EP3474374B1 - Antenna system for circular polarised satellite radio signals on a vehicle - Google Patents

Description

The invention relates to an antenna arrangement for receiving circularly polarized satellite radio signals, in particular for satellite radio navigation.

In the case of satellite navigation systems in particular, it is particularly important to be economical both with regard to the transmission power emitted by the satellite and the efficiency of the receiving antenna. Due to polarization rotations on the transmission path, satellite radio signals are usually transmitted with circularly polarized electromagnetic waves and are used for all known satellite navigation systems. Modern navigation systems provide, in particular for global accessibility in connection with high navigation accuracy in mobile navigation, to evaluate the radio signals received from several satellite navigation systems at the same time. Such systems receiving in a network are summarized under the term GNSS (Global Navigation Satellite System) and contain known systems such as GPS, GLONASS, Galileo and Beidou etc. Satellite antennas for navigation on vehicles are usually on the electrically conductive outer skin of the Vehicle body built up. Circularly polarized satellite receiving antennas are used, such as those from the publications DE-A-10 2009 040 910 , DE-A-40 08 505 and DE-A-101 63 793 are known. Antennas which are particularly suitable for installation on vehicles are those which are characterized by a low overall height in connection with low-cost manufacturability. This includes, for example, those from the Pamphlet DE-A-10 2009 040 910 known circular, polygonal or square ring line antenna designed as a resonance structure with a small structural volume, which is particularly required for mobile applications. The antenna has a necessary conductive footprint of relatively small size and is very low with a height of less than one tenth of the free space wavelength. Patch antennas are known according to the prior art as further antennas for satellite navigation on vehicles, but these are less efficient in terms of reception at a low elevation angle. One of the challenges for satellite antennas for GNSS is the requirement for a large frequency bandwidth, which, for example, in GPS is through the frequency band L1 with the center frequency 1575 MHz (required bandwidth approx. 80 MHz) and the frequency band L2 with the center frequency 1227 MHz (required bandwidth approx. 53 MHz) is specified. This requirement is covered, for example, by separate antennas assigned to one of the two frequency bands L1 or L2, or by an antenna comprising both frequency bands. Systems for the simultaneous evaluation of signal contents in the frequency bands L1 and L2 place particularly high demands on the properties of the antennas, in particular due to the limited space available, as is always the case in vehicle construction. The use of separate antennas for the two frequency bands in close proximity to one another involves the problem of mutual electromagnetic coupling with the effect of influencing the directional patterns as well as the polarization purity and especially the cross-polarization in areas of low elevation angles. Due to the signals from the positioning satellites arriving at low elevation angles, the suppression of the opposite polarization direction - cross-polarization (LHCP) - is of particular importance with regard to precise positioning results, even with sufficient antenna gain in the desired - mostly right-handed circular (RHCP) - polarization direction. The accuracy of the location result is thus particularly on the ratio of the desired polarization to the cross-polarization of the satellite receiving antenna - i.e. its cross-polarization distance - dependent.

On the other hand, the realization of a satellite navigation antenna is technically difficult, which with a center frequency of about 1385 MHz covers both frequency bands with a bandwidth of about 360 MHz and also meets the sometimes strict requirements for the cross-polarization distance and the antenna gain in areas of low elevation angles.

As already mentioned, satellite receiving antennas with a small overall volume are particularly suitable for use on vehicles. Prior art antennas of this type are known as patch antennas. However, these are less efficient in terms of reception at a low elevation angle. This disadvantage is partially remedied by ring line antennas, such as those in the DE-A-10 2009 040 910 are described. However, it is also desirable for such antennas to improve the cross-polarization distance, in particular in the area of low elevation angles.

A specific requirement for the design of the antenna system for use on vehicles often results from the limitation of the available installation space, which is often characterized by an azimuthally non-uniform environment of the satellite navigation antenna. Satellite antennas are usually set up on horizontal surfaces of the electrically conductive outer skin of a vehicle. For example, the immediate vicinity of the upper edge of the cutout of the rear window - that is, the rear edge of the roof - is often specified as a preferred location of such a satellite receiving antenna on the electrically conductive vehicle roof. In many cases, the vehicle roof is curved and sloping towards the edge of the window, so that the satellite antenna is not set up on an azimuthally flat and completely horizontal conductive surface. This has a disadvantageous effect both on the azimuthal circular diagram and, in particular, on the azimuthal direction-dependently on the cross-polarization distance and the gain, in particular at low elevation angles. This disturbance of the reception properties of the satellite antenna always arises in those cases in which the antenna is partially built in the vicinity of the edge area of the horizontal body surface.

The US 2013/0500371 A1 discloses an antenna arrangement with a receiving antenna which is surrounded by a plurality of parasitic elements in the form of directors or reflectors, the latter being each provided with a plurality of switches in order to change the directional characteristic of the antenna.

The EP 0 340 404 A2 discloses L-shaped parasitic elements for receiving circularly polarized waves.

In the WO 2008/054803 A2 an antenna system with a controllable radiation field is disclosed.

It is the object of the invention to specify an antenna arrangement with a low overall height on a vehicle for circularly polarized satellite radio signals which, with sufficient gain at low elevation angles of the radiation pattern, has a high cross-polarization spacing.

This object is achieved by the features of claim 1.

According to the invention, an antenna arrangement (1) for receiving circularly polarized satellite radio signals with free space wavelength λ and frequency f comprises at least one circularly polarized satellite receiving antenna (2) positioned over an electrically conductive base surface (3), in particular for satellite navigation with a relative antenna height ha / λ <0.15, whose floor plan is a Circle K is inscribed around its phase center PZ with the relative antenna radius ra / λ <0.15. There is also a director (4) which comprises a horizontal electrical conductor (5) with two conductor ends (11) which is guided over a director length Ld at a director height hd above the conductive base area (3), at least approximately a lateral surface Mz of a cylinder oriented perpendicular to the conductive base area with a cylinder radius rz and a central axis Z through the phase center PZ of the satellite receiving antenna (2), the horizontal electrical conductor (5) being angled at its two conductor ends (11) and from there as vertical conductor (6) runs towards the conductive base surface (3) and is connected to it in an electrically conductive manner. The director (4) can design the director length Ld, the director height hd and the vertical conductor (6) be matched in such a way that its natural resonance frequency is set in the frequency vicinity of the frequency f.

• Es kann sein, dass
• die relative Direktorlänge im Bereich 0,2 < Ld /λ < 0,4 gewählt ist
• die relative Direktorhöhe im Bereich 0,03 < hd /λ < 0,15 gewählt ist
• der relative Zylinderradius im Bereich 0,15 < rz/λ < 0,5 gewählt ist.

Advantageous embodiments can be designed as follows:

• It may be that
• the relative director length is selected in the range 0.2 <Ld / λ <0.4
• the relative director height is selected in the range 0.03 <hd / λ <0.15
• the relative cylinder radius is selected in the range 0.15 <rz / λ <0.5.

It may be that the elongated horizontal electrical conductor 5 is either curved in a plan view, or is straight-lined in the manner of a secant, as it approaches the curved lateral surface Mz of the cylinder.

It may be that the director length Ld is selected to be somewhat shorter than the resonance length, i.e. about 90% of half the free space wavelength λ and the cylinder radius rz about 20% of the free space wavelength λ.

To reduce the cross polarization at low elevation angles over the entire azimuth angle range, at least three directors 4 are arranged azimuthally uniformly around the satellite receiving antenna 2 and the cylinder radius rz is chosen to be no more than half a free space wavelength.

It may be that to compensate for an impairment of the azimuthal directional diagram and the cross-polarization distance caused by the azimuthal sectorally non-uniform environment, in particular at elevation angles around 30 °, the at least one director 4 for targeted non-uniform change in the horizontal directional characteristic in one Distance of not more than half a free space wavelength λ from the phase center PZ is appropriately positioned azimuthally.

It may be that there is an electrically conductive ground plate 3a resting on the electrically conductive outer skin of the vehicle as a mechanical support for the satellite receiving antenna 2 and the at least one director 4, on which the ground points are formed for the electrically effective connection of the director 4 to the conductive base area 3 are.

It may be that the director 4 is designed in the form of a wire.

It may be that the ground plate 3a is at least partially designed from an electrically conductive sheet metal surface, and the director 4 as sheet metal strip 21 is cut out of this sheet metal surface except for a connecting web 26 as a ground point 8 and bent out of the sheet metal surface by the bending angle 10 is.

It may be that for azimuthal sectoral increase of the antenna gain for low elevation angles at least two directors 4 are arranged closely adjacent to one another along the cylinder jacket Mz and the adjacent conductor ends 11 of the elongated horizontal electrical conductors 5 are capacitively coupled to one another.

It may be that for azimuthally independent increase of the antenna gain and to further improve the cross-polarization distance, the satellite receiving antenna 2 is completely surrounded in azimuthally symmetrical form by directors 4 that are adjacent to one another and capacitively coupled with one another with regard to their conductor ends 11.

It may be that the directors 4 consist of electrically conductive sheet metal and are each angularly shaped and bent at the conductor ends 11 of the elongated electrical conductor 5 in such a way that a sheet metal flag 12 is formed in each case and by the flag surfaces that are parallel to one another neighboring directors 4 the capacitive coupling is effected.

It is possible that the directors 4 arranged in a ring are combined to form a mechanically coherent ring made of sheet metal, the connection of the directors 4 to one another being provided via, in particular, short connecting webs 26, which are placed on the ground plate 3a and electrically connected to it at the ground points 8 are conductively connected.

It may be that the satellite receiving antenna 2 consists of a circularly polarized loop antenna 13 with a relative height ha / λ 0.1 and its vertical projection is inscribed in a circle with the relative antenna radius ra / λ ∼ 0.13 around its phase center PZ and
the relative director length Ld / λ ∼ 0.3 and
the relative director height hd / λ ∼ 0.07 and
the relative cylinder radius are selected in the range rz / λ ∼ 0.2.

It may be that the satellite receiving antenna 2 is formed as a circularly polarized patch antenna 14.

An antenna arrangement 1 according to the invention has the advantage that when using a predetermined satellite receiving antenna 2 suitable for receiving the positioning satellites but not specified in more detail, the radiation properties can be improved in a targeted manner by the design and placement of the directors 4 according to the invention with regard to gain and cross-polarization suppression .

A particular advantage of the invention is also that it makes it possible, in the case of an azimuthally non-uniform environment of the antenna arrangement 1, to remedy the disruption of its omnidirectional radiation pattern with regard to gain and cross-polarization distance caused thereby.

Another advantage of an antenna arrangement 1 according to the invention is that the directors 4 can be manufactured and attached particularly easily, which also enables them to be implemented using simple bent sheet-metal or wire structures.

According to the invention, an antenna arrangement 1 for receiving circularly polarized satellite radio signals of free space wavelength λ with at least one circularly polarized satellite receiving antenna 2 with phase center PZ arranged over an essentially horizontally oriented outer skin of a vehicle 7 serving as an electrically conductive base area 3. This has a relative antenna height ha / λ <0.15 and is inscribed with its vertical projection in a circle K with the relative antenna radius ra / λ <0.15 around its phase center PZ. There is at least one director 4, which is formed from a substantially elongated horizontal electrical conductor 5 and which over the director length Ld below the director height hd above the conductive base 3 approximately along the lateral surface of a vertically oriented cylinder with a cylinder radius rz and a central axis Z is passed through the phase center PZ of the satellite antenna 2. The horizontal electrical conductor 5 is kinked at both ends of the length L and runs as a vertical conductor 6 towards the conductive base surface 3 and is conductively connected to it. The relative director length Ld is selected in the range 0.2 <Ld / λ <0.4. The relative director height hd is selected in the range 0.03 <hd / λ <0.15. The relative cylinder radius is selected in the range 0.15 <rz / λ <0.4.

• Fig. 1:
  Räumliche Darstellung einer Antennenanordnung 1 nach der Erfindung mit elektrisch kleiner Satellitenempfangsantenne 2 mit Phasenzentrum PZ im Zentrum Z auf der Außenhaut eines Fahrzeugs 7 als elektrisch leitende Grundfläche 3, azimutal umgeben von erfindungsgemäßen Direktoren 4. Diese bestehen beispielhaft jeweils aus einem geradlinigen horizontalen elektrischen Leiter 5 der Länge Ld, welcher unter einer Höhe hd geführt ist und welcher sich an seinen beiden Enden jeweils mit einem zur leitenden Grundfläche 3 hin führenden vertikalen Leiter 6 fortsetzt, dessen unteres Ende über einen Massepunkt 8 mit der leitenden Grundfläche 3 leitend verbunden ist. Die horizontalen Leiter 5 sind geradlinig annähernd entlang der Mantelfläche Mz eines senkrecht orientierten Zylinders mit Zylinderradius rz geführt. Die elektrisch kleine Satellitenempfangsantenne 2 ist einem Bauraum der Höhe ha und dem Kreis K mit dem Antennenradius ra um ihr Zentrum Z einbeschrieben.
• Fig.1a
  Draufsicht auf eine Antennenanordnung 1 nach der Erfindung, wie in Fig. 1a, zur Darstellung der Anordnung der in Draufsicht gekrümmten Direktoren 4 mit jeweils einem entlang der Mantelfläche Mz unter der Höhe hd gekrümmt verlaufenden horizontalen Leiter 5 als Segment einer kreisförmigen Höhenlinie der Mantelfläche Mz des senkrecht orientierten Zylinders mit dem Zylinderradius rz.
• Fig. 2:
  Draufsicht auf eine Antennenanordnung 1 nach der Erfindung, wie in Fig. 1, zur Darstellung der Anordnung der Direktoren 4 mit jeweils einem unter der Höhe hd geradlinig verlaufenden horizontalen Leiter 5 im Wesentlichen als Sekante einer kreisförmigen Höhenlinie der Mantelfläche Mz des senkrecht orientierten Zylinders mit Zylinderradius rz.
• Fig. 3:
  Gegenüberstellung des vertikalen Richtdiagramms in Fig. 3a einer Satellitenempfangsantenne 2 und des vertikalen Richtdiagramms in Fig. 3b derselben Satellitenempfangsantenne 2 in einer Antennenanordnung 1 nach der Erfindung jeweils für die gewünschte zirkulare Polarisationsrichtung RHCP und die Kreuzpolarisationsrichtung LHCP jeweils mit Kennzeichnung der Einfallsrichtung unter dem Elevationswinkel von 20° (Zenitwinkel 70°) und dem Elevationswinkel von 5° (Zenitwinkel 85°).
  Es ergeben sich bei Bandmitte im Band L1 (f = 1.565 MHz):
  Antennengewinn unter Elevationswinkel 20°: RHCP Fall a) 0dB, Fall b) 2dB Antennengewinn unter Elevationswinkel 20°: LHCP Fall a) -8dB, Fall b) -1.5dB Antennengewinn unter Elevationswinkel 5°: RHCP Fall a) -4dB, Fall b) 0dB Antennengewinn unter Elevationswinkel 5°: LHCP Fall a) -5,2dB, Fall b) -0,5dB Resultat: Der RHCP-Antennengewinn der Antennenanordnung 1 nach der Erfindung übertrifft den Antennengewinn der Einzelantenne um 4dB bei einem Elevationswinkel von 5° und um ca. 2 dB bei einem Elevationswinkel von 20°.
• Fig. 4:
  Vergleich der Azimutaldiagramme in Entsprechung der vertikalen Richtdiagramme in Fig. 3 in Frequenzbandmitte von L1 (f = 1.565MHz).
  Elevationswinkel = 20°.
  a) Satellitenempfangsantenne 2 b) Antennenanordnung 1 nach der Erfindung. Resultat: mit der Antennenanordnung 1 nach der Erfindung wird bei einem Elevationswinkel von 20° eine deutliche Erhöhung um ca. 2dB erzielt.
• Fig. 5:
  Vergleich der vertikalen Richtdiagramme wie in Fig. 3, jedoch bei Bandmitte im Band L2 (f= 1.225 MHz):
  a) Satellitenempfangsantenne 2 b) Antennenanordnung 1 nach der Erfindung Resultat: Der RHCP-Antennengewinn der Antennenanordnung 1 nach der Erfindung übertrifft den Antennengewinn der Einzelantenne um 1,5dB bei einem Elevationswinkel von 5° und um ca. 0,7dB bei einem Elevationswinkel von 20°.
• Fig. 6:
  Vergleich der Azimutaldiagramme wie in Fig. 5 bei Bandmitte im Band L2 (f = 1.225 MHz):
  a) Satellitenempfangsantenne 2 b) Antennenanordnung 1 nach der Erfindung Resultat: Mit der Antennenanordnung 1 nach der Erfindung wird bei einem Elevationswinkel von 20° eine Erhöhung um ca. 0,7 dB erzielt.
• Fig. 7:
  Vertikale Richtdiagramme der Antennenanordnung 1 nach der Erfindung an den Frequenzbandgrenzen des Frequenzbandes L2.
  1. a) bei der unteren Frequenzbandgrenze (f = 1200 MHz) und
  2. b) der oberen Frequenzbandgrenze (f = 1250 MHz) des Navigations-Frequenzbandes L2.
• Fig. 8:
  Räumliche Darstellung einer Antennenanordnung 1 nach der Erfindung wie in Fig. 1, jedoch mit aus elektrisch leitendem Blech bestehenden Direktoren 4. Die auf der Fahrzeug- Außenhaut aufliegende Masseplatte 3a als mechanischer Träger des Satellitenempfangsantenne 2 und der Direktoren 4 ist im Beispiel als Blechfläche 3a dargestellt. Die Direktoren 4 sind aus dieser Blechfläche 3a bis auf einen, die Masseanbindung bildenden Verbindungssteg 26 als Drehpunkt - welcher auch als Massepunkt 8 wirkt - ausgeschnitten und aus der Blechfläche 3a um den Ausbiegewinkel 10 ausgebogen.
• Fig. 9:
  Darstellung der aus fahrzeugtechnischer Sicht bevorzugten Bauräume Br1 - Br 7 für Satelliten-Empfangsantennen 2 auf der elektrisch leitenden Außenhaut eines Kraftfahrzeugs 7. Der als Br0 gekennzeichnete Ort in der Mitte des Fahrzeugdaches 16 ist aus antennentechnischer Sicht zu bevorzugen, scheidet jedoch im Allgemeinen aus fahrzeugtechnischer Sicht aus. Die aus fahrzeugtechnischer Sicht akzeptierten Bauräume Br1- Br6 befinden sich sämtlich im Randbereich des Fahrzeugdaches 17 mit den bekannten nachteiligen Einflüssen der seitlichen Dachkante 17, der vorderen Dachkante 18a und der hinteren Dachkante 18 bezüglich des Strahlungsdiagramms von Satelliten-Empfangsantennen 2 mit Rundstrahlcharakteristik. Wenig geeignet sind auch Bauräume auf dem Heckdeckel 19, zum Beispiel Br7, aufgrund der die Strahlung abschattenden Wirkung des Fahrzeug-Oberbaus.
• Fig.10:
  Anbringung der Antennenanordnung 1 nach der Erfindung mit den angegebenen Abmessungen für GNSS- Anwendungen zum Beispiel am Bauraum Br2 in Fig. 9. Der die Rundstrahlung einschränkende Effekt der hinteren Dachkante 18 sowie der Krümmung des Fahrzeugdachs 16 mithilfe der im Wesentlichen parallel zur hinteren Dachkante 18 verlaufenden Direktoren 4 wird erfindungsgemäß durch Anhebung des Antennengewinns in Fahrtrichtung für niedrige Strahlungs-Elevationswinkel wesentlich gemildert. Eine zum Beispiel seitlich am Bauraum Br6 angebrachte Satelliten-Empfangsantenne 23 für den Empfang von Satelliten-Rundfunksignalen bei der Frequenz von ca. 2,3 GHz wird in sehr vorteilhafter Weise bezüglich ihrer Strahlungseigenschaften durch die Antennenanordnung 1 nach der Erfindung praktisch nicht beeinträchtigt. Der nach rechts weisende Pfeil bezeichnet die Fahrtrichtung.
• Fig. 11:
  Anbringung der Satellitenempfangsantenne 2 am Bauraum Br2 und der Empfangsantenne 23 am Bauraum Br 6 wie in Fig. 10, jedoch mit azimutal rundum angeordneten Direktoren 4 zur Anhebung des Antennengewinns für Rundstrahlung bei niedrigen Elevationswinkeln. Die Strahlungseigenschaften der Satellitenempfangsantennen 23 sind bei geeigneter Wahl der Direktorhöhe hd und des Ausbiegewinkels 10 durch die Anwesenheit der Antennenanordnung 1 nach der Erfindung praktisch nicht beeinträchtigt.
• Fig. 12:
  Antennenanordnung 1 nach der Erfindung mit zueinander dicht benachbart - als Segmente entlang dem Zylindermantel - angeordneten Direktoren 4, welche ringförmig um die Satellitenempfangsantenne 2 angeordnet sind. Die zueinander benachbarten Leiterenden 11 der längsgestreckten horizontalen Leiter 5 sind kapazitiv miteinander verkoppelt. Die Direktoren 4 sind, wie in Fig. 8 als Blechstreifen 9 aus der Blechfläche der Masseplatte 3a ausgeschnitten und um den Ausbiegewinkel 10 von 90° ausgebogen. Die Leiterenden 11 der längsgestreckten elektrischen Leiter 5 sind in der Weise eckig ausgeformt und bezogen auf das Zentrum Z radial nach außen gebogen, dass jeweils eine Blechfahne 12 gebildet ist und die kapazitive Kopplung durch die parallel zueinanderstehenden Fahnenflächen der jeweils einander benachbarten Direktoren 4 bewirkt ist.
• Fig. 13:
  Antennenanordnung 1 nach der Erfindung wie in Fig. 12 mit dem Unterschied, dass zur Verringerung des Platzbedarfs die Blechfahnen 12 zur Bildung der kapazitiven Kopplung - bezogen auf das Zentrum Z - radial nach innen gebogen sind.
• Fig. 14:
  1. a) Gestaltung der die Satellitenempfangsantenne 2 umringenden Direktoren 4, wie in Fig. 13, jedoch als zusammenhängend, aus einem Blech geschnittener und geformter Blechring 25. Die dabei entstandenen Verbindungsstege 26 an den unteren Enden der vertikalen Leiter 6 bilden durch Aufsetzen des Blechrings 25 auf die Masseplatte 3a und mit deren elektrischen Verbindung die Massepunkte 8. die vertikalen Pfeile beschreiben die Richtung, in welcher der Blechring 25 auf die Masseplatte 3a aufgesetzt wird. Die Satellitenantenne 2 ist in dieser Figur nicht gezeigt.
  2. b) Darstellung der Antennenanordnung 1 nach der Erfindung mit einem auf der Masseplatte 3a aufgesetzten und mit dieser an den Massepunkten 8 elektrisch leitend verbundenen Blechring 25 wie unter a) mit der Satellitenempfangsantenne 2 im Zentrum zum Beispiel am Bauraum Br 2. Die weitere Satellitenempfangsantenne 23 ist, wie in den Fig. 10 und 11, am Bauraum 6 angebracht.

The invention is explained in more detail below on the basis of exemplary embodiments. The corresponding figures show in detail:

• Fig. 1 :
  Spatial representation of an antenna arrangement 1 according to the invention with an electrically small satellite receiving antenna 2 with phase center PZ in the center Z on the outer skin of a vehicle 7 as an electrically conductive base area 3, azimuthally surrounded by directors 4 according to the invention Length Ld, which is guided below a height hd and which continues at both ends with a vertical conductor 6 leading to the conductive base 3, the lower end of which is conductively connected to the conductive base 3 via a ground point 8. The horizontal conductors 5 are guided in a straight line approximately along the lateral surface Mz of a vertically oriented cylinder with a cylinder radius rz. The electrically small satellite receiving antenna 2 is inscribed around its center Z in an installation space of height ha and the circle K with the antenna radius ra.
• Fig.1a
  Top view of an antenna arrangement 1 according to the invention, as shown in FIG Fig. 1a To illustrate the arrangement of the directors 4 curved in plan view, each with a horizontal conductor 5 curved along the lateral surface Mz below the height hd as a segment of a circular contour line of the lateral surface Mz of the vertically oriented cylinder with the cylinder radius rz.
• Fig. 2 :
  Top view of an antenna arrangement 1 according to the invention, as shown in FIG Fig. 1 To illustrate the arrangement of the directors 4, each with a horizontal ladder 5 running in a straight line below the height hd, essentially as a secant of a circular contour line of the lateral surface Mz of the vertically oriented cylinder with cylinder radius rz.
• Fig. 3 :
  Comparison of the vertical directional diagram in Fig. 3a a satellite receiving antenna 2 and the vertical directional diagram in FIG Figure 3b the same satellite receiving antenna 2 in an antenna arrangement 1 according to the invention, each for the desired circular polarization direction RHCP and the cross polarization direction LHCP, each with marking of the direction of incidence at the elevation angle of 20 ° (zenith angle 70 °) and the elevation angle of 5 ° (zenith angle 85 °).
  In the middle of the band in the L1 band (f = 1,565 MHz):
  Antenna gain under elevation angle 20 °: RHCP case a) 0dB, case b) 2dB Antenna gain under elevation angle 20 °: LHCP case a) -8dB, case b) -1.5dB Antenna gain under elevation angle 5 °: RHCP case a) -4dB, case b ) 0dB antenna gain at an elevation angle of 5 °: LHCP case a) -5.2dB, case b) -0.5dB Result: The RHCP antenna gain of the antenna arrangement 1 according to the invention exceeds the antenna gain of the individual antenna by 4dB at an elevation angle of 5 ° and by approx. 2 dB at an elevation angle of 20 °.
• Fig. 4 :
  Comparison of the azimuthal diagrams in correspondence with the vertical directional diagrams in Fig. 3 in the middle of the frequency band of L1 (f = 1.565MHz).
  Elevation angle = 20 °.
  a) Satellite receiving antenna 2 b) Antenna arrangement 1 according to the invention. Result: with the antenna arrangement 1 according to the invention, a significant increase of approximately 2 dB is achieved at an elevation angle of 20 °.
• Fig. 5 :
  Comparison of the vertical directional diagrams as in Fig. 3 , but in the middle of the band L2 (f = 1,225 MHz):
  a) Satellite receiving antenna 2 b) Antenna arrangement 1 according to the invention Result: The RHCP antenna gain of the antenna arrangement 1 according to the invention exceeds the antenna gain of the individual antenna by 1.5dB at an elevation angle of 5 ° and by about 0.7dB at an elevation angle of 20 °.
• Fig. 6 :
  Comparison of the azimuthal diagrams as in Fig. 5 at mid-band in band L2 (f = 1,225 MHz):
  a) Satellite receiving antenna 2 b) Antenna arrangement 1 according to the invention Result: With the antenna arrangement 1 according to the invention, an increase of approximately 0.7 dB is achieved at an elevation angle of 20 °.
• Fig. 7 :
  Vertical directional diagrams of the antenna arrangement 1 according to the invention at the frequency band limits of the frequency band L2.
  1. a) at the lower frequency band limit (f = 1200 MHz) and
  2. b) the upper frequency band limit (f = 1250 MHz) of the navigation frequency band L2.
• Fig. 8 :
  Spatial representation of an antenna arrangement 1 according to the invention as in FIG Fig. 1 , but with directors 4 made of electrically conductive sheet metal. The ground plate 3a resting on the vehicle outer skin as a mechanical carrier for the satellite receiving antenna 2 and the directors 4 is shown in the example as sheet metal surface 3a. The directors 4 are cut out of this sheet metal surface 3a except for a connecting web 26 forming the ground connection as a fulcrum - which also acts as a ground point 8 - and are bent out of the sheet metal surface 3a by the bending angle 10.
• Fig. 9 :
  Representation of the preferred installation spaces Br1 - Br 7 for satellite receiving antennas 2 on the electrically conductive outer skin of a motor vehicle 7 from a vehicle technology point of view. The location marked Br0 in the middle of the vehicle roof 16 is preferable from an antenna technology point of view, but is generally different from a vehicle technology point of view out. The installation spaces Br1-Br6 accepted from a vehicle perspective are all located in the edge area of the vehicle roof 17 with the known disadvantageous influences of the side roof edge 17, the front roof edge 18a and the rear roof edge 18 with regard to the radiation pattern of satellite reception antennas 2 with omnidirectional characteristics. Installation spaces on the trunk lid 19, for example Br7, are also not very suitable because of the effect of the vehicle superstructure which shadows the radiation.
• Fig. 10 :
  Attachment of the antenna arrangement 1 according to the invention with the specified dimensions for GNSS applications, for example on the installation space Br2 in Fig. 9 . The effect of the rear roof edge 18, which restricts the omnidirectional radiation, as well as the curvature of the vehicle roof 16 with the aid of the directors 4, which run essentially parallel to the rear roof edge 18, is substantially mitigated according to the invention by increasing the antenna gain in the direction of travel for low radiation elevation angles. A satellite receiving antenna 23 attached to the side of the installation space Br6 for the reception of satellite broadcast signals at the frequency of approximately 2.3 GHz is very advantageously practically not impaired in terms of its radiation properties by the antenna arrangement 1 according to the invention. The arrow pointing to the right indicates the direction of travel.
• Fig. 11 :
  Attachment of the satellite receiving antenna 2 to the installation space Br2 and the receiving antenna 23 to the installation space Br 6 as in FIG Fig. 10 , but with azimuthally arranged directors 4 all around to increase the antenna gain for omnidirectional radiation at low elevation angles. The radiation properties of the satellite receiving antennas 23 are practically not impaired by the presence of the antenna arrangement 1 according to the invention given a suitable choice of the director height hd and the bending angle 10.
• Fig. 12 :
  Antenna arrangement 1 according to the invention with directors 4 arranged closely adjacent to one another - as segments along the cylinder jacket - which are arranged in a ring around the satellite receiving antenna 2. The conductor ends 11 of the elongated horizontal conductors 5 which are adjacent to one another are capacitively coupled to one another. The directors 4 are, as in Fig. 8 cut out as a sheet metal strip 9 from the sheet metal surface of the ground plate 3a and bent out by the bending angle 10 of 90 °. The conductor ends 11 of the elongated electrical conductors 5 are angularly shaped and bent radially outward relative to the center Z that a sheet metal lug 12 is formed in each case and the capacitive coupling is brought about by the parallel lug surfaces of the respective adjacent directors 4.
• Fig. 13 :
  Antenna arrangement 1 according to the invention as in Fig. 12 with the difference that, in order to reduce the space requirement, the sheet metal lugs 12 to form the capacitive coupling - relative to the center Z - are bent radially inward.
• Fig. 14 :
  1. a) Design of the directors 4 surrounding the satellite receiving antenna 2, as in FIG Fig. 13 , but as a coherent sheet metal ring 25 cut and formed from sheet metal. The connecting webs 26 at the lower ends of the vertical conductors 6 formed by placing the sheet metal ring 25 on the ground plate 3a and with their electrical connection form the ground points 8 the direction in which the sheet metal ring 25 is placed on the ground plate 3a. The satellite antenna 2 is not shown in this figure.
  2. b) Representation of the antenna arrangement 1 according to the invention with a sheet metal ring 25 placed on the ground plate 3a and electrically conductively connected to it at the ground points 8 as under a) with the satellite receiving antenna 2 in the center, for example on the installation space Br 2. The further satellite receiving antenna 23 is as in the Fig. 10 and 11 , attached to the installation space 6.

The invention is based on a circularly polarized satellite receiving antenna 2 located above an electrically conductive base area 3, the relative antenna height ha / λ of which, based on the free space wavelength λ, is less than 0.15. This extremely small height ha of the antenna is associated with the problematic property that its radiation gain decreases very quickly towards smaller elevation angles. This is also associated with an increased decrease in the cross-polarization distance. This effect can be mitigated by the presence of the directors 4 to such an extent that a satellite receiving antenna 2 with the specified structural volume on the electrically conductive outer skin of a vehicle 7 can also be used for qualified location determination with the aid of satellite navigation. In this case, satellite reception signals are to be evaluated for the navigation, which are incident at the low elevation angle of 20 ° up to an elevation angle of 5 °. The extremely strong drop in antenna gain at such low elevation angles for the desired polarization direction of such a low one Satellite receiving antenna 2 over a conductive base 3 is based on the weakness of the horizontal component of its electric radiation field. According to the invention, this weakness is alleviated by the use of the directors 4 around the satellite receiving antenna 2 and the antenna gain is increased for low elevation angles.

The directors form an arch or a (U-shaped) gate in relation to the base area (cf. Fig. 1 ), which consists of the vertical conductor 5 and the two vertical conductors 6.

The mode of operation of the directors 4 can be checked for plausibility on the basis of the spatial representation of the antenna arrangement 1 according to the invention in FIG Fig. 1 and their top view in the Figures 1a and 2 explain approximately. Here, the azimuthally almost complete encompassing of the satellite receiving antenna 2 with directors 4 leads to the desired increase in the antenna gain in the case of omnidirectional radiation. The satellite receiving antenna 2 designed 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 conductors 5 are each connected to a ground point 8 with the conductive base 3 via the vertical conductors 6. Thus, secondary currents are formed on the electrically excited director 4 and in particular also on the horizontal electrical conductor 5, which, with a suitable choice of the director length in the range 0.2 <Ld / λ <0.45, the director height in the range 0.03 <hd / λ <0.15 and the cylinder radius in the range 0.15 <rz / λ <0.5, which determines the distance between the directors 4 and the center Z of the antenna arrangement 1, generate a radiation field. This is superimposed on the radiation field of the satellite receiving antenna 2 in such a way that the desired increase in the antenna gain occurs, in particular for low elevation angles. A director length Ld which is shorter than half a free space wavelength λ, that is to say that the natural resonance frequency of the Director 4 is selected slightly lower than the satellite reception frequency f. The small selected deviation of the satellite frequency f from the natural resonance frequency of the director 4 is the reason for the associated increase in the currents on the director 4 and, in combination with the appropriately set cylinder radius rz, the resulting, in relation on the phase position constructive superposition of the director radiation field with the radiation field of the satellite receiving antenna 2 in the sense of the task to be solved. The horizontal electrical conductors 5 above the electrically conductive base 3 below the director height hd each form an electrical line terminated at both conductor ends 11 via the vertical conductor 6 with the characteristic impedance ZL, the size of which depends on the conductor width 27 or the sheet metal strip width 21 and the conductor spacing 28 of the horizontal electrical conductor 5 is given by the conductive base 3. When designing a director 4 from wire, for example, by adjusting the running capacitance and running inductance of the horizontal electrical conductor 5, e.g. B. using a meander-shaped installation, the wave impedance ZL can be varied within wide limits. A fine adjustment of the distance rz of the director 4 from the center Z as well as the choice of a suitable wave impedance ZL and the self-inductance of the vertical conductors 6 enables the optimization of the radiation pattern of the antenna arrangement 1 in terms of the object of the invention.

In the Figures 3 to 7 Examples of measurement results in the form of vertical and horizontal sections of radiation diagrams of antenna arrangements 1 according to the invention are shown and compared with corresponding measurement results of a satellite antenna 2 over a conductive base area 3 without directors 4 according to the invention. The improvements achieved in the area of low elevation angles are specified in detail in connection with the above descriptions of the figures.

Manufacturing costs and ease of implementation are essential for use in vehicle construction. In an advantageous embodiment of the invention, as in Fig. 8 shown, the ground plate 3a resting on the outer skin of the vehicle 7 is designed as a mechanical support for the satellite receiving antenna 2 and the directors 4 and is made of sheet metal. A particular advantage here is the possibility, according to the invention, of cutting the directors 4 from the sheet metal and bending them out by the bending angle 10. The cutting and bending processes required for this can be carried out extremely inexpensively in mass production with very good reproducibility.

From a vehicle technical point of view, installation spaces - Br1 - Br6 in - are mainly available for attaching a satellite receiving antenna 2 Fig. 9 - available in the edge zones on the vehicle roof. As a consequence of the azimuthally non-uniform environment already mentioned, there is a significant impairment of the azimuthal directional diagram and the cross-polarization distance. There is also a shift in the phase center PZ of the antenna arrangement 1, which has a negative effect on the navigation result, as a function of the solid angle of the incident satellite reception signals.

In particular at elevation angles around 20 °, the non-uniform change in the horizontal directional characteristic can be counteracted with a specifically positioned director 4. This measure according to the invention is particularly helpful when choosing the preferred installation spaces Br1, Br2, and Br6 on the vehicle roof 16, in which due to the abrupt breaking off of the conductive base surface 3 on the rear roof edge 18 at the upper edge of the rear window 15 and the curvature that is often present there of the vehicle roof 16, the radiation pattern of a satellite receiving antenna 2 is generally severely impaired.

With the growing number of satellite radio services for satellite navigation and satellite broadcasting, the installation spaces are more compact and the radiation characteristics are impaired by electromagnetic coupling. In the example already described above in Fig. 10 the satellite receiving antenna 2 for GNSS is attached in an arrangement according to the invention with two opposing directors 4 on the installation space Br2 and the satellite receiving antenna 23 for radio reception at approximately 2.3 GHz on the installation space Br6. Both antennas are designed as ring line antennas 13 in the example. It is shown to be very advantageous here that the strict requirements for the radiation characteristics of the satellite broadcast receiving antenna 23 are not impaired by the presence of the directors 4 according to the invention. Due to the large distance between the natural resonance frequency of the directors 4 and the frequency of the satellite broadcasting, the secondary currents which the satellite broadcast antenna 23 causes on the directors 4 are sufficiently small that their effect on the radiation characteristics of the satellite broadcast antenna 23 is negligible. This effect is pronounced in such a way that the disturbance of the radiation properties of the satellite broadcast antenna 23 in Fig. 11 is small even when the satellite receiving antenna 2 for GNSS is completely surrounded by directors 4.

Similar to in Fig. 11 is the satellite receiving antenna 2 in Fig. 12 completely surrounded by directors 4, which however - even more than in Fig. 11 in a further advantageous embodiment of the invention - are arranged in close order on top of one another, that is to say at a close distance along the cylinder jacket ZM. The conductor ends 11 of the elongated horizontal electrical conductors 5 which are adjacent to one another are capacitively coupled to one another. This coupling achieves a further improvement in the cross-polarization distance and the azimuthal independence of the phase center at low elevation angles. It results from an additional assignment with secondary currents on the horizontal electrical conductors 5, which results from the capacitive bridging of the voltage differences between the adjacent conductor ends 11, which are formed over the vertical electrical conductors 6. The phases of the currents on the satellite receiving antenna 2, which change with the azimuthal angle, cause the excitation of secondary currents with different phases in the different directors 4. These secondary currents generate different voltages on the inductive effects of the adjacent vertical electrical conductors 6, the difference being via the capacitive Coupling produces the desired effect of improving the cross polarization distance.

As related to Fig. 11 described, the directors 4 are cut out of the sheet-like ground plate 3a except for the short connecting webs 26 and bent out of the sheet-metal ground plate 3a along the bending line 24, the bending angle 10 being selected to be 90 °. To intensify the capacitive coupling, the conductor ends 11 of the elongated electrical conductor 5 are shaped flat and angular in such a way that a sheet metal lug 12 is formed in each case. The sheet metal lugs 12 are bent radially outward - in relation to the center Z - in such a way that the surfaces of two adjacent sheet metal lugs 12 are aligned essentially parallel to one another and thus the increased capacitive coupling is achieved. Although the illustrated realization of an antenna arrangement 1 according to the invention appears to be complicated, it can nevertheless be produced extremely inexpensively by means of stamping and bending technology in series production. To reduce the transverse extent of the antenna arrangement 1, the in the Fig. 12 illustrated sheet metal lugs 12 - be bent radially inward - based on the center Z -, as shown Fig. 13 emerges.

In a further advantageous embodiment of the invention are in Figure 14a the directors joined together in a ring to form a mechanically connected ring made of sheet metal. They are via short connecting bridges 26 connected to each other. Provision is made for the ring made of sheet metal to be placed on the ground plate 3a - as indicated by the vertical arrows - and to connect the connecting webs 26 to the ground points 8 located on the ground plane 3 in an electrically conductive manner, as shown in FIG Figure 14b emerges.

List of names

• Antenna arrangement 1
• Satellite receiving antenna 2
• electrically conductive base 3
• Ground plane 3a
• Director 4
• horizontal electrical conductor 5
• vertical conductor 6
• Outer skin of a vehicle 7
• Earth points 8
• Sheet metal strips 9
• Bending angle 10
• Ladder ends 11
• Metal flag 12
• Loop antenna 13
• Patch antenna 14
• Rear window 15
• Vehicle roof 16
• lateral roof edge 17
• rear roof edge 18
• front roof edge 18a
• Trunk lid 19
• Front cover 20
• Sheet metal strip width 21
• Cutting lines 22
• further satellite receiving antenna 23
• Bending line 24
• Sheet metal ring 25
• Connecting webs 26
• Ladder width 27
• Distance between conductors 28
• Free space wavelength λ
• Antenna height ha
• Phase center PZ
• Antenna radius ra
• Cylinder radius rz
• central axis Z
• Director length Ld
• Director height hd
• Circle K
• Cylinder jacket Mz
• Installation space Br1 - Br7
• Wave resistance ZL

Claims (15)

1. An antenna arrangement (1) for the reception of circularly polarized satellite radio signals having the free space wavelength λ and the frequency f, said antenna arrangement (1) comprising at least one circularly polarized satellite reception antenna (2) positioned above an electrically conductive base surface (3), in particular for satellite navigation with a relative antenna height ha/λ < 0.15 whose outline is inscribed by a circle K about its phase center PZ having the relative antenna radius ra/λ < 0.15,
   comprising the following features:

   a director (4) is present which comprises a horizontal electrical conductor (5) which has two conductor ends (11) and which is guided over a director length Ld at a director height hd above the conductive base surface (3), 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 (2), wherein the horizontal electrical conductor (5) is angled at its two conductor ends (11) and extends from there as a vertical conductor (6) in each case toward the conductive base surface (3) and is electrically conductively connected thereto;

   the director (4) is adapted by designing the director length Ld, the director height hd and the vertical conductors (6) in a manner such that its natural resonant frequency is set in frequency proximity to the frequency f.
2. An antenna arrangement (1) in accordance with claim 1,
   characterized in that
   the director length is selected in the range 0.2 < Ld /λ < 0.45;
   the director height hd is selected in the range 0.03 < hd /λ < 0.15; and
   the cylinder radius is selected in the range 0.15 < rz/λ < 0.5.
3. An antenna arrangement (1) in accordance with claim 1 or claim 2,
   characterized in that
   the horizontal electrical conductor (5) is designed in a straight line, with the two vertical conductors (6) in particular being arranged in the region of the jacket surface Mz.
4. An antenna arrangement (1) in accordance with any one of the claims 1 to 3,
   characterized in that
   the director length Ld is selected as shorter than approximately 90% half the free space wavelength λ and the cylinder radius rz is selected as approximately 20% of the free space wavelength λ.
5. An antenna arrangement (1) in accordance with any one of the claims 1 to 4,
   characterized in that,
   in order to reduce the cross-polarization at small angles of elevation over the total azimuth angle range, at least three directors (4) are arranged azimuthally uniformly about the satellite reception antenna (2), with the cylinder radius rz in particular being selected as not larger than half a free space wavelength.
6. An antenna arrangement (1) in accordance with any one of the claims 1 to 5,
   characterized in that,
   in order to compensate an impairment of the azimuthal directional pattern and of the cross-polarization spacing caused by an azimuthally sectorally irregular environment, in particular with angles of elevation around 30°, the at least one director (4) is positioned at a spacing of no more than half a free space frequency wavelength λ remote from the phase center PZ for a direct irregular change of the horizontal directionality.
7. An antenna arrangement (1) in accordance with any one of the claims 1 to 6,
   characterized in that
   an electrically conductive ground plate (3a) is present as a mechanical carrier of the satellite reception antenna (2) and of the at least one director (4), with ground points (8) being formed on said ground plate (3a) for an electrically effective connection of the director (4).
8. An antenna arrangement (1) in accordance with claim 7,
   characterized in that
   the ground plate (3a) is designed at least in part from an electrically conductive sheet metal surface; and in that the director (4) is cut as a sheet metal strip (21) out of this sheet metal surface, except for a connection web (26) as a ground point (8), and is bent out of the sheet metal surface by a bend angle (10).
9. An antenna arrangement (1) in accordance with any one of the claims 1 to 7,
   characterized in that
   the director (4) is configured in wire form.
10. An antenna arrangement (1) in accordance with any one of the claims 1 to 9,
    characterized in that,
    for the azimuthally sectoral raising of the antenna gain for small angles of elevation, at least two directors (4) are arranged closely adjacent to one another along the cylinder jacket Mz and the mutually adjacent conductor ends (11) of the horizontal electrical conductors (5) are capacitively coupled to one another.
11. An antenna arrangement (1) in accordance with any one of the claims 1 to 10,
    characterized in that,
    for the azimuthally independent raising of the antenna gain and for a further improvement of the cross-polarization spacing, the satellite reception antenna (2) is completely surrounded in an azimuthally symmetrical form by mutually adjacent directors (4) which are capacitively coupled to one another with respect to their conductor ends (11).
12. An antenna arrangement in accordance with any one of the claims 1 to 8 and 10 to 11,
    characterized in that
    a plurality of directors (4) are provided which comprise electrically conductive sheet metal and are respectively shaped and bent in angled form at the conductor ends (11) of the elongated electrical conductor (5) in a manner such that a respective sheet metal lug (12) is formed, with a capacitive coupling being effected by lug surfaces of the respective mutually adjacent directors (4) in parallel with one another.
13. An antenna arrangement (1) in accordance with claim 12,
    characterized in that
    the directors (4) are combined in a contiguous manner to form a mechanically coherent ring of sheet metal, with the connection of the directors (4) being given by connection webs (26) which are placed on a ground plate (3a) and are electrically conductively connected to it at ground points (8).
14. An antenna arrangement (1) in accordance with claims 1 to 13,
    characterized in that
    the satellite reception antenna (2) is a circularly polarized loop antenna (13) having a relative height ha/λ ∼ 0.1 and its vertical projection is inscribed by a circle having the relative antenna radius ra/λ ∼ 0.13 about its phase center PZ; and
    the director length Ld /λ ∼ 0.3 is selected;
    the director height hd/λ ∼ 0.07 is selected; and
    the cylinder radius rz/λ ∼ 0.2 is selected.
15. An antenna arrangement (1) in accordance with any one of the claims 1 to 13,
    characterized in that
    the satellite reception antenna (2) is formed as a circularly polarized patch antenna (14).

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