WO2020225415A1

WO2020225415A1 - A system and method for beam steering of electromagnetic waves

Info

Publication number: WO2020225415A1
Application number: PCT/EP2020/062847
Authority: WO
Inventors: Zizheng CAO; Antonius Marcellus Jozef Koonen
Original assignee: Eindhoven Technical University
Current assignee: Eindhoven Technical University
Priority date: 2019-05-08
Filing date: 2020-05-08
Publication date: 2020-11-12
Anticipated expiration: 2021-11-08

Abstract

A system for beam steering, the system comprising a group of antenna elements spaced equally apart, wherein the antenna elements are arranged to transmit an electromagnetic wave, the system further comprising a tunable coupler arranged to split an input signal to be transmitted into two output signals with a tunable power ratio, two delay structures, wherein each delay structure is arranged for splitting and providing one of the two output signals to each of the antenna elements of the group, wherein in the group, the antenna elements are arranged in a given order from a first element to a last element, wherein a first of the two delay structures provides the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order from the first to the last element, while the second of the two delay structures provides the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order but from the last to the first element; wherein each antenna element is associated with a combiner for combining output signals provided thereto into a combined output signal of that combiner, for the purpose of transmitting the electromagnetic wave based on said combined signal.

Description

Title

A system and method for beam steering of electromagnetic waves.

Technical field

The present disclosure generally relates to the field of antennas and more specifically to a system for and a method of beam steering of electromagnetic waves.

Background

Beamforming and beam steering of electromagnetic waves, for example radio and optical waves, may be needed for many applications such as high- capacity radio wireless communication, optical wireless communication, radar, Light Detection and Ranging (LiDAR), arrayed ultrasonic equipment and Sound Navigation and Ranging (SONAR). Traditionally, the propagated electromagnetic wave is radiated from a transmitter and/or collected by a receiver to/from many directions. Depending on the application, the propagated electromagnetic wave may be a radio frequency (RF) wave, or an optical wave or it may be a mechanical wave.

Irrespective of whether there is an object of interest in a specific direction, the energy is transmitted in/collected from a wide range of directions. By spatially focusing, i.e. beamforming the radio/optical signal to a specified direction, the energy required for realizing a function such as data transmission, data detection, or energy transfer can be efficiently reduced.

Moreover, spatial interference between the radiated beams can be reduced by beam forming, which yields

• a better spatial de-multiplexing of parallel data streams, enabling a higher data capacity;

• a better determination of the directions of reflection, thus reducing multipath effects which may deteriorate system performance.

Using the same total transmitted power from multiple antennas, the beamforming can provide a stronger received signal since the signals from different transmitter antennas are coherently summed up. To lead the focused wave to a desired direction, a beam steering function is thus required together with beamforming.

The most popular and powerful scheme to enable beam steering is the well-known Phased Array Antenna, PAA, which is an array of antenna elements that are driven with signals with well-determined phase relations between those elements. Here, an antenna refers to a radiator of all kinds of waves which can be regarded as propagating phase fronts, hence including RF waves, optical waves as well as acoustic waves. The present disclosure considers radio electromagnetic wireless communication for illustrating the beam steering, but the principle highlighted in the present disclosure is equally applicable to all kinds of electro-magnetic waves.

To illustrate the beam-steering principle, a typical 1-by-4 radio phased array antenna transmitter 100 can be used to steer a radio beam as shown in Fig. 1 , by tuning the phase shifts between the signals feeding different antenna elements.

In such a scheme, d is the distance between two adjacent antenna elements, Q is the angle at which the outgoing signal is emitted, and Af is the phase delay between the signals from two adjacent antenna elements. With an equal distance d between the antenna elements, Af can be expressed as: A<p=(2TT//\)xcfxsin0. It is clear that, to set a different angle Q of the outgoing signal, the phase delay needs to be adjusted flexibly by tuning the phase shifters.

As shown in Fig. 2, in general, for a one-dimensional 1-by -N PAA 200, the required number of phase shifters is N- 1. For a two-dimensional N-by-N PAA, which is able to steer the beam in two dimensions, the number is (N- 1)². Such large number of phase shifters critically limits the implementation and application of a PAA because of the following issues:

Complexity and cost are both increased with the increasing number of phase shifters needed.

The individual phase shifters need to be carefully calibrated separately.

Usually, phase shifters are placed close to the antennas, and the spacing between two antennas should usually be less than half of the signal’s wavelength when higher-order side lobes of the beam should be avoided. Operation at higher frequency means shorter wavelength and thus the space needed for the phase shifter may become smaller than the physically possible size of a phase shifter. All this may imply that a conventional phase shifter solution does not fit anymore. Therefore it is of interest to reduce the number of phase shifters. The present disclosure discloses a system for and a method of beam steering that allows for the reduction of the number of phase shifting elements required.

Summary

It is an object of the present disclosure to provide a system for beam steering, wherein the system has a reduced amount of phase shifters compared to the prior art. It is a further object to provide for a corresponding method.

In a first aspect, there is provided a system for beam steering, the system comprising a group of antenna elements (1..N) spaced equally apart, wherein the antenna elements (1..N) are arranged to transmit an electromagnetic wave, the system further comprising:

a tunable coupler (i) arranged to split an input signal to be transmitted into two output signals with a tunable power ratio, wherein the two output signals are provided to two delay structures, respectively;

two delay structures, wherein each delay structure is arranged for splitting and providing one of the two output signals provided by the tunable coupler, and for providing these to each of the antenna elements (1..N) of the group;

wherein in the group, the antenna elements (1..N) are arranged in a given order from a first element (1) to a last element (N), wherein a first of the two delay structures provides the output signal thereof to each of the antenna elements (1..N) with an increasing delay per each antenna element (1..N) in the order from the first ( 1 ) to the last element (N), while the second of the two delay structures provides the output signal thereof to each of the antenna elements (1..N) with an increasing delay per each antenna element in the order but from the last (N) to the first element

(

wherein each antenna element is associated with a combiner for combining output signals provided thereto into a combined output signal of that combiner thereby, each antenna element is arranged to transmit the electromagnetic wave based on the combined signal.

The inventors have found that it is possible to reduce the number of phase shifters from N-1, in accordance with the prior art, to one (1). More specifically, to reduce to a single tunable power coupler. This is valid for a one-dimensional 1-by- N PAA. The inventors have further found that it is possible to reduce the number of phase shifters from ( N-1 )² to three (3), i.e. more specifically three tunable power couplers, for a two-dimensional N-by-N PAA, thereby dramatically reducing the hardware complexity. This is explained in more detail later below.

The above is based on the concept wherein a tunable power coupler can be used, instead of N- 1 phase shifters, to create linearly progressive phase shifts to the antenna elements, which is elucidated in more detail with respect to the figures.

The inventors have found that it is possible to predefine two arrays of vectors, i.e. an array of vectors is a set of phase shifts assigned to a different antenna element, and then to subsequently combine two arrays of vectors with different weights, i.e. power ratio, to generate a new weighted array of vectors. The progressive phase difference between the elements of the generated weighted arrays of vectors may be tuned by the weights, i.e. power ratio, for example by a controller.

The directionality of the beam can thus be tuned by controlling the ratio of the tunable coupler.

In accordance with the present disclosure, the tunable coupler is arranged to split the input signal to be transmitted into two output signals with a tunable power ratio.

The above entails that the tunable coupler outputs two output signals which are shaped identically but may have different amplitudes. As will be discussed later, the amplitude ratio between the two output signals is used, in accordance with the present disclosure, to perform the beam steering.

The tunable coupler may be directed to split RF waves, optical waves, or acoustic waves. Any known implementation may be used for this purpose.

Each delay structure is arranged to provide a particular signal with different delay to the respective antenna elements. This may be accomplished using different lengths for the respective paths.

For example, the first delay structure may comprise a splitter for splitting the first output signal of the tunable coupler to N output signals. The splitter may thus have N output branches. Each output branch is connected to a single antenna element. For example, the first output branch is connected to the first antenna element, the second output branch is connected to the second antenna element, etc., the N-th output branch is connected to the N-th antenna element. The second delay structure may comprise a splitter for splitting the second output signal of the tunable coupler to N output signals. This splitter may thus also have N output branches. Each output branch is connected to a single antenna element but in a different order compared to the splitter of the first delay structure. For example, the first output branch is connected to the N-th antenna element, the second output branch is connected to the (L/-1 )-th antenna element, etc., and the N-th output branch is connected to the first antenna element.

The length of the paths between the antenna elements and the corresponding splitter may differ in order to assure that the signals arrive at the antenna elements with adequate different phases.

It is further noted that the present disclosure is elaborated with respect to tunable couplers having two output signals, and thus also two delay structures. However, the present disclosure is also applicable to situations wherein the tunable couplers have more than two output signals, and the system thus has more than two delay structures, i.e. one for each output of the tunable coupler.

It is even further noted that the present disclosure, i.e. the beam steering, may be directed to optical wireless communication, radar, Light Detection and Ranging, LiDAR, arrayed ultrasonic equipment and Sound Navigation and Ranging, SONAR.

The specific details of the system are elucidated in more detail with respect to the figures.

In an example, each delay structure comprises:

- a power splitter for splitting the respective output signal into a plurality (N) of output signals, and

- a plurality (N) of tapped delay lines for connecting the corresponding power splitter to each respective of the antenna elements (1..N) for providing the output signal thereof to each of the antenna elements.

In an alternative example, each delay structure comprises a plurality (N) of in series cascaded power splitters, wherein each power splitter is arranged to provide an output signal to a corresponding antenna element ( 1..N ).

The inventors have found that at least two implementations exist for the delay structures which effectuate that the signals arrive at the antenna elements with differing phase delays. As a first option, there is provided a splitter for splitting the output of the tunable coupler into N branches. Each of the branches is then connected to a single antenna element. The length of these connections, i.e. paths / delay lines, may differ to realize that the output signals of the splitter arrive with different phase delay at the corresponding antenna element. This is a parallel solution, and it is explained in more detail with respect to figure 10.

As a second option, there may be provided one effective path which travels along each of the antenna elements, wherein, at or nearby the position of each antenna element, a splitter may be provided for assuring that the adequate signal is provided to that respective antenna element. As such, N splitters are provided in series. This is a series cascaded solution, and it is explained in more detail with respect to figure 11.

In an example, the system further comprises two controllable phase shifters, wherein the controllable phase shifters are each connected in between the tunable coupler and any of the two delay structures for controlling phases of output signals originating from the tunable coupler.

In a further example, the tunable coupler is implemented as a Mach- Zehnder interferometer.

In another example, the distance between antenna elements is smaller or equal to half of the wavelength of the electromagnetic wave to be transmitted.

To avoid any grating lobes, the distance between two adjacent antenna element is, preferably, not larger than half the wavelength of a radiated electromagnetic wave. For light waves, such a separation of the antenna elements at less than half a wavelength is usually difficult to obtain. Taking 1550 nm wavelength as an example, the networks of vertical radiators, phase shifters and amplitude controllers distribution then need to be very compact, in the sub-micrometer level.

In such a case, it may be beneficial to use the implementation of figure 1 1 as in that case a bi-directional tapped line architecture is used to realize the system. The distance between the power splitters may be used for determining / realizing the relative phase delays for the signals arriving at the respective antenna elements. The distance of the paths between the power splitter and the corresponding antenna element may be the same for efficiency reasons. Following the above, the distance between the power splitters is leading for obtaining the desired phase shift, not the distance between the antenna elements.

In an example, the system comprising a multiple of groups ( 1..n ) of antenna elements (1..N) arranged to transmit an electromagnetic wave, the multiple of groups ( 1..n ) being arranged in a given group order from a first group ( 1 ) to a last group ( n )

- wherein each of the two delay structures is arranged for splitting and providing one of the two output signals provided by the tunable coupler, and for providing these to each of the antenna elements (1..N) of each of the groups ( 1..n );

- wherein in each group ( 1..n ), the antenna elements (1..N) are arranged in a given order from a first element (1) to a last element (N),

- wherein a first of the two delay structures is arranged to provide the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order from the first ( 1 ) to the last element (N) and with an increasing delay per each respective first ( 1 ) to last (N) antenna element of each of the groups ( 1..n ) in the group order from the first ( 1 ) to the last group (n), while the second of the two delay structures provides the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order but from the last (N) to the first antenna element ( 1 ) and with an increasing delay per each respective first ( 1 ) to last (N) antenna element of each of the groups ( 1..n ) in the group order from the first ( 1 ) to the last group (n);

the system further comprising:

a further tunable coupler (ii) arranged to split an input signal to be transmitted into two further output signals with a tunable power ratio, wherein the two further output signals are provided to two further delay structures;

a base tunable coupler (Hi), arranged to split a base input signal to be transmitted into the input signal of the tunable coupler and the input signal of the further tunable coupler, with a tunable power ratio;

two further delay structures, wherein each further delay structure is arranged for splitting one of the two further output signals provided by the further tunable coupler (i), and for providing these to each of the antenna elements (1..N) of each of the groups ( 1..n)\

- wherein a first of the two further delay structures is arranged to provide the further output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order from the first {1) to the last element ( N ) and with an increasing delay per each respective first ( 1 ) to last antenna element (N) of each of the groups ( 1..n ) in the group order but from the last (n) to the first ( 1 ) group while the second of the two further delay structures provides the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order but from the last (N) to the first antenna element ( 1 ) and with an increasing delay per each respective first ( 1 ) to last (N) antenna element of each of the groups ( 1..n ) in the group order but from the last (n) to the first ( 1 ) group;

This example is directed to a 2D antenna element array. This particular example is shown in figure 12 and is elucidated in more detail with respect to the figures.

The above described example may be explained as follows. First, there is a base tunable coupler that is arranged to split a base input signal to be transmitted into two base signals with a tunable power ratio.

One of the two base signals is provided to the tunable coupler (i). The other of the two base signals is provided to the further tunable coupler (ii).

Each of these two tunable couplers (i, ii) is arranged to split the corresponding base signal into two output signals with a tunable power ratio.

(1 ) Let’s first discuss the tunable coupler (i). In order to understand its principle, an example of an antenna array is given. Assume that there is a matrix of A/-rows and n-columns. The columns stand for the number of groups as disclosed above. The rows stand for the number of antenna elements per group.

The matrix of antenna elements may be denoted as AE(1 , 1), being the first antenna element in group one. AE(n, 1) may be directed to the first antenna element in group n. AE(1 ,N) may be directed to the A/th antenna element of group one. Finally, AE(n,N) may be directed to the A/th antenna element of group n.

The first output of the tunable coupler (/) is connected to a first delay structure. The first delay structure is arranged to provide the first output of the tunable coupler to each of the antenna elements in the above described matrix, however, with a particular increasing delay per antenna element. That is, delays increase in the column direction as well as in the row direction. So, the delays increase from antenna element 1 to N, and from groups 1 to n.

The second output of the tunable coupler (/) is connected to a second delay structure. The second delay structure is arranged to provide the second output of the tunable coupler to each of the antenna elements in the above described matrix, however, with another particular increasing delay per antenna element. That is, delays increase in the reverse column direction as well as in the row direction. So, the delays increase from antenna element N to 1 , and from groups 1 to n.

(2) Let’s now discuss the further tunable coupler (ii).

The first output of the further tunable coupler (/) is connected to a first further delay structure. The first further delay structure is arranged to provide the first output of the further tunable coupler to each of the antenna elements in the above described matrix, however, with a particular increasing delay per antenna element. That is, delays increase in the column direction as well as in the reverse row direction. So, the delays increase from antenna element 1 to N, and from groups n to 1.

The second output of the further tunable coupler (/) is connected to a second further delay structure. The second further delay structure is arranged to provide the second output of the further tunable coupler to each of the antenna elements in the above described matrix, however, with another particular increasing delay per antenna element. That is, delays increase in the reverse column direction as well as in the reverse row direction. So, the delays increase from antenna element N to 1 , and from groups n to 1.

In the end, for each antenna element, four signals are to be combined: two signals originating from the tunable couple (/) and two signals originating from the further tunable coupler (ii). This may be accomplished using the parallel solution as described above, or the cascaded solution as provided above. For example, first the signals from tunable coupler (i) may be combined into N combined signals, and the signals from the further tunable coupler (//) may be combined into N further combined signals. At each antenna element, one of the N combined signals may further be combined with one of the N further combined signals.

It is noted that controllable phase shifters may be placed behind each tunable coupler for separately fine tuning each of the output signals of the tunable coupler.

In a further example, the system further comprises a controller arranged for controlling any of the tunable couplers for controlling the power ratio between the output signals of the respective tunable coupler, thereby controlling a beam steering pattern of the system

The controller may use electronic means for its control functions, for example, an electronic Integrated Circuit, IC, a Field Programmable Gate Array, FPGA, or anything alike.

In a second aspect of the present disclosure, there is provided a method of operating a system in accordance with any of the previous claims, wherein the method comprises the steps of:

splitting, by the tunable coupler (i) an input signal to be transmitted into two output signals with a tunable power ratio;

splitting and providing, by the two delay structures, one of the two output signals to each of the plurality of antenna elements (7..L/);

combining, by each of the combiners associated with the antenna elements, the two output signals provided by the two delay structures.

In an example, the method comprises the step of:

splitting, by each of the power splitters, the respective output signal into a plurality (N) of output signals.

In a further example, the method comprises the step of:

providing, by each of the plurality (N) of in series cascaded power splitters its input signal to a corresponding antenna element.

In yet another example, the tunable coupler is implemented as a Mach-Zehnder interferometer. In a further example, the distance between antenna elements is smaller or equal to half of the wavelength of the electromagnetic wave to be transmitted.

In an example, the method further comprises the steps of:

splitting and providing, by each of the two delay structures, one of the two output signals to each of the antenna elements ( 1..N) of each of the groups (1..n),

wherein a first of the two delay structures provides the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order from the first ( 1 ) to the last element ( N ) and with an increasing delay per each respective first (1) to last (N) antenna element of each of the groups ( 1..n ) in the group order from the first ( 1 ) to the last group (n), while the second of the two delay structures provides the output signal thereof to each of the antenna elements) with an increasing delay per each antenna element in the order but from the last (N) to the first antenna element ( 1 ) and with an increasing delay per each respective first ( 1 ) to last (N) antenna element of each of the groups ( 1..n ) in the group order from the first ( 1 ) to the last group (n);

splitting, by the further tunable coupler, an input signal to be transmitted into the two further output signals with a tunable power ratio;

; - splitting and providing, by each of the two further delay structures, one of the two further output signals to each of the antenna elements (1..N) of each of the groups (1..n);

wherein a first of the two further delay structures provides the further output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order from the first ( 1 ) to the last element (N) and with an increasing delay per each respective first ( 1 ) to last antenna element (N) of each of the groups ( 1..n ) in the group order but from the last (n) to the first ( 1 ) group while the second of the two further delay structures provides the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order but from the last (N) to the first antenna element ( 1 ) and with an increasing delay per each respective first ( 1 ) to last (N) antenna element of each of the groups ( 1..n ) in the group order but from the last (n) to the first ( 1 ) group; combining, by a combiner associated with each antenna element, output signals provided thereto into a combined output signal of that combiner, for the purpose of transmitting the electromagnetic wave based on the combined signal.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

Brief description of the Drawings

Fig. 1. Basic concept of a one-dimensional 4-element phased array transmitter

Fig. 2. The number of phase shifters in 1-D and 2-D phases array antennas

Fig. 3. Basic concept of cascaded angle offset phased array

Fig. 4. Modeling of 1 D cascaded angle offset phased array antennas Fig. 5. The phase and amplitude tuning based on 1 D cascaded angle offset phased array antennas. The x-axis is the index of each element antenna and the y-axis is the phase in degrees.

Fig. 6. The far-field pattern simulation on a 1-D linear cascaded angle offset phased array antennas

Fig. 7. Far-field patterns when sweeping o from 0.1 to 2.0 with a step of 0.1. Three different subsets are shown, with a) Da=12°, b) Da=6°, and c) Da=18°.

25

Fig. 8. Far-field patterns for a=18° with o sweeping from 0.1 to 2.0, to 4.0, and to 8.0. The number of sweeping steps is 20.

Fig. 9. Far-field patterns with o sweeping from 0.1 to 8.0 with linear and logarithmic distribution of o.

Fig. 10. Implementation scheme of an 1-D CAO-PA.

Fig. 1 1. The implementation scheme of a compact 1-D CAO-PA.

Fig. 12. The implementation scheme of a compact 2-D CAO-PA.

Detailed description

Fig. 3 illustrates the basic concept of a cascaded angle offset phased array 300. Each dashed circle denotes the initial phase of continuous waves at the same carrier frequency. The angles of the arrows denote the value of phases (angle offsets). In the first row, a series of cascaded angle offsets are generated with the phase offset

of the n-th phase shifter denoted as:

90°— (w - l) x 30°

Similarly, the second row denotes another series of cascaded angle offsets generated with the function as:

90° + (M - 1) X 30°

The continuous waves with the two series of cascaded angle offsets are then combined by summing them with different power ratios as shown in the third and fourth rows. The resulting combined signals are represented by the black arrows. The combined continuous waves are then launched to a linear array of antennas. As shown in the third row of Fig. 3, the power ratio is 1 : 1 , which yields that the generated waves only have two angle offsets, namely -/+ 90°.

As shown in the fourth row, when the power ratio is changed, the combined phases will be tuned quasi-linearly, which fits a linear phased antenna array. The amplitude imbalance can be introduced as well as detailed in Fig. 4. Such amplitude imbalance can be compensated by automatic power amplifiers before each antenna 400. Further investigation shows that the amplitude imbalance does not hinder the beam steering function as shown in Figs. 6 up to 8, but only introduce different radiation power. Therefore, a gain control amplifier can be used to compensate the power difference as shown in Fig. 10-12. The required gain will be pre-calculated based on different tuning configurations.

Mathematical model of CAO-PA

The detailed mathematical model of cascaded angle offset phased array antennas is shown in Fig. 4, where a linear 1 -by-N phased array is shown. The left and right lines denote the two phase distributed networks with the two cascaded angle offsets (vectors). The input wave generating green dash lines is expressed as:

S, (?) = Ae^Jmr A denotes the amplitude and w denotes the angular frequency of the input wave. The input wave of red one is expressed as:

S_r (t) = Be^JtW+p

5 B, w, and b denote amplitude, angular frequency and initial phase of the input wave. The individual output waves in line n with cascaded angle offsets of green and red networks are shown as follows, respectively.

SJt,n,Aa) = Ae^,“'"ⁱ“ⁱ

10

n is the index of output while Da is the phase difference between two adjacent output waves. Here the phase difference Da is equal for both left and right networks. Note that the phase difference for left and right networks is not necessary

15 the same. The amplitude distribution (for example A in Equation above) can also be varied versus the antenna index. Moreover, the cascaded angle offset can be both linear as the example shown in the equation above and nonlinear. The two output waves of red and green networks are combined as shown in the 3rd and 4th rows of Fig. 2.

20 The combined waves at each antenna can then be further expressed as:

If we further define B/A=s , we can have the following equation:

P2 contains the amplitude and phase items for each antenna. To analyse the group of phase shifts and amplitudes, the phase of, and the absolute value of P2 are analysed based on the below equations:

As the results shown in Fig. 7-9, once the Aa and s are tuned, the relation of phase shifts and amplitudes towards the index n of the output (connected to each element antenna) are changed. Following the quasi-linear phase curves and amplitude curves are discussed.

Quasi-linear phase tuning based on CAO-PA

The phase and amplitude tuning of each antenna can be deduced from the equation provided earlier. As an example, given Q, and a equal to 6°, when sweeping o from 0.1 to 2 with a step of 0.1 , the phase shifts and amplitudes towards output (antenna) 5 index n are shown in the first row in Fig. 5. The second row are with the same parameters except that a is set to 12°. The x-axis is the index of each antenna while the y-axes are the angle (in degrees) and amplitude (in dB scale). It is clear that the phase difference a controls the derivative of phase alongside index of antenna.

Also it is found that a larger a induces a larger nonlinearity in the curves of phase shifts and amplitudes. We do see that there is a power imbalance among different antennas but it is less 5 dB, which can be easily compensated by an automatic power control amplifier, which is shown in Fig. 10 as an example.

Beam steering based on CAO-PA

To further evaluate the beam steering performance using the proposed CAO-PA concept, we apply the phase shifts and amplitude weights (as shown in Fig. 5) to an 1-D linear antenna array 600 as shown in Fig. 6. The number of antenna elements is N. Each element antenna is ideally an omni-directionally emitting element where the distance d between the antennas is set to L/2 (with l being the wavelength of the wave, so =df\ e.g. , for =60GHz, l is 5mm). The far field pattern (FFP) of such an array is expressed as:

FFPs at different angle (Q) are shown in polar coordinate as shown in

Fig. 7-8.

The simulated FFP-s 700 are shown in Fig. 7. As mentioned before, the imbalanced power of each synthesized beam will be compensated by gain-tunable amplifier, the power of each beam has been normalized for better comparison. As we can see, the parameter a controls the steering angle of the beam. More than 10° scanning is achieved with Da=18°. As s increases beyond 2, the non-equal beam distribution can be observed as shown 800 in Fig. 8. The number of sweeping steps is 20.

Since the direction (Q) of the steered beam may is not linear versus power ratio (s), by introducing a nonlinear distribution of s, a quasi-equal beam distribution can be achieved as shown 900 in Fig. 9. The value of power ratio at each sweeping step is s(m), where m is the sweeping index. The number of total sweeping steps is 20.

Here the function of each step of s distribution is logarithmic, which can be expressed as:

where the step size (D) is (8.0-0.1)/20=0.395. Even we use logarithmic function as an example, but other nonlinear distribution of phase/amplitude can be used to address this issue.

Implementation of an 1 -D CAO-PA

A typical 1-D CAO-PA 1000 / 1010 is schematically shown in Fig. 10A/B. A tunable coupler is employed to split the input signal into two paths with a tunable power ratio, one to the left side power splitter, and one to the right side power splitter. Such device can be realized by a Mach-Zehnder interferometer or other types of power coupler/splitter as shown in Fig. 10. Its complexity is comparable to that of an active phase shifter. Then the signals after the power splitters are then phase shifted by two set of taped delay lines, the phase and amplitude through each delay line is fixed with predefined values. The power splitters and the taped delay lines are well-known for RF (or microwave) and lightwave. A gain-tunable amplifier is used to compensate the power imbalance between different power ratios. The advantages of our proposed scheme can be summarized as follows:

- The networks for phase/amplitude distribution are fully passive, do not require active elements, and hence do not need remote feeding and maintenance;

- No multiple tunable phase shifter is used but only one tunable coupler is used to tune the phased array and further to steer a beam;

- the proposed concept is applicable for all wave types, including radio waves and light waves;

- Optimization can be achieved via better phase/amplitude arrangement (linear phase or nonlinear).

Implementation of a compact 1 -D CAO-PA

To avoid the grating lobes, the distance between two adjacent antennas should not be larger than half the wavelength of a radiated radio wave. For lightwaves, separation of the elements at less than half a wavelength is very difficult. Taking 1550 nm wavelength as an example, the networks of vertical radiators, phase shifters and amplitude controllers distribution are expected to be very compact, in the sub-micrometer level. Here we propose a compact implementation of 1-D CAO- PA.

As shown 1 100 in Fig. 1 1 , a bi-directional tapped line architecture is used to realize an 1-D CAO-PA. In the green network, the split input signal is propagating from left to right via power splitters. The power is tapped out at each antenna with a fixed phase difference a, which is determined by the propagation length (delay line) in

between the taps: a = 360°xl/l

The delay is then accumulated afterwards which allows a highly efficient delay line with very compact footprint. By launching the input signal from the other side, a negative delay (thus negative a) can be generated as in the red network shown in Fig. 1 1.

It is noted that the distance between the power splitter and the corresponding antenna may be construed the same, i.e. the paths between the power splitters and the corresponding antenna may have equal length to assure consistency in the phase delay.

Implementation of a compact 2-D CAO-PA

Based on the proposed compact 1-D CAO-PA, a 2-D CAO-PA can also be realized as shown 1200 in Fig. 12. In the first stage, the power ratio o1 is tuned via the middle tunable coupler. Then two tunable couplers (in the left and the right) are used to tune the power with the same power ratio o². In this way, the advantages are:

- Very compact network for 2-D phase/amplitude distribution;

- No active element in the radiation region;

- Only 3 active elements needed for 2-D beam steering.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit 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 measured 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 the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope thereof.

Claims

1. A system for beam steering, the system comprising a group of antenna elements (1..N) spaced equally apart, wherein the antenna elements (1..N) are arranged to transmit an electromagnetic wave, the system further comprising:

two delay structures, wherein each delay structure is arranged for splitting one of the two output signals provided by the tunable coupler, and for providing theseto each of the antenna elements (1..N) of the group;

wherein in the group, the antenna elements (1..N) are arranged in a given order from a first element (1) to a last element (N), wherein a first of the two delay structures provides the output signal thereof to each of the antenna elements (1..N) with an increasing delay per each antenna element ( 1..N) in the order from the first ( 1 ) to the last element (N), while the second of the two delay structures provides the output signal thereof to each of the antenna elements (1..N) with an increasing delay per each antenna element in the order but from the last (N) to the first element

(

2. The system in accordance with claim 1 , wherein each delay structure comprises:

- a plurality (N) of tapped delay lines for connecting the corresponding power splitter to each respective antenna elements (1..N) for providing the output signal thereof to each of the antenna elements.

3. The system in accordance with claim 1 , wherein each delay structure comprises a plurality (N) of in series cascaded power splitters, wherein each power splitter is arranged to provide an output signal to a corresponding antenna element (1..N).

4. The system in accordance with any of the previous claims, wherein the system further comprises two controllable phase shifters, wherein the controllable phase shifters are each connected in between the tunable coupler and any of the two delay structures for controlling phases of output signals originating from the tunable coupler.

5. The system in accordance with any of the previous claims, wherein the tunable coupler is implemented as a Mach-Zehnder interferometer.

6. The system in accordance with any of the previous claims, wherein the distance between the antenna elements (1..N) is smaller or equal to half of the wavelength of the electromagnetic wave to be transmitted.

7. A system in accordance with any of the previous claims, the system comprising a multiple of groups ( 1..n ) of antenna elements (1..N) arranged to transmit an electromagnetic wave, the multiple of groups ( 1..n ) being arranged in a group order from a first group (1) to a last group ( n )

wherein each of the two delay structures is arranged for splitting one of the two output signals provided by the tunable coupler, and for providing these to each of the antenna elements (1..N) of each of the groups ( 1..n );

wherein in each group ( 1..n ), the antenna elements (1..N) are arranged in a given order from a first element (1) to a last element (N),

wherein a first of the two delay structures is arranged to provide the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order from the first ( 1 ) to the last element (N) and with an increasing delay per each respective first ( 1 ) to last (N) antenna element of each of the groups ( 1..n ) in the group order from the first ( 1 ) to the last group (n), while the second of the two delay structures provides the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order but from the last (N) to the first antenna element ( 1 ) and with an increasing delay per each respective first (7) to last (L/) antenna element of each of the groups ( 1..n ) in the group order from the first ( 1 ) to the last group (n);

the system further comprising:

a further tunable coupler (i) arranged to split an input signal to be transmitted into two further output signals with a tunable power ratio, wherein the two further output signals are provided to two further delay structures;

a base tunable coupler, arranged to split a base input signal to be transmitted into the input signal of the tunable coupler and the input signal of the further tunable coupler, with a tunable power ratio;

two further delay structures, wherein each further delay structure is arranged for splitting one of the two further output signals provided by the further tunable coupler (i), and for providing these to each of the antenna elements (1..N) of each of the groups ( 1..n );

wherein a first of the two further delay structures is arranged to provide the further output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order from the first ( 1 ) to the last element ( N ) and with an increasing delay per each respective first ( 1 ) to last antenna element (N) of each of the groups ( 1..n ) in the group order but from the last (n) to the first ( 1 ) group while the second of the two further delay structures provides the output signal thereof to each of the antenna elements with an increasing delay per each antenna element in the order but from the last (N) to the first antenna element ( 1 ) and with an increasing delay per each respective first ( 1 ) to last (N) antenna element of each of the groups ( 1..n ) in the group order but from the last (n) to the first ( 1 ) group;

8. The system in accordance with claim 7, wherein the system further comprises a plurality of further controllable phase shifters, wherein the plurality of further controllable phase shifters are each arranged controlling phases of output signals originating from any of the tunable coupler, the further tunable coupler and the base tunable coupler.

9. The system in accordance with any of the previous claims, wherein the system further comprises a controller arranged for controlling any of the tunable couplers for controlling the power ratio between the output signals of the respective tunable coupler, thereby controlling a beam steering pattern of the system.

10. The system in accordance with any of the previous claims, wherein the system is arranged for any of:

transmitting an optical electromagnetic wave;

transmitting an Radio Frequency, RF, electromagnetic wave.

1 1. A method of operating a system in accordance with any of the previous claims, wherein the method comprises the steps of:

splitting, by the tunable coupler (/) an input signal to be transmitted into two output signals with a tunable power ratio;

splitting and providing, by each of the two delay structures, one of the two output signals to each of the antenna elements ( 7..L/);

combining, by each of the combiners associated with the antenna elements, output signals provided thereto into a combined output signal of that combiner, for the purpose of transmitting the electromagnetic wave based on the combined signal.

12. The method in accordance with claim 1 1 and in accordance with claim

2 or a claim dependent thereof, wherein the method comprises the step of:

13. The method in accordance with claim 1 1 and in accordance with claim

3 or a claim dependent thereof, wherein the method comprises the step of:

providing, by each of the plurality (N) of in series cascaded power splitters an output signal to an antenna element connected thereto.

14. The method in accordance with any of the claims 1 1 - 13, wherein the tunable coupler is implemented as a Mach-Zehnder interferometer.

15. The method in accordance with any of the claims 1 1 - 13 and in accordance with claim 7 or a claim dependent thereof, wherein the method further comprises the steps of:

; - splitting and providing, by each of the two further delay structures, one of the two further output signals to each of the antenna elements ( 1..N) of each of the groups (1..n);