Antenna arrangement for circularly polarized satellite radio signals on a vehicle

Abstract

An antenna arrangement for the reception of circularly polarized satellite radio signals having a free space wavelength and a frequency f comprises at least one circularly polarized satellite reception antenna positioned above an electrically conductive base surface whose outline is inscribed by a circle K about its phase center PZ having a relative antenna radius ra/<0.15. A director is present that comprises a horizontal electrical conductor that has two conductor ends and that is guided over a director length Ld at a director height hd above the conductive base surface. The horizontal electrical conductor is angled at its two conductor ends and extends from there as vertical conductor in each case toward the conductive base surface.

Claims

1. An antenna arrangement for the reception of circularly polarized satellite radio signals having a free space wavelength and a frequency f, the antenna arrangement comprising at least one circularly polarized satellite reception antenna positioned above an electrically conductive base surface, with a. relative antenna height ha/<0.15 whose outline is inscribed by a circle K about its phase center PZ having a relative antenna radius ra/<0.15, the antenna arrangement further comprising the following features: a director that comprises a horizontal electrical conductor that has two conductor ends and that is guided over a director length Ld at a director height hd above the conductive base surface, and indeed at least approximated to a jacket surface Mz of a cylinder oriented perpendicular to the conductive base surface and having a cylinder radius rz and a central axis Z through the phase center PZ of the satellite reception antenna, wherein the horizontal electrical conductor is angled at its two conductor ends and extends from there as vertical conductor in each case toward the conductive base surface and is electrically conductively connected thereto; the director being adapted by designing the director length Ld, the director height hd, and the vertical conductor in a manner such that. its natural resonant frequency is set in frequency proximity to the frequency f.

2. The antenna arrangement in accordance with claim 1, wherein said at least one circularly polarized satellite reception antenna is for satellite navigation.

3. The antenna arrangement m accordance with claim 1, wherein the director length is selected in the range 0.2<Ld/<0.45; the relative director height is selected in the range 0.03<hd/<0.15; and the cylinder radius is selected in the range 0.15<rz/<0.5.

4. The antenna arrangement in accordance with claim 1, wherein the horizontal electrical conductor is designed in a straight line.

5. The antenna arrangement in accordance with claim 4 wherein the two vertical conductors are arranged in the region of the jacket surface Mz.

6. The antenna arrangement in accordance with claim 1, wherein the director length is selected as shorter than approximately 90% of half the free space wavelength and the cylinder radius rz is selected as approximately 20% of the free space wavelength .

7. The antenna arrangement in accordance with claim 1, wherein, in order to reduce the cross-polarization at small angles of elevation over the total azimuth angle range, at least three directors are arranged azimuthally uniformly about the satellite reception antenna.

8. The antenna arrangement in accordance with claim 7, wherein the cylinder radius rz is selected as not larger than half a free space wavelength.

9. The antenna arrangement in accordance with claim 1, wherein, in order to compensate an impairment of the azimuthal directional pattern and of the cross-polarization spacing, caused by an azimuthally sectorally irregular environment, the at least one director is positioned at a spacing of no more than half a free space frequency wavelength remote from the phase center PZ for a direct irregular change of the horizontal directionality.

10. The antenna arrangement in accordance with claim 9, wherein the azimuthally sectorally irregular environment comprises angles of elevation around 30 .

11. The antenna arrangement in accordance with claim 1, wherein an electrically conductive ground plate is present as a mechanical carrier of the satellite reception antenna and of the at least one director on which ground points are formed for an electrically active connection of the director.

12. The antenna arrangement in accordance with claim 11, wherein the ground plate is designed at least in part from an electrically conductive sheet metal surface; and wherein the director is cut out of this sheet metal surface except for a connection web as a ground point and is bent out of the sheet metal surface by a bend angle.

13. The antenna arrangement in accordance with claim 1, wherein the director is configured in wire form.

14. The antenna arrangement in accordance with claim 1, wherein for the azimuthally sectoral raising of the antenna gain for small angles of elevation at least two directors are arranged closely adjacent to one another along the cylinder jacket Mz; and wherein the mutually adjacent conductor ends of the horizontal electrical conductors are capacitively coupled to one another.

15. The antenna arrangement in accordance with claim 1, wherein for the azimuthally independent raising of the antenna gain and for a further improvement of the cross-polarization spacing, the satellite reception antenna is completely surrounded in an azimuthally symmetrical form by mutually adjacent directors that are capacitively coupled to one another with respect to their conductor ends.

16. The antenna arrangement in accordance with claim 1, wherein a plurality of directors are provided that comprise electrically conductive sheet metal and are respectively shaped and bent angled form at the conductor ends of the elongated electrical conductor in a manner such that. a respective sheet metal lug is formed, with a capacitive coupling being effected by lug surfaces of the respective mutually adjacent directors in parallel with one another.

17. The antenna arrangement in accordance with claim 16, wherein the directors are arranged in ring form are combined in a contiguous manner to form a mechanically coherent ring of sheet metal, with the connection of the directors being given by connection webs that are placed on a ground plate and are connected to it electrically conductively at ground points.

18. The antenna arrangement in accordance with claim 1, wherein the satellite reception antenna is a circularly polarized loop antenna having a relative height ha/0.1 and its vertical projection is inscribed by a circle having the relative antenna radius ra/0.13 nm about its phase center PZ; and the director length Ld/0.3 is selected; the director height hd/0.07 is selected; and the cylinder radius rz/0.2 is selected.

19. The antenna arrangement in accordance with claim 1, wherein the satellite reception antenna is formed as a circularly polarized patch antenna.

Description

(1) The invention will be explained in more detail in the following with reference to embodiments. The associated Figures show in detail:

(2) FIG. 1A:

(3) a spatial representation of an antenna arrangement 1 in accordance with the invention having an electrically small satellite reception antenna 2 having a phase center PZ at the center Z on the outer skin of a vehicle 7 as an electrically conductive base surface 3, azimuthally surrounded by directors 4 in accordance with the invention. They respectively comprise by way of example a straight-line horizontal electrical conductor 5 of the length Ld that is led below a height hd and that continues at its two ends in each case with a vertical conductor 6 leading toward the conductive base surface 3 and whose lower end is conductively connected to the conductive base surface 3 via a ground point 8. The horizontal conductors 5 are led in a straight line approximately along the jacket surface Mz of a perpendicularly oriented cylinder having a cylinder radius rz. The electrically small satellite reception antenna 2 is inscribed by a construction space of a height ha and by the circle K having the antenna radius ra about its center Z;

(4) FIG. 1B

(5) a plan view of an antenna arrangement 1 in accordance with the invention as in FIG. 1A for representing the arrangement of the directors 4 curved in a plan view having a respective horizontal conductor 5 extending in a curved manner along the jacket surface Mz below the height hd as a segment of a circular level curve of the jacket surface Mz of the perpendicularly oriented cylinder having the cylinder radius rz;

(6) FIG. 2:

(7) a plan view of an antenna arrangement 1 in accordance with the invention as in FIG. 1A for representing the arrangement of the directors 4 having a respective horizontal conductor 5 extending in a straight line below the height hd substantially as a secant of a circular level curve of the jacket surface Mz of the perpendicularly oriented cylinder having the cylinder radius rz;

(8) FIGS. 3A and 3B:

(9) a comparison of the vertical directional pattern in FIG. 3A of a satellite reception antenna 2 and of the vertical directional pattern in FIG. 3B of the same satellite reception antenna 2 in an antenna arrangement 1 in accordance with the invention in each case for the desired circular polarization direction RHCP and the cross-polarization direction LHCP in each case with a marking of the direction of incidence at the angle of elevation of 20 (zenith angle 70) and the angle of elevation of 5 (zenith angle 85).

(10) There results with a band center in the band L1 (f=1.565 Mz):

(11) antenna gain at angle of elevation 20, RCHP case a) 0 dB; case b) 2 dB

(12) antenna gain at angle of elevation 20; LCHP case a) 8 dB, case b) 1.5 dB

(13) antenna gain at angle of elevation 5; RCHP case a) 4 dB; case b) 0 dB

(14) antenna gain at angle of elevation 5; LCHP case a) 5.2 dB; case b) 0.5 dB

(15) Result: the RHCP antenna gain of the antenna arrangement 1 in accordance with the invention exceeds the antenna gain of the single antenna by 4 dB at an angle of elevation of 5 and by approximately 2 dB at an angle of elevation of 20;

(16) FIGS. 4A and 4B:

(17) a comparison of the azimuthal diagrams in correlation with the vertical directional patterns in FIGS. 3A and 3B at the frequency band center of L1 (f=1.565 MHz). Angle of elevation=20, and specifically, FIG. 4A, a satellite reception antenna 2 and FIG. 4B, an antenna arrangement 1 in accordance with the invention. Result: a considerable increase by approximately 2 dB is achieved using the antenna arrangement 1 in accordance with the invention at an angle of elevation of 20;

(18) FIGS. 5A and 5B:

(19) a comparison of the vertical directional patterns as in FIGS. 3A and 3B, but at band center in the band L2 (f=1.225 MHz):

(20) FIG. 5A, a satellite reception antenna 2 and FIG. 5B, an antenna arrangement 1 in accordance with the invention.

(21) Result: the RHCP antenna gain of the antenna arrangement 1 in accordance with the invention exceeds the antenna gain of the single antenna by 1.5 dB at an angle of elevation of 5 and by approximately 0.7 dB at an angle of elevation of 20;

(22) FIGS. 6A and 6B:

(23) a comparison of the azimuthal patterns as in FIGS. 5A and 5B, at band center in the band L2 (f=1.225 MHz), and specifically FIG. 6A, a satellite reception antenna 2 and FIG. 6B, an antenna arrangement 1 in accordance with the invention. Result: a considerable increase by approximately 0.7 dB is achieved using the antenna arrangement 1 in accordance with the invention at an angle of elevation of 20;

(24) FIGS. 7A and 7B:

(25) a vertical directional patterns of the antenna arrangement 1 in accordance with the invention at the frequency band boundaries of the frequency band L2, with FIG. 7A, at the lower frequency band boundary (f=1200; MHz);

(26) and FIG. 7B, at the upper frequency band boundary (f=1250 MHz) of the navigation frequency band L2;

(27) FIG. 8:

(28) a spatial representation of an antenna arrangement 1 in accordance with the invention as in FIG. 1A, but with directors 4 comprising electrically conductive sheet metal. The ground plate 3a lying on the outer skin of the vehicle as a mechanical carrier of the satellite reception antenna 2 and of the directors 4 is shown as a sheet metal surface 3a in the example. The directors 4 are cut out and are bent out of the sheet metal surface 3a by the bend angle 10 from this sheet metal surface except for a connection web 26 forming the ground connection as a center of rotationthat also acts as a ground point 8;

(29) FIG. 9:

(30) a representation of the construction spaces Br1-Br7 preferred from a technical vehicle aspect for satellite reception antennas 2 on the electrically conductive outer skin of a motor vehicle 7. The location at the center of the vehicle roof 16 marked as Br0 is to be preferred from a technical antenna aspect but can generally be precluded from a technical vehicle aspect. The construction spaces Br1-Br6 accepted from a technical vehicle aspect are all located in the marginal region of the vehicle roof 17 with the known disadvantageous influences of the lateral rood edge 17, of the front roof edge 18a, and of the rear roof edge 18 with respect to the radiation pattern of satellite reception antennas 2 having omnidirectional characteristics. Construction spaces on the rear cover 19, for example Br7, are also less suitable due to the effect of the upper vehicle structure shading the radiation;

(31) FIG. 10:

(32) an attachment of the antenna arrangement 1 in accordance with the invention having the indicated dimensions for GNSS applications, for example at construction space Br2 in FIG. 9. The effect of the rear roof edge 18 restricting the omnidirectionality and of the curvature of the vehicle roof 16 with the aid of the directors 4 extending substantially in parallel with the rear roof edge 18 is substantially alleviated in accordance with the invention by raising the antenna gain in the direction of travel for small angles of elevation of radiation. A satellite reception antenna 23 laterally attached to the construction space Br6, for example, for the reception of satellite radio signals at the frequency of approximately 2.3 GHz is in a very advantageous manner practically not impaired with respect to its radiation properties by the antenna arrangement 1 in accordance with the invention The arrow facing to the right marks the direction of travel;

(33) FIG. 11:

(34) an attachment of the satellite reception antenna 2 to the construction space Br2 and of the reception antenna 23 to the construction space Br6 as in FIG. 10, but with directors 4 arranged all around azimuthally for raising the antenna gain for omnidirectionality at small angles of elevation. The radiation properties of the satellite reception antennas 23 are practically not impaired by the presence of the antenna arrangement in accordance with the invention with a suitable choice of the director height hd and of the bend angle 10;

(35) FIG. 12:

(36) an antenna arrangement 1 in accordance with the invention having directors 4 that are arranged tightly adjacent to one anotheras segments along the cylinder jacketsaid directors 4 being arranged in ring form around the satellite reception antenna 2. The mutually adjacent conductor ends 11 of the elongated horizontal conductors 5 are capacitively coupled to one another. The directors 4 are, as in FIG. 8, cut out as strips 9 of sheet metal from the sheet metal surface of the ground plate 3a and are bent by the bend angle 10 of 90. The conductor ends 11 of the elongated electrical conductors 5 are shaped in angular form and are bent radially outwardly with respect to the center Z in a manner such that a respective sheet metal lug 12 is formed and the capacitive coupling is effected by the lug surfaces standing in parallel with one another of the respective mutually adjacent directors 4;

(37) FIG. 13:

(38) an antenna arrangement 1 in accordance with the invention as in FIG. 12, but with the difference that, to reduce the space requirements, the sheet metal lugs 12 are radially inwardly bentwith respect to the center Zto form the capacitive coupling;

(39) FIGS. 14A and 14B:

(40) FIG. 14A, a design of the directors 4 surrounding the satellite reception antenna 2, as in FIG. 13, but as a sheet metal ring 25 cut and shaped coherently from a metal sheet. The connection webs 26 at the lower ends of the vertical conductors 6 created in this process form the ground points 8 by placing the sheet metal ring 25 on the ground plate 3a and with their electrical connection; the vertical arrows describe the direction in which the sheet metal ring 25 is placed onto the ground plate 3a. The satellite antenna 2 is not shown in this Figure;

(41) FIG. 14B, a representation of the antenna arrangement 1 in accordance with the invention with a sheet metal ring 25 placed on the ground plate 3a and electrically conductively connected thereto at the ground points 8 as under a) with the satellite reception antenna 2 at the center, for example at the construction space Br2. The further satellite reception antenna 23 is, as in FIGS. 10 and 11, attached to the construction space 6.

(42) The invention starts from a circularly polarized satellite reception antenna 2 which is located above an electrically conductive base surface 3 and whose relative antenna height ha/ with respect to the free space wavelength is smaller than 0.15. The problematic property is associated with this extremely small height ha of the antenna that its radiation gain drops very fast toward smaller angles of elevation. This is likewise associated with an amplified reduction in the cross-polarization spacing. This effect can be alleviated so much by the presence of the directors 4 that a satellite reception antenna 2 having the predefined construction volume on the electrically conductive outer skin of a vehicle 7 can also be used for qualified location determination with the aid of the satellite navigation. In this respect, satellite reception signals have to be evaluated for the navigation that are incident at the small angle of elevation of 20 down to an angle of elevation of 5. The extremely strong drop of the antenna gain at such small angles of elevation for the desired polarization direction of such a small satellite reception antenna 2 above a conductive base surface 3 is based on the weakness of the horizontal component of its electrical radiation field. This weakness is alleviated in accordance with the invention by the use of the directors 4 about the satellite reception antenna 2 and the raising of the antenna gain for small angles of elevation succeeds.

(43) The directors form, with respect to the base surface, an arch or a (U-shaped) gate (cf. FIG. 1A) that comprises the vertical conductor 5 and the two vertical conductors 6.

(44) A plausibility observation can explain the mode of operation of the directors 4 in an approximated manner with reference to the spatial representation of the antenna arrangement 1 in accordance with the invention in FIG. 1A and its plan view in FIGS. 1B and 2. In this respect, the azimuthally almost complete surrounding of the satellite reception antenna 2 by directors 4 results in the desired raising of the antenna gain with omnidirectionality. The satellite reception antenna 2 configured for circular polarization excites the electrical conductors of the directors 4 with the currents flowing on it. The conductor ends 11 of the horizontal electrical conductor 5 are each connected via the vertical conductors 6 at a ground point 8 to the conductive base surface 3. Secondary currents are thus formed on the electrically excited director 4 and in particular also on the horizontal electrical conductor 5 that generate a radiation field on a suitable choice of the director length in the range 0.2<Ld/<0.45, of the director height in the range 0.03<hd/<0.15, and of the cylinder radius in the range 0.15<rz/<0.5 that determines the spacing of the directors 4 from the center Z of the antenna arrangement. Said radiation field is superposed on the radiation field of the satellite reception antenna 2 in a manner such that the desired raising of the antenna gain is in particular adopted for small angles of elevation. A director length Ld that is shorter than half a free space wavelength is particularly effective, that is the natural resonant frequency of the director 4 is selected a little smaller than the satellite reception frequency f. The difference, that is selected as small, of the satellite frequency f from the natural resonant frequency of the director 4 establishes the increase associated therewith of the currents on the director 4 and, in combination with the suitably set cylinder radius rz, the constructive superposition of the director radiation field resulting therefrom with respect to the phasing with the radiation field of the satellite reception antenna 2 in the sense of the object to be satisfied. The horizontal electrically conductive conductors 5 above the electrically conductive base surface 3 below the director height hd each form an electrical line ended at both conductor ends 11 via the vertical conductors 6 with the wave resistance ZL whose amount is given by the conductor width 26 or by the width 21 of the sheet metal strip and by the conductor spacing 28 of the horizontal electrical conductor 5 from the conductive base surface 3. On a design of a director 4, for example, from wire, the wave resistance ZL can be varied in wide limits by setting the ongoing capacitance and the ongoing inductance of the horizontal electrical conductor 5, e.g. with the aid of a meandering shifting. A fine adjustment of the spacing rz of the director 4 from the center Z and the selection of a suitable wave resistance ZL as well as the natural inductance of the vertical conductors 6 enables the optimization of the radiation pattern of the antenna arrangement 1 in the sense of the object of the invention.

(45) Measurement results in the form of vertical and horizontal sections of radiation patterns of antenna arrangements 1 in accordance with the invention are shown by way of example in FIGS. 3A to 7B and are compared with corresponding measurement results of a satellite antenna 2 above a conductive base surface 3 without directors 4 in accordance with the invention. The achieved improvements in the region of small angles of elevation are indicated in detail in connection with the above descriptions of the Figures.

(46) The manufacturing costs and the simple implementation capability are essential for the use in automotive construction. In an advantageous embodiment of the invention, as shown in FIG. 8, the ground plate 3a lying on the outer skin of the vehicle 7 is designed as a mechanical carrier of the satellite reception antenna 2 and of the directors 4 and is produced from sheet metal. The possibility results as a special advantage here in accordance with the invention of cutting the directors 4 out of the sheet metal and of bending them out thereof by the bend angle 10. The cutting and bending processes required for this purpose can be carried out extremely inexpensively in mass production with very good reproducibility.

(47) From a technical vehicle aspect, construction spacesBr1-Br6 in FIG. 9in the marginal zones on the vehicle roof are primarily available for the attachment of a satellite reception antenna 2. A significant impairment of the azimuthal directional pattern and of the cross-polarization results as a consequence of the already mentioned azimuthally irregular environment. A shift of the phase center PZ of the antenna arrangement 1 that degrades the navigation result equally results in dependence on the spatial angle of the incident satellite reception signals.

(48) The irregular change of the horizontal directionality can in particular already be counteracted by a targeted director 4 placement at angles of elevation around 20. This measure in accordance with the invention is particularly helpful on the selection of construction spaces Br1, Br2, and Br6 preferred from a technical vehicle aspect on the vehicle roof 16 in which due to the abrupt interruption of the conductive base surface 3 at the rear roof edge 18 at the upper margin of the rear window pane 15 and due to the curvature of the vehicle roof 16 that is frequently present there, the radiation characteristics of a satellite reception antenna 2 are highly impaired as a rule.

(49) As the number of satellite radio services for satellite navigation and satellite radio increases, the construction spaces are placed more closely and the radiation characteristics are impaired by electromagnetic coupling. In the example already described above in FIG. 10, the satellite reception antenna 2 for GNSS is attached in an arrangement in accordance with the invention with two mutually oppositely disposed directors 4 to the construction space Br2 and the satellite reception antenna 23 for the radio reception at approximately 2.3 GHz is attached to the construction space Br6. Both antennas are designed as loop antennas 13 in the example. It is shown very advantageously here that the strict demands on the radiation characteristics of the satellite radio reception antenna 23 are not impaired by the presence of the directors 4 in accordance with the invention. Due to the large spacing between the natural resonant frequencies of the directors 4 and the frequency of the satellite radio, the secondary currents that the satellite radio antenna 23 causes on the directors 4 are sufficiently small that their effect on the radiation characteristics of the satellite radio antenna 23 can be neglected. This effect is pronounced in a manner such that the disruption of the radiation properties of the satellite radio antenna 23 is FIG. 11 is even small when the satellite reception antenna 2 for GNSS is completely surrounded by directors 4.

(50) In a similar manner as in FIG. 11, the satellite reception antenna 2 in FIG. 12 is completely surrounded by directors 4 that, howevermore than in FIG. 11 in a further advantageous embodiment of the inventionare arranged in close order after one another, that is in a close spacing along the cylinder jacket ZM. The mutually adjacent conductor ends 11 of the elongated horizontal electrical conductors 5 are capacitively coupled to one another. A further improvement of the cross-polarization spacing and of the azimuthal independence of the phase center at small angles of elevation is achieved with this coupling. It results from an additional configuration with secondary currents on the horizontal electrical conductors 5 that are adopted from the capacitive bypassing of the voltage differences between the adjacent conductor ends 11 that form via the vertical electrical conductors 6. The phases of the currents on the satellite reception antenna 2 that vary with the azimuthal angle effect the excitation of secondary currents having different phases in the different directors 4. These secondary currents generate different voltages on the inductive effects of the mutually adjacent vertical electrical conductors 6 and the difference of these voltages causes the desired effect of the improvement of the cross-polarization spacing via the capacitive coupling.

(51) As described in connection with FIG. 11, the directors 4 are cut out of the sheet metal-shaped ground plate 3a with the exception of the short connection webs 26 and are bent out of the sheet metal-shaped ground plate 3a along the bend line 24, with the bend angle 10 being selected at 90. To intensify the capacitive coupling, the conductor ends 11 of the elongated electrical conductor 5 are formed areally and in angular form in a manner such that a respective sheet metal lug 12 is formed. The sheet metal lugs 12 are outwardly radially bentwith respect to the center Zin a manner such that the areas between two adjacent sheet metal lugs 12 are aligned substantially in parallel with one another and the increased capacitive coupling is thus achieved. Even though the shown implementation of an antenna arrangement 1 in accordance with the invention apparently appears complicated, it can nevertheless be manufactured extremely inexpensively by stamping and bending techniques in mass production. To reduce the transverse extent of the antenna arrangement 1, the sheet metal lugs 12 shown in FIG. 12 can be radially inwardly bentwith respect to the center Zas can be seen from FIG. 13.

(52) In a further advantageous embodiment of the invention, the directors in FIG. 14A are assembled contiguously in ring form to form a mechanically coherent ring of sheet metal. They are connected to one another via short connection webs 26. Provision is made to place the ring manufactured from sheet metal onto the ground plate 3aas the vertical arrows indicateand to connect the connection webs 26 electrically conductively to the ground points 8 located on the ground surface 3 as can be seen from FIG. 14B.

REFERENCE NUMERAL LIST

(53) 1 antenna arrangement 2 satellite reception antenna 3 electrically conductive base surface 3a ground plate 4 director 5 horizontal electrical conductor 6 vertical conductor 7 outer skin of a vehicle 8 ground points 9 sheet metal strip 10 bend angle 11 conductor ends 12 sheet metal lug 13 loop antenna 14 patch antenna 15 rear window pane 16 vehicle roof 17 lateral roof edge 18 rear roof edge 18a front roof edge 19 rear cover 20 front cover 21 sheet metal strip width 22 section lines 23 further satellite reception antenna 24 bend line 25 sheet metal ring 26 connection webs 27 conductor width 28 conductor spacing free space wavelength ha antenna height PZ phase center ra antenna radius rz cylinder radius Z central axis Ld director length hd director height K circle Mz cylinder jacket Br1-Br7 construction space ZL wave resistance