ES2441471B2 - Dual frequency band antenna feeder with different circular polarization in each band - Google Patents

Abstract

Dual frequency band antenna feeder with different circular polarization in each band, high electrical performance and great versatility in mechanical interconnection. The feeder is based on a new architecture that uses a diplexer (200) that combines the two input signals (L {sub, 1}, L {sub, 2}) in different frequency bands and with the same linear polarization in one waveguide, while providing high isolation between frequency bands. The single-mode waveguide of the diplexer output allows the routing of the signals in the most convenient way without any geometric restriction until reaching a two-phase polarizer (210) that is responsible for producing the necessary phase shifts, around + 90º and - 90º, in each of the bands to obtain the desired circular polarizations with a low level of axial relationship in each frequency band.

Description

TECHNICAL SECTOR The object of the invention is a new antenna feeder for two frequency band communications systems with opposite circular polarizations in each of them, which has numerous advantages both in the electrical characteristics of the feeder and in the mechanical connections of The various components.

Numerous communications systems, including satellite communications, demand this type of characteristics, being of great importance both the electrical characteristics, especially the isolation between bands and the axial relationship, as well as the versatility of interconnection of the constituent elements.

BACKGROUND OF THE INVENTION Microwave electromagnetic signals, usually in the range between 1 and 100 Gigahertz (GHz), are commonly used for the transmission and reception of all types of information. In addition to the aforementioned frequency property, these electromagnetic signals also have a polarization characteristic. In the case of application in the communication systems, the different polarizations used are: vertical, horizontal, circular to the right (C +) and circular to the left (C-). If the polarization is circular (C + and C-), the parameter called axial relationship is used to measure its purity. Very low axial ratio values (high polarization purity) are necessary for the proper functioning of communications equipment.

In a large number of communications systems and in particular on satellite satellites, two different frequency channels or bands (first or low band and second or high band) are used for the transmitted and received signal, respectively. These two bands should interact as little as possible, which is equivalent to high isolation between the two. In addition, the use of different circular polarization is required in each of the bands, either right-hand circular in the band

first and left in the second band (C1 + and Cr) or vice versa (Cr and C2 +). To all this we must add the need to use a single antenna for reasons of saving in the mass and volume of the satellite. In this way it is necessary to use an antenna feeder that provides the electromagnetic signals with the

5 desired frequency and polarization characteristics.

A typical antenna feeder for the generation of different circular polarization in two frequency bands is formed by the following components.

10 • Orthogonal mode transducer (OMT, Orthomode Transducer).

•

Multimode waveguide.

•

Single phase polarizer, with:

15 a) Lineat double polarization modal transition

b) 90 ° double band phase shifter

20 This architecture is classic and widely used in the communications industry. Each of the constituent elements of this feeder is well known and detailed descriptions can be found in patent documents US6473053-B1, US422841 O-A and in the bibliographic references indicated below.

25 The main drawbacks of current antenna feeder systems can be summarized as:

Use of waveguide with double plane of symmetry or symmetry with respect to 90 ° rotation between the orthogonal mode transducer and the single phase polarizer. This condition imposes a strict online arrangement of the feeder elements

No possibility of modification.

The axial length of the feeder is large, which causes severe difficulties in positioning the feeder in many situations and in particular in satellite systems.

The axial length of the feeder directly influences the dissipation losses of the device. At greater length, greater losses, this being a clear drawback of systems based on current architectures and that could be remedied with architectures such as those of the present invention that resulted in shorter signal guidance lengths.

Deterioration of the electrical characteristics when joining the various elements that constitute the complete feeder. Specifically, the axial relationship and isolation between transmitter and receiver, parameters of great importance in communications applications.

The separation between bands and the bandwidth of each band is intrinsically limited, with minimal improvement options. It must be remembered that new communications systems require greater bandwidth and greater separation.

Difficulty of design and scalability when you want to improve the benefits obtained. In particular, even forcing the design process to the fullest (which is hardly approachable by many companies in the sector), high axial and isolation ratios cannot be satisfied simultaneously.

The object of the present invention is a new concept of antenna feeder that resolves the previously described limitations of current systems, in addition to introducing new electrical and mechanical performance.

Bibliographic references

[11 J. M. Rebollar, el. to the. "A dual Irequency OMT in the Ku band lar TT&C applications", in IEEE Antennas and Propagation Society International Symposium, Jun. 1998.

(2) J. A. Ruiz-Cruz, et. Al. "Optimal configurations for integrated antenna feeders with linear dual-polarization and multiple frequency bands," IET Microwaves, Antennas Propagation, Jun. 2011.

(3] U. Rosenberg, the. Al. "Power splitting transition tor circularly polarized feed networks", IEEE Microwave and Guided Wave Letters, Aug. 2000

[4] G. A. E. Crane et. to the. "Corrugated waveguide polarizers tor high performance feed 5 systems," Antennas and Propagation Society International Symposium, Jun 1980.

(5) J. Uher, J. Bornemann, and U. Rosenberg, Waveguide components for antenna leed systems: Theory and CAD. Arteeh house Norwood, MA, 1993.

10 (6] J. M. Rebollar, J. Esteban, "CAD of corrugated circular-rectangular waveguide polarizers", Eighth International Conference on Antennas and Propagation, 1993, pp. 845-848 vol.2.

DESCRIPTION OF THE INVENTION The object of the present invention is a double-band and circular polarization feeder based on the use of a diplexer and a two-phase polarizer that generates right circular polarization in the first band and left in the second band (C1 + and Cd , or vice versa (Cr and C2 +), which allows to significantly improve the

20 electrical characteristics of the feeders currently used, and also eliminates the mechanical restrictions of the current ones.

The dual frequency band antenna feeder with different circular polarization in each band object of the present invention comprises: a diplexer configured to combine two input signals in different frequency bands and with the same linear polarization; -a single-mode transmission medium responsible for transmitting the combined signal from the diplexer; -a two-phase polarizer configured to receive the combined signal from

30 of the single-mode transmission medium and generating at the output a right-hand circular polarization in one of the frequency bands and to the left in the other frequency band, said two-phase polarizer comprising:

• a simple linear polarization modal transition responsible for dividing

the linear input polarization in two orthogonal linear polarizations 35 on the same waveguide, and

• a two-phase phase shifter in charge of introducing a phase difference between the two orthogonal linear polarizations of substantially +900 and 90 ° in each of the frequency bands.

In the antenna feeder of the present invention the diplexer and the biphase polarizer are connected by flexible waveguide, so they do not need to be aligned on the axial axis of the feeder.

The two-phase phase shifter can be formed by a combination of section guides

10 circular, square, rectangular, ridge or elliptical alternated. Thus, for example, it may consist of a combination of alternating square and rectangular guides, alternating rectangular and circular guides, or any other possible combination.

The present invention has a direct and immediate application in the industry of

15 satellite communications, both on ground equipment and on satellite ships. It also presents the significant advantages already described, specifically, improvement of electrical performance and versatility of mechanical interconnection of the components, compared to the alternative currently used in the industry.

BRIEF DESCRIPTION OF THE FIGURES Next, a series of drawings that help to better understand the invention and that expressly relate to an embodiment of said invention which is presented as a non-limiting example thereof is described very briefly.

25 Figure 1 shows a block diagram of the typical antenna feeder according to the state of the art.

Figure 2 represents, according to the state of the art, a typical phase difference diagram of a double frequency band phase shifter.

Figure 3 shows, according to the state of the art, a 3D representation of a typical antenna feeder with OMT plus single phase polarizer.

Figure 4 represents a block diagram of the antenna feeder of the present invention.

Figure 5 shows a phase difference diagram of a two phase phase shifter.

Figures 6A, 68 and 6e show a 3D representation of a preferred scheme 5 with a diplexer based on low pass and high pass filters in rectangular guide and a two phase + 90 ° 1_90 ° polarizer in square and rectangular guide.

Figures 7 A and 7B show a 3D representation of another possible embodiment of antenna feeder with a diplexer based on band pass filters with circular cavities 10 and a two-phase + 90 ° / _90 ° polarizer in circular and rectangular guide.

Figures SA, 88, BG, 8D and BE show a 3D representation of another possible embodiment of antenna feeder with a diplexer based on low pass and high pass filters in rectangular guide and a biphase + 90 ° / _90 ° polarizer in circular guide Y

15 the optics.

DESCRIPTION OF A PREFERRED EMBODIMENT Figure 1 shows a block diagram of a typical antenna feeder, according to the state of the art, for the generation of different circular polarization in

20 two frequency bands. This feeder consists of the following components:

• Orthogonal mode transducer 100, or orthodontic transducer. It allows to separate into two different physical ports, port of the first band 104 Y

25 port of the second band 106, each of the orthogonal linear polarizations (L1, L2) of the common port 102 of the transducer. In this classical architecture for this type of problem, the orthogonal linear polarizations (L1, L2) go in different frequency bands.

30 • Multimode waveguide 108. This waveguide propagates the two orthogonal linear polarizations (L1, L2) between the orthogonal mode transducer 100 and the single phase polarizer 110.

Typically multimode waveguide 108 has two planes of symmetry in its cross section to control the generation of higher order modes and

the isolation of orthogonal linear polarizations, and usually has symmetry with respect to a 90 ° rotation on the axial axis of the feeder 116 that connects with the antenna 120 (typically of horn), connection axis with the single phase polarizer 110 and the antenna 120. In addition, the guide must have a minimum length to avoid the interaction of higher modes between the orthogonal mode transducer 100 and the single phase polarizer 110, and it cannot be bent / curved so as not to generate higher modes in the waveguide, which imposes large mechanical restrictions on the antenna feeder. The object of the present invention will avoid all these restrictions.

• Single phase polarizer 110. This element generates a circular polarization at the output, right in the first band and left in the second (C1 + and C2-)

or vice versa (Cr and Cz +), from two linear orthogonal input polarizations operating both in the low band and in the high band. This element is in turn composed of a modal transition of linear double polarization 112 and a phase-phase phase shifter 114.

The modal transition of linear double polarization 112 is the necessary interface between the orthogonal mode transducer 100 and the single phase phase shifter 114. This element is responsible for adapting the linear orthogonal linear polarizations for the correct excitation of the single phase phase shifting element.

The single phase phase shifter 114 double band of 90 ° is the element responsible for producing the 90 ° phase difference between the two linear orthogonal polarizations of equal amplitude from the modal transition of linear double polarization 112. The single phase phase shifter 114 must produce the 90 ° phase difference in the double frequency band of the feeder.

An example of the typical phase curve of a single phase phase shifter 114 of 90 ° and double frequency band is shown in Figure 2, where the horizontal axis is the frequency axis, the vertical axis shows the differential offset between the two linear polarizations Orthogonal and shaded regions represent the operating frequency bands of single phase phase shifter 114. As a consequence, the feeder output signal has circular polarization of opposite signs in each band (C1 + and C ..-). This signal directly feeds the antenna 120, typically a horn with revolution symmetry. This single phase phase shifter 114 of 90 ° provides a 90 ° offset with the same sign in both the first and second bands, which could be called a single phase polarizer. In the present invention, without

5 However, a biphase polarizer is used.

The architecture represented in Figure 1 is well known and widely used in the communications industry. Figure 3 shows a 3D view of a typical antenna feeder based on this architecture: the mode transducer

10 orthogonal 100, the modal transition of linear double polarization 112, the phase-phase offset element 114 between two orthogonal modes and a transition to the antenna input guide 120, typically a horn with circular guide input.

A block diagram of the antenna feeder object 15 of the present invention is shown in Figure 4. The constituent elements are:

• A diplexer 200, capable of combining in a common port 202 of the diplexer two signals from different inputs (port of the first band 204 and port of the second band 206) and at different frequencies with the

20 same linear polarization. The diplexer 200 in turn is typically constituted by two filters and a union of waveguides. The filters can be either bandpass filters, either a high pass filter and another low pass filter, or any combination that provides the desired diplexing. In any case, the diplexer configuration does not change the new concept.

25 antenna feeder. These types of devices are well known and often used in the communications sector, with a wide range of commercial suppliers.

• Single mode transmission medium 208 in which the two have been combined

30 frequency bands (first band and second band). It is an arbitrary waveguide (it could not have two planes of symmetry or have symmetry with respect to 90 ° rotation) and through which a single mode is propagated (L1 and L2 have the same linear polarization, but they go in different frequency bands). Here you can include flexible guides or elbows and turns

35 arbitrary. This situation makes an essential difference compared to

regular feeders. This item or items can be found.

commercially

• Two-phase 210 polarizer: This element generates a circular polarization to the

5 output (right in the first band and left in the second, C1 + and C2-, or vice versa, C1- and C2 +) from a linear input polarization. This element is in turn composed of a simple linear polarization modal transition 212 and a biphase phase shifter 214.

10 The simple linear polarization modal transition 212 has any type of single-mode waveguide at the input and a waveguide that supports two linear polarizations orthogonal to the output. This element is the necessary interface between diplexer 200 and phase shifter 214. This element is responsible for adapting the linear input polarization to excite

15 correctly the phase shifter 214.

The phase shifter 214 is the element that introduces a difference of

phase between orthogonal polarizations of 900 and _900 in the first and

second frequency band, respectively, see ref. [6].

As shown in the figure, unlike the typical antenna feeder, there is no axial axis of the feeder. In addition, L1 and L2 are the same polarization in the same mode, operating in different bands.

25 Figure 5 illustrates the phase curve of a two-phase phase shifter. The frequency scale is represented on the horizontal axis, while the phase difference between two linear and orthogonal polarizations is shown on the vertical axis. The shaded regions represent the operating frequency bands of the 214 phase shifter. This device can be implemented and / or industrialized using techniques

30 machining well known and widely used in the industry.

Finally, at the output of the feeder, a signal with the desired circular polarization is generated in each frequency band. Said signal feeds the antenna 120, which will typically be a smooth or corrugated horn with revolution symmetry.

Different possible embodiments that serve to show the characteristics and versatility of the present invention are described below.

Figures 6A, 68 and 6e show a possible embodiment of the antenna feeder of the present invention. Figure 6A shows the 3D representation of the waveguides that form the device, whose coating is metallic as shown in Figure 6B. Figure 6e shows the cut of the metal envelope of Figure 68 in a plane perpendicular to the rectangular waveguides of the feeder.

The feeder starts with a diplexer 200 based on low pass and high pass filters with routing elbows. Said diplexer 200 is formed by a low pass filter 226 using a rectangular corrugated waveguide in the E-plane and by a high pass filter 228 formed by a cut waveguide in the lower frequency band. The two filters are multiplexed using a guide junction 230 composed of various steps on the narrow face of the rectangular cross section. At the entrance of each of the filters both transformers and elbows 224 have been used to pass to the desired waveguides, as well as placing the interfaces in the required relative positions. Both the number of corrugations in the low pass filter 226 and the length of the cutting guide in the high pass filter 228 will determine the insulation between frequency bands. This value can be increased by simply increasing the order of the filters. In addition, it is completely fixed by the design parameters of the diplexer 200 and is completely independent of the rest of the feeder elements.

At the output of the diplexer 200 is a single mode transmission means 208, implemented in the form of a rectangular waveguide that only propagates a linear polarization mode. On this guide, the two signals of each of the bands from the rectangular input guides (220, 222) to the diplexer are propagated, specifically the high and low band signal come from guides 222 and 220, respectively.

Next to the single-mode rectangular guide 208 is the two-phase polarizer 210, formed by a simple linear polarization modal transition 212 from the two orthogonal modes to the input mode, consisting of several centered steps that pass from a rectangular section waveguide to square section Besides, the

rectangular guide 232 and square guide 234 of the simple linear polarization modal transition 212 have a 45 ° rotation on their relative position. The square section guide 234 in turn constitutes the first element of the two-phase phase shifter 214 and supports two modes with orthogonal linear polarizations. These two modes are excited with the same amplitude and in the two frequency bands from the rectangular input waveguide 208 to the simple linear polarization modal transition.

212.

Biphase phase shifter 214 is composed of a periodic guide section 236,

10 formed in turn by several sections of alternating high-width square and rectangular guides. Said periodic guide 236 supports two orthogonal linear polarizations with different propagation constants. The difference between the two propagation constants is of the opposite sign in each of the frequency bands. The value of propagation constants can be obtained from a

15 rigorous analysis of the scatter diagram of the periodic guide 236. This analysis also provides the initial dimensions and the number of sections necessary to obtain the phase shift of 900 and _900 in the first and second frequency band, as shown in Figure 5. The number of sections and dimensions of the periodic guide 236 depend on the bandwidth and the separation between bands of

20 frequency, as well as, of the required axial relationship specifications. Once the initial dimensions of the biphase phase shifter 214 are obtained, it is necessary to modify some of the first sections of the periodic guide 236 in order to adapt to the input and output interfaces.

25 Since the input signals to the biphase polarizer 210 in each frequency band have the same linear polarization, the final result at the output of the polarizer is that of signals with different circular polarizations in each frequency band.

30 In this case, the two-phase polarizer 210 also includes a transformer 238 of the square output guide of the two-phase phase shifter 214 with a circular guide, whose only objective is to adapt between guides of different cross-section and in this way adapt the signal to the interface of horn antenna input, usually circular section.

The external shape of the metal housing in Figure 68 is independent of the electrical behavior of the feeder and in general will depend on the mechanical manufacturing process used. Although the implementation can be done using various manufacturing processes well known in the industry, such as milling, EDM or electroforming. A section according to a plane perpendicular to the rectangular inlet guides (220, 222) is shown in Figure 6e. This figure shows how the interior of the feeder does not contain additional elements such as sheets, posts or pins, which also contributes to improving its electrical characteristics against manufacturing tolerances, as well as improving maximum power

10 that can handle and decrease the generation of Passive Intermodulation Products (PIMP 's).

Figures 7A and 7B show a second possible embodiment of antenna feeder. The first element is a diplexer 200 based on band pass filters with 15 circular cavities, in a configuration known as two-channel manifold, high band 250 and low band 252, and with a short circuit 256 at the end that allows to improve the multiplexing characteristics. Each of the channel filters (250, 252) is dual mode and four order. The resonant cavities 254 are formed by guides of elliptical section of low eccentricity which allow the two resonant modes to be properly excited. Diplexer 200 and biphase polarizer 210 are connected by a rectangular guide 208 that supports a single linear polarization in both frequency bands. The length of this guide can in turn adopt very low values since the cutoff frequency of higher modes is well above the operating bands and therefore they are quickly attenuated without degrading the electrical characteristics of the feeder. The next element of the feeder is the two-phase polarizer 210 formed by a simple linear polarization modal transition 212 constituted by rectangular, elliptical and circular guide sections, and by a two-phase phase shifter 214 in the form of a periodic guide 260. The two-phase phase shifter 214 is formed by guides of rectangular section of great high-width and circular ratio 30 alternated, which provide a total phase difference close to 900 and _900 in the first and second frequency band, respectively. The two-phase phase shifter 214 allows to generate at the output of the feeder 264, through a transformer 262, the circular polarization required in each band and with a low level of axial relation. In addition, the polarization characteristics are exclusively determined by the

two-phase polarizer 210 And they are not affected by the final interconnection of two-phase polarizer 210 and the diplexer 200.

Another additional embodiment is that shown in Figures SA, 8B, SE, 80, SE, 8F Y

5 aG, where the antenna feeder is formed by a diplexer 200 composed of high pass filters 270 and low pass 272 similar to that shown in Figure 6A, a single mode transmission means 208 implemented in the form of a single mode routing waveguide that can have arbitrary elbows and turns or be flexible, and a two-phase 210 polarizer. In Figures BA and 88 the single-mode waveguide of

The routing 208 is represented in the form of a double 1800 elbow to route the signal, but it can be replaced by a flexible guide (see Figures Be at 8G). In this embodiment, the great interconnection versatility of the different elements of the antenna feeder is shown, including the possibility of the flexible guide that allows the diplexer 200 and the biphase polarizer 210 to be placed in relative positions

15 arbitrary. In addition all this without degrading the electrical characteristics of the feeder, specifically, insulation and axial relationship. In this case, the two-phase phase shifter 214 consists of alternating circular and elliptical cross-section guides.

20 It is important to note that the examples shown in the preferred embodiments are only three of the many possible examples. Thus, for example, diplexers 200 and biphase polarizers 210 could be proposed with a structure or constitution different from those shown, provided they perform the same function. Likewise, the different diplexers and biphase polarizers shown in the preferred embodiments

25 of Figures 6, 7 and 8 can be combined with each other resulting in new antenna feeder configurations, although all of them are within the general scheme of Figure 4 proposed in the present invention. Although the present invention has been described with some preferred embodiments, numerous variations and modifications are possible and apparent to those skilled in the art.

30 matter. All of them are within the scope of the present invention and obey the antenna feeder scheme proposed herein.

Claims (2)

1. Dual frequency band antenna feeder with different circular polarization in each band, characterized in that it comprises: 5-a diplexer (200) configured to combine two input signals (L ,. L2) in different frequency bands and with the same linear polarization; -a single mode transmission medium (208) responsible for transmitting the combined signal (L "L) from the diplexer (200); -a two-phase polarizer (210) configured to receive the combined signal (L1, 10 L2) coming from the single-mode transmission medium (208) and generating at the output a right-hand circular polarization in one of the frequency bands and to the left in the other frequency band, said two-phase polarizer (210) comprising: • a simple linear polarization modal transition (212) responsible for divide the linear input polarization into two orthogonal linear polarizations 15 on the same waveguide, and • a two-phase phase shifter (214) responsible for introducing a difference of phase between the two linear orthogonal polarizations of +900 and _900 in each of the frequency bands. Antenna feeder according to any one of the preceding claims, characterized in that the diplexer (200) and the biphase polarizer (210) are connected by flexible waveguide. 3. Antenna feeder according to any of the preceding claims, 25 characterized in that the two-phase phase shifter (214) is formed by a combination of alternating circular, square, rectangular, ridge or elliptical section guides.