Abstract:
A wireless device has a module with a communications port and an antenna electrically coupled to the communications port, the antenna having multiple folds. The antenna has a shunt stub connected to a ground plane and a radiating portion that has multiple folds, or wiggles, allowing good electrical performance to be achieved with a minimal size.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     This disclosure relates to wireless devices, more particularly to antenna used in wireless devices.  
         [0003]     2. Background  
         [0004]     Wireless devices send and receive signals through an antenna. For transmission, the antenna converts electrical signals from a power amplifier to electro-magnetic fields and radiates those fields out in a desired manger. When receiving, the antenna receives radiated electro-magnetic fields and converts them back to electrical signal for interpretation and operation by the wireless device.  
         [0005]     Many different types of antenna are being used in wireless applications. A common one is an inverted ‘F’ antenna. It has two ‘fingers’ that provide electrical connection to the wireless device, and a long, straight arm that typically parallels an edge of the printed circuit board upon which the wireless device is mounted. The inverted F antenna provides good electrical performance, but has a rather large physical size. Another option is an antenna that is shaped similar to a ‘question mark,’ but the physical size is comparable to the inverted F antenna.  
         [0006]     Wireless devices, because of their freedom from cables and wires, are particularly suited for small, portable implementations. One of the main physical constraints on making the device smaller is the size of the antenna. However, smaller antennas need to be able to match the electrical performance of the larger antenna.  
       SUMMARY  
       [0007]     One embodiment of the invention is a wireless device has a module with a communications port and an antenna electrically coupled to the communications port, the antenna having multiple folds.  
         [0008]     Another embodiment of the invention is an antenna having a shunt stub connected to a ground plane and a radiating portion that has multiple folds, or wiggles, allowing good electrical performance to be achieved with a minimal size.  
         [0009]     Another embodiment of the invention is a method of manufacturing an antenna with multiple folds. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Embodiments of the invention may be best understood by reading the disclosure with reference to the drawings, wherein:  
         [0011]      FIG. 1  shows an inverted F antenna.  
         [0012]      FIG. 2  shows an embodiment of a substrate having a module and an antenna having multiple folds.  
         [0013]      FIG. 3  shows an embodiment of an antenna having multiple folds and a vertical shunt stub.  
         [0014]      FIG. 4  shows an embodiment of an antenna having multiple folds and a horizontal shunt stub.  
         [0015]      FIG. 5  shows a graph of antenna return loss versus frequency for different substrate thicknesses.  
         [0016]      FIGS. 6   a - 6   c  shows a flowchart of an embodiment of a method to manufacture an antenna having multiple folds on a substrate.  
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0017]     An embodiment of an inverted F antenna is shown in  FIG. 1 . The substrate  10  has mounted on it a module  12 . The substrate may be a printed circuit board, or equivalent, such as a layered ceramic substrate. The substrate provides electrical connections for the module to allow it to be connected to power, communications and other types of traces in the substrate. For example, this substrate may have an edge connector  15  that allows the substrate to be inserted into a slot on a larger substrate, such as a mother board. The mother board provides power, ground and signals to the individual conductors such as  17  of the edge connector. These conductors are then connected through traces on the substrate to the module.  
         [0018]     The substrate may also provide a conductor  14  between a connector  16  for the inverted F antenna  18 . The shunt stub  19  provides the connection between the radiating portion of the antenna and the module  12 . The connector  16  would comprise a communications port that allows the module  12  to provide signals to be radiated out of the antennas, and to allow the module  12  to receive signals from the antenna for conversion and operation.  
         [0019]     As can be seen in  FIG. 1 , the size of the substrate  10  is largely dependent upon the size of the inverted F antenna  18 . This is due to the necessary size of the antenna to provide good electrical performance. As mentioned previously, it is generally desirable to reduce the size of wireless modules and the antenna is one of the main physical constraints on the size.  
         [0020]     An alternative design is an antenna shaped much like a question mark,‘?’ However, the necessary size of this antenna is similar to that of the inverted F antenna, constraining the size of the unit to be of a larger-than-desirable size.  
         [0021]     In  FIG. 2 , an embodiment of an antenna having multiple folds is shown. This may be referred to as a ‘wiggle’ antenna. The actual sizes of the modules and antennas may vary, but the comparative sizes between them can be seen by comparing  FIGS. 1 and 2 . In this embodiment, the two substrates have a similar vertical extent, but the folded antenna substrate shown in  FIG. 2  has less than half the horizontal extent of the inverted F antenna substrate.  
         [0022]     In  FIG. 2 , the substrate  20  has a module  22  with connectors such as  26 . A conductor  24  connects the module  22  to the connector  26 , although the actual conductor may not be seen if it is buried in the layers of the substrate. The conductor  24  provides a communications port for the module  22 . In one embodiment the module  22  is a Universal Serial Bus (USB) module that communicates with other devices using the USB communications protocol. The substrate  20  may or may not have other features, such as the edge connector of substrate  10  shown in  FIG. 1 .  
         [0023]     The antenna  28  has multiple folds, such as  32   a  and  32   b . The embodiment of  FIG. 2  has a vertical shunt stub  30 . The selection of a vertical shunt stub or a horizontal shunt stub is left up to the system designer, and the selection of a vertical shunt stub in this particular embodiment is merely for demonstration purposes only. Examples of horizontal and vertical shunt stub configurations are shown in  FIGS. 3 and 4 .  
         [0024]      FIG. 3  shows a vertical shunt stub wiggle antenna. The antenna is manufactured out of a substrate that has a bottom layer metal  40  and a top layer metal  44 . The bottom layer metal is shown on the left. It has a width WG and a height HGB. A notch  42  having a height H 5  and a width W 3  is shown in this embodiment as being in the upper left hand corner of the bottom layer metal. This is merely for demonstrative purposes and the notch can be provided in any position in the bottom layer metal that will allow proper connection of the antenna.  
         [0025]     The antenna in this embodiment is formed out of the top layer metal  44  shown on the right. The top layer metal has a height HGT that may be less than that of the bottom layer metal height HGB. The radiating portion of the antenna has a connecting arm  46  that connects via a connector pad  54 . The antenna has multiple folds such as  48 , each spaced a distance G apart and having an interior height of H 1 , spaced from the bottom layer metal a distance H 2 .  
         [0026]     The connecting arm and the width of the folds of the antenna are generally the same, shown here as width W. The exterior height of the antenna would therefore be the interior height H 1  plus the width of the antenna itself at the top of the folds, W. The antenna has a tip  50 , having a length L_tip. The individual selection of these dimensions is left up to the designer and the constraints of the module for which the antenna is being designed.  
         [0027]     In this embodiment the shunt stub  52  is a vertical shunt stub. The shunt stub  52  is spaced a distance G 3  from the first of the antenna folds. The shunt stub  52  will typically be as wide as the folds of the antenna, for ease of manufacturing. In this embodiment, it can be seen that the bottom of the folds of the antenna are spaced a distance H 6  from the top layer of metal  44 . For comparative purposes, the distance H 6  in  FIG. 3  is substantially equal to the distance H 3 +W+H 2  of  FIG. 4 .  
         [0028]     In addition to the radiating portion of the antenna, the antenna has a shunt stub  52 . In one embodiment the radiating portion and the shunt stub are manufactured out of the same layer. No limitation that these structures be manufactured separately should be inferred. As can be seen in  FIG. 3 , the shunt stub  52  is connected to the bottom layer metal  40 . This provides an extended ground plane for the antenna. The extended ground plane improves the antenna return loss and bandwidth control. Return loss is typically defined as the difference, usually expressed in decibels (dB), compared between the incident voltage or current on a transmission line and the reflected current or voltage as measured at a particular point. This will be discussed further with regard to  FIG. 5 . The position and size of the shunt stub also assists in achieving the desired resonant behavior.  
         [0029]     With regard to bandwidth control, the bandwidth control may be improved by the distance between the top layer and the bottom layer of metal in the substrate. This distance is referred to as the offset. There is an optimum offset for a given frequency and a given substrate thickness. The ground offset acts as a tuning element for the antenna, similar to a tuning capacitor. The performance of a wiggle antenna at different board thicknesses is shown in  FIG. 5 .  
         [0030]     In  FIG. 4 , an embodiment of an antenna with a horizontal shunt stub is shown. In this embodiment, the connecting arm of the antenna  46  is connected to the pad  54  and the folds of the antenna  48  are spaced apart a distance G, as in the horizontal embodiment shown in  FIG. 4 . Shunt stub  52  is spaced above the top layer of metal  44  by a distance H 3 , and from the bottom of the folds of the antenna by a distance H 2 .  
         [0031]     As discussed above with regard to  FIG. 4 , the use of a wiggle antenna reduces the size of the antenna, while still providing good return loss performance.  FIG. 5  shows a graph of return loss versus frequency for four different thicknesses of substrates. In this graph, the substrates were printed circuit boards, but no limitation of the use of PCBs as the substrate is intended or implied.  
         [0032]     On the graph, curve  60  is the performance specification for return loss. Curve  62  is the return loss performance for a wiggle antenna on a substrate thickness of 15 mils. It must be noted that the thickness of the substrate is the separation between the top layer metal and the bottom layer metal. Curve  64  is for a substrate that is 32 mils thick. Curve  66  is for a substrate that is 47 mils thick and curve  68  is for a substrate that is 63 mils thick. As can be seen by these results, the return loss is more than satisfactory for a wiggle antenna.  
         [0033]     The wiggle antenna manufacture is not much more complicated than the manufacture of an inverted F antenna or similar construction, such as a question mark antenna. The process will be discussed relative to the bottom layer metal and the top layer metal shown in  FIGS. 3 and 4 .  
         [0034]     In  FIG. 6   a , bottom layer metal  40  is shown with the notch  42  in the upper left hand corner. As mentioned previously, the notch may be located at any position as desired by the system designer and for ease of manufacturing. In  FIG. 6   a , the contact pad  54  is provided, adjacent the notch  42 .  
         [0035]     When top metal layer  44  is formed or otherwise provided, it results in the structure shown in  FIG. 6   b . In one embodiment, where the antenna is formed out of the top layer metal, the top layer of metal may cover all the bottom layer of metal from this view. As discussed with regard to  FIGS. 3 and 4 , the dimensions of the folds of the antenna may be uniform. This allows the metal to be patterned and etched with fewer steps.  
         [0036]     For example, assume a process where the metal is patterned with a UV-cured mask. The photoresist or other masking material is formed on the top layer of the metal. Using reticles to form the appropriate patterns, the photoresist is cured in a pattern such as the one shown in  FIG. 6   c . The uniformity of the structure dimensions allows fewer reticles to be used and easier step-and-repeat processes to form the folds of the antenna.  
         [0037]     In  FIG. 6   d , the metal that is exposed is etched and the mask cleaned away, leaving the structures shown in  FIG. 3 . The antenna  48  is connected to the conductor pad  54 , and the vertical stub  52  is connected to the bottom layer metal  40 . The process for the vertical stub antenna would be very similar. As mentioned above, the discussion of the antenna may refer to a radiating portion and a shunt stub as though they were separate structures. However, in reality, these structures may be formed out of the same layer of metal at the same time.  
         [0038]     In this embodiment, the antenna was formed in the top layer of metal and the bottom layer of metal is used for the ground plane. However, the reverse could also be implemented. The basic process would be to form a layer of metal on a substrate and then pattern and etch the metal to form the antenna with multiple folds. The metal layer from which the antenna is formed could be the top layer or the bottom layer.  
         [0039]     For example, the metal layer formed on the substrate could be the bottom metal layer formed directly on the substrate. Alternatively, the metal layer could be the top metal layer formed on the substrate overlying other layers, including the bottom metal layer. It seems to result in a simpler manufacturing flow to use the top layer for the antenna and the bottom layer for the ground plane, but the process may be adjusted as necessary by the system designer.  
         [0040]     The wiggle antenna has several advantages. The smaller size allows the overall unit to be smaller, as is desirable in wireless devices. The use of the extended ground plane on the front (top layer) or back (bottom layer) of the substrate provides improved return loss performance. Similarly, the extended ground plane allows better bandwidth control. The position and size of the shunt stub can be manipulated to allow for a particular resonant behavior.  
         [0041]     It should be appreciated that reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Therefore, it is emphasized and should be appreciated that two or more references to “an embodiment” or “one embodiment” or “an alternative embodiment” in various portions of this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined as suitable in one or more embodiments of the invention.  
         [0042]     Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment.