Phase compensated power divider for a vertical polarized three-dimensional (3D) antenna

Aspects of the disclosed technology provide solutions for splitting power between different parts of a waveguide. Features inside of a waveguide may include an input and interconnected vertical and horizontal hollow spaces (i.e. channels). Other features may include structures (i.e. septum features) that reflect a portion of electromagnetic energy moving in a channel and may allow another portion of that electromagnetic (EM) energy to pass around those septum features. A horizontal channel of a waveguide may lead to several vertical channel of the waveguide and the septum features may reflect EM energy toward one particular vertical channel such that an amount of EM energy output from that particular vertical channel may be increased as compared to amounts of EM energy output from other vertical channels of the waveguide. Geometries of the waveguide features may focus emitted EM energy by splitting the EM energy into several different parts.

BACKGROUND

1. Technical Field

The present disclosure is generally related to radar antennas. More specifically, the present disclosure is directed to a three-dimensional (3D) radar antenna.

Autonomous vehicles (AVs) are vehicles having computers and control systems that perform driving and navigation tasks that are conventionally performed by a human driver. As AV technologies continue to advance, they will be increasingly used to improve transportation efficiency and safety. As such, AVs will need to perform many of the functions that are conventionally performed by human drivers, such as performing navigation and routing tasks necessary to provide a safe and efficient transportation. Such tasks may require the collection and processing of large quantities of data using various sensor types, including but not limited to cameras and/or Light Detection and Ranging (LiDAR) sensors, and radar elements disposed on the AV.

DETAILED DESCRIPTION

Methods and apparatuses associated with the present disclosure may split power of a radar signal between different parts of a waveguide. A waveguide may include a port through which electromagnetic (EM) energy is received and may include surfaces that reflect (EM) energy within the waveguide. Features inside of a waveguide may include bumps or blocks that cause a height or width of a waveguide to change because these bumps/blocks may act to reflect a portion of EM energy toward a direction. Such blocks or bumps are referred herein as a septum, septums, or septum features. In an instance when a wave guide includes a channel (hollow portion) that extends in a horizontal direction and several other channels (hollow portions) that extend in a vertical direction, septum features included in the waveguide may reflect EM energy toward one particular vertical channel such that an amount of EM energy output from that particular vertical channel may be increased as compared to amounts of EM energy output from other vertical channels of the waveguide. These septum features' shape and their locations may affect an amount of reflected EM energy and an amount of EM energy that is allowed to pass around over the septum features. The reflections of EM energy may also result in a change in phase of EM energy being emitted from the particular vertical channel. Because of this vertically polarized radar signals may be emitted from different parts of a waveguide that have a desired shape, power, and phase relationships. Lengths of specific parts of a channel may also affect how power is split between multiple different emitting elements of an antenna. Geometries used may be adapted for use with specific types of radar signals or frequency of signals.

FIG.1illustrates a perspective view of a three-dimensional (3D) waveguide antenna that divides power of a radar signal based on the use of an impedance matching network. The 3D antenna100ofFIG.1includes an input portion where radar signals are introduced into the waveguide input110of the power divider. After entering the 3D waveguide antenna100at input port110, power of the radar signal is split through an E-plane waveguide power divider section of the waveguide120that unevenly distributes power of the radar signal to three antenna elements130that each output portions of the radar signal power provided to input110. This allows for radar signal energy to be emitted from the antenna outputs such that each of the antenna elements130can emit vertically polarized radar signals with desired magnitude and phase. For an AV application, the magnitude and phase at the three outputs may be chosen to minimize sidelobe level of the far-field radiation in the vertical plane. The antenna can take on the form of the open-ended waveguide and tapered sectoral horns. Once radar energy is introduced via input100it may travel in an upward direction, into the power divider channel120, and into towers130. Radar energy may then be emitted from the antenna100to the outside world via open-ended waveguides or tapered sectoral horns. The shape of the antenna100emits radar signals with a vertical polarization. Radar energy may be emitted from holes or openings (not illustrated) located at the top of antenna elements130.

While antenna100could be formed out of a block of metal, antenna100may alternatively be manufactured by forming one or more parts of the structure of the antenna100by injection molding. For example, a base for the antenna could be made out of plastic that is subsequently coated with a metallic coating. Internal and/or external surfaces of this plastic material could be coated with a metallic material (e.g. nickel, silver, gold, aluminum, or other metal) that reflects radar energy. Here two different pieces of the antenna may be made via injection molding, those pieces could be coated, and then the pieces could be bonded together to form the structure illustrated inFIG.1. Exemplary coating processes include yet are not limited to a spray process, a sputtering process, or a vapor deposition process. In certain instances, an electrically conductive nickel coating could be sprayed onto surfaces of the antenna, for example using a commercially available conductive nickel spray paint or a gold or palladium coating.

FIG.2Aillustrates a cross-sectional view of the three-dimensional (3D) waveguide antenna and the power divider ofFIG.1. The cross-sectional side view200A ofFIG.2Aincludes input210, power divider220, and antenna elements (230-L,230-M, &230-R). Septum features240included within the power divider220and possibly in an input portion of the waveguide act as reactive elements (e.g. a capacitor). A left portion of power divider220(i.e.220-L) extends past a left side of left antenna element230-L forming a short ended waveguide or stub portion of the waveguide. A right portion of power divider220(i.e.220-R) extends past a right side of right antenna element230-R forming a second short ended waveguide or stub portion of the waveguide. Dimensions associated with septum features240and short ended waveguides tune impedances of a waveguide. Impedances of the waveguide may vary depending on heights or width of septum features240as well as a distance that a septum feature is from a center of a waveguide. The length and width of a short-ended waveguide may also affect the tuning of the waveguide impedance.

The tuning of the waveguide affects how power of a radar signal is divided between the three different antenna elements230-L,230-M, &230-R. This tuning may affect magnitudes and phase relationships of signals emitted from the different antenna elements230-L,230-M, &230-R. The arrowed lines included in the waveguide are indicative of waves of radar energy moving through an interior of waveguide antenna200A. The arrowed lines that exit the waveguide antenna200A through the top side of antenna elements230-L,230-M, &230-R may exit through holes (i.e. openings in the waveguide) located in each of these antenna elements. Note that the waves of radar signal energy must move around or between septum elements as radar signals move through the waveguide200A.

FIG.2Billustrates a side cross-sectional view200B of the waveguide antenna200A. This side view200B includes input210, septum elements240, power divider220, and an antenna element230.

FIG.2Cillustrates an equivalent circuit that may be used to model the waveguide antenna200A ofFIGS.2A &2B. Note that this equivalent circuit includes capacitors (CTW & CS), inductors (LIM & LTW), and different impedances (Z0, ZIM, ZD, ZA, & ZRAD). Energy of the radar signal that enters the waveguide through the input on the left side ofFIG.2Cthrough impedance Z0 and to an impedance matching network that includes inductor LIM and impedance ZIM. Shapes associated with potentially septum feature sizes included in an input portion IN of a waveguide may be adjusted to affect values of impedance Z0, inductance LEVI, and impedance ZIM.

After a radar signal passes through the impedance matching network ofFIG.2, it may pass into a circuit that includes inductor LTW and capacitor CTW that form an equivalent circuit of a three-way power divider (or splitter) portion of the waveguide. Values of inductor LTW and capacitor may be associated with shapes and sizes of the power divider220portion of waveguide200A. Outputs of the three way power divider equivalent circuit provide radar energy to three circuits that are represented in the equivalent circuit by different impedances and capacitances. One output from the three-way equivalent circuit goes to a circuit that includes impedance ZD-1, capacitor CS-1, delay line DL-1(i.e. a stub delay), impedance ZA-1, and impedance ZRAD-1. A second output from the three-way equivalent circuit goes to a circuit that includes impedance ZD-2, capacitor CS-2, a delay line DL-2(i.e a stub delay), impedance ZA-2, and impedance ZRAD-2. A third output from the three-way equivalent circuit goes to a circuit that includes impedances ZA-3and ZRAD-3.

These three different circuits may be used to model magnitudes and phases of radar signal energy that travel to and that are emitted by the three different antenna elements230-L,230-M, and230-R ofFIG.2. Impedances ZD-1, ZD-2, ZA-1, ZA-1, ZA-2, ZRAD-1, ZRAD-2, and ZRAD-3may be functions of the dimensions of various elements of antenna200A ofFIG.2. Values of capacitance of capacitors CS-1and CS-2may be a function of heights or widths of septum features240. Impedances ZRAD-1, ZRAD-2, and ZRAD-3may correspond to a output impedance of antenna elements230-L,230-M, and230-R. Stub delays DL-1and DL-2may be a function of a length of stub elements220-L and220-R of the antenna200A ofFIG.2.

Geometries of antenna200A may be tuned to specific sets of radar frequencies, for example to a band of frequencies that span from 76 GHz to 81 GHz or to frequencies of about 120 GHz.

As mentioned above, the arrowed lines within cross-sectional view200A the waveguide antenna represent electromagnetic energy or waves that flow through internal hollow portions of the waveguide antenna. Note that this energy represented by the arrowed lines moves through hollow spaces in the power divider: in an upward direction from input210, in left and right directions along channel220, and in an upward direction into vertical channels of antenna elements230. Note that some of this electromagnetic energy is reflected off of internal features of the wave guide that include short-ended waveguides and spectrum features240.

FIG.2Billustrates a second cross-sectional view of the three-dimensional (3D) waveguide antenna ofFIG.1. Side view200B is an edge of the antenna input210only one of the three antenna elements230ofFIG.2Ais visible. This side view200B includes a line that represents a boundary point between horizontal channel220and tower230. A bottom portion of channel220illustrates a point where input210ends and channel220begins.

FIGS.3A &3Billustrate cross-sectional views of a three-dimensional (3D) waveguide antenna that has features that are similar to yet slightly different from the features of the waveguide antenna ofFIG.2.FIG.3Aincludes a side cross-sectional view300A of the waveguide antenna.FIG.3Bincludes an end view300B of the waveguide antenna. The waveguide antenna ofFIG.3includes input310, power divider section320, spectrum features340, antenna elements330, and antenna stub portions320-L &320-R that are very similar to elements of the waveguide antenna ofFIG.2. Here however, the spectrum features340may be shaped and have the same wall thickness as other parts of the waveguide antenna where the spectrum features240ofFIG.2may be solid pieces.FIG.3also includes a change in width of the waveguide where input310has a different width than a second part350of the waveguide. This change in width near the input of the waveguide may also adjust impedances associated with the waveguide antenna.FIG.3also includes arrowed lines that represent waves of radar energy moving into, moving through, and being emitted out of the waveguide antenna300A.

FIGS.4A &4Billustrate cross-sectional views of a three-dimensional (3D) waveguide antenna that has features that are similar to yet slightly different from the features of the waveguide antenna ofFIG.3.FIG.4Aincludes a side cross-sectional view400A of the waveguide antenna.FIG.4Bincludes an end view400B of the waveguide antenna. The waveguide antenna ofFIG.4includes input410, power divider section420, spectrum features440, antenna elements430, and antenna stub portions440-L &420-R that are very similar to elements of the wave guide antenna ofFIG.2. Some of the spectrum features440ofFIG.4have a slightly different orientation than the spectrum features340ofFIG.2.

FIG.5illustrates circuits that may be coupled to a substrate that includes an array of vertically polarized waveguide antennas.FIG.5includes circuit assembly510that may be included in a printed circuit board assembly (PCBA), a multichip module, or a monolithic microwave integrated circuit (MMIC). The circuit assembly510ofFIG.5includes a set of signal processing circuits520, a power supply530, a radio frequency (RF) MIMIC chip540, transmission lines550, and waveguide interface transition components560. In operation, signal processing circuits may send signals to and possibly receive signals from radio frequency MIMIC540. Radio frequency MMIC540may send signals using transmission lines550to waveguide interface transmission components560such that radar energy may be passed to an array of waveguide antennas.

FIG.5also includes substrate570that includes an array of waveguide antennas580. Openings590in the top of substrate570are locations where radar energy is emitted from waveguide antennas580.