Abstract:
A wave receiving apparatus comprising a reflector; a conduit for guiding waves, having an open end allowing entrance of polarized waves reflected by the reflector; a septum polarizer monolithically formed with the conduit for effecting a circular-linear polarization conversion; a pair of signal collectors pointing to the same direction or towards each other and positioned at a distance of quarter-wavelength away from the rear end of the conduit for receiving wave signals; and a circuitry module, positioned sidelong next to said conduit seen from said open end into said conduit, to which the signal collectors are electrically connected for handling wave signals.

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to Taiwan application No. 090213599 entitled “Wave receiving apparatus with parallel feeding elements” filed on Aug. 9, 2001. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to satellite communication technology. More particularly it relates to a wave feed structure for use in conjunction with an antenna dish for receiving satellite signals from space. 
     2. Description of the Related Art 
     Satellite communication is gaining importance in this world of real-time digital distribution of audio and video data around the globe. It is known that for the purpose of increasing the data capacity of a satellite system, for example a direct broadcast system (DBS), the technique of giving polarizations to data-carrying waves is commonly utilized. Polarization of an electromagnetic wave refers to the direction of the time-varying electric intensity field vector of the wave traveling in space. A linearly polarized (LP) wave is one whose electric intensity field vector points to a fixed direction, and a circularly or elliptically polarized (CP or EP) wave is one whose electric intensity field vector rotates periodically. Just as a LP wave can be decomposed into horizontal and vertical components in space quadrature, a traveling wave with circular or elliptic polarization can be constructed by superposition of two LP waves in space and time quadrature, that is, a horizontally polarized (HP) wave and a vertically polarized (VP) wave of 90-degree phase difference. In a typical satellite communication system, an antenna in the form of a reflector or dish with particular surface curvature is utilized to focus polarized waves collected from space into a signal feed device, such as a LNBF (Low Noise Block with integrated Feed) module, located in the focal point of the reflector surface. Since the reflector/LNBF assembly is a ground receiver with spatially fixed reception pins for detecting electric fields of waves transmitted from an orbiting satellite, when receiving CP waves characterized by rotating electric fields a device known as polarizer is required to convert CP waves into LP waves with spatially fixed electric fields for easy reception and vice versa. 
     FIG. 1, FIG. 2, and FIG. 3 illustrate the structure and construction of prior art LNBFs with polarizers. In FIG. 1 a , LNBF  100  includes a waveguide  110  having a horn opening at one end for receiving polarized waves reflected from an antenna dish which convey audio and video signals in satellite communication. The received waves are guided afterward along the hollow conduit there within. A LNB circuits unit  120  disposed near the sidewall of the waveguide  110  is responsible for adapting the received audio and video signals for output to a TV set or other user device. In the example of FIG. 1 b , LNBF  150  also includes a waveguide  160  for guiding received waves and a LNB circuits unit  170  for handling the signals contained in the received waves, but the LNB circuits unit  170  is mounted at the rear end of the waveguide  160 . The LNBF  100  is shorter in overall length compared to the LNBF  150 , and projects a smaller frontal area from a perspective looking into the horn opening. This is advantageous because when two LNBFs are required for an antenna dish capable of simultaneously receiving signals of two satellites, a LNBF with small frontal area allows itself to be more closely bundled with the adjacent one to reduce the lateral distance of the wave-receiving horns so that both can be more closely positioned at the focal point of the antenna dish, thereby upgrading their performance. It should be observed that the relative position between the waveguide and signal handling circuits in a LNBF module is subjected to system design choices. 
     FIG. 2 a  illustrates a polarizer  200  in the shape of two conducting plates set diametrically on the inner wall of the waveguide  110 . The physical effect of the polarizer  200  is to alter the cross-sectional area of waveguide  110  in such a way that one component of an incoming CP wave shifts phase relative to the other component in time quadrature, and the CP wave is converted into two in-phase LP components when the phase shift between them reaches 90 degrees. Another example for producing phase shift in polarized waves is illustrated in FIG. 2 b , wherein a dielectric slab  210  is added to the conducting waveguide  110  which alters due to changes in dielectric constant the phase velocity of one component of the received CP wave relative to the other to effect the CP/LP conversion. 
     FIG. 3 is a cross-sectional view of the waveguide  110 , showing the polarizer  200  diagonally placed therein and a pair of signal collector pins  310 ,  320 , one horizontal and the other vertical, protruding from the LNB circuits unit  120  into the hollow conduit thereof for collecting signals induced by the electric fields of polarized waves guided there within. Theoretically the conductor polarizer  200 , and similarly the dielectric polarizer  210 , is capable of converting the incoming CP wave into a LP wave that is to be received by the signal collector pins  310 ,  320 . But in practice the conversion may be incomplete due to an imperfect polarizer or polarization distortions found in the received waves after traveling through the impure medium of atmosphere, so that signal collector pins may experience signal interferences when placed too close to each other. To avoid incomplete conversion, or cross-polarization, and to attain better pin-to-pin isolation, conventional design therefore places the signal collector pins a distance apart from each other along the axis of the waveguide as illustrated in FIG.  4 . Usually a separating distance of half wavelength of the received wave is required for acceptable performance. Yet the distancing of the signal collector pins extends the overall length of the waveguide and hence a structurally bulky LNBF is formed. 
     In addition to the shortcomings of incomplete conversion of polarization and extended structure, conventional LNBF is disadvantageous in that, as shown in FIG.  3  and FIG. 4, the L-shaped collector pin  310  protruding form the LNB circuits unit  120  can not be easily and precisely positioned because it is not straight and conventionally Teflon materials are used to wrap around it which might produce gaps that make pin displacement and rotation possible, thereby causing inaccurate signal reception. Conventional LNBF is also disadvantageous in its manufacture processes. In the case of FIG. 2 a , the waveguide  110  and the conducting polarizer  200  cannot be integrally formed as one piece by casting due to the shape of the polarizer  200 . That is, the closed end portion of the waveguide  110  needs to be fixed to the rest after the cylindrical portion of the waveguide  110  and the conducting polarizer  200  are fabricated. Similarly in the case of FIG. 2 b , additional step of bonding or gluing the dielectric polarizer  210  to the inner wall of the cylindrical portion of the waveguide  110  is necessary after the waveguide  110  is molded. In both cases, the waveguide/polarizer structure requires extra manual labor in its production. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to overcome the shortcomings of conventional LNBF described in the last section. The present invention consists of a conduit for guiding waves, having an open end allowing entrance of polarized waves reflected by the reflector; a septum polarizer monolithically formed with the conduit for effecting a circular-linear polarization conversion; a pair of signal collectors pointing to the same direction or towards each other and positioned at a distance of quarter-wavelength away from the rear end of the conduit for receiving wave signals; and a circuitry module, positioned sidelong next to said conduit seen from said open end into said conduit to which the signal collectors are electrically connected for handling wave signals. 
     Under such construction, the manual labor in the manufacture process is reduced by monolithically forming the septum polarizer with the conduit. The frontal area of the wave receiving apparatus is minimized by placing the circuitry module on the side instead of on the back of the wave-guiding conduit. Pin-to-pin isolation is improved by using the septum polarizer that thoroughly divides the conduit. And overall length of the conduit decreases, as the signal collectors are distanced less than half wavelength apart. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following detailed description, which is given by way of example, and not intended to limit the scope of the invention to the embodiments described herein, can best be understood in conjunction with the accompanying drawings, in which: 
     FIG. 1 a  and FIG. 1 b  illustrate the size and shape of two examples of conventional LNBF. 
     FIG. 2 a  and FIG. 2 b  illustrate two examples of polarizer installed inside a waveguide according to the prior art. 
     FIG. 3 illustrates how the signal reception pins and the polarizer relate to one another in the hollow conduit of waveguide of a conventional LNBF. 
     FIG. 4 illustrates how the signal reception pins are distanced form each other in the hollow conduit of waveguide of a conventional LNBF. 
     FIG. 5 illustrates the shape of the first embodiment of a polarized wave receiver according to the present invention. 
     FIG. 6 a  and FIG. 6 b  illustrate the spatial relationship between the polarizer and reception pins in the waveguide of the first embodiment according to the present invention. 
     FIG. 7 illustrates the shape of the second embodiment of a polarized wave receiver according to the present invention. 
     FIG. 8 a , FIG. 8 b  and FIG. 8 c  illustrate the spatial relationship between the polarizer and reception pins in the waveguide of the second embodiment according to the present invention. 
     FIG. 9 illustrates one implementation of the present invention with antenna dish 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Herein below is presented a detailed description of the present invention conforming to the disclosure requirement according to patent law. First please refer to FIG. 5, which illustrates the shape of the first embodiment of a polarized wave receiver according to the present invention. Polarized wave receiver  500  consists of a hollow waveguide  510  for guiding electromagnetic waves with polarizations and a side-mounted LNB unit  510  for handling signals contained in the received waves. The waveguide  510  includes an open end  512  that has practically a horn-like profile for collecting waves, and is closed at the other end  511  to establish a rear end boundary for the waves propagating therein. As already explained hereinabove, by placing the LNB unit  510  along the sidewall instead of the closed end  511  of the waveguide  510 , the wave receiver  500  possesses a reduced frontal area which permits more compact arrangements when applied to a dual-feed satellite antenna system. 
     FIG. 6 a  and FIG. 6 b  illustrate the spatial relationship between the polarizer and reception pins in the waveguide of the first embodiment according to the present invention. A septum polarizer  600 , with stepped front edge, is longitudinally formed in the waveguide  510  and partitions the waveguide cavity into two in which reception pin  610 ,  620 , both sticking out from the LNB unit  520  with a L shape and hidden inside a linkage structure  590 , are located respectively. The septum polarizer  600  is substantially a conducting plate extending longitudinally towards the open end and can therefore be molded monolithically with the waveguide  510  without the shortcomings explained hereinabove of additional manual labor in fixing the rear end of waveguide and gluing dielectric slab. The septum polarizer  600  also works better in effecting CP/LP conversion for it divides the waveguide  510  into two smaller separate waveguides, a structure not realized by the diagonally-placed plate polarizer  200  and dielectric polarizer  210  of FIG. 2, which minimizes the cross-polarization interferences between reception pins  610 ,  620 . This is reflected in the present embodiment that a good pin-to-pin isolation can be obtained even though the reception pins  610 ,  620  are arranged to lie in the same cross section plane of the waveguide  510  without the requisite quarter-wavelength distancing as shown in FIG.  4 . One observes in this regard that the waveguide  510  is made at least a quarter wavelength shorter than those described hereinabove. 
     The septum polarizer  600  functions with such an effect that a right-hand circularly polarized (RHCP) wave propagating across the feed horn  512  will be converted into a LP wave and at the same time directed to the upper cavity  611  to be received by the reception pin  610  positioned a quarter wavelength from the rear end  511 . By the same token, a left-hand circularly polarized (LHCP) wave propagating across the feed horn  512  will be converted into a LP wave directed to the lower cavity  621  to be received by the reception pin  620  which is also positioned a quarter wavelength from the rear end  511 . The CP/LP conversion is basically resulted from interactions of waves with the stepped front edge. Accordingly, the reception pins  610 ,  620  are located after the front edge portion where polarization conversion is completed. It should be understood by one skilled in the art that a septum polarizer with other front edge profiles could also do the same. By properly choosing the length of the polarization-converting portion of the septum polarizer  600  and the relative position of the reception pins  610 ,  620 , a shorter waveguide  510  and hence a more compact polarized wave receiver  500  is obtained. 
     Although the wave receiver  500  in the first example possesses advantages over the prior art, one may observe that it still needs improvement, for the L-shaped reception pins  610 ,  620  suffer the same problem of imprecise positioning and hence inaccurate reception as described in the example of FIG.  3 . The second embodiment of the present invention provides a way to resolve this problem. FIG. 7 illustrates the shape of the second embodiment of a polarized wave receiver according to the present invention. As in the first embodiment, the wave receiver  700  also consists of a LNB unit  720  attached to the side wall of a waveguide structure  710  that is closed at the rear end  711  but open at the opposite end to form a feed horn structure  712  for collecting waves. The main difference in the second embodiment is that the linkage structure  590  requisite for accommodating the L-shaped reception pins in the first embodiment is eliminated, thereby giving the wave receiver  700  a simplified profile. 
     FIG. 8 a , FIG. 8 b  and FIG. 8 c  illustrate the spatial relationship between the polarizer and reception pins in the waveguide of the second embodiment according to the present invention. The internal structure of the waveguide  710  is similar to the first embodiment, except that, for the purpose of eliminating the L-structure of reception pins and minimizing the problem of imprecise positioning and inaccurate reception thereof, the polarizer  800  separates the waveguide  710  into upper cavity  811  having a greater depth D 1  and lower cavity  821  having a depth D 2  less than D 1 . A reception pin  810  in the form of a straight wand sticks out directly from the circuits of the LNB unit  720 , and through an opening  801  disposed in an suitable location on the polarizer  800  behind the rear end boundary of the lower cavity  821  protrudes into the upper cavity  811  for receiving LP waves converted from RHCP waves entering into the feed horn  712 . Similarly, a straight reception pin  820  sticks out directly from the circuits of the LNB unit  720 , and through the side wall of the waveguide  710  protrudes into the lower cavity  821  for receiving LP waves converted from LHCP waves entering into the feed horn  712 . One readily observes that the reception pins  810 ,  820  protrude laterally into waveguide cavities from the same direction, while in the example of FIG. 6 b  the reception pins  610 ,  620  protrude diametrically from opposite directions. A skilled artist should realize that by rendering the reception pins straight precise positioning and accurate reception could be more easily achieved without the problems of pin displacement and rotation encountered in previous examples. 
     The reception pin  810  is placed a quarter wavelength away from the rear end of the upper cavity  811 , and the reception pin  820  is placed a quarter wavelength away from the rear end of the lower cavity  821 . Since the reception pin  810  is behind the rear end boundary of the lower cavity  821 , such a construction creates a pin-to-pin distance of no less than a quarter wavelength in the longitudinal direction of the waveguide  710 . Even so, it is still possible and beneficial in the present embodiment to limit the distance to less than a half wavelength employed in the example of FIG.  4 . In this regard, the overall length of the waveguide  710  and the wave receiver  700  is reduced and the advantage is preserved. 
     FIG. 9 illustrates one implementation the polarized wave receiver of the present invention with an antenna dish in a satellite antenna system. The satellite antenna system  900  includes an antenna dish or reflector  901  for collecting electromagnetic waves transmitted by a satellite and a wave receiver  904  for receiving and processing the waves collected and reflected by the dish surface. The wave receiver  904  is shorter and more compact than conventional ones and possesses other advantages already described hereinabove. It is placed preferably at the focal point of the antenna dish  901  for best reception if the dish surface is a paraboloid. In dual-feed applications, it may also be placed along with other similar LNBF at the focal point of the antenna dish  901  that has a surface capable of receiving waves from different satellites simultaneously. The present invention is particularly useful under such circumstances due to its reduced size and frontal area. 
     Having described the present invention, it is noted that the embodiments and particular features and functions as disclosed hereinabove are for the purpose of disclosure only and are not in any sense for limiting the scope of the invention. Small modifications and juxtapositions of one or more of the functional elements anticipated by those skilled in the art without departing the spirit of present invention is to be regarded as a part of the invention. Therefore, that the scope of present invention is determined by the appended claims is fully understood.