Patent Publication Number: US-2010109940-A1

Title: Simulating a Radar Signal Reflected From a Moving Target

Description:
The present invention claiming priority from U.S. provisional patent application serial No. 61/109,526, filed on Oct. 30, 2008. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to simulating a radar signal reflected from a moving target. 
     BACKGROUND TO THE INVENTION 
     The use of radar devices for detecting the speed of moving targets, e.g. on-road vehicles, is well-known. Testing such devices involves presenting the device with a signal that is intended to simulate the radar signal transmitted by the device being reflected from a moving target of a known speed and checking the speed reading taken by the device. A tuning fork can be used to produce this type of simulated signal, but the signal produced by a fork is a double sideband signal. Many radar devices reject double sideband signals to improve immunity to spurious signals. Electronic devices that generate simulated reflected signals are also known. However, such simulation devices tend to be bulky and have limited functionality. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention are intended to address at least some of the abovementioned problems. 
     According to a general aspect of the present invention there is provided a device adapted to simulate a radar-signal reflected from a moving target, the device including: 
     a receiver for receiving a radar signal; 
     a device for modulating the radar signal with a Doppler frequency to produce a modulated signal simulating the radar signal reflected from a moving target; 
     a transmitter for transmitting, the modulated signal. 
     The device may include a housing including a handle portion. The housing may include an integrated interface for receiving user input and a display. 
     The device for modulating the radar signal may be arranged to simulate the radar signal reflected from a simulated moving target having a length selected by a user. The simulated moving target length may be selected from a plurality of options, each of the options representing a class or category of vehicle, e.g. a car/automobile, a bus/motor-home and a lorry/truck. 
     The device for modulating the radar signal may be arranged to apply a cosine correction to the modulated signal, the cosine correction being based on an angle selected by a user that corresponds to an angle of transmission of the received radar signal. 
     The device for modulating the radar signal may use a direct digital synthesiser arrangement. The direct digital synthesiser arrangement may include first and second direct digital synthesisers connected to a quadrature mixer device. The first and second direct digital synthesisers may be connected I and Q inputs of the quadrature mixer device and the first and second digital synthesisers may be clocked from a common clock source to ensure that output frequencies of the first and second direct digital synthesisers are identical and have a required phase difference. The device for modulating the radar signal may be a single sideband modulator. The device may allow a user to select a simulated target moving away from, or approaching, a radar device that produces the radar signal in use. 
     The device may include a first circuit board including a microprocessor and at least part of the digital synthesiser arrangement and a second circuit board including at least the transmitter and the receiver. The first and second circuit boards may be arranged in parallel within a housing for the device. 
     Whilst the invention has been described above, it extends to any inventive combination of features set out above or in the following description. Although illustrative embodiments of the invention are described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to these precise embodiments. As such, many modifications and variations will be apparent to practitioners skilled in the art. Furthermore, it is contemplated that a particular feature described either individually or as part of an embodiment can be combined with other individually described features, or parts of other embodiments, even if the other features and embodiments make no mention of the particular feature. Thus, the invention extends to such specific combinations not already described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be performed in various ways, and, by way of example only, embodiments thereof will now be described, reference being made to the accompanying drawings in which: 
         FIG. 1  is a schematic diagram showing components of one example of the signal simulator device; 
         FIG. 2  is a diagram illustrating an “across the road” radar device that can be used with the simulator device; 
         FIG. 3  is an exterior view of the example signal simulator device, and  FIGS. 4 and 5  are example user interface displays generated by the simulator device. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring initially to  FIG. 1  the example device  100  includes components arranged on first  102  and second  104  circuit boards. The first circuit board  102  includes a reference frequency  106  connected to a microcontroller  108 . An example of a suitable microcontroller is the dsPIC33FJ128GPX02/X04, which includes various onchip features such as a programmable memory, Timers, Direct Memory Access, Universal Asynchronous Receiver-Transmitter and a 16-bit dual channel Digital to Analogue Converter, but it will be understood that other types of microprocessors can be used. The microcontroller  108  is connected to user interface components including a keypad  110 , an LCD display  112  and a buzzer  113 . These user interface components are exemplary only and variations could be used, e.g. touch-screens. 
     The microprocessor  108  is also configured to control a first Direct Digital Synthesiser  114 A and a second Direct Digital Synthesiser  114 B (both of which also receive a reference frequency from a frequency source  106 ). The synthesisers may comprise the AD9833 DDS from Analog Devices, Inc of Norwood, Mass., USA, for example. The first and second synthesisers output to respective first and second amplifiers  116 A,  116 B. 
     The first and second amplifiers  116 A,  116 B are connected to a quadrature mixer device  118  mounted on the second circuit board  104 . The mixer device may comprise the HMC524LC3B from Hittite Microwave Corporation of Chelmsford, Mass., USA, for example. The first synthesiser  114 A/amplifier  116 A provide the in phase channel and are connected to the I input of the mixer device  118 . The second synthesiser  114 B/amplifier  116 B provide the quadrature phase channel and are connected to the Q input of the mixer device  118 . The mixer device also receives an input from a microwave receiver antenna  120  (via an amplifier  122 ). The output of the mixer device is connected to a microwave transmitting antenna  124 . The mixer  118 , receiver antenna  120 , amplifier  122  and transmit antenna  124  are all mounted on the second circuit board  104  in the example device. In one practical embodiment of the device, the second circuit. board  104  is fitted on top of the first circuit board  102  within a housing. Having the microwave transmitter and receiver components at least fitted on a separate circuit board to the other components of the device, with one board located on top of the other, results in a relatively compact design. Thus, all the circuitry can fit inside a housing that is lightweight and easy to store/transport, which makes the hand-held device easy and comfortable to use. 
     In use, the device  100  is activated so that the receive antenna  120  is able to receive a signal from a remote radar device. An example of a suitable radar device is the AGD340 produced by AGD Systems Ltd of Gloucestershire, United Kingdom. The received radar signal is amplified by device  122  and applied to the quadrature mixer  118 . The quadrature mixer modulates the signal from the radar with a Doppler frequency that is applied to its I and Q inputs. Having the Doppler signals generated by direct digital synthesis allows accurate frequency and phase control of the I and Q signals that is important for the quadrature mixer to function correctly. Further, the direct digital synthesis devices  114 A,  114 B are clocked by the same clock source to ensure their output frequencies are identical and have a required/preset phase difference. By using a quadrature mixer  118  a single sideband Doppler target is simulated, allowing a target either moving towards or away from the radar device to be simulated. The output of the mixer  118  is then applied to the transmit antenna  124 , which radiates the modulated signal back towards the radar device, thus simulating a moving target. 
     To correctly simulate a moving target the required Doppler frequency can be determined using the equation below: 
     
       
         
           
             
               F 
               d 
             
             = 
             
               
                 - 
                 2 
               
               · 
               
                 
                   
                     V 
                     t 
                   
                   · 
                   
                     F 
                     t 
                   
                 
                 c 
               
             
           
         
       
     
     F d =Doppler Frequency 
     F t =Transmitter Frequency 
     V t =Velocity of target 
     c=Speed of light 
     This equation is effectively implemented by instructions processed by components of the device  100  in order to produce a signal simulating the received radar signal reflecting from a target of a certain speed (the interface described below can allow a user of the device  100  to select the speed). 
     In addition to allowing the speed and direction of the simulated moving target to be chosen, embodiments of the device  100  can also allow for correction to the Doppler frequency generated. In a known type of radar device commonly called an “across the road” radar (e.g. AGD340 produced by AGD Systems Ltd) the signal is transmitted by the radar device  200  across a road  202  at an angle θ, as illustrated schematically in  FIG. 2 . The radar device  200  will make a cosine correction to the Doppler signal it receives back from a moving target so as to record the correct speed of the target on the road  202 . In order for the device  100  to work properly with this type of radar device a cosine correction needs to be made to the simulated reflected signal. The device  100  can be configured for use with “across the road radars” by a user, who enters the angle of the signal transmitted by the radar device  200  (information regarding the angle for these types of radar devices is readily available by the manufacturers and will be known to the user). The device  100  can then determine the required Doppler frequency using the equation below and use this to produce the modulated signal: 
     
       
         
           
             
               F 
               d 
             
             = 
             
               
                 - 
                 2 
               
               · 
               
                 
                   
                     V 
                     t 
                   
                   · 
                   
                     F 
                     t 
                   
                   · 
                   
                     cos 
                      
                     
                       ( 
                       θ 
                       ) 
                     
                   
                 
                 c 
               
             
           
         
       
     
     Some “across the road” radars determine the type of the vehicle being detected by measuring how long a vehicle stays in the beam transmitted by the radar device. The period of time for which the target/vehicle stays in the radar beam is dependent on the vehicle length. The device  100  can be configured to simulate a number of different vehicle types and allow a user to select one of these. For each vehicle type a different length is used to determine for how long the device  100  simulates a target after being triggered. The duration of the signal transmitted by the device  100  is given by the equation below: 
     
       
         
           
             T 
             = 
             
               L 
               
                 V 
                 t 
               
             
           
         
       
     
     L=Target Simulated Length 
     V t =Velocity of target 
     T=Target Simulation Time 
       FIG. 3  shows an example of the device  100  where the circuitry is contained with a housing  302 . The housing includes an elongate handle portion  304  and a user interface portion  306  at one end. The user interface includes an LCD display  308 , a power on/off button  310 , menu navigation buttons  312 A,  312 B, menu option select button  314  and an “activate test” button  316 . It will be appreciated that the user interface items shown are exemplary only and variations are possible, e.g. numerical keypad, roller-ball, etc. In use, the user holds the back of the device  100  in the general direction of a radar device and presses the “activate test” button  316 . The buzzer  113  in the device emits a sound whilst a target is being simulated to allow the user to easily establish when the device is actively simulating i.e the device is transmitting the modulated signal. The device  100  can be powered by a battery (not shown) fitted within the housing  302 . The battery can comprise two M batteries. 
       FIGS. 4 and 5  show examples of displays that the device can generate on the LCD  308 .  FIG. 4  illustrates an example of the display being used to configure/display the type of radar signals to be received and transmitted by the device  100 . Display position  402  can either show “Advance” (as in the example) or “Recede”, which denotes the notional direction of the simulated moving target with respect to the radar signal source. The directional information can be supplemented by a representation of the radar device and an arrow pointing away/towards from it. Display position  404  can show the type of vehicle being simulated. A car is shown in the example display, but other types of vehicles, e.g. bus, truck, etc, can be selected. Alternatively, a numerical value indicating the length of the simulated vehicle could be entered. 
     Display position  406  shows the speed of the simulated moving target. In the example the speed is 131 kilometres per hour (speed unit shown at display position  407 ), but it will be understood that different unit, e.g. miles per hour, could be selected/used. The user can either select a numerical value representing the desired speed, or select a pre-set speed from a set, e.g. 21 km/hr, 38 km/hr, . . . , 250 km/hr. Display position  408  gives the cosine (radar mounting angle), shown as 22° in the example. Display position  410  is an icon that can be selected by the user to access a set-up menu. 
       FIG. 5  shows an example of the set-up menu display. The version of the radar device with which the device  100  is to be used can be selected at location  502 . Selecting different radar types changes the other options available. For instance, if the device is to be used against a sign driver radar then no cosine correction option will be displayed. The speed display units and cosine angle mentioned above can be selected at locations  504  and  506 , respectively. Selecting the “save settings” option  508  allows changes that have been made to the configuration of the device to be stored in the non-volatile memory of the microprocessor. 
     It will be appreciated that some of the functionalities described above are optional and simplified versions of the device may be provided with only a subset of the functions. The device provides a compact Doppler signal simulator that is flexible and easy to use.