Typically, a radio link is set up between two points by mounting an antenna on a tower or other structure at each point and then adjusting the orientation of each antenna in turn, in both elevation and azimuth to find the optimum alignment. In a typical installation there are two or more antennas at each end of the link, and for each transmitting antenna a selection can be made as to the optimum antenna to operate as the receiver.

Each such test requires a large number of personnel, in particular riggers to physically adjust the antennas'alignments, and commissioning engineers to take the necessary measurements. A typical operation requires the physical movement of the antenna relative to its mount by turning a locating screw with a spanner whilst monitoring for the optimum signal level. This is not a task that can be carried out with great precision, especially since the location of the antenna is usually necessarily in an exposed location. It is also not possible in practice to test both directions of transmission simultaneously, in particular because this would require riggers to be working too close to a transmitting antenna. In practice, riggers are required to descend the antenna tower between test transmissions. It is also necessary to test the link at various different frequencies within the bandwidth over which the antenna is to operate. The process is therefore very time consuming. Over the duration of the process, variations in environmental conditions such as the weather can affect the properties of the signals and mask the looked-for variations in signal strength caused by the adjustments in alignment.

With the increasing use of high speed digital communications, improved signal quality is required. However, the higher frequencies (in the Gigahertz band) now being used require greater accuracy in alignment. There is also more variation in signal strength due to environmental conditions-for example at these frequencies the wavelength is comparable with that of waves on the surface of the sea, so sea conditions can interfere with signals. Moreover, attenuation by liquid water is significant at these frequencies, so clouds or rain can affect the results.

It is therefore desirable to develop a test process which can be performed rapidly enough for an optimum alignment to be determined in a period short enough for weather and other environmental conditions to be substantially constant. A reduction in the number of personnel required, particularly for the unpleasant and potentially hazardous job of climbing an antenna tower to physically adjust the antenna alignments, would also be desirable.

According to the invention there is provided a method for aligning radio antennas with each other for the creation of a fixed radio link, comprising the steps of mounting powered actuators on antennas forming each end of the link, the actuators being arranged to adjust the alignments of the antennas, and to be replaced by fixed securing means subsequent to the alignment process, the alignment process being performed from a remote position and comprising the steps of: controlling the movement of the actuators to adjust the antenna alignments, continuously measuring the variations in the properties of a signal transmitted over the link as the actuators are moved to adjust the alignment of the antennas; identifying an optimum set of actuator positions, and fixing the antennas in the optimum positions.

According to a second aspect of the invention, there is provided apparatus for aligning radio antennas with each other for the creation of a fixed radio link, the apparatus comprising one or more powered actuators, each having means for mounting on an antenna such that it can adjust the alignment of the antenna, actuator securing means for temporarily securing the actuators to the antennas to allow their subsequent recovery and re-use, control means for controlling the movement of the or each actuator to vary the alignments of the antennas, measurement means for measuring properties of a signal transmitted over the link, means for allowing identification of an optimum actuator position, locking means forfixing the antennas in the optimum position, means for operating the control means and locking means, and monitoring the measurement means, from a position remote from the actuators.

Two or more actuators may be provided on the same antenna, for controlling orientation in two dimensions. In a preferred arrangement, signal quality is monitored continuously as the alignment of an antenna is adjusted, an optimum alignment position is identified, and the antenna is then positioned in the so-identified optimum alignment by means of the actuators. The means to lock the position of the antennas may be incorporated in the actuators or by separate locking means.

As will be described in relation to the preferred embodiment, the invention may be used for aligning the members of an array of antennas at one location with those of a corresponding array at another location By arranging for the antennas to be adjusted by powered actuators it is possible for the entire process to be carried out by one operator, controlling the actuators at both ends of the radio link remotely. However, a suitable powered actuator such as an electric or hydraulic ram is expensive, and it would be costly to provide all antennas with such equipment which is only required for use in the alignment phase. Therefore, according to the invention, the actuators are designed for temporary attachment to the antennas, so that they can be replaced by a fixed securing means once alignment has been performed. They can then be re-used on further installation work. To this end, the actuators are preferably provided with clamps for securing to the antenna structure independently of the existing manual adjustment system with which most antennas are fitted, so that after alignment is completed the manual adjustment system can be used to secure the antenna in position before recovery of the actuators. This recovery process requires riggers to ascend the antenna tower, but is a much simpler and quicker job than the prior art alignment task, and can be performed at any convenient time after the adjustment process has been completed.

An embodiment of the invention will now be described, by way of example, with reference to the drawings, in which: Figure 1 illustrates a typical antenna, showing the mechanical alignment system.

Figure 2 illustrates the same antenna with powered actuators fitted according to the invention Figure 3 illustrates an alignment system according to the invention, having six antennas each fitted as shown in the arrangement of Figure 2

Figure 4 is an iilustrative plot generated during the process of the invention.

Figure 1 illustrates schematically a fixed frame 1 forming part of a mast, tower, or other fixed structure. Mounted on the frame 1 are several antennas 10,20, 30 (see Figure 3), of which one antenna 10 (viewed obliquely from the rear) is shown in Figure 1. The antenna has a transceiver 11 which is supplied by means of an electrical lead 12. The antenna 10 is adjustably mounted on the frame 1 by means of four locating screws 3,4,5,6 fixed to the antenna 10 and releasably connected to the frame 1 by means of respective locking clamps 13,14,15,16. The angular position of the antenna 10 relative to the frame 1 can be adjusted by releasing one of the clamps 13,14,15,16, operating one of the locating screws to move the antenna and then locking the screw in its new position by means of the clamp. For example, the antenna may by rotated about a vertical axis defined by the clamps 13, 15 by releasing the clamps 14,16, adjusting the orientation of the antenna by operating one of the respective locating screws 4 (the other screw 6 being free to move in the complementary direction with respect to its clamp 16) and then locking the screws 4,6 in their new positions using the clamps 14,16. Adjustment about a transverse horizontal axis defined by the clamps 14,16 can be performed in a similar manner by adjusting the screws 3,5.

The signal strength received by the transceiver 11 from a second antenna (whose own alignment may have been adjusted in a similar manner) can be monitored by a detector connected to the electrical lead 12. The process is repeated for the antennas at both ends of the radio link as many times as necessary to determine the optimum combination of antenna alignments. This process is cumbersome and time- consuming, requiring staff to be present at both the transmitting and receiving antennas. Adjustment has to be carried out on a trial and error basis, with the rigging crew responsible for carrying out the adjustments to the set screws having to move to a place of safety whilst each test is carried out, because of the strong radiation fields present close to an operational antenna. In a large installation with several antennas the duration of the process is long in comparison with changes in ambient conditions which may affect the results of the measurements.

Figure 2 illustrates schematically an antenna assembly of the kind shown in Figure 1, but fitted with alignment apparatus according to the invention. Two of the adjustment screws 3,4 and associated clamps 13,14 have been released or

removed completely and in their place are respective powered actuators 7,8 temporarily secured to the frame 1 and antenna 10 by brackets (not shown) fitted for the purpose. The actuators 7,8 may be electrically or hydraulically powered rams, controlled (see figure 3) through respective control wires 17,18 from a central location 7 (see figure 3), or by a wireless connection (not shown). The actuators 7,8 may be used to continuously adjust the alignment of the antenna 10 relative to the frame 1 until an optimum arrangement is identified. The actuators 7,8 are then returned to their optimum positions. A rigging crew can then return to the antenna 10 at a convenient time to re-instal the adjustment screws 3,4, (without further adjusting the position of the antenna 10) and then recover the actuators 7,8, and their control wires 17,18 or wireless connection equipment, and the fixing brackets, for re-use on another installation project.

Figure 3 shows a complete installation project comprising a first antenna array 10,20,30 mounted on a first tower 1, and a second antenna array 40,50,60 mounted on a second tower 9, which are arranged to be aligned with each other. As already shown in detail in Figure 2 for antenna 10, each antenna 10,20,30,40,50, 60 is fitted with a pair of actuators having respective control leads 17,18; 27,28; 37,38; 47,48; 57,58; 67,68; and a lead 12,22,32,42,52,62 from its respective transceiver.

The control leads are connected to a control unit 7, which may be placed at any convenient location. Although shown as fixed leads, wireless connections may be used, provided they do not interfere with the transmissions of the antennas under installation. As shown the control unit comprises two adjustment controls 77,78 for adjusting the positions of the respective actuators 7,8, and six selection switches 71 - 76 for connecting one of the pairs of control leads 17,18; 27,28; 37,38; 47,48; 57,58; 67,68 to the respective adjustment controls to select which antenna is to be to adjusted. Thus, if alignment of the antenna 40 is to be adjusted about the vertical axis the user selects the switch 74 (to connect control wires 47,48 to the adjustment controls 77,78), and then operates the adjustment control 78 to operate the actuator connected to the lead 48.

A monitoring unit 8 is provided which is connected to the transceiver of each antenna 10, 20,30,40,50,60 by its respective lead 12,22,32,42,52,62. A series of switches 81,82,83,84,85,86 is provided to allow the respective

transceiver lead to be connected to an output 87, which displays signal strength, and provides the facility to carry out the following series of tests of signal quality against actuator position.

Panning in azimuth and elevation after identification of the main lobe 90 Cross-polar discrimination Launcher (feed assembly) bi-polar tilts (for over-water hops) Hop responses (using co-polar and cross-polar scalar measurements) Test transmissions are made from the transceiver of one of the antennas 10 on the first mast 1 and received at the transceiver of one of the antennas 60 on the other mast 9 (or vice versa), whilst the position of one of the two antennas 10,60 is being adjusted as described above. Thus if antenna 10 is to transmit to antenna 60 whilst the actuator 7 of antenna 10 is being operated, the user will select switches 71 and 86 and then operate controller 77. This will cause the elevation actuator 7 (Figure 2) to travel through its range, causing the alignment of the antenna 10 to vary. As this happens the signal strength detected by the transceiver of antenna 60 will vary, and a plot of signal strength R (x) against actuator position x will be displayed on the display 87 of the monitoring unit. A typical such plot is shown in Figure 4. After carrying out a wide pan, which will identify the main lobe 90 and side lobes 91,92 shown in Figure 4, the user can focus on the main lobe and repeats a narrow pan to identify from the plot the optimum actuator position Xmax at which R (x) is a maximum (90), corresponding to the main lobe of the antenna, and can then return the actuator 7 to this position using the controller 77.

The antenna can then be adjusted in azimuth by using the controller 78 to operate the other actuator 8. When the switch 71 controlling the actuators 7,8 of antenna 10 is switched off, the actuators are locked so that antenna is then fixed in position.

It will be understood that the human operator in this embodiment may be replaced by a computer running an algorithm under the control of inputs 12,22,32, 42,52,62 from the transceivers 11, 21,31,41,51,61, to generate signals on the output connections 17,18,27,28,37,38,47,48,57,58,67,68 for transmission to the respective actuators. As will be understood by those skilled in the art, any or all of the software used to implement the invention can be contained on various transmission and/or storage mediums such as a floppy disc, CD-ROM, or magnetic

tape so that the program can be loaded onto one or more general purpose computers or could be downloaded over a computer network using a suitable transmission medium.

By concentrating all monitoring and control in one location, under the control of one person or computer, the alignment process is greatly simplified. Moreover, because the antenna alignment can be carried out remotely, transmissions do not need to be switched off whilst adjustments are made as would be necessary for safety reasons if a rigging crew had to be present to perform those adjustments manually. This allows signal quality to be measured continuously, rather than incrementally, greatly accelerating a process that could otherwise take several weeks (if several antennas on each mast have to be aligned) to be performed in a few hours.

As well as the manpower efficiencies achieved by this acceleration, enhanced accuracy is achieved because environmental conditions which may influence signal quality are less likely to vary significantly during the shortened testing period.