Patent Description:
Therefore, radar systems that are lighter, are less-dense, are less-expensive, are less power hungry, and can scan a FOV more quickly, than traditional radar systems have been developed for such applications.

An example of such a radar system that has been developed for use in automobiles includes a digital beam-forming (DBF) receive-antenna array having, e.g., at least four to eight individual antenna segments (the number of antenna segments is typically limited to the number of antenna channels that the system circuitry supports, e.g., one antenna segment per antenna channel).

During a transmit period, the system circuitry effectively energizes all of the antenna segments with the same signal, i.e., with respective signals each having the same magnitude and phase, such that the array "sprays" signal energy over a fixed FOV. Put another way, the simultaneous energizing of all the antenna segments with respective signals each having the same magnitude and phase generates a main transmit beam that is stationary, i.e., not steered. In order to cover a useable FOV, this transmit main beam is often fairly wide, e.g. more than <NUM> degrees in azimuth (AZ).

During a receive period, the system circuitry can post-process, dynamically, a respective gain and phase shift from any receive antenna segment, so as to digitally form and steer a receive beam that is significantly narrower than the transmit beam; the system can steer the receive beam to only a single position, or to multiple positions, within a single receive period.

Unfortunately, a problem with such a radar system is that the receive DBF can be performed only within the region illuminated by the transmit beam. The number of receiver-array segments/channels that are present are utilized to divide the fixed transmit FOV into equal segments; that is, the number of receiver-array segments/channels defines the receive resolution of the DBF, and, ultimately, defines the receive resolution of the entire radar system. The receive resolution defined in this manner is often referred to as the Rayleigh resolution, and represents a fundamental limit of the radar's performance. For example, a radar system that were to illuminate an FOV of <NUM>° in AZ on transmit and that were to include four receive channels would possess a Rayleigh resolution of about <NUM>° across this FOV. An alternate choice could be made to widen the FOV to <NUM>° in AZ, which, with the same four receive channels, would give a Rayleigh resolution of about <NUM>°. Thus, a fundamental trade-off between FOV and Rayleigh resolution exists in such a system.

Designing such a radar to illuminate a large FOV in transmit and also to possess a high Rayleigh resolution in receive would require a large number of antenna segments/channels.

Unfortunately, engineering limits to the number of channels which can be practically included in such a radar has, to date, limited the Rayleigh performance of such radars systems.

One approach to improve the Rayleigh resolution of a system with a fixed number of antenna channels is to place the receive antennas/antenna segments further apart, i.e., to design a sparse receive array.

But such a sparse array can cause spatial aliasing, which produces side-lobes and grating lobes that can hinder the radar system's ability to detect, to identify, and to map objects. One reason for such aliasing-induced side-lobes and grating lobes is that the radar system's sparse receive-antenna array does not meet the Nyquist criteria for maximum segment spacing, which is λ/<NUM>. For example, to obtain a Rayleigh resolution of <NUM>° in the AZ dimension, the antenna would need to have dimensions on the order of 50λ. Distributing a small number of segments/channels, e.g., four to eight, across a distance of 50λ would result in an average segment spacing of <NUM>. 25λ to <NUM>. 5λ, which is <NUM> to <NUM> times the maximum Nyquist spacing of λ/<NUM>. Consequently, the system would suffer from significant side-lobes and grating lobes.

Of course, to reduce spatial aliasing, a designer could reduce the effective size of the antenna by reducing the spacing between the antenna segments.

But reducing the size of the antenna limits the minimum width of the receive beam that the radar system could generate.

Therefore a designer of such a sparse-antenna-array radar system (i.e., a radar system with a larger antenna aperture and a limited number of antenna channels) is faced with trading off beam width for aliasing, and vice-versa. That is, the narrower the receive-beam width, the greater the level of aliasing, and the lower the level of aliasing, the wider the receive-beam width. <CIT> describes a transmit and receive phased array configured to align a null of a transmit beam with a grating lobe of a receive beam. <CIT> describes a phased-array transceiver configured to align a grating lobe in a transmit beam and a grating lobe in a receive beam, or to align a grating null in a transmit beam and a grating null in a receive beam. <CIT> describes a radar device including transmitting and receiving antenna arrays each including subarray elements. <CIT> describes a reconfigurable holographic antenna. <CIT> describes a surface scattering antenna.

In an embodiment, an antenna subsystem according to claim <NUM> is provided.

For example, such an antenna subsystem effectively spatially filters a receive beam pattern generated by the receive antenna with a transmit beam pattern generated by the transmit antenna to reduce aliasing. For example, the envelope of a main transmit beam can exclude, or at least can attenuate, side lobes of the receive beam pattern. Furthermore, a null of a side lobe of the receive beam pattern can be aligned with a peak of a side lobe of the transmit receive pattern. Moreover, a peak of a side lobe of the receive beam pattern can be aligned with a null of a side lobe of the transmit receive pattern.

In an embodiment, a radar subsytem according to claim <NUM> is provided and provides a high Rayleigh resolution (i.e., a narrow Half Power Beam Width (HPBW)) with significantly reduced aliasing as compared to prior radar systems. The radar system includes an analog transmit array with the ability to electronically adjust the transmit beam pattern and to act as a spatial filter for the receive antenna pattern, and includes a Nyquist complete or a sparse digital beam-forming (DBF) array antenna for generating a receive beam that subtends the transmit antenna's main illumination beam. By appropriately designing and driving the transmitting and receiving antennas, the radar system effectively can generate and steer a beam of narrow width (e.g., ≤ <NUM>° in both the AZ and elevation (EL) dimensions). Moreover, the radar system can do this without requiring the large number of antenna channels (e.g., <NUM> to <NUM>) typically required for such performance. For example, an embodiment of a radar system with only twelve antenna channels for the receive sparse DBF array antenna effectively can generate and steer a beam of a width of approximately <NUM>° in AZ and <NUM>° EL; therefore, such a radar system has significantly better angular performance than prior radar systems with a similar number of antenna channels.

The words "approximately" and "substantially" may be used below to indicate that two or more quantities can be exactly equal, or can be within ± <NUM> % of each other due to manufacturing tolerances, or other design considerations, of the physical structures described below.

<FIG> is a diagram of a Metamaterial Electronic Steering Array (MESA) transmit-antenna section <NUM> and a sparse DBF receive-antenna section <NUM> of a radar system <NUM>, according to an embodiment; the radar system, which is further described below in conjunction with <FIG>, can include other components not shown in <FIG>, such as amplifiers, phase shifters, and other drive circuitry. Furthermore, the transmit-antenna section <NUM> can form an entire transmit antenna of the radar system <NUM>, or only a section of the transmit antenna, which may include one or more other sections similar to the section <NUM>; similarly, the receive-antenna section <NUM> can form an entire receive antenna of the radar system, or only a section of the receive antenna, which may include one or more other sections similar to the section <NUM>. Moreover, the radar system <NUM> can be configured to operate in any conventional radar frequency band; for example, the radar system can be configured to operate in the W band, which ranges from <NUM> - <NUM>, and can be tuned for operation between <NUM> - <NUM>. In addition, an example of the structure and operation of a MESA transmit-antenna section that a designer can use as the transmit-antenna section <NUM> is described below in conjunctions with <FIG>.

The transmit-antenna section <NUM> includes one or more electronically steerable/switchable arrays (ESA), for instance, but not necessarily, a MESA. Furthermore, the transmit-antenna section <NUM> can have any suitable dimensions, such as of approximately W = 10λ × H = 3λ, or W = 12λ × H = 4λ. These dimensions, which define an aperture of the transmit-antenna section <NUM>, also affect the minimum Half-Power Beam Width (HPBW) of the transmit beam in the AZ and EL dimensions because it is known that the HPBW is inversely proportional to aperture size. For example, for W = 12λ × H = 4λ, an embodiment of the transmit-antenna section <NUM> can generate a transmit beam having a minimum HPBW of <NUM>° in the AZ dimension and <NUM>° in the EL dimension.

Each ESA of the transmit-antenna section <NUM> (only one ESA shown in <FIG>) includes a respective one analog RF channel input <NUM>, where the RF signal is distributed throughout the ESA area and/or to the sub-elements of the ESA by conventional methods, e.g., a waveguide, a transmission line, or microstrips.

Each ESA of the transmit-antenna section <NUM> also includes one or more control lines <NUM>, either digital or analog, which provide for the electronic control of the transmit-array beam steering. This control can be implemented as a single digital line <NUM>, as a collection of digital lines (e.g., a digital bus), or as a collection of analog lines.

Furthermore, the one or more control lines <NUM> are each configured to carry a respective control signal that, depending on the collective state of the control signal(s) over time (e.g., logic high or logic low, or array of analog voltages), electronically activates a particular configuration of the transmit-array section <NUM>, the configuration describing a particular transmit-beam position, transmit-beam side-lobe level, transmit-beam HPBW, etc..

Moreover, multiple ESAs can be configured to work together, each with its own analog-transmit input, by coordinating and synchronizing the transmit-array configurations sent via the respective control lines <NUM>.

Still referring to <FIG>, the receive-antenna section <NUM> includes an array <NUM> of antenna elements <NUM>, which antenna elements can also be called "antenna segments," or "segments. " The array <NUM> is segmented into rows <NUM> and columns <NUM> of antenna elements <NUM>. For example, the array <NUM> can have six columns <NUM> and two rows <NUM> for a total of twelve antenna elements <NUM>. Alternatively, for example, as shown in <FIG>, the array <NUM> can have five columns <NUM> and two rows <NUM> for a total of ten antenna elements <NUM>.

Furthermore, the respective phase center <NUM> of each antenna segment <NUM> is coupled to a single RF receive channel (not shown in <FIG>), such that the receive-antenna section <NUM> is a digital beam-forming (DBF) array. Each receive channel can include a respective amplifier (not shown in <FIG>), a respective down-converter (not shown in <FIG>), a respective Analog-to-Digital Converter (ADC) (not shown in <FIG>), and other RF, analog, and digital components that allow the radar system <NUM> to measure and digitize the respective signal received by each corresponding antenna element <NUM>. Furthermore, the receive-antenna section <NUM> can have any suitable dimensions, such as, for example, of approximately W = 25λ × H = 10λ. These dimensions, which define an aperture of the receive-antenna section <NUM>, also affect the minimum Half-Power Beam Width (HPBW) of the receive beam in the AZ and EL dimensions because it is known that the HPBW is inversely proportional to aperture size. For example, for W = 25λ × H = 10λ, an embodiment of the receive-antenna section <NUM> can generate a receive beam having a minimum HPBW of <NUM>° in the AZ dimension and <NUM>° in the EL dimension.

Moreover, the antenna elements <NUM> within the receive-antenna array <NUM> can be of any shape and material that provides advantageous antenna-element characteristics, such as, for example, efficiency, gain, bandwidth, HPBW in the AZ and EL dimensions, etc..

In addition, each of the antenna elements <NUM> can include one or more sub-elements. For example, in configurations such as microstrip-fed patch array, CPW patch array, etc., an antenna element <NUM> can include multiple sub-elements.

Still referring to <FIG>, operation of the radar system <NUM> is described according to an embodiment.

In general, because the ESA transmit-antenna section <NUM> generates a transmit beam with side lobes of relatively low power, and the radar system <NUM> aligns the receive beam (or receive beams, see below) within the transmit beam, the redirected transmit energy received by the receive-beam-pattern side lobes is significantly reduced as compared to prior radar systems. Therefore, even if the receive-beam-pattern side lobes are relatively large, and, therefore, can result in significant spatial aliasing, adding the controlled ESA transmit beam pattern (as opposed to the transmit "blast" or "spray" of prior radar systems) with relatively low-magnitude transmit-beam-pattern side lobes significantly reduces aliasing because a larger percentage of the redirected transmitted energy is received by the receive beam(s), and a lower percentage of the redirected transmitted energy is received by the receive side lobes, as compared to prior radar systems. Put another way, by including the ESA transmit-antenna section <NUM>, the radar system <NUM> can generate, with a "sparse" receive DBF array <NUM> (i.e., an array with antenna segments <NUM> spaced apart by a distance >> λ/<NUM>), an effective receive beam (i.e., the beam resulting from the combination of the transmit and receive beams) having a HPBW that is much narrower than would otherwise be possible with the DBF array alone or paired with the "blast" or "spray" transmission of prior radar systems.

In more detail, the radar system <NUM> steers a transmit beam in a chosen AZ direction and chosen EL direction using the one or more ESA control lines <NUM>. These chosen directions, constrained by the HPBW of the ESA transmit beam, collectively define a region of illumination within which the receive DBF array <NUM> can operate with significantly reduced spatial aliasing.

This area of illumination can be resolved with relatively high Rayleigh resolution by the DFB array <NUM>, and the transmit-antenna section <NUM> can then illuminate a new area through reconfiguration of the transmit-antenna section <NUM> and its transmit-beam pattern using the one or more control lines <NUM>. A very wide FOV can be covered through the sequential reconfiguration of the transmit-antenna section <NUM> and its transmit beam pattern from a current illumination area to a new illumination area followed by resolution using the DBF array <NUM>. The sequence of this illumination can be ordered (e.g., raster scan, conical scan), disordered (random, Hadamard), or dynamically or intelligently sequenced (task-able illumination, prioritized FOV time-weighting, etc.).

Still referring to <FIG>, the radar system <NUM> steers the receive-array beam(s) as follows.

In an embodiment, the radar system <NUM> operates in a continuous-wave (CW) mode in which it generates the transmit beam and the receive beam simultaneously. But the radar system <NUM> also can be configured to operate in a pulsed mode in which it generates one or more "pulses" of the transmit beam, deactivates the transmit beam, activates the receive beam, deactivates the receive beam, and repeats this procedure. Even though the below description presumes that the radar system <NUM> is operating in a CW mode, the below description is also applicable to the radar system operating in a pulsed mode.

The radar system <NUM> simultaneously steers one or more receive beams by selectively applying, to the respective signal received by each antenna segment <NUM>, a respective complex-element weighting, which effectively applies to the respective signal a respective phase shift and a respective gain (the gain can be less than, equal to, or greater than one). That is, the radar system <NUM> operates the receive-antenna array <NUM> as a true phased array.

In an embodiment in which the radar system <NUM> generates only a single receive beam, even with only twelve antenna segments <NUM>, the radar system can generate the receive beam having a relatively narrow width (e.g., <NUM>° HPBW in the AZ dimension), and can steer the beam in the AZ dimension in very fine steps (e.g., <NUM>° steps). Because, as described above, the transmit beam super-tends the receive beam, the radar system <NUM> can steer the receive beam within the Transmit Illumination Solid Angle (TISA), e.g., the region bounded by the HPBW of the transmit beam. The steps may or may not be such that a receive beam in one position overlaps an adjacent previous position of the receive beam.

In another embodiment, the radar system <NUM> simultaneously generates a "bundle" of receive beams that "fit" into the TISA region. For example, if the TISA region is likened to a box of spaghetti, then each strand of spaghetti in the bundle represents a respective receive beam. In this embodiment, because the bundle of receive beams "fills" the TISA, the radar system <NUM> need not steer the receive beams as described in the above embodiment. That is, in this embodiment, the radar system <NUM> simultaneously covers, with multiple receive beams, the TISA region, whereas in the above-described embodiment, the radar system sequentially steers a single receive beam from receive-beam position to receive-beam position to cover the TISA region over a period of time.

In yet another embodiment, the radar system <NUM> simultaneously generates a bundle of receive beams that 'fit' within the TISA region but do not 'fill' it. Then, the radar system sequentially steers the bundle of receive beams from bundle position to bundle position to cover the TISA region over a period of time. A bundle position may or may not overlap another bundle position.

In still another embodiment, the bundle of receive beams includes fewer beams than needed to "fill" the TISA region. Therefore, the radar system <NUM> can steer the bundle, or one or more receive beams within the bundle, so that at least one receive beam occupies each region within the TISA region before the radar system reconfigures the transmit ESA(s) to steer the transmit beam to another position.

Hereinafter, the radar system <NUM> is described as generating and steering a single receive beam, it being understood that the description also applies to the radar system simultaneously generating and steering a plurality (e.g., a bundle) of receive beams unless otherwise noted.

<FIG> is a diagram of the receive-antenna section <NUM>, the array <NUM> of antenna elements <NUM>, the phase centers <NUM> of the antenna elements, and a magnified view of one of the antenna elements <NUM>, according to an embodiment. In this embodiment, which is not intended to be limiting, each antenna element <NUM> includes a micro-strip-fed series subarray of patch sub-elements <NUM>.

<FIG> is a plot that depicts the design of the elemental beam pattern <NUM> (the pattern of the receive beam) in the AZ and EL dimensions. The elemental beam pattern <NUM>, and its characteristic HPBW in AZ and EL, define the FOV over which each receive channel, and, therefore, ultimately over which the receive array <NUM>, is able to receive signals. In turn, the element beam pattern <NUM> also defines the FOV over which the entire radar system can operate.

Referring to <FIG>, in one embodiment, the receive elements <NUM> are designed with a number and geometry of sub-elements <NUM> that impart to the receive array <NUM> a total HPBW of about <NUM>° degrees in the AZ dimension and of about <NUM>° degrees in the EL dimension, allowing for a radar system <NUM> with a very wide FOV in the AZ dimension and a somewhat constricted FOV in the EL dimension.

<FIG> is a diagram of the area of the receive-antenna section <NUM>, and the receive array <NUM>.

<FIG> are plots of the receive-beam patterns <NUM> and <NUM> in the AZ dimension and in the EL dimension, respectively, which patterns result from the geometric arrangement of the array <NUM>; the geometric arrangement of the array <NUM> is typically referred to as the "array-factor.

Referring to <FIG>, the array-factor beam pattern (the AZ and EL receive-beam patterns viewed together) is affected by the choice of complex weights (amplitude and phase) that are applied to the receive channels, and there are a very large number of possible receive-beam patterns that generate individual beams or bundles of beams as discussed above. Said differently, the AZ and EL receive-beam patterns <NUM> and <NUM> in <FIG> result only from the geometry of the array <NUM> (i.e., the relative positions of the antenna elements <NUM>), and the choice of the complex receive weights.

The array-factor receive-beam pattern possesses beam characteristics such as HPBW, beam-angle, and side-lobe-level, which are affected by the choice of the complex receive weights. The AZ pattern <NUM> includes a receive beam <NUM> and major side lobes <NUM> and <NUM>. The major side lobes <NUM> and <NUM> each have a maximum power level greater than one half the power level of (i.e., less than <NUM> dB down from) the power level of the receive beam <NUM>. Similarly, the EL pattern <NUM> includes the receive beam <NUM> and major side lobes <NUM> and <NUM>.

A goal of a radar-system designer of the radar system <NUM> (<FIG> and <FIG>) is to maximally exclude the side-lobes <NUM>, <NUM>, <NUM>, and <NUM> from the HPBW regions of the transmit beam in both AZ and EL dimensions by aligning the transmit and receive patterns to maximally exclude side-lobes outside the region of interest.

<FIG> is a diagram that depicts the transmit beam pattern <NUM>, the receive-element beam pattern <NUM>, and the beam pattern in the AZ dimension for the receive array <NUM> for an embodiment. The receive-element beam pattern <NUM> is due to the arrangement, size, shape, etc. of the antenna sub-elements <NUM> (<FIG>). As can be seen, a majority of the receive spatial aliasing lies outside the HPBW of the transmit beam pattern <NUM>; therefore, the combination of the transmit-antenna section and the sparse receive-antenna section highly suppresses the receive spatial aliasing in AZ.

<FIG> is a diagram that depicts the transmit beam pattern <NUM>, receive-element beam pattern <NUM>, and the beam pattern of the receive array <NUM>, in the EL dimension, for an embodiment. As can be seen, a majority of the receive spatial aliasing lies outside the HPBW of the transmit beam pattern <NUM>; therefore, the combination of the transmit-antenna section and the sparse receive-antenna section highly suppresses the receive spatial aliasing in EL.

To the extent that there are practical limits on the shape of the transmit beam, e.g., the sharpness with which the transmit beam progresses from its central region through its HPBW and to lower levels, to the extent that there are practical limits on the shape, location, and level, of the side-lobes of the transmit beam, and considering that these limitations exist in both AZ and EL, a designer of the radar system <NUM> may face challenges at reducing the side-lobes of the radar system to a desired level for a particular application.

Consequently, to further reduce spatial aliasing side-lobes that may exist in AZ and EL, and as described below in conjunction with <FIG>, the radar-system designer can also leverage the plurality of allowable receive-array <NUM> geometric configurations.

In considering the above, it is noted that the sparsification of the receive array - that is, the separation of array elements by much greater than λ/<NUM> - in addition to offering the benefit of reduced required channel count over a given receive area, also offers additional degrees of freedom in the placement of the receive elements <NUM>. Said differently, a fixed number of receive elements <NUM> placed over a large area have a number of possible positional configurations in which they do not collide or overlap, the number of such possible positional configurations growing with the area of the receive-antenna array <NUM>.

<FIG> is a diagram of a receive-antenna array section <NUM>, which the can be used in the radar system <NUM> instead of the receive-antenna array section <NUM> of <FIG>, <FIG>, and <FIG>.

<FIG> are plots of the beam-and-side-lobe patterns <NUM> and <NUM> in the AZ and EL dimensions, respectively, as generated by the antenna section <NUM> for a single receive beam (if the radar system <NUM> generates a bundle of receive beams, then these plots are for each receive beam in the bundle).

Referring to <FIG>, as described below, the receive-antenna section <NUM> can generate major receive side lobes that are of lower power than the major receive side lobes <NUM>, <NUM>, <NUM>, and <NUM> (<FIG>) generated by the receive antenna <NUM> (<FIG>), and, therefore, can further decrease aliasing caused by the receive side lobes.

Like the receive-antenna section <NUM> of <FIG> and <FIG>, the receive-antenna section <NUM> includes ten antenna segments <NUM> each having six antenna sub-elements <NUM> (not shown in <FIG>).

But unlike the receive-antenna section <NUM> of <FIG> and <FIG>, the antenna segments <NUM> are not arranged in the Cartesian vertical columns <NUM> and horizontal rows <NUM> of <FIG>, but are instead arranged in the pattern shown in <FIG>. As described below, this receive-antenna pattern significantly reduces the levels of the major receive side lobes in both the AZ and EL dimensions, and, therefore, further reduces aliasing, as compared to the receive-antenna section <NUM> of <FIG>.

Still referring to <FIG>, the AZ beam pattern <NUM> of the receive-antenna section <NUM> includes a receive beam <NUM> and receive side lobes <NUM> and <NUM>. The side lobes <NUM> closest to the receive beam <NUM> each have a maximum power level that is at least <NUM> dB down from the power level of the receive beam <NUM>. Therefore, even though the side lobes <NUM> are close to, and may even be within, the HPBW region of the transmit beam <NUM> in the AZ dimension, the side lobes <NUM> provide a significant reduction in aliasing compared to the level of aliasing generated by the receive-antenna section <NUM> of <FIG> because the power level of each of the side lobes <NUM> is at least <NUM> dB down from the power levels of the closest side lobe <NUM> generated by the receive-antenna section <NUM>. And even though the side lobes <NUM> are close to, and may even be within, the HPBW region of the transmit beam <NUM> in the AZ dimension, the side lobes <NUM> provide a significant reduction in aliasing compared to the level of aliasing generated by the receive-antenna section <NUM> of <FIG> because the power level of each of the side lobes <NUM> is at least <NUM> dB down from the power levels of the closest side lobe <NUM> (<FIG>) generated by the receive-antenna section <NUM>.

Similarly, the EL pattern <NUM> includes the receive beam <NUM> and side lobes <NUM> and <NUM>. The side lobes <NUM> closest to the receive beam <NUM> each have a maximum power level that is at least <NUM> dB down from the power level of the beam <NUM>. Therefore, even though the side lobes <NUM> are close to, and may even be within, the HPBW region of the transmit beam <NUM> in the EL dimension, the side lobes <NUM> provide a significant reduction in aliasing compared to the level of aliasing generated by the receive-antenna section <NUM> of <FIG> because the power level of each of the side lobes <NUM> is at least <NUM> dB down from the power levels of the closest side lobes <NUM> (<FIG>) generated by the receive-antenna section <NUM>. And the receive side lobes <NUM> closest to the receive beam <NUM> each have a maximum power level that is at least <NUM> dB down from the power level of the beam <NUM>. Therefore, even though the side lobes <NUM> are close to, and may even be within, the HPBW region of the transmit beam <NUM> in the EL dimension, the side lobes <NUM> provide a significant reduction in aliasing compared to the level of aliasing generated by the receive-antenna section <NUM> of <FIG> because the power level of each of the side lobes <NUM> is at least <NUM> dB down from the power levels of the closest side lobes <NUM> generated by the receive-antenna section <NUM>.

Still referring to <FIG>, alternate embodiments of the receive-antenna section <NUM> are contemplated. For example, the number, pattern, and configuration of the antenna segments <NUM> can be different than as shown in, and as described above in conjunction with, <FIG>. For example, the receive-antenna section <NUM> can have more or fewer than twelve antenna segments <NUM>, the antenna segments can be arranged differently than shown in <FIG>, and each antenna element <NUM> can have various configurations of sub-elements <NUM> in terms of the number, location, shapes, and designs of the sub-elements.

<FIG> is a plot of the radar system <NUM> effective (two-way) AZ beam pattern <NUM> resulting from the combination of the patterns (<FIG>) of the receive-antenna sub-elements <NUM> (<FIG>), the receive-antenna array <NUM> (<FIG>), and the transmit-antenna section <NUM> (<FIG>), according to one embodiment. To generate the effective pattern <NUM>, the receive-array and receive-sub-element beam patterns of the AZ pattern <NUM> of <FIG> (in units of power or magnitude) are multiplied together and by the transmit beam pattern of the AZ pattern <NUM> (in the same units of power or magnitude) at each beam angle. The effective AZ pattern <NUM> has significantly lower side-lobe levels, and thus has significantly superior alias rejection, as compared to the AZ receive-array beam pattern, the AZ receive-sub-element beam pattern, or the AZ transmit beam pattern of <FIG>.

<FIG> is a plot of the radar system <NUM> effective (two-way) EL beam pattern <NUM> resulting from the combination of the patterns (<FIG>) of the receive-antenna sub-elements <NUM> (<FIG>), receive array <NUM> (<FIG>), and the transmit-antenna section <NUM> (<FIG>), according to an embodiment. To generate the effective pattern <NUM>, the receive-array and receive-sub-element beam patterns of the EL pattern <NUM> of <FIG> (in units of power or magnitude) are multiplied together and by the transmit beam pattern of the EL pattern <NUM> (in the same units of power or magnitude) at each beam angle. The effective pattern <NUM> has significantly lower side-lobe levels, and thus has significantly superior alias rejection, as compared to either the EL receive-array beam pattern, the EL receive-sub-element beam pattern, or the EL transmit-beam pattern of <FIG>.

Referring to <FIG>, a technique is described to further reduce aliasing as compared to the above-described embodiments of the radar system <NUM>, according to an embodiment not forming part of the claimed invention. More specifically, a designer of the radar system <NUM> can alter the design of an ESA transmit antenna to align nulls of the transmit beam-and-side-lobe pattern (in the AZ or EL dimension) with the peaks of the side lobes of the receive beam-and-side-lobe pattern (in the AZ or EL dimension), or to align the side-lobe peaks of the transmit beam-and-side-lobe pattern with the nulls of the receive beam-and-side-lobe pattern. Such alignment effectively causes the transmit nulls/peaks to "cancel" the receive peaks/nulls in the effective beam-and-side-lobe pattern.

<FIG> is a diagram of a transmit-antenna section <NUM>, which is similar to the transmit-antenna section <NUM> of <FIG> except that the transmit-antenna section <NUM> has two MESA halves (sub-sections) <NUM> and <NUM> separated by a vertical distance Δy between the geometric centers <NUM> and <NUM> of the respective MESAs. The transmit-antenna section <NUM> can form a portion of, or an entire, transmit antenna, and Δy can be adjusted to shift the nulls and peaks of the transmit EL beam-and-side-lobe pattern in the EL dimension. This shift is typically symmetrical about the transmit beam. For example, increasing Δy causes the nulls and side lobes of the transmit EL beam-and-side-lobe pattern to move closer towards the transmit beam, and decreasing Δy causes the nulls and side lobes of the transmit EL beam-and-side-lobe pattern to move farther away from the transmit beam.

<FIG> is a plot of the transmit EL beam-and-side-lobe pattern <NUM> of the transmit-antenna section <NUM> (<FIG>) overlaying the receive EL beam-and-side-lobe pattern <NUM> of a receive-antenna section that can be similar to the receive-antenna section <NUM> of <FIG>. For example, nulls <NUM> and <NUM> of the transmit EL pattern <NUM> are approximately aligned with peaks of side lobes <NUM> and <NUM> of the receive EL pattern <NUM>, and nulls <NUM> and <NUM> of the receive EL pattern <NUM> are approximately aligned with the peaks of side lobes <NUM> and <NUM> of the transmit EL pattern <NUM>.

<FIG> is the plot of <FIG> for EL = AZ = <NUM>°.

<FIG> is a plot of the effective EL beam pattern <NUM> resulting from the combination of the transmit and the receive beam patterns <NUM> and <NUM> of <FIG> for EL = AZ = <NUM>°.

<FIG> is a plot of a transmit AZ beam-and-side-lobe pattern <NUM> of the transmit-antenna section <NUM> (<FIG>) that yields the transmit EL pattern <NUM> of <FIG>, overlaying a receive AZ beam-and-side-lobe pattern <NUM> of the receive-antenna section that yields the receive EL pattern <NUM> of <FIG>, for EL = AZ = <NUM>°.

<FIG> is a plot of the effective AZ beam pattern <NUM> resulting from the combination of the transmit and receive beam patterns <NUM> and <NUM> of <FIG> for EL = AZ = <NUM>°.

Continuing with the discussion of <FIG>, but referring now to <FIG>, the side-lobe and spatial-aliasing reduction achieved using the above technique is maintained as both transmit and receive arrays are steered in the EL dimension.

<FIG> is a plot of a transmit EL beam-and-side-lobe pattern <NUM> of the transmit-antenna section <NUM> that yields the transmit patterns of <FIG> overlaying a receive EL beam-and-side-lobe pattern <NUM> of the receive-antenna section that yields the receive patterns of <FIG>, in which EL = <NUM>° and AZ = <NUM>°.

<FIG> is a plot of the effective EL beam pattern <NUM> resulting from the combination of the transmit and receive beam patterns <NUM> and <NUM> of <FIG>, in which EL = <NUM>° and AZ = <NUM>°.

<FIG> is a plot of a transmit AZ beam-and-side-lobe pattern <NUM> of the transmit-antenna section <NUM> that yields the transmit EL pattern <NUM> of <FIG>, overlaying a receive AZ beam-and-side-lobe pattern <NUM> of the receive-antenna section that yields the receive EL pattern <NUM> of <FIG>, in which EL = <NUM>° and AZ = <NUM>°.

<FIG> is a plot of an effective AZ beam pattern <NUM> resulting from the combination of the transmit and receive beam patterns <NUM> and <NUM> of <FIG>, in which EL = <NUM>° and AZ = <NUM>°.

Furthermore, sometimes a peak of a side lobe of a receive beam-and-side-lobe pattern coincides with a peak of a side lobe of a transmit beam-and-side-lobe pattern. That is, instead of acting to reduce the magnitude of the effective side lobe, a receive side lobe and a transmit side lobe are additive such that they act to increase the magnitude of the effective side lobe resulting from the combination of the aligned/coinciding transmit and receive side lobes.

<FIG> is a plot of a transmit EL beam-and-side-lobe pattern <NUM> of the transmit-antenna section <NUM> (<FIG>) that yields the transmit patterns of <FIG> overlaying a receive EL beam-and-side-lobe pattern <NUM> of an of the receive-antenna section <NUM> (<FIG>) that yields the receive patterns of <FIG>, in which EL = <NUM>° and AZ = <NUM>°.

<FIG> is a plot of an effective (two-way) EL beam pattern <NUM> resulting from the combination of the transmit and receive beam patterns <NUM> and <NUM> <FIG>, in which EL = <NUM>° and AZ = <NUM>°.

<FIG> is a plot of a transmit AZ beam-and-side-lobe pattern <NUM> of the transmit-antenna section <NUM> (<FIG>) that yields the transmit patterns of <FIG> overlaying a receive AZ beam-and-side-lobe pattern <NUM> of an of the receive-antenna section <NUM> (<FIG>) that yields the receive patterns of <FIG>, in which EL = <NUM>° and AZ = <NUM>°.

<FIG> is a plot of an effective (two-way) AZ and EL beam pattern <NUM> resulting from the combination of the transmit and receive beam patterns <NUM> and <NUM> of <FIG>, in which EL = <NUM>° and AZ = <NUM>°.

Referring to <FIG>, unfortunately, at an AZ angle of approximately <NUM>°, the peak of a transmit side lobe <NUM> coincides with a peak of a receive side lobe <NUM> such that the combination of the side lobes <NUM> and <NUM> forms a significant effective side lobe <NUM>.

<FIG> is a diagram of a transmit-antenna section <NUM>, according to an embodiment in which the section <NUM> can form a portion of, or an entire, transmit antenna. The transmit-antenna section <NUM> includes two vertically stacked but separated transmit sub-sections or portions <NUM> and <NUM>, each of which can be a respective MESA.

A technique for misaligning, or decorrelating, the peaks of the transmit side lobes and receive side lobes <NUM> and <NUM> of <FIG> is to shift, or slide, the transmit portion <NUM> of the transmit-antenna section <NUM> in the horizontal (AZ) dimension relative to the transmit portion <NUM>.

<FIG>, which is similar to <FIG>, is a plot of a transmit EL beam-and-side-lobe pattern <NUM> of an embodiment of the transmit-antenna section <NUM> (<FIG>) that yields the transmit patterns of <FIG> overlaying a receive EL beam-and-side-lobe pattern <NUM> of an embodiment of the receive-antenna section <NUM> (<FIG>) that yields the receive patterns of <FIG>, according to an embodiment in which EL = <NUM>° and AZ = <NUM>°.

<FIG>, which is similar to <FIG>, is a plot of an effective (two-way) EL beam pattern <NUM> resulting from the combination of the transmit and receive beam patterns <NUM> and <NUM> <FIG>, according to an embodiment in which EL = <NUM>° and AZ = <NUM>°.

<FIG> is a plot of a transmit AZ beam-and-side-lobe pattern <NUM> of an embodiment of the transmit-antenna section <NUM> (<FIG>) that yields the transmit patterns of <FIG> overlaying a receive AZ beam-and-side-lobe pattern <NUM> of the receive-antenna section <NUM> (<FIG>) that yields the receive patterns of <FIG>, according to an embodiment in which EL = <NUM>° and AZ = <NUM>°.

<FIG> is a plot of an effective AZ beam pattern <NUM> resulting from the combination of the transmit and receive beam patterns <NUM> and <NUM> of <FIG>, according to an embodiment in which EL = <NUM>° and AZ = <NUM>°.

Referring to <FIG> and <FIG>, at the AZ angle of approximately <NUM>°, the AZ shift of the transmit portion <NUM> of the transmit antenna section <NUM> relative to the transmit portion <NUM> shifts the peak of the transmit side lobe <NUM> to the left in <FIG> such that the peak no longer coincides with the peak of the receive side lobe <NUM>. Furthermore, this shift also reduces the magnitude of the peak of the transmit side lobe <NUM>. Therefore, the magnitude of the effective side lobe <NUM> formed by the combination of the side lobes <NUM> and <NUM> is significantly reduced (by approximately <NUM> dB) from the magnitude of the side lobe <NUM> in <FIG>.

Referring again to <FIG>, as well as to <FIG>, the technique of shifting, in AZ (and/or shifting in EL), the transmit portion <NUM> (<NUM>) relative to transmit portion <NUM> (<NUM>) can be applied to decorrelate transmit and receive side lobes at other beam angles in the AZ dimension. A designer can select the magnitude and polarity/direction of the shift that yields the best overall side-lobe uncorrelation over all beam angles in the AZ dimension for a particular application.

Another technique for reducing aliasing due to the receive antenna receiving redirected transmitted energy along one or more receive side lobes is to take advantage of the plurality of complex weights which can be applied to each of the receive channels, noting the fact that multiple choices for the complex weight vector may result in receive arrays with nearly identical main-beams, but with very different side-lobe patterns.

This technique can be applied to selectively reduce one or more of the receive side lobes by adjusting the complex weighting of each of one or more of the receive antenna segments <NUM> (<FIG>) for each of one or more positions of the receive beam (or bundle of receive beams). A designer can determine, by simulation or measurement, the major receive side lobes at a receive-beam position, and can determine the best complex weighting for each antenna segment <NUM> to impart to the receive beam (or bundle of receive beams) the desired beam characteristics (e.g., HPBWs in the AZ and EL dimensions) and to impart to the major receive side lobes the desired side-lobe characteristics (e.g., magnitude, phase). Then, the designer can program the radar system <NUM> to implement these respective determined complex weightings for the antenna segments <NUM> while the receive beam has the corresponding receive-beam position. The designer can repeat this procedure for one or more positions of the receive beam, and can store, e.g., in a look-up table (LUT), the respective complex weightings for each antenna segment <NUM> for each receive-beam position.

<FIG> is a block diagram of a radar subsystem <NUM>, which includes an antenna group or subsystem <NUM> including one or more of the transmit and receive antennas <NUM>, <NUM>, <NUM>, and <NUM> of <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, according to an embodiment in which the radar subsystem <NUM> can be the same as, or can be substituted for, the radar system <NUM> of <FIG>.

In addition to the antenna group <NUM>, the radar subsystem <NUM> includes a transceiver <NUM>, a beam-steering controller <NUM>, a radar processing unit <NUM>, and a master controller <NUM>, which components can be circuits that are hardwired, that are data-stream configurable, that execute software, or that are subcombination or combination of such circuits.

The antenna subsystem <NUM> includes a transmit antenna <NUM>, which can include one or more of the transmit-antenna sections <NUM> (<FIG>), <NUM> (<FIG>), and <NUM> (<FIG>), and includes a receive antenna <NUM>, which can include one or more of the receive-antenna sections <NUM> (<FIG> and <FIG>) or <NUM> (<FIG>). As described above, the transmit antenna <NUM> is configured to generate one or more transmit-beam patterns have one or more desired characteristics, and the receive antenna <NUM> is configured to generate one or more receive-beam patterns having one or more desired characteristics, such that the transmit-beam patterns combine with the respective receive-beam patterns to form spatial filters.

The transceiver <NUM> includes transmit circuitry <NUM> and receive circuitry <NUM>. The transmit circuitry <NUM> includes a voltage-controlled oscillator (VCO) <NUM>, a preamplifier <NUM>, and an amplifier (PA) <NUM>. The VCO <NUM> is configured to generate a signal having a frequency f<NUM> = c/λ<NUM>, which is the frequency for which the transmit antenna <NUM> is designed. The preamplifier <NUM> is configured to amplify the VCO signal, and the PA <NUM> is configured to amplify the signal from the preamplifier. The receiver circuitry <NUM> includes a respective receive channel <NUM> for each antenna segment <NUM> of the receive antenna <NUM>. Each a low-noise amplifier (LNA) <NUM>, a mixer <NUM>, and an analog-to-digital converter (ADC) <NUM>. The LNA <NUM> is configured to amplify signals received by the receive antenna <NUM>. The mixer <NUM> is configured to shift the frequencies of the amplified received signals down to a base band, and the ADC <NUM> is configured to convert the down-shifted analog signals to digital signals for processing by the radar processing unit <NUM>.

The beam-steering controller <NUM> is configured to steer the transmitting beams generated by the one or more MESA transmit antennas <NUM> by generating, on the control lines <NUM> (<FIG>) the control signals to the antenna units that compose the one or more transmit antennas as a function of time and main-transmit-beam position. By appropriately generating the control signals, the beam-steering controller <NUM> is configured to selectively activate and deactivate the antenna elements of the one or more MESA transmit antennas <NUM> according to selected spatial and temporal patterns. Beam steering of a transmit antenna, such as the one or more MESA transmit antennas <NUM>, is described below in conjunction with <FIG>.

The radar processing unit <NUM> is configured to receive each of the digitized baseband received signals from the receiver <NUM>, and to process the signals to form, and to steer, a receive beam as described above. As described above, the radar processing unit <NUM> is configured to generate, at any given time, a respective receive beam pattern by amplifying each of the digitized signals with a respective gain, and by shifting each of the digitized signals by a respective phase. By changing the gains and the phase shifts as a function of time, the radar processing unit <NUM> effectively steers one or more main receive beams of the receive beam pattern. And the radar processing unit <NUM> provides the radar data carried by the formed receive beam pattern to a conventional data-processing circuit for further processing for, e.g., detecting an object along a receive beam, and determining the object's location and velocity. For example, data-processing circuit can be configured to analyze the signals from the receiver <NUM> to, e.g., identify a detected object and the object's location and velocity, and to determine what action, if any, that a system including, or coupled to, the radar subsystem <NUM> should take. For example, if the system is a self-driving vehicle or a self-directed drone, then the data-processing circuit is configured to determine what action (e.g., braking, swerving), if any, the vehicle should take in response to the detected object. Alternatively, the radar processing unit <NUM> can be configured to perform such further processing of the radar data instead of, or in addition to, the data-processing system.

The master controller <NUM> is configured to control the transceiver <NUM>, the beam-steering controller <NUM>, and the radar processing unit <NUM> in response to radar control signals from a radar-system controller (not shown in <FIG>. For example, assuming that the one or more transmit antennas <NUM> are designed to operate at frequencies in a range centered about f<NUM>, the master controller <NUM> is configured to adjust the frequency of the signal generated by the VCO <NUM> for, e.g., environmental conditions such as weather, the average number of objects in the range of the one or more transmit antennas and one or more receive antennas <NUM>, and the average distance of the objects from the one or more transmit and receive antennas, and to conform the transmit signal to spectrum regulations. Further in example, the master controller <NUM> can be configured to issue, to the beam-steering controller <NUM> and to the radar processing unit <NUM>, commands that cause the beam-steering controller and the radar processing unit to form transmit and receive beams, respectively, that correspond to the commands.

Operation of the radar subsystem <NUM> is described below, according to an embodiment. Any of the system components, such as the master controller <NUM>, can store in a memory, and execute, software/program instructions to perform the below-described actions. Alternatively any of the system components, such as the system controller (not shown in <FIG>), can store, in a memory, a data set, such as firmware, that when loaded configures one or more of the system components to perform the below-described actions. Or any of the system components, such as the system controller, can be hardwired to perform the below-described actions.

The master controller <NUM> generates a control voltage that causes the VCO <NUM> to generate a signal at a frequency within a frequency range centered about f<NUM>. For example, f<NUM> can be in the range of approximately <NUM> Gigahertz (GHz) - <NUM>.

The VCO <NUM> generates the signal, and the PA <NUM> and amplifier <NUM> amplify the signal and provide the amplified signal to the one or more transmit antennas <NUM>.

While the amplifier <NUM> is coupling the transmit signal to the one or more transmit antennas <NUM>, the beam-steering controller <NUM>, in response to the master controller <NUM>, is generating control signals to the antenna units of the one or more transmit antennas. These control signals cause the one or more transmit antennas to generate and to steer one or more main signal-transmission beams. As described above in conjunction with <FIG>, <FIG>, and <FIG>, the control signals cause the one or more main signal-transmission beams to have desired characteristics, and also cause the transmission side lobes to have desired characteristics such as suitable total side-lobe power and a suitable side-lobe level (e.g., between the smallest main signal-transmission beam and the largest side lobe).

Then, the master controller <NUM> causes the VCO <NUM> to cease generating the transmit signal.

Next, while the VCO <NUM> is generating no signal, the LNAs <NUM> respectively amplify the signals received from the respective receive-antenna segments <NUM>.

Then, the mixers <NUM> respectively down-convert the amplified signals received from the LNAs <NUM> from a frequency, e.g., at or near f<NUM>, to a baseband frequency.

Next, the ADCs <NUM> convert the analog down-converted signals to respective digital signals.

Then, the master controller <NUM> generates and sends one or more control signals to the radar processing unit <NUM>.

These control signals cause the radar processing unit <NUM> to generate and to steer one or more main signal-receive beams by applying, to each of the digitized signals from the receiver circuit <NUM>, a suitable respective gain and phase shift. As described above in conjunction with <FIG>, <FIG>, and <FIG>, the control signals cause the radar processing unit <NUM> to generate the one or more main signal-receive beams to have desired characteristics, and also to generate the side lobes to have desired characteristics such as suitable total side-lobe power and a suitable side-lobe level.

Next, radar processing unit <NUM>, or the data-processing circuit (not shown in <FIG>), analyzes the amplified and phase-shifted digital signals to obtain information from the signals and to determine what, if anything, should be done in response to the information obtained from the signals.

The radar subsystem <NUM> can repeat the above cycle one or more times.

Still referring to <FIG>, alternate embodiments of the radar subsystem <NUM> are contemplated. For example, the radar subsystem <NUM> can include one or more additional components not described above, and can omit one or more of the above-described components. Furthermore, functions or operations attributed to one component of the radar subsystem <NUM> can be performed by another component of the radar subsystem or by another component outside of the radar subsystem.

<FIG> is a block diagram of a system, such as a vehicle system <NUM>, which includes the radar subsystem <NUM> of <FIG>, according to an embodiment. For example, the vehicle system <NUM> can be an unmanned aerial vehicle (UAV) such as a drone, or a self-driving car.

In addition to the radar subsystem <NUM>, the vehicle system <NUM> includes a drive assembly <NUM> and a system controller <NUM>.

The drive assembly <NUM> includes a propulsion unit <NUM>, such as an engine or motor, and a steering unit <NUM>, such as a rudder, flaperon, pitch control, or yaw control (for, e.g., an UAV or drone), or a steering wheel linked to steerable wheels (for, e.g., a self-driving car).

The system controller <NUM> is configured to control, and to receive information from, the radar subsystem <NUM> and the drive assembly <NUM>. For example, the system controller <NUM> can be configured to receive locations, sizes, and speeds of nearby objects from the radar subsystem <NUM>, and to receive the speed and traveling direction of the vehicle system <NUM> from, e.g., a GPS receiver (not shown in <FIG>) or from a sensor (e.g., accelerometer, also not shown in <FIG>) on board the system <NUM>.

Operation of the vehicle system <NUM> is described below, according to an embodiment. Any of the system components, such as the system controller <NUM>, can store in a memory, and execute, software/program instructions to perform the below-described actions. Alternatively any of the system components, such as the system controller <NUM>, can store, in a memory, firmware that when loaded configures one or more of the system components to perform the below-described actions. Or any of the system components, such as the system controller <NUM>, can be circuitry hardwired to perform the below-described actions.

The system controller <NUM> activates the radar subsystem <NUM>, which, as described above in conjunction with <FIG>, provides to the system controller information regarding one or more objects in the vicinity of the vehicle system <NUM>. For example, if the vehicle system <NUM> is an UAV or a drone, then the radar subsystem can provide information regarding one or more objects (e.g., birds, aircraft, and other UAVs/drones), in the flight path to the front, sides, and rear of the UAV/drone. Alternatively, if the vehicle system <NUM> is a self-driving car, then the radar subsystem <NUM> can provide information regarding one or more objects (e.g., other vehicles, debris, pedestrians, bicyclists) in the roadway to the front, sides, and rear of the vehicle system.

In response to the object information from the radar subsystem <NUM>, the system controller <NUM> determines what action, if any, the vehicle system <NUM> should take in response to the object information. Alternatively, the master controller <NUM> (<FIG>) of the radar subsystem <NUM> can make this determination and provide it to the system controller <NUM>.

Next, if the system controller <NUM> (or master controller <NUM> of <FIG>) determined that an action should be taken, then the system controller causes the drive assembly <NUM> to take the determined action. For example, if the system controller <NUM> or master controller <NUM> determined that a UAV system <NUM> is closing on an object in front of the UAV system, then the system controller <NUM> can control the propulsion unit <NUM> to reduce air speed. Or, if the system controller <NUM> or master controller <NUM> determined that an object in front of a self-driving system <NUM> is slowing down, then the system controller <NUM> can control the propulsion unit <NUM> to reduce engine speed and to apply a brake. Or if the system controller <NUM> or master controller <NUM> determined that evasive action is needed to avoid an object (e.g., another UAV/drone, a bird, a child who ran in front of the vehicle system <NUM>) in front of the vehicle system, then the system controller <NUM> can control the propulsion unit <NUM> to reduce engine speed and, for a self-driving vehicle, to apply a brake, and can control the steering unit <NUM> to maneuver the vehicle system away from or around the object.

Still referring to <FIG>, alternate embodiments of the vehicle system <NUM> are contemplated. For example, the vehicle system <NUM> can include one or more additional components not described above, and can omit one or more of the above-described components. Furthermore, the vehicle system <NUM> can be a vehicle system other than a UAV, drone, or self-driving car. Other examples of the vehicle system <NUM> include a watercraft, a motor cycle, a car that is not self-driving, and a space craft. Moreover, a system including the radar subsystem <NUM> can be other than a vehicle system.

<FIG> is a plan view of the transmit-antenna section <NUM> of <FIG> in which the transmit-antenna section is a holographic-aperture antenna section having multiple waveguides <NUM><NUM> - <NUM>n and corresponding conductive antenna elements <NUM><NUM> - <NUM>n, according to an embodiment. The waveguides <NUM> are conventional rectangular-strip transmission-line waveguides, only the top portions of which are visible in <FIG>, and are approximately parallel to one another. The antenna elements <NUM><NUM> - <NUM>n are arranged over the waveguides <NUM> in respective one-dimensional arrays. For example, the antenna elements <NUM><NUM> are arranged in a one-dimensional array over the waveguide <NUM><NUM>, the antenna elements <NUM><NUM> are arranged in a one-dimensional array over the waveguide <NUM><NUM>, and so on. Assuming that the transmit-antenna section <NUM> is designed to transmit and receive signals at a wavelength of λ<NUM>, the waveguides <NUM> are spaced apart from one another, on longitudinal center, by a distance d<NUM> ≈ λ<NUM>/<NUM>, and the antenna elements <NUM> within each one-dimensional array are spaced apart from one another by a distance d<NUM> << λ<NUM>. For example, λ<NUM>/<NUM> < d<NUM> < λ<NUM>/<NUM>. Furthermore, each of the waveguides <NUM> has approximately the same length l of between approximately <NUM>λ<NUM> - <NUM>λ<NUM>, or the length l can be even longer than <NUM>λ<NUM>.

<FIG> is a cut-away side view of the transmit-antenna section <NUM> of <FIG>, taken along line A-A of <FIG>, according to an embodiment. Although only the waveguide <NUM><NUM> and the corresponding antenna elements <NUM><NUM> are shown in <FIG>, the following discussion also applies to the other waveguides and antenna elements.

The waveguide <NUM><NUM> includes a coupling layer <NUM> having an adjustable impedance about a frequency f<NUM> = c/λ<NUM>, a conductive layer/strip <NUM><NUM>, and a dielectric layer <NUM>, where c is the speed of light in free space. Although not shown, the transmit-antenna section <NUM> includes a conductive plane, such as a ground plane, disposed beneath the dielectric layer <NUM>. In operation, a signal guided by the waveguide <NUM><NUM> propagates along the dielectric layer <NUM> between the conductive strip <NUM><NUM> and the ground plane. Although the transmit-antenna section <NUM> can include a single coupling layer <NUM> and a single dielectric layer <NUM> common to all of the waveguides <NUM>, the antenna section includes separate conductive strips <NUM>, one strip per waveguide. It is these strips <NUM>, and the corresponding antenna elements <NUM>, that are spaced apart by the distance d<NUM> (see <FIG>).

Each antenna element <NUM><NUM>, and a coupling region <NUM><NUM> of the layer <NUM> disposed below the antenna element, form a respective antenna unit <NUM><NUM>. For example, the antenna element <NUM><NUM>,<NUM> and the coupling region <NUM><NUM>,<NUM> of the layer <NUM> form an antenna unit <NUM><NUM>,<NUM> of the transmit antenna-section <NUM>.

<FIG> is a side view and electrical diagram of the antenna unit <NUM><NUM>,<NUM> of <FIG>, and the portion of the conductive strip <NUM><NUM> of the waveguide <NUM><NUM> corresponding to the antenna unit, according to an embodiment.

The coupling region <NUM><NUM>,<NUM> can be modeled as a lumped adjustable-impedance element <NUM><NUM>,<NUM>, which is electrically coupled between the conductive strip <NUM><NUM> and the antenna element <NUM><NUM>,<NUM>. A conductive control line <NUM><NUM>,<NUM> is directly coupled to the lumped element <NUM><NUM>,<NUM>, or is indirectly coupled to the lumped element via the conductive antenna element <NUM><NUM>,<NUM> as shown. As described below, a controller (e.g., the master controller <NUM> of <FIG>) can selectively couple and uncouple the signal propagating along the waveguide <NUM><NUM> to and from the antenna element <NUM><NUM>,<NUM>, and can thus selectively activate and deactivate the antenna element, by selectively changing the bias signal (e.g., a bias voltage) on the control line <NUM><NUM>,<NUM>. Furthermore, a low-pass filter <NUM><NUM>,<NUM> can be serially coupled between the lumped element <NUM><NUM>,<NUM> and the controller to uncouple, from the controller, high-frequency energy from the signal propagating along the waveguide <NUM><NUM>.

And the portion of the conductive strip <NUM><NUM> corresponding to the antenna unit <NUM><NUM>,<NUM> includes a gap <NUM><NUM>,<NUM>, which can be filled with that same material that forms the coupling layer <NUM>, and which is configured to couple the signal propagating along the waveguide <NUM><NUM> to the antenna unit.

Still referring to <FIG>, during operation of the antenna unit <NUM><NUM>,<NUM>, in response to the control signal on the control line <NUM><NUM>,<NUM> having a level that inactivates the lumped element <NUM><NUM>,<NUM>, the coupling region <NUM><NUM>,<NUM> presents a large impedance to the gap <NUM><NUM>,<NUM>, and thus blocks the signal propagating along the waveguide <NUM><NUM> from coupling to, and exciting, the antenna element <NUM><NUM>,<NUM>. Therefore, the antenna element <NUM><NUM>,<NUM> radiates little or no energy.

In contrast, in response to the control signal on the control line <NUM><NUM>,<NUM> having a level that activates the lumped element <NUM><NUM>,<NUM>, the coupling region <NUM><NUM>,<NUM> presents a small impedance to the gap <NUM><NUM>,<NUM>, and thus couples the signal propagating along the waveguide <NUM><NUM> to the antenna element <NUM><NUM>,<NUM> such that the signal excites the antenna element. Therefore, the excited antenna element <NUM><NUM>,<NUM> radiates energy at the same frequency or frequencies as the frequency or frequencies of the signal propagating along the waveguide <NUM><NUM>. For example, when the lumped element <NUM><NUM>,<NUM> is active, the coupling region <NUM><NUM>,<NUM> is configured to form, together with the antenna element <NUM><NUM>,<NUM>, a series-resonant circuit having a resonant frequency of approximately f<NUM>. As known, at its resonant frequency, a series-resonant circuit has a low impedance, ideally zero impedance. Because the signal propagating along the waveguide <NUM><NUM> has a frequency of approximately f<NUM>, the region <NUM><NUM>,<NUM>, when the lumped element <NUM><NUM>,<NUM> is active, presents a low impedance to the signal. To implement such a selectively resonant circuit, the lumped element <NUM><NUM>,<NUM> can be, or can include, a semiconductor device, such as a PN-junction diode, field-effect transistor (FET), or other device that, when activated, alters the impedance of the coupling region <NUM><NUM>,<NUM> such that the coupling region forms, at f<NUM>, a series-resonant circuit with the antenna element <NUM><NUM>,<NUM>, or between the conductive strip <NUM><NUM> and the antenna element.

Still referring to <FIG>, although only the antenna unit <NUM><NUM>,<NUM> is described, all of the other antenna units <NUM> of the transmit-antenna section <NUM> (<FIG> and <FIG>) can have the same structure, and can operate in the same manner, as the antenna unit <NUM><NUM>,<NUM>.

Referring to <FIG> and <FIG>, further details of the transmit-antenna section <NUM> and the antenna units <NUM> can be found in the following documents, which are incorporated by reference herein: <CIT>, and <CIT>. Furthermore, each of the subsections <NUM> and <NUM> of the transmit-antenna section <NUM> of <FIG>, and each of the subsections <NUM> and <NUM> of the transmit-antenna section <NUM> of <FIG>, can be similar in structure and operation to the transmit-antenna section <NUM>.

From the foregoing it will be appreciated that, although specific embodiments have been described herein for purposes of illustration, various modifications may be made without deviating from the scope of the disclosure as defined by the appended claims.

Claim 1:
An antenna subsystem (<NUM>), comprising:
a sparse receive antenna (<NUM>, <NUM>, <NUM>) including an array (<NUM>) of receive elements (<NUM>) each configured to receive a respective signal having a wavelength and each spaced apart from each adjacent one of the receive elements (<NUM>) by a respective first distance that is more than one half of the wavelength; and
an electronically steerable transmit antenna (<NUM>, <NUM>, <NUM>, <NUM>) including:
an array of transmit elements (<NUM>) each configured to radiate a respective signal having the wavelength and each spaced apart from each adjacent one of the transmit elements (<NUM>) by a respective second distance that is less than one half of the wavelength,
a first transmit-antenna section (<NUM>,<NUM>) having a first subarray of the transmit elements (<NUM>), and
a second transmit-antenna section (<NUM>,<NUM>) having a second subarray of the transmit elements (<NUM>), stacked with the first transmit-antenna section (<NUM>,<NUM>) in a first dimension, and offset from the first transmit-antenna section in a second dimension orthogonal to the first dimension.