The invention relates to steering a radiation lobe of an array antenna without turning the antenna itself. The steering arrangement is aimed for the base station antennas in mobile communication networks and for vertical adjusting of the transmitting direction, in particular.
The traffic capacity of radio networks is increased by dividing a geographic area to so-called cells and by using the same carrier frequencies simultaneously in different cells, as known. The capacity of a network is the higher the smaller the cells are and the closer to each other the cells are in which the same carrier frequencies can be used. Instead of an omnidirectional antenna, a plurality of antennas radiating controllably in different sectors are often used in the base stations of the cells. In that case the base stations at a certain distance from each other, using the same carrier frequency, interfere less with the transmitted signals of each other. This means that the reuse distance of frequencies can be reduced and the capacity of the network thus further increased.
Both the transmitting power and the direction of the transmitting in the vertical plane of an antenna radiating in a certain sector have to be chosen so that the coverage area is sufficient, but on the other hand the interfering influence in the neighboring cell is slight enough. The angle between the middle direction of the transmitting main lobe and the horizontal direction is called “tilt angle”. If no changes were to happen in the circumstances, the tilt angle would be constant without adjusting possibility. However, in practice the traffic intensity in the cells fluctuates a great deal. During minor traffic it is advantageous to keep the tilt angle smaller than during heavy traffic, because in that case the connection quality in the border regions of the cells becomes better without the total interference remarkably growing in the neighboring cells. In addition, the shape of the built environment in the cell can change so much that there is reason to change the tilt angle.
Changing the direction of the antenna radiation lobe, without turning the antenna mechanically, succeeds when an array of radiators is applied. When the phases of the carriers fed to the radiators in a row are arranged to have suitably different values, the lobe turns off into the desired direction from the normal of that row, as known. Changing the tilt angle then requires adjustable phase shifters in the feed paths of the radiators and that the radiators are located in a substantially vertical row. The radiator row can deviate from the vertical direction as much as a typical tilt angle is achieved without any phase shifts. After that the tilt angle can be changed upwards and downwards by means of phase shifts.
The phase shifts needed in the feed of an adjustable antenna are so great at the maximum that in practice only transmission line type solutions come into question as phase shifters. The physical length or at least the electric length of a transmission line has to be changeable by electric control. A wholly electric adjustable phase shifter is obtained, when the length of the transmission line is changed e.g. by means of diode switches or ferrite pieces being located in the space where the field propagates in the transmission line. In the latter case the permeability of the ferrite and thus the effective phase coefficient of the whole transmission line is changed. A disadvantage of these kinds of electric solutions is the losses caused by them, and in the case of diodes also the non-linearity. They are also expensive, if the phase shifters are made satisfactory for transmitting use by power capacity. Therefore the phase shifters used in the transmitters of base stations are in practice electromechanical so that they include a structural part movable by an actuator, the location of which part determines the (electric) length of the transmission line. In this description and claims such a structural part, movable along a line, is called “slide”.
A simple electromechanical phase shifter has a straight transmission line and a slide, by which a tapping is formed in the line. A radio frequency signal is fed to the line end and is taken out from the tapping. When e.g. a 225-degree phase shift is needed, the distance between the line end and the slide is adjusted to have value 0.625λ. λ is the wavelength in the line and it depends on the dielectricity and permeability of the medium between the line conductors. The length of the transmission line has to correspond directly to the greatest phase shift needed, of course. The length of the transmission line and thus the space required for the circuitry is reduced, when a reflection in the transmission line is utilized. In this case a short-circuit, and not a tapping, is formed in the transmission line by means of a movable slide. A signal, or electromagnetic field, arriving to the short point reflects to the reverse direction, as known. When the signal has arrived back to the starting end, it has travelled a double distance, for which reason also the phase shift is double compared to the structure, where the signal is taken out from the tapping being located at the same distance. For obtaining a certain maximum phase shift, a line having half length is then sufficient. That kind of shorted transmission line requires a separating element as an additional structure, which element separates the reflected signal, being in the same line with the incoming signal, to a transmission path of its own for feeding to the antenna. A circulator, for example, is suitable as such a separating element. A shorted line together with a circulator forms a phase shifter. More generally, in this description and claims a phase shifter using signal reflection includes also a separating element.
In this description and patent claims the term “reflection line” means a transmission line having in its tail end a circuit, which causes a reflection, so that a signal fed to the starting end comes also out from the starting end.
Using two parallel reflection lines and a four-port hybrid as a separating element instead of one reflection line and a circulator, a higher power capacity and better linearity are achieved.
The reflection lines are located parallelly, and crosswise between them there is a shared dielectric slide 130. One end of the slide implements the short-circuit in the first reflection line 141 and the opposite end implements the short-circuit in the second reflection line 142. The slide fills in its location almost wholly the space between the ground conductors in both lines. For the centre conductor of each line the slide has a flat hole in the direction of the line. As can be seen, the short-circuit is not galvanic. The dielectric medium only enhances the capacitance between the centre conductor and ground conductors in the location of the slide so much that there prevails almost a short-circuit in the operating frequencies of the antenna.
Because of the structure described above the reflection lines become as much longer or shorter, when the slide 130 is moved. They are always equal in length, in which case the phase shifts always are equal in them. This is necessary in order to get the partial signals with the same phase to the fourth port of the hybrid 150 for summing and feeding to the antenna.
In
The phase shifter according to
From the publication WO01/13459 is known an arrangement comprising more than one similar differential phase shifters as in the previous example. The transmission lines of the phase shifters have the same midpoint of the curvature, and their slides are moved by a common rotatable arm, which functions as an input line, at the same time.
An object of the invention is to implement the steering of the antenna radiating lobe in a new and advantageous way compared with the prior art. The arrangement according to the invention is characterized in that which is specified in the independent claim 1. Some advantageous embodiments of the invention are specified in the dependent claims.
The basic idea of the invention is as follows: The radiators of an array antenna are arranged in at least one row. Two radiators of a row, which are located equidistant from the middle point of that row, form a radiator pair. To steer the radiation lobe, the phase of the signal of the first radiator in the pair is e.g. advanced and the phase of the signal of the second radiator in the pair is lagged by equivalent amount. For this aim each radiator is fed through a phase shifter comprising at least one reflection line and a separating element. A reflection line for the first radiator and a reflection line for the second radiator are implemented by a transmission line, which is shared between these radiators. The radio frequency signal to be led to the first radiator is fed to the first end of this transmission line, and the signal to be led to the second radiator is fed to the second, opposite end of the same transmission line. In the transmission line there is a reflection point, the place of which can be moved. One reflection line is located from the reflection point to a direction of the transmission line and the other reflection line is located from the reflection point to the opposite direction of the transmission line. The above-mentioned phase changes take place by moving the reflection point along the transmission line. For moving the reflection point the transmission line has one movable or several fixed reflection circuits. In the former case the reflection circuits of the different transmission lines are slides attached to one and the same movable arm. In the latter case one of the reflection circuits of each transmission line is activated at a time. If the number of the radiator pairs is more than one, the phase adjusting for the all radiator pairs is implemented simultaneously by the common control. The greater the distance of the radiators of a radiator pair from the middle of the row, the more the phase of their signals is changed.
An advantage of the invention is that the phase shift structure is relatively space-saving. This is due to that the phase shifters are of reflection type, and on the other hand that each phase shifter pair functions differentially. Without the latter characteristics separate transmission lines would be needed for both radiators of a radiator pair, which transmission lines would have the same length as the shared transmission line according to the invention. Another advantage of the invention is that the structure according to it is simple, which results in high reliability and relatively low production costs. One factor for the simplicity is that it is not necessary to feed the signals through the moving part of the phase shifter.
The invention is described in detail below. The description refers to the enclosed drawings, in which
a presents an example of an arrangement according to the invention for steering the antenna radiating lobe;
b presents an example of location of the radiators of
a presents an example of the slides belonging to the structure according to
b presents an equivalent circuit of the reflection circuit implemented by a slide according to
a presents another example of a reflection circuit according to the invention;
b presents an equivalent circuit of the reflection circuit according to
a shows an example of an arrangement according to the invention, for steering the radiating lobe of an array antenna. The array antenna comprises in this example four radiators, which are located in a row according to the example of
The arrangement comprises a power divider 310 and one reflection-type phase shifter for each radiator. The divider can be e.g. a 4-way Wilkinson divider or it can include first a 2-way divider and then two 2-way dividers as well, connected to the outputs of the first divider. Each phase shifter is functionally similar to the phase shifter in
A radio frequency signal IN coming from the power amplifier of the transmitter is divided into four parts by the divider 310, the parts being a first division signal E1, a second division signal E2, a third division signal E3 and a fourth division signal E4. The first division signal E1 is led to the first port of the first hybrid 351, and it will be got out as phased from its fourth port, which is connected to the first radiator 371. Correspondingly, the second division signal E2 is led to the first port of the second hybrid 352, and it will be got out as phased from its fourth port for leading to the second radiator 372. The second port of the first hybrid 351 is connected to the first end of the first transmission line 321 by an intermediate line, and the third port is connected to the first end of the second transmission line 322 by another intermediate line. Correspondingly, the second port of the second hybrid 352 is connected to the second end of the first transmission line 321, and the third port is connected to the second end of the second transmission line 322. For the phase shift of the first E1 and second E2 division signal are then used the same two transmission lines, different ends of these lines, the short-circuits therebetween being shared. The slides 331, 332, by which those short-circuits are implemented, are side by side because of their attaching way described above. In that case the first reflection line 341, which is formed of a portion of the first transmission line 321 between its first end and the first slide 331 and of said intermediate line between the second port of the first hybrid 351 and the first end of the first transmission line, has the same length as the third reflection line 343, which is formed of a portion of the second transmission line 322 between its first end and the second slide 332 and of said intermediate line between the third port of the first hybrid 351 and the first end of the second transmission line. Owing to the same (electric) length, also the delays and phase shifts caused by the first and third reflection line are equal. This results in that the halves of the first division signal E1, reflected from the short-circuit points of the first and second transmission line, are combined as in-phase in the fourth port P4 of the first hybrid 351, and the first division signal, as a whole and with desired phase, is managed to be led to the first radiator 371. Correspondingly, the second division signal E2, as a whole and with desired phase, is managed to be led to the second radiator 372 through the fourth port of the second hybrid 352.
As mentioned, the slides of the arched transmission lines are attached to the arm 361, which is substantially perpendicular to the transmission lines. When the arm is rotated round the axis 362, the slides move simultaneously side by side, each along its own transmission line. When the slides are in the middle of the transmission lines, the phase shifts of the first E1 and second E2 division signal naturally are equal, and these signals have no phase difference in the radiators. When the arm 361 has been rotated closer to the first ends of the transmission lines, the phase shift of the first division signal has been reduced by a certain amount, and the phase shift of the second division signal has been increased by the same amount, because certain portions of the first and second transmission lines have changed from the propagation path of the first division signal to the propagation path of the second division signal. Therefore the phase of the transmitting signal of the first radiator 371 is advanced in respect to the phase of the transmitting signal of the second radiator 372, which matter has the effect that the main radiation lobe turns downwards, if the radiator row is vertical as seen from the direction of the main lobe. When the arm 361 is rotated towards the second ends of the transmission lines, the effect naturally is vice versa.
The third 353 and fourth 354 hybrid and the third 323 and fourth 324 transmission line form a similar phase shift structure for the third E3 and fourth E4 division signal as the first and second hybrid and the first and second transmission line for the first and second division signal. The third and fourth transmission line has the same curvature midpoint as the first and second transmission line, and their slides are attached to the same arm 361. The third and fourth transmission line are closer to the curvature midpoint, and thereby to the axis 362, than the first and second transmission line, for which reason they are shorter compared with the latter lines. The length difference is compensated so that the intermediate lines between the third and fourth transmission line and the third 353 and fourth 354 hybrid are correspondingly longer than the intermediate lines between the first and second transmission line and the first 351 and second 352 hybrid. More accurately, all eight lines between a middle of an arched transmission line and a port of a hybrid have the equal electrical length. That the third 323 and fourth 324 transmission line are shorter means also that the adjusting range for the third and fourth division signal is narrower than the adjusting range for the first and second division signal. This is not a drawback, because that is just how the matter has to be. The third and fourth division signal are led to the third 373 and fourth 374 radiator being located closer to the middle of the radiator row than the first and second radiator. The phase of the transmitting signals of the third and fourth radiator has to be changed less than the phase of the transmitting signals of the outermost radiators in order for the shape of the radiation lobe to remain, when the lobe is turned.
In the example of
a shows an exemplary section drawing about a part of the structure according to
a shows another example of a reflection circuit according to the invention. Mechanically it is a slide also in this case. The slide 530 comprises a thin dielectric plate 502 having at least the same width as the whole transmission line with planar structure. The lower surface of the plate is located against the transmission line conductors. On the upper surface of the plate there is a first conductive area 503 at the first ground conductor GNC1 of the transmission line and a second conductive area 504 at the second ground conductor GNC2. In addition, on the upper surface of the plate 502 there is a third 505 and fourth 506 conductive area, both at the centre conductor CNC of the transmission line and at a certain distance from each other. The first and second conductive areas are connected to each other by a conductor wire. Between this conductor wire and the third conductive area 505 it is connected a first coil L1. Correspondingly between the conductor wire and the fourth conductive area 506 is connected a similar second coil L2. Then the structure is symmetrical so that it looks similar seen from both ends of the transmission line.
In
The reflection circuit above is a stop band filter by nature, when the transmission line is matched to its characteristic impedance at the line ends. The parts of the circuit are designed so that the operating band of the antenna to be fed falls into the stop band of the filter. Because of the symmetrical structure the circuit functions as a similar band stop filter for the signals leaving either end of the transmission line, reflecting these signals with equal phase shift back to their starting end. Naturally, the stop band filter can be implemented also by a different circuit as that presented in
Owing to the oblique position of the portions of the first and second transmission lines, the width of their slides can not be only the same as of a transmission line, and also not separate because of the closeness of the lines. So the first and second lines have a shared slide 631, which extends in the arm direction over the total range, which is given when the first and second lines are projected to a straight line parallel to the arm. Also the third and fourth transmission lines have, in the example of
In order to obtain different phase shifts for the signals of the radiator pairs, the phase shifters are connected in cascade: After the first phase shift a signal is divided in half, one part is led to a radiator, and to the other part is made a second phase shift, after which the other part is led to the radiator of its own. Consistent with this, the radio frequency signal IN, coming from the transmitter power amplifier, is first divided to two parts in the divider 711. The first division signal E13 is led to the first port P1 of the first hybrid 751, and it will be got out as phased from its fourth port P4. The phase shift takes place in the reflection lines 741 and 743, which include the first ends of the first and second transmission lines as far as the slides and the lines between these transmission lines and the first hybrid, in the same way as in
The first 821 and second 822 transmission lines are for the outer radiator pair 871, 872, and the third 823 and fourth 824 transmission lines are for the inner radiator pair 873, 874. All transmission lines are equally long. The middle reflection circuit of each transmission line is at the halfway point of the transmission line. The other reflection circuits are on both sides of the middle circuit, with regular distances in this example. For the phase shifts of the signals of the inner radiators to be smaller than of the signals of the outer radiators, the reflection circuits of the third and fourth transmission lines are closer to each other than the reflection circuits of the first and second transmission lines. When the middle reflection circuits are activated, the signals of all radiators have the same phase. In the example of the drawing the second output S2 of the decoder 860 is set to the active state. The second output is connected to the second reflection circuits in order, as viewed from the first and third radiators. These second reflection circuits, or the reflection circuit 831 of the first transmission line, the reflection circuit 832 of the second transmission line, the reflection circuit 833 of the third transmission line and the reflection circuit 834 of the fourth transmission line, thus reflect the signals arriving to it from both sides. Therefore the phase of the transmitting signal of the first radiator 871 is advanced in respect of the phase of the transmitting signal of the second radiator 872, and the phase of the transmitting signal of the third radiator 873 is advanced in respect of the phase of the transmitting signal of the fourth radiator 874, which matter has the effect that the main radiation lobe turns downwards.
Above is described an arrangement for steering the radiation lobe of an array antenna, the arrangement being based on the reflection-type phase shifters and differential phase shift regarding a radiator pair. The described structure can differ from what is presented in details. The number of the antenna radiators can naturally vary. The number can also be odd, in which case the phase of the transmitting signal of the middle radiator is not adjustable. The transmission lines can be implemented in different ways, e.g. their conductors can be relatively rigid and air-insulated. Both in an air-insulated structure and in a structure using a circuit board the conductors, which are separated from the ground, of the transmission lines, hybrids and dividers can be unitary strips without junctions. Correspondingly, some ground conductors can form a unitary strip with each other. Also the implementing way of the slides can vary; their conductive part can e.g. be just an extension of a conductive arm. The inventive idea can be applied in different ways within the limits defined by the independent claim 1.
Number | Date | Country | Kind |
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20055285 | Jun 2005 | FI | national |
Number | Date | Country | |
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Parent | PCT/FI2006/050199 | May 2006 | US |
Child | 11946600 | Nov 2007 | US |