WO1999004451A1

WO1999004451A1 - Satellite recognizer system

Info

Publication number: WO1999004451A1
Application number: PCT/IL1997/000242
Authority: WO
Inventors: Israel Koffman; Erez Shabirow
Original assignee: Orbit Communications, Tracking And Telemetry Ltd.
Priority date: 1997-07-16
Filing date: 1997-07-16
Publication date: 1999-01-28
Also published as: AU3458097A

Abstract

A satellite system for a receiver installed on a mobile platform, to point a receiver antenna towards a transmitting satellite, comprising a directional antenna mounted on a positioner. The positioner points the antenna in a desired direction. A satellite receiver includes means for measuring the parameters of the signals. A controller is connected to the receiver and positioner, to control the receiver and positioner. A method for satellite detection, signal measurement and satellite authentication in a satellite tracking receiver installed on a mobile platform, comprising the steps of: A) Choose satellite to receive (2) and prepare receiver and antenna for satellite search; B) perform satellite (2) detection, by performing a scan in azimuth until a signal is received from satellite (2), so that during the scan, the azimuth angle (33) is changed while elevation angle (34) is kept constant; C) measure the parameters of the received signals; and D) perform satellite authentication, by comparing the known characteristics of satellite (2) determined in step A) with the results of measurements in step C).

Description

Satellite Recognizer System

Technical Field

The present invention concerns systems for pointing a receiver antenna towards a transmitting satellite

The invention relates in particular to such systems in which the receiver is mounted on a mobile platform, and wherein the orientation of the receiver platform is determined from the signals received from a satellite

Background Art

At present, to receive a specific satellite program, it is required to know the location of the receiver platform This information is then used to compute the direction in space to a satellite which is transmitting the desired program The receiver antenna can then be set to point in that direction, towards that satellite

The information regarding the direction to satellite includes the azimuth and elevation angles The azimuth angle to satellite is relative to North, and the elevation angle is relative to the local horizontal plane. The mobile receiver platform may include, for example, a railway tram, a ship, a car, an airplane or any mobile means of transportation. The antenna elevation angle is simply the vertical angle to a horizontal plane.

To point the antenna in azimuth, however, there is required additional information, that is the orientation of the receiver platform relative to North. This is required since the angle of the receiver antenna can be only set relative to the platform the antenna positioner is mounted thereon, whereas the direction to satellite is relative to the North

Whereas the location of the receiver platform can be found with relative ease, for example using the GPS system, the orientation of the receiver platform is more difficult to find

A compass can be used as known in the art, however this method may be ineffective if there are large metallic/ferromagnetic parts, as can be found in the structure of a ship or train. These parts create a disturbance in the terrestrial magnetic field, and the compass reading is erroneous.

Other factors may interfere with the compass, like strong electrical currents, electrical motors and transformers.

There may also be other considerations, like the high cost of a compass connected to the satellite receiver, or that of having to interface with systems in the train or the ship. Thus, there is a requirement for means to find the orientation of the platform the receiver antenna is mounted thereon. Throughout the present disclosure, the terms "orientation" and "angle to North" are used interchangeably, and are considered to have the same meaning.

Disclosure of Invention

It is an object of the present invention to provide a satellite receiver with means for measuring the orientation of the receiver platform according to signals from the satellite.

This object is achieved by a receiver as disclosed in claim 1 .

In accordance with the invention, the object is basically accomplished by setting the receiver antenna in the required elevation angle, and performing a scan in azimuth, until the signal from the satellite is received. The difference between the expected angle to satellite relative to North, and the azimuth angle of the receiver antenna, gives the orientation of the receiver platform.

It is another object of the present invention to provide means for resolving the ambiguity in finding the orientation of the receiver platform, in case several satellites are received. The object is achieved with the inclusion in the receiver of means for measuring the various parameters of the satellite signal, and controller with means for using these parameters to distinguish the desired satellite.

Furthermore, a novel procedure for a computer-controlled antenna scan is disclosed, to detect and recognize the desired satellite. A two-step method is disclosed, for fast antenna pointing toward the satellite and subsequent precise satellite tracking, to maximize the signal strength or the signal to noise ratio.

Another object of the invention is to provide for a satellite receiver adapted for efficient operation with a digital controller.

Thus, the receiver includes means for communication with the controller, a writtable memory means for storing parameters so that there is no need to repeatedly send these parameters from controller, and means for accepting and executing commands from controller, commands relating to the operation of the receiver.

Brief Description of Drawings

The invention will now be described by way of example and with reference to the accompanying drawings in which: Fig. 1 illustrates the spatial geometry of receiver antenna and satellite.

Fig. 2 depicts a functional diagram of the system for satellite signal reception and for finding the orientation of the receiver platform.

Fig. 3 details the structure and operation of the satellite receiver with means for signal reception and measurement and including means for remote computer control.

Modes for Carrying Out the Invention

Fig. 1 depicts the space geometry of receiver antenna 3 pointing towards transmitting satellite 2. This is the desired situation, to allow the directional antenna 3 to receive the maximal signal from satellite 2, to allow the best reception of the satellite program.

The receiving antenna 3 is directional, having a maximum reception gain in a direction corresponding to direction vector 31 , which it is desired to point towards satellite 2.

The space angle of antenna 3 comprises the angles of azimuth, elevation and polarization. The receiver, on a mobile platform, may be located anywhere on planet earth, that is the globe 1. At any specific location thereof, there is a local horizontal plane 11 - that is, horizontal at that location, or tangential to the surface of planet earth 1 at that location. The local plane 11 coincides with the receiver system platform, that is the platform the receiver and the antenna positioner mounted thereon.

Thus, the elevation angle 34 of antenna 3 is the vertical angle between plane 11 and direction vector 31 to satellite 2.

Accordingly, the azimuth angle 33 is defined as the angle on plane 11 , between projection 32 of vector 31 on plane 11 , and the North direction 12, also on plane 11 . The North direction 12, is the local North, on horizontal local plane 11 .

If antenna 3 performs a scan in azimuth (about a vertical axis) by changing the azimuth angle 33, while keeping the elevation angle 34 at a fixed value, then the direction vector 31 describes a circular path 36 in space, as detailed in Fig. 1 . This type of antenna scan is used to detect and identify a satellite, are detailed below.

Moreover, this scan allows for measuring the orientation of the receiver platform according to signals from the satellite 2. This object is basically accomplished by setting the receiver antenna 3 in the required elevation angle 34, and performing a scan in azimuth, until the signal from the satellite 2 is received. The difference between the expected angle to satellite relative to North, and the azimuth angle 33 of the receiver antenna, gives the orientation of the receiver platform.

The methods for use of the computer-controlled satellite receiver are now disclosed at the system level, as abbreviated Methods 1 through 3. A detailed description of these methods is included below, with reference to the block diagram functional description in Fig. 2. The stages in the abbreviated procedures include references to the detailed procedures, to be described later on in the application.

Method 1 (abbreviated)

An exemplary algorithm for implementing the method for satellite detection, signal measurement and satellite authentication according to the present invention comprises the following steps:

1. Choose satellite to receive 2, compute direction and parameters of that satellite (direction including azimuth angle 33 and elevation angle 34); prepare receiver and antenna for satellite search (detailed below as steps A - E in detailed Method 1 ); 2. Satellite 2 detection, by performing a scan in azimuth until a signal is received from satellite 2. During the scan, the azimuth angle 33 is changed while elevation angle 34 is kept constant, so that the direction vector 31 describes a circular path 36 in space; path 36 includes the satellite 2 thereon, so that eventually antenna 3 points towards satellite 2. This event is recognized by the satellite signal being detected in the satellite receiver (detailed as steps F - G below) .

The antenna scan in azimuth is then stopped, so the antenna remains pointing towards the satellite;

3. Measurement of received signals (detailed as steps H - I below); and

4. Satellite authentication, by comparing the known characteristics of satellite 2 determined in step (1 ) with the results of measurements in step (3) (detailed as step J below) .

Method 2 (abbreviated)

An algorithm for implementing the method for measuring the orientation of the receiver platform comprises the following steps:

1 . Choose satellite to receive 2, compute direction and parameters of that satellite (direction including azimuth angle 33 and elevation angle 34); prepare receiver and antenna for satellite search (detailed below as steps A - B in detailed Method 2);

2. Satellite 2 detection, by performing a scan in azimuth until a signal is received from satellite 2; signal measurement and satellite authentication (detailed as step C below); and

3. Compute the orientation of the platform, from the expected direction of satellite (azimuth to North, angle 33) and the actual azimuth angle of antenna 3 relative to positioner (detailed as step D below).

Method 3 (abbreviated)

An exemplary algorithm for implementing a two-step method for pointing a receiver antenna towards a satellite according to the present invention comprises the following steps:

1 . Point the antenna in the expected direction of the chosen satellite, wherein the expected direction is computed from the known location of satellite and receiving platform, and the known orientation of the receiving platform (detailed as steps A - F in detailed Method 3 below) ; and 2. perform fine adjustments of the antenna direction and track the satellite, by initiating antenna 3 scan about the direction vector 31 to satellite 2, and analyzing the measurements on the signals received from satellite (detailed as step G below).

Fig. 2 details the functional description for a satellite recognizer receiver, with receiver antenna 3 pointing in the spatial direction vector of reception 31 , that is the direction to a satellite (not shown) . Vector 31 is the space direction of maximum reception of antenna 3, or the main lobe of directional antenna 3.

The positioner 38 is a device for pointing the reception vector 31 of antenna 3 in any desired direction, within set limits, and according to commands from a controller 5, through an input channel 522. Channel 522 is used to transfer commands to antenna positioner 38 regarding the azimuth and elevation angles required of antenna 3.

Optionally, channel 522 may also be used to convey to controller 5 information regarding the actual, instantaneous angles of antenna 3, as well as additional information, like status from limit switches. Commands setting the polarization of antenna 3 may be issued (not shown) either by controller 5 through channel 522, or by receiver 4. The actual implementation depends on the specific embodiment for antenna 3 and positioner 38. Receiver means 4 receives signals from antenna 3 through RF input channel 41 1. Usually, antenna 3 has a LNA (low noise amplifier) attached thereto, or a LNB (low noise block, including antenna feeder and LNA) . Receiver 4 includes means (not shown) for receiving signals, amplification, video/audio detection, and measurement of signal parameters like signal strength and signal to noise ratio.

Receiver means 4 is computer controlled, according to input control signals from controller 5, through input channel 471 . That is, the information pertaining to a plurality of channels can be programmed into receiver 4, including for each channel: the frequency, polarity, bandwidth, frequency of the audio subcarrier. In other embodiments, additional information may be included, and/or part of the above items may be discarded, without departing from the spirit and scope of the present invention.

Additionally, output channel 472 is used to send status and reception-related data like result of measurements performed on the received signals, from receiver 4 to controller 5.

Controller means 5 receives user's commands through channel 531 , sends reception status back through channel 532. Channel 531 may include, for example, a keyboard or pushbuttons or a sensitive display or other means sensitive to input from the user. Channel 532 may include a display or status lights or a combination thereof, or other means for conveying information to the user.

Controller 5 controls the direction of antenna 3 by sending control signals to positioner 38 and receiving information on antenna angle, through channel 522.

Serial or parallel means may be used in channel 522. The embodiment preferably includes serial means which have lower cost and are more reliable), for example RS-232C.

Controller 5 computes direction to satellite using either information relating to the location of the satellite (not shown) together with the receiving platform location and orientation, and/or signals from receiver 4 versus space angle of antenna 3. These means are used to detect, identify and continuously track the satellite. Methods for satellite tracking and for the determination of receiving platform orientation are detailed below.

Location information is input to controller 5 through channel 551 . This may include information from the global positioning system GPS, or other automatic or manual means for location determination.

Receiver 4 extracts the information in the RF input channel 41 1 , that is the video and/or audio, and outputs it as electrical signals on video output channel 431 and audio output channel 441 to user. This is the ultimate purpose of the system - to receive and provide to user the signals received from a satellite.

Methods for utilizing the abovedetailed receiver system, including receiver means 4, controller 5 and positioner 38 will now be disclosed. These methods detail, at the block diagram level, the abbreviated methods disclosed above at the system level.

Method 1 (detailed)

A. controller 5 accepts user's commands, like the desired TV program, via inputs 531 and the present location through channel 551 ;

B. controller 5 chooses, from the information stored therein, a satellite which it is desirable to receive;

C. the information pertaining to the satellite chosen in step (B) above is sent from controller 5 to receiver 4 to be stored therein, through channel 471 . The information may include, for each of a plurality of channels pertaining to that satellite, the frequency, polarity, bandwidth, frequency of the audio subcarrier. This comprises the programmed channel information;

D. controller 5 sets receiver 4 to one of the programmed channels;

E. positioner 38 is set so that the direction vector 31 of antenna 3 corresponds to the direction to satellite: the azimuth is set to an arbitrary angle, and the elevation is set to the expected angle of elevation of the chosen satellite;

F. controller 5 controls positioner 38 to perform a scan in azimuth, while continuously monitoring the receiver 4 for any signal detected, and positioner 38 for the completion of a complete, 360 degrees, scan in azimuth. If a signal was detected, then stop the antenna scan;

G. if a complete scan was performed - set receiver 4 to another of the programmed channels, and try again - go to step E above, for another scan in azimuth, if all the programmed channel were tried- then the receiver cannot be pointed to that chosen satellite;

H. if receiver 4 indicates there is a received signal - then perform signal measurements. Receiver 4 sends to controller 5, through channel 472, the results of the measurement; I. controller 5 directs the receiver 4 to switch to another of the programmed channels, and to repeat the measurements; this is repeated for several channels, for example 10 of the active channels for that satellite; and

J. controller 5 decides, according to the measurements performed on several of the active channels, whether the results correspond to the chosen satellite. If yes- this is a positive identification of the satellite, and then controller 5 keeps the antenna 3 pointed towards that satellite. This is the satellite authentication state. If negative- then go to step F, continue scan in azimuth.

Thus, the receiver structure detailed above, and the abovedetailed method of its use, provide means for detecting a satellite even though the orientation of the receiving platform may not be known. It also provides means for identifying the satellite according to its transmitted channels, to ensure that the desired satellite was detected. This may also resolve the ambiguity in finding the orientation of the receiver platform, in case several satellites are received.

In another embodiment of Method 1 , in step (B) the controller 5 is provided in real time with the information regarding a satellite which it is required to receive. In another embodiment of Method 1 , in step (C), the information pertaining to the satellite chosen in step (B) is sent to receiver 4 by the user, in real time (not a stored information).

An optional addition to step (J) of satellite authentication, may include an antenna scan in elevation about the direction of the satellite under evaluation. This is to ensure that the satellite was received in the main lobe of the antenna, in which case the maximum reception signal strength will be in a direction about that of the antenna prior to scan.

If this condition is not met, then the signal received may correspond to a satellite in another direction, received through a sidelobe of the receiver antenna. The scan may be performed both in azimuth and elevation but, since the satellite under evaluation was arrived at during a scan in azimuth, with the antenna pointing in the direction of maximum received signal strength, a further scan in azimuth is deemed unnecessary.

Method 2 (detailed)

B. controller 5 chooses, from the information stored therein, a satellite which it is desirable to receive. The information includes, inter alia, the azimuth direction to the satellite, that is the horizontal direction relative to North;

C. the controller 5 performs signal detection, satellite identification and enters the satellite authentication state, according to Method 1 above; and

D. the present horizontal angle of positioner 38 is subtracted from the expected azimuth to North of the chosen satellite. The difference is the orientation coefficient K, used to translate between angle to North and angle of antenna 3 relative to positioner 38.

Advantages of the method:

1 . The coefficient K is actually indicative of the orientation of the receiving platform. It is equal to the angle to North of the antenna, while the positioner 38 is at angle zero.

2. Using this orientation information, it is possible to point the antenna 3 directly to any desired satellite: controller 5 directly computes the azimuth (to North) and elevation angles, and then the azimuth angle of antenna relative to positioner 38.

Method 3 (detailed)

A. controller 5 accepts user's commands via inputs 531 and the present location through channel 551 ;

C. the information pertaining to the satellite chosen in step (B) above is sent from controller 5 to receiver 4 to be stored therein, through channel 471 . The information includes, for each of a plurality of channels pertaining to that satellite, the frequency, polarity, bandwidth, frequency of the audio subcarrier. This comprises the programmed channel information; D. controller 5 computes the azimuth angle of antenna 3 relative to positioner 38 , using the orientation method detailed in Method 2 above;

E. antenna 3 is set to point towards the desired satellite, in the direction with elevation angle as found in step (B), and azimuth angle as computed in step (D);

F. satellite identification/authentication is performed, according to the method detailed in Method 2 above. This ends the first step, of coarse antenna pointing toward the satellite; and

G. controller 5 initiates small deviations in the azimuth and elevation of antenna 3, and monitors the signal strength results in receiver 4. The axis of the antenna 3, or the mean value of the antenna direction, is brought to the direction which maximizes the signal strength.

In another embodiment of step (G) above, the measured signal to noise ratio (SNR) can be used in lieu of the signal strength. In still another embodiment, a combination thereof may be used, with signal strength being used for the initial antenna direction, and signal to noise ratio for fine tuning, in the final stage, and for continuous satellite tracking thereafter. Advantages of this method:

1 . It achieves both a fast method for pointing the antenna, and also a precise pointing result. The antenna is brought in a short time in the direction of the satellite, making the most from the available information regarding the satellite location, the platform location and orientation. Then tracking is achieved using the information from the received signal itself

2. Use of signal strength or signal to noise measurement can achieve the best quality picture which is possible. This is the preferred criterion for directing the antenna, to optimize the benefit to user.

Thus, a novel procedure for a computer-controlled antenna scan was disclosed, to detect and recognize the desired satellite. A two-step method was disclosed, for fast antenna pointing toward the satellite and subsequent precise satellite tracking, to achieve a good signal strength and/or signal to noise ratio.

Referring to Fig. 3, RF front end 41 receives the input signal from satellite (not shown) through RF input channel 41 1 . The RF signal arrives from a (not shown) LNB or LNA, or directly from the antenna. Low Noise Amplifier LNA or Low Noise Block LNB include amplifier means close to the antenna, to improve the signal to noise ratio of the system, as known in the art.

The front end 41 performs receiver functions as known in the art, and outputs the baseband video and/or audio signals to units 42, 43 and 44, as detailed below. Usually, the detection of the video/audio signals is performed by an FM demodulator included in the receiver.

Measuring unit 42 automatically performs various measurements on the received baseband signal, and outputs the results to processor 47. These are then transferred to a controller (not shown) through channel 472, to allow the abovedetailed satellite detection and authentication processes.

The measurements results may include the signal strength or input signal level, the video signal to noise ratio, presence of video signal (a logic signal, indicating for example the presence of a video signal with a logic "1 " in positive logic), the presence of an audio signal (a digital signal as well). Other parameters of the received signal may be used, without departing from the scope of the present invention.

Signal level and signal to noise ratio are preferably measured on a logarithmic scale, with results preferably in decibels (dB). This allows for efficient measurement, transmission of results and information evaluation in the controller. The logic signals for video/audio presence allow the controller to act fast, being given a clear, immediate indication of a reception from satellite and the type of that reception This facilitates the fast performance of the procedures for satellite detection and authentication as detailed above

The signal to noise ratio may be measured, for example, using samples during the synchronization intervals, where specific fixed levels for black or white are expected Any variations on these levels indicate noise

For the analog variables like signal strength and signal to noise ratio, both a digital and an analog output (not shown) may be included This allows the receiver to be used with various types of controllers, both those utilizing analog inputs as well as controllers using digital signals So, a truly modular system is achieved

Video signal processing unit 43 automatically corrects the video signal according to commands from automatic signal level and polarity setting unit 45 Unit 45 detects the polarity of the video signal and initiates a correction in unit 43, so that the output video signal 431 delivered to user will always have a positive polarity

Additionally, baseband and video signals undergo an automatic gain control, also in units 43 and 45, for automatic signal level stabilization Audio signal processing unit 44 extracts the audio signal which is available as a subcarrier of the baseband video signal. The audio is output to user through audio output channel 441.

The processor means 47 controls the operation of the receiver units, and communicates with an external controller (not shown). Processor 47 includes a (not shown) central processing unit, input/output means for interfacing with other devices, and memory means for storing the microprocessor programs and the programmed channels.

Input channel 471 is used by processor 47 to receive commands and parameters from a controller (not shown) . The parameters may include information for the channels to program in the receiver. Each programmed channel may include data for an arbitrarily chosen satellite channel, like its frequency, polarity, type of signal (video/audio) , location of audio subcarrier (distance in frequency from carrier), bandwidth of IF.

A command from the controller (not shown) may include a request to activate a specific programmed channel, in which case the parameters for that channel are transferred from processor 47 to RF front end 41 , to tune to that channel.

One parameter is the receive frequency, which in the present embodiment is in the range 920 to 2050 MHz. An additional parameter for each channel is the intermediate frequency (IF) bandwidth In a preferred embodiment, the bandwidth is either 27 MHz or 18 M Hz

A third parameter may be the audio subcarrier frequency, in a range which may be within 5 5 to 8 5 M Hz

Another parameter, the polarity of the received signal, results in a command to power supply means 46, which receives electrical power through channel 461 and generates all the electrical voltages like 461 , 462, 463, 464 as required for the receiver units One of these voltages, output 464, is delivered to the LNB unit to control the polarity of the received signal In one embodiment of the invention, one of two values 13 V/18 V determines the polarity to be vertical or horizontal , respectively

The output channel 472 is used to send status and reception-related data from processor 47 to a controller (not shown) These may include the presence of video/audio signals, signal strength , signal to noise ratio

RF test generator 48 is used for self-diagnostics or self-test It can generate, as required by the user through channel 471 or as part of routine self-tests on power-up , various signals including a color bar or an RF signal with emphasis and triangular The test results may be sent back via output channel 472 The 22 kHz generator 49 is used to generate that signal, which is transferred to the RF unit 41 , and under control of processor 47.

Thus, the satellite receiver is adapted for efficient operation with a digital controller. The receiver includes means in processor 47 for communication with controller through channels 471 and 472, a writtable memory means in processor 47 for storing parameters so that there is no need to repeatedly send these parameters from controller, and means in processor 47 for accepting and executing commands from controller, commands relating to the operation of the receiver

The memory (not shown) in processor 47 is adapted for storing information for a plurality of satellite channels

Various embodiments and applications and will occur to persons skilled in the art upon reading the above disclosure

For example, although the invention details a method to find the orientation of the receiver platform, it is also possible to find the location of the platform, if movement is constrained to a predefined path, like a railway train in a specific course. In that case, the path can be stored in the controller's memory, to include the location and orientation in specific increments i (1 to n), say each 10 km apart. While the platform is at any location, the controller assumes the location to be that of i, chooses a satellite to be found there and initiates the satellite detection and authentication procedure per Method 1 . If the procedure achieves a successful result (a satellite with the expected parameters is found) then the location corresponds to the assumed location. If not, the next location is tried , and the next, until a match is found This corresponds to the actual location of the platform on the a priori known path.

The method can be refined to include interpolation calculations, in case the satellite was received at a direction close to, although not precisely equal to, the expected value.

Although the invention has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the application of the principles of the invention Numerous modifications may be made therein and other arrangements may be devised without departing from the spirit and scope of the invention.

Claims

1. A satellite tracking system for a receiver installed on a mobile platform, to point a receiver antenna towards a transmitting satellite, comprising:

(A) a directional receiver antenna for receiving signals transmitted as radio waves from said satellite, mounted on a positioner, said positioner including means for pointing said antenna in a desired azimuth and elevation angle relative to said mobile platform, according to input control signals;

(B) satellite receiver means connected to said antenna and including: RF front end for processing said received signals, video and/or audio detector means for extracting the information in said signals received from said satellite, and means for measuring the parameters of said received signals, wherein the frequency and channel and related parameters of said receiver are programmable through a control input; and

(C) controller means connected to said receiver and said positioner, and including means for receiving user's commands and data, means for controlling said receiver parameters, means for processing said results of measurements on said signals, and means for controlling said azimuth and elevation angle of said positioner according to said user's commands and said measurement results.

2. The satellite tracking system for a receiver according to claim 1 , wherein said programmable parameters of the receiver include the frequency, polarity, bandwidth and/or the frequency of the audio subcarrier.

3. The satellite tracking system for a receiver according to claim 1 , wherein said means for measuring the received signal include means for measuring the signal strength and/or signal to noise ratio, and means for detecting the presence of video or audio within the received channel

4. The satellite tracking system for a receiver according to claim 1 , wherein said controller means further includes memory means for storing receiver parameters for a plurality of channels, wherein said parameters for each programmed channel may include data for an arbitrarily chosen satellite channel, like its frequency, polarity, type of signal (video/audio), location of audio subcarrier (distance in frequency from carrier) , bandwidth of IF.

5. A method for satellite detection, signal measurement and satellite authentication in a satellite tracking receiver installed on a mobile platform, comprising the steps of:

(A) Choose satellite to receive 2, compute direction and parameters of the satellite, and prepare receiver and antenna for satellite search, wherein said direction includes the azimuth angle 33 and elevation angle 34; (B) perform satellite 2 detection, by performing a scan in azimuth until a signal is received from satellite 2, so that during the scan, the azimuth angle 33 is changed while elevation angle 34 is kept constant, so that the direction vector 31 describes a circular path 36 in space; path 36 includes the satellite 2 thereon, so that eventually antenna 3 points towards satellite 2, and this event is recognized by the satellite signal being detected in the satellite receiver, and the azimuth scan is then stopped, so that the antenna points towards the satellite;

(C) Measure the parameters of the received signals; and

(D) perform satellite authentication, by comparing the known characteristics of satellite 2 determined in step (A) with the results of measurements in step (C)

6. The method for satellite detection according to claim 5, further including, after step (D) , the following step

(E) compute the orientation of the mobile platform, from the expected direction of satellite (azimuth to North, angle 33) and the actual azimuth angle of antenna 3 relative to positioner

7. The method for satellite detection according to claim 5, further including, after step (D) , the following step.

(E2) perform fine adjustments of the antenna direction and track the satellite, by initiating antenna 3 scan about the direction vector 31 to satellite 2, and analyzing the measurements on the signals received from satellite, so that the center of the scan corresponds to maximum received signal strength or maximum signal to noise ratio

8. A method for satel lite detection, signal measurement and satellite authentication in a satellite tracking receiver installed on a mobile platform, comprising the steps of

A. controller 5 accepts user's commands, like the desired TV program, via inputs 531 and the present location through channel 551 ,

B. controller 5 chooses, from the information stored therein, a satellite which it is desirable to receive,

C. the information pertaining to the satellite chosen in step (B) above is sent from controller 5 to receiver 4 to be stored therein, through channel 471 . The information may include, for each of a plurality of channels pertaining to that satellite, the frequency, polarity, bandwidth, frequency of the audio subcarrier This comprises the programmed channel information, D. controller 5 sets receiver 4 to one of the programmed channels;

F. controller 5 controls positioner 38 to perform a scan in azimuth, while continuously monitoring the receiver 4 for any signal detected, and positioner 38 for the completion of a complete, 360 degrees, scan in azimuth. If a signal was detected, then stop the antenna scan,

H. if receiver 4 indicates there is a received signal - then perform signal measurements. Receiver 4 sends to controller 5, through channel 472, the results of the measurement;

I. controller 5 directs the receiver 4 to switch to another of the programmed channels, and to repeat the measurements; this is repeated for several channels, for example 10 of the active channels for that satellite; and J. controller 5 decides, according to the measurements performed on several of the active channels, whether the results correspond to the chosen satellite. If yes- this is a positive identification of the satellite, and then controller 5 keeps the antenna 3 pointed towards that satellite. This is the satellite authentication state If negative- then go to step F, continue scan in azimuth

9. The method for satellite detection according to claim 8, wherein in stage (B) said controller 5 may choose a satellite which it is desirable to receive, either from the information stored therein, or according to a command received in real time from the user

10. The method for satellite detection according to claim 8, wherein in stage (C), said information pertaining to the satellite chosen in step (B) above is sent to receiver 4 either from controller 5, or according to a command received in real time from the user, and wherein said information may include, for a plurality of channels pertaining to that satellite, the frequency, polarity, bandwidth, frequency of the audio subcarrier This comprises the programmed channel information