearly polarized input signal 102, e.g., as shown in Figure 5 .

[0093] It is to be understood that the horn antenna element 100 is configured to simultaneously transmit and receive signals. For example, K-band signals can be received on each port while Ka-band signals are transmitted.

[0094] The two single linear polarization ports 501, 502 can be configured to simultaneously receive and transmit within the K-band frequency range 1110 and the Ka-band frequency range 1120, e.g., as shown in Figure 11 and Figure 12 .

[0095] In one exemplary configuration of the horn antenna element, the reflection coefficients 1101 of the two single linear polarization ports 501, 502 can be below a predetermined threshold, e.g., below -15 dB, and can be free of resonances in both the K-band 1110 and the Ka-band 1120, e.g., as shown in Figure 11 .

[0096] In one exemplary configuration of the horn antenna element, the axial ratio 1201 of the grid-based circularly polarized output signal 106 can be below 1 dB in both the K-band 1110 and the Ka-band 1120, e.g., as shown in Figure 12 .

[0097] The septum polarizer 110 can include continuous ridge waveguide geometries 511, 512, 513, 514, 611, 612 from the two single linear polarization ports 501, 502 to the four-ridge waveguide 121 of the horn radiator 120, e.g., as shown in Figure 5 and Figure 6 .

[0098] The septum polarizer 110 can be stepped 801, 802, 803, 804, e.g., as shown in Figure 8 to convert the linearly polarized input signal 102 to the circularly polarized output signal 104.

[0099] The cross-section of the quadruple-ridge waveguide 121 of the horn radiator 120 can correspond to the cross-section of the aperture grid 124 of the horn radiator 120, e.g. as shown in Figure 3 .

[0100] The geometry of the horn radiator 120 can be oversized with respect to the wavelength at the specified maximum operating frequency, e.g. larger than the wavelength at one or more specified maximum operating frequencies. Such a specified maximum operating frequency can be e.g. the end of the Ka band or higher.

[0101] Figure 2 is a schematic diagram illustrating an airborne satellite communication system 200 according to the present application.

[0102] The airborne satellite communication system 200 comprises a horn antenna element 100 as shown in Figure 1 or Figures 3 to 10 The airborne satellite communication system 200 further comprises a multi-axis positioner 203 configured to permanently align 204 the horn antenna element 100 to a given target satellite 201. A processor or controller can be used to align the horn antenna to the satellite 201. The position of the satellite can be detected by receiving a signal from the satellite. The processor can align the multi-axis positioner 203 based on the determined satellite position.

[0103] The multi-axis positioner 203 and the horn antenna element 100 can be mounted on an aircraft 202, e.g. at the rear wing of the aircraft 202.

[0104] Figure 3 is a front view 300 illustrating an exemplary horn antenna element 100 according to the present application.

[0105] The quadruple-ridge waveguides 124a, 124b, 124c, 124d are in vacuum. The view on the grid 124 (shown in Figure 1 ) shows the division of a single horn into a virtual 2x2 array. The volume inside the horn is first split into 4 equal parts, pre-forming the virtual 2x2 array, and finally it is completed with the grid covering the 2x2 array. All parts involve quadruple-ridge waveguide features 301a, 301b, 301c, 301d, 311a, 311b, 311c, 311d.

[0106] The input geometry of the quadruple-ridge waveguide 121 is illustrated by the structure 310 comprising four symmetrically formed ridges 311a, 311b, 311c, 311d of equal size. The upper ridges 311a and the lower ridges 311c are parallel to the left and right sides of the waveguide. The left side ridges 311d and the right side ridges 311b are parallel to the upper and lower sides of the waveguide.

[0107] The aperture grid 124 is formed as an array of quad-ridge waveguides 124a, 124b, 124c, 124d. In this example, a 2x2 array of quad-ridge waveguides 124a, 124b, 124c, 124d is shown. However, in another example, the array can be a 3x3 array or a 4x4 array or a higher dimensional array. In another example, even non-square sized arrays can be implemented, such as a 2x3 array, a 2x4 array, a 3x4 array, etc.

[0108] The quad-ridge waveguides 124a, 124b, 124c, 124d of the aperture grid 124 are symmetrically formed such that each of the quad-ridge waveguides 124a, 124b, 124c, 124d has the same cross-section. For example, the aperture grid 124 can have a square cross-section (e.g. with rounded edges) of size A. Then, in this implementation the cross-sections of the quad-ridge waveguides 124a, 124b, 124c, 124d can each be a square (also with rounded edges) of size A / 4.

[0109] However, in another example, even different cross-sections of the quad-ridge waveguides 124a, 124b, 124c, 124d can be implemented.

[0110] Each of the quad-ridge waveguides 124a, 124b, 124c, 124d of the aperture grid 124 includes four ridges 301a, 301b, 301c, 301d.

[0111] The ridges 311a, 311b, 311c, 311d of the quad-ridge waveguide 121 of the input geometry and the array of ridges 301a, 301b, 301c, 301d of the quad-ridge waveguides 124a, 124b, 124c, 124d of the aperture grid 124 are formed in a non-overlapping manner. That is, as can be seen from Figure 3 the two sets of ridges do not overlap.

[0112] However, in another example, an overlapping design can be implemented. Then, the ridge 311a can overlap with the ridge 301b and with the corresponding ridge of the quad-ridge waveguide 124b. Similarly, the ridge 311b can overlap with the corresponding ridges of the quad-ridge waveguides 124b and 124c; the ridge 311c can overlap with the corresponding ridges of the quad-ridge waveguides 124c and 124d; and the ridge 311d can overlap with the corresponding ridges of the quad-ridge waveguides 124d and 124a.

[0113] Figure 4 A perspective view 400 of an exemplary horn antenna element 100 according to the present application is shown. The grid 124 in front of the horn (as Figure 1 shown) is visible to divide the horn aperture into a virtual 2x2 array. The grid shows a quad-ridge waveguide like geometry to enable dual band (very wide band) operation.

[0114] Figure 5 A 3-dimensional representation 500 of an exemplary horn antenna element 100 according to the present application is shown. Shown is the vacuum part of the horn antenna element 100, i.e. vacuum inside both the horn radiator 120 and the septum polarizer 110 embedded in the quad-ridge waveguide 121. Continuous ridge waveguide geometries 511, 512, 513, 514 are realized from the single linear polarized ports 501, 502 to the horn aperture 124.

[0115] Figure 6 A back view 600 of an exemplary horn antenna element 100 according to the present application is shown. Shown is the vacuum part of the horn antenna element 100, i.e. vacuum inside both the horn radiator 120 and the septum polarizer 110 embedded in the quad-ridge waveguide 121. The back view is looking towards the two orthogonal polarized ports 501, 502 of the septum polarizer 110. Ridge waveguide geometries 611, 612 are realized at the input ports 501, 502. In Figure 6 The transformation steps towards the septum polarizer 110 are visible. The ridge geometries 611, 612 are chosen to reduce the size of the waveguide’s cross section (but keep the cut-off frequency as low as possible) to be able to build a feed network around it.

[0116] Figure 7 A cut view 700 of an exemplary horn antenna element 100 according to the present application is shown.

[0117] The septum polarizer 110 with its characteristic stepped shape is visible, transforming the linear polarized input signal 102 received at the input ports 501, 502 into a circular polarized output signal 104 at the common port 112.

[0118] The input TE1,0 mode is split into a mode combination of TE1,0 (702) and TE0,1 (701) with + / - 90° phase difference in between, resulting in a LHCP signal (704) or RHCP signal (703) to be radiated.

[0119] Figure 8 A cut view side view 800 of an exemplary horn antenna element 100 according to the present application is shown. The polarizer “steps” 801, 802, 803, 804 are visible. The “stepped” geometry can make the manufacturing of the components easier.

[0120] Figure 9 A cut view perspective 900 of an exemplary horn antenna element 100 according to the present application is shown. The polarizer “steps” 801, 802, 803, 804 are visible.

[0121] Figure 10A cross-sectional elevation view 1000 illustrating an exemplary horn antenna element 100 according to the present application is shown. The polarizer 110 is fully embedded into the quad-ridged waveguide geometry.

[0122] Figure 11 A performance plot illustrating S-parameters 1100 of the exemplary horn antenna element 100 according to the present application is shown. The above graph illustrates exemplary S- parameter performance data.

[0123] S11 is the reflection coefficient 1101 of the linear polarized ports 501, 502, which is below 15 dB and does not have any resonances in both K-band / Ka-band. The K-band is denoted 1110 and the Ka-band is denoted 1120.

[0124] S21 is the isolation 1102 between the two linear polarized ports 501, 502, which shows the characteristic dual-band behavior. The isolation 1102 is sufficiently high for both the K-band Rx frequency range (17.7-20.2 GHz) and the Ka-band Tx frequency range (27.5-30 GHz).

[0125] Figure 12 A performance plot illustrating the axial ratio 1200 of the exemplary horn antenna element 100 according to the present application is shown.

[0126] The graph illustrates the expected very good axial ratio 1201 performance with values < 1 dB in both the Rx frequency range and the Tx frequency range, i.e. the K-band Rx frequency range (17.7-20.2 GHz) and the Ka-band Tx frequency range (27.5-30 GHz).

[0127] The horn antenna element 100 as presented in the present application can be used as, but is not limited to, a Ka-band antenna as part of an airborne satellite communication system. The horn antenna element 100 can be implemented together with another antenna design for Ku-band, so that the user has the advantage of choosing between a Ku-band product or a Ka-band product using the same platform. For example, the antenna can be used as a tail-mounted antenna, or as another type of antenna. The horn antenna element 100 can also be used as an antenna in other frequency ranges not described in the present application.

[0128] While particular features or aspects of the disclosure can have been disclosed in one implementation, or carried out in one manner, specific features or aspects can be combined with or substituted for other features or aspects in other implementations as can be desired or advantageous for any given or particular application. Furthermore, to the extent that terms have been used in the detailed description or claims, such terms can be given their broadest possible interpretation, such as to include similar things to that which are specifically described. Likewise, the terms "example," "for example," and "e.g." have been used to merely indicate an example, and not an ideal or superior implementation. The terms "coupled" and "connected," along with derivatives can have been used. It should be understood that these terms can have been used to indicate that two elements cooperate or interact with each other, regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.

[0129] While particular aspects have been illustrated and described, it would be the understanding of those skilled in the art that various alternatives and / or equivalents can be substituted for the specific aspects shown and described without departing from the scope of the present application. The present application is intended to cover any adaptations or variations of the specific aspects discussed herein.

[0130] While the elements in the claims have been presented in a certain order, the mere fact that they can be recited in such an order does not necessarily dictate that the elements be implemented in such order. Nothing in the disclosure is intended to be dependent on the particular order used in this claims.

[0131] In light of the foregoing teachings, a number of alternatives, modifications, and variations will be apparent to those skilled in the art. Of course, those skilled in the art will readily recognize that there are a number of ways of adapting the present application for different applications. While the present application has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes can be made thereto without departing from the scope of the present application. It is therefore intended that there be no limitation on the scope of the present application except as to the appended claims and their equivalents. Accordingly, while the present application is susceptible to various modifications and alternative forms, specific aspects have been shown by way of example in the drawings and are described herein in detail. It should be understood, however, that the intention is not to limit the application to the particular embodiments described but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the application as defined by the appended claims and their equivalents.

[0132] The following reference numerals have been used in the present application:

[0133] 100 horn antenna element

[0134] 102 linear (or orthogonal) polarized input signal

[0135] 104 circular polarized output signal

[0136] 106 grid-based circular polarized output signal, i.e. circular polarized output signal after passing through a grid

[0137] 110 septum polarizer

[0138] 111 input port

[0139] 112 common port (of the septum polarizer)

[0140] 120 horn radiator

[0141] 121 quad-ridge waveguide

[0142] 124 aperture grid

[0143] 124a, 124b, 124c, 124d array of quad-ridge waveguides of the aperture grid

[0144] 200 airborne satellite communication system

[0145] 201 satellite

[0146] 202 aircraft

[0147] 203 multi-axis positioner

[0148] 204 alignment direction of the horn antenna element

[0149] 301a, 301b,

[0150] 301c, 301d ridge 311a, 311b, 311c, 311d of the array of quad-ridge waveguides of the aperture grid ridge 501, 502 of the quad-ridge waveguide of the horn radiator input geometry linearly polarized input port of the septum polarizer and the horn antenna element

[0151] 511, 512, 513, 514 continuous-ridge waveguide geometry

[0152] 611, 612 continuous-ridge waveguide geometry

[0153] 701 TE1,0 mode

[0154] 702 TE0,1 mode

[0155] 703 RHCP signal

[0156] 704 LHCP signal

[0157] 801, 802, 803, 804 stepped profile of the septum polarizer

[0158] 1110 K-band

[0159] 1120 Ka-band

[0160] 1101 S11 parameter, reflection coefficient of the linearly polarized port

[0161] 1102 S21 parameter, isolation between two linearly polarized ports

[0162] 1201 Axial ratio of the grid-based circularly polarized output signal

Claims

1. A horn antenna element, the horn antenna element comprising: A septum polarizer configured to convert a linearly polarized input signal into a circularly polarized output signal at a common port; as well as A horn radiator, the horn radiator comprising: An input geometry, formed as a four-ridged waveguide, is used to receive the circularly polarized output signal at the common port; and An aperture grid, used to radiate a grid-based circularly polarized output signal, wherein the aperture grid is formed as an array of four-ridged waveguides. The septum polarizer is embedded at the common port in the four-ridged waveguide of the input geometry.

2. The horn antenna element according to claim 1, in, The input geometry's four-ridged waveguide comprises four symmetrically formed ridges of equal size.

3. The horn antenna element according to claim 1, wherein, The aperture grid is formed as a 2×2 array of four-ridged waveguides.

4. The horn antenna element according to claim 1, in, The four ridge waveguides of the aperture grid are formed symmetrically, and each of the four ridge waveguides of the aperture grid has the same cross-section.

5. The horn antenna element according to claim 1, in, Each of the four-ridged waveguides in the aperture grid comprises four ridges.

6. The horn antenna element according to claim 1, in, The ridges of the four-ridged waveguides in the input geometry and the ridges of the array of four-ridged waveguides in the aperture grid are formed in a non-overlapping manner.

7. The horn antenna element according to claim 1 or 2, in, The septum polarizer is configured to split the input TE1,0 mode of the linearly polarized input signal into a combination of TE1,0 and TE0,1 modes with a + / -90 degree phase difference between them, thereby generating a left-hand circularly polarized LHCP signal or a right-hand circularly polarized RHCP signal to be radiated by the horn radiator.

8. The horn antenna element according to claim 1 or 2, wherein the horn antenna element comprises: Two single-polarization ports are configured to receive and / or transmit the corresponding linear polarization components of the linearly polarized input signal.

9. The horn antenna element according to claim 8, in, The two single-line polarization ports are configured to simultaneously receive and transmit within the K-band and Ka-band frequency ranges.

10. The horn antenna element according to claim 8, in, The reflection coefficients of the two single-line polarization ports are below a predetermined threshold, and there is no resonance in either the K-band or the Ka-band.

11. The horn antenna element of claim 10, wherein the predetermined threshold is -15dB.

12. The horn antenna element according to claim 8, in, The axial ratio of the grid-based circularly polarized output signal is less than 1 dB in both the K-band and Ka-band.

13. The horn antenna element according to claim 8, in, The septum polarizer includes a continuous ridge waveguide geometry of the four-ridge waveguide from the two single-line polarization ports to the input geometry of the horn radiator; and The septum polarizer is stepped to convert the linearly polarized input signal into the circularly polarized output signal.

14. The horn antenna element according to claim 1 or 2, in, The cross-section of the four-ridged waveguide of the input geometry of the horn radiator corresponds to the cross-section of the aperture grid of the horn radiator.

15. The horn antenna element according to claim 1 or 2, in, The geometry of the horn radiator is too large relative to the wavelength at the specified maximum operating frequency.

16. The horn antenna element according to claim 15, in, The geometry of the horn radiator is greater than one or more wavelengths at the specified maximum operating frequency.

17. An airborne satellite communication system, the airborne satellite communication system comprising: The horn antenna element according to any one of the preceding claims; as well as A multi-axis positioner configured to permanently align the horn antenna element with a given target satellite.

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