EP0374722A1 - Directional antenna having an adaptively controlled subreflector - Google Patents

Directional antenna having an adaptively controlled subreflector Download PDF

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Publication number
EP0374722A1
EP0374722A1 EP89123081A EP89123081A EP0374722A1 EP 0374722 A1 EP0374722 A1 EP 0374722A1 EP 89123081 A EP89123081 A EP 89123081A EP 89123081 A EP89123081 A EP 89123081A EP 0374722 A1 EP0374722 A1 EP 0374722A1
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Prior art keywords
subreflector
reflector
antenna according
sub
rotation
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EP89123081A
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German (de)
French (fr)
Inventor
Karl-Peter Dr.-Ing. Dombek
Volker Dr.-Ing. Hombach
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Kabelmetal Electro GmbH
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Kabelmetal Electro GmbH
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Publication of EP0374722A1 publication Critical patent/EP0374722A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/12—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system using mechanical relative movement between primary active elements and secondary devices of antennas or antenna systems
    • H01Q3/16—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system using mechanical relative movement between primary active elements and secondary devices of antennas or antenna systems for varying relative position of primary active element and a reflecting device
    • H01Q3/20—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system using mechanical relative movement between primary active elements and secondary devices of antennas or antenna systems for varying relative position of primary active element and a reflecting device wherein the primary active element is fixed and the reflecting device is movable

Definitions

  • the invention relates to a double reflector antenna which can be used in particular in digital radio relay to compensate for interference caused by multipath propagation.
  • K.-P. Dombek on "Reduction of multipath interference by adaptive beam orientation” European Conference on Radio-Relay-Systems, Conf. Publ. ECRR, VDE-Verlag, 1986, p.400-406
  • small angular deflections of the main lobe of the transmitting and / or receiving antenna can effectively reduce interference due to multipath propagation, such as occurs on radio links in unfavorable weather conditions.
  • the necessary swivel range of the main lobe is less than two half-widths.
  • the invention has for its object to reduce interference due to multipath propagation and to keep the amount of equipment as small as possible.
  • Fig. 1 explains the operation of the invention in more detail.
  • the asymmetrical double reflector antenna bundles the received electromagnetic wave at the paraboloidal main reflector 1, deflects it at the subreflector 2 and thus leads it to the horn exciter 3.
  • the signal picked up by horn exciter 3 reaches receiver 4. Fading, which occurs on the transmission link due to multipath propagation, is particularly noticeable by frequency-selective changes in the group delay and the attenuation of the received signal. Depending on the width of the transmitted frequency band, the receiver must therefore detect these changes at several points and feed them to the fault evaluation circuit 5.
  • the evaluation circuit 5 emits a control pulse for the electric motor 6, which can be implemented in particular as a stepper motor. So that the rotatably mounted sub-reflector 2 is tilted by a small angle.
  • the horizontal axis of rotation 7 of the sub-reflector preferably passes through the center of the aperture, but can also be attached at other points of the sub-reflector if it is necessary for reasons of space.
  • the tilting of the sub-reflector causes the main lobe of the antenna to deflect in the elevation plane. If the reception quality deteriorates further as a result, the evaluation circuit 5 causes a sub-reflector rotation in the opposite direction.
  • the evaluation circuit thus works in a control loop which strives to set the best possible reception quality by changing the angular position of the sub-reflector and the associated deflection of the main lobe.
  • the subreflector Since the subreflector has a relatively small mass, it can be moved relatively quickly. In conventional 3-m directional radio antennas, a maximum stroke of the lower or upper edge of the sub-reflector of 2 to 4 cm is possible with a beam deflection 8 of a half-value width. Since the propagation conditions to be compensated only change relatively slowly in the event of a fault (periods of around one second can still be regarded as stationary), the speed of the control loop is sufficient, even though it contains mechanically moved elements. In the large asymmetrical double reflector antennas used in directional radio, the subreflector is usually located under a protective cover, so that no special measures for weather protection of the pivot bearings, joints and the motor are necessary.
  • the received signal passes through the down mixer 10 to the intermediate frequency amplifier 11.
  • the frequency-dependent transmission characteristic of the propagation path is determined by at least three narrowband bandpass filters 12 and detectors 13.
  • the multiplexer 14 switches the amplitude values one after the other via the analog-digital converter 15 to the input of the microcomputer 16. If the set threshold value of the dispersion is exceeded, the microcomputer 16 gives the necessary pulses to the motor control circuit 17 for actuating the stepping motor 6 then turns the subreflector.
  • the sensitivity of the control loop can be increased by superimposing a slight modulation in the form of a uniform vibration of the sub-reflector.
  • this measure has a very broadband effect to reduce interference due to multipath propagation.
  • An advantage of the invention over other measures to compensate for loss is also to be seen in the fact that existing double reflector antennas can usually be retrofitted very easily without the excitation system having to be replaced. Neither a second antenna nor additional exciters or receivers are required. If the main lobe is deflected by less than two half-widths, no significant deterioration in the sub-Zipple level 9 and the cross-polarization diagram compared to the original disturbed signal can be observed.

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  • Variable-Direction Aerials And Aerial Arrays (AREA)
  • Aerials With Secondary Devices (AREA)

Abstract

An evaluation circuit (5) detects the dispersion of the directional radio signal occurring on the test route and, with the aid of the motor (6), adjusts the angle of incidence of the subreflector (2) in such a way that the major lobe of the antenna is deflected by up to two halfpower widths. As a result, the wanted and interference signals arriving from various directions are weighted differently before they reach the receiver.

Description

Die Erfindung betrifft eine Doppelreflektorantenne, die insbesondere im digitalen Richtfunk zur Kompensation von Störungen durch Mehrwegeausbreitung eingesetzt werden kann. In K.-P. Dombek über "Reduction of multipath interference by adaptive beam orientation", European Conference on Radio-­Relay-Systems, Conf. Publ. ECRR, VDE-Verlag, 1986, S.400-406, wird gezeigt, daß durch kleine Winkelauslenkungen der Hauptkeule von Sende- und/oder Empfangsantenne Störungen durch Mehrwegeausbreitung, wie sie bei ungünstigen Wetterlagen auf Richtfunkstrecken auftreten, wirksam vermindert werden können. Der notwendige Schwenkbereich der Hauptkeule liegt bei weniger als zwei Halbwertsbreiten.The invention relates to a double reflector antenna which can be used in particular in digital radio relay to compensate for interference caused by multipath propagation. In K.-P. Dombek on "Reduction of multipath interference by adaptive beam orientation", European Conference on Radio-Relay-Systems, Conf. Publ. ECRR, VDE-Verlag, 1986, p.400-406, it is shown that small angular deflections of the main lobe of the transmitting and / or receiving antenna can effectively reduce interference due to multipath propagation, such as occurs on radio links in unfavorable weather conditions. The necessary swivel range of the main lobe is less than two half-widths.

Es gibt verschiedene Möglichkeiten, die Keulenauslendkung zu bewirken. In der oben angegebenen Literaturstelle und in der Patentanmeldung P 38 29 370.6 werden hierfür z. B. mehrere in der Brennebene versetzt angebrachte Erreger benutzt. Werden die Signale dieser Erreger in einem Diversityempfänger kombiniert, so bedarf es hierzu eines speziellen Doppelempfängers und zweier HF-Verbindungsleitungen zwischen Antenne und Empfänger. Werden die Signale direkt am Doppelerreger kombiniert, so benötigt man ein relativ aufwendiges, verlustbehaftetes, elektronisch steuerbares Netzwerk. Erschwerend kommt in beiden Fällen noch hinzu, daß der doppelte Aufwand für Erreger, Polarisations- und Frequenzweichen erforderlich ist.There are various ways to effect club deflection. In the literature cited above and in patent application P 38 29 370.6, z. B. uses several exciter mounted in the focal plane. If the signals from these exciters are combined in a diversity receiver, this requires a special double receiver and two RF connecting lines between the antenna and the receiver. If the signals are combined directly on the double exciter, a relatively complex, lossy, electronically controllable network is required. To make matters worse in both cases, the double effort for exciters, polarization and crossovers is required.

Der Erfindung liegt die Aufgabe zugrunde, Störungen durch Mehrwegeausbreitung zu vermindern und den Geräteaufwand möglichst klein zu halten.The invention has for its object to reduce interference due to multipath propagation and to keep the amount of equipment as small as possible.

Eine Drehung der Gesamtantenne scheidet wegen der zu bewegenden großen Masse und der damit verbundenen mechanischen Probleme aus. Es ist jedoch bekannt, daß bei einer Keulenauslenkung durch Drehung des Subreflektors nur eine relativ geringe Masse bewegt werden muß. Die Aufgabe wird bei der im Hauptanspruch gekennzeichneten Erfindung dadurch gelöst, daß durch geringfügige Drehung des Subreflektors und eine damit verbundene Auswertung einer störungsproportionalen Größe (insbesondere in bezug auf dispersive Störungen) eine Stellgröße gewonnen wird, mit deren Hilfe eine den Störungen entgegenwirkende Steuerung des Subreflektorwinkels möglich wird. Die Ansprüche 2 bis 5 zeigen Beispiele für die Gewinnung dieses Störungskriteriums mit Hilfe handelsüblicher Richtfunkempfänger auf. Die Ansprüche 6 und 7 kennzeichnen spezielle Ausführungsformen.

  • Die Fig. 1 zeigt einen schematischen Aufbau der Anordnung gemäß der Erfindung und
  • Fig. 2 zeigt das Schaltbild einer Möglichkeit der Störungsauswertung.
A rotation of the overall antenna is ruled out because of the large mass to be moved and the mechanical problems associated with it. However, it is known that in the case of a club deflection, only a relatively small mass has to be moved by rotating the sub-reflector. The object is achieved in the invention characterized in the main claim that a manipulated variable is obtained by means of a slight rotation of the sub-reflector and an associated evaluation of a disturbance-proportional variable (in particular with regard to dispersive disturbances), with the aid of which control of the sub-reflector angle which counteracts the disturbances is possible becomes. Claims 2 to 5 show examples of how this interference criterion can be obtained with the aid of commercially available directional radio receivers. Claims 6 and 7 characterize special embodiments.
  • Fig. 1 shows a schematic structure of the arrangement according to the invention and
  • Fig. 2 shows the circuit diagram of a possibility of fault evaluation.

Die Fig. 1 erläutert die Wirkungsweise der Erfindung näher. Die asymmetrische Doppelreflektorantenne bündelt die empfangene elektromagnetische Welle am paraboloidförmigen Hauptreflektor 1, lenkt sie am Subreflektor 2 um und führt sie so schließlich dem Hornerreger 3 zu. Das vom Horn­erreger 3 aufgenommene Signal gelangt zum Empfänger 4. Schwund, der auf der Übertragungsstrecke aufgrund von Mehrwegeausbreitung auftritt, macht sich vor allem durch frequenzselektive Änderung der Gruppenlaufzeit und der Dämpfung des empfangenen Signals bemerkbar. Der Empfänger muß daher je nach Breite des übertragenen Frequenzbandes an mehrenen Stellen diese Änderungen detektieren und der Störungsauswerteschaltung 5 zuführen.Fig. 1 explains the operation of the invention in more detail. The asymmetrical double reflector antenna bundles the received electromagnetic wave at the paraboloidal main reflector 1, deflects it at the subreflector 2 and thus leads it to the horn exciter 3. The signal picked up by horn exciter 3 reaches receiver 4. Fading, which occurs on the transmission link due to multipath propagation, is particularly noticeable by frequency-selective changes in the group delay and the attenuation of the received signal. Depending on the width of the transmitted frequency band, the receiver must therefore detect these changes at several points and feed them to the fault evaluation circuit 5.

Bei Verschlechterung der Qualität des Empfangssignals gibt die Auswerteschaltung 5 einen Steuerimpuls für den Elektromotor 6, der insbesondere als Schrittmotor ausgeführt werden kann, ab. Damit wird der drehbar gelagerte Subreflektor 2 um einen kleinen Winkel verkippt. Die horizontale Drehachse 7 des Subreflektors geht vorzugsweise durch die Aperturmitte, kann aber auch an anderen Stellen des Subreflektors angebracht sein, wenn es aus Platzgründen notwendig ist. Die Verkippung des Subreflektors bewirkt eine Auslenkung der Hauptkeule der Antenne in der Elevationsebene. Wenn sich hierdurch die Empfangsqualität weiter verschlechtert, wird von der Auswerteschaltung 5 eine Subreflektordrehung in entgegengesetzte Richtung veranlaßt. Die Auswerteschaltung arbeitet so in einem Regelkreis, der bestrebt ist, durch Änderung der Winkellage des Subreflektors und der damit verbundenen Auslenkung der Hauptkeule die bestmögliche Empfangsqualität einzustellen.If the quality of the received signal deteriorates, the evaluation circuit 5 emits a control pulse for the electric motor 6, which can be implemented in particular as a stepper motor. So that the rotatably mounted sub-reflector 2 is tilted by a small angle. The horizontal axis of rotation 7 of the sub-reflector preferably passes through the center of the aperture, but can also be attached at other points of the sub-reflector if it is necessary for reasons of space. The tilting of the sub-reflector causes the main lobe of the antenna to deflect in the elevation plane. If the reception quality deteriorates further as a result, the evaluation circuit 5 causes a sub-reflector rotation in the opposite direction. The evaluation circuit thus works in a control loop which strives to set the best possible reception quality by changing the angular position of the sub-reflector and the associated deflection of the main lobe.

Da der Subreflektor eine relativ kleine Masse besitzt, kann er verhältnismäßig schnell bewegt werden. Bei üblichen 3-m-­Richtfunkantennen kommt bei einer Keulenauslenkung 8 von einer Halbwertsbreite ein maximaler Hub des unteren bzw. oberen Randes des Subreflektors von 2 bis 4 cm in Frage. Da sich die auszugleichenden Ausbreitungsbedingungen im Störungsfall nur relativ langsam ändern (Zeiträume von etwa einer Sekunde können noch als stationär angesehen werden), reicht die Geschwindigkeit des Regelkreises, obwohl er mechanisch bewegte Elemente enthält, voll aus. Bei den im Richtfunk eingesetzten großen asymmetrischen Doppelreflektorantennen befindet sich der Subreflektor üblicherweise unter einer Schutzhülle, so daß hier keine besonderen Maßnahmen zum Wetterschutz der Drehlager, Gelenke und des Motors notwendig werden.Since the subreflector has a relatively small mass, it can be moved relatively quickly. In conventional 3-m directional radio antennas, a maximum stroke of the lower or upper edge of the sub-reflector of 2 to 4 cm is possible with a beam deflection 8 of a half-value width. Since the propagation conditions to be compensated only change relatively slowly in the event of a fault (periods of around one second can still be regarded as stationary), the speed of the control loop is sufficient, even though it contains mechanically moved elements. In the large asymmetrical double reflector antennas used in directional radio, the subreflector is usually located under a protective cover, so that no special measures for weather protection of the pivot bearings, joints and the motor are necessary.

Fig. 2 zeigt ein spezielles Ausführungsbeispiel für die Störungsauswerteschaltung 5. Vom Erreger 3 gelangt das empfangene Signal über den Abwärtsmischer 10 zum Zwischenfrequenzverstärker 11. Im Zwischenfrequenzbereich wird die frequenzabhängige Übertragungscharakteristik der Ausbreitungsstrecke durch mindestens drei schmalbandige Bandpaßfilter 12 und Detektoren 13 ermittelt. Der Multi­plexer 14 schaltet die Amplitudenwerte nacheinander über den Analog-Digital-Wandler 15 an den Eingang des Mikrocomputers 16. Bei Überschreitung des eingestellten Schwellenwertes der Dispersion gibt der Mikrocomputer 16 die nötigen Impulse an die Motorsteuerschaltung 17 zur Betätigung des Schrittmotors 6, der dann den Subreflektor dreht. Die Empfindlichkeit des Regelkreises kann durch Überlagerung einer geringfügigen Modulation in Form einer gleichmäßigen Schwingung des Subreflektors erhöht werden.2 shows a special exemplary embodiment of the interference evaluation circuit 5. From the exciter 3, the received signal passes through the down mixer 10 to the intermediate frequency amplifier 11. In the intermediate frequency range, the frequency-dependent transmission characteristic of the propagation path is determined by at least three narrowband bandpass filters 12 and detectors 13. The multiplexer 14 switches the amplitude values one after the other via the analog-digital converter 15 to the input of the microcomputer 16. If the set threshold value of the dispersion is exceeded, the microcomputer 16 gives the necessary pulses to the motor control circuit 17 for actuating the stepping motor 6 then turns the subreflector. The sensitivity of the control loop can be increased by superimposing a slight modulation in the form of a uniform vibration of the sub-reflector.

Da die Subreflektordrehung eine optimale Ausrichtung der Antennenhauptkeule bewirkt, wirkt diese Maßnahme zur Verminderung von Störungen durch Mehrwegeausbreitung sehr breitbandig. Ein Vorteil der Erfindung gegenüber anderen schwundkompensierenden Maßnahmen ist auch darin zu sehen, daß vorhandene Doppelreflektorantennen meist sehr einfach nachgerüstet werden können, ohne daß das Erregersystem ausgetauscht werden muß. Es werden weder eine zweite Antenne noch zusätzliche Erreger oder Empfänger benötigt. Bei einer Auslenkung der Hauptkeule um weniger als zwei Halbwertsbreiten ist keine wesentliche Verschlechterung des Nebenzipelpegels 9 und des Kreuzpolisierungsdiagramm im Vergleich zum ursprünglichen gestörten Signal zu beobachten.Since the subreflector rotation effects an optimal alignment of the main antenna lobe, this measure has a very broadband effect to reduce interference due to multipath propagation. An advantage of the invention over other measures to compensate for loss is also to be seen in the fact that existing double reflector antennas can usually be retrofitted very easily without the excitation system having to be replaced. Neither a second antenna nor additional exciters or receivers are required. If the main lobe is deflected by less than two half-widths, no significant deterioration in the sub-Zipple level 9 and the cross-polarization diagram compared to the original disturbed signal can be observed.

Claims (7)

1. Richtfunkantenne, im wesentlichen bestehend aus einem Hauptreflektor, einem Subreflektor, der um eine horizontale Achse drehbar gelagert ist, einem Hornerreger und einer Störungsauswerteschaltung, dadurch gekennzeichnet, daß in einem Regelkreis das Ausgangssignal der Auswerteschaltung zur Nachsteuerung des Subreflektors derart verwendet wird, daß die Hauptkeule der Antenne zum Ausgleich von Störungen durch Mehrwegeausbreitung um bis zu zwei Halbwertsbreiten in der Elevation ausgelenkt wird.1. microwave antenna, consisting essentially of a main reflector, a subreflector, which is rotatably mounted about a horizontal axis, a horn exciter and a fault evaluation circuit, characterized in that the output signal of the evaluation circuit is used in a control circuit for readjustment of the subreflector so that the Main lobe of the antenna is deflected by up to two half-widths in the elevation to compensate for interference caused by multipath propagation. 2. Richtfunkantenne nach Anspruch 1, dadurch gekennzeichnet, daß die Steuergröße zur Subreflektordrehung aus der selektiven Pegelüberwachung für die adaptive Entzerrung im ZF-Bereich handelsüblicher Richtfunkempfänger gewonnen wird.2. Directional radio antenna according to claim 1, characterized in that the control variable for subreflector rotation is obtained from the selective level monitoring for the adaptive equalization in the IF range of commercially available directional radio receivers. 3. Richtfunkantenne nach Anspruch 1, dadurch gekennzeichnet, daß die Steuergröße zur Subreflektordrehung durch Auswertung der AGC-Spannung in einem oder mehreren benachbarten RF-Kanälen gewonnen wird.3. Directional radio antenna according to claim 1, characterized in that the control variable for subreflector rotation is obtained by evaluating the AGC voltage in one or more adjacent RF channels. 4. Richtfunkantenne nach Anspruch 1, dadurch gekennzeichnet, daß die Steuergröße zur Subreflektordrehung durch Aus­ wertung des Pilottons und/oder des TV-Synchronsignals in einem oder mehrenen benachbarten RF-Kanälen gewonnen wird.4. microwave antenna according to claim 1, characterized in that the control variable for sub-reflector rotation by off evaluation of the pilot tone and / or the TV sync signal is obtained in one or more adjacent RF channels. 5. Richtfunkantenne nach Anspruch 1, dadurch gekennzeichnet, daß die Steuergröße zur Subreflektordrehung durch eine Auswertung des Basisbandsignals, insbesondere aus der Steuergröße eines adaptiven Entzerrers gewonnen wird.5. microwave antenna according to claim 1, characterized in that the control variable for subreflector rotation is obtained by evaluating the baseband signal, in particular from the control variable of an adaptive equalizer. 6. Richtfunkantenne nach vorhergehenden Ansprüchen, dadurch gekennzeichnet, daß der Stellgröße des Subreflektors eine geringe Modulation überlagert wird, durch deren Auswertung sich die Empfindlichkeit und das Ansprechverhalten der Auswerteschaltung verbessern läßt.6. Directional radio antenna according to the preceding claims, characterized in that a slight modulation is superimposed on the manipulated variable of the sub-reflector, by the evaluation of which the sensitivity and the response of the evaluation circuit can be improved. 7. Richtfunkantenne nach vorhergehenden Ansprüchen, dadurch gekennzeichnet, daß die Auswerteschaltung zur Erzeugung des Subbreflektorsteuersignals einen Mikrorechner verwendet, in dem auch Ansprechwellen und Hysterese­verhalten festgelegt werden.7. microwave antenna according to the preceding claims, characterized in that the evaluation circuit for generating the sub-reflector control signal uses a microcomputer in which response waves and hysteresis behavior are also defined.
EP89123081A 1988-12-22 1989-12-14 Directional antenna having an adaptively controlled subreflector Withdrawn EP0374722A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19883843144 DE3843144A1 (en) 1988-12-22 1988-12-22 DIRECTIONAL RADIO ANTENNA WITH ADAPTIVALLY CONTROLLED SUBREFECTOR
DE3843144 1988-12-22

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EP0374722A1 true EP0374722A1 (en) 1990-06-27

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EP89123081A Withdrawn EP0374722A1 (en) 1988-12-22 1989-12-14 Directional antenna having an adaptively controlled subreflector

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EP (1) EP0374722A1 (en)
DE (1) DE3843144A1 (en)
FI (1) FI896177A0 (en)
NO (1) NO895157L (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2553302A (en) * 2016-08-30 2018-03-07 Avanti Communications Group Plc Satellite equipment

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19805625A1 (en) * 1998-02-12 1999-08-19 Sucker Detection of electromagnetic radiation sources within the C or Ku bands for telephone communication satellites

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE705372C (en) * 1934-07-06 1941-04-25 Telefunken Gmbh Maximum direction finder
US2531454A (en) * 1942-02-04 1950-11-28 Sperry Corp Directive antenna structure
US3882503A (en) * 1960-08-17 1975-05-06 Gte Sylvania Inc Wave detection apparatus
DE2555872A1 (en) * 1974-12-12 1976-06-16 Westinghouse Electric Corp ANTENNA CONTROL AND REGULATING DEVICE
GB2088173A (en) * 1980-11-25 1982-06-03 Rca Corp Apparatus for automatically steering an electrically steerable television antenna

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE705372C (en) * 1934-07-06 1941-04-25 Telefunken Gmbh Maximum direction finder
US2531454A (en) * 1942-02-04 1950-11-28 Sperry Corp Directive antenna structure
US3882503A (en) * 1960-08-17 1975-05-06 Gte Sylvania Inc Wave detection apparatus
DE2555872A1 (en) * 1974-12-12 1976-06-16 Westinghouse Electric Corp ANTENNA CONTROL AND REGULATING DEVICE
GB2088173A (en) * 1980-11-25 1982-06-03 Rca Corp Apparatus for automatically steering an electrically steerable television antenna

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2553302A (en) * 2016-08-30 2018-03-07 Avanti Communications Group Plc Satellite equipment

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NO895157L (en) 1990-06-25
NO895157D0 (en) 1989-12-20
DE3843144A1 (en) 1990-06-28
FI896177A0 (en) 1989-12-21

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