Patent Grant
7123876
1. Field of the Invention
The invention relates to vehicle mounted satellite antennae. More particularly, the invention relates to a vehicle mounted satellite antenna which is easy to install, has a low profile, and which is operable while the vehicle is in motion.
2. State of the Art
It has long been known to mount a satellite antenna (dish) atop a vehicle for purposes of communicating with a geostationary or other type of satellite. The initial applications for mounting a satellite dish on a vehicle were military communication and remote television news broadcasting. Consequently, the first methods of mounting a satellite dish included a telescoping mast which was hingedly coupled to the vehicle. When the vehicle was in motion, the mast would be retracted and folded with the satellite dish lying end up on the roof or a side wall of the vehicle. The dish would be deployed only when the vehicle was stationary. Such a deployable vehicle mounted satellite dish is disclosed in U.S. Pat. No. 5,961,092 to Coffield. Until recently, no vehicle mounted satellite antennae were operable while the vehicle was in motion. The relatively large size of a conventional satellite dish antenna presents significant wind resistance if deployed on a vehicle in motion. This wind resistance adversely affects the operation of the vehicle and subjects the satellite dish to potential wind damage. Moreover, satellite dishes must be accurately aimed at a satellite within a relatively narrow aperture or “look window”. In order to operate a satellite dish mounted on a vehicle in motion, it would be necessary to constantly re-aim the dish in order to maintain communication with the satellite.
Recently, satellite antennae have been developed which may be deployed on a vehicle and operated while the vehicle is in motion. Such antennae are disclosed in U.S. Pat. No. 5,398,035 to Densmore et al., U.S. Pat. No. 5,982,333 to Stillinger, and U.S. Pat. No. 6,049,306 to Amarillas. These antenna systems generally include a satellite antenna of reduced size and a solenoid system for aiming the antenna. The solenoid system is coupled to a feedback system and/or vehicle motion detectors in order to automatically re-aim the antenna as the vehicle is in motion. In order to reduce aerodynamic drag and protect the antenna from wind damage, an aerodynamic radome is often used to cover the antenna.
Vehicle mounted satellite antennae which are operable while the vehicle is in motion, can provide one-way or two-way satellite communications. Some applications for such antennae include satellite television reception, telephony in remote locations where cellular telephone service is unavailable, and broadband data communications. The application of television reception may be advantageously applied in common carrier transportation such as long distance buses, in recreational vehicles including boats, and in the rear seats of family mini-vans. The application of remote telephony may be applied in the same situations as well as in various other governmental and commercial settings. The application of broadband data communication may also be applied in many personal, commercial, and governmental settings.
Broadband satellite communication, such as television reception or broadband data communication, requires a high gain antenna with high cross-polarization isolation and low signal sidelobes. Satellite antenna gain is proportional to the aperture area of the reflector. Stationary satellite antennae typically utilize a circular parabolic reflector. Satellite antennae designed for use on a moving vehicle have a low profile. In order to maintain gain, these low profile antenna are short but wide so that the overall aperture area is kept high. However, this design strategy only works to a point. When the width to height ratio exceeds a certain value such as 2, the efficiency of the antenna is adversely affected. The presently available vehicle mountable satellite antenna for commercial and personal use are no shorter than approximately fifteen inches in height.
In addition to the issue of providing low profile tracking antennae, the process of installing a satellite antenna on a vehicle is not trivial. Holes must be drilled through the roof (or body panel) of the vehicle; coaxial cable must be routed from the antenna to a receiver or transceiver; and power cables must be routed to the antenna's tracking system. The installation process is therefore time consuming and costly.
It is therefore an object of the invention to provide a vehicle mountable satellite antenna.
It is also an object of the invention to provide a vehicle mounted satellite antenna which is operable while the vehicle is in motion.
It is another object of the invention to provide a vehicle mounted satellite antenna which has a low profile.
It is also an object of the invention to provide a vehicle mounted satellite antenna which has high gain.
It is another object of the invention to provide a vehicle mounted satellite antenna which has high efficiency.
It is still another object of the invention to provide a vehicle mountable satellite antenna which is easy to install.
In accord with these objects which will be discussed in detail below, the satellite antenna of the present invention includes two low profile paraboloid linear reflector antenna assemblies mounted on a rotatable platform which is rotatably coupled to a base plate. Each antenna assembly is provided with two sub-reflectors with a plastic matching element between them. The two antenna assemblies are mounted parallel to each other and are pivotable relative to the rotatable platform. A first servo motor is coupled to the rotatable platform for azimuth tracking. A second servo motor is coupled by a rigid arm to both antenna assemblies for elevation tracking. The two antennae assemblies are each provided with a line feed for receiving a polarized satellite signal. A number of slot antenna probes are located in the back of each antenna assembly. The signal is coupled from the slot antenna into a microwave PCB or waveguide in the back of each antenna. The antenna probes are attached to a microwave circuit board, where two orthogonal linearly polarized signals are extracted. The two linearly polarized signals are fed into a 90° hybrid and two circularly polarized signals are extracted. The signals of the same circular polarization from the same antenna assembly are amplified and combined into a single signal in a beam forming network (BFN) circuit on the microwave PCB.
In order to correct for time delay difference in the signals received by the two antenna assemblies, a phase shifter is employed to correct for the phase shift for the signal received from one antenna before it is combined with the other antenna. A unique feature of this antenna design is that only one phase shifter is required, thereby achieving a very low cost design as compared to the conventional phased array antenna implementation which typically requires a large number of phase shifters.
According to an alternate embodiment, the backside of each antenna dish is provided with a rectangular wave guide structure with a step tooth polarizer stud in the middle of the wave guide. The polarizer stud within the rectangular wave guide converts the signal from linear polarization to circular polarization. Each antenna contains two rows of multiple antenna feeds distributed over the entire length of the antenna. The upper row of antenna feeds extracts a (left or right) circularly polarized signal and the lower row of antenna feeds extracts a (right or left) circularly polarized signal. Each row of antenna feeds is connected via a circuit board or wave guide to a beam forming network (BFN) where signals are amplified and combined into a single signal. The output of one of the BFNs is connected to the input of a phase shifter via a flexible coaxial cable. The output of the other BFN is connected to either an attenuator or an amplifier (depending on whether the phase shifter amplifies or attenuates the other signal) and then to one input port of a two-to-one combiner via a flexible coaxial cable. The output of the phase shifter is connected to the other input port of the combiner. The amplifier or attenuator is used to amplify or attenuate the signal by the same amount as the gain or loss of the phase shifter so that the power of the signals from both BFN's are equal before they are combined.
Dividing the antenna physical aperture into two or more paraboloid linear dishes reduces the overall height of the antenna array by half. Providing each cylindrical dish with multiple feeds instead of single feed maintains the overall antenna efficiency.
The combined signal from the two paraboloid linear antennae is routed through a rotary joint, which routes the received signal to circuits located under the rotatable platform but above the base plate. According to the preferred embodiment of the invention, the circuits between the rotatable platform and the base plate include a re-transmitter for transmitting received satellite signals (at a longer wavelength) to a first receiver inside the vehicle. A second receiver is also preferably provided on the base plate. According to one embodiment of the invention, the second receiver is used to receive channel selection signals and other control signals transmitted by a transmitter inside the vehicle. According to another embodiment, a transceiver is used at the base plate to provide two-way wireless communication with equipment, such as telephones and computers, through another transceiver inside the vehicle.
The use of the re-transmitter and second receiver between the rotatable platform and the base plate eliminates the need for signal wiring between the antennae assembly and the interior of the vehicle. According to a preferred embodiment of the invention, an independent power supply is also provided between the rotatable platform and the base plate to eliminate the need for power wiring between the antennae assembly and the interior of the vehicle. According to one preferred embodiment, the independent power supply includes a storage device such as a battery or a coil and a charging device such as a wind powered generator. A solar cell array may also be used as a charging device.
According to other aspects of the invention, electronic dithering systems are used to track a satellite quickly while a vehicle is in motion. Methods are also provided for adjusting the bias of motion sensors via the use of longitudinal and lateral accelerometers. Methods are also provided for receiving either circularly polarized or linearly polarized signals. According to one embodiment of the invention, the “data port” of a conventional satellite receiver settop box is used determine the appropriate phase shift in the antennae array for a selected channel.
According to another aspect of the invention, the antenna system is provided with a retractable radome. When the antenna is not in use, the two cylindrical dishes are aimed straight up, decreasing the overall height of the system, and the radome is retracted.
Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures.
a ia a plan view of one embodiment of an azimuth turntable drive;
b is a plan view of an alternate embodiment of an azimuth turntable drive;
a is an enlarged view of a portion of
a and 7b illustrate methods of the invention for determining appropriate phase shift for a selected channel;
Referring now to
As shown in
An alternative embodiment is shown in
As shown in
As seen best in
The two antennae 12, 14 are each provided with a line feed for receiving a polarized satellite signal. In the preferred embodiment, slot antenna probes (
Turning now to
Various pieces shown in
In both the antenna assemblies shown in
The BFN 34′ suitable for use with the antenna assembly shown in
The connection of DC power and various control signals is effected via the slip ring 20. The preferred embodiment of the slip ring is a number of concentric circular traces on a circuit board surrounding the rotary joint and mounted to the rotatable platform. A corresponding number of brushes are mounted on another circuit board surrounding the rotary joint and mounted on the base plate. The brushes are preferably made from beryllium copper pins with brush blocks on their ends. The brush blocks are made from a phosphor bronze alloy with silver plating. The circuit boards are aligned so that each brush block contacts one of the circular traces.
The remainder of the components of the system 100 which are located on the exterior of the vehicle include a power supply/charger 102, a battery 104, a solar cell 106 and/or a wind powered generator 108, preferably an AC adaptor 110, tracking circuitry/microprocessor 112, an azimuth motor 114, a retransmitter 116, a retransmission antenna 118, and a receiver 120 having an antenna 121. The power supply 102 provides power to all of the components from the battery 104 and/or from a solar cell 106, wind powered generator 108, or AC adaptor 110. It will be appreciated that when power is available from the solar cell 106, wind powered generator 108, or AC adaptor 110, it may be used by the power supply 102 to charge the battery. It will also be appreciated that the AC adapter 110 is preferably included so that the battery not be depleted in situations where AC power is available, e.g. on a boat moored in a slip. The azimuth, elevation control and motor driver/antenna tracking control/sensor 112 control the azimuth motor 114 (rotating platform) and elevation motors 22 which points the antennas to the desired direction and keeps them locked on to a satellite. These circuits also control the phase shifter control 43 and receive RSSI (received signal strength indicator) input from both the retransmitter 116 (for satellite tracking) and the receiver 120 (for channel selection). As mentioned above, the retransmitter 116 retransmits signals received by the antennae 12, 14 via a different wavelength antenna 118 to a vehicle inboard unit (described below), and the receiver 120 receives signals via an antenna 121 from the vehicle inboard unit.
The vehicle inboard unit components are shown at the lower portion of
In order to point the antennae at the desired satellite position while the vehicle is moving, the antenna controller 112 (preferably embodied in a microprocessor) steers the antennae in both azimuth and elevation angle in response to motion sensors 113 to achieve motion compensation. The preferred embodiment uses accelerometers and yaw, roll, and pitch sensors to sense the yaw, pitch, roll rates, longitudinal and lateral acceleration of the vehicle. The estimated yaw, roll and pitch rates are integrated to yield the vehicle yaw, pitch, and roll angle. This is used in a coordination transformation to the earth-fixed coordinate system to determine the azimuth and elevation travel of the antennae. The antennae will be turned in the opposite directions by the same amount to counteract the vehicle motion. Any resulting pointing error is detected by a dithering process and corrected by the antenna tracking system 112. Drift due to the inertia bias is the most significant source of pointing error and the tracking system compensates for it with dithering.
The motion compensation is accomplished through the following azimuth (Az) and elevation (El) update Equations (1) and (2).
Azk+1=Azk−(φx cos(Azk)tan(Elk)+φysin(Azk)tan(Elk)+φz)Δt (1)
Elk+1=Elk−(−φx sin(Azk)+φy cos(Azk))Δt (2)
where
Azk+1 is the new azimuth angle estimate relative to the vehicle body coordinate,
Azk is the most recent azimuth angle derived from the motor encoder output,
Elk+1 is the new elevation angle estimate relative to the vehicle body coordinate,
Elk is the most recent elevation angle derived from the motor encoder output,
φx, φy, φz are the newest roll, pitch, yaw sensor outputs minus the estimated bias, i.e., φx=φx,raw−roll bias, φy=φy,raw−roll bias, φz=φz,raw−roll bias, and φx,raw, φy,raw, φz,raw are the raw output of the roll, pitch, yaw sensors, and
Δt is the update time interval.
For accurate motion compensation, it is important that the bias for each sensor be properly estimated and compensated. A simple way to estimate the roll and pitch bias according to the invention is to monitor the output of longitudinal and lateral accelerometers as follows. The acceleration on the longitudinal accelerometer is y=g sin (roll angle) where g is the gravity acceleration. If y is not changing, there is no roll angle change and the readout of the roll angle sensor is the bias in roll sensor. The acceleration on the lateral accelerometer is x=g sin (pitch angle) where g is the gravity acceleration. If x is not changing, there is no pitch angle change and the readout of the pitch angle sensor is the bias in pitch sensor. When the antenna has locked on and tracked the satellite signal, the estimate of the yaw sensor bias can be performed using either of the following pairs of Equations (3) and (4) or (5) and (6).
Yaw Sensor Bias=ΔAz+ΔEl tan(Az)tan(El) (3)
and
Pitch sensor bias=ΔEl sec(Az) (4)
assuming that roll bias has been calibrated to zero, or,
Yaw Sensor Bias=ΔAz+ΔEl cot(Az)tan(El) (5)
and
Pitch sensor bias=ΔEl csc(Az) (6)
assuming that pitch bias has been calibrated to zero,
where ΔAz and ΔEl are the antenna correction rates derived from monitoring the motor encoder output.
The bias calculation algorithm described above allows the biases in the roll, pitch, and yaw sensors to be continuously estimated and updated and removed from the measurements.
A preferred embodiment for the antenna controller 112 obtains an estimate of the pointing angle error by “mechanically dithering” the antenna position. An antenna pointing error estimate is then used to refine the antenna pointing with a close loop tracking operation. According to the antenna tracking algorithm, the antenna is dithered to the left, right, up, and down of the target by a certain amount. The received signal strength indicator (RSSI) is monitored during this dithering action to determine the pointing error of the antennae. The antennae pointing is then adjusted toward the direction of maximum signal strength to refine the antennae tracking.
According to a preferred embodiment of the invention, the antenna controller 112 obtains an estimate of the pointing angle error by “electronically dithering” the antenna position. Electronic dithering in the elevation direction is achieved by changing (incrementing or decrementing) the phase shift of the phase shifter by a certain amount. This is equivalent to moving the antenna beam (upward or downward) in elevation. Dithering in the azimuth direction is achieved by adding phase shift in the BFN. The signals from the antenna probes are split into two groups within the BFN, each containing signals from half the number of the probes. One group contains signals from one side of the BFN and one group contains signal from the other side of BFN. The signals within each group are amplified and combined into a single signal. One of the combined signals is passed through a phase shifter before combining with another signal. By adjusting (incrementing or decrementing) the phase shift through the phase shifter by a certain amount, the azimuth direction of the antenna beam can be dithered.
Although the electronic dithering is achieved by adjusting the phase shift of the phase shifter, the electronic dithering is different from the conventional phased-array antenna where the electronic beam can be steered via the use of the phase shifters. The key difference between the electronic dithering operation and the operation of a phased array antenna is that the former only needs to move the antenna beam by a small amount while the latter needs to steer the antenna beam toward all possible scan angles to target a signal source. The design and implementation of the “electronic dithering” antenna and the phased array antenna are therefore quite different. The advantage of the “electronic dithering” is that the power required is reduced as compared to that required for constantly mechanically dithering the antenna assembly. A second advantage is that the “electronic dithering” can be performed at a much faster speed than the “mechanical dithering”. Fast dithering operation means the antenna can track faster, which can eliminate the need for motion compensation and all the components (accelerometers and pitch, and yaw sensors) required by the motion compensation, resulting in a significantly lower cost implementation. It should be also noted that the “electronic dithering” operation described above is not limited to the present embodiment of the paraboloid linear antenna. The same principle can be applied to other type of antenna as long as there is a way of adjusting the phase shift to move the antenna beam to a slight offset angle with respect to the target pointing angle of the antenna.
When the antennae assembly is first powered up, the controller microprocessor 112 which controls the azimuth and elevation motors 114 and 22 commands the two motors to move and monitors the optical encoders to check if the two motors respond to the command. After that, the motion compensation algorithm is turned on. The antennae are moved to scan through possible satellite positions to search for a satellite signal. The typical method is to scan the 360 degree azimuth angle at a given elevation, incrementally change the elevation angle, and repeat the azimuth scan. Preferably, an electronic compass is utilized and the location of the satellite is known. Thus, it will not be necessary to scan the entire hemisphere, but only a relatively small region based on the accuracy of the compass and the satellite position. The antennae dither action is not turned on during the initial satellite location. The antennae controller monitors the RSSI via the power monitor. If the power monitor detects that the signal strength exceeds a certain threshold, the scanning is stopped immediately and the antennae dithering algorithm is turned on to allow the antennae to track the signal. The demodulator 126 and the data processor 128 are monitored to see if the antennae are pointed at the desired satellite and if the signal is properly decoded. If that is the case, the signal lock is achieved. Otherwise, the antenna dithering is disabled and the scanning is resumed.
If the signal lock is achieved, the antennae tracking algorithm continues to refine the antennae tracking. The processor which controls the motors continues to report the motor position with a time tag. In the preferred embodiment, the motor position is translated into a satellite position (elevation and azimuth) in space. In the case that the signal is blocked by trees, buildings, or other obstacles, the power monitor and the receive data processor can immediately detect the loss of signal. The antenna tracking algorithm will command the motor controller to move the antenna back to point at the last satellite position recorded, when the satellite signal was properly decoded. In addition, upon loss of signal, the antenna dithering tracking algorithm will be temporarily turned off. If the power monitor detects the signal power (exceeding some threshold) again or the data processor detects the signal lock again, the antenna dithering algorithm will be turned on again to continue tracking. After a certain time-out period if no signal strength exceeding the threshold is detected by the power monitor or the data processor does not detect signal lock, the antenna scanning algorithm will be initiated to scan for signal again. The antenna scanning algorithm for signal re-acquisition will scan in a limited region around the last satellite position recorded, when the satellite signal was properly decoded. If the scanning does not find the satellite signal, a full scan of 360 degrees of azimuth angle and all possible elevation angles will be conducted.
Depending on the elevation angle, the satellite signal will arrive at each antenna at a different time; the lower the elevation angle, the greater the difference in signal arrival time between the two paraboloid linear antennae. The phase shifter 41 is used to compensate for the signal phase difference between the received signals from the two paraboloid linear antennae such that the resultant phase of the two received signal is the same resulting in maximum combined power. If the phase shifter is not used to compensate the phase difference, the two resultant signal phases can differ by 180 degrees, the two signals can cancel each other, resulting in minimum power. The amount of phase shift in the phase shifter is determined by the elevation angle and the separation of the two antennas according to Equation (7) below, where D is the distance between the antennae, θ is the elevation angle, and λ is the wavelength of the received signal.
φ(in radians)=D*COS θ/λ (7)
The signal experiences different delays before it arrives at the different antennas. The difference in signal delays depends on the elevation arrival angle of the signal relative to the antenna. The phase shifter is used to compensate for the phase differences between the signals from the two (or more) antennas due to the difference in signal delays. The elevation angle information needed by the phase shifter is provided by the motion compensation and antenna tracking subsystem.
A typical satellite system has multiple frequency-division channels over the entire band. As an example, the Direct Broadcast Satellite (DBS) frequency band is from 12.2 to 12.7 GHz. The signal is transmitted via two antenna polarizations (left-handed circular and right-handed circular polarization). Each antenna polarization carries 16 transponder channels over the entire frequency band (12.2 GHz to 12.7 GHz). The satellite receiver/set top box receives only one (transponder) channel within the entire band at a time. The phase shift compensation required by each phase shifter will depend on which channel the user is receiving as shown in the Equation (8),
Phase Shift=wi*Δτ (8)
where wi is the frequency of the user channel, and Δτ is the path delay. For the DBS example, the phase shift at the lowest channel (at 12.2 GHz) and the highest channel (at 12.7 GHz) with a path delay of around 7 inches differs by 106.7 degrees. Thus, it is necessary to know which transponder channel the user is viewing in order to compensate for phase shift properly.
The user channel information can be retrieved from the satellite receiver/set top box. In the normal operation mode of the satellite receiver/set top box, the user commands the satellite receiver/set top box via an infrared remote controller or front panel keypad. Most satellite receivers/set top boxes have an additional external data interface called the “data port” (or “low speed data port” for DBS specifically) which also allows the user to control the satellite receivers/set top boxes via a personal computer or similar device. According to one aspect of the invention, this data port is used to retrieve the user channel information so that the proper phase shift compensation can be applied to the antennae array.
The “data port” interface can override the remote controller and front panel keypad as the primary control for the satellite receiver/set top box. In this mode, the satellite receiver/set top box receives the user command from the “data port” but does not execute it. When the user commands the satellite receiver to select a specific channel, this user command information can be retrieved from the “data port”. According to the invention, once the user command is retrieved from the “data port”, the same command is looped back into the satellite receiver/set top box via the data port to be executed. Since the loop back time delay is very short, the set top box appears to be directly under the user command. The user command retrieved from the “data port” is parsed to decode which transponder channel the user has selected. This user channel information and elevation angle are used to compute the required phase shift to control the phase shifter. A detailed example of the operation flow for DBS set top box “low speed data port” interface is described below with reference to
Note that the user transponder channel decoded via data port can be passed to tuner1116 of the re-transmitter and tuner2124 to set the proper tuner frequency for the selected channel.
By using the “data port” in this manner, the “phased-array” satellite antenna can be operated with any off-the-shelf satellite receiver/set top box having a “data Port”.
The implementation of a precise phase shifter over the entire operating temperature range and the operational life of the product is complicated and typically expensive. Another approach, according to the preferred embodiment, is to use a low cost, less precise phase shifter and, during signal reception, dither the phase shift to determine which phase shift produces the highest signal strength. The function of the phase shift control 43 is to perform such a dithering function and to monitor the output signal strength. It is expected that the optimal phase shift for a certain elevation angle will drift very slowly over time. Thus, the dithering operation of the phase shifter does not need to be repeated very often for a given elevation angle.
Referring now to
Turning now to
Referring now to
It will be appreciated that when the antennae are rotated away from an elevation of 90°, the antenna 14 will eventually block a portion of the look window of the antenna 12. As the antennae are rotated closer to the 15° elevation, the antenna 14 will block the look window of the antenna 12. In order to reduce blockage, the axis of the antenna 14 is located approximately one half inch lower than the axis of the antenna 12. With this arrangement, at an elevation of approximately 20°, the antenna 14 blocks the antenna 12 by approximately 12.5% as illustrated in
When the separation between the two antennae is larger, the blockage decreases. However, the array pattern sidelobe effects become more severe, when the two antennae are spaced farther apart from each other. In addition, the array pattern sidelobe effects becomes more severe when the antenna is pointing toward a higher elevation angle.
A potential problem due to the array pattern sidelobe is that the antenna may receive the signal from the sidelobe instead of the main lobe. This results in reduced antenna gain, causing the overall received signal-to-noise ratio to degrade. To reduce the array pattern effects at higher elevation, the two antennae need to be moved closer together. However, this will result in more signal blockage at lower elevation when the two antennas are closer. One solution to the array pattern sidelobe and blockage problem is to use the mechanical linkage as depicted in
A different solution is to take some signal loss due to blockage at lower elevation, as illustrated in
Another solution is to employ multiple motors to move the two antennae. Two motors are used to adjust the antennae elevation and a third motor is used to move one antenna closer to the other one, when the antennae are pointing at higher elevation angles.
Each of these three solutions simultaneously address the array pattern antenna side lobe issues and the blockage issues. The second solution allows a good compromise to be achieved.
As mentioned above, in order to avoid drilling through the vehicle, the signal received by the antennae is re-transmitted at a different frequency to a receiver inside the vehicle. This requires a downconverter and a local frequency source. The satellite signal is typically broadband (such as 500 MHz for DBS), carrying a number of relatively narrow band channels. The allowable bandwidth for re-transmitting the satellite signal into the vehicle is typically narrower, e.g. 100 MHz. The local frequency source is implemented with a tuner to select the desired portion (channel) of the satellite frequency band to be re-transmitted.
Presently preferred embodiments of a tuner/re-transmitter 116 and a receiver 124 are illustrated in
The receiver 124 is similar in design to the retransmitter 116. The receiver includes a low noise amplifier (LNA) 224, a mixer 226, a VCO, a synthesizer 230, a loop filter 232, a ×2 multiplier 234, a ÷2 divider 236, and an oscillator 238. The operation of the receiver is similar to that described above with respect to the retransmitter. The receiver receives the 5.25–5.35 GHz from the retransmitter and downconverts the signal to a lower frequency range (e.g., 950 MHz–1.45 GHz) which is then processed by the demodulator (126 in
An alternative embodiment of a re-transmission scheme is to demodulate and decode the satellite signal. The signal transmitted by a satellite typically consists of a number of signals which are frequency division multiplexed (FDM) from 16 to 32 transponders in a satellite. A single channel satellite demodulator and decoder selects one transponder signal to process. The data carried by a transponder signal can be further broken down into multiple time division multiplexed (TDM) data streams. The multiplexed digital data streams are processed via a signal de-multiplexer and a router, and some of the data streams are retransmitted with off-the-shelf wireless LAN equipment such as IEEE 802.11a or 802.11b transceivers. The demultiplexer disassembles the desired data streams to be retransmitted and repackages these data streams into the format used by the 802.11 or Bluetooth transceivers. The router reassembles the reformatted data streams into the symbol stream to be re-transmitted and attaches the ID of the destination transceiver to the data stream. This method may be preferable if the satellite antenna is used for bidirectional data communications. The satellite communications can also be used as a backhaul network connection of the local area network (LAN) to the WAN (wide area network). It is also desirable in situations where a network of devices need to be coupled to the same satellite antenna.
As mentioned above, the presently preferred power source includes a wind powered generator.
P=Cp×ρ/2×V3×Ra (9)
The output of the DC generator is routed to charge a battery and a DC-to-DC converter which regulates the output power to 12V, 5V, and 3.3V as required.
The output of the generator is used to charge a rechargeable user replaceable battery pack contained within the radome, and the battery pack is used to power the antennae assembly. Alternatively, a coil and capacitor arrangement such as disclosed in U.S. Pat. No. 5,917,310 may be used in lieu of a rechargeable battery. As mentioned above, a photovoltaic panel array may also be used in addition to or in place of the wind generator to ensure that the battery maintains an adequate charge. Also as mentioned above, an AC power adapter is optionally provided in situations where the vehicle will remain stationary within range of an AC power source, e.g. on a boat moored in a slip, or an RV parked in an RV park.
Another embodiment to provide power to the antennae assembly is to employ a switch circuit which converts a DC power supply inside the vehicle (for example, from the 12 V cigarette lighter) to an AC signal at, e.g. 100 kHz. The switching AC signal is passed through the vehicle window through an inductively coupled or capacitively coupled device. The inductively coupled or capacitively coupled device is attached to the opposite sides of the window at the same position. The inductively coupled or capacitively coupled device allows the electrical energy to be coupled through the window and passed to the antenna assembly on top of the vehicle.
There have been described and illustrated herein several embodiments of a low profile satellite antenna system for mounting on a vehicle. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as so claimed.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5119501 | Perry et al. | Jun 1992 | A |
| 5398035 | Densmore et al. | Mar 1995 | A |
| 5452869 | Basuthakur et al. | Sep 1995 | A |
| 5528250 | Sherwood et al. | Jun 1996 | A |
| 5739784 | Jan et al. | Apr 1998 | A |
| 5764199 | Ricardi | Jun 1998 | A |
| 5917310 | Baylis | Jun 1999 | A |
| 5961092 | Coffield | Oct 1999 | A |
| 5982333 | Stillinger et al. | Nov 1999 | A |
| 5983071 | Gagnon et al. | Nov 1999 | A |
| 6049306 | Amarillas | Apr 2000 | A |
| 6433736 | Timothy et al. | Aug 2002 | B1 |
| 20020051091 | Dedieu et al. | May 2002 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20030083063 A1 | May 2003 | US |
