Patent Publication Number: US-2010128671-A1

Title: Interference-free antenna module and WiFi network system using the antenna module

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an interference-free antenna module and a wireless fidelity (WiFi) network system and, more particularly, to an interference-free antenna module capable of improving the efficiency and the signal to noise ratio (SNR) of the transmission of a high frequency signal between a WiFi base station and a consumer equipment, and the system using the interference-free antenna module to effectively expand the coverage of the WiFi base station under the condition of maintaining a desired quality of service (QoS) in addition to improving the efficiency of the transmission of a high frequency signal between a WiFi base station and a consumer equipment. 
     2. Description of Related Art 
     In recent years, WiFi technology has been widely implemented in the wireless network systems of metropolitan areas, and people can access internet wherever by using a notebook computer or a personal digital assistant (PDA) with wireless capabilities, thereby gaining the goal of mobile broadband. As shown in  FIG. 1 , a typical WiFi network system includes a WiFi base station  11  and a consumer equipment  12 . The WiFi base station  11  is electrically coupled to a remote server  14  (such as a digital switch) through a physical network line  13 . The consumer equipment  12  (such as a cell phone, a notebook computer, a PDA and the like) transmits signals to the WiFi base station  11  via wireless network, and the WiFi base station subsequently forwards the signals to the remote server  14  through the physical network line  13 . Similarly, the signals are delivered in reverse direction to the WiFi base station  11  through the physical network line  13  and subsequently transmitted to the consumer equipment  12  covered by the WiFi base station  11  via wireless network. 
     Therefore, the efficiency of wireless network in transmitting signals between a WiFi base station and a consumer equipment in a typical WiFi network system is quite important. In addition, buildings, moving vehicles and dirty air particles in a metropolitan area can cause poor transmission efficiency of the wireless network. Therefore, it is hard to raise the signal to noise ratio (SNR) on signal transmission, and likely resulting in signal loss. In order to maintain a desired QoS, for the typical WiFi network system, it is necessary to reduce the coverage of the WiFi base station. However, it largely increases the entire deployment cost of the typical WiFi network system, for it requires more WiFi base stations, which may affect on the health of people around the WiFi base stations. 
     To overcome the aforementioned problems, in the industry, a smart antenna is proposed as a solution to replace the antenna of the WiFi base station. The smart antenna can only receive the high frequency signals which are at a specific frequency, from a specific direction, and within a special time slot. Accordingly, other high frequency signals with different frequencies or from different directions (such as the high frequency signals reflected by the buildings or transmitted to the WiFi base stations by other consumer equipments) are not received by the smart antenna, and the signal transmission efficiency between the WiFi base station and the consumer equipment is improved. However, the smart antenna is very expensive; the cost could be even higher than the entire WiFi base station. Thus, for the industry, WiFi base stations with the smart antenna could not be implemented widely. Namely, the aforementioned solution by using the smart antenna could only solve the aforementioned problem partially. Therefore, it is desirable to provide an improved antenna and WiFi network system to mitigate and/or obviate the aforementioned problems. 
     Therefore, there is a need for the industry to have an interference-free antenna module, which is capable of improving the transmission efficiency of high frequency signals between a WiFi base station and a consumer equipment, and a WiFi network system, which is capable of improving the transmission efficiency of high frequency signals between a WiFi base station and a consumer equipment, and effectively expanding the coverage area of WiFi base stations under the condition of maintaining a certain level of quality of service (QoS). 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an interference-free antenna module, which can increase the signal transmission efficiency between a WiFi base station and a consumer equipment and also the SNR of high frequency signal transmission. 
     Another object of the present invention is to provide a WiFi network system, which can increase the signal transmission efficiency between a WiFi base station and a consumer equipment, and effectively expand a coverage of the WiFi base station while maintaining a desired QoS. 
     To achieve the objects, an interference-free antenna module is provided, which is implemented in a wireless fidelity (WiFi) base station with a signal processor and applied to a high frequency signal transmission between the WiFi base station and a consumer equipment. The antenna module includes a plurality of high frequency transceivers facing different directions respectively, and an antenna controller electrically coupled to the high frequency transceivers. The antenna controller is electrically coupled to the signal processor in order to receive a signal transmitting/receiving request output by the signal processor to accordingly select a high frequency transceiver to transmit or receive a circularly polarized high frequency signal. In addition, the interference-free antenna module is also implemented in a consumer equipment, and it includes a consumer equipment interference-free antenna module and a second signal processor. The consumer equipment interference-free antenna module has a circular polarization antenna unit to transmit or receive a circularly polarized second high frequency signal. 
     To achieve the objects, a WiFi network system is provided. The system includes: a WiFi base station having an interference-free antenna module and a first signal processor, the interference-free antenna module having a plurality of first high frequency transceivers and a first antenna controller electrically coupled to the first high frequency transceivers respectively, the first antenna controller being electrically coupled to the first signal processor for selecting one of the first high frequency transceivers to transmit or receive a circularly polarized first high frequency signal based on a signal transmitting/receiving request output by the first signal processor; and a consumer equipment having a consumer equipment interference-free antenna module and a second signal processor, the consumer equipment interference-free antenna module having a circular polarization antenna unit to transmit or receive a circularly polarized second high frequency signal. The first high frequency transceivers face different directions respectively, and one of them faces the consumer equipment. 
     Therefore, the high frequency signals transmitted by the high frequency transceivers of the interference-free antenna module in the invention have a circular polarization characteristic (such as a left-hand circular polarization), and when the circularly polarized high frequency signals are reflected by an obstacle (such as a building or vehicle), the circular polarization characteristic is consequently changed (such as changed from a left-hand circular polarization into a right-hand circular polarization). Therefore, only a high frequency signal with a specific circular polarization (such as a left-hand circular polarization) can be delivered to the signal processor of the consumer equipment. In this case, even if the reflected high frequency signal or signals are delivered to the circular polarization antenna unit of the consumer equipment, they cannot enter the signal processor of the consumer equipment due to the right-hand circular polarization characteristic. Namely, the noises produced by the reflected high frequency signal or signals are effectively suppressed, so the SNR of transmitting the high frequency signals can be raised and the transmission efficiency of the high frequency signal between a WiFi base station and a consumer equipment is raised. 
     Similarly, since the high frequency transceivers of the respective antenna modules of both the WiFi base station and the consumer equipment in the WiFi network system can transmit or receive a circularly polarized high frequency signal, the corresponding consumer equipment (or the WiFi base station) can easily receive a high frequency signal with a specific circular polarization when the WiFi base station (or the consumer equipment) transmits the high frequency signal with the specific circular polarization, and the SNR and transmission efficiency of transmitting the high frequency signal are accordingly raised. Therefore, the coverage of the WiFi base station in the WiFi network can be expanded while the system maintains the desired QoS. 
     Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a typical WiFi network system; 
         FIG. 2  is a schematic view of an interference-free antenna module according to an embodiment of the invention; 
         FIG. 3  is a schematic view of a WiFi network system according to an embodiment of the invention; 
         FIG. 4  is a schematic view of a WiFi base station of a WiFi network system according to an embodiment of the invention; 
         FIG. 5  is a schematic view of a WiFi base station of a WiFi network system that is installed on the roof of a room according to an embodiment of the invention; and 
         FIG. 6  is a schematic view of a consumer equipment interference-free antenna module of a WiFi network system according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 2  is a schematic view of an interference-free antenna module according to an embodiment of the invention. As shown in  FIG. 2 , the module includes a plurality of high frequency transceivers  21  to  26  and an antenna controller  27 . The high frequency transceivers  21  to  26  face different directions respectively, and the antenna controller  27  is electrically coupled to the high frequency transceivers  21  to  26  respectively. 
     In addition, the WiFi base station (shown later) with the interference-free antenna module has a signal processor (shown later), and the antenna controller  27  is electrically coupled to the signal processor. The antenna controller  27  is based on a signal transmitting/receiving request output by the signal processor to select one of the high frequency transceivers  21  to  26  to transmit or receive a circularly polarized high frequency signal. 
     As shown in  FIG. 6 , the consumer equipment in this embodiment includes a consumer equipment interference-free antenna module  41  and a second signal processor  42 . The consumer equipment interference-free antenna module  41  has a circular polarization antenna unit  411 . In this embodiment, the circular polarization antenna unit  411  includes a horizontal antenna portion  4111 , a vertical antenna portion  4112  and a signal mixing portion  4113 , and the signal mixing portion  4113  is electrically coupled to the horizontal antenna portion  4111  and the vertical antenna portion  4112  respectively. In addition, a horizontal high frequency signal transmitted or received by the horizontal antenna portion  4111  and a vertical high frequency signal transmitted or received by the vertical antenna portion  4112  have a 90-degree phase difference. 
     Besides, the antenna module is implemented in a WiFi base station (shown later) and applied to the transmission of high frequency signals between the WiFi base station (shown later) and the interference-free antenna module of the consumer equipment (shown later). 
     The interference-free antenna module shown in  FIG. 2  has six high frequency transceivers  21  to  26 , each of them is a patch array antenna and has a rectangle plate  211 ,  221 ,  231 ,  241 ,  251 ,  261  respectively. In this embodiment, the six rectangle plates  211 ,  221 ,  231 ,  241 ,  251 ,  261  have a size of 5 cm×5 cm. Besides, the antenna controller  27  includes a circular polarization filter portion  271  to filter the high frequency signals respectively received by the high frequency transceivers  21  to  26 . Thus, only a high frequency signal with a specific circular polarization (such as left-hand circular polarization) can be delivered to the signal processor (shown later) of the WiFi base station. 
     Further, in this embodiment, the antenna controller  27  includes an electronic scan switch circuit board  272  to rapidly switch and select one of the high frequency transceivers  21 ,  22 ,  23 ,  24 ,  25  or  26  electronically based on a signal transmitting/receiving request output by the signal processor to thereby transmit or receive a circularly polarized high frequency signal. In this embodiment, the frequency of the circularly polarized high frequency signals transmitted or received by the high frequency transceivers  21 ,  22 ,  23 ,  24 ,  25  and  26  is approximately 2.4 GHz (the actual frequency may slightly vary upon the practical needs.) 
     It is noted that the number of high frequency transceivers of the interference-free antenna module can be one to six, depending on the practical needs, but not limited to six as cited in this embodiment. In addition, depending on the practical needs, each of the high frequency transceivers can be a different type of antenna, such as a waveguide slot array antenna or a sector horn antenna, which is capable of transmitting or receiving a circularly polarized high frequency signal, but not limited to the patch array antenna as cited in this embodiment, and all the high frequency transceivers do not need to be the same type of antenna. The high frequency signal can range between 2.3 GHz and 2.5 GHz, depending on the practical needs (such as in different environments), but not limited to 2.4 GHz as cited in this embodiment. 
     As stated, since the high frequency signals transmitted by the high frequency transceivers of the interference-free antenna module have a circular polarization characteristic (such as left-hand circular polarization), the circular polarization characteristic changes (such as from left-hand polarization to right-hand circular polarization) once the high frequency signals are reflected by an obstacle (such as a building or vehicle). Thus, as the circular polarization filter portion of the consumer equipment has a limit that only the high frequency signal with a specific circular polarization (such as left-hand circular polarization) can pass and then be delivered to the signal processor, the high frequency signals reflected by the obstacle cannot be delivered to the signal processor of the consumer equipment even if they enter the circular polarization antenna unit of the consumer equipment. Accordingly, the noises produced by the reflected high frequency signals are effectively suppressed, and the interference-free antenna module of the invention is able to raise the SNR of transmitting the high frequency signals. 
     Similarly, since the high frequency signals transmitted by the circular polarization antenna unit of the consumer equipment has a circular polarization characteristic (such as left-hand circular polarization), the circular polarization characteristic changes (such as from a left-hand circular polarization to a right-hand circular polarization) once the high frequency signals are reflected by an obstacle (such as a building or vehicle). Thus, the circular polarization filter portion of the antenna controller of the interference-free antenna module has a limit that only a high frequency signal with a specific circular polarization (such as left-hand circular polarization) can pass and be delivered to the signal processor of the WiFi base station, the high frequency signals reflected by the obstacle cannot be delivered to the signal processor of the WiFi base station even if they enter the high frequency transceivers of the interference-free antenna module. Accordingly, the noises produced by the reflected high frequency signals are effectively suppressed, and the interference-free antenna module of the invention is able to raise the SNR of transmitting the high frequency signals. 
     Since the circular polarization characteristic of the high frequency signals changes once the signals are reflected by the obstacle, the circular polarization characteristic can be restored (back to the left-hand circular polarization in the first transmission) when the high frequency signals are reflected again. In this case, although the circularly polarized high frequency signals (transmitted by the circular polarization antenna unit of the consumer equipment) which have been reflected twice can pass the circular polarization filter portion of the antenna controller of the interference-free antenna module and be delivered to the signal processor of the WiFi base station, the intensity of the high frequency signals has decayed to a very low level, and the signal transmission between the WiFi base station and the consumer equipment is not affected by the noises produced by the high frequency signals which have been reflected twice. 
     Similarly, although the circularly polarized high frequency signals (transmitted by the high frequency transceivers of the interference-free antenna module) which have been reflected twice can pass the circular polarization filter portion of the consumer equipment and be delivered to the signal processor, the intensity of the high frequency signals has decayed to a very low level, and the signal transmission between the WiFi base station and the consumer equipment is not affected by the noises produced by these high frequency signals which have been reflected twice. 
     Therefore, the interference-free antenna module can raise the transmission efficiency of transmitting high frequency signals between a WiFi base station and a consumer equipment, and the SNR of transmitting the high frequency signals is not decreased because of those high frequency signals which have been reflected twice. 
       FIG. 3  is a schematic view of a WiFi network system according to an embodiment of the invention. As shown in  FIG. 3 , the WiFi network system includes a WiFi base station  3  and a consumer equipment  4 . The distance between the WiFi base station  3  and the consumer equipment  4  can exceed 250 meters. In this case, the coverage of the WiFi base station  3  in the invention is far greater than that of a typical WiFi base station (the radius is about 75 to 150 meters). 
       FIG. 4  is a schematic view of the WiFi base station  3  according to an embodiment of the invention. As shown in  FIG. 4 , the WiFi base station  3  includes an interference-free antenna module  31  and a first signal processor  32 . The interference-free antenna module  31  has a plurality of first high frequency transceivers  311  to  316  and a first antenna controller  317 . The first high frequency transceivers  311  to  316  face different directions respectively. The first antenna controller  317  is electrically coupled to the first high frequency transceivers  311  to  316  respectively. In addition, the first antenna controller  317  is electrically coupled to the first signal processor  32  in order to select one of the first high frequency transceivers  311 ,  312 ,  313 ,  314 ,  315  or  316  based on a signal transmitting/receiving request output by the first signal processor  32  to thereby transmit or receive a circularly polarized first high frequency signal. Meanwhile, as shown in  FIG. 3 , the WiFi base station  3  is electrically coupled to a remote server  34  through a physical network line  33 . In this embodiment, the physical network line  33  can be a network cable of a backbone network, and the remote server is a server located in a switch room. 
       FIG. 5  is a schematic view of the WiFi base station  3  installed on the roof of a room according to an embodiment of the invention. As shown in  FIG. 5 , the WiFi base station  3 , which has a metal case  35 , is installed on the roof of a room. The first high frequency transceivers  311  to  316  are implemented respectively on the metal case  35  facing different directions to thereby transmit or receive the circularly polarized first high frequency signals at different directions. 
       FIG. 6  is a schematic view of the consumer equipment interference-free antenna module  4  according to an embodiment of the invention. As shown in  FIG. 6 , the consumer equipment  4  includes a consumer equipment interference-free antenna module  41  and a second signal processor  42 . The consumer equipment interference-free antenna module  41  has a circular polarization antenna unit  411  to transmit or receive a circularly polarized second high frequency signal. In this embodiment, the circular polarization antenna unit  411  includes a horizontal antenna portion  4111 , a vertical antenna portion  4112  and a signal mixing portion  4113 , and the signal mixing portion  4113  is electrically coupled to the horizontal antenna portion  4111  and the vertical antenna portion  4112  respectively. In addition, a horizontal high frequency signal transmitted or received by the horizontal antenna portion  4111  and a vertical high frequency signal transmitted or received by the vertical antenna portion  4112  have a 90-degree phase difference. 
     In addition, since the circular polarization antenna unit  411  functions as a circular polarization filter, only a second high frequency signal with a specific circular polarization (such as a left-hand circular polarization) can be delivered to the second signal processor  41 . Further, as shown in  FIG. 3 , one of the first high frequency transceivers  311 ,  312 ,  313 ,  314 ,  315  and  316  faces the consumer equipment  4  (in this case, the first high frequency transceiver  311 ). The consumer equipment  4  is a WiFi mobile phone. 
     The antenna module  31  shown in  FIG. 4  has six first high frequency transceivers  311  to  316 , which are patch array antennas, and each of them has a rectangle plate  3111 ,  3121 ,  3131 ,  3141 ,  3151 ,  3161  with a size of 5 cm×5 cm. The first antenna controller  317  includes a circular polarization filter portion  3171  to filter the first high frequency signals received by the high frequency transceivers  311  to  316  respectively. Thus, only a first high frequency signal with a specific circular polarization (such as a left-hand circular polarization) can be delivered to the first signal processor  32  of the WiFi base station  3 . 
     Further, in this embodiment, the first antenna controller  317  includes an electronic scan switch circuit board  3172  to rapidly switch and select one of the first high frequency transceivers  311 ,  312 ,  313 ,  314 ,  315  and  316  electronically based on a signal transmitting/receiving request output by the first signal processor  32  to thereby transmit or receive a circularly polarized first high frequency signal. In this embodiment, the frequency of the first circularly polarized high frequency signals transmitted or received by the first high frequency transceivers  311 ,  312 ,  313 ,  314 ,  315  and  316  is around 2.4 GHz (the actual frequency may slightly vary upon the practical needs.) 
     As shown in  FIG. 3 , when the WiFi base station  3  receives a signal, which needs to be forwarded to the consumer equipment  4 , through the physical network line  33 , the WiFi base station  3  converts the signal into a corresponding circularly polarized first high frequency signal. Next, the first antenna controller  317  of the WiFi base station  3  selects the first high frequency transceiver  311  facing the consumer equipment  4  to transmit the first high frequency signal, and the circular polarization antenna unit  411  of the consumer equipment  4  thus receives the first high frequency signal. 
     In addition, when the consumer equipment  4  wishes to deliver a signal to the remote server  34 , the circular polarization antenna unit  411  of the consumer equipment  4  transmits a corresponding second high frequency signal, with a circular polarization. In this case, the first antenna controller  317  of the WiFi base station  3  selects the first high frequency transceiver  311  facing the consumer equipment  4  to receive the second high frequency signal. Next, the WiFi base station  3  converts the received second high frequency signal into a circuit signal and forwards the signal to the remote server  34  through the physical network line  33 . 
     It is noted that the number of first high frequency transceivers of the interference-free antenna module can be one to six, depending on the practical needs, but not limited to six as cited in this embodiment. In addition, depending on the practical needs, each of the high frequency transceivers can be a different type of antenna, which is capable of transmitting or receiving a circularly polarized high frequency signal, such as a waveguide slot array antenna or a sector horn antenna, but not limited to the patch array antenna as cited in this embodiment, and all the high frequency transceivers do not need to be the same type of antenna. The frequency of the first high frequency signal and the second high frequency signal can range between 2.3 GHz and 2.5 GHz, depending on the practical needs (such as in different environments), but not limited to 2.4 GHz as cited in this embodiment. 
     As stated, in this embodiment, since the WiFi base station  3  of the WiFi network system uses the first high frequency transceiver  311  of the interference-free antenna module  31  to transmit the first high frequency signal, which has a circular polarization characteristic (such as left-hand circular polarization), when the first high frequency signal is reflected by an obstacle (such as a building or vehicle), the circular polarization characteristic is changed (such as from left-hand circular polarization to right-hand circular polarization). Thus, as the circular polarization antenna unit  411  of the consumer equipment interference-free antenna module  41  of the consumer equipment  4  has a limit that only a first high frequency signal with a specific circular polarization (such as a left-hand circular polarization) can pass and be delivered to the second signal processor  42 , the first high frequency signals reflected by the obstacle cannot be delivered to the second signal processor  42  of the consumer equipment  4  even if they enter the circular polarization antenna unit  411  of the consumer equipment interference-free antenna module  41  of the consumer equipment  4 . 
     Similarly, since the high frequency signals transmitted by the circular polarization antenna unit  411  of the consumer equipment  4  have a circular polarization characteristic (such as a left-hand circular polarization), the circular polarization characteristic of the high frequency signals is changed (such as from left-hand to right-hand circular polarization) after being reflected by an obstacle (such as a building or vehicle). Thus, in this embodiment, as the circular polarization filter portion  3171  of the WiFi base station  3  of the WiFi network has a limit that only a high frequency signal with a specific circular polarization (such as a left-hand circular polarization) can pass and be delivered to the first signal processor  32 , the high frequency signals reflected by the obstacle cannot be delivered to the first signal processor  32  of the WiFi base station  3  even if they enter the high frequency transceivers  311  to  316  of the interference-free antenna module of the WiFi base station  3  of the WiFi network system. Accordingly, the noises produced by the high frequency signals which have been reflected are effectively suppressed, and the WiFi network system of another embodiment can improve the transmission efficiency of the high frequency signals between a WiFi base station and a consumer device. 
     Since the circular polarization characteristic of the high frequency signals is changed after the signals being reflected by the obstacle, the circular polarization characteristic can be restored to the original circular polarization (such as the left-hand circular polarization) when the high frequency signals are reflected again. In this case, although the circularly polarized high frequency signals (transmitted by the circular polarization antenna unit of the consumer equipment), which have been reflected twice, can pass the circular polarization filter portion  3171  of the first antenna controller  317  of the WiFi base station  3  of the WiFi network system to be delivered to the signal processor  32 , the strength of the high frequency signals is decayed to a very low level after being reflected twice, and the signal transmission between the WiFi base station and the consumer equipment is not affected by the noises produced by the high frequency signals, which have been reflected twice. 
     Similarly, although the circularly polarized high frequency signals (transmitted by the first high frequency transceivers  311  to  316  of the interference-free antenna module  312  of the WiFi base station  3  of the WiFi network system) can pass the circular polarization filter portion of the consumer equipment to the signal processor after being reflected twice, the strength of the high frequency signals is also decayed to a very low level after being reflected twice, and the signal transmission between the WiFi base station and the consumer equipment is not affected by the noises produced by the high frequency signals which have been reflected twice. Therefore, in the other embodiment, the WiFi network system can improve the transmission efficiency of a high frequency signal between the WiFi base station and the consumer equipment, and the SNR of transmitting the high frequency signal is not reduced by the high frequency signals which have been reflected twice. In addition, the system can effectively expand the coverage of the WiFi base station while maintaining a desired QoS. 
     Briefly, since the high frequency signals transmitted by the high frequency transceivers of the interference-free antenna module have a circular polarization characteristic (such as a left-hand circular polarization), and in this case the circular polarization characteristic of the high frequency signals is changed (such as from left-hand circular polarization to right-hand circular polarization) after being reflected by an obstacle (such as a building or vehicle), only a high frequency signal with a specific circular polarization (such as a left-hand circular polarization) can be delivered to the signal processor of the consumer equipment. The high frequency signals, which have been reflected by the obstacle, cannot be delivered to the signal processor of the consumer equipment even if they enter the circular polarization antenna unit of the consumer equipment, because their circular polarization characteristic is changed (in this case, it is changed to right-hand circular polarization). Accordingly, the noises produced by the high frequency signals which have been reflected are effectively suppressed, and the interference-free antenna module of the invention can improve the SNR and the transmission efficiency of transmitting the high frequency signals between the WiFi base station and the consumer equipment. 
     Similarly, since all of the high frequency transceivers respectively belonged to the antenna module in the WiFi base station and the consumer equipment of the WiFi network system can transmit or receive a circularly polarized high frequency signal, the corresponding consumer equipment (or WiFi base station) can easily receive the circularly polarized high frequency signal when the WiFi base station (or the consumer equipment) transmits the circularly polarized high frequency signal, and the SNR and the transmission efficiency of transmitting the high frequency signals are both improved. Therefore, the coverage of the WiFi base station of the WiFi network system can be expanded while the system remains a certain desired QoS. 
     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.