BACKGROUND Generally, there have been two basic types of center-fed reflector antenna systems: the "Cassagrain"system and center waveguides with various back feed options. Herein,"E"in connection with transmission waves refers to an electric wave, and"H"refers to a magnetic wave. The abbreviation"EM"is employed to denote"electromagnetic". The Cassagrain systems generally provide efficient transmission with balanced E and H plane patterns.

However, these systems generally produce substantial obstruction of the wave energy reflected from the main reflector or antenna dish.

FIGURE 1 illustrates a typical prior art Cassagrain reflector antenna system.

Generally a waveguide 102 extends forth from a main reflector 101 and directs wave energy toward subreflector 103 employing a horn geometry at the end of the waveguide 102.

Generally, the subreflector 103 may be located at a distance which is selected for effective E and H plane control. The space along a radiation path leading out of the center of the main reflector 101 is generally the most important region for transmitting waves from the main reflector in order to obtain a desirable radiation pattern with minimal side lobes. The Cassagrain antenna presents the problem that this transmission path is substantially blocked by subreflector 103. Because the subreflector 103 blocks an important region of the reflector's transmission and reception path, the beam formed by the combination of those reflections which are not obstructed by the subreflector 103 usually includes substantial side lobes and is generally inefficient from a power standpoint.

Another prior art waveguide feed system includes a waveguide which has a cap at one end for directing transmission energy toward a main reflector. Where a small cap, or "bottlecap"as it is often called, is used, there is generally less transmission obstruction than with Cassagrain systems. However, employing a waveguide cap generally does not permit good balancing of the E and H patterns. As a result, the side lobe levels from the main reflector are generally poor, and the efficiency mediocre. Proper control of the E and H plane patterns generally requires careful placement of the reflector, in this case a cap, with respect

to the end of the waveguide. Performance problems with the bottlecap wave reflector generally arise because the proximity of the cap to the waveguide removes the option of strategically locating the cap and thereby disables the control of the E and H plane patterns.

Another type of prior art system involves bending the waveguide so as to point toward the main reflector and deploying a single hom at the end of the waveguide to feed energy toward the main reflector. Such an approach generally enables the E and H patterns to be balanced. However, transmission obstruction caused by the waveguide geometry generally causes high obstruction-induced side lobe levels.

It is a problem in the art that existing antenna systems do not simultaneously provide for an unobstructed reflection path from a main reflector while also allowing independent control of E and H plane patterns.

It is a problem in the art that when using waveguide caps, E and H patterns are not balanced, thereby resulting in poor side lobe levels from the main reflector and mediocre transmission efficiency.

It is a still further problem in the art that Cassagrain systems present obstructions of substantial size in a central region of the reflector's radiation path.

It is a still further problem in the art that the use of horn mounted on a waveguide to feed a main reflector causes blockage which causes high side lobe levels in a resulting radiation pattern.

SUMMARY OF THE INVENTION These and other objects, features and technical advantages are achieved by a system and method which split a waveguide signal directed along a center waveguide into a plurality of divided waveguide signals and carefully redirect the divided signals along selected paths back toward a main reflector so as to achieve minimum obstruction of the plurality of beams resulting in an improved radiation pattern with reduced side lobes. Preferably, equipment for generating the plurality of divided signals and aiming these signals toward the main reflector is disposed within a footprint which is very small in relation to the diameter of the main reflector thereby resulting in correspondingly small side lobes in the radiation pattern generated by reflections from the main reflector dish. The inventive system and method, in a corresponding manner, operates to provide an equivalently efficient reception pattern with low side lobes for the case of energy inbound to the reflector.

Paths leading away from a main center waveguide are referred herein as"waveguide segments"or split waveguide portions."Energy transmitted within the waveguide is referred to as the"waveguide signal,"and energy within the split waveguide portions as"signals," "split signals,"or"split waveguide signals."The region to which the entire antenna system effectively transmits energy to is referred to as a"transmission pattern,"and the region from which energy is received is referred to as a"reception pattern." In a preferred embodiment, each of the waveguide segments leading away from the center waveguide is preferably directed toward the reflector dish and ends in a termination point, or air interface. Herein, the term"tributary"refers to paths or signals which lead from a common origin or destination along a plurality of separate paths, such as the case of waveguide segments leading away from the center waveguide.

In a preferred embodiment, a center waveguide extends outward from a main reflector surface. The waveguide is preferably split into two portions thereby forming a"tee"in the E plane with each such portion carrying a separate component of the original signal. The two

portions, or waveguide segments, are then preferably bent at an E plane bend thereby further redirecting the split beams back toward the main reflector.

In a preferred embodiment, the inventive mechanism enables accurate and efficient transmission and reception of EM energy. For the case of antenna reception, energy is received by the main reflector from a plurality of transmitters, which may be at customer premise sites, and reflected toward the termination points of the split waveguide portions.

The energy received at the termination points, or airborne waveguide reception energy, is then preferably directed along the feed lines or waveguide portions or segments in the form of waveguide signals. The waveguide signals are preferably redirected by an E-plane bend or other suitable device, and combined into a single waveguide signal for transmission along the center waveguide employing an E-plane tee which preferably further reorients the waveguide signal for transmission toward appropriate reception circuitry.

In general, a conceptually ideal configuration for a reflector antenna system would comprise a radiation source located at the focal point of the main reflector, thereby generating a transmission suitable for generating ideal E and H plane distributions in the reflected energy, and for ensuring optimal symmetry for transmissions to all points on the dish. The ideal source would preferably occupy no physical space so as to avoid obstructing energy reflected by the main reflector. This ideal configuration would then operate to produce an essentially perfect radiation pattern with no side lobes. The ideal configuration is evidently unrealizable because of the need for a radiation source which has no volume and which has no physical structure holding it in place at the ideal location. The inventive design attempts to supply a radiation mechanism for the reflector which operates to emulate a single source transmission with two closely spaced transmission sources symmetrically located with respect to the ideal source location and embodied in a physically realizable design.

In a preferred embodiment, the split portions of the waveguide, or waveguide segments, and their respective termination points, are preferably located in very close proximity to one another, so as to closely emulate a single source transmission. The

preferably two termination points are also preferably located equidistant from the main reflector focal point. Preferably, the termination points of the two split waveguide portions each illuminate an associated portion of the reflector dish thereby preferably providing symmetrical wave energy reflections from the two halves of the reflector surface. There may, but need not be, overlap between the portions of the reflector dish associated with each of the two split waveguide portions. Although the waveguide and feed structure do present some obstruction to waves reflected from the reflector surface, the obstruction faced by energy reflected from both portions of the reflector surface are substantially equivalent.

In contrast, the single bent waveguide and hom arrangement of the prior art will generally illuminate one side of the reflector more than the other and also provide an obstruction which asymmetrically blocks energy from some portions of the dish more than others. Accordingly, the prior art system will generally transmit more energy from the"horn side"of the bent waveguide than from the opposing side of the bent waveguide and will accordingly produce a radiation pattern which is geometrically biased toward one side of the reflector. This biased radiation pattern will also generally include substantial side lobe levels.

Accordingly, the inventive antenna system presents considerable advantages of the prior art bent waveguide embodiment.

The present invention also presents considerable advantages not experienced by merely placing two of the prior art bent waveguides with radiating horns next to each other.

Placing two prior art bent waveguides next to each other would substantially increase the obstruction of the reflector's reflection path thereby exacerbating the problem of undesired destructive interference and associated high side lobe levels in the resulting radiation pattern.

Employing two separate prior art bent waveguides terminating in horns would also make it difficult to bring the radiating two horns of the bent waveguides into close proximity which is desirable to emulate operation of a single ideal radiation source, as discussed above.

Furthermore, merely placing two bent waveguides next to each other leaves open the possibility that transmissions from the two horns might destructively interfere with one

another. The deployment of two separate waveguides would also require deploying the additional hardware associated with a second waveguide.

In a preferred embodiment of the present invention, the inventive split waveguide incorporates features which overcome the above-stated difficulties associated with merely placing two bent waveguides having transmission homs side by side. The deployment of one rather than two main waveguides substantially reduces the obstruction of the dish reflection path. Necking down or tapering the cross sectional area of the single center waveguide to a greater degree with increasing proximity to the feed structure still further reduces obstruction of the dish reflection path. Furthermore, the use of a single center waveguide with a feed structure which splits the waveguide into two or more waveguide segments enables the termination points or air interfaces of the two or more waveguide segments to be readily placed in close proximity to one another thereby more effectively emulating the ideal of a single radiation source than would be possible by placing two similar bent waveguide structures adjacent to one another.

In a preferred embodiment, the tee and bend, or other appropriate devices, operate, along with the feed lines, to split the waveguide portions away from the center waveguide toward the left and right when viewed in the E plane, thus establishing and E-plane tee, and an E-plane bend. Performing this division in the E-plane is convenient since the thickness of the E plane of a waveguide is generally less than that of the H plane. Thus, the use of an E plane tee and an E plane bend, as described above, enables waveguide segments to spread out within the greater available depth or thickness of the H plane of the waveguide. However, in an alternative embodiment, the waveguide could be split toward the left and right within the H plane, and this variation is included in the scope of the present invention.

In a preferred embodiment, the undivided portion of the waveguide, or center waveguide, is"necked down"or tapered to an increasing degree with increasing proximity to the feed structure atop the center waveguide. The reduction in diameter of the center waveguide enables the waveguide segments to be closer together and enables the overall feed

structure to obstruct the dish reflection path less than if the waveguide were of constant diameter.

In a preferred embodiment, the width and height of the feed structure may be selected and optimized in relation to the reflector dish to beneficially affect the radiation pattern.

Generally, the feed structure's height is aligned with the E plane, and its width with the H plane. Independent control of the width and height of the feed structure preferably enable independent control of the E and H plane distributions. Ensuring proper matching of the E and H plane distributions minimizes undesired destructive interference, thereby minimizing side lobes and improving the radiation pattern.

In a preferred embodiment, in addition to disposing the feed structure in a small footprint to minimize obstruction of waves reflected off the main reflector, the overall reflector antenna system may be disposed in a smaller footprint than a prior art antenna system capable of transmitting a pattern of comparable magnitude. Because of the obstruction presented by subreflectors in prior art reflector antenna systems, main reflectors have been enlarged to provide for greater area on the main reflector from which waves may be reflected without being blocked by the subreflector. Such main reflector enlargement is unnecessary in the present invention because of the reduced reflection path obstruction, thereby enabling the antenna system to achieve greater transmission signal magnitude gain for a constant main reflector size than prior art systems.

It is an advantage of the present invention that the E and H plane patterns can be independently controlled and optimized.

It is a further advantage of the present invention that tapered design of the center waveguide enables the feed structure to be disposed atop the center waveguide with minimal obstruction of the main reflector's reflection path.

It is a still further advantage of the present invention that the small size of the feed structure presents minimal obstruction for waves being reflected from the main reflector, thereby enabling a desirable transmission pattern with reduced side lobe levels.

It is a still further advantage of the present invention that the reduced obstruction of reflected waves presented by the inventive feed enables a reduction in size of the main reflector while maintaining the same transmission intensity as prior art antenna systems.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: FIGURE 1 illustrates a typical prior art Cassagrain antenna system; FIGURE 2 depicts a center fed reflector antenna system according to a preferred embodiment of the present invention; FIGURE 3 depicts a detailed E plane view of the waveguide and feed according to a preferred embodiment of the present invention; FIGURE 4 depicts a top view of the waveguide and feed according to a preferred embodiment of the present invention; FIGURE 5 depicts an isometric view of the waveguide and feed according to a preferred embodiment of the present invention; FIGURE 6 depicts a theoretically ideal single transmission source for achieving ideal illumination of the reflector and an ideal radiation pattern; FIGURE 7 depicts a subreflector system and radiation pattern typical in a prior art system; and FIGURE 8 depicts a waveguide configuration and resulting radiation pattern according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION FIGURE 2 depicts a center fed reflector antenna system 200 according to a preferred embodiment of the present invention. FIGURE 2 presents an E plane cross section view of the inventive reflector fed antenna system.

In a preferred embodiment, a waveguide 202 extends out from a main reflector 201 in a direction substantially normal to the plane of the main reflector 201 at the junction point of the waveguide 202 and the main reflector 201. Preferably, the center waveguide 202 terminates in a feed or feed structure 203 which redirects the energy transmitted in the waveguide back toward the main reflector 201. Generally, physical and EM properties of the feed 203 affect the properties of EM transmission back to the reflector 201 and of the EM energy reflected from reflector 201. The waveguide 202 may be affixed to the reflector 201 or affixed to a bracket and suspended in position above the reflector. The invention is not limited to the deployment of any particular attachment mechanism for center waveguide 202.

In a preferred embodiment, feed or feed structure 203 comprises equipment for splitting an original signal directed away from reflector 201 along waveguide 202 into a plurality of divided signals and for redirecting the split or divided signals back toward the reflector 201. Although the specific example of the inventive device depicted in FIGURE 2 will be discussed in detail, it will be noted that the original signal may be split into any number of divided signals, and angularly redirected by a range of different angular distances within feed structure 203. Furthermore, the splitting or division of the original signal need not occur at only one point, but may be accomplished in stages at different points within feed structure 203. Similarly, the angular redirection of either the original signal or of the split signals may be accomplished at a number of different stages within feed structure 203.

In a preferred embodiment, for the case of transmission by antenna system 200, waveguide 202 carries an original signal toward feed 203. Within feed 203, an E-plane tee 204 preferably splits the original signal into two substantially equal split signals and redirects each split signal by approximately ninety degrees, one toward the left and the other toward

the right from the direction of the original signal in the view of FIGURE 2. Preferably, the waveguide itself is split into two split portions, waveguide segments, or feed lines, each of which carries a split signal. The split signals are preferably of substantially equal magnitude.

The E plane tee preferably operates as a power divider between the various waveguide segments. Thereafter, the E plane bend operates to redirect the waveguide segments by approximately 90 degrees more, thereby redirecting the waveguide portions toward the reflector dish. It will be appreciated that the angular redirection need not be distributed equally between the E plane tee and the E plane bend. The redirection may be accomplished in varying amounts by one or more devices of varying geometries within feed structure 203.

In an alternative embodiment, the center waveguide 202 need not be split only two ways employing a tee. The number of waveguide segments leading away from center waveguide 202 may be a number greater than two, and a wide range of devices may be employed for accomplishing a required junction between the waveguide segments and the center waveguide 202, and all such variations are included in the scope of the present invention.

In an alternative embodiment, the signals on the waveguide segments connected to the center waveguide need not be substantially equal but may have magnitudes which are adjustable according to the needs of a particular application. For example, where various split signals are used to illuminate concentric regions of a reflector dish, the signals illuminating outer portions of the reflector may be reduced in magnitude to provide aperture tapering, if desired, and all such variations are included in the scope of the invention.

In a preferred embodiment, feed structure 203 is disposed within a small footprint thereby minimizing obstruction of the radiation path of main reflector 201. Furthermore, the external geometry of feed 203 is preferably shaped so as to further reduce obstruction of both transmitted and received wave energy by minimizing protrusion of the feed structure 203 into the radiation path of main reflector 201.

It will be appreciated that the above discussion of center fed antenna system 200 operates to receive energy in a similar but reverse manner to the operation of outbound transmitted energy discussed above. For the case of reception at antenna system 2G0, energy arrives at reflector dish 201 from a reception pattern (not shown), wherein broadcasting customer premise sites are preferably located, which is analogous to the radiation or transmission pattern discussed in the case of outbound transmissions. Incoming energy arrives at reflector 201 and is directed toward termination points 206 of the waveguide segments in feed 203. The airborne waveguide reception energy received at termination points 206 is converted into waveguide signals in the preferably two split waveguide portions. The signals in the split waveguide portions are then preferably redirected at the E plane bends 205, and then preferably combined into a single signal at the E plane tee 204.

The combined signal is then preferably further redirected at the E plane tee so as to travel along waveguide 202 toward reception circuitry (not shown) at the other end of waveguide 202.

In a preferred embodiment, feed 203 is integrated into the construction of center waveguide 202. The waveguide 202 may still consist of more than one part, but each part may incorporate part of the feed and part of the shaft of the center waveguide 202.

Alternatively, feed 203 may be a separate part which is attachable to waveguide 202. Where feed 203 is a separate part, different feeds 203, having different geometric characteristics, and possibly, different numbers of waveguide segments along which to direct split signals, may be attachable to a single waveguide, thereby providing for the ability to connect and disconnect, in a modular manner, a variety of different feeds to a single waveguide.

FIGURE 3 depicts a detailed E plane view of waveguide 202 and feed 203 according to a preferred embodiment of the present invention. FIGURE 4 depicts a top view of the waveguide 202 and feed 203 according to a preferred embodiment of the present invention.

The dimension C 301 (FIGURE 3) indicates the focal length of reflector 201. Dimension A 401 identifies the width dimension of the waveguide 202, and dimension B 402 identifies the

height of the waveguide 202. The ability to independently control the values of dimensions A 401 and B 402 of waveguide 202 preferably enables the independent control of the E and H plane distributions of airborne waveguide transmissions emerging from feed 203.

In a preferred embodiment, optimum illumination of the dish is obtained with a transmission having a sine wave distribution across the dish for both the E and H planes wherein the transmission intensity is 10 decibels (dB) lower at the periphery of dish 201 than at the center of dish 201. Such a transmission generally provides good efficiency with low side lobe levels. A transmission having such a 10 dB difference is referred to herein as having a 10 dB pattern.

Generally, the dimensions of reflector 201 and focal length 301 determine an angle "X"between the center portion waveguide 202 and a straight line between termination point 206 and an edge of reflector 201. The dimensions of A 401 and B 402 (FIGURE 4) generally operate to determine the distribution of transmission energy across reflector 201 for a fixed value of angle X. Generally, as dimensions A 401 and B 402 get smaller, a beam emerging from termination point 406 gets wider, thereby generally reducing the difference in illumination intensity between the center and the periphery of reflector 201. This difference in illumination intensity may be reduced to as little as 3 dB. Conversely, increasing dimensions A 401 and B 402 generally narrows the beam emerging from termination point 206 and generally increases the difference in illumination intensity between the center and periphery of reflector 201. Generally, for a known diameter and focal length of reflector 201, the values of A 401 and B 402 which will produce at 10 dB pattern may be unambiguously determined.

In a preferred embodiment, feed 203 is shaped so as to minimally obstruct the path of reflection from reflector 201. In the E plane cross section view of FIGURE 3, the external contour of split waveguide portion 207 is preferably shaped so as to provide the desired aperture for termination point 206 while minimizing interception of waves reflected from reflector 201.

In a preferred embodiment, the bottom of feed 203 is located in substantial proximity to the focal point of reflector 201, which reflector is preferably parabolic. Preferably, the focal length 301 and diameter of reflector 201 are selected in cooperation with one another so to produce an optimal radiation pattern.

FIGURE 5 depicts an isometric view of a portion of the waveguide 202 and feed 203 according to a preferred embodiment of the present invention. It is noted that the aperture of the termination point 206 of each waveguide segment or split portion of the waveguide is preferably sized so as to minimize obstruction of the reflection path from main reflector 201 (FIGURE 2) while still enabling appropriate illumination of respective portions of reflector 201 (FIGURE 2).

In a preferred embodiment, two parts such as the one depicted in FIGURE 5 are preferably joined so as to form a waveguide/feed combination. Each part may be milled or cast, and the parts then joined to generate an inexpensive option for producing the inventive feed structure. With this arrangement, for each half of the waveguide/feed combination as shown in FIGURE 5, the feed and waveguide"halves"are integrated into a single part.

Alternatively, a part such as the one depicted in FIGURE 5 may be fastened to a simple flat plate to create an even simpler and less expensive solution.

Although the embodiment of FIGURE 5 depicts a two way split of the original signal on waveguide 202, the invention is not limited to this embodiment. The original signal may be split into other numbers of split signals or divided signals and still be within the scope of the present invention.

In a preferred embodiment, the use of polytetrafluoroethylene (TEFLON (D) in the construction of waveguide 202 may be employed to enhance the EM transmission properties of the waveguide. Generally, filling a waveguide with a low loss plastic, such as polytetrafluoroethylene, operates to enable an increase in transmission bandwidth of a waveguide of given dimensions while maintaining good performance. Generally, two

parameters relevant for selection of materials to be deployed within waveguides are the dielectric constant and the loss tangent.

Generally, the bandwidth of a particular waveguide with known dimensions increases with increasing dielectric constant of the material disposed within the waveguide, thereby operating to favor use of material with a high dielectric constant. Due to considerations arising from the boundary between air and plastic within a waveguide however, an optimal dielectric constant for the material disposed in the waveguide is generally between 2 and 3.

Two exemplary materials suitable for use in waveguides for transmission bandwidth enhancement are TEFLON@ and cross-linked polystyrene with dielectric constants of 2.1 and 2.54, respectively. Generally, the loss tangent of a material indicates a rate at which radio frequency (RF) energy is converted into heat. TEFLON has a low loss tangent which, in combination with its dielectric constant, makes it a desirable material for deployment in waveguides.

Preferably, the enhancement of transmission properties preferably increases the available EM transmission bandwidth per unit of waveguide volume, thereby enabling a smaller waveguide and feed package to provide the same transmission bandwidth as a waveguide of larger size which does not include TEFLON. Such size reduction may be beneficially employed to still further reduce the footprint within the main reflector's reflection path of the waveguide and feed. The use of polytetrafluoroethylene may be used to particular advantage in the tapered portion of the waveguide (the portion closest to the feed) in order to preserve the bandwidth of the waveguide even where the waveguide has a small cross-sectional area. It will be appreciated that other plastics, including cross-linked polystyrene, and other materials may be substituted for TEFLON to enhance waveguide performance, and all such variations are included within the scope of the present invention.

FIGURE 6 depicts a theoretically ideal single transmission source for achieving ideal illumination of the reflector and an ideal radiation pattern. An ideal point transmission source 602 would uniformly illuminate reflector 601 and occupy no space so as to thereby present no 804961. 1

obstruction to waves reflected from reflector 601 toward radiation pattern 603. Consistent with this conceptually ideal arrangement, the E and H plane distributions would be perfectly aligned resulting in an ideal transmission pattern and reception pattern, be in the correct location, and include no side lobes. Since the described conceptually ideal arrangement is not physically realizable, practical antenna systems have attempted to imitate it as closely as possible. In the following, a prior art antenna and the inventive antenna, as well as their respective radiation patterns are discussed.- FIGURE 7 depicts a subreflector system and radiation pattern typical in a prior art system similar to the Cassagrain system discussed in connection with FIGURE 1. As previously discussed, one prior art antenna system includes a waveguide 702 which transmits energy toward subreflector 703 which illuminates reflector 701 thereby generating transmission and reception pattern 704. After reflector 701 is illuminated with energy from subreflector 703 much of the energy reflected from reflector 701 is blocked by subreflector 703 thereby causing undesired destructive interference in radiation pattern 704. The presence of a subreflector in a central region of the reflection path of reflector 701 causes many non- idealities in radiation pattern 704 including diminished intensity, a shape altered from that ideally desired, and the presence of undesired side lobes.

FIGURE 8 depicts a waveguide configuration and resulting radiation pattern according to a preferred embodiment of the present invention. In the inventive antenna system, for outbound energy transmission, energy is transmitted along waveguide 202, split among preferably two waveguide segments which end in termination points 206 which then illuminate their respective sectors of reflector dish 201. Energy reflected from reflector dish 201 combines to form radiation pattern 801. Since there is some amount of physical obstruction in the reflection path of reflector 201 in the form of the waveguide 202 and feed 203, some reflected energy is blocked and does not contribute to radiation pattern 801.

Although the obstruction presented by waveguide 202 and feed 203 causes some non- idealities in radiation pattern 801, these are generally far reduced in comparison with the non-

idealities of radiation pattern 704 because of the much reduced obstruction of the reflected wave path in comparison with that presented by the subreflector 703 (FIGURE 7) in the prior art svstem.

The inventive antenna is designed to emulate the conceptually ideal single point transmission source of FIGURE 6. Accordingly, the two waveguide portions are located close to each other and are preferably located equidistant from the location of the single point source in FIGURE 6. The use of two closely spaced transmission sources and the minimal obstruction of the reflection path of reflector 201 preferably combine to generate a transmission pattern which has minimal side lobes and is close to the ideal in terms of shape and intensity.

In a preferred embodiment, a number of features preferably combine to produce efficient and accurate transmission and reception of radio transmissions by the inventive antenna system. The features preferably include establishing two radiation sources 206 which are preferably proximate to each other and which are symmetrically located with respect to an ideal single point source.

In a preferred embodiment, a second factor beneficially affecting the transmission pattern is that of disposing the waveguide 202 and feed 203 in a small footprint thereby minimizing obstruction of the reflection path of main reflector 201 and the undesired destructive interference and side lobes which result from such obstruction. Generally, the ratio of the feed diameter to the diameter of the main reflector is proportional to the side lobe levels of the radiation pattern. It is therefore highly desirable to reduce the size of the feed for a given reflector size. Furthermore, once a feed of reduced size is achieved, the reduced obstruction of the reflector antenna path enables an antenna system to produce a radiation pattern of a particular intensity employing a smaller reflector dish thereby enabling not only the feed, but the entire antenna assembly to be disposed in a smaller package.

For example, in a typical prior art Cassagrain system, a reflector dish of 13.5 inches is employed in conjunction with a subreflector with a 2 inch diameter. Generally, the dish is

designed to be larger in order to compensate for the considerable obstruction of the dish's reflection path presented by the subreflector. In contrast, in one embodiment of the inventive antenna system, the feed is about 0.5 inches in diameter. Because of the reduced obstruction of the dish's reflection path in comparison with that presented by the subreflector, the dish or reflector may be reduced in size while maintaining the a radiation pattern of substantially the same intensity. One embodiment of the inventive antenna system employs a dish having a diameter of approximately 10.5 inches to provide an antenna gain comparable to the above mentioned Cassagrain system, with improved side lobe level control.

Generally, the side lobe level is proportional to the ratio of the diameter of any obstruction in the dish's reflection path to the diameter of the dish. For the exemplary prior art subreflector system discussed above, the pertinent ratio is 2/13.5 = 0.148. Whereas, in example of the inventive system discussed above, this ratio is 0.5/10.5 = 0.0476. These numbers represent approximately a three fold reduction in side lobe level magnitude in going from the prior art subreflector system to the inventive split waveguide system. Preferably, in the inventive system, the energy not being wasted producing undesired side lobes is productively directed toward the desired radiation pattern thereby providing an additional benefit to antenna system performance.

Alternatively, the side lobe level reduction benefit may be applied toward reducing the total energy required of the inventive antenna system for transmission purposes and a more sensitive and accurate signal detection ability for reception purposes. For both transmission and reception purposes, a reduced need for energy may enable less powerful and less cumbersome electrical equipment and circuitry to be employed thus leading to cost savings.

In a preferred embodiment, the above factors operate to benefit both transmission and reception of wave energy at the inventive antenna system. With respect to incoming signals, the inventive antenna system preferably operates to establish efficient reception such that signals arriving from areas from which reception is desired, such as designated customer

premise sites, combine constructively so as to produce clear and strong signals at waveguide 202. Furthermore, signals transmitted from regions from which reception is not desired are preferably not received with substantial intensity at waveguide 202. A desired transmission pattern having low side lobes is thereby established which applies equivalently for the cases of both outbound and inbound radio transmission.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.