GB2182206A - Adaptable transmitter and antenna arrangement - Google Patents

Abstract

An array of dipoles (12) is fed from a plurality of low power transmitters (T1 to T8) by way of a network of hybrids (H1 to H8). Different combinations of transmitter phases cause the power to be routed to different groups of the dipoles (12) to enable the same array to simulate a plurality of different arrays. The dipoles are in eight pairs A1 to A8 and, in a first mode power is routed equally to all dipole pairs, in a second mode the power is routed to the lower four dipole pairs A2, A4, A6 and A8 only, in a third mode only to two columns of dipole pairs A3, A4, A5 and A6 and in a fourth mode to two dipole pairs A4 and A6 only. Although switches may be employed for various purposes, such as establishing the transmitter phases, slewing the antenna beam and interrupting feeders which should carry no power, switching is at low power levels only. <IMAGE>

Description

SPECIFICATION Adaptable transmitter and antenna arrangement The present invention relates to an adaptable transmitter and antenna arrangement which can provide any one of a plurality of different patterns of coverage.

A conventional h.f. transmitting station comprises at least one and usually several high-powertransmitters housed in a central building and a number of aerial arrays supported by masts ortowers spread out round the periphery of a field. The transmitters have to be coupled to the aerial arrays by long lengths of high-power feeders and, in order to allow anytransmitterto be connected to any aerial, a high-power switching matrix has to be included. This is illustrated, in part, in Figure 1, which is described below.

Each aerial array is fairly fixed as regards its radiation parameters. That is, a given array has fixed beam widths in the horizontal and vertical planes and has a fixed angle offire in the vertical plane. These parameters are determined bythe number of dipole radiators in the array and their layout in the vertical plane as illustrated in Figure 2. The only degree of flexibility is in the slew or angle of fire in the horizontal plane,which may be varied by up to 300. In a wide-frequency-band array the parameters are also intrinsically related to the input frequency, butthis is not considered here.Asa resultofthesefixed radiation parameters, several aerial arrays are required to fire in a particular direction so that, at different times, transmission may be made to different distances and to cover different areas of land in front of the aerial array.

The object of the present invention isto enable the different patterns of coverage to be achieved more efficiently, in particular by reducing the cost of antennas, feeders and switching arrangements.

The arrangement according to the invention is defined in the appended claims.

The invention will be described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure lisa schematic diagram of a conventional HF transmitting station, Figure2 illustrates a single antenna array as employed in the priorart, Figure 3 illustrates a transmitting station embodying the invention, Figure 4 illustrates a 0 -180 hybrid which may be used in the present invention, Figure 5illustrates the properties ofthe hybrid of Figure 4, Figure 6 shows some corresponding phaser diagrams, and Figure 7 is a more detailed schematic diagram of an arrangement embodying the invention.

Referring to Figure 1, a conventional transmitter station includes a plurality of aerial arrays 1 or, 10B, 1 OC strung between towers 11 and comprising dipoles 12 in front of reflecting screens 13. The station also includes at least onetransmitter, usually more than one, and two transmitters 14A and 14B are illustrated. A high power switching matrix 15 enables any transmitter to be coupled to any aerial array by way of a corresponding high power feeder 1 6A, 168, 160. The feeders are usually long and are expensive, as is the switching matrix 15, because of the need to handle full transmitter power. The feeders terminate in feed networks (not shown) which distribute the power to the dipoles 12.The antenna arrangement is also expensive because ofthe number oftowers 11 and aerial arrays required.

A high frequency broadcasting transmitter station may require a selection of aerial arrays such as H4/4/-, H2/2/-, H4/2/- and H2/4/- arrays where the initial H denotes horizontal dipoles, and the first and second digits indicate the number of dipoles wide and the numberofdipoles high in the array. Figure 2A is a front elevation of a H4/4- array with half-wave dipoles 12 in a 4-by-4 array at a half-wavelength pitch both horizontally and vertically. The screen 13 informed by horizontal wires. Support wires and feeders are not shown. The scree 13 is only partially indicated.Figure 2B shows the array in side elevation with its vertical radiation pattern 17 and the pattern 18 which results when the array is only two dipoles high and which exhibits less gain, a higher take-off angle and a greater beam-width.

Figure 2C is a plan view with the horizontal radiation pattern 19 and the pattern 20 which results when the array is only two dipoles wide. Table 1 givesthe parameters of the arrays listed above, assuming thatthe bottom row of dipoles is half a wavelength above ground level.

Table 1 Array Noof Noof Horiz Vert Vert Array type dipoles dipoles beam beam take off gain wide high width width angle H4/4/- 4 4 26 10 10 21dBi H2/2/- 2 2 48" 18 17 16dBi H4/2/- 4 2 26 18 17 19dsi H2/4/- 2 4 48" 10 10 18dBi In a conventional transmitter station there may thus be a 4-by-4 array, a 4-by-2 array, a 2-by-4 array and a 2-by-2 array - a total of 36 dipoles with four individual high-power feeders and feed networks.The embodiment of the invention to be described below provides the same facilities using only one 4-by-4 array, a feed arrangement in which no one feeder carries more than a half of the transmitted power, and in which no high-power switching is required.

Figure 3 illustrates the general arrangement with a single aerial array 10 fed from eight low power transmitters T1 to T8 by way of a feed network in the form of a hybrid matrix 21. As will be explained in detail below, the combined powerfrom the eight transmitters can be coupled to all or selected subsets ofthe dipoles 12 in the array 10 without any high-power switching. That is not to say that no switching is employed.

Switching may be required to slew the radiation pattern, to minimize coupling to unused parts of the array 10 and in drive arrangementsforthe hybrid matrix 21, but switching will be at one-eighth orone-quarterpower levels. The total transmitter power matches the power of the single transmitter 14A or 148 (Figure 1) which would normally be used. Because the individual transmitters and other components are low power, system reliability is increased. Moreover, the low power transmitters can be near the aerial array, so avoiding long, expensive feeders.

The hybrid matrix 21 uses hybrids which are well known in themselves. Although other types may be used, a four-port, crossover rat-race ortransformer 00i 800 hybrid is preferred, in part because oftheir excellent bandwidths. These and many other kinds of hybrid are described in "Hybrid networks and their uses in radio-frequency circuits", R G Manton,The Radio and Electronic Engineer Vol 54 No 11112, Nov/Dec 1984, pp 473-489.

Figure 4A illustrates the structure ofthe crossover rat-race hybrid. Four nodes 22 are connected byfour quarter wavelength lengths 23 oftransmission line. The nodes are connected to ports Ato D all presenting an impedance Z. The lengths 23 oftransmission line having a characteristic impedance Z0 = 2112Z. The length of line between ports B and D has its conductors crossed over, whereby this length behaves as if it had an electrical length not of a quarterwaveiength, but of with the important advantage of a slower rate of change of length with frequency - hence the high bandwidth. Figure 4B is a corresponding symbolic representation with the crossed-over length identified by the legend 1800, denoting its extra effective electrical length.

Figure 5 shows the properties ofthe hybrid when driven in various ways. Powers are shown by two values of which the first is power magnitude normalized to transmitter power equal to unity, while the second is phase angle. Figures 5A and 5B show power splitting from a single transmitter connected not adjacent and adjacent the 1 80" section respectively. Figures 5C, 5D and 5E show some of the possibilities when driving ports B and C with two transmitters of equal power but differing phases. The present invention makes use of these different possibilities to determine the power routing in dependence upon the phases ofthe transmitters T1 to T8.More specifically, when the two inputs are in phase quadrature, power divides equally between the two output ports, but also in phase quadrature. This can be used in distributing powerto different parts of the aerial array, and the phase quadrature relationship can be removed by use of a quarter wavelength delay. On the other hand, when the two inputs are in-phase or antiphase, power all passes to one output port; the other has no output. This can be used in routing powerto one part ofthe array and removing itfrom another part of the array.

If all phase angles which are integral multiples of 450 are considered, there are 32 different possible phase combinations forthe B and C inputs to a hybrid. However, there are only four basic patterns which are illustrated in the phasor diagrams of Figure 6Ato 6D. Figure 6A corresponds to Figure 5C, Figure 68 corresponds to Figure 5E and Figure 6C corresponds to Figure 5D. All other possibie situations are derived from Figures 6Ato 6D by simple rotations.

Figure 7 shows the complete arrangement configured for operation as a straight H4/4- array. The eight transmitters T1 to T8 are grouped in four pairs P1 (T1, T2), P2 (T3, T4), P3 (T5, T6) and P4 (T7, T8). Thetwo transmitters of each pair are connected to the B and C ports of a first bank of hybrids H1 to H4corresponding to the pairs P1 to P4 respectively. The A ports of the hybrids H1 to H4 are connected to feeders F1 to F4 all ofthe same electrical length (which is treated as zero for explanatory purposes).The D ports ofthe hybrids H1 to H4 are connected to feeders FSto F8 also of the same said electrical length, except for the selective inclusion of quarter- or half-wave loops L1 to L4 into the feeders F5 to F8. These loops are controlled by switches S1 to S8 which are set as shown to introduce quarter wave loops into all the feeders FSto F8 for the H414/- mode. Other settings ofthe switches will be explained below.

The feeders F1 to F8 are connected to the B and C ports of a second bank of hybrids H5 to H8. The D output feeders F5, F6 from H1 and H2 go to H5, the A output feeders F1, F2 from H1 and H2 go to H6, the Aoutput feeders F3, F4from H3 and H4 go to H7 and the D output feeders F7, F8 from H3 and H4 go to H8.

The A ports of the hybrids H5 to H8 are connected to feeders F9 to Fl 2 which are all of equal length (assumed to be 0 ) and are connected to pairs A2, A4, A6 and A8 respectively of the dipoles 12. These pairs comprise vertically adjacent dipoles in the two bottom rows ofthe 4-by-4 array, running moreover from leftto rightacrossthe array in columns C1 toy4.

The D ports ofthe hybrids H5 to H8 are connected to feeders Fl 3 to Fl 6 which are also of equal length but a quarter wavelength longer than the feeders F9 to F12, as indicated by 90" loops L5 to L8 in the feeders Fl 3to Fl 6. These feeders are connected to pairs Al, A3, A5 and A7 respectively ofthe dipoles, namelyvertically adjacent dipoles in the two top rows of the 4-by-4 array, running moreover from left to right acrossthe array in the columns Cl to C4.Thetop pairs of dipoles lie in a pair row R1 and the bottom pairs lie in a pairrowR2.

Figure 7 has been marked to showthe appropriatetransmitter phasesto use in all of thetransmittersT1 to T8 when operating in H4/4/- mode. The left hand half of the drawing has also been marked with the resultant phase angles at the outputs of the hybrids and as shifted by the extra feeder lengths represented by the loops such as L1 and L5. It will be seen that all dipole pairs Al toA8 are driven at the same phase and this isin accordance with the H4/4/- mode.The phase is shown as -90" because it has been assumed thatthefeeders F1 to F4 have electrical lengths of 0 (integral number of wavelengths long) and the feeders F5 to F8 are ofthe same length plus the 90 length switched in at the loops L1 to L4. In practice the lengths of the feeders F1 to Fl 6 may be such as to establish any arbitrary phase angle at the feed points ofthe dipoles; the point is thatthe phase will be the same for all dipoles and may be indicated as a relative phase of00.

This is the convention adopted in Table 2 at the end ofthis description which lists the transmitter phases for eight different modes (a) to (f) and the resultant dipole powers and relative phases. Mode (a) is the mode specifically illustrated in Figure 7 and described above. Mode (b) is the H2/2/- mode in which all transmitters are in phase. It is readily seen that the hybrids H1 to H4 only provide power on their A outputs, of the hybrids H5 to H8 onlythe hybrids H6 and H7 are driven and that these again provide power only on theirA outputs.

Accordingly, the power of all eight transmitters flows exclusively to the A4 and A6 dipole pairs, establishing the H2/2/- configuration. In practice isolation may be imperfect, due to mutual coupiing between dipoles, and it may be desirable to incorporate switches (not shown) in the feeders so that the switches in feeders which should not be carrying power can be opened. It will be appreciated that these switches, likethe switches S1 to S8, need not be high power devices.

The remaining modes of Table 2 will be readily understood. It should perhaps be mentioned that modes (e) and (f) are left and right H4141- modes because one half of the dipole array is driven with a phase lag relativeto the other half. The switches S1 to S8 are provided to enable an even greater slew to be achieved by increasing the phase delay of one half of the array to 1 80". The settings ofthese switches are given in Table 3 forthethree cases of normal (all the modes listed in Table 2), wide slew left and wide slew right.

Table 3 Mode S1 & 3 S2 & 4 S5 & 7 S6 & 8 Normal Open Closed Open Closed Wide slew left Open Open Closed Don't care Wide slew right Closed Don'tcare Open Open The transmitter phases for wide slew left and wide slew right are as in modes (e) and (f) of Table 2 respectively.

Analysing the principle of operation of Figure 7 in somewhat more general terms, it can be seen thatthe hybrids H5 to H8 can either distribute power to both ofthe rows R1 and R2 of dipole pairs, or only to one row, depending upon whetherthese hybrids are driven with quadrature inputs or non-quadrature inputs. In similar manner, the hybrids H1 to H4 make it possible to distribute powerto all of the columns C1 to C40rto route power only to the columns C2 and C3 oronly to the columns C1 and C4. In practice, the useful modes restrict powerto the row R2 and/orto the coiumns C2 and C3.The two sets of hybrids enable the array of dipoles to be partitioned in two dimensions. More complex partitioning schemes could clearly be devised and be based upon hybrids with different properties from those utilised in the embodiment described above.

Any convenient technology may be employed to selectthe phases of the transmitters driving the first set of hybrids. The transmitter carrier phases may themselves be switched. Alternatively the transmitters may be all co-phased and different loops may be switched in between the transmitters and the hybrids H1 to H4to establish the correct relative phases at the hybrid ports. Yet another possibility is to provide another system of hybrids (not shown) of the same nature as the system of Figure 7 but used reciprocally with the inputs and outputs interchanged.If wheat are now the inputs are driven by co-phased transmitters and these are selectively switched on and off, equal powers but with differing phases will be produced atthe outputs which are connected to the B and C ports of the hybrids H1 to H4. Once again, only low level power switching is involved.

Although the invention has been described in connection with an h.f. broadcasting system,the arrangement is not restricted to any particularfrequency of operating or application.

Table 2 Mode Transmitter Powers & Phases Corresponding Dipole Powers Aerial & Relative Phase Type (a) T1=1,-90 T3=1,-180 T5=1,-180 T7=1,-90 A1=1,0 A3=1,0 A5=1,0 A7=1,0 H4/4/ T2=1,0 T4=1,-90 T6=1,-90 T8=1,1 A2=1,0 A4=1,0 A6=1,0 A8=1,0 no slew (b) 1,0 1,0 1,0 1,0 0 0 0 0 H2/2/ 1,0 1,0 1,0 1,0 0 4,0 4,0 0 no slew (c) 1,-90 1,-90 1,-90 1,-90 0 0 0 0 H4/2/ 1,0 1,0 1,0 1,0 2,0 2,0 2,0 2,0 no slew (d) 1,0 1,-90 1,-90 1,0 0 2,0 2,0 0 H2/4/ 1,0 1,-90 1,-90 1,0 0 2,0 2,0 0 no slew (e) 1,-180 1,-270 1,-180 1,-90 1,-90 1,-90 1,0 1,0 H/4/4/ siewed left 1,-90 1,-180 1,-90 1,0 1,-90 1,-90 1,0 1,0 approx 10 (f) 1,-90 1,-180 1,-270 1,-180 1,0 1,0 1,-90 1,-90 H4/4/ slewed right 1,0 1,-90 1,-180 1,-90 1,0 1,0 1,-90 1,-90 approx 10

Claims (12)

1. An adaptabletransmitterand antenna arrangement comprising an array of radiating elements,a plurality oftransmitters and a network of hybrids connected between the transmitters and the radiating elements, the network being such that it transfers the powerfrom the transmitters to different groups ofthe radiating elements in correspondence with different combinations of transmitter phases at the input to the network.

2. An arrangement according to claim 1,wherein one ofthe said groups consists of all oftheradiating elements.

3. An arrangement according to claim 2, wherein the network of hybrids comprises a plurality of cascaded sets of hybrids, each set of hybrids routing powertowards all of a corresponding set of radiating elements when a first phase relationship between the inputs to the hybrids obtains and routing power to some only of the corresponding set of radiating elements when a second phase relationship between the inputs to the hybrids obtains.

4. An arrangement according to claim 3, wherein the array of radiating elements is a rectangular array of elements in rows and columns and there are two sets of hybrids, one of which routes power to half only ofthe columns of elements when the second phase relationship obtains forthat set, and the other of which routes power to half only of the rows of elements when the second phase relationship obtains for that set.

5. An arrangement according to any of claims 1 to 4, wherein at least one said combination oftransmitter phases establishes a phase shift across a dimension of the array of radiating elements so as to produce a slewed beam.

6. An arrangement according to claim 5, comprising switching means in the network of hybrids for varying the electrical length of feeders therein, so asto enhance the said phase shift.

7. An arrangement according to any of claims 1 to 6, comprising switches in feeders within the network of hybrids and/or between this network and the radiating elements, for interrupting those feeders which are theoretically carrying no power when a given combination of transmitter phases obtains.

8. An arrangement according to any of claims 1 to 7, wherein the hybrids are four-port, crossover rat-race hybrids.

9. An arrangement according to any of claims 1 to 7, wherein the hybrids arefour-port,transformer hybrids.

10. An arrangement according to any of claims 1 to 9, wherein thetransmittercarrier phases are switchableforselecting the different combinations oftransmitter phases at the inputs to the network.

11. An arrangement according to any of claims 1 to 9, wherein thetransmitters have fixed phases and comprising switching means between the transmitters and the network of hybrids for selectively introducing differentelectrical lengths so as to select the different combinations of transmitter phases atthe inputs to the network.

12. An arrangement according to any of claims 1 to 9, comprising a second, reciprocal network of hybrids between the transmitters and the first said network of hybrids, and means for selecting which trnasmitters are powered so as to selectthe different combinations oftransmitter phases at the inputs to the first said network.