Aperture coding for transmit and receive beamforming

A frequency-modulated continuous wave (FMCW) coded aperture radar (CAR) implemented on an integrated circuit (IC) to step through a range of frequencies in each sweep and a method of assembling the FMCW CAR implemented on an IC are described. The CAR implemented on the IC includes an antenna element to transmit or receive at a given time duration, a transmit channel to process a signal for transmission, the transmit channel including a transmit switch configured to change a state of a transmit phase shifter between two states based on a first code, and a receive channel to process a received signal, the receive channel including a receive switch configured to change a state of a receive phase shifter between two states based on a second code. A switch controller controls the first code and the second code and controls the first code to remain constant within the sweep.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Stage of PCT Application No. PCT/US2015/065381, filed on Dec. 11, 2015, the disclosure of which is incorporated in its entirety herein by reference.

FIELD OF THE INVENTION

The subject invention relates to aperture coding for transmit and receive beamforming.

BACKGROUND

Certain radar applications require high angular resolution. High-angular resolution requires a large aperture sensor array, which requires elements separated by a half wavelength. This leads to a large number of sensors and transmit/receive channels. The large number of transmit and receive channels can prove impractical due to their large cost. In addition to high angular resolution, low sidelobes are also important in radar sensors. Low sidelobes better isolate the angular location of objects and keep strong scatterers from dominating the signals when they are directly adjacent to weaker scatterers. For example, in the automotive application, trucks, which are strong scatterers, may be prevented from dominating the signals over motorcycles, which are relatively weaker scatterers, by keeping sidelobes low. Further, the ability to use fast Fourier transform (FFT) processing at the receiver, rather than correlation processing, simplifies the receiver in the radar system. Accordingly, it is desirable to provide a radar system that provides digital beamforming on both the transmit and the receive sides while maintaining the ability to use FFT processing.

SUMMARY OF THE INVENTION

In an exemplary embodiment, a frequency-modulated continuous wave (FMCW) coded aperture radar (CAR) implemented on an integrated circuit (IC) to step through a range of frequencies in each sweep includes an antenna element configured to transmit or receive at a given time duration; a transmit channel configured to process a signal for transmission, the transmit channel including a transmit switch configured to change a state of a transmit phase shifter between two states based on a first code; a receive channel configured to process a received signal, the receive channel including a receive switch configured to change a state of a receive phase shifter between two states based on a second code; and a switch controller configured to control the first code and the second code, wherein the switch controller controls the first code to remain constant within the sweep.

According to another exemplary embodiment, a method of assembling a frequency modulated continuous wave (FMCW) coded aperture radar (CAR) on an integrated circuit (IC) to step through a range of frequencies in each sweep includes disposing an antenna element to transmit or receive energy at a given time duration; arranging a transmit channel to process a signal for transmission; changing, using a transmit switch of the transmit channel, a state of a transmit phase shifter between two states based on a first code; arranging a receive channel to process a received signal; changing, using a receive switch of the receive channel, a state of a receive phase shifter between two states based on a second code; and controlling the first code and the second code using a switch controller, the switch controller controlling the first code to remain constant within the sweep.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numeral indicate like or corresponding parts and features.

As noted above, high angular resolution can be desirable in certain applications. Exemplary applications include autonomous driving and high-end active sensing features in vehicles. Embodiments of the systems and methods detailed herein relate to a radar system with digital beamforming (DBF) of transmit and receive beams with multiplicative beam patterns. Single-bit transceiver codes are used, as detailed below, to facilitate FFT processing of received signals. The embodiments are equally applicable to vehicles (e.g., automobiles, farm and construction vehicles) and to non-vehicles (e.g., consumer electronics, appliances, manufacturing systems).

In accordance with an exemplary embodiment of the invention,FIG. 1illustrates a coded aperture radar (CAR)1integrated circuit (IC)100. The exemplary CAR1includes an array of four antenna elements10that are shared by the transmit channel20and the receive channel30. The CAR1includes other components outside the IC100that are known and not discussed herein. A Tx/Rx selector40coupled to a direct current (dc) power source45controls whether the transmit channel20or the receive channel30uses the respective antenna element10for each given transmit channel20/receive channel30pair. The Tx/Rx selector40associated with each transmit channel20/receive channel30pair is controlled by a central Tx/Rx selector42for the IC100. A given antenna element10may be used to transmit or receive but not both at the same time. One antenna element10of the CAR1may transmit (associated Tx/Rx selector40selects the transmit channel20) while another antenna element10of the CAR1receives (associated Tx/Rx selector40selects the receive channel30). In alternate embodiments, the CAR1may include more or fewer antenna elements10than shown inFIG. 1. In alternate embodiments, the transmit channel20and receive channel30may not share the same antenna element10.

Each transmit channel20includes a switch22, a differential amplifier25, and a power amplifier (PA)27and could include additionally known transmitter components. Each receive channel30includes a low noise amplifier (LNA)32, switch35, and differential amplifier37and could include additional components, as well. The CAR1is a frequency modulated continuous wave (FMCW) radar such that each transmission sweeps a range of frequencies. This sweep of a range of frequencies is repeated for a number of transmissions. The range of frequencies may be centered around 76.5 gigaHertz (GHz), for example, and is selected based on the specific application. The switches22,35implement the code that is further detailed below. The switch22, which is associated with the transmit channel20maintains the same code for a given frequency sweep. The switch35, which is associated with the receive channel30, may change the code (according to some sequence) within a frequency sweep but repeat the code sequence from sweep to sweep. The greater the number of codes used in the receive channel30for a given sweep, the lower the multiplicative noise level that arises from coded aperture beam forming and the lower the ambiguity in range, velocity, and angles. The operation according to this embodiment (i.e., maintaining transmit channel20code constant within a sweep and repeating the code sequence of the receive channel30from sweep to sweep) gives rise to multiplicative transmit and receive patterns that reduce sidelobes. In alternate embodiments, the code sequence of the receive channel30may not be repeated. The switches22,35associated with each transmit channel20/receive channel30pair are centrally controlled by a switch controller47of the IC100.

Energy transmitted via one or more transmit channels20is input at input line50and is divided at splitter55. The input line50may additionally include a serial communication line. In alternate embodiments, a dedicated line may be used for low-frequency communication. The communication line may be decoded at the asynchronous serial communication and decoding processor60. In the exemplary embodiment shown inFIG. 1, the serial communication line of the input line50may include information to change a seed at62that is used by the pseudorandom generator at65. The pseudorandom generator65generates the codes input to the switch controller47. In alternate embodiments, the communication (provided over the input line50or in a dedicated line) may, itself, provide the codes to the switch controller47without the need for the seed at62and the pseudorandom generator at65. Signals received by one or more of the receive channels30may be aggregated at75and output over an output line70. The input line50and output line70may include filters53, as shown inFIG. 1, and additional known components.

As noted above, the switch controller47controls each of the switches22,35of each of the transmit channel20/receive channel30pairs to implement a code. The code controls the phase shifter bit associated with each transmit channel20and receive channel30. That is, the switch22and differential amplifier25determine if a transmitted signal is shifted 180 degrees or not (is shifted 0 degrees) based on the code provided by the switch controller47to the switch22. On the receive channel side30, the switch35and differential amplifier37determine whether the received signal is not shifted or is shifted 180 degrees based on the code provided to the switch35by the switch controller47. As noted above, the code on the transmit channel20side is such that the code may not be changed during a given frequency sweep. Ensuring that the sweep duration is significantly longer (e.g., ten times) than the round trip delay time of the furthest scatterer ensures that all scattered signals resulting from one sweep are modulated by the same transmit code. This, in turn, facilitates the use of simple FFT processing (rather than the need for correlation processing) of received signals. The code on the receive channel30side is such that the code may be changed within a given frequency sweep in a sequence and this code sequence may be repeated from sweep to sweep to achieve multiplicative transmit and receive patterns for lower sidelobes. For the FMCW CAR1, the code changes (in the transmit channel20and the receive channel30) facilitate determination of angular information, the frequency sweeping facilitates determination of range information, and the change in phase from sweep to sweep due to radial movement of targets facilitates determination of radial velocity information. The CAR1according to the exemplary embodiments detailed herein facilitate high angular resolution and FFT processing.

FIG. 2is a block diagram of a system200including an array of CAR1ICs100according to an exemplary embodiment. The exemplary system200shown inFIG. 2includes four of the ICs100detailed inFIG. 1, with each CAR1on each IC100including four antenna elements10. On the transmit side, a voltage controlled oscillator (VCO)210output is split by a splitter220. One of the outputs of the splitter220is sent to a power amplifier230that amplifies the VCO210output and provides the RF input to the splitter240for distribution to each of the ICs100. Energy received by the different antenna elements10is summed at250, and the RF output is provided to a low noise amplifier (LNA)260. The LNA260output is mixed with the VCO210output provided by the splitter220at the mixer270. The mixer270output is converted to a digital output by the analog-to-digital converter (ADC)280. The digital output may then be further processed. As noted above, the CAR1of each IC and the code employed in the transmit channel20and receive channel30, as detailed above, facilitates high angular resolution and the ability to process the received signals with FFT processing.

FIG. 3illustrates exemplary arrangements of transmit and receive antenna elements10in arrays according to embodiments. The antenna elements10may be arranged to result in the 16-by-4 array shown inFIG. 3. For each array310,320,330,340, each antenna element10is transmitting (T) or receiving (R) as indicated. As array310shows, all of the antenna elements10are transmitting. As array320shows, all of the aperture elements10are receiving. Arrays330and340indicate that some of the aperture elements10are transmitting while others are receiving. Array340, in particular, indicates that the transmit and receive functions are interleaved along the azimuth orientation but do not vary along elevation. For any of the arrays shown inFIG. 3, the code could be varied as discussed above. That is, for the transmitting antenna elements10, the code (and corresponding phase) may be changed from one sweep to the next. For the receiving antenna elements10, the code may be changed even during a sweep.