A delay line assembly for broadband photonic beamforming

Abstract

This disclosure relates to a delay line assembly for a beamforming network of a phased antenna array (PAA). The delay line assembly comprises N > 1 delay lines, each configured to carry an optical signal, and each comprising M > 1 switchable delay elements arranged in series. Each delay element of a delay line is configured to provide, when switched on, a different delay for the optical signal than the other delay elements of the delay line. The delay lines further have different maximum achievable delays and comprise each a fixed delay element for the optical signal. The fixed delay element is arranged at the beginning or end of the respective delay line and in series with the delay elements. The fixed delay of a delay line is smaller than that of another delay line, if the maximum achievable delay of the delay line is larger than that of the other delay line.

Description

[0001] A DELAY LINE ASSEMBLY FOR BROADBAND PHOTONIC BEAMFORMING

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to photonic beamforming, for instance, in the field of telecommunications. The disclosure proposes a delay line assembly for a beamforming network of a phased antenna array (PAA) device, wherein the delay line assembly enables broadband photonic beamforming of the PAA device. The disclosure also proposes a PAA device that includes the delay line assembly and includes a PAA optically connected to the delay line assembly.

[0004] BACKGROUND

[0005] With the increasing demand on telecommunications and data traffic, it is a must to constantly improve and research on these technologies. A result from this research is the current development of the 5thgeneration (5G) wireless communication system, and in the next years the 6thgeneration (6G) wireless communication system. Some demands for future wireless communication systems include higher broadband for the communication signals, and a greater control over both the direction and the directivity of the communication signals. This is where beamforming has become a key technology.

[0006] PAA technology has increased the communication efficiency by transmitting microwave signals within a specific direction with a high directivity and fast beam steering capability. PAAs have originated much research for high performance wireless communication and radar systems, in both military and civilian applications, with an enormous potential for wireless communication systems in the near future.

[0007] A PAA is a structure that is composed of multiple antennas, which are disposed in onedimensional or two-dimensional configurations, and which can act as radiating elements or as receivers. In a PAA device, which includes at least a PAA and a beamforming network, a signal from a radio frequency (RF) source is sent and processed by the beamforming network, and is then provided to the antennas of the PAA to radiate the signal. When the individual signals, which are radiated by the different antennas, interfere in the far-field, the signals may do this in such a way that a constructive interference signal is generated in a given spatial direction. Thus, a beam is formed in this given spatial direction, which is referred to as the beam direction.

[0008] In a conventional electronic PAA, each antenna is connected with a phase shifter to a back end of the beamforming network. When the signal enters the beamforming network, the phase of the signal is tuned by the phase shifters. Thereby, the relative phase between the antennas is tuned. By controlling the phase shifters and the phases between the antennas, the beam direction can be set and changed. It is usually possible to set different beam directions over a range of positive and negative pointing angles, wherein a pointing angle denotes the angle between a particular beam direction and a reference 0° beam direction that is defined for the PAA.

[0009] However, the microwave phase shift is dependent of frequency, which leads to the so- called beam squint effect. The beam squint effect causes the beam directions for different microwave frequencies to diverge at increased pointing angles. Due to this effect, the conventional electronic PAA has an instantaneous bandwidth of only several hundred MHz. The beam squint effect is illustrated in FIG. 1, which shows two graphs that plot signal amplitude over pointing angle for frequencies of 9 GHz, 10GHz, and 11 GHz, respectively. For the left graph, the nominal (i. e. , desired and / or set) pointing angle is 20°, while for the right graph the nominal pointing angle is 40°. It can be seen from the comparison of the left graph and the right graph that for the larger nominal pointing angle of 40° the divergence of the beam directions for the three different frequencies (as defined by the corresponding signal amplitude peaks at these frequencies) is higher than for the lower nominal pointing angle of 20°. That means, the different frequencies lead to a divergence of the actual pointing angles from each other and the nominal pointing angle.

[0010] Optically beamformed PAAs, which employ optical true-time delay (OTTD), can overcome the beam squinting problem. Therefore, they can have a wider operating bandwidth, and can control the entire signal spectrum to steer the beams at the same actual pointing angles for different frequencies. Micro wave photonics techniques bring also other important added values, such as low weight, low loss, and immunity to electromagnetic interference. In order to have the beam directions at the same actual pointing angle for all frequencies, the phase of the optical signal related to each antenna has to be made independent of frequency. This can be done by using time delays instead of phase shifts. There are several ways to implement these time delays between the antennas of the PAA. For instance, integrated waveguides may be used. The most relevant techniques, which use integrated waveguides technology, are nowadays based on micro-ring resonators (MRRs) and optical switchable delay waveguides.

[0011] For example, optical true-time delay lines (OTTDLs) based on cascaded MRRs have been proposed. However, these OTTDLs have bandwidths smaller than 10 GHz, which restricts the application to broadband operations. MRR schemes present not only this issue, but also the fact that MRR structures require complex control schemes, high power consumption, and their spectra responses are very sensitive to the fabrication and thermal variations. With all that, despite being capable of providing a continuous tunable delay, the inconveniences seem to have a heavier impact than the benefits regarding the implementation in wireless communication systems.

[0012] Another approach is based on switched delay lines, in particular switched OTTDLs. This approach is illustrated in FIG. 2, wherein specifically one of multiple switched delay lines 200 is depicted. As shown, each switched delay line 200 comprises different lengths of integrated optical waveguides 201a and 201b, which are interconnected by means of integrated photonic switches 202, in order to provide tunable delays (delay stages) of the switched delay line 200, with which the total delay of the delay line 200 can be tuned in discrete steps. Such switched delay lines 200 have the advantage of providing a much wider operation bandwidth, simple signal processing and controlling, high delay precision, and a large tolerance to fabrication errors and thermal variations. The switched delay lines 200 can also provide large delays with a broad bandwidth and a low temperature sensitivity.

[0013] As shown in FIG. 2 and 3, the switched delay lines 200 are connected by the tunable switchers 202, which can each comprise two 3-dB directional couplers and a two parallel waveguide sections loaded with phase shifters. Discrete variable delays can be obtained in each delay stage by switching between a long path and a short delay path (reference) in with the tunable switcher 202. Thus, each delay line 200 can be encoded as a bit word. In a conventional switched delay line architectures, which may be used for a beamforming network of a PAA device, the number of available pointing angles for beams depends on the number Moi bits (i. e. , the number of switchable delay elements 602) of each switchable delay line 200, and on the number A of delay lines 200, according to the following equation:

[0014] The parenthesis on the previous equation denotes the truncation of positive real numbers.

[0015] As an example, a PAA device architecture including a PAA with 8 antennas and a delay line assembly for the beamforming network with 8 delay lines 200 may be considered. Each delay line may be a 5-bit switched delay line 200, i.e., may have 5 tunable switchers 202. In this example, the maximum possible delay achievable for each antenna / delay line would be 31U, and the maximum possible delay AT between the antennas of the PAA would be 4U, wherein U is a predetermined delay that is a unit delay for each delay line 200. Each delay stage can provide the unit delay U or a multiple thereof (see FIG. 3). As the Equation 1 above predicts, the number of pointing angles in such an architecture is 9.

[0016] As long as the number of antennas increases, so does the directivity, but with a lower number of pointing angles. Increasing the number of bits (switchable delay elements) is also a possible solution to obtain a higher number of delays between the antennas of the PAA, and thus a higher resolution, i.e., more pointing angles. Unfortunately, this implies more active elements on the photonic chip, larger size and increased power consumption.

[0017] SUMMARY

[0018] This disclosure and its solution are based further on the following considerations.

[0019] An exemplary solution for the above-mentioned trade-off between active elements and resolution is a delay line assembly 400, which is shown in FIG. 4. This exemplary delay line assembly 400 has 8 delay lines 401, wherein each delay line 401 is a 5-bit delay line (has 5 tunable switchers 402) as in the example given above. This solution can achieve a much larger number of delays, which results in 32 different states and pointing angles. The solution can, in particular, accomplish delays AT between the antennas from 0 to 31U. This is possible, because the unit delay r is different in each delay line 401. In particular, as shown, the unit delay r ranges from U to 8U in subsequent delay lines (from top to bottom delay line in FIG. 4), wherein U is again a predetermined delay. In previous architectures, like that shown in FIG. 3, the unit delay was the same value in every delay line 200.

[0020] The exemplary solution shown in FIG. 4 provides not only a larger number of pointing angles, but also an easier way to encode their path through the beamforming network, wherein the same bit word can be used for all the delay lines 401. This bit word represents, in binary, the pass of the signal over a respective delay line 401, where 0 means the optical signal in a delay stage (including tunable switcher 402) takes the short path, and 1 means it takes the long path.

[0021] A broadband design for this architecture is able to span the 8-18 GHz band, with delays AT between antennas from 0 to 31U, with an example of U = 2 ps. Unfortunately, a drawback of this broadband design is that it fails to provide correct pointing for negative pointing angles for frequencies that are different from 16 GHz. This is shown in FIG. 5, which depicts three graphs showing peak signal amplitudes of different beams over the pointing angle. It can be seen that for frequencies of 10 GHz and 13 GHz, negative pointing angles cannot be set correctly.

[0022] When AT is too big, the pointing angles become frequency dependent. Despite using OTTDLs as the switched delay lines 401, this solution is sensitive to frequency (i.e., beam squint occurs, whereby the pointing angle changes with the frequency).

[0023] In view of the above, this disclosure aims to provide an improved switched delay line assembly for a beamforming network, in particular, by solving the drawbacks mentioned above. An objective of this disclosure is to address the inability to set correctly also negative pointing angles for all frequencies in the solution shown in FIG. 4. Another objective is to achieve a high resolution of pointing angles with the minimum number of active elements. These and other objectives are achieved by the solution of this disclosure as described in the independent claims. Advantageous implementations are further defined in the dependent claims.

[0024] A first aspect of this disclosure provides a delay line assembly for a beamforming network of a PAA device, the delay line assembly comprising: a plurality of N delay lines, where N > 1, the delay lines being each configured to carry an optical signal, wherein the delay lines each comprise a plurality of M switchable delay elements arranged in series, where M > 1, wherein each switchable delay element of a respective delay line is configured to provide, when the delay element is switched on, a different delay for the optical signal than the other switchable delay elements of the respective delay line, wherein the delay lines have different maximum delays, wherein the maximum achievable delay of the respective delay line is based on the sum of the delays from all the delay elements of the respective delay line, when these delay elements are switched on, wherein the delay lines each comprise a fixed delay element configured to provide a fixed delay for the optical signal, wherein the fixed delay of the respective delay line is arranged at the beginning or end of the respective delay line in series with the switchable delay elements, and wherein the fixed delay of the respective delay line is smaller than the fixed delay of another delay line, if the maximum delay of the respective delay line is larger than the maximum delay of the other delay line.

[0025] The fixed delay element in each delay line of the delay line assembly enables the setting of correct negative pointing angles for all frequencies. Thus, the issues mentioned for the assembly in FIG. 4 are overcome, and an improved delay line assembly for a beamforming network is provided. The delay line assembly achieves a high resolution of positive and negative pointing angles, while requiring only a minimum number of active elements.

[0026] In an implementation form of the first aspect, the delay lines are arranged one next to the other in a first direction and each extend into a second direction, and the maximum delays increase linearly from a first delay line to a last delay line of the delay lines arranged in the first direction. This increasing maximum delay of the subsequent delay lines enables higher delays between antennas of the PAA device, to which the delay line assembly may be configured to convey the optical signal. This results in an increased number of pointing angles.

[0027] In an implementation form of the first aspect, the fixed delays decrease linearly from the first delay line to the last delay line of the delay lines arranged in the first direction.

[0028] This allows a large number of negative pointing angles to be set correctly.

[0029] In an implementation form of the first aspect, each delay element of the respective delay line is configured to provide a unit delay of the respective delay line or a multiple of the unit delay of the respective delay line, and wherein the unit delays increase linearly from the first delay line to the last delay line of the delay lines arranged in the first direction.

[0030] In an implementation form of the first aspect, the delays provided by the delay elements of the respective delay line increase from a first delay element to a last delay element of the respective delay line.

[0031] This increases the number of possible pointing angles. For instance, the delay provided by each delay element may be a multiple of, e.g. twice, the delay of the previous delay element along the delay line, in direction of the optical signal.

[0032] In an implementation form of the first aspect, the delay line assembly comprises 8 delay lines and 5 switchable delay elements per delay line.

[0033] In an implementation form of the first aspect, the switchable delay elements of the respective delay line are configured to provide a delay of, respectively, 1, 2, 4, 8, and 16 times the unit delay of the respective delay line.

[0034] In an implementation form of the first aspect, the unit delay of the first delay line is n = U, wherein U is a predetermined delay, the unit delay of the second delay line is T2 = 2U, the unit delay of the third delay line is rs = 3U, the unit delay of the fourth delay line is T4 = 4U, the unit delay of the fifth delay line is rs = 5U, the unit delay of the sixths delay line is re = 6U, the unit delay of the seventh delay line is r? = 7U, and the unit delay of the eighth delay line is rs = 8U. The value of the predetermined delay U may depend, for example, on at least one of: the number of antennas of the PAA, for which the delay line assembly may be used; and the separation of the antennas; and the maximum frequency of the system.

[0035] In an implementation form of the first aspect, the fixed delay of the fixed delay element of the first delay line is 81 = 112U, the fixed delay of the fixed delay element of the second delay line is 82 = 96U, the fixed delay of the fixed delay element of the third delay line is 83 = 80U, the fixed delay of the fixed delay element of the fourth delay line is 84 = 64U, the fixed delay of the fixed delay element of the fifth delay line is 85 = 48U, the fixed delay of the fixed delay element of the sixth delay line is 86 = 32U, the fixed delay of the fixed delay element of the seventh delay line is 87 = 16U, and the fixed delay of the fixed delay element of the eighth delay line is 88 = 0.

[0036] In an implementation form of the first aspect, the delay lines are each configured to be encoded as a bit word, wherein each bit of the bit word corresponds to one of the switchable delay elements of the delay lines being either switched on or switched off.

[0037] The delay line assembly of the first aspect thus provides an easy way to encode the path of the optical signal through the delay line assembly. For instance, the same bit word can be used for all the delay lines.

[0038] In an implementation form of the first aspect, each switchable delay element is an integrated photonic switch.

[0039] In an implementation form of the first aspect, each switchable delay element is switchable between a shorter path and a longer path for the optical signal, wherein the longer path compared to the shorter path provides the delay of the delay element.

[0040] In an implementation form of the first aspect, each switchable delay element comprises a tunable coupler and two parallel waveguide sections configured to provide, respectively, the shorter path and the longer path, the two parallel waveguide sections being connected to the tunable coupler. In an implementation form of the first aspect, the delay line assembly is a switched OTTD element.

[0041] A second aspect of this disclosure comprises a PAA device comprising: a PAA comprising a plurality of antennas; and a beamformer network comprising the delay line assembly according to the first aspect or any of its implementation forms, wherein each delay line of the delay line assembly is arranged to convey an optical signal to or from one of the antennas of the PAA.

[0042] In summary of the above aspects and implementation forms, this disclosure proposes anew delay line assembly for a new beamforming network architecture, wherein the delay line assembly may be based switched delay lines using OTTD technology. In the proposed delay line assembly, the unit delay (also referred to as basic delay) on each delay line may be different, for instance, may be linearly increased from one delay line to the next. This may allow obtaining higher delays between the antennas of the PAA, which may further result in a larger number of pointing angles. In addition, the delay line assembly includes a fixed delay before each delay line, which makes possible a correct negative angle pointing for all frequencies.

[0043] This disclosure thus solves the problem found on the architecture in FIG. 4, namely being not able to achieve correct frequency -independent positive and negative pointing angles (see FIG. 5). However, far beyond, this disclosure also represents a breakthrough in the field of optically beamformed PAAs, since it increases notably the resolution (number of pointing angles) for the same number of active components.

[0044] It has to be noted that certain entities like devices, elements, units and means described in this disclosure could be implemented using software or hardware elements or any kind of combination thereof. All steps performed by the various entities, which may be described in this disclosure, as well as the functionalities described to be performed by the various entities, are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities.

[0045] Even if, in the following description of specific examples and embodiments of this disclosure, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities could be implemented in respective software or hardware elements, or any kind of combination thereof.

[0046] BRIEF DESCRIPTION OF DRAWINGS

[0047] The above described aspects and implementation forms will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

[0048] FIG. 1 illustrates the beam squint effect for an RF beamformer, due to which the actual pointing angle changes with frequency and diverges from the nominal pointing angle.

[0049] FIG. 2 shows an exemplary architecture for an M-bit switched OTTDL, where U is the unit delay of the delay line.

[0050] FIG. 3 shows an exemplary architecture of a 5 -bit photonic beamforming network with 8 delay lines, and illustrates a tunable switcher between paths of different lengths, the tunable switcher using the cross and bar states in a Mach-Zehnder-Interferometer.

[0051] FIG. 4 shows an exemplary delay line assembly with 8 delay lines and 5 delay bits delay stages per delay line. The increasing delay of each bit corresponds to a different unit delay, which gets larger for each delay line.

[0052] FIG. 5 shows a comparison between radiation patterns at different frequencies for the delay line assembly of FIG. 4, demonstrating that there is a constant solution only for positive pointing angles.

[0053] FIG. 6 shows a delay line assembly according to this disclosure.

[0054] FIG. 7 shows a delay line assembly according to this disclosure with specific fixed

[0055] (pre-compensating) delays. FIG. 8 shows radiation paterns for 15 GHz, 20 GHz and 30 GHz of the delay line assembly of FIG. 7, demonstrating that there is a constant solution for positive and negative pointing angles for all frequencies.

[0056] FIG. 9 shows a PAA device according to this disclosure.

[0057] DETAILED DESCRIPTION OF EMBODIMENTS

[0058] FIG. 6 shows a delay line assembly 600 according to this disclosure. The delay line assembly 600 can be used for a beamforming network of a PAA device (e.g., as described later with respect to FIG. 9). The delay line assembly 600 may, accordingly, be a part of the PAA device. In particular, the delay line assembly 600 is suitable for a beamforming network architecture, which uses switched delay lines, which may be OTTDLs.

[0059] The delay line assembly 600 comprises a plurality of N delay lines 601, where N is an integer and N > 1. Just as an example used for illustration, N = 3 in FIG. 6. Each of the delay lines 601 is configured to carry an optical signal, for example, toward (indicated by the arrow of each delay line 601) or from (opposite direction) one of the antennas of a PAA.

[0060] The delay lines 601 each comprise a plurality of M switchable delay elements 602 arranged in series, wherein M is an integer and M > 1. Just as an example used for illustration, M = 3 in FIG. 6. Each switchable delay element 602 of a respective delay line 601 is configured to provide - when the switchable delay element 602 is switched on - a different delay for the optical signal than the other switchable delay elements 602 of the respective delay line 601. This is exemplarily indicated in FIG. 1 by the different sizes of the delay elements 602 in each delay line 601. For example, each delay element 602 may be switchable between a shorter path and a longer path for the optical signal, wherein the longer path compared to the shorter path provides the delay of the delay element. For example, when the delay element 602 is switched on, the optical signal takes the longer path, and when the delay element 602 is switched off, the optical signal takes the shorter path.

[0061] Further, the delay lines 601 of the delay line assembly 600 have different maximum achievable delays, wherein the maximum achievable delay of the respective delay line 601 is based on the sum of the delays from all the delay elements 602 of the respective delay line 601, when these delay elements 602 are switched on. That is, when all the delay elements 602 of the respective delay line 601 would be switched on at the same time, the optical signal would be delayed by the maximum achievable delay of this delay line 601 while being conveyed by the delay line 601.

[0062] In addition, the delay lines 601 of the delay line assembly 600 each comprise a fixed delay element 603, which is configured to provide a fixed delay for the optical signal. The fixed delay element 603 of the respective delay line 601 is arranged at the beginning (as illustrated in FIG. 6), at the end of the respective delay line 601 (not shown), or at any point in the middle of the line, as long as the optical signal would be forced to pass through this fixed delay, and in series with the switchable delay elements 602 of the respective delay line 601. The fixed delay of the delay element 603 of the respective delay line 601 is smaller than the fixed delay of the delay element 603 of another delay line 601, if the maximum achievable delay of the respective delay line 601 is larger than the maximum achievable delay of the other delay line 601. This is indicated by the different sizes of the fixed delay elements 603 in FIG. 1. That is, the larger the maximum achievable delay of a delay line 601, the smaller the fixed delay. Notably, the fixed delay of a fixed delay element 603 of a delay line 601 may also be zero, but only for one delay line 601 of the delay line assembly 600.

[0063] Due to the fact that the delay line assembly 600 of this disclosure includes the fixed delay element 603 on each delay line 601, correct negative pointing angles can be achieved when the delay line assembly 600 is used in a beamforming network of a PAA device. This is, because increasing and decreasing delays between antennas of the PAA device can be achieved.

[0064] FIG. 7 shows a delay line assembly 600 according to this disclosure, which builds on the delay line assembly 600 shown in FIG. 6. Same elements in FIG. 6 and FIG. 7 are labelled with the same reference signs, and may be implemented likewise.

[0065] In particular, FIG. 7 shows an example of a delay line assembly 600 for a PAA with 8 antennas. That is, the delay line assembly 600 of FIG. 7 has 8 delay lines 601, wherein each delay line 601 is a 5-bit switched delay line (has 5 delay elements 602), and wherein each delay line 601 has a fixed delay element 603. The delay lines 601 are arranged one next to the other in a first direction 701, and each extends into a second direction 702.

[0066] The maximum achievable delays of the delay lines 601 increase linearly from a first delay line 601a to a last delay line 601b along the first direction 701. That is, the last delay line 602b in the first direction 701 has the largest maximum achievable delay. Because of this, the fixed delay of the fixed delay element 603 of this last delay line 602b may be zero. The value of the fixed delay of the fixed delay element 603 arranged in series with the delay elements 602 of this delay line 601, depends on the position n of the delay line 601 in the delay line assembly 600, on the total number of delay lines N of the delay line assembly 600, and on the number of delay stages M. For a general design, the value of the fixed delay of the fixed delay element 603 for the nthdelay line would be:

[0067] How this addition of the fixed delay to each delay line 601 may work is exemplified in Table 1 below. Three different delays AT between antennas of the PAA have been calculated (-16U, 0U, 10U), and are shown with their corresponding bit word. The delay between the delay lines 601 is constant, and the delay of each delay line 601 of the 8 delay lines (Line 1 - Line 8) is calculated adding the fixed delay of the fixed delay element 603 with the delay from the bit selected.

[0068] Table 1. Example of 3 different delays between antennas of the PAA In a design of a PAA device with the delay line assembly 400 of FIG. 4, the first pointing angle (bit word 00000) was broadside. With the solution of this disclosure shown in FIG. 7, the broadside direction corresponds to the bit word 10000, and the PAA device starts pointing to the minimum pointing angle. With this correction the maximum achievable delay between of antennas of the PAA is 2M-1U, in the example with M = 5 accordingly 16U.

[0069] For a PAA device with the delay line assembly 400 of FIG. 4, the delays of each delay line 401 can be swept from OU to 31U, and the delays between antennas ranges from -4U to 4U. At this point, the time delays are so great that frequency independence is lost. However, for a PAA device with the delay line assembly 600, the delays can be swept from -16U to 15U. Thus, the same number of 32 possible delays is achieved, without compromising the frequency independence.

[0070] The array factor is an expression that drives the behavior of PAAs. The array factor is defined as the sum of the contribution from each antenna to the total electric field. It depends on the amplitude term |Ei|, the distance traveled by the wave, ar, and the position of each element, .

[0071] With our architecture, the array factor can be expressed as a function of the delay between adjacent antennas AT.

[0072] The maximum time delay between antennas with this architecture is 2M-IU. From this expression one may obtain the condition of the value for the predetermined delay U and for the unit delay r on each delay line, trying to cancel the internal parenthesis on the sine function for any possible angle 0. 1 d U -2(M-D C

[0073] The result is a real broadband design, which allows frequency -independent positive and negative pointing angles, and optimizes the design to the maximum the number of delay element 602 used. Further, a high pointing angle resolution is provided, comparable to that achieved by continuous tunable delay structures. This can be seen in FIG. 8, which shows radiation patterns in three graphs for three different frequencies 15 GHz, 20 GHz and 30 GHz of a PAA device with the delay line assembly 600 of FIG. 6. FIG. 8 demonstrates that there is a constant solution for positive and negative pointing angles for all frequencies.

[0074] FIG. 9 shows a PAA device 900 according to this disclosure. The PAA device 900 comprises a PAA with a plurality of antennas 901. Further, the PAA device 900 comprises a beamformer network comprising the delay line assembly 600 as described above. Each delay line 601 of the delay line assembly 600 is arranged to convey an optical signal to or from one of the antennas 901 of the PAA. The present disclosure enables true broadband operation for the PAA device 900. Thus, optimum operation in terms of maximum number of pointing angles and squint-free operation can be achieved.

[0075] The main difference of the delay line assembly 600 of the present disclosure to the delay line assembly 400 of the exemplary solution shown in FIG. 4 is the use of the fixed delay elements 603 for the various delay lines 601, which fixed delay elements 603 may be arranged before or after the switchable delay elements 602 of each delay line 601, and in series with these switchable delay elements 602. The fixed delays of the fixed delay elements 603 allow positive and negative pointing angles for the entire bandwidth region of the PAA device 900.

[0076] Overall, the great improvement of the delay line assembly 600 of this disclosure compared to conventional alternatives is the optimization of the number of pointing angles obtained (resolution) with respect to the number of active elements used. Although there are exemplary solutions that already achieve a large number of pointing angles, the solution of this disclosure also meets the conditions of high bandwidth and pointing range. Continuing with the example that has been followed throughout this disclosure, a 5-bit delay line assembly 600 for a beamforming network with 8 delay lines 601 may have a number of pointing angles of 32, wherein in other exemplary solutions this maximum number of possible pointing angles was only 9. To achieve similar resolution and bandwidth performance with other solutions, one would have to use 7 delay elements per delay line compared to 5 delay elements 602 needed with the solution of this disclosure. That means 16 more Mach-Zehnder Interferometers, more power consumption, more insertion and propagation losses and more possible fabrication errors. The present disclosure has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed matter, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word “comprising” does not exclude other elements or steps and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

CLAIMS1. A delay line assembly (600) for a beamforming network of a phased antenna array device, the delay line assembly (600) comprising: a plurality of N delay lines (601), where N > 1, the delay lines (601) being each configured to carry an optical signal, wherein the delay lines (601) each comprise a plurality of M switchable delay elements (602) arranged in series, where M > 1, wherein each switchable delay element (602) of a respective delay line (601) is configured to provide, when the delay element (602) is switched on, a different delay for the optical signal than the other switchable delay elements (602) of the respective delay line (601), wherein the delay lines (601) have different maximum achievable delays, wherein the maximum achievable delay of the respective delay line (601) is based on the sum of the delays from all the delay elements (602) of the respective delay line (601), when these delay elements (602) are switched on, wherein the delay lines (601) each comprise a fixed delay element (603) configured to provide a fixed delay for the optical signal, wherein the fixed delay of the respective delay line (601) is arranged at the beginning or end of the respective delay line (601) in series with the switchable delay elements (602), and wherein the fixed delay (603) of the respective delay line (601) is smaller than the fixed delay of another delay line (601), if the maximum achievable delay of the respective delay line (601) is larger than the maximum achievable delay of the other delay line (601).

2. The delay line assembly (600) according to claim 1, wherein the delay lines (601) are arranged one next to the other in a first direction (701) and each extend into a second direction (702), and wherein the maximum achievable delays increase linearly from a first delay line (601a) to a last delay line (601b) of the delay lines (601) arranged in the first direction (701).

3. The delay line assembly (600) according to claim 2 wherein the fixed delays (603) decrease linearly from the first delay line (601a) to the last delay line (601b) of the delay lines (601) arranged in the first direction (701).

4. The delay line assembly (600) according to one of the claims 1 to 3, wherein each delay element (602) of the respective delay line (601) is configured to provide a unit delay (703) of the respective delay line (601) or a multiple of the unit delay (703) of the respective delay line (601), and wherein the unit delays (703) increase linearly from the first delay line (601a) to the last delay line (601b) of the delay lines (601) arranged in the first direction (701).

5. The delay line assembly (600) according to one of the claims 1 to 4, wherein the delays provided by the delay elements (602) of the respective delay line (601) increase from a first delay element (602a) to a last delay element (602b) of the respective delay line (601).

6. The delay line assembly (600) according to one of the claims 1 to 5, comprising 8 delay lines (601) and 5 switchable delay elements (602) per delay line (601).

7. The delay line (600) assembly according to the claims 4 and 6, wherein the switchable delay elements (602) of the respective delay line (601) are configured to provide a delay of, respectively, 1, 2, 4, 8, and 16 times the unit delay (703) of the respective delay line (601).

8. The delay line assembly (600) according to one of the claims 4 to 6, wherein: the unit delay (703) of the first delay line (601) is n = U, wherein U is a predetermined delay, the unit delay (703) of the second delay line (601) is T2 = 2U, the unit delay (703) of the third delay line (601) is rs = 3U, the unit delay (703) of the fourth delay line (601) is T4 = 4U, the unit delay (703) of the fifth delay line (601) is rs = 5U, the unit delay (703) of the sixths delay line (601) is T6 = 6U, the unit delay (703) of the seventh delay line (601) is T7 = 7U, and the unit delay (703) of the eighth delay line (601) is rs = 8U.

9. The delay line assembly (600) according to claim 8, wherein: the fixed delay of the fixed delay element (603) of the first delay line (601) is si =the fixed delay of the fixed delay element (603) of the second delay line (601) is 82= 96U, the fixed delay of the fixed delay element (603) of the third delay line (601) is 83 = 80U, the fixed delay of the fixed delay element (603) of the fourth delay line (601) is 84 = 64U, the fixed delay of the fixed delay element (603) of the fifth delay line (601) is 85 = 48U, the fixed delay of the fixed delay element (603) of the sixth delay line (601) is 86 = 32U, the fixed delay of the fixed delay element (603) of the seventh delay line (601) is 87 = 16U, and the fixed delay of the fixed delay element (603) of the eighth delay line (601) is 88 = 0.

10. The delay line assembly (600) according to one of the claims 1 to 9, wherein the delay lines (601) are each configured to be encoded as a bit word, wherein each bit of the bit word corresponds to one of the switchable delay elements (602) of the delay lines (601) being either switched on or switched off.

11. The delay line assembly (600) according to one of the claims 1 to 10, wherein each switchable delay element (602) is an integrated photonic switch.

12. The delay line assembly (600) according to one of the claims 1 to 11, wherein each switchable delay element (602) is switchable between a shorter path and a longer path for the optical signal, wherein the longer path compared to the shorter path provides the delay of the delay element.

13. The delay line assembly (600) according to claim 12, wherein each switchable delay element (602) comprises a tunable coupler and two parallel waveguide sections configured to provide, respectively, the shorter path and the longer path, the two parallel waveguide sections being connected to the tunable coupler.

14. The delay line assembly (600) according to one of the claims 1 to 13, wherein the delay line assembly (600) is a switched optical true-time delay element.

15. A phased antenna array device (900) comprising: a phased antenna array comprising a plurality of antennas (901); and a beamforming network comprising the delay line assembly (600) according to one of the claims 1 to 14, wherein each delay line (601) of the delay line assembly (600) is arranged to convey an optical signal to or from one of the antennas (901) of the phased antenna array.

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