WO2019120513A1

WO2019120513A1 - Analog beam steerable phased-array antenna and method

Info

Publication number: WO2019120513A1
Application number: PCT/EP2017/083811
Authority: WO
Inventors: Shi CHENG; Wenxin Yuan; Ulrik Imberg; Xiaoming Shi
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2017-12-20
Filing date: 2017-12-20
Publication date: 2019-06-27
Anticipated expiration: 2020-06-20

Abstract

An analog beam steerable phased-array antenna (700), comprising a first travelling-wave subarray (710) comprising antenna elements (705), having a first phase offset (φ1) between each pair of neighbouring antenna elements (705); a second travelling-wave subarray (720) comprising antenna elements (705), having a second phase offset (φ2) between each pair of neighbouring antenna elements (705), which is different from the first phase offset (φ1); a phase shifter (730) arranged at a first end (711) of the first travelling-wave subarray (710); a central feed (750), configured to feed at least one of the first travelling-wave subarray (710), and the second travelling-wave subarray (720), with an electromagnetic signal, coupled via the phase shifter (730); a first termination load (760) arranged at a second end (712) of the first travelling-wave subarray (710); and a second termination load (770) arranged at a first end (721) of the second travelling-wave subarray (720).

Description

ANALOG BEAM STEERABLE PHASED-ARRAY ANTENNA AND METHOD

TECHNICAL FIELD

Implementations described herein generally relate to an analog beam steerable phased- array antenna, and a method for controlling the analog beam-steerable phased-array antenna.

BACKGROUND

Beamforming is one of the most important key features in the upcoming 5G high-band, high-power massive Multiple-Input and Multiple-Output (MIMO) Active Antenna Systems (AASs), which boosts the communication system throughputs by maximising received power at User Equipment (UE) and minimising interferences.

The mainstream beamforming techniques can be categorised as Digital Beam Forming (DBF) and Analog Beam Forming (ABF). The former relies on amplitude and phase adjustments of digital data streams to realise desired radiation patterns whereas the latter uses electrically tunable phase shifters and Variable Gain Amplifiers (VGAs )/ tunable attenuators to manipulate excitation to each antenna element/ subarray to generate desired radiation patterns. DBF offers the greatest degree of freedom for amplitude and phase tuning so that it provides the highest quality of beamforming. However, each independent digital data stream necessitates a full hardware chain. This fact leads to the highest system complexity and implementation cost, especially at 5G high-band, millimetre- wave frequencies due to extremely high sampling rates as much as several Giga Hertz. ABF is a much more energy and cost-effective approach, but it only offers limited degree of freedom for amplitude and phase adjustments so that it provides degraded quality of beamforming. Hybrid Beam Forming (HBF) concept is a compromising solution where a large number of antenna elements/ subarrays are divided into a number of clusters. ABF technique is employed within each cluster whereas DBF is utilised to form desired radiation patterns using selected clusters.

In a previously known conventional beam steerable phased-array architecture, each antenna element is connected to the multi-stage, corporate feed network via an electrically tunable phase shifter. Phase shifter setting (phase shift) for each antenna element often differs with the others in order to steer the antenna beam to a desired angle. Therefore, multi-bit (or continuously tunable) phase shifters are required to support different beam steering angles. A simplified version of a corporate-feed beam steerable array comprises multiple antenna elements, grouped into clusters so that the number of required phase shifters can be significantly reduced at the expense of degraded beam steering performance and flexibility. This simplified architecture lowers hardware implementation costs and shrinks feed network footprints. But the fact that each phase shifter needs to provide different phase shift setting in comparison with the others for any specific beam steering angle requires complicated multi-bit (or continuously tunable) phase shifters associated with complex driver circuits.

In a different type of conventional electrically steerable phased-array architecture, where multiple phase shifters are connected in series with antenna elements instead of in parallel. This architecture removes the need for large parallel feed networks and makes use of progressive phase shifts by cascading multiple phase shifters. So the equal phase shift settings can be applied to all phase shifters for beam steering. Cascading multiple phase shifters inevitability results in increased losses.

Yet a conventional solution comprises a beam-steerable leaky-wave microstrip antenna array. Each radiating element in the presented array is loaded with a varactor diode. Adjusting control Direct Currency (DC) voltage (Vdc) applied across all varactors leads to varying capacitance so that alters phase differences between each neighbouring radiating elements to steer the antenna beam.

Another known solution comprises an electrically steerable single-layer microstrip travelling-wave antenna w / varactor diodes based phase shifters, being designed of a similar concept as the previously discussed Fixed-frequency beam-steerable leaky-wave microstrip antenna.

Varactor diodes based phase shifters are implemented on the same metallic layer as the patch elements are used to provide a variable progressive phase shift in the array. Two antennas for the 5.8 GHz Industrial, Scientific and Medical (ISM) band, manufactured as single layer printed designs on a standard Polytetrafluoreten (PTFE) soft substrate, are demonstrated. A ten-element beam-tilting vertical array using transmission type phase shifters was realised, yielding between 11.8 to 13.9 dBi gain for the 0° to 11° beam tilt tuning range. Using wide phase tuning range reflection type phase shifters a five-element horizontally scanning array with 32° to 32° steering range and 10.9-11.3 dBi gain has been realised. When it comes to millimetre frequencies, excessively high losses in phase shifters are problematic. A previously known switched beam antenna concept suitable for low-cost millimetre-wave applications is also known. The concept uses multiple travelling-wave patch arrays that together with the beam selection switches are realised on a single substrate, where the antenna and circuits are etched from the same metal layer. With its simple design and building practice, the concept provides good producibility at frequencies up to approximately 80 GHz. An experimental study is presented in which four-beam antennas for 24 GHz are built and measured.

The prior art briefly presented herein, all suffer from various technical problems and constraints. In the cases of conventional electrically steerable corporate-feed and travelling-wave arrays, excessive implementation costs, large footprints (including driver circuits for diodes) as well as high system complexity are major drawbacks.

Simplified corporate-feed beam-steering phased arrays consisting of fewer phase shifters, may address these issues to some extent at the expense of reduce beam agility. But they still need relatively large parallel feed networks and progressive phase shifts from multi-bit (or continuously tunable) phase shifters that are often costly and lossy, particularly at high frequencies. Challenging amplitude tapering for side-lobe suppression is another disadvantage in corporate-feed arrays.

Simplified switched-beam, travelling-wave arrays are the simplest phased-array architecture. Such arrays eliminate the need for phase shifters and rely on progressive phase shift embedded in serial transmission lines to achieve beam tilt with minimal losses and miniaturised footprints. Intrinsic amplitude tapering due to exponential decay in element excitation results in low side-lobe without using any additional amplitude tapering techniques. Poor beam agility (e.g. 2 switched beams) is one of the major drawbacks. More switched beams can be supported by adding more arrays, but this solution increases footprints dramatically. Large beam squint as a results of progressive phase shift from series feed sets an upper limit for maximum bandwidths of such phased-arrays. This is a generic issue for any travelling-wave arrays.

It would be desired to realise an electrically steerable array antenna with low implementation cost, small footprints, reasonable system complexity, sufficient side-lobe suppression, high gain/ efficiency, moderate beam agility, and minimal beam squint. SUMMARY

It is therefore an object to obviate at least some of the above mentioned disadvantages and to improve the performance in an electrically steerable array antenna.

This and other objects are achieved by the features of the appended independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect, an analog beam-steerable phased-array antenna is provided. The analog beam-steerable phased-array antenna is a first travelling-wave subarray comprising a plurality of antenna elements, having a first phase offset between each pair of neighbouring antenna elements. Further, the analog beam-steerable phased-array antenna comprises a second travelling-wave subarray comprising a plurality of antenna elements, having a second phase offset between each pair of neighbouring antenna elements, which is different from the first phase offset. In addition, the analog beam-steerable phased-array antenna also comprises a phase shifter arranged at a first end of the first travelling-wave subarray. The analog beam-steerable phased-array antenna furthermore comprises a central feed, configured to feed at least one of the first travelling-wave subarray, and the second travelling-wave subarray, with an electromagnetic signal, coupled via the phase shifter arranged at a first end of the first travelling-wave subarray. The analog beam- steerable phased-array antenna comprises a first termination load arranged at a second end of the first travelling-wave subarray. In further addition, the analog beam-steerable phased-array antenna comprises a second termination load arranged at a first end of the second travelling-wave subarray.

By utilising travelling wave subarrays, implementation costs are decreased as system complexity is reduced, while high gain / efficiency is maintained. Thereby an improved performance in the electrically steerable array antenna is achieved. The central feed of the asymmetrical travelling-wave subarrays provides a self-compensation for appeared beam squint.

In a first possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, the antenna beam of the first travelling-wave subarray and the antenna beam of the second travelling-wave subarray are tilted.

Thereby, an adjustment of the antenna beam is created. In a second possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, or according to the first possible implementation thereof, the tilt of the antenna beam of the first travelling-wave subarray and the antenna beam of the second travelling-wave subarray are performed by adjusting spacing between neighbouring antenna elements in the first travelling-wave subarray and the second travelling-wave subarray, and by adjusting electrical length of transmission lines between the antenna elements of the first travelling-wave subarray and the second travelling-wave subarray.

By adjusting the described physical parameters of the travelling-wave subarrays, pre-tilt of the antenna beams may be altered into a desired value.

In a third possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, or according to any previously disclosed possible implementation thereof, the first phase offset between each pair of neighbouring antenna elements in the first travelling-wave subarray is greater than 360 degrees for frequencies of intended operation of the first travelling-wave subarray. Also, the second phase offset between each pair of neighbouring antenna elements in the second travelling-wave subarray is smaller than 360 degrees for frequencies of intended operation of the second travelling-wave subarray.

In a fourth possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, or according to the first or second previously disclosed possible implementation thereof, the first phase offset between each pair of neighbouring antenna elements in the first travelling-wave subarray is smaller than 360 degrees for frequencies of intended operation of the first travelling-wave subarray. Further, the second phase offset between each pair of neighbouring antenna elements in the second travelling- wave subarray is greater than 360 degrees for frequencies of intended operation of the second travelling-wave subarray.

In a fifth possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, or according to any previously disclosed possible implementation thereof, the analog beam-steerable phased-array antenna comprises a phase shifter arranged at a second end of the second travelling-wave subarray.

In a sixth possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, or according to any previously disclosed possible implementation thereof, the phase shifter arranged at a first end of the first travelling-wave subarray, and / or the phase shifter arranged at the second end of the second travelling- wave subarray, may comprise a few-bit phase shifter.

Thereby, production costs are reduced in comparison with using multi-bit, or continuously tunable phase shifters. Also, an improved efficiency is achieved.

In a seventh possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, or according to any previously disclosed possible implementation thereof, the analog beam-steerable phased-array antenna comprises a third travelling-wave subarray comprising a plurality of antenna elements, having a third phase offset between each pair of neighbouring antenna elements. Also, the analog beam- steerable phased-array antenna comprises a third termination load arranged at a first end of the third travelling-wave subarray. Furthermore, the analog beam-steerable phased- array antenna also comprises a fourth termination load arranged at a second end of the second travelling-wave subarray. The analog beam-steerable phased-array antenna furthermore comprises a first switch, configured to alter feed between either the first travelling-wave subarray, and the second travelling-wave subarray, or the second travelling-wave subarray, and the third travelling-wave subarray.

By cloning the first travelling-wave subarray and mirror it, the third travelling-wave subarray may be created, thereby achieving a symmetrical FOV.

In an eighth possible implementation of the analog beam-steerable phased-array antenna according to the seventh possible implementation of the first aspect, the third phase offset between each pair of neighbouring antenna elements is smaller than 360 degrees for frequencies of intended operation of the third travelling-wave subarray.

In a ninth possible implementation of the analog beam-steerable phased-array antenna according to the seventh possible implementation of the first aspect, the third phase offset between each pair of neighbouring antenna elements is greater than 360 degrees for frequencies of intended operation of the third travelling-wave subarray.

In a tenth possible implementation of the analog beam-steerable phased-array antenna according to the seventh, the eighth, or the ninth possible implementation of the first aspect, the analog beam-steerable phased-array antenna comprises a phase shifter arranged at a second end of the third travelling-wave subarray. Further, the analog beam- steerable phased-array antenna comprises a second switch configured to alter feed between either the phase shifter arranged at the second end of the second travelling-wave subarray, and the fourth termination load, arranged at the second end of the second travelling-wave subarray. The analog beam-steerable phased-array antenna furthermore comprises a third switch configured to alter feed between either a fourth phase shifter arranged at the first end of the second travelling-wave subarray, and the second termination load, arranged at the first end of the second travelling-wave subarray.

Thereby, further implementation details are described in order to improve the beam forming.

In an eleventh possible implementation of the analog beam-steerable phased-array antenna according to the seventh, the eighth, the ninth, or the tenth possible implementation of the first aspect, at least one of the second termination load or the fourth termination load comprises a coupler-based phase shifter.

By using coupler-based phase shifters, the number of required switches may be further decreased, which reduces production costs.

In a twelfth possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, or according to any previously disclosed possible implementation thereof, the second travelling-wave subarray is in active state, together with either the first travelling-wave subarray, or alternatively the third travelling-wave subarray.

In a thirteenth possible implementation of the analog beam-steerable phased-array antenna according to the first aspect, or according to any previously disclosed possible implementation thereof, the analog beam-steerable phased-array antenna comprises a fixed phase shift value between any two directly connected phase shifters in active state.

According to a second aspect, a method is provided for controlling an analog beam- steerable phased-array antenna according to the first aspect, or any previously disclosed implementation thereof. The method comprises feeding a central feed of the analog beam- steerable phased-array antenna. Further, the method also comprises adjusting phase shifters of the analog beam-steerable phased-array antenna for creating a switched plurality of antenna beams. By utilising travelling wave subarrays, implementation costs are decreased as system complexity is reduced, while high gain / efficiency is maintained. Thereby an improved performance in the electrically steerable array antenna is achieved.

In a first possible implementation of the method according to the second aspect, a switch is controlled, to select two travelling-wave subarrays to be set in active state.

Thereby an improved performance within the wireless communication system is provided.

Other objects, advantages and novel features of the aspects of the invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are described in more detail with reference to attached drawings in which:

Figure 1A illustrates a beam steerable phased-array based on travelling-wave array according to an embodiment.

Figure 1 B illustrates a beam steerable phased-array based on travelling-wave array according to an embodiment.

Figure 2A illustrates an analog beam steerable phased-array according to an embodiment.

Figure 2B illustrates an analog beam steerable phased-array according to an embodiment.

Figure 2C illustrates an analog beam steerable phased-array according to an embodiment.

Figure 2D illustrates an analog beam steerable phased-array according to an embodiment.

Figure 3 illustrates an analog beam steerable phased-array according to an embodiment.

Figure 4A illustrates a simulated amplitude and phase response of the electrically reconfigurable feed network, according to an embodiment.

Figure 4B illustrates a simulated amplitude and phase response of the electrically reconfigurable feed network, according to an embodiment. Figure 4C illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 4D illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 4E illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 4F illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 5A illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 5B illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 5C illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 5D illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 5E illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 5F illustrates a simulated amplitude and phase response of the electrica reconfigurable feed network, according to an embodiment.

Figure 6 illustrates a simulated realised gain radiation patterns of the electrica steerable travelling-wave phased-array, according to an embodiment.

Figure 7 illustrates a simulated realised gain radiation patterns of the electrica steerable travelling-wave phased-array, according to an embodiment.

Figure 8 illustrates a simulated realised gain radiation patterns of the electrica steerable travelling-wave phased-array, according to an embodiment.

Figure 9 is a flow chart illustrating a method according to an embodiment of the inv- ention.

DETAILED DESCRIPTION

Embodiments of the invention described herein are defined as an analog beam steerable phased-array antenna and a method for controlling it, which may be put into practice in the embodiments described below. These embodiments may, however, be exemplified and realised in many different forms and are not to be limited to the examples set forth herein; rather, these illustrative examples of embodiments are provided so that this disclosure will be thorough and complete.

Still other objects and features may become apparent from the following detailed description, considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the herein disclosed embodiments, for which reference is to be made to the appended claims. Further, the drawings are not necessarily drawn to scale and, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.

Figure 1A and Figure 1B are two schematic illustrations over an analog beam-steerable phased-array topology comprising multiple travelling-wave subarrays. The analog beam- steerable phased-array antenna 700 comprises a first travelling-wave subarray 710 and a second travelling-wave subarray 720.

The first travelling-wave subarray 710 comprises a plurality of antenna elements 705, which may have a first phase offset fi between each pair of neighbouring antenna elements 705 greater than 360 degrees. Correspondingly, the second travelling-wave subarray 720 comprising a plurality of antenna elements 705, which may have a second phase offset f₂ between each pair of neighbouring antenna elements 705, smaller than 360 degrees.

In some embodiments, the relation between the first offset fi and the second offset f₂ may be the opposite, i.e. first phase offset fi may be smaller than 360 degrees while the second offset may be greater than 360 degrees.

The first travelling-wave subarray 710 has a first end 711 and a second end 712, and the second travelling-wave subarray 720 has a first end 721 and a second end 722.

A phase shifter 730 may be arranged at the first end 711 of the first travelling-wave subarray 710. In the embodiment illustrated in Figure 1 B, also another phase shifter 740 is arranged at the second end 722 of the second travelling-wave subarray 720. The phase shifter 730, arranged at the first end 711 of the first travelling-wave subarray 710, and / or the phase shifter 740, arranged at the second end 722 of the second travelling-wave subarray 720, may be few-bit phase shifters or low-bit phase shifters in some embodiments, such as e.g. 1-bit phase shifters. However, in some embodiments, the phase shifter 730, arranged at the first end 71 1 of the first travelling-wave subarray 710, and/ or the phase shifter 740, arranged at the second end 722 of the second travelling- wave subarray 720, may comprise high-bit phase shifters with low insertion loss, or high insertion loss high-bit phase shifters at the expense of increased hardware cost and excessive losses. Further, the phase shifters 730, 740 may be coupler based in some embodiments.

Also, a first termination load 760 arranged at the second end 712 of the first travelling-wave subarray 710, and a second termination load 770 is arranged at the first end 721 of the second travelling-wave subarray 720.

Furthermore, the analog beam-steerable phased-array antenna 700 also comprises a central feed 750 of the first travelling-wave subarray 710, and the second travelling-wave subarray 720 via at least one of the herein mentioned phase shifters 730, 740.

The beam-steerable phased-array 700 is based on the travelling-wave array concept but with central feeding of asymmetrical travelling-wave subarrays 710, 720 (for beam squint self-compensation) and simplified electrically reconfigurable low-bit phase shifters.

Travelling wave subarrays 710, 720 have been chosen to lower implementation cost, miniaturise footprints, reduce system complexity, and maintain high gain / efficiency by eliminating lossy multi-bit phase shifters and large multi-stage parallel feed networks. Simple electrically tunable low-loss, low-bit (e.g. 1-bit) phase shifters 730, 740 may be employed to resolve the issue of poor beam agility with maintained antenna gain / efficiency. The well-known issue of beam squint in travelling-wave/ leaky-wave arrays is addressed by central feed 750 of the asymmetrical travelling-wave subarrays 710, 720 for self-compensation.

The disclosed analog beamforming array architecture comprises several building blocks comprising simplified low-bit phase shifters 730, 740, asymmetrical travelling-wave subarrays 710, 720 with pre-tilted beams. In a non-limiting example, the beam tilt may for instance be e.g., -7° beam tilt from the first/ left subarray 710 when fed from its right end 711 and the same or similar beam tilt from the second/ right subarray 720 when fed from its left end 722, as well as a single-stage power splitting section that can be in the form of a power divider, a branch-line coupler or a rat-race coupler, cf. Figure 1A. Beam pre-tilt can be adjusted by carefully tuning electrical lengths of transmission lines or spacing between neighbouring radiating elements in the design in some embodiments.

In the case of the first/ left subarray 710, a first phase offset fi may be applied for each pair of neighbouring antenna elements 705, which may be set to a value either greater than 360°; or smaller than 360° for frequencies of intended operation of the first travelling-wave subarray 710.

Both uniform and non-uniform phase offsets f-i_, f₂ and element spacing can be applied in the subarrays 710, 720 in different embodiments. With the aid of few-bit phase shifters 730, 740, different relative phase differences of two subarrays 710, 720 can be achieved to steer the combined antenna beam to multiple directions. For instance, 3 switched beams can be generated using two few-bit/ low-bit/ 1-bit phase shifters 730, 740, as illustrated in Figure 1 B. It is noted that the antenna beam from the first/ left subarray 710 rotates counter-clockwise with increased operational frequency when the first/ left subarray 710 is fed from the right end 71 1 and fi is greater than 360 degrees. In the case of feeding from its left end and fi is greater than 360 degrees or feeding from its right end and fi is smaller than 360 degrees, its antenna beam instead rotates clockwise.

The antenna beam from the second/ right subarray 720 rotates towards different directions (i.e. clockwise/ counter clockwise) depending on which end is fed and the value of f₂.

Two antenna beams thus may compensate each other over the operation frequency range to ensure (nearly) zero beam squint of the combined antenna beam. The Field Of View (FOV) of the entire electrically steerable phased-array is determined by a number of factors such as the number of radiating elements 705 in each array 710, 720, spacing between neighbouring elements, phase shifter phase tuning ranges, acceptable Side Lobe Levels (SLLs), as well as operational frequency range. The FOV of 0° to -15° is given as an example in Figures 1A-1 B, and it can be expanded at the expense of increased SLLs. Wider operational frequency range also leads to higher SLLs at the upper and lower frequencies.

The antenna beam of the first travelling-wave subarray 710, and the antenna beam of the second travelling-wave subarray 720 may thereby be tilted. The tilt of the antenna beam of the first travelling-wave subarray 710 and the antenna beam of the second travelling-wave subarray 720 may be performed by adjusting spacing between antenna elements 705 of the first travelling-wave subarray 710 and the second travelling-wave subarray 720; and adjusting electrical length of transmission lines between the antenna elements 705 of the first travelling-wave subarray 710 and the second travelling-wave subarray 720.

The described analog beam steering phased-array architecture may be deployed either in a purely analog beamforming or hybrid beamforming AAS. It is based on travelling-wave/ leaky-wave subarrays 710, 720 connected with simplified electrically reconfigurable feed networks, which can be implemented using conventional transmission lines or waveguides integrated with tunable/ switchable components, e.g. PIN diodes, varactor diodes, Radio Frequency Micro Electro Mechanical System (RF MEMS) switches, or transistors. Amplitude tapering is realised by intrinsic exponential excitation decay in each travelling- wave subarray so that the new phased-array architecture eliminates the need for dedicated VGAs and tunable attenuators.

Another approach to increase FOV is to clone the first phased-array 710 of the beam- steerable phased-array 700 in Figure 1A-1 B and mirror it to achieve a symmetrical FOV in the positive angular range. One of the two subarrays 710, 720 can be reused for size reduction, as illustrated in Figure 2A-2D, thereby creating a third analog beam-steerable phased-array 810. This analog beam-steerable phased-array 810 is capable of supporting 6 switched beams using phase shifters 730, 740. In the embodiment illustrated in Figure 2D, the number of phase shifters 730, 740 of the embodiment illustrated in Figure 1 B is doubled from 2 to 4; and 3 additional Single-Pole, Double-Throw (SPDT) switches may be added in some embodiments.

The illustrated embodiment of the analog beam-steerable phased-array antenna 700 in Figure 2A-2D, comprises a third travelling-wave subarray 810 comprising a plurality of antenna elements 705, having a third phase offset f₃ between each pair of neighbouring antenna elements 705, identically with, or at least somewhat resembling, the first travelling- wave subarray 710. Thus, the third phase offset f₃ may be greater than 360 degrees in some embodiments wherein the first phase offset fi also is greater than 360 degrees; and the third phase offset f₃ may be smaller than 360 degrees in some embodiments wherein the first phase offset fi also is smaller than 360 degrees.

The third travelling-wave subarray 810 comprises a first end 811 and a second end 812. Another phase shifter 820 may be arranged at the second end 812 of the third travelling- wave subarray 810, and a third termination load 830 may be arranged at the first end 811 of the third travelling-wave subarray 810. Further, yet a phase shifter 840 may be arranged at the first end 721 of the second travelling-wave subarray 720 as illustrated in Figure 2B, and a fourth termination load 850 may be arranged at a second end 722 of the second travelling-wave subarray 720.

The beam steerable phased-array antenna 700 in the embodiment of Figure 2A may be switched into two distinct operative modes by a first switch 860. Thereby, the analog beam- steerable phased-array antenna 700, wherein the second travelling-wave subarray 720 is in active state together with either the first travelling-wave subarray 710, or the third travelling-wave subarray 810. The expression “active state”, as utilised herein when discussing travelling-wave subarrays 710, 720, 810, indicates that an electromagnetic signal is provided by the central feed 750 to the travelling-wave subarrays 710, 720, 810 in active state, operated by the first switch 860. The travelling-wave subarrays 710, 720, 810 in active state thereby are enabled to emit a radio signal.

Via the first switch 860, the feed may be altered between the first travelling-wave subarray 710, via the phase shifter 730 arranged at the first end 711 of the first travelling-wave subarray 710, and the second travelling-wave subarray 720, via the phase shifter 740 arranged at the second end 722 of the second travelling-wave subarray 720; and the second travelling-wave subarray 720, via the phase shifter 840, arranged at the first end 721 of the second travelling-wave subarray 720, and the third travelling-wave subarray 810 via the phase shifter 820, arranged at the second end 812 of the third travelling-wave subarray 810, in some embodiments, as illustrated in Figure 2D.

Further, a second switch 870 may be provided, configured to alter feed between either the phase shifter 740 arranged at the second end 722 of the second travelling-wave subarray 720, and the fourth termination load 850, arranged at the second end 722 of the second travelling-wave subarray 720.

Also, a third switch 880 may be provided, configured to alter feed between either the phase shifter 840, arranged at the first end 721 of the second travelling-wave subarray 720, and the second termination load 770, arranged at the first end 721 of the second travelling- wave subarray 720.

The switches 860, 870, 880 may comprise a Single-Pole, Double Throw switch (SPDT), a Single Pole, Triple Throw (SPTT) switch, etc. In some embodiments, there may be applied a fixed phase shift value DQ between any two directly connected phase shifters 730, 740, 820, 840 in active state.

Figure 3 displays an alternative way to implement an electrically reconfigurable feed network for the new analog beam steerable phased-array to supported 6 switched beams. Four branch-line couplers with Single-Pole, Single-Throw (SPST) switches loaded interconnects may be employed to replace four 1-bit phase shifters 730, 740, 820, 840 and 2 SPDT switches in the phased-array architecture presented in Figure 2A-2D. One of the most attractive advantages of this array architecture is the reduced number of switches (e.g. PIN diodes may be used at high frequencies) in comparison with the previous one. However, larger amplitude and gain imbalance is a potential issue for wideband applications.

According to some embodiments, at least one of the previously described second termination load 770, or the fourth termination load 850 may comprise a coupler-based phase shifter 910, 920.

In the embodiment illustrated in Figure 3, the analog beam-steerable phased-array antenna 700 may comprise a second switch configured to alter feed between either the phase shifter 740, arranged at the second end 722 of the second travelling-wave subarray 720, and the fourth termination load 850, arranged at the second end 722 of the second travelling-wave subarray 720. The analog beam-steerable phased-array antenna 700 also may comprise a third switch configured to alter feed between either the phase shifter 840, arranged at the first end 721 of the second travelling-wave subarray 720, and the second termination load 770, arranged at the first end 721 of the second travelling-wave subarray 720.

Further, the phase shifters 730, 740, 820, 840 may comprise a SPDT switch, a SPST switch, a SPTT switch, etc., denoted S₂, S₃, S₄, S₅, S₆, S₇, Se, S₉ in Figure 3.

Furthermore, a fixed phase shift may be applied between two phase shifters 730, 740, 820, 840 in active state. For example, the fixed phase shift may be about 180 degrees (non- limiting example).

Table 1

Table 1 shows an example of 1-bit phase shifter settings to realise 6 switched beams using the phased-array architectures depicted in Figure 2A, Figure 2B, Figure 2C, Figure 2D, and Figure 3. A fixed 180° phase shift may be applied between each pair of phase shifters 730, 740, 820, 840, in some embodiments.

Figure 4A- 4F presents simulated amplitude and phase response of the entire 28 GHz electrically reconfigurable feed network when exciting the first/ left subarray 710 and the second/ centre subarray 720 in the first beam steerable phased-array architecture, see Figure 2D, with different phase shifter settings to generate switched beams #1 to #3 (equal amplitude and phase response for beams #4 to #6 due to the symmetry of the feed network). High frequency PIN diodes are used for building 1-bit phase shifters and SPDT switches. Micro strip based feed network was first simulated in a full-wave electromagnetic simulator, ANSYS Electronics Desktop, and then imported into Key-sight Advanced Design System (ADS) together with PIN diode S-parameter model provided by the supplier for simulating the complete electrically reconfigurable feed network in the circuit simulator. Conductive and dielectric losses from micro-strip lines and PIN diodes losses are all included simulated results. Figures 5A-5F presents simulated amplitude and phase response of the entire 28 GHz electrically reconfigurable feed network when exciting first/ left subarray 710 and the second/ centre subarray 810 in the second beam-steerable phased-array architecture illustrated in Figure 3, with different coupler based phase shifter settings to generate switched beams #1 to #3 (equal amplitude and phase response for beams #4 to #6 due to the symmetry of the feed network). All simulations were conducted following the same procedure as for the first phased-array.

Figure 6 illustrates a simulated realised gain, excluding feed network insertion losses radiation patterns of the electrically steerable travelling-wave phased-array at low band with 6 different feed network settings.

Figure 7 illustrates a simulated realised gain, excluding feed network insertion losses radiation patterns of the electrically steerable travelling-wave phased-array at mid band with 6 different feed network settings.

Figure 8 illustrates a simulated realised gain, excluding feed network insertion losses radiation patterns of the electrically steerable travelling-wave phased-array at high band with 6 different feed network settings.

Simulated realised gain radiation patterns of the electrically steerable phased-array fed by the feed network either in the embodiment illustrated in Figure 2D, or the embodiment illustrated in Figure 3, array architectures at different frequencies are presented in Figure 6- 8. A FOV of -15° to +15° is achieved by 6 switched beams.

Figure 9 is a flow chart illustrating embodiments of a method 1500 in a wireless communication system. The method 1500 aims at controlling an analog beam-steerable phased-array antenna 700.

To appropriately control the analog beam-steerable phased-array antenna, the method 1500 may comprise a number of method steps 1501-1503.

It is however to be noted that any, some or all of the described steps 1501-1503, may be performed in a somewhat different chronological order than the enumeration indicates, be performed simultaneously or in a somewhat adjusted order according to different embodiments. Further, it is to be noted that some method steps may be performed in a plurality of alternative manners according to different embodiments, and that some such alternative manners may be performed only within some, but not necessarily all embodiments. The method 1500 may comprise the following steps:

Step 1501 comprises feeding a central feed 750 of the analog beam-steerable phased- array antenna 700. Step 1502 comprises adjusting phase shifters 730, 740, 820, 840 of the analog beam- steerable phased-array antenna 700 for creating a switched plurality of antenna beams.

Step 1503, which only may be comprised in some embodiments, comprises controlling a switch 860, 870, 880, to select two travelling-wave subarrays 710, 720, 810 to be set in active state.

The described method steps 1501-1503 to be performed for controlling an analog beam- steerable phased-array antenna 1500 may be implemented through the one or more processing circuits in a radio network node together with computer program product for performing the functions of the steps 1501-1503.

Thus a computer program comprising program code for performing the method 1500 according to any of steps 1501-1503, for controlling an analog beam-steerable phased- array antenna 700 when the computer program is loaded into the processing circuits.

The computer program product mentioned above may be provided for instance in the form of a data carrier carrying computer program code for performing at least some of the steps 1501-1503 according to some embodiments when being loaded into the respective processing circuits. The data carrier may be, e.g., a hard disk, a CD ROM disc, a memory stick, an optical storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold machine readable data in a non-transitory manner. The computer program product may furthermore be provided as computer program code on a server and downloaded to the radio network node remotely, e.g., over an Internet or an intranet connection.

The terminology used in the description of the embodiments as illustrated in the accompanying drawings is not intended to be limiting of the described method 1500 and / or analog beam-steerable phased-array antenna 700. Various changes, substitutions and / or alterations may be made, without departing from the invention as defined by the appended claims.

As used herein, the term "and / or" comprises any and all combinations of one or more of the associated listed items. In addition, the singular forms "a", "an" and "the" are to be int erpreted as“at least one”, thus also possibly comprising a plurality of entities of the same kind, unless expressly stated otherwise. It will be further understood that the terms "includes", "comprises", "including" and / or "comprising", specifies the presence of stated features, actions, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, actions, integers, steps, operations, elements, components, and / or groups thereof. A single unit such as e.g. a processor may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/ distributed on a suitable medium, such as an optical storage medium or a solid- state medium supplied together with or as part of other hardware, but may also be distributed in other forms such as via Internet or other wired or wireless communication system.

Claims

1. An analog beam-steerable phased-array antenna (700), comprising:

a first travelling-wave subarray (710) comprising a plurality of antenna elements (705), having a first phase offset (f-i) between each pair of neighbouring antenna elements (705);

a second travelling-wave subarray (720) comprising a plurality of antenna elements (705), having a second phase offset (f₂) between each pair of neighbouring antenna elements (705), which is different from the first phase offset (f-i);

a phase shifter (730) arranged at a first end (711 ) of the first travelling-wave subarray (710);

a central feed (750), configured to feed at least one of the first travelling-wave subarray (710), and the second travelling-wave subarray (720), with an electromagnetic signal, coupled via the phase shifter (730) arranged at a first end (71 1 ) of the first travelling-wave subarray (710);

a first termination load (760) arranged at a second end (712) of the first travelling- wave subarray (710); and

a second termination load (770) arranged at a first end (721 ) of the second travelling-wave subarray (720).

2. The analog beam-steerable phased-array antenna (700) according to claim 1 , wherein the antenna beam of the first travelling-wave subarray (710) and the antenna beam of the second travelling-wave subarray (720) are tilted.

3. The analog beam-steerable phased-array antenna (700) according to claim 2, wherein the tilt of the antenna beam of the first travelling-wave subarray (710) and the antenna beam of the second travelling-wave subarray (720) are performed by:

adjusting spacing between antenna elements (705) of the first travelling-wave subarray (710) and the second travelling-wave subarray (720); and

adjusting electrical length of transmission lines between the antenna elements (705) of the first travelling-wave subarray (710) and the second travelling-wave subarray (720).

4. The analog beam-steerable phased-array antenna (700) according to any one of claims 1-3, wherein:

the first phase offset (f-i) between each pair of neighbouring antenna elements (705) in the first travelling-wave subarray (710) is greater than 360 degrees for frequencies of intended operation of the first travelling-wave subarray (710); and

the second phase offset (f₂) between each pair of neighbouring antenna elements (705) in the second travelling-wave subarray (720) is smaller than 360 degrees for frequencies of intended operation of the second travelling-wave subarray (720).

5. The analog beam-steerable phased-array antenna (700) according to any one of claims 1-3, wherein:

the first phase offset (f-i) between each pair of neighbouring antenna elements (705) in the first travelling-wave subarray (710) is smaller than 360 degrees for frequencies of intended operation of the first travelling-wave subarray (710); and

the second phase offset (f₂) between each pair of neighbouring antenna elements (705) in the second travelling-wave subarray (720) is greater than 360 degrees for frequencies of intended operation of the second travelling-wave subarray (720).

6. The analog beam-steerable phased-array antenna (700) according to any one of claims 1-5, further comprising:

a phase shifter (740), arranged at a second end (722) of the second travelling- wave subarray (720).

7. The analog beam-steerable phased-array antenna (700) according to any one of claims 1-6, wherein the phase shifter (730) arranged at a first end (711 ) of the first travelling-wave subarray (710), and the phase shifter (740) arranged at a second end (722) of the second travelling-wave subarray (720) comprise few-bit phase shifters.

8. The analog beam-steerable phased-array antenna (700) according to any one of claims 1-7, further comprising:

a third travelling-wave subarray (810) comprising a plurality of antenna elements (705), having a third phase offset (f₃) between each pair of neighbouring antenna elements (705);

a third termination load (830) arranged at a first end (811 ) of the third travelling- wave subarray (810);

a fourth termination load (850) arranged at a second end (722) of the second travelling-wave subarray (720); a first switch (860), configured to alter feed between either:

the first travelling-wave subarray (710), and the second travelling-wave subarray (720); or

the second travelling-wave subarray (720), and the third travelling-wave subarray (810).

9. The analog beam-steerable phased-array antenna (700) according to claim 8, wherein the third phase offset (f₃) between each pair of neighbouring antenna elements (705) is smaller than 360 degrees for frequencies of intended operation of the third travelling-wave subarray (810).

10. The analog beam-steerable phased-array antenna (700) according to claim 8, wherein the third phase offset (f₃) between each pair of neighbouring antenna elements (705) is greater than 360 degrees for frequencies of intended operation of the third travelling-wave subarray (810).

1 1. The analog beam-steerable phased-array antenna (700) according to any one of claims 8-10, further comprising:

a phase shifter (820), arranged at a second end (812) of the third travelling-wave subarray (810);

a second switch (870) configured to alter feed between either:

the phase shifter (740), arranged at the second end (722) of the second travelling-wave subarray (720), and

the fourth termination load (850), arranged at the second end (722) of the second travelling-wave subarray (720); and

a third switch (880) configured to alter feed between either:

a phase shifter (840), arranged at the first end (721 ) of the second travelling- wave subarray (720), and

the second termination load (770), arranged at the first end (721 ) of the second travelling-wave subarray (720).

12. The analog beam-steerable phased-array antenna (700) according to any one of claims 8-1 1 , wherein at least one of the second termination load (770) or the fourth termination load (850) comprises a coupler-based phase shifter (910, 920).

13. The analog beam-steerable phased-array antenna (700) according to any one of claims 1-12, wherein the second travelling-wave subarray (720) is in active state, together with either the first travelling-wave subarray (710), or alternatively the third travelling-wave subarray (810).

14. The analog beam-steerable phased-array antenna (700) according to any one of claims 1-13, further comprising a fixed phase shift value (DQ) between any two directly connected phase shifters (730, 740, 820, 840) in active state.

15. A method (1500) for controlling an analog beam-steerable phased-array antenna (700) according to any one of claims 1-14, comprising:

feeding (1501 ) a central feed (750) of the analog beam-steerable phased-array antenna (700);

adjusting (1502) phase shifters (730, 740, 820, 840) of the analog beam-steerable phased-array antenna (700) for creating a switched plurality of antenna beams.

16. The method (1500) according to claim 15, further comprising:

controlling (1503) a switch (860, 870, 880), to select two travelling-wave subarrays (710, 720, 810) to be set in active state.