Abstract:
A radar sensor system and method for vehicles. An example radar system includes a processor, a plurality of transceivers having antenna(e). The antenna of the transceivers are located at various points around the vehicle. The transceivers include receive and transmit electronics that are in signal communication with the corresponding antenna. The transmit electronics output radar signals via the antenna. The transmit electronics include a voltage controlled oscillator (VCO), a dielectric resonator oscillator (DRO), a phase locked loop (PLL) component and a direct digital synthesizer (DDS). The receive electronics receive from the antenna any radar reflections corresponding to the outputted radar signals and send signals associated with the radar reflections to the processor. The processor generates output signals based on the signals received from the plurality of transceivers.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    There are multiple automotive, marine and aviation applications where small, low cost millimeterwave (MMW) radar sensors are distributed around a vehicle to provide functions, such as adaptive cruise control, anti-collision warning, brake applications, parking, marine threat detection or marine docking guidance. 
         [0002]    Many developers have created low cost MMW sensors, particularly for the automotive marketplace where production numbers can be in the 100,000s. Most use modulation that is either FM/CW or UltraWideband. In the typical application, each sensor provides its own modulation and signal processing in a single package. Adding more sensors requires adding complete radar and signal processing/control systems to each location and then combining data from each in yet another computing platform. This duplicates many functions. 
         [0003]    The RF implementation of the MMW Radar subsystems has either been overly complex (frequency multiplication systems) or overly simple with poor RF performance (MMW Oscillator directly connected to an antenna and modulated). Both systems generate very high phase noise and varying modulation characteristics over time and environmental changes. 
         [0004]    U.S. Pat. No. 7,324,039 to Boltovets et al. attempts to generate a MMW radar signal by frequency multiplication of an open loop X band Voltage Controlled Oscillator. This choice for FM/CW modulation also directly multiplies any modulation non-linearity and causes phase noise to increase by a factor of 20 Log N where N is the multiplication factor. Both factors significantly degrade the performance of the resulting system. 
         [0005]    Overly simple systems that employ a directly modulated MMW VCO to avoid the use of frequency multiplication achieve an overly sensitive VCO that is easily made non-linear by circuit effects, temperature or movement of objects present in the antenna beam. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a low cost means to achieve the needed sensitivity of the microwave or MMW radar sensors with low phase noise and accurate modulation at the lowest possible cost of signal generation and signal processing. The proposed system has the advantage being scaled in size from one sensor to many sensors, all served by a common control and signal processing system. 
         [0007]    An example radar system includes a processor and a plurality of transceivers having antenna(e). The transceivers and/or antennas of the transceivers are located at various points around the vehicle. The transceivers include receive and transmit electronics that are in signal communication with the corresponding antenna for outputting radar signals. The transmit electronics include a voltage controlled oscillator (VCO), a dielectric resonator oscillator (DRO), a phase locked loop (PLL) component and a direct digital synthesizer (DDS). The receive electronics receive from the antenna any radar reflections corresponding to the outputted radar signals and send signals associated with the radar reflections to the processor. The processor generates output signals based on the signals received from the plurality of transceivers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
           [0009]      FIG. 1  is a block diagram of a system implemented on a vehicle or a building; 
           [0010]      FIGS. 2 and 3  are system diagrams of example transceivers formed in accordance with embodiments of the present invention; and 
           [0011]      FIGS. 4-6  illustrate the systems of  FIG. 1  implemented on various vehicles. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    As shown in  FIG. 1 , the present invention provides a system  20  that includes a master signal processor  22  in signal communication with one or more radar components  24 . The radar components  24  translate an operating frequency to Microwave or millimeterwave (MMW) range by mixing it with an “open loop” oscillator that operates at MMW frequencies that offers frequency stability over time, temperature and vibration, such as a Dielectric Resonator Oscillator (DRO) (example DROs are produced by Honeywell Inc.). The DRO provides excellent frequency stability over time, temperature and load conditions with very low phase noise. An array of radar components  24  are mounted to a vehicle or building and are controlled by the processor  22 . The processor  22  determines if any of the radar components  24  have sensed any objects and outputs that determination to an operator. 
         [0013]    The processor  22  provides control signals for altering the modulation or antenna scanning at each radar component  24 . The processor  22  is programmable such that a sequence of modulation rates can be applied to the radar components  24  so that each is optimized for its application and location on a vehicle. The results measured by adjacent radar components  24  can be directly compared to generate additional intelligence about the dangers or situation around the vehicle. 
         [0014]    The processor  22  permits the coordination of the multiple sensors (the radar components  24 )—causing them to be synchronous and have specific offset frequencies in order to prevent jamming/interfering with each other. The processor  22  also has the ability to “sweep” from sensor to sensor to collect an overall image/data of the surroundings by interrogating them sequentially. This permits a single DSP/signal processing capability to be reused multiple times, thereby producing the unexpected results of reduced cost, power consumption, volume and weight. The processor  22  can also dwell at one sensor (the radar components  24 ) for as long as needed or jump between sensors as required as well with no particular pattern, according to the surveillance needs. 
         [0015]    As shown in  FIG. 2 , an example radar component  24 - 1  includes a suitable microwave or MMW voltage controlled oscillator (VCO)  40  and a DRO  42  that is tuned to a frequency at a predefined level below the lowest expected VCO frequency. The output of the VCO and the DRO are mixed at a mixer  48  to generate an intermediate (IF) that may be divided down to produce an input signal to a phase locked loop (PLL) chip  50 , such as that produced the ADF  4111  PLL manufactured by Analog Devices. The PLL chip  50  provides some frequency division and a Phase/Frequency detector and a charge pump are used to close the PLL chip  50 . The PLL chip  50  includes the charge pump, phase/freq detector and frequency division component. The PLL chip  50  provides desired linearity and low phase noise present in both the DRO and VCO of approximately (−100 dBc/Hz at 100 KHz). 
         [0016]    In one embodiment, as shown in  FIG. 2 , the radar component  24 - 1  is a dual antenna transceiver. As shown in  FIG. 3 , a radar component  24 - 2  is a single antenna transceiver. The receiver and transmitter components within the radar components  24 - 1  and  24 - 2  are the same except that the single antenna transceiver includes a circulator device attached to the antenna. A direct digital synthesizer (DDS)  52  provides a reference input signal to the PLL chip  50  based on signal from a clock  54 . In one example, the clock  54  is a 125 MHz clock that causes the DDS  52  to produce the reference input signal at 25-31.25 MHz. The DDS frequencies are independent of the VCO and of the MMW operating frequency. The output of the PLL chip  50  is amplified and filtered then input to the VCO  40 . The VCO  40  generates a signal that is amplified, filtered by a band pass filter, sent to the mixer  48  and then sent to a transmit antenna and receive antenna mixer via couplers. 
         [0017]    The RF input to the mixer  48  is a sample of the entire transmitted bandwidth of the MMW sensor. So for example, if the sensor transmits between 24.00 GHz and 24.20 GHz (200 MHz BW) then the input to 48 RF port is 24.00 to 24.20 GHz. The exact bandwidth depends on the frequency division and the programmed frequency division within the PLL chip itself. So this system is programmable for many frequency ranges. 
         [0018]    For a 24 GHz Radar that has FM/CW modulation between 24.00 and 24.20 GHz select a VCO that tunes from F (24.00 GHz) to F+0.2 GHz (24.2 GHz). Then one chooses a DRO at F−0.8 (23.2 GHz). When the DRO frequency is mixed with the VCO frequency range between 24 and 24.2 GHz the difference of the two frequencies is 0.8 to 1.0 GHz. Those difference frequencies of 0.8 to 1.0 GHz are the input to the PLL where it is divided by 32 within the PLL chip (e.g., ADF  4111 ) to produce 25-31.25 MHz that is in turn compared to the DDS input over the same frequency range. The use of the DRO to create a modest IF frequency range near 1 GHz is critical to permitting very low frequency divider ratios or the elimination of frequency multiplication modules. The DRO preserves very low phase noise that would otherwise be substantially higher with other methods. 
         [0019]    If a wider bandwidth is desired, it is easy to increase the DDS bandwidth from 6.25 MHz to 12.5 MHz. The DDS chirp bandwidth is multiplied by the PLL via the divider ratio. So if the divide ratio is 32 and the DDS chirps over 12.5 MHz then 32×25=400 MHz of Chirp bandwidth with no change in phase noise performance from the 200 MHz chirp bandwidth. In this case the IF frequency range at the input to the PLL chip (ADF  4111 ) would increase from the original 0.8 to 1.0 GHz to 0.8 to 1.2 GHz. This IF frequency range will track the actual bandwidth of the modulated millimeter wave frequency source. 
         [0020]    In one embodiment, carbon fiber composites enclose each of the radar components  24  to provide exceptionally strong and EMI/EMC absorption that prevents the radar components  24  from jamming or being jammed by other sensors on other vehicles etc. and at the same time provides physical protection from an outdoor environment. 
         [0021]    A receive side of the radar components  24 - 1  and  24 - 2  includes common radar receiver components. The received signals are converted to digital then sent to the master processor  22  for analysis. Communication between the components  24 - 1  and  24 - 2  can be done over a data bus, fiber optic coils, wirelessly or by any other comparable means. 
         [0022]    The sensors operate in the same band (i.e., 24 GHz, 77 GHz, 35 GHz, 95 GHz) but not at the same exact frequency ranges. Because the master controller  22  can command the sensors  24  it can do two things: 1) command specific frequency ranges for the FM/CW modulation that is offset in frequency from any other sensor  24  by at least 1 to 2 times the IF frequency of the receiver (receiver mixer output); 2) it can synchronize the start and stop times of the sensors to be exact so that the programmed frequency difference between the sensors is always maintained throughout the frequency modulation period. That exactly prevents jamming or interaction among the sensors. 
         [0023]      FIG. 4  illustrates a top, partial view of a ship having four radar components  24  mounted on exterior surfaces of the ship and the master processor  22  being located to receive data from the radar components  24 .  FIGS. 5 and 6  illustrate similar systems mounted on a car and an aircraft. 
         [0024]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. In one embodiment, the system  20  is adaptable to any legal radar band up to 95 GHz with a common digitally synthesized control loop. It can go higher than 95 GHz. There is no fundamental limitation at 95 GHz except that most typical operating bands end there. When you get to 100 GHz and above you get close to bands known as “Near IR”—meaning that you are approaching the wavelengths of Infrared radiation. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.