CA3059076C - Reducing beamwidth dispersion and improving pattern quality for antenna arrays - Google Patents
Reducing beamwidth dispersion and improving pattern quality for antenna arrays Download PDFInfo
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- CA3059076C CA3059076C CA3059076A CA3059076A CA3059076C CA 3059076 C CA3059076 C CA 3059076C CA 3059076 A CA3059076 A CA 3059076A CA 3059076 A CA3059076 A CA 3059076A CA 3059076 C CA3059076 C CA 3059076C
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P5/00—Coupling devices of the waveguide type
- H01P5/12—Coupling devices having more than two ports
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P5/00—Coupling devices of the waveguide type
- H01P5/02—Coupling devices of the waveguide type with invariable factor of coupling
- H01P5/022—Transitions between lines of the same kind and shape, but with different dimensions
- H01P5/028—Transitions between lines of the same kind and shape, but with different dimensions between strip lines
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q21/00—Antenna arrays or systems
- H01Q21/0006—Particular feeding systems
- H01Q21/0075—Stripline fed arrays
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Abstract
Systems and methods for reducing beamwidth dispersion and sidelobes across a wide band of frequencies when a single antenna array is used to service that band of frequencies. Azimuth staggering the antenna array elements may be used to reduce the grating lobes in the higher parts of the frequency band. As well, when using a splitter, using a longer or a wider transmission line or using transmission lines with voids for impedance matching may also be used.
Description
CO. 03059076 2019-10-04 REDUCING BEAMWIDTH DISPERSION AND IMPROVING PATTERN QUALITY
FOR ANTENNA ARRAYS
TECHNICAL FIELD
[0001] The present invention relates to the field of antennas. More specifically, the present invention relates to systems and methods for use with a dispersive beamformer.
BACKGROUND
FOR ANTENNA ARRAYS
TECHNICAL FIELD
[0001] The present invention relates to the field of antennas. More specifically, the present invention relates to systems and methods for use with a dispersive beamformer.
BACKGROUND
[0002] In antenna arrays, the spacing between elements is a fixed number. Therefore, for an antenna array to be used at different frequencies over a wide frequency band, the effective electrical spacing between array elements varies. This results in a wide range of variation of the azimuth beamwidth over this frequency band.
[0003] One approach which has been used to reduce the variation of beamwidth over the band is to use different arrays for different parts of this wide frequency band. In other cases, the dispersion of the beam pattern as well as high grating lobes over the ultra-wide frequency band was tolerated.
Unfortunately, this suboptimum solution has been accepted as the cost of wanting an antenna array that can service a very wide band of frequencies.
Unfortunately, this suboptimum solution has been accepted as the cost of wanting an antenna array that can service a very wide band of frequencies.
[0004] As noted above, one approach is to use different sets of antenna elements (i.e. different arrays or interleaved arrays) to service different parts of this wide band of frequencies. This use of two sets of elements for two bands will, of course, lead to higher costs and larger antennas. The other approach is, as noted above, to accept suboptimum performance from the antenna array.
[0005] There is therefore a need for systems and methods which mitigate if not overcome the shortcomings of the prior art.
SUMMARY
SUMMARY
[0006] The present invention provides systems and methods for reducing beamwidth dispersion across a wide band of frequencies when a single antenna array is used to service that band of frequencies. Azimuth staggering the antenna array elements may be used to reduce the grating lobes in the higher parts of the frequency band. As well, when using a splitter, using a longer or a wider transmission line or using transmission lines with voids for impedance matching may also be used.
[0007] The techniques and systems disclosed herein include a solution for reducing dispersion over the wide frequency band by introducing the concept of a dispersive beam former. The approaches disclosed herein can considerably improve grating lobes and side lobes in bisector arrays. As well, to vary the array weightings through the frequency band, two methods are used and these methods allow for the variation of the weightings in a way that compensates for the effect of variable array spacing with respect to the signal wavelength. For a bisector array, this is combined with the new concept of a Wilkinson azimuth beamformer to further improve the sidelobe level. Staggering in azimuth in a bisector array is introduced to reduce the grating lobes at higher part of the frequency band. This document also discloses a splitter with proper dispersion to compensate for the dispersion caused by array spacing. Also included in this document is the design of a 3 output splitter based on the new approach of a dispersive transformer and on the concept of using voids or slots inside transmission lines for impedance matching. In addition, also disclosed is an implementation of a 4 port antenna designed using a dispersive beamformer.
[0008] Also disclosed in this document is an azimuth staggered architecture for a bisector antenna. This bisector antenna is designed to avoid grating lobes in an azimuth pattern. Finally, also disclosed is the design of a dispersive Wilkinson azimuth beamformer which provides bisector beams with minimum beamwidth dispersion over the frequency band.
[0009] In a first aspect, the present invention provides a transmission network having at least two transformer transmission lines for feeding at least one signal to at least one antenna element, the network comprising:
- at least one transformer transmission line of said at least two transformer transmission lines, said at least one transformer transmission line having at least one void for adjusting an impedance of said transmission network.
- at least one transformer transmission line of said at least two transformer transmission lines, said at least one transformer transmission line having at least one void for adjusting an impedance of said transmission network.
[0010] In a second aspect, the present invention provides a transmission network for feeding at least one signal to at least two antenna elements, the network comprising:
- a splitter subnetwork for splitting said at least one signal into at least two signals for said at least two antenna elements, the subnetwork comprising at least one first transmission line and at least one second transmission line, said at least one second transmission line having a width lesser than a width of said at least one first transmission line;
wherein said widths of said transmission lines are adjusted for better impedance matching.
- a splitter subnetwork for splitting said at least one signal into at least two signals for said at least two antenna elements, the subnetwork comprising at least one first transmission line and at least one second transmission line, said at least one second transmission line having a width lesser than a width of said at least one first transmission line;
wherein said widths of said transmission lines are adjusted for better impedance matching.
[0011] In a third aspect, the present invention provides an impedance transformer transmission line for use in a beamforming network, the transformer transmission line having a length of approximately 3A0/4 wherein Ao is a wavelength of a center frequency for a frequency band for which the transformer transmission line is to be used with.
[0012] In a fourth aspect, the present invention provides a beamformer network for use with at least two antennas, the beamformer comprising a Wilkinson divider subcircuit.
[0012a] The present description also discloses the following aspects:
1. A transmission network, as part of a signal splitter, having at least two transformer transmission lines for feeding at least one signal to at least two antenna elements, the transmission network comprising:
Date Recue/Date Received 2023-01-18 - at least one transformer transmission line of said at least two transformer transmission lines, said at least one transformer transmission line having at least one void for adjusting an impedance of said transmission network, wherein said transformer transmission line has a length of approximately 3A0/4 wherein Ao is a wavelength of a center frequency for a frequency band for which the transformer transmission line is to be used with, and - a splitter subnetwork for splitting said at least one signal into at least two signals for said at least two antenna elements, the splitter subnetwork comprising at least one first transmission line and at least one second transmission line, said at least one second transmission line having a width lesser than a width of said at least one first transmission line;
wherein said at least one transformer transmission line is a microstrip line;
wherein said transmission network intentionally introduces a dispersion of at least one beam produced by said transmission network; and wherein said widths of said transmission lines are adjusted for better impedance matching.
2. The transmission network according to aspect 1, wherein the length of said at least one transformer transmission line is adjusted to adjust a transmission coefficient of said at least one transmission line.
3. The transmission network according to aspect 1, wherein a width of said at least one transformer - 4a -Date Recue/Date Received 2023-01-18 transmission line is adjusted to adjust a transmission coefficient of said at least one transformer transmission line.
4. The transmission network according to aspect 1, wherein the length and a width of said at least one transformer transmission line is adjusted to adjust a transmission coefficient of said at least one transmission line.
5. The transmission network according to aspect 1, wherein said at least one void comprises at least one slot within said at least one transmission line.
6. The transmission network according to aspect 5, wherein said at least one slot comprises at least one rectangular slot.
7. The transmission network according to aspect 5, wherein said at least one slot comprises at least one elliptical slot.
8. The transmission network according to aspect 1, wherein a width of said at least one transmission line is adjusted for better impedance matching.
9. The transmission network according to aspect 1, wherein at least one of said at least one first transmission line has voids for adjusting an impedance of said at least one first transmission line.
10. The transmission network according to aspect 1, wherein at least one of said at least one second transmission line has voids for adjusting an impedance of said at least one second transmission line.
- 4b -Date Recue/Date Received 2023-01-18 11. The transmission network according to aspect 1, wherein said splitter subnetwork comprises one first transmission line and two second transmission lines, said first transmission line being placed between said two second transmission lines.
12. The transmission network according to aspect 11, wherein said first transmission line has a width larger than a width for said second transmission lines.
[0012a] The present description also discloses the following aspects:
1. A transmission network, as part of a signal splitter, having at least two transformer transmission lines for feeding at least one signal to at least two antenna elements, the transmission network comprising:
Date Recue/Date Received 2023-01-18 - at least one transformer transmission line of said at least two transformer transmission lines, said at least one transformer transmission line having at least one void for adjusting an impedance of said transmission network, wherein said transformer transmission line has a length of approximately 3A0/4 wherein Ao is a wavelength of a center frequency for a frequency band for which the transformer transmission line is to be used with, and - a splitter subnetwork for splitting said at least one signal into at least two signals for said at least two antenna elements, the splitter subnetwork comprising at least one first transmission line and at least one second transmission line, said at least one second transmission line having a width lesser than a width of said at least one first transmission line;
wherein said at least one transformer transmission line is a microstrip line;
wherein said transmission network intentionally introduces a dispersion of at least one beam produced by said transmission network; and wherein said widths of said transmission lines are adjusted for better impedance matching.
2. The transmission network according to aspect 1, wherein the length of said at least one transformer transmission line is adjusted to adjust a transmission coefficient of said at least one transmission line.
3. The transmission network according to aspect 1, wherein a width of said at least one transformer - 4a -Date Recue/Date Received 2023-01-18 transmission line is adjusted to adjust a transmission coefficient of said at least one transformer transmission line.
4. The transmission network according to aspect 1, wherein the length and a width of said at least one transformer transmission line is adjusted to adjust a transmission coefficient of said at least one transmission line.
5. The transmission network according to aspect 1, wherein said at least one void comprises at least one slot within said at least one transmission line.
6. The transmission network according to aspect 5, wherein said at least one slot comprises at least one rectangular slot.
7. The transmission network according to aspect 5, wherein said at least one slot comprises at least one elliptical slot.
8. The transmission network according to aspect 1, wherein a width of said at least one transmission line is adjusted for better impedance matching.
9. The transmission network according to aspect 1, wherein at least one of said at least one first transmission line has voids for adjusting an impedance of said at least one first transmission line.
10. The transmission network according to aspect 1, wherein at least one of said at least one second transmission line has voids for adjusting an impedance of said at least one second transmission line.
- 4b -Date Recue/Date Received 2023-01-18 11. The transmission network according to aspect 1, wherein said splitter subnetwork comprises one first transmission line and two second transmission lines, said first transmission line being placed between said two second transmission lines.
12. The transmission network according to aspect 11, wherein said first transmission line has a width larger than a width for said second transmission lines.
13. The transmission network according to aspect 9, wherein said voids comprise at least one slot within said at least one first transmission line.
14. The transmission network according to aspect 10, wherein said voids comprise at least one slot within said at least one second transmission line.
15. The transmission network according to aspect 12, wherein said first transmission line has at least one void on said first transmission line to adjust an impedance of said first transmission line.
16. The transmission network according to aspect 1, wherein said transformer transmission line is part of the signal splitter.
17. The transmission network according to aspect 16, wherein said signal splitter comprises a plurality of transmissions lines, said transformer transmission line being one of said plurality of transmission lines.
18. The transmission network according to aspect 16, wherein a width of said transformer transmission line is - 4c -Date Recue/Date Received 2023-01-18 adjusted to adjust a transmission coefficient of said transformer transmission line.
19. The transmission network according to aspect 1, wherein said transformer transmission line comprises at least one void for adjusting an impedance of said transformer transmission line.
20. The transmission network according to aspect 19, wherein said at least one void comprises at least one rectangular slot.
21. The transmission network according to aspect 19, wherein said at least one void comprises at least one elliptical slot.
22. A beamformer network for use with at least two antennas, the beamformer comprising:
- a Wilkinson divider subcircuit; and - at least one transformer transmission line as defined in aspect 1.
- a Wilkinson divider subcircuit; and - at least one transformer transmission line as defined in aspect 1.
23. The beamformer network according to aspect 22, wherein said beamformer is used with a bisector array.
24. The beamformer network according to aspect 22, wherein the length of transformer transmission lines in said beamformer network are adjusted to affect beamwidth dispersion of antenna beams produced by said at least two antennas.
25. The beamformer network according to aspect 22, wherein a width of transformer transmission lines in said beamformer network are adjusted to affect beamwidth - 4d -Date Recue/Date Received 2023-01-18 dispersion of antenna beams produced by said at least two antennas.
26. The beamformer network according to aspect 22, wherein said beamformer network is used with an antenna array, said antenna array having antenna elements which are staggered in an azimuth plane.
27. The transmission network according to aspect 1, wherein said length of said transformer transmission line intentionally introduces an intentional dispersion to compensate the existing dispersion of a beamwidth over a wide frequency band of a beam produced by a system using a beamformer network.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The embodiments of the present invention will now be described by reference to the following figures, in which identical reference numerals in different figures indicate identical elements and in which:
FIGURE I shows two variations of a transformer with the two variations have different lengths;
- 4e -Date Recue/Date Received 2023-01-18 FIGURES 2A and 2B are plots illustrated the return loss and transmission coefficient for the two transformers in Figure 1;
FIGURE 3A illustrates a 3-way splitter with a longer transformer length of approximately 32w/4;
FIGURE 3B shows a plot of the performance of the splitter in Figure 3A;
FIGURE 4A is a 3-way splitter with a conventional transformer length of approximately Xo/4;
FIGURE 4B is a plot of the performance of the splitter illustrated in Figure 4A;
FIGURE 5A is a diagram illustrated a 3-way splitter according to one aspect of the invention;
FIGURE 5B is a plot of the performance of the splitter illustrated in Figure 5A;
FIGURE 6A illustrates another 3-way splitter according to yet another aspect of the invention;
FIGURE 6B is a plot of the performance of the splitter illustrated in Figure 6A;
FIGURE 6C illustrates a variant of the 3-way splitter illustrated in Figure 6A;
FIGURES 7A and 7B are plots of the performance of the splitter illustrated in Figure 6A for two different sets of line widths;
FIGURE 8 illustrates an antenna array which uses the splitter illustrated in Figure 6A;
FIGURES 9A and 93 illustrate patterns for different frequencies for an antenna using the beamformer illustrated in Figure 6A;
FIGURE 10 illustrates a tri-band antenna with two highband sides fed with different beamformer networks;
FIGURES 11A, 11B, and 11C illustrate overlaid patterns for different frequencies using antenna arrays which use different beamforming networks;
FIGURES 12A and 12B illustrate a conventional wideband beamforming network and its performance;
FIGURES 13A, 13B, and 13C illustrate a Wilkinson ABFN
according to another aspect of the invention and its performance plots;
FIGURES 14A, 143, and 14C illustrate a variant of the beamforming network illustrated in Figure 13A along with its performance plots;
FIGURE 15 illustrates an antenna array illustrating another aspect of the present invention;
FIGURE 16A illustrates beam patterns for an antenna using a conventional ABFN;
FIGURE 16B illustrates beam patterns for an antenna using a Wilkinson ABFN and using azimuth antenna array staggering according to yet another aspect of the present invention; and FIGURES 17A, 17B, and 17C illustrate beam patterns for the antenna illustrated in Figure 15 at different frequencies.
DETAILED DESCRIPTION
[0014] The concept of a dispersive beamformer is related to the design of a beamformer which has a dispersive amplitude over a given frequency band. When dealing with a fixed physical spacing between antenna elements in an antenna array, an increase in the frequency entails an increase in this physical spacing relative to the signal's wavelength. This causes the resulting beam to be narrower in beamwidth. To provide an antenna array suitable for a very wide frequency band and with only a small variation in the beamwidth over that frequency band, the weightings for the antenna elements can be adjusted. Specifically, the weightings for the various antenna elements can be adjusted such that the side array elements are fed with less power compared to the middle array elements as the signal frequency increases. This will provide much less dispersion of beamwidth over the frequency band.
[0015] One innovative approach for introducing intentional dispersion in a splitter used in a transmission network is to use the natural dispersion of a microstrip line combined with the intrinsic properties of transmission lines.
[0016] If a longer transmission line is used, the phase difference between any two frequencies in the frequency band would be greater than if a shorter transmission line was used. This means that, for a given frequency band, a longer transmission line increases the difference between electrical length of the line between the two end frequencies of that band compared to a shorter transmission line.
[0017] Referring to Figure 1, an example of the above is provided. For an impedance transformer, if, instead of a Xo/4 transformer, a 3X0/4 transformer was used (with Xo being the wavelength at the center frequency of the frequency band), an impedance match will still exist at the middle frequencies of the frequency band.
However, this matching deteriorates as the frequencies change through the band due to a more rapid change of impedance for the 3X014 transmission line. A 3A0/4 transmission line deviates from the required electrical length for a transformer faster as frequency changes from the middle frequency toward the edges of the band. This can be seen in Figures 2A and 2B. Figure 2A shows the return loss while Figure 2B
shows the transmission coefficient for the two transmission lines in Figure 1. The green plots in Figures 2A and 2B are for the 3X0/4 transmission line while the purple plots are for the Xo/4 transmission line.
[0018] It should be noted that, in a microstrip line, due to the inhomogeneous media of propagation, the slope of the phase velocity varies with frequency and the value of the phase velocity depends on the width of the transmission line. This means that inhomogeneous transmission lines (such as microstrip lines) with certain physical lengths and different widths have different electrical lengths.
[0019] In one aspect of the invention, these usually undesired qualities are combined in an innovative splitter that provides amplitude dispersion over a wide frequency band of 1.71-2.69GHz.
-B-[0020] In one aspect of the invention, a dispersive splitter (see Figure 3A) has matching arms that are chosen as having a length around 3X0/4 instead of the usual 23/4.
This amplifies the difference between frequency behavior of middle branch impedance and the two side branch impedances through the frequency band and therefore makes the splitting ratio different across the band. This is because the splitting ratio is a function of the line impedances at each frequency. As shown in Figure 3B, by slightly changing the middle frequency from 321.o/4, the splitting ratio and the impedance matching can be controlled.
[0021] Referring to Figure 4A, illustrated is a traditional non-dispersive splitter with a Xo/4 transformer. Figure 4B shows the performance of this traditional splitter which shows a constant transmission through the band.
In the splitter in Figure 4A, the distance indicated by the arrows is approximately Xo/4.
[0022] Referring to Figure 5A, illustrated is a dispersive beamformer according to one aspect of the invention.
The line widths and length of transformer for this beamformer are optimized to have the required weightings with low taper at the beginning of the frequency band and high taper at the end of the frequency band. The performance of this beamformer is shown in the plots in Figure 5B. As can be seen, the 3-way splitter in Figure 5A has a middle transmission line with a much larger width than the two side transmission lines. In one Implementation, the distance indicated by the arrows is approximately 53 mm and the line widths are 2.8mm for the middle branch and 0.6mm for the outside branches.
[0023] To improve the impedance matching for the azimuth beamforming network (ABFN), voids may be placed in the transmission line. In one implementation, these voids take the form of slots. For the beamformer illustrated in Figure 5A, slots may be placed within the wider, middle transmission line to result in the beamformer illustrated in Figure 6A. The result is a well matched dispersive splitter. The performance of this splitter is illustrated in the plots of Figure 6B. In one implementation, the distance indicated by the arrows in Figure GA is approximately 53 mm.
[0024] In another implementation of the azimuth beamforming network with improved impedance matching, the voids were in the form of elliptical slots (see Figure 6C).
This is in contrast to the implementation illustrated in Figure 6A where the voids were in the form of rectangular slots.
[0025] The plots in Figure 7A show the weightings and the input reflection for the splitter in Figure EA in terms of absolute magnitude. The particular splitter illustrated in Figure 6A is designed for a variable power ratio from 0.8:1:0.8 at the beginning of the frequency band to a 0.17:1:0.17 ratio at the end of the frequency band. The widths of transmission lines, in one implementation, are 2.8mm for the middle transmission line and 0.6mm for the side transmission lines. It should be noted that the same concept may be used with any other power dividing ratio. In another implementation with less tapering, the transmission line are: line widths of 2.7mm for the middle transmission line and 0.9mm for the side transmission lines with a transmission ratio of 0.82:1:0.82 at the beginning to 0.3:1:0.3 at the end of frequency band.
The transformer length is optimized for such tapering as 5 lmm. Results for this other implementation are shown in Figure 7B. In both Figures 7A and 7B, the weightings are shown in magnitude while in the rest of the Figures, unless otherwise indicated, the weightings are shown in dB.
[0026] The splitter illustrated in Figure 6A has been tested in a number of different antenna arrays and has shown superior performance in stabilizing beam width when compared to a usual 33deg antenna.
[0027] Referring to Figure 8, an antenna array using the splitter illustrated in Figure 6A is illustrated. The antenna array in Figure 8 has two side by side, 4 port 33 deg antenna array using the dispersive beamforming network illustrated in Figure 6A.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The embodiments of the present invention will now be described by reference to the following figures, in which identical reference numerals in different figures indicate identical elements and in which:
FIGURE I shows two variations of a transformer with the two variations have different lengths;
- 4e -Date Recue/Date Received 2023-01-18 FIGURES 2A and 2B are plots illustrated the return loss and transmission coefficient for the two transformers in Figure 1;
FIGURE 3A illustrates a 3-way splitter with a longer transformer length of approximately 32w/4;
FIGURE 3B shows a plot of the performance of the splitter in Figure 3A;
FIGURE 4A is a 3-way splitter with a conventional transformer length of approximately Xo/4;
FIGURE 4B is a plot of the performance of the splitter illustrated in Figure 4A;
FIGURE 5A is a diagram illustrated a 3-way splitter according to one aspect of the invention;
FIGURE 5B is a plot of the performance of the splitter illustrated in Figure 5A;
FIGURE 6A illustrates another 3-way splitter according to yet another aspect of the invention;
FIGURE 6B is a plot of the performance of the splitter illustrated in Figure 6A;
FIGURE 6C illustrates a variant of the 3-way splitter illustrated in Figure 6A;
FIGURES 7A and 7B are plots of the performance of the splitter illustrated in Figure 6A for two different sets of line widths;
FIGURE 8 illustrates an antenna array which uses the splitter illustrated in Figure 6A;
FIGURES 9A and 93 illustrate patterns for different frequencies for an antenna using the beamformer illustrated in Figure 6A;
FIGURE 10 illustrates a tri-band antenna with two highband sides fed with different beamformer networks;
FIGURES 11A, 11B, and 11C illustrate overlaid patterns for different frequencies using antenna arrays which use different beamforming networks;
FIGURES 12A and 12B illustrate a conventional wideband beamforming network and its performance;
FIGURES 13A, 13B, and 13C illustrate a Wilkinson ABFN
according to another aspect of the invention and its performance plots;
FIGURES 14A, 143, and 14C illustrate a variant of the beamforming network illustrated in Figure 13A along with its performance plots;
FIGURE 15 illustrates an antenna array illustrating another aspect of the present invention;
FIGURE 16A illustrates beam patterns for an antenna using a conventional ABFN;
FIGURE 16B illustrates beam patterns for an antenna using a Wilkinson ABFN and using azimuth antenna array staggering according to yet another aspect of the present invention; and FIGURES 17A, 17B, and 17C illustrate beam patterns for the antenna illustrated in Figure 15 at different frequencies.
DETAILED DESCRIPTION
[0014] The concept of a dispersive beamformer is related to the design of a beamformer which has a dispersive amplitude over a given frequency band. When dealing with a fixed physical spacing between antenna elements in an antenna array, an increase in the frequency entails an increase in this physical spacing relative to the signal's wavelength. This causes the resulting beam to be narrower in beamwidth. To provide an antenna array suitable for a very wide frequency band and with only a small variation in the beamwidth over that frequency band, the weightings for the antenna elements can be adjusted. Specifically, the weightings for the various antenna elements can be adjusted such that the side array elements are fed with less power compared to the middle array elements as the signal frequency increases. This will provide much less dispersion of beamwidth over the frequency band.
[0015] One innovative approach for introducing intentional dispersion in a splitter used in a transmission network is to use the natural dispersion of a microstrip line combined with the intrinsic properties of transmission lines.
[0016] If a longer transmission line is used, the phase difference between any two frequencies in the frequency band would be greater than if a shorter transmission line was used. This means that, for a given frequency band, a longer transmission line increases the difference between electrical length of the line between the two end frequencies of that band compared to a shorter transmission line.
[0017] Referring to Figure 1, an example of the above is provided. For an impedance transformer, if, instead of a Xo/4 transformer, a 3X0/4 transformer was used (with Xo being the wavelength at the center frequency of the frequency band), an impedance match will still exist at the middle frequencies of the frequency band.
However, this matching deteriorates as the frequencies change through the band due to a more rapid change of impedance for the 3X014 transmission line. A 3A0/4 transmission line deviates from the required electrical length for a transformer faster as frequency changes from the middle frequency toward the edges of the band. This can be seen in Figures 2A and 2B. Figure 2A shows the return loss while Figure 2B
shows the transmission coefficient for the two transmission lines in Figure 1. The green plots in Figures 2A and 2B are for the 3X0/4 transmission line while the purple plots are for the Xo/4 transmission line.
[0018] It should be noted that, in a microstrip line, due to the inhomogeneous media of propagation, the slope of the phase velocity varies with frequency and the value of the phase velocity depends on the width of the transmission line. This means that inhomogeneous transmission lines (such as microstrip lines) with certain physical lengths and different widths have different electrical lengths.
[0019] In one aspect of the invention, these usually undesired qualities are combined in an innovative splitter that provides amplitude dispersion over a wide frequency band of 1.71-2.69GHz.
-B-[0020] In one aspect of the invention, a dispersive splitter (see Figure 3A) has matching arms that are chosen as having a length around 3X0/4 instead of the usual 23/4.
This amplifies the difference between frequency behavior of middle branch impedance and the two side branch impedances through the frequency band and therefore makes the splitting ratio different across the band. This is because the splitting ratio is a function of the line impedances at each frequency. As shown in Figure 3B, by slightly changing the middle frequency from 321.o/4, the splitting ratio and the impedance matching can be controlled.
[0021] Referring to Figure 4A, illustrated is a traditional non-dispersive splitter with a Xo/4 transformer. Figure 4B shows the performance of this traditional splitter which shows a constant transmission through the band.
In the splitter in Figure 4A, the distance indicated by the arrows is approximately Xo/4.
[0022] Referring to Figure 5A, illustrated is a dispersive beamformer according to one aspect of the invention.
The line widths and length of transformer for this beamformer are optimized to have the required weightings with low taper at the beginning of the frequency band and high taper at the end of the frequency band. The performance of this beamformer is shown in the plots in Figure 5B. As can be seen, the 3-way splitter in Figure 5A has a middle transmission line with a much larger width than the two side transmission lines. In one Implementation, the distance indicated by the arrows is approximately 53 mm and the line widths are 2.8mm for the middle branch and 0.6mm for the outside branches.
[0023] To improve the impedance matching for the azimuth beamforming network (ABFN), voids may be placed in the transmission line. In one implementation, these voids take the form of slots. For the beamformer illustrated in Figure 5A, slots may be placed within the wider, middle transmission line to result in the beamformer illustrated in Figure 6A. The result is a well matched dispersive splitter. The performance of this splitter is illustrated in the plots of Figure 6B. In one implementation, the distance indicated by the arrows in Figure GA is approximately 53 mm.
[0024] In another implementation of the azimuth beamforming network with improved impedance matching, the voids were in the form of elliptical slots (see Figure 6C).
This is in contrast to the implementation illustrated in Figure 6A where the voids were in the form of rectangular slots.
[0025] The plots in Figure 7A show the weightings and the input reflection for the splitter in Figure EA in terms of absolute magnitude. The particular splitter illustrated in Figure 6A is designed for a variable power ratio from 0.8:1:0.8 at the beginning of the frequency band to a 0.17:1:0.17 ratio at the end of the frequency band. The widths of transmission lines, in one implementation, are 2.8mm for the middle transmission line and 0.6mm for the side transmission lines. It should be noted that the same concept may be used with any other power dividing ratio. In another implementation with less tapering, the transmission line are: line widths of 2.7mm for the middle transmission line and 0.9mm for the side transmission lines with a transmission ratio of 0.82:1:0.82 at the beginning to 0.3:1:0.3 at the end of frequency band.
The transformer length is optimized for such tapering as 5 lmm. Results for this other implementation are shown in Figure 7B. In both Figures 7A and 7B, the weightings are shown in magnitude while in the rest of the Figures, unless otherwise indicated, the weightings are shown in dB.
[0026] The splitter illustrated in Figure 6A has been tested in a number of different antenna arrays and has shown superior performance in stabilizing beam width when compared to a usual 33deg antenna.
[0027] Referring to Figure 8, an antenna array using the splitter illustrated in Figure 6A is illustrated. The antenna array in Figure 8 has two side by side, 4 port 33 deg antenna array using the dispersive beamforming network illustrated in Figure 6A.
[0028] Referring to Figures 9A and 9B, illustrated are patterns for an antenna (using the beamforming network illustrated in Figure 6A) designed for 1.85-1.995 GHz and 2.49-2.69 GHz bands. In Figure 9A, the plots are for the frequency of 1.9 GHz while Figure 9B shows the plots for a frequency of 2.63 GHz. The beamwidth variation between these two far apart frequencies is only 3 degrees (i.e. from 39 degrees to 36 degrees).
[0029] In another test, a tri-band antenna with added elements for lower frequencies (850MHz) was used. The antenna used is shown in Figure 10. For this test, one side of the highband array was fed a signal using the normal beamformer of Figure 4A (the section circled and labelled "a" in Figure 10). For the other side, the beamformer show in Figure 6A was used with line widths of 2.7mm for middle transmission line and 0.9mm for the side transmission lines (the section circled and labelled "b" in Figure 10). The plots of the results are shown in Figures 11A, 11B, and 110.
Figure 11A illustrates the resulting overlaid patterns for 1900 and 2630 mHz using the normal beamforming network while Figure 11B shows the resulting overlaid patterns for 1900 and 2630 MHz for the dispersive beamforming network illustrated in Figure 6A. As can be seen, a beamwidth variation from 29 deg to 44deg (approximately 15deg) was observed between the two frequencies (1.9 GHz and 2.63GHz) for the side with normal beamformer. For the dispersive beamformer, the beamwidth variation was from 31deg to 38deg (a 7 deg variation). Figure 11C shows the results of using the beamformer in Figure 6A with a line width of 2.8mm for the middle transmission line and 0.6mm for the side transmission lines. As can be seen, the difference between the patterns for the two sides at two different frequencies is considerable.
For bisector arrays, beamforming is more complex and requires a semi-Butler matrix structure. That being said, the dispersive beamformer concept can also be applied to this more complex beamformer.
Figure 11A illustrates the resulting overlaid patterns for 1900 and 2630 mHz using the normal beamforming network while Figure 11B shows the resulting overlaid patterns for 1900 and 2630 MHz for the dispersive beamforming network illustrated in Figure 6A. As can be seen, a beamwidth variation from 29 deg to 44deg (approximately 15deg) was observed between the two frequencies (1.9 GHz and 2.63GHz) for the side with normal beamformer. For the dispersive beamformer, the beamwidth variation was from 31deg to 38deg (a 7 deg variation). Figure 11C shows the results of using the beamformer in Figure 6A with a line width of 2.8mm for the middle transmission line and 0.6mm for the side transmission lines. As can be seen, the difference between the patterns for the two sides at two different frequencies is considerable.
For bisector arrays, beamforming is more complex and requires a semi-Butler matrix structure. That being said, the dispersive beamformer concept can also be applied to this more complex beamformer.
[0030] The dispersive beamformer described above uses the concepts of:
1) using longer transformer lines such that the difference in electrical length of the transformer line between two end frequencies of a band is greater than it would be if a shorter transmission line were used 2) taking advantage of the phase velocity slope's dependency on frequency and on the width of the microstrip transmission line.
These two concepts can be used to good advantage when applied to bisector arrays.
1) using longer transformer lines such that the difference in electrical length of the transformer line between two end frequencies of a band is greater than it would be if a shorter transmission line were used 2) taking advantage of the phase velocity slope's dependency on frequency and on the width of the microstrip transmission line.
These two concepts can be used to good advantage when applied to bisector arrays.
[0031] Referring to Figure 12A, a 2x4 wideband azimuth beamformer designed to cover the 1695-2690MHz frequency band is illustrated. The plot of the transmission coefficients for this beamformer is illustrated in Figure 12B. When the beamformer in Figure 12A is used to feed a suitable antenna array, the poor output match of the beamformer causes reflections from the array elements to reflect back on to the array. This effectively changes the weightings of the array and increases the azimuth sidelobes. To considerably improve on the beamwidth pattern, Wilkinson unequal power dividers internal to the semi-Butler beamformer may be used.
[0032] Further to the above, two versions of a Wilkinson azimuth beamforming network according to further aspects of the invention are illustrated in Figures 13A and 14A. In both these versions of a dispersion ABFN, the large difference between each branch's line widths helps to reduce overall beamwidth dispersion by introducing dispersive weightings as shown in Figure 13B. As noted before, when the difference in the width of two transmission lines in a splitter is high or large, the dispersive behaviour of the two lines is more apparent. This can then be used to provide dispersive weightings in a shorter length of transmission line as shown in Figure 3B.
[0033] Referring to Figure 13A, this version of a dispersion ABFN has one stage of output matching. This single stage causes lower values of input isolation. For this circuit, a 100 ohm resistor is between points 7-8 and 9-10 in the circuit. The transmission coefficients for this ABFN are shown in Figure 13B while the isolation and return loss performance is shown in Figure 13C.
[0034] To improve input isolation, a second version of a dispersion ABFN is illustrated in Figure 14A. This version uses two stage output matching. For the circuit in Figure 14A, a 100 ohm resistor is placed between points 7-8 and 9-10 in the circuit. The transmission coefficients for this ABFN are shown in Figure 14B while the isolation and return loss performance is shown in Figure 14C.
[0035] It should be noted that both versions of the ABFN
beamformer (illustrated in Figures 13A and 14A) have been tested. When compared to the beamformer illustrated in Figure 12A, the dispersion beamformers showed a marked improvement in performance.
beamformer (illustrated in Figures 13A and 14A) have been tested. When compared to the beamformer illustrated in Figure 12A, the dispersion beamformers showed a marked improvement in performance.
[0036] It should be noted that, in addition to reducing overall beamwidth dispersion, using the dispersion ABFN also has further benefits. By using the concept of a Wilkinson divider, this reduces the effect of mutual coupling between antenna elements on the ABFN's performance, thereby allowing for the reduction in the spacing between antenna elements. This leads to an improvement in not just the second sidelobe level (SLL) but also in the cross over at the edge of the sector due to a wider beamwidth.
[0037] The quality of the resulting pattern may also be improved by merely adjusting the arrangement of the antenna array elements. The antenna array elements may be staggered in the array in azimuth. The staggering of the array elements helps to reduce the second azimuth SLL as well as other grating lobes. An example of an antenna array applying this approach is shown in Figure 15. To compensate for the effect of staggering on the elevation pattern, separate phase adjustments on the feeding cables for left and right beams may be needed.
[0038] As noted above, the azimuth staggering helps to reduce the second azimuth SLL and, especially, the second sidelobe and grating lobes. The reduction arises by effectively reducing the element spacing in the azimuth plane. This can be explained by considering that each element of the second group of two rows in the azimuth plane is located somewhere between two elements of the first group of two rows in the azimuth plane.
[0039] It should be noted that, since the azimuth beam is offset from boresight, the staggering has a destructive effect on the elevation pattern and this needs to be compensated for. The staggering changes the phase center of the array for the right and left beams. The right beam phase center for the second group of rows compared to the first group of rows is less delayed while the left beam phase center is more delayed for the second group of rows. To compensate for the effect of staggering on the elevation pattern, separate phase adjustments on the feeding cables for left and right beams should be applied. The second row of two element groups needs to be more delayed for the right beam while it should be less delayed for the left beam. Depending on the direction of staggering and the amount of staggering, these arrangements may be different.
[0040] Referring to Figures 16A and 16B, the patterns of an antenna array which does not use array azimuth element staggering (Figure 16A) and an antenna array which staggers the antenna array elements in azimuth (Figure 16B) is shown. For the patterns, a signal at a frequency of 2360 MHz was used. The superior performance of the new beamformer can be seen, especially when considering the second and first azimuth SLL, wider azimuth beamwidth, and a better crossover at sectors (+/-60deg).
[0041] Referring to Figure 17A, 17B, and 170, the pattern behaviour for the antenna array in Figure 15 can be seen. In Figure 17A, the pattern behaviour at 1.85 GHz is shown. For Figure 17B, the pattern behaviour at 2.17 GHz is shown. For Figure 170, the pattern behaviour at 2.69 GHz is shown.
[0042] A person understanding this invention may now conceive of alternative structures and embodiments or variations of the above all of which are intended to fall within the scope of the invention as defined in the claims that follow.
Claims (27)
1. A transmission network, as part of a signal splitter, having at least two transformer transmission lines for feeding at least one signal to at least two antenna elements, the transmission network comprising:
- at least one transformer transmission line of said at least two transformer transmission lines, said at least one transformer transmission line having at least one void for adjusting an impedance of said transmission network, wherein said transformer transmission line has a length of approximately 3X0/4 wherein Xo is a wavelength of a center frequency for a frequency band for which the transformer transmission line is to be used with, and - a splitter subnetwork for splitting said at least one signal into at least two signals for said at least two antenna elements, the splitter subnetwork comprising at least one first transmission line and at least one second transmission line, said at least one second transmission line having a width lesser than a width of said at least one first transmission line;
wherein said at least one transformer transmission line is a microstrip line;
wherein said transmission network intentionally introduces a dispersion of at least one beam produced by said transmission network; and wherein said widths of said transmission lines are adjusted for better impedance matching.
- at least one transformer transmission line of said at least two transformer transmission lines, said at least one transformer transmission line having at least one void for adjusting an impedance of said transmission network, wherein said transformer transmission line has a length of approximately 3X0/4 wherein Xo is a wavelength of a center frequency for a frequency band for which the transformer transmission line is to be used with, and - a splitter subnetwork for splitting said at least one signal into at least two signals for said at least two antenna elements, the splitter subnetwork comprising at least one first transmission line and at least one second transmission line, said at least one second transmission line having a width lesser than a width of said at least one first transmission line;
wherein said at least one transformer transmission line is a microstrip line;
wherein said transmission network intentionally introduces a dispersion of at least one beam produced by said transmission network; and wherein said widths of said transmission lines are adjusted for better impedance matching.
2. The transmission network according to claim 1, wherein the length of said at least one transformer transmission line Date Recue/Date Received 2023-01-18 is adjusted to adjust a transmission coefficient of said at least one transmission line.
3. The transmission network according to claim 1, wherein a width of said at least one transformer transmission line is adjusted to adjust a transmission coefficient of said at least one transformer transmission line.
4. The transmission network according to claim 1, wherein the length and a width of said at least one transformer transmission line is adjusted to adjust a transmission coefficient of said at least one transmission line.
5. The transmission network according to claim 1, wherein said at least one void comprises at least one slot within said at least one transmission line.
6. The transmission network according to claim 5, wherein said at least one slot comprises at least one rectangular slot.
7. The transmission network according to claim 5, wherein said at least one slot comprises at least one elliptical slot.
8. The transmission network according to claim 1, wherein a width of said at least one transmission line is adjusted for better impedance matching.
9. The transmission network according to claim 1, wherein at least one of said at least one first transmission line has voids for adjusting an impedance of said at least one first transmission line.
10. The transmission network according to claim 1, wherein at least one of said at least one second transmission line Date Recue/Date Received 2023-01-18 has voids for adjusting an impedance of said at least one second transmission line.
11. The transmission network according to claim 1, wherein said splitter subnetwork comprises one first transmission line and two second transmission lines, said first transmission line being placed between said two second transmission lines.
12. The transmission network according to claim 11, wherein said first transmission line has a width larger than a width for said second transmission lines.
13. The transmission network according to claim 9, wherein said voids comprise at least one slot within said at least one first transmission line.
14. The transmission network according to claim 10, wherein said voids comprise at least one slot within said at least one second transmission line.
15. The transmission network according to claim 12, wherein said first transmission line has at least one void on said first transmission line to adjust an impedance of said first transmission line.
16. The transmission network according to claim 1, wherein said transformer transmission line is part of the signal splitter.
17. The transmission network according to claim 16, wherein said signal splitter comprises a plurality of transmissions lines, said transformer transmission line being one of said plurality of transmission lines.
18. The transmission network according to claim 16, wherein a width of said transformer transmission line is adjusted to Date Recue/Date Received 2023-01-18 adjust a transmission coefficient of said transformer transmission line.
19. The transmission network according to claim 1, wherein said transformer transmission line comprises at least one void for adjusting an impedance of said transformer transmission line.
20. The transmission network according to claim 19, wherein said at least one void comprises at least one rectangular slot.
21. The transmission network according to claim 19, wherein said at least one void comprises at least one elliptical slot.
22. A beamformer network for use with at least two antennas, the beamformer comprising:
- a Wilkinson divider subcircuit; and - at least one transformer transmission line as defined in claim 1.
- a Wilkinson divider subcircuit; and - at least one transformer transmission line as defined in claim 1.
23. The beamformer network according to claim 22, wherein said beamformer is used with a bisector array.
24. The beamformer network according to claim 22, wherein the length of transformer transmission lines in said beamformer network are adjusted to affect beamwidth dispersion of antenna beams produced by said at least two antennas.
25. The beamformer network according to claim 22, wherein a width of transformer transmission lines in said beamformer network are adjusted to affect beamwidth dispersion of antenna beams produced by said at least two antennas.
Date Recue/Date Received 2023-01-18
Date Recue/Date Received 2023-01-18
26. The beamformer network according to claim 22, wherein said beamformer network is used with an antenna array, said antenna array having antenna elements which are staggered in an azimuth plane.
27. The transmission network according to claim 1, wherein said length of said transformer transmission line intentionally introduces an intentional dispersion to compensate the existing dispersion of a beamwidth over a wide frequency band of a beam produced by a system using a beamformer network.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
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| US201762501978P | 2017-05-05 | 2017-05-05 | |
| US62/501,978 | 2017-05-05 | ||
| PCT/CA2018/050232 WO2018201223A1 (en) | 2017-05-05 | 2018-02-28 | Reducing beamwidth dispersion and improving pattern quality for antenna arrays |
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| US5966102A (en) * | 1995-12-14 | 1999-10-12 | Ems Technologies, Inc. | Dual polarized array antenna with central polarization control |
| US7873326B2 (en) * | 2006-07-11 | 2011-01-18 | Mojix, Inc. | RFID beam forming system |
| TW200843201A (en) * | 2007-03-16 | 2008-11-01 | Rayspan Corp | Metamaterial antenna arrays with radiation pattern shaping and beam switching |
| EP2698870A1 (en) * | 2012-08-14 | 2014-02-19 | Alcatel-Lucent | Antenna feed |
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