Methods and devices for a MIMO radar

Abstract

Multiple-In-Multiple-Out ("MIMO") antenna array device for radar, comprising the following: a receiver antenna arrangement, wherein the receiver antenna arrangement comprises a plurality of receiver antenna elements (152A,..., 152N) of an antenna array arranged in a pattern such that a first receiver antenna element (RX1) is located approximately one unit away from a second receiver antenna element (RX2), a third receiver antenna element (RX3) is located approximately two units away from the second receiver antenna element (RX2), and a fourth receiver antenna element (RX4) is located approximately four units away from the first receiver antenna element (RX1); and a transmitter antenna arrangement, wherein the transmitter antenna arrangement comprises one or more transmitter antenna elements (146A,...,146N) of an antenna array arranged in a pattern such that a first transmitter antenna element (TX1) is placed at a distance of approximately five units from the third receiver antenna element (RX3), and wherein the first transmitter antenna element (TX1) and the third receiver antenna element (RX3) are placed on one side of a printed circuit board.

Description

AREA OF REVELATION

[0001] Embodiments of this disclosure relate generally to multiple-in-multiple-out ("MIMO") antennas, in particular MIMO antennas for radar. STATE OF THE ART

[0002] Modern MIMO radar systems are used in various applications, such as telecommunications, automotive applications, and the like. The aperture size of a MIMO radar system is a key factor influencing the angular resolution and the number of channels within the aperture. The spacing between each pair of adjacent channels also contributes to angular ambiguity.

[0003] To reduce overall system costs, the design of a MIMO radar system with a limited antenna area and a limited number of transmit ("TX") and receive ("RX") channels is preferred. Conventional radar aperture designs, including traditional single-input multiple-output ("SIMO") radar systems and MIMO radar systems, use a two-way channel spacing of half a wavelength. The total radar aperture size of an N-channel radar can be (N-1)*λ / 2 or N*λ / 2 when the antenna patch area is included.

[0004] To increase angular resolution, some MIMO radar systems currently use antenna structures with a channel spacing greater than λ / 2, or half a wavelength. However, such MIMO radar systems can exhibit poorer performance due to angular ambiguities caused by grating lobes in the antenna pattern.

[0005] US 2019 / 0049577 A1 discloses a MIMO radar device and a vehicle.

[0006] US 2017 / 0293028 A1 concerns an imaging radar sensor with horizontal digital beam shaping and vertical object measurement by phase comparison with offset transmitters.

[0007] WO 2017 / 179515 A1 discloses a MIMO radar device and a vehicle. JP 2007 333656 A discloses a radar device.

[0008] Wikipedia, online encyclopedia: Golomb ruler. Version of 11.4.2016, URL: https: / / de.wikipedia.org / w / index.php?title=Golomb-Lineal&oldid=153394404, [accessed on 28.5.2025] describes a Golomb ruler or Golomb standard in number theory. BRIEF DESCRIPTION OF THE INVENTION

[0009] The claimed subject matter is defined in independent claim 1. Advantageous embodiments are described in the dependent claims.

[0010] The innovations described in the claims are each characterized by several aspects, none of which is solely responsible for their desirable characteristics. Without limiting the scope of protection of the claims, some outstanding features of this disclosure are now briefly described.

[0011] One aspect of this disclosure relates to a multiple-in-multiple-out (“MIMO”) antenna array device comprising: a receiver antenna arrangement, wherein the receiver antenna arrangement comprises a plurality of receiver antenna elements of an antenna array arranged in a pattern in which a first receiver antenna element is at a first distance next to a second receiver antenna element and the second receiver antenna element is at a second distance next to a third receiver antenna element; and a transmitter antenna arrangement, wherein the transmitter antenna arrangement comprises a first transmitter antenna element located at a third distance next to the third receiver antenna element, wherein the first distance, the second distance, and the third distance are different distances, the third distance being approximately five times the first distance.

[0012] In some embodiments, the receiver antenna arrangement further comprises a pattern in which the first receiver antenna element is at a fourth distance next to a fourth receiver antenna element and the fourth receiver antenna element is at a fifth distance next to a fifth receiver antenna element, wherein the first distance, the second distance, the third distance, the fourth distance and the fifth distance are different distances.

[0013] In some embodiments, the transmitter antenna arrangement further comprises a pattern in which a second transmitter antenna element is located at a sixth distance from the fifth receiver antenna element and a third transmitter antenna element is located at a seventh distance from the second transmitter antenna element, wherein the first distance, the second distance, the third distance, the fourth distance, the fifth distance and the sixth distance are different distances.

[0014] In some embodiments, the first distance is half a wavelength.

[0015] In some embodiments, the second distance is one wavelength.

[0016] In some embodiments, the third distance is two wavelengths.

[0017] In some embodiments, the receiver antenna arrangement and the transmitter antenna arrangement are arranged in a pattern in which the receiver antenna elements and the one or more transmitter antenna elements are positioned along a single axis.

[0018] Another aspect of the disclosure includes a multiple-in-multiple-out ("MIMO") antenna array device for radar, comprising: a receiver antenna arrangement, wherein the receiver antenna arrangement comprises a plurality of receiver antenna elements of an antenna array arranged in a pattern in which a first receiver antenna element is located at a distance of approximately one unit from a second receiver antenna element, a third receiver antenna element is located at a distance of approximately two units from the second receiver antenna element, and a fourth receiver antenna element is located at a distance of approximately four units from the first receiver antenna element;and a transmitter antenna arrangement, wherein the transmitter antenna arrangement comprises one or more transmitter antenna elements of an antenna array arranged in a pattern in which a first transmitter antenna element is placed at a distance of approximately five units from the third receiver antenna element and on one side of the printed circuit board.

[0019] In some embodiments, the transmitter antenna arrangement further includes a second transmitter antenna element located approximately ten units away from the fourth receiver antenna element.

[0020] In some embodiments, the transmitter antenna arrangement further includes a third transmitter antenna element located approximately eleven units away from the second transmitter antenna element.

[0021] In some embodiments, the receiver antenna arrangement and the transmitter antenna arrangement are arranged in a pattern in which the receiver antenna elements and the transmitter antenna elements are positioned along a single axis.

[0022] In some embodiments, the distance from one unit is half a wavelength.

[0023] In some embodiments, the distance from one unit is half a wavelength + / - 10%.

[0024] In some embodiments, the distance from one unit is half a wavelength + / - 25%.

[0025] Another aspect of the disclosure includes a multiple-in-multiple-out ("MIMO") antenna array device for transmitting high-frequency signals, comprising: an antenna element arrangement, wherein the antenna element arrangement comprises a plurality of antenna elements arranged in a pattern in which a first antenna element is next to a second antenna element, a third antenna element is next to the second antenna element, a fourth antenna element is next to the first antenna element, and a fifth antenna element is next to the third antenna element, wherein each of the antenna elements comprises a transmitting antenna element and / or a receiving antenna element, wherein the antenna elements of the antenna element arrangement are placed along a single axis, and wherein the spacing between adjacent antenna elements in the antenna element arrangement is not uniform.where the distance between the third antenna element and the fifth antenna element is approximately five times the distance between the first antenna element and the second antenna element.

[0026] In some embodiments, the distance between two adjacent antenna elements contains half a wavelength.

[0027] In some embodiments, a distance between two other adjacent antenna elements contains a wavelength.

[0028] In some embodiments, a distance between two other adjacent antenna elements contains two wavelengths.

[0029] In some embodiments, the antenna element arrangement includes a fourth antenna element next to the third antenna element, a fifth antenna element next to the fourth antenna element, and a sixth antenna element next to a fifth antenna element, wherein the first, second, third, and fourth antenna elements are receiver antenna elements, and the fifth, sixth, and seventh antenna elements are transmitter antenna elements, wherein the distances between adjacent antenna elements in the antenna element arrangement are not uniform.

[0030] In some embodiments, the antenna element arrangement includes a fifth antenna element next to the third antenna element, a sixth antenna element next to the fourth antenna element, a seventh antenna element next to the sixth antenna element, and an eighth antenna element next to the seventh antenna element, wherein the first, second, third, fourth, and fifth antenna elements are receiver antenna elements, and the sixth, seventh, and eighth antenna elements are transmitter antenna elements, wherein the distances between adjacent antenna elements in the antenna element arrangement are not uniform.

[0031] For the purposes of this brief presentation of the disclosure, certain aspects, advantages, and novelty features of the innovations have been described herein. It is understood that not all of these advantages may necessarily be achieved according to any particular embodiment. Thus, the innovations may also be designed or implemented in such a way that only one advantage or only one group of advantages, as taught herein, is achieved or optimized, without necessarily achieving other advantages, as may be taught or suggested herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Now, embodiments of this disclosure will be described with reference to the accompanying drawings, using non-exclusive examples. Fig. Figure 1A is an illustration of a single-input multiple-output ("SIMO*") antenna array according to some embodiments. Fig.Figure 1B is an illustration of a multiple-input multiple-output ("MIMO") antenna array according to some embodiments. Fig. Figure 2 is a mapping of virtual channels for a single-input multiple-output ("SIMO") antenna array according to some embodiments. Fig. Figure 3 is a diagram of virtual channels for a multiple-input multiple-output ("MIMO") antenna array according to some embodiments. The Fig. 4A, Fig. 4B and Fig. Figures 4C are illustrations of effective apertures and corresponding radiation characteristics according to some embodiments. Fig. Figure 4A shows an effective aperture and a radiation characteristic for a radar system with 3 virtual channels according to some embodiments. Fig.Figure 4B shows an effective aperture and a radiation characteristic for a radar system with 4 virtual channels according to some embodiments, wherein there is a spacing of half a wavelength between each channel. Fig. Figure 4C shows an effective aperture and a radiation characteristic for a radar system with 8 virtual channels according to some embodiments, wherein there is a distance of half a wavelength between all channels. In Fig. Figure 5A shows an example of the angular resolution of a radar system with 4 virtual channels according to some embodiments. In Fig. Figure 5B shows an example of the angular resolution of a radar system with 12 virtual channels according to some embodiments. In Fig.Figure 6A is an example of the angular resolution of a radar system with 2 virtual channels in which two transmitter antenna elements are one wavelength apart, as shown in some embodiments. In Fig. 6B is an example of a radiation characteristic of the radar system according to Fig. 6A is shown. In Fig. 6C is a radar system with 8 virtual channels in which two transmitter antenna elements are four wavelengths apart, as shown in some embodiments. In Fig. 6D is an example of a radiation characteristic of the radar system according to Fig. 6C shown. In Fig. Figure 7 shows a MIMO radar system with several different distances between the 12 virtual channels according to some embodiments. In Fig. 8 are distances between pairs of virtual channels of the radar system of Fig.7 shown according to some embodiments. Fig. Figure 9 is a diagram of a radiation characteristic for the radar system of Fig. 7. Fig. Figure 10A is a representation of a radar system in which tapering and spacing adjustment between antenna elements are applied to two transmitter antenna elements. Fig. 10B is a diagram of a radiation characteristic for the radar system of Fig. 10A. Fig. Figure 11 is an image of offset beams for the radar system of Fig. 10A. In Fig. Figure 12A shows a MIMO radar system with several different distances between the 15 virtual channels according to some embodiments. In the Fig. 12B-1, 12B-2, 12B-3 and 12B-4 are distances between pairs of virtual channels of the radar system of Fig. 12A shown. DETAILED DESCRIPTION

[0033] The following detailed description of specific embodiments contains various descriptions of concrete embodiments. However, the innovations described herein can be implemented in numerous different ways, as defined and covered by the claims. This description refers to the drawings, in which the same reference numerals can indicate identical or functionally similar elements. It is understood that elements depicted in the figures are not necessarily drawn to scale. Furthermore, it is understood that certain embodiments may contain more elements than are shown in a drawing and / or a subset of the elements shown in a drawing. In addition, some embodiments may incorporate any suitable combination of features from two or more drawings.The headings herein have been included for convenience only and do not necessarily affect the scope of protection or the meaning of the claims.

[0034] The disclosed systems and methods include a multiple-in-multiple-out (“MIMO”) antenna array. In some embodiments, the MIMO antenna array includes an arrangement of antenna elements. The arrangement of antenna elements can include a transmitter arrangement and / or a receiver arrangement, each arrangement containing a plurality of antenna elements. Advantageously, the arrangement of antenna elements can provide a higher angular resolution without the appearance of grid lobes. The transmitter and / or receiver antenna elements can be spaced such that this results in improved virtual channel characteristics compared to conventional configurations. Weighting and / or taper can be applied to the transmitter and / or receiver antenna elements to reduce the sidelobe levels of the virtual two-way radiation patterns. In some embodiments, the MIMO radar antenna array includes a transmitter arrangement and a receiver arrangement.The transmitter arrangement can contain a variety of transmitting antenna elements of an antenna array. The receiver arrangement can contain a variety of receiving antenna elements of an antenna array.

[0035] In some embodiments, the receiver arrangement can include a plurality of receiver antenna elements of an antenna array arranged in a pattern. In one embodiment, a first receiver antenna element can be located one unit away from a second receiver antenna element. A third receiver antenna element can be located two units away from the second receiver antenna element. A fourth receiver antenna element can be located four units away from the first receiver antenna element. A first receiver antenna element can be placed between the second and fourth receiver antenna elements. A second receiver antenna element can be placed between the first and third receiver antenna elements. A fourth receiver antenna element can be located next to the first receiver antenna element. A first receiver antenna element can be located next to the second receiver antenna element.A second receiver antenna element can be located next to the third receiver antenna element. This special receiver arrangement allows for combinations with transmitter antenna elements to create virtual channels with the size of an effective aperture. Advantageously, the receiver arrangement can result in several different spacings between pairs of virtual channels. These varying spacings can lead to a higher angular resolution without the appearance of grid lobes.

[0036] In some embodiments, the transmitter arrangement can include a plurality of transmitting antenna elements of an antenna array arranged in a pattern. A first transmitting antenna element can be located five units away from the third receiving antenna element and placed on one side of the circuit board. A second transmitting antenna element can be located ten units away from the fourth receiving antenna element. A third transmitting antenna element can be located eleven units away from the second transmitting antenna element. A first transmitting antenna element can be located next to the third receiving antenna element. A second transmitting antenna element can be located next to the fourth receiving antenna element. A third transmitting antenna element can be located next to the second transmitting antenna element. By combining the special receiving arrangement with the transmitting arrangement, virtual channels can be created.The transmitter arrangement can advantageously result in several different spacings between pairs of virtual channels. These varying spacings can lead to a higher angular resolution without the appearance of grid lobes.

[0037] In some embodiments, the first receiver antenna element, the second receiver antenna element, the third receiver antenna element and / or the fourth receiver antenna element are placed between the second transmitter antenna element and the third transmitter antenna element.

[0038] In some embodiments, the transmitter and / or receiver antenna elements can be spaced apart at intervals of units of half a wavelength, half a wavelength + / - 10% and / or half a wavelength + / - 25%. Single-input-multiple-output (“SIMO”) and multiple-input-multiple-output (“MIMO”) antenna arrays

[0039] Fig.Figure 1A is a diagram of a single-input multiple-output (“SIMO”) antenna array according to some embodiments. The SIMO antenna array may include a transmitter with one or more antennas fed by the fixed and power amplifiers, and / or a receiver with multiple independent antennas. In the example of Fig. Figure 1A shows a data source 102 that can feed one or more fixed and power amplifiers (PAs) 104A, 104B, 104N (hereinafter collectively referred to as "power amplifiers 104"). The power amplifiers can feed one or more transmitter antenna elements 106A, 106B, 106N (hereinafter collectively referred to as "transmitter antenna elements 106"). The power amplifiers 104A and 104N and the transmitter antenna elements 106A, 106N are optional. The transmitter antenna elements 106 can produce a radiation pattern 108.

[0040] In some embodiments, the SIMO antenna array can receive electromagnetic energy 110. The electromagnetic energy 110 can be the energy reflected due to the radiation characteristic 108. The SIMO antenna array can receive the electromagnetic energy 110 at the receiver antenna elements 112A, 112B, 112N-1, 112N (hereinafter collectively referred to as "receiver antenna elements 112").The electromagnetic energy 110 can be amplified by low-noise amplifiers 114A, 114B, 114N-1, 114N (hereinafter collectively referred to as "low-noise amplifiers (LNA) 114"), down-converted by mixers 116A, 116B, 116N-1, 116N (hereinafter collectively referred to as "mixer 116"), amplified by programmable gain amplifiers (PGA) 118A, 118B, 118N-1, 118N (hereinafter collectively referred to as "programmable gain amplifier 118"), converted into a digital value by analog-to-digital converters (ADCs) 120A, 120B, 120N-1, 120N (hereinafter collectively referred to as "analog-to-digital converter 120"), and by digital phase shifters 122A. The phase shifts of the 122B, 122N-1, and 122N (hereinafter collectively referred to as "digital phase shifters 122") are phase-shifted and combined by an adder 1240. The digital phase shifters 122 and / or other components in the receiver can perform digital beamforming (DBF) for the receiver antenna array.

[0041] Fig.Figure 1B is a diagram of a multiple-input multiple-output (“MIMO”) antenna array according to some embodiments. The MIMO antenna array may include a transmitter with one or more antennas fed by amplifiers with adjustable gain, and / or a receiver with multiple antennas. In the example of Fig. Figure 1A shows a data source 142 that can feed one or more adjustable power amplifiers 144A, 144B, 144N (hereinafter collectively referred to as "power amplifiers 144") for adjusting the gain and phase and / or for switching the signal on or off. The power amplifiers can feed one or more transmitting antenna elements 146A, 146B, 146N (hereinafter collectively referred to as "transmitting antenna elements 146"). The transmitting antenna elements 146 can produce one or more radiation patterns 148A, 148B, 148N (hereinafter collectively referred to as "radiation patterns 148").

[0042] The MIMO antenna array can receive electromagnetic energy 150. The electromagnetic energy 150 can be reflected by an object in the region of the radiation characteristic 148. The electromagnetic energy 150 can be received by the receiver antenna elements 152A, 152B, 152C, 152D (hereinafter collectively referred to as "receiver antenna elements 152").The signal can be amplified by low-noise amplifiers 154A, 154B, 154C, 154D (hereinafter collectively referred to as "low-noise amplifiers 154"), down-converted by mixers 156A, 156B, 156C, 156D (hereinafter collectively referred to as "mixers 156"), amplified by amplifiers 158A, 158B, 158C, 158D with programmable gain (hereinafter collectively referred to as "amplifiers 158 with programmable gain"), converted into a digital value by analog-to-digital converters 160A, 160B, 160C, 160D (hereinafter collectively referred to as "analog-to-digital converters 160"), or converted into a digital value by digital phase shifters 162A, 162B, 162C, 162D (hereinafter collectively referred to as "digital phase shifters"). The data (labeled 162) is phase-shifted and combined by an adder 1640. The value of the digital data can also be set (not shown) before it is combined by the adder 1640.Digital beamforming for the receiver antenna array can be performed using the digital phase shifters 162 and the setting of the value. Virtual channels for a single-input multiple-output ("SIMO") and a multiple-input multiple-output ("MIMO") antenna array

[0043] Fig. Figure 2 is a diagram of virtual channels for a single-input multiple-output (“SIMO”) antenna array according to some embodiments. The SIMO antenna array can include a single transmitting antenna element TX1 and four receiving antenna elements RX1, RX2, RX3, RX4. The spacing between the receiving antenna elements can be approximately half a wavelength, half a wavelength ± 5%, half a wavelength ± 10%, half a wavelength ± 25%, or the like.

[0044] In some embodiments, the effective aperture of the single transmitting antenna element TX1 and the four receiving antenna elements RX1, RX2, RX3, RX4 can be three half wavelengths (1.5λ, where λ is one wavelength) or two wavelengths if the antenna patch area is included, provided the receiver antenna elements are spaced half a wavelength apart. The combination of a single transmitting antenna element TX1 and the four receiving antenna elements RX1, RX2, RX3, RX4 can produce four virtual channels CH1, CH2, CH3, CH4. Because the receiver antenna elements RX1, RX2, RX3, RX4 are spaced half a wavelength apart, the total width of the virtual channels CH1, CH2, CH3, CH4 can be three half wavelengths; therefore, the effective aperture can be three half wavelengths or two wavelengths if the antenna patch area is included.

[0045] In an alternative embodiment, the same size of effective aperture can be achieved by using four transmitter antenna elements separated by half a wavelength and a single receiver antenna element.

[0046] Fig. Figure 3 is a mapping of virtual channels for a uniformly spaced multiple-input multiple-output (MIMO) antenna array. The MIMO antenna array can contain three transmitting antenna elements TX1, TX2, TX3 and four receiving antenna elements RX1, RX2, RX3, RX4. The spacing between the receiving antenna elements can be approximately half a wavelength, and the spacing between the transmitting antenna elements can be two wavelengths. Other spacings can also be used.

[0047] In some embodiments, the effective aperture of the three transmitting antenna elements TX1, TX2, TX3 and the four receiving antenna elements RX1, RX2, RX3, RX4 can be eleven half wavelengths (5.5λ) when the receiver antenna elements are spaced half a wavelength apart and two wavelengths apart when the transmitting antenna elements are spaced two wavelengths apart, or six wavelengths when the antenna patch area is included. The group of four receiving antenna elements RX1, RX2, RX3, RX4 can generate four virtual channels for each of the transmitting antenna elements TX1, TX2, TX3.

[0048] In some embodiments, the four receiver antenna elements RX1, RX2, RX3, RX4, which receive the signal from the first transmitter antenna element TX1, can establish the first set of virtual channels CH1, CH2, CH3, CH4. The spacing between the virtual channels of this first set (CH1, CH2, CH3, CH4) can be half a wavelength. The four receiver antenna elements RX1, RX2, RX3, RX4, which receive the signal from the second transmitter antenna element TX2, establish the second set of virtual channels (CH5, CH6, CH7, CH8). The spacing between the virtual channels of this second set (CH5, CH6, CH7, CH8) can also be half a wavelength. The four receiver antenna elements RX1, RX2, RX3, RX4, which receive the signal from the third transmitter antenna element TX3, establish the third set of virtual channels (CH9, CH10, CH11, CH12).There can be a distance of half a wavelength between the virtual channels of the third set of virtual channels CH9, CH10, CH11, CH12.

[0049] All channels can be separated by half a wavelength, corresponding to the distance between the four receiver antenna elements RX1, RX2, RX3, and RX4. The three sets of virtual channels can each be separated by the same distance. The three sets of virtual channels can be separated by two wavelengths based on the distances between the three transmitter antenna elements TX1, TX2, and TX3. Accordingly, the last channel in the first set, CH4, can be located next to the first channel in the second set, CH5, and half a wavelength away from it. The last channel in the second set, CH8, can be located next to the first channel in the third set, CH9, and half a wavelength away from it. The total effective aperture can be eleven half wavelengths, or six wavelengths if the antenna patch area is included.

[0050] The Fig. 4A, Fig. 4B and Fig. Figures 4C are illustrations of effective apertures and corresponding radiation characteristics for the achievable standard angular resolution after digital beamforming according to some embodiments. Fig. Figure 4A depicts a radar system with an effective aperture of 3 virtual channels. According to some embodiments, all channels can be half a wavelength apart. A radar system as shown in Fig. 4A can be implemented using a single transmitter antenna element TX1 and three receiver antenna elements RX1, RX2, RX3. Alternatively, the radar system can be implemented using three transmitter antenna elements TX1, TX2, TX3 and a single receiver antenna element RX1. At a value of -3 dB, the angular resolution ranges from -30 to 30 degrees, resulting in an angular resolution of 60 degrees.

[0051] In Fig.Figure 4B depicts a radar system with an effective aperture of four virtual channels according to some embodiments, with each channel spaced half a wavelength apart. Such a radar system can be implemented using a single transmitting antenna element TX1 and four receiving antenna elements RX1, RX2, RX3, and RX4. Alternatively, the radar system can be implemented using four transmitting antenna elements TX1, TX2, TX3, and TX4 and a single receiving antenna element RX1. Furthermore, the radar system can be implemented using two transmitting antenna elements TX1 and TX2 and two receiving antenna elements RX1 and RX2. The angular resolution can range from -18 to 18 degrees at a value of -3 dB, resulting in an angular resolution of 36 degrees.

[0052] In Fig.4C is a radar system with an effective aperture of 8 virtual channels according to some embodiments, wherein there is a spacing of half a wavelength between each channel. An example of this radar system may include a single transmitting antenna element TX1 and eight receiving antenna elements RX1, RX2, RX3, RX4, RX5, RX6, RX7, RX8, or the like. Alternatively, two transmitting antenna elements TX1, TX2 and four receiving antenna elements RX1, RX2, RX3, RX4 may be used; four transmitting antenna elements TX1, TX2, TX3, TX4 and two receiving antenna elements RX1, RX2 may be used; and / or eight transmitting antenna elements TX1, TX2, TX3, TX4, TX5, TX6, TX7, TX8 and a single receiving antenna element RX1 may be used. The angular resolution can range from -7.3 to 7.3 degrees at a value of -3 dB, resulting in an angular resolution of 14.6 degrees.

[0053] In Fig.Figure 5A shows the angular resolution of a radar system with 4 virtual channels according to some embodiments. The radar system with 4 virtual channels in Fig. 5A comprises a transmitter assembly containing a single transmitter antenna element TX1 and a receiver assembly containing four receiver antenna elements RX1, RX2, RX3, and RX4. Consequently, four virtual channels CH1, CH2, CH3, and CH4 are formed. The grid behind the vehicle represents an example of the angular resolution of the radar system with four virtual channels.

[0054] In Fig. Figure 5B shows the angular resolution of a radar system with 12 virtual channels according to some embodiments. The radar system with 12 virtual channels in Fig.5B includes a transmitter array containing three transmitter antenna elements TX1, TX2, TX3, and a receiver array containing four receiver antenna elements RX1, RX2, RX3, RX4. Consequently, 12 virtual channels CH1, CH2, CH3, CH4, CH5, CH6, CH7, CH8, CH9, CH10, CH11, CH12 are formed. The grid behind the vehicle represents an exemplary angular resolution of the 12-virtual-channel radar system. The 12-virtual-channel radar system produces a grid behind the vehicle with a resolution three times finer than that of the [unclear text]. Fig. The radar system shown in 5A has 4 virtual channels. Behavior at a channel spacing of more than half a wavelength

[0055] To achieve better angular resolution, SIMO and MIMO antenna arrays can be arranged to include receiver and transmitter antenna element arrangements with a channel spacing of more than half a wavelength. This type of configuration has the disadvantage of poorer angular ambiguity due to grating lobes in the antenna characteristic.

[0056] In Fig. Figure 6A is a radar system with two virtual channels in which two transmitting antenna elements are one wavelength apart, as shown in some embodiments. The distances between the transmitting antenna elements are greater than half a wavelength by a factor of 2. Accordingly, the two virtual channels CH1 and CH2 are one wavelength apart, and the size of an effective aperture in the radar system is one wavelength.

[0057] In Fig. 6B is the radiation characteristic of the radar system according to Fig.Figure 6A shows some embodiments. As shown, the angular resolution for the main lobe at -3 dB ranges from approximately -16 to 16 degrees, for a total angular resolution of approximately 32 degrees for the main lobe. However, the radiation pattern includes grid lobes from -90 degrees to -48 degrees and from 48 degrees to 90 degrees. Accordingly, the occurrence of the grid lobes introduces angular ambiguity into the radar system. Embodiments of this disclosure advantageously overcome these grid lobe problems.

[0058] In Fig.6C is a radar system with 8 virtual channels in which two transmitting antenna elements TX1, TX2 are four wavelengths apart, as shown in some embodiments. The receiver arrangement can include four receiver antenna elements RX1, RX2, RX3, RX4, which are one wavelength apart. Due to the receiver and transmitting arrangements, 8 virtual channels CH1, CH2, CH3, CH4, CH5, CH6, CH7, CH8 are generated. The 8 virtual channels CH1, CH2, CH3, CH4, CH5, CH6, CH7, CH8 are each one wavelength apart. Accordingly, the size of an effective aperture in the radar system is seven wavelengths, or fifteen half wavelengths when the antenna patch area is included.

[0059] In Fig. 6D is the radiation characteristic of the radar system after processing by digital beamforming according to Fig.Figure 6C shows some embodiments. As shown, the angular resolution for the main lobe at -3 dB ranges from approximately -5 to 5 degrees, for a total angular resolution of approximately 10 degrees for the main lobe. However, the radiation pattern also shows grid lobes from -90 degrees to -70 degrees and from 70 degrees to 90 degrees. Accordingly, the angular ambiguity for the radar system is also worsened due to the grid lobes. Multiple-Input-Multiple-Output ("MIMO") antenna array with varying spacing between twelve virtual channels

[0060] To overcome the problems associated with angular ambiguity due to grating lobes, the systems and methods described herein incorporate a MIMO antenna array with a transmitter array containing a plurality of transmitter antenna elements arranged in a specific pattern, and / or a receiver array containing a plurality of receiver antenna elements arranged in a specific pattern. The transmitter and / or receiver array results in several different spacings between pairs of virtual channels.

[0061] In Fig. Figure 7 shows a MIMO radar system with several different spacings between the 12 virtual channels according to some embodiments. In some embodiments, the radar system can be Fig.7. It may be mounted on or integrated into a car and used for collision avoidance, adaptive cruise control, autonomous driving, and the like. In some embodiments, the radar system may be Fig. 7. They are emitted at relatively high frequencies, such as 77 GHz or 24 GHz. Other frequencies can also be used.

[0062] The radar system of Fig.Figure 7 can contain four receiver antenna elements RX1, RX2, RX3, RX4 and three transmitter antenna elements TX1, TX2, TX3. The principles and advantages disclosed herein are illustrated in connection with four receiver antenna elements and three transmitter antenna elements, but are also applicable when more or fewer receiver and / or transmitter antenna elements are present. The distances between the four receiver antenna elements can vary. For example, the first receiver antenna element RX1 can be located next to the second receiver antenna element RX2 and spaced one unit apart from it. The third receiver antenna element RX3 can be located next to the second receiver antenna element RX2 and spaced two units apart from it.The fourth receiver antenna element RX4 may be located next to the first receiver antenna element RX1 and spaced four units apart from the first receiver antenna element RX1. When two antenna elements are described herein as being located side by side, no further antenna element of either receiver or transmitter type is present between the two antenna elements. In some embodiments, the receiver antenna elements and / or the transmitter antenna elements are positioned along a single axis.

[0063] In some embodiments, the MIMO radar system may include a transmitter array. The transmitter array may include a placement of transmitter antenna elements with varying distances between them. For example, the first transmitter antenna element, TX1, may be located next to the third receiver antenna element, RX3, at a distance of 5 units. The second transmitter antenna element, TX2, may be located ten units away from the fourth receiver antenna element, RX4. The third transmitter antenna element, TX3, may be located next to the second transmitter antenna element, TX2, at a distance of 11 units.

[0064] In some embodiments, the distance from one unit is half a wavelength. In some embodiments, the distance from one unit is half a wavelength + / - 0.1%, + / - 0.2%, + / - 0.5%, + / - 1%, + / - 2%, + / - 5%, + / - 10%, + / - 15%, + / - 20%, + / - 25%, + / - 30%, + / - 35% and / or the like.

[0065] In some embodiments, one or more transmitter and / or receiver antenna array elements include a subarray.

[0066] The radar system of Fig. 7 has 12 virtual channels CH1, CH2, CH3, CH4, CH5, CH6, CH7, CH8, CH9, CH10, CH11, CH12 through the four receiver antenna elements RX1, RX2, RX3, RX4, which receive signals from the three transmitter antenna elements TX1, TX2, TX3.

[0067] In Fig. 8 are distances between pairs of virtual channels of the radar system of Fig.Figure 7 illustrates some embodiments. The transmitter and receiver arrangement of the transmitter and receiver antenna elements establishes several different spacings of virtual channel pairs. For example, the spacing between virtual channels CH2 and CH3 is one unit. The spacing between virtual channels CH3 and CH4 is two units. The spacing between virtual channels CH2 and CH4 is three units. The table below lists several different spacings of virtual channel pairs: Pairing of virtual channels Distance between pairing of virtual channels CH10-CH11 Distance from one unit CH11-CH12 Distance of two units CH10-CH12 Distance of three units CH9-CH10 Distance of four units CH9-CH11 Distance of five units CH11-CH5 Distance of six units CH10-CH5 Distance of seven units CH12-CH6 Distance of eight units CH12-CH7 Distance of nine units CH11-CH6 Distance of ten units CH11-CH7 Distance of eleven units CH10-CH7 Distance of twelve units CH11-CH8 Distance of thirteen units CH10-CH8 Distance of fourteen units CH9-CH6 Distance of fifteen units CH9-CH7 Distance of sixteen units CH7-CH1 Distance of seventeen units CH6-CH1 Distance of eighteen units CH8-CH2 A distance of nineteen units CH8-CH3 Distance of twenty units CH7-CH2 Distance of twenty-one units CH7-CH3 Distance of twenty-two units CH6-CH3 Distance of twenty-three units CH7-CH4 Distance of twenty-four units CH6-CH4 Distance of twenty-five units CH5-CH2 Distance of twenty-six units CH5-CH3 Distance of twenty-seven units CH11-CH1 Distance of twenty-eight units CH10-CH1 Distance of twenty-nine units CH12-CH2 Distance of thirty units CH12-CH3 Distance of thirty-one units CH11-CH2 Distance of thirty-two units CH10-CH2 Distance of thirty-three units CH10-CH3 Distance of thirty-four units CH11-CH4 Distance of thirty-five units CH10-CH4 Distance of thirty-six units CH9-CH2 Distance of thirty-seven units CH9-CH3 Distance of thirty-eight units CH9-CH4 Distance of forty units

[0068] As shown in the table above, the specific transmitter and receiver arrangement of transmitter and receiver antenna elements in the radar system of Fig.Seven pairs of virtual channels with spacings of several different units between the pairs. The transmitter arrangement, which contains a pattern of a multitude of transmitting antenna elements, and the receiver arrangement, which contains a pattern of a multitude of receiving antenna elements, as shown in Fig. Figure 7 shows how to create virtual channels with spacings of virtual channel pairs covering distances of 1-38 and 40 units, as shown in Fig. 8 shown. Advantageously, the main lobe is relatively narrow in width for a relatively good resolution, the side lobes are smaller, and no grating lobes occur, which would otherwise cause angular ambiguity.

[0069] Fig. Figure 9 is an illustration of a radiation characteristic after processing by digital beamforming for the radar system of Fig.7. The radiation pattern shows a main lobe with a 3 dB lobe width of approximately 4 degrees. The value of the side lobes has been reduced. Advantageously, no grating lobes are present. Percentage adjustment of distances between virtual channel pairings

[0070] The radiation pattern of a radar system with several different spacings between pairs of virtual channels can contain sidelobes of varying values. In some embodiments, the transmitter and / or receiver arrangement can be modified to improve the radiation pattern. For example, the sidelobes can be reduced in size. The transmitter and / or receiver arrangement can be modified by adjusting one or more spacings between pairs of virtual channels. This adjustment can be experimental. For example, the distance between two transmitter antenna elements can be reduced by 25%.

[0071] In some embodiments, the transmitter and / or receiver arrangement can be modified by adjusting the phase of one or more receiver and / or transmitter antenna elements. For example, the first two receiver antenna elements, RX1 and RX2, can be phase-adjusted by 3 degrees. The phase shifters can adjust the phase in the digital domain.

[0072] In some embodiments, the transmitter and / or receiver arrangement can be modified by applying a taper and / or weighting to one or more receiver and / or transmitter antenna elements. For example, a weighting of 50% can be applied to two transmitter antenna elements. In some embodiments, the weighting is applied digitally.

[0073] In some embodiments, a percentage adjustment can be made to one or more receiver antenna elements and / or one or more transmitter antenna elements. In some embodiments, the one or more receiver antenna elements and / or the one or more transmitter antenna elements that cause a greater change in sidelobe power than other antenna elements can be identified, for example, by simulation. Simulation can determine that the identified one or more receiver antenna elements and / or the identified one or more transmitter antenna elements are more sensitive than the other antenna elements.Subsequently, adjustments can be made to the identified one or more receiver antenna elements and / or the identified one or more transmitter antenna elements to improve the radiation characteristics. For example, the designer may determine that adjustments need to be made to the identified one or more receiver antenna elements and / or the identified one or more transmitter antenna elements with regard to sidelobe performance, that the main lobe width needs to be narrower, that the performance for lobe control angles needs to be improved, that changes need to be made at certain frequencies and / or frequency ranges, that changes need to be made to certain antenna types, and / or the like.These adjustments are often made by antenna designers as part of the design process and can be based on simulation results and / or laboratory experiments.

[0074] In one embodiment of a radar system, a 50% tapering is applied to two transmitting antenna elements TX1 and TX3, while no tapering is applied to the other transmitting and receiving antenna elements TX2, RX1, RX2, RX3, and RX4, as indicated by a 1.0 taper. Signal tapering may include a weighting factor, which can reduce a value based on that weighting factor. Furthermore, the spacing between a pair of receiving antenna elements RX4 and RX1 is adjusted from 4 units to 3.5 units.

[0075] Fig.Figure 10B shows a radiation pattern for a radar system according to some embodiments. By applying tapering to the two transmitting antenna elements TX1 and TX3, and adjusting the spacing between the pair of receiver antenna elements RX4 and RX1 from 4 units to only 3.5 units, the sidelobe value is reduced to -7 dB.

[0076] Fig. Figure 11 is an image of offset beams for the radar system of Fig. 10A according to some embodiments. The offset beams can be generated by applying digital beamforming. In Fig. Figure 11 shows offset rays in the range of + / - 30 degrees, each with a 3-degree gap. Multiple-Input-Multiple-Output ("MIMO") antenna array with varying spacing between fifteen virtual channels

[0077] In Fig.Figure 12A depicts a MIMO radar system with several different spacings between the 15 virtual channels according to some embodiments. The radar system of Fig.12A comprises five receiver antenna elements RX1, RX2, RX3, RX4, RX5 and three transmitter antenna elements TX1, TX2, TX3. In some embodiments, the distances between the five receiver antenna elements may vary. In some embodiments, the first receiver antenna element RX1 may be located next to the second receiver antenna element RX2 and spaced four units apart from it. In some embodiments, the third receiver antenna element RX3 may be located one unit away from the second receiver antenna element RX2. In some embodiments, the fourth receiver antenna element RX4 may be located two units away from the third receiver antenna element RX1. In some embodiments, the fifth receiver antenna element RX5 may be located six units away from the fourth receiver antenna element RX4.

[0078] In some embodiments, the first transmitting antenna element TX1 can be located 12 units away from the fifth receiving antenna element RX5. In some embodiments, the second transmitting antenna element TX2 can be located 12 units away from the first receiving antenna element RX1. In some embodiments, the third transmitting antenna element TX3 can be located 19 units away from the second transmitting antenna element TX2.

[0079] The radar system of Fig. 12A can contain 15 virtual channels CH1, CH2, CH3, CH4, CH5, CH6, CH7, CH8, CH9, CH10, CH11, CH12, CH13, CH14, CH15, which are generated by the five receiver antenna elements RX1, RX2, RX3, RX4, RX5, which receive signals from the three transmitter antenna elements TX1, TX2, TX3.

[0080] In the Fig. 12B-1, 12B-2, 12B-3 and 12B-4 are distances between pairs of virtual channels of the radar system of Fig.Figure 12A shows some embodiments. The transmitter and receiver arrangement of the transmitter and receiver antenna elements can establish several different spacings between virtual channel pairs. In some embodiments, the spacing between virtual channels CH7 and CH8 is one unit. In some embodiments, the spacing between virtual channels CH8 and CH9 is two units. In some embodiments, the spacing between virtual channels CH7 and CH9 is three units. The table below lists several different spacings between virtual channel pairs: Pairing of virtual channels Distance between pairing of virtual channels CH7-CH8 Distance from one unit CH8-CH9 Distance of two units CH7-CH9 Distance of three units CH6-CH7 Distance of four units CH6-CH8 Distance of five units CH9-CH10 Distance of six units CH6-CH9 Distance of seven units CH8-CH10 Distance of eight units CH7-CH10 Distance of nine units CH15-CH7 Distance of ten units CH15-CH8 Distance of eleven units CH14-CH6 Distance of twelve units CH6-CH10 Distance of thirteen units CH13-CH6 Distance of fourteen units CH12-CH6 Distance of fifteen units CH14-CH7 Distance of sixteen units CH14-CH8 Distance of seventeen units CH13-CH7 Distance of eighteen units CH13-CH8 A distance of nineteen units CH12-CH8 Distance of twenty units CH13-CH9 Distance of twenty-one units CH12-CH9 Distance of twenty-two units CH11-CH7 Distance of twenty-three units CH11-CH8 Distance of twenty-four units CH14-CH10 Distance of twenty-five units CH11-CH9 Distance of twenty-six units CH13-CH10 Distance of twenty-seven units CH12-CH10 Distance of twenty-eight units CH10-CH3 Distance of twenty-nine units CH9-CH1 Distance of thirty units CH10-CH4 Distance of thirty-one units CH8-CH1 Distance of thirty-two units CH7-CH1 Distance of thirty-three units CH9-CH2 Distance of thirty-four units CH9-CH3 Distance of thirty-five units CH8-CH2 Distance of thirty-six units CH8-CH3 Distance of thirty-seven units CH7-CH3 Distance of thirty-eight units CH8-CH4 Distance of thirty-nine units CH7-CH4 Distance of forty units CH6-CH2 Distance of forty-one units CH6-CH3 Distance of forty-two units CH15-CH1 Distance of forty-three units CH6-CH4 Distance of forty-four units CH8-CH5 Distance of forty-five units CH7-CH5 Distance of forty-six units CH15-CH2 Distance of forty-seven units CH15-CH3 Distance of forty-eight units CH14-CH1 Distance of forty-nine units CH15-CH4 Distance of fifty units CH13-CH1 Distance of fifty-one units CH12-CH1 Distance of fifty-two units CH14-CH2 Distance of fifty-three units CH14-CH3 Distance of fifty-four units CH13-CH2 Distance of fifty-five units CH13-CH3 Distance of fifty-six units CH12-CH3 Distance of fifty-seven units CH13-CH4 Distance of fifty-eight units CH12-CH4 Distance of fifty-nine units CH11-CH2 Distance of sixty units CH11-CH3 Distance of sixty-one units CH14-CH5 A gap of sixty-two units CH11-CH4 A gap of sixty-three units CH13-CH5 A gap of sixty-four units CH12-CH5 A gap of sixty-five units CH11-CH5 A gap of sixty-nine units

[0081] As shown in the table above, the specific transmitter and receiver arrangement of transmitter and receiver antenna elements in the radar system of Fig.12A Pairings of virtual channels with spacings of several different units between the pairings. The transmitter arrangement, which contains a pattern of a plurality of transmitting antenna elements, and the receiver arrangement, which contains a pattern of a plurality of receiving antenna elements, as in Fig. As shown in Figure 12A, virtual channels are created with spacings of pairs of virtual channels covering spacings of 1-65 and 69 units, as shown in the Fig. 12B-1, 12B-2, 12B-3 and 12B-4 are shown. The main lobe is advantageously much narrower, the side lobes are smaller, and grating lobes are prevented from affecting the angular resolution.

[0082] The disclosed systems and methods can incorporate a multiple-in-multiple-out (“MIMO”) antenna array, while the arrangement of antenna elements provides relatively good angular resolution for radar and simultaneously reduces the occurrence of grid lobes. The transmitter and receiver antenna elements can be spaced apart to improve performance while reducing costs. In some embodiments, the transmitter and / or receiver antenna elements can be spaced at intervals of half a wavelength ± 10% or ± 25%. In some embodiments, the first receiver antenna element can be four units away from a second receiver antenna element, a third receiver antenna element can be one unit away from the second receiver antenna element, and a fourth receiver antenna element can be two units away from the third receiver antenna element. Applications

[0083] All the principles and advantages discussed herein are applicable not only to the systems described above but also to other systems. The elements and processes of the various embodiments described above can be combined to provide further embodiments. Some of the embodiments described above have provided examples in connection with transceiver ICs. However, the principles and advantages of the embodiments can also be used in connection with any other systems, devices, or methods for which any of the teachings herein might be useful. For example, any of the principles and advantages discussed herein can be implemented in connection with any devices whose transmit and receive paths require calibration.Although the digital signal processor is described for both sending and receiving, multiple processors (e.g., separate digital signal processors for a transmitter and a receiver) are also possible. Although connection paths via a coupler are described in connection with some embodiments, other suitable components can also be used to connect signal paths.

[0084] Aspects of this disclosure can be implemented in various electronic devices. Examples of electronic devices include consumer electronics products, components of consumer electronics products such as semiconductor chips and / or modules housed in enclosures, electronic testing equipment, wireless communication devices, personal area network communication devices, mobile communication infrastructure such as a base station, etc.Examples of consumer electronics products include a mobile phone, such as a smartphone; a wearable device, such as a smartwatch or earphones; a telephone; a television; a computer monitor; a computer; a router; a modem; a handheld device; a laptop computer; a tablet computer; a personal digital assistant (PDA); a microwave oven; a refrigerator; an electronic system for vehicles, such as an electronic system for cars; a stereo system; a DVD player; a CD player; a digital music player, such as an MP3 player; a radio; a camcorder; a camera, such as a digital camera; a portable memory chip; a washing machine; a dryer; a washer-dryer; a peripheral device; a watch; a lidar system (Lidar = Light Detecting and Ranging); etc. Furthermore, electronic devices may contain semi-finished products. Concluding remarks

[0085] Unless the context otherwise requires, the words "comprise" or "exhibit," "comprehensive" or "exhibiting," "contain," "containing," and the like, in the description and claims, are generally to be interpreted as expressing inclusiveness, as opposed to exclusivity or completeness, i.e., as meaning "including, but not limited to." The word "coupled," as used generally herein, refers to two or more elements, which may be coupled either directly to one another or via one or more intermediate elements. Likewise, the word "connected," as used generally herein, refers to two or more elements, which may be connected either directly or via one or more intermediate elements.Furthermore, the words "herein", "above", "below", and words with a similar meaning, when used in this application, refer to the entire present application and not to specific sections thereof. Where the context permits, words in the detailed description of certain embodiments above that use the singular or plural form also include the plural or singular form, respectively. The word "or" in relation to a list of two or more elements is generally intended to include all of the following interpretations of the word: any single element in the list, all elements in the list, and any combination of the elements in the list.

[0086] Furthermore, conditional formulations, including those using words such as "may," "could," "possibly," "perhaps," "e.g.," "for example," "approximately," and the like, are intended, unless expressly stated otherwise or understood differently in the context in which they are used, to generally express that certain embodiments may contain certain features, elements, and / or states, while other embodiments may not. Therefore, it should not be generally inferred from such conditional formulations that features, elements, and / or states are in any way required for one or more embodiments, or that one or more embodiments necessarily contain a logic for deciding whether these features, elements, and / or states are included or must be implemented in a particular embodiment.

[0087] Although certain embodiments have been described, these embodiments are merely exemplary and are not intended to limit the scope of protection of the disclosure. Many other embodiments of the new methods, devices, and systems described herein are conceivable; furthermore, various omissions, substitutions, and modifications are possible in the embodiments of the methods, devices, and systems described herein without departing from the inventive concept of the disclosure. For example, circuit blocks described herein can be removed, relocated, added, subdivided, combined, and / or modified. Each of these circuit blocks can be implemented in many different ways.The accompanying claims and their equivalents are intended to cover all embodiments or modifications that fall within the scope of protection of the disclosure or are compatible with the inventive concept of the disclosure.

Claims

[1] Multiple-In-Multiple-Out (“MIMO”) antenna array device for radar, comprising: a receiver antenna arrangement, wherein the receiver antenna arrangement comprises a plurality of receiver antenna elements (152A,..., 152N) of an antenna array arranged in a pattern such that a first receiver antenna element (RX1) is located approximately one unit away from a second receiver antenna element (RX2), a third receiver antenna element (RX3) is located approximately two units away from the second receiver antenna element (RX2), and a fourth receiver antenna element (RX4) is located approximately four units away from the first receiver antenna element (RX1); and a transmitter antenna arrangement, wherein the transmitter antenna arrangement comprises one or more transmitter antenna elements (146A,...,146N) of an antenna array arranged in a pattern such that a first transmitter antenna element (TX1) is placed at a distance of approximately five units from the third receiver antenna element (RX3), and wherein the first transmitter antenna element (TX1) and the third receiver antenna element (RX3) are placed on one side of a printed circuit board. [2] MIMO antenna array device according to claim 1, wherein the transmitter antenna arrangement further comprises a second transmitter antenna element (TX2) located approximately ten units away from the first transmitter antenna element (TX1). [3] MIMO antenna array device according to claim 2, wherein the transmitter antenna arrangement further comprises a third transmitter antenna element (TX3) located approximately eleven units away from the second transmitter antenna element (TX2). [4] MIMO antenna array device according to any one of claims 1 to 3, wherein the receiver antenna arrangement and the transmitter antenna arrangement are arranged in a pattern such that the receiver antenna elements (152A,..., 152N) and the transmitter antenna elements (146A,...,146N) are arranged along a single axis. [5] MIMO antenna array device according to any one of claims 1 to 4, wherein a distance of one unit is half a wavelength. [6] MIMO antenna array device according to any one of claims 1 to 4, wherein a distance of one unit is half a wavelength + / - 10%. [7] MIMO antenna array device according to any one of claims 1 to 4, wherein a distance of one unit is half a wavelength + / - 25%.

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