Abstract:
A level sensing device with a high frequency radar system is provided. The radar system includes a radar high frequency module, a carrier board and a controller. The radar high frequency module is mounted on the carrier board using surface mount techniques. The controller includes a processor and the radar high frequency module has a plurality of components including one or more microwave integrated circuits, a radiating patch antenna, and coupling means for channeling a radiated signal from the patch antenna out of the module. The components are encapsulated to form the module and the coupling means includes a dielectric rod.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/GB2008/050161 filed Mar. 7, 2008 and claims the benefit thereof. The International Application claims the benefits of Great Britain Application No. 0705449.7 GB filed Mar. 22, 2007; both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates to a level sensing device using a high frequency radar system, in particular for range finding and level sensing of bulk materials, or fluids. 
       SUMMARY OF INVENTION 
       [0003]    For radars operating at high frequencies (HF) using monolithic microwave integrated circuits (MMICs) packaged as bare die, construction costs have traditionally been high. In addition, the transition to the antenna has required complex precision construction and the MMICs are delicate components requiring protection which further complicates the issue of manufacture. Conventionally, modules with the MMICs mounted onto them are connected to carrier circuit boards using bond wires or soldered wire links. The complete assembly then has to be protected in a housing. Antenna connections are frequently made using precision transitions to waveguide, which can be time consuming and expensive to manufacture. Furthermore, for level sensing, the size of aperture available to operate the radar through is limited and at conventional frequencies this can lead to poor resolution. However, increasing the frequency of operation leads to higher costs for components and manufacturing. In addition, level sensing, or range finding to determine quantities of bulk materials, particularly powdered materials, such as cement or flour, takes place in an environment which is hostile for electronic components. Fluid level monitoring may take place in remote situations, where maintenance is difficult, so a reliable device is particularly important. 
         [0004]    In accordance with a first aspect of the present invention, a level sensing device comprises a high frequency radar system, the system comprising a radar high frequency module, a carrier board and a controller; wherein the radar high frequency module is mounted on the carrier board using surface mount techniques; wherein the controller comprises a processor; wherein, the radar high frequency module comprises a plurality of components including one or more monolithic microwave integrated circuits (MMICs) packaged as bare die, a radiating patch antenna, and coupling means for channelling a radiated signal from the patch antenna out of the module, wherein the radar high frequency module components are encapsulated to form the module; and, wherein the coupling means comprises a dielectric rod. 
         [0005]    The present invention addresses the problems caused by the physical environment in which the level sensing device must operate, by providing a compact, well protected package, using a dielectric rod, rather than a traditional antenna and complicated waveguide transitions. 
         [0006]    The system can operate over a wide frequency range, but preferably, the radar system operates in the millimetre band. 
         [0007]    This gives improved resolution and higher gain for a given available aperture size. 
         [0008]    Typically, the operating frequency is between 40 and 120 GHz, more typically in the region of about 75 to 85 GHz. 
         [0009]    This frequency range gives particularly good results for returns off dry or dusty materials. 
         [0010]    Preferably, the components are encapsulated with a material which provides screening of the microwave components. 
         [0011]    The packaging provides both physical protection from the environment, and protection from electrical interference. Providing both a screening and a protective function in the same part is convenient and saves in manufacturing costs. 
         [0012]    Preferably, the controller causes a radiated signal to be channelled toward a target material; wherein a return radar signal is received in the radar system; and wherein the processor processes the return signal to determine a level of the target material. 
         [0013]    This can be used on any type of target material to determine its level at the point to which the signal is directed. 
         [0014]    The invention can be used for determining levels of fluids or bulk products in open environments, such as rivers or gravel yards, but in one embodiment, the target material is in a container. 
         [0015]    The return signal can be used in combination with a known total height of the container to determine where the level of the material is. 
         [0016]    Preferably, the processor extracts from a store, information relating to the target material and the container, and derives an approximate volume of the material in the container. 
         [0017]    This can be helpful to determine how soon a silo e.g. on a production line for concrete structures, needs to be refilled based on the amount of material remaining and likely rate of use. 
         [0018]    The level sensor may be used on many different objects, but typically, the target material comprises a fluid or bulk product, for example concrete, flour, grain or oil. Alternatively, in open air situations, the fluid may be water, such as reservoir levels, or waste products, such as in sewage treatment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    An example of a level sensing device using a high frequency radar system according to the present invention will now be described with reference to the accompanying drawings in which: 
           [0020]      FIG. 1  illustrates a conventional construction of a radar module; 
           [0021]      FIG. 2  illustrates construction of a high frequency radar module for use in a level sensing device according to the present invention; 
           [0022]      FIG. 3  illustrates two examples of use of a level sensing device using a high frequency radar system according to the present invention in an enclosed area; 
           [0023]      FIG. 4  illustrates an example of the present invention, used in an open environment; and, 
           [0024]      FIG. 5  is a block diagram of a level sensing device according to the present invention in more detail. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0025]      FIG. 1  illustrates a conventional construction of a radar module  1 . A radar technology printed circuit board (PCB)  2  is provided with a recess  3  into which a radio frequency (RF) substrate  4  is located and fitted by locating pins, or fixings  5 . A waveguide transition  7  is provided on a high frequency module which is illustrated in more detail in the exploded section of  FIG. 1 . The RF substrate, or metal backing  4  contacts a ground plane of the PCB  2 . Dielectric and MMIC components  6 ,  9  are provided on the RF substrate  4  and joined via bondwires  10 . The HF module is also electrically joined to the PCB via bondwires  11 . In order to protect the HF module and its connection to the PCB, a casing is provided which is located by pins, or fixings  12  and sealed by seals  13 . Conventionally, the output of the waveguide transition  7  is coupled into a waveguide  14  to exit the module. 
         [0026]    The present invention solves the construction problems of the conventional device by packaging the MMICs in a module  28  that can be used as a component in standard printed circuit board assembly. This is shown in  FIG. 2 . The module is formed as a microwave substrate  20 , such as liquid crystaline polymer (LCP), on a ground plane  21 , supported by a rigidiser  22 , which in this example is made from flame resistant  4  (FR 4 ) material. MMICs  23  used in the radar HF module are mounted in pockets in the microwave substrate  20 . Connections  24  are made from the MMICs  23  to the substrate  20  using bondwires. The connections are brought out through the rigidiser  22  using vias and surface mount pads  25  are formed on the FR 4  rigidiser to allow the module to be connected to a radar technology carrier PCB  26 . A screening can  27  is fitted to the edges of the substrate  20 . The module  28  provides protection for the MMICs  23  by virtue of its enclosed structure. The radar HF module also includes a pre-focus rod  29  that is driven by a radiating patch antenna  30  to form part of the overall antenna system. The pre-focus rod captures radiation from the patch antenna on the HF module and channels the radiation along the length of the antenna. The end of the pre-focus rod is tapered to provide a launch of the channelled wave into free space. This can be used as the system antenna, or for illuminating a dielectric lens (not shown) placed in front of the dielectric rod to form narrow beams. Alternatively, the radiation may be fed into other beamforming type devices, such as a horn, a waveguide extended horn, or a reflector antenna. 
         [0027]    An example of an application of the system of the present invention is shown in  FIG. 3 .  FIG. 3   a  shows the use of level sensing in a storage vessel, or silo  31  at least partially filled  32  with bulk material  33 , such as flour, grain, cement, or fluid such as oil, fuel, or water. A signal  34  is radiated from a level sensor  35  toward the fill level  32  of the material and the return  36  is received and processed in the system. The available aperture in a silo is limited by the desire to avoid making holes in the container. Conventional level sensors operate in the 6, 10 or 24 GHz range, whereas the preferred frequency range of the present invention is around 77 GHz which gives a higher gain for the available aperture in the vessel, as well as a better return off dry, or dusty solids. 
         [0028]    To measure the level of material within a container, the radar system emits radiation at a suitable frequency and the returns are processed in conjunction with known information about the overall height and volume of the container. Level sensing may be used as part of a process for controlling manufacture, so that the amount of material used up, or remaining in the silo  31  can be determined and appropriate top ups built into the production process to minimise downtime. Since filling and emptying of the silos is usually done through vents  37 ,  38  aligned along the axis, the position of the level sensing device can be offset to one side, or other of the central axis in the silo to obtain a more accurate estimate, as illustrated in  FIG. 3   b , so that the measured level can be treated as an approximation of the actual level if it were flat. In this example, an approximation of the remaining volume can be made since the return is not off the peak, but off an average point. 
         [0029]    Another example of level sensing is in its application to measuring fluid levels in open environments. Examples of this include measuring height of water in a river or reservoir, or wave height beneath oil rigs, so that advance warning can be given of potentially dangerous situations.  FIG. 4  illustrates an example of measuring river height. A level sensing device  35  according to the invention is installed beneath a bridge  60  over a river  64 . At regular intervals, the radar system emits radiation  36  at a suitable frequency and the returns  34  are processed to determine the river level, or a change in level. Triggers can be set based on expected results for the river level at that point which, with a suitable wireless communication system (not shown), allows a wireless transmission  61  to send an alert if the level rises above the norm. If desired, data sent  62  from other points, e.g. a second bridge  63 , upstream on the river  64  may be used in setting, or adapting the triggers. 
         [0030]      FIG. 5  illustrates a block diagram of a level sensing device according to the present invention in more detail. A waveform generator  40  produces the waveform required for the radar. A transmitter (Tx)  41  produces the required transmit power at the radar operating frequency in response to the waveform generator output  42 . A transmit/receive (T/R) block  43  separates the transmitter signal  44  into an output  45  through an antenna from the return signal received through the antenna. A first stage receiver (Rx)  47  acts on the receiver signals to translate the return signal to a lower frequency for further processing. The transmitter  41 , T/R block  43 , antenna  46  and first stage receiver  47  are included in the HF module  48 . A second stage receiver (Rx)  49  acts on the first stage receiver signals  50  to provide a drive signal  51  for an analogue to digital converter (ADC). The output  53  from the analogue to digital converter  52  is input to a digital processor  54 . The processor block processes the return signal to determine a level of the target material, or fluid. 
         [0031]    The present invention reduces the cost of manufacturing a system for operation at high frequencies by encapsulating all RF components in a single screened module, which can be incorporated into a manufactured item using production line surface mount techniques, rather than hand assembly and reduces the overall number of passes for each of the manufacturing steps. The components themselves may still be relatively expensive, but the modular structure allows a simple production facility to produce the radar systems without changing their equipment by buying in the modules. These can be made in a clean room by a company specialising in that type of manufacture, but the company producing the finished product does not need to invest in this type of facility. 
         [0032]    The use of a dielectric rod to extract the radiation from the encapsulated package is a further simplification, in contrast to the use of waveguide transitions which are very complex to manufacture. 
         [0033]    Unlike the conventional manufacturing process whereby a module was laid onto a carrier circuit board and bonded, then covered over for protection and other components were soldered onto the board in their positions afterwards, the present invention allows most of the assembly to be done in factories which do not have a clean room and the high frequency radar module is manufactured off-site by specialist, then incorporated as part of an assembly line.