Abstract:
Various exemplary embodiments relate to an antenna feed configured to receive a signal having a wavelength. They antenna feed may include a cylindrical body and four pin groups. Each pin group may include two pins in close proximity extending across the center of the cylindrical body. One of the two pins may be rotated approximately 22.5° from the angle of the other pin. Each pin group may be spaced approximately one quarter of a wavelength away from each other, and may be rotated approximately 22.5° from the angle of the previous pin group.

Description:
TECHNICAL FIELD 
     Various exemplary embodiments disclosed herein relate generally to antennas and orthomode couplers. 
     BACKGROUND 
     An antenna is a device that may be used to transmit or receive electromagnetic waves. The electromagnetic waves may be signals that carry information. The antenna may receive a signal by collecting electromagnetic waves in an electrical mode of a transmission line. The antenna may transmit a signal by converting the transmission line electrical mode into electromagnetic waves in free space. Antennas often use waveguides to transmit the electromagnetic waves. The electromagnetic waves have a polarization that may need to be known and controlled. Antennas may be vertically or horizontally polarized with respect to earth. The two polarizations may need to be separated or isolated from each other because they may contain different signals or information. In the case of high density antennas, the antenna feed may include two waveguides attached to an antenna feed horn. The waveguides may be bent in the same plane to minimize antenna pattern distortions. The waveguides may have additional bends to attach the waveguides to the feed in a way that accepts two orthogonal polarizations. Accordingly, there is a need to rotate the polarization of electromagnetic waves in a feed while minimizing the loss and size of the antenna feed horn, while also providing a large bandwidth of operation. 
     SUMMARY 
     A brief summary of various exemplary embodiments is presented. Some simplifications and omissions may be made in the following summary, which is intended to highlight and introduce some aspects of the various exemplary embodiments, but not to limit the scope of the invention. Detailed descriptions of exemplary embodiments adequate to allow those of ordinary skill in the art to make and use the inventive concepts will follow in later sections. 
     Various exemplary embodiments relate to an antenna feed configured to receive a signal having a wavelength, including: a cylindrical body; a first pin group including a first pin extending across the center of the cylindrical body at a first angle, and a second pin extending across the center of the cylindrical body at an angle rotated approximately 22.5° from the angle of the first pin, wherein the first and second pins of the first pin group are spaced in close proximity; a second pin group including a third pin extending across the center of the cylindrical body at an angle approximately equal to the angle of the second pin of the first pin group, and a fourth pin extending across the center of the cylindrical body at an angle rotated approximately 22.5° from the angle of the third pin, wherein the third and fourth pins of the second pin group are spaced in close proximity, and wherein the second pin group is spaced approximately one quarter of a wavelength away from the first pin group; a third pin group including a fifth pin extending across the center of the cylindrical body at an angle approximately equal to the angle of the fourth pin of the second pin group, and a sixth pin extending across the center of the cylindrical body at an angle rotated approximately 22.5° from the angle of the fifth pin, wherein the fifth and sixth pins of the third pin group are spaced in close proximity, and wherein the third pin group is spaced approximately one quarter of a wavelength away from the second pin group; and a fourth pin group including a seventh pin extending across the center of the cylindrical body at an angle approximately equal to the angle of the sixth pin of the third pin group, and an eighth pin extending across the center of the cylindrical body at an angle rotated approximately 22.5° from the angle of the seventh pin, wherein the seventh and eighth pins of the fourth pin group are spaced in close proximity, and wherein the fourth pin group is spaced approximately one quarter of a wavelength away from the third pin group. 
     In some embodiments, the antenna feed further includes: a first pair of capacitive tuning probes in line with the first pin group and rotated approximately 90° from the angle of the second pin, wherein each probe in the first pair of capacitive tuning probes are arranged on opposite sides of the cylindrical body; a second pair of capacitive tuning probes in line with the second pin group and rotated approximately 90° from the angle of the fourth pin, wherein each probe in the second pair of capacitive tuning probes are arranged on opposite sides of the cylindrical body; a third pair of capacitive tuning probes in line with the third pin group and rotated approximately 90° from the angle of the sixth pin, wherein each probe in the third pair of capacitive tuning probes are arranged on opposite sides of the cylindrical body; and a fourth pair of capacitive tuning probes in line with the fourth pin group and rotated approximately 90° angle of the from the eighth pin, wherein each probe in the fourth pair of capacitive tuning probes are arranged on opposite sides of the cylindrical body. 
     Various exemplary embodiments further relate to an antenna feed configured to receive a signal having a wavelength, including: a cylindrical body; a series of pin groups extending across the center of the cylindrical body, wherein the series of pin groups are spaced at approximately equal distances and rotated an approximately equal number of degrees, and wherein the series of pin groups extend along a length of the cylindrical body for a distance of less than one wavelength of the signal; and a series of capacitive tuning probes, wherein the series of capacitive tuning probes are aligned with the series of pin groups and are rotated approximately 90° from the series of pin groups. 
     In some embodiments, the antenna feed rotates the polarization of the signal by approximately 90°. In some embodiments, the antenna feed rotates a horizontally polarized signal to a vertically polarized signal. In some embodiments, the antenna feed rotates a vertically polarized signal to a horizontally polarized signal. In some embodiments, the antenna feed rotates the polarization of the signal over a length of three quarters of wavelength. In some embodiments, the antenna feed rotates the polarization of the signal over a length of less than one wavelength. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better understand various exemplary embodiments, reference is made to the accompanying drawings, wherein: 
         FIG. 1  illustrates a perspective view of an embodiment of an antenna feed; 
         FIG. 2  illustrates a side view of an embodiment of the antenna feed; and 
         FIG. 3  illustrates an end view of an embodiment of the feed. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, in which like numerals refer to like components or steps, there are disclosed broad aspects of various exemplary embodiments. 
     Antenna feeds may rotate a polarization of a signal. The polarization may be rotated using various devices and methods. For example, a signal may be rotated 90° by using a series of rotating pins inside of the antenna feed, as shown in U.S. Pat. No. 3,924,205, hereby incorporated by reference. The conventional pins may be spaced at close intervals that are much smaller than the wavelength of the signal. The conventional pins may also be rotated a small number of degrees. The conventional pins may be rotated over a length of one wavelength or more, making the length of the antenna feed longer than one wavelength. 
       FIG. 1  illustrates a perspective view of an embodiment of an antenna feed  100 . The feed  100  may be configured to operate with a signal at specific frequencies. The feed  100  may have a cylindrically shaped wall  101 . The feed  100  may include four pin groups  102   a - 102   d . Each pin group  102   a - 102   d  may include at least two pins rotated axially approximately 22.5° from each other. The two pins in each pin group  102   a - 102   d  may be spaced in close proximity to each other to form an approximate “X” shape. Each of the pin groups  102   a - 102   d  may extend across the center of the feed  100  and may attach to the wall  101 . The first pin group  102   a  may be at a first angle, for example 0°. The second pin group  102   b  may be rotated approximately 22.5° from the first pin group  102   a . One pin of the second pin group  102   b  may be at approximately the same angle as one pin of the first pin group  102   a . The third pin group  102   c  may be rotated approximately 22.5° from the second pin group  102   b , or approximately 45° from the first pin group  102   a . One pin of the third pin group  102   c  may be at approximately the same angle as one pin of the second pin group  102   b . The fourth pin group  102   d  may be rotated approximately 22.5° from the third pin group  102   b , or approximately 67.5° from the first pin group  102   a . One pin of the fourth pin group  102   d  may be at approximately the same angle as one pin of the third pin group  102   c . All of the pin groups  102   a - 102   d  may be rotated in the same direction, either clockwise or counter-clockwise. The 22.5° rotation in the pin groups  102   a - 102   d  may provide a 90° rotation in the polarization of the signal. For example, an input signal with vertical polarization may be rotated 90° and output with horizontal polarization. Alternatively, an input signal with horizontal polarization may be rotated 90° and output with vertical polarization. 
     The feed  100  may further include four pairs of capacitive tuning probes  104   a - 104   d . The four pairs of capacitive tuning probes  104   a - 104   d  may correspond with each of the four pin groups  102   a - 102   d . The first pair of capacitive tuning probes  104   a  may be rotated approximately 90° from the first pin group  102   a . The second pair of capacitive tuning probes  104   b  may be rotated approximately 90° from the second pin group  102   b . The third pair of capacitive tuning probes  104   c  may be rotated approximately 90° from the third pin group  102   c . The fourth pair of capacitive tuning probes  104   d  may be rotated approximately 90° from the fourth pin group  102   d . The four pairs of capacitive tuning probes  104   a - 104   d  may improve the bandwidth of the feed  100  by cancelling an inductive mismatch caused by the polarization rotation of the four pin groups  102   a - 102   d.    
       FIG. 2  illustrates a side view of an embodiment of the antenna feed  100 . The first pair of capacitive tuning probes  104   a  may be in line with the first pin group  102   a . The second pair of capacitive tuning probes  104   b  may be in line with the second pin group  102   b . The third pair of capacitive tuning probes  104   c  may be in line with the third pin group  102   c . The fourth pair of capacitive tuning probes  104   d  may be in line with the fourth pin group  102   d . The two pins of each pin group  102   a - 102   d  may be spaced in close proximity to each other. Each of the four pin groups  102   a - 102   d  and four pairs of capacitive tuning probes  104   a - 104   d  may be spaced apart a distance approximately equal to one quarter of the wavelength of the signal. 
     By spacing the pin groups  102   a - 102   d  at quarter length intervals, fewer pins may be required than with a conventional antenna feed. Additionally, the feed  100  may have a shorter length than a conventional antenna feed. The feed  100  may rotate the polarization of a signal 90° over a length of only three quarters of a wavelength, while a conventional antenna feed may perform the rotation over a length of one wavelength or more. Additionally, by using only four pin groups in combination with the capacitive tuning screws, the feed  100  may have a greater bandwidth than a conventional antenna feed. Further, the use of four pin groups reduces complexity and the cost of manufacturing. 
       FIG. 3  illustrates an end view of an embodiment of the feed  100 . The first pin group  102   a  may include two pins rotated axially approximately 22.5°. The second pin group  102   b  may be rotated axially approximately 22.5° from the first pin group  102   a . The second pin group  102   b  may include two pins rotated axially approximately 22.5°. One pin of the second pin group  102   b  may be at the same angle as one pin of the first pin group  102   a  and may be hidden by the first pin group  102   a  when the feed  100  is viewed on end as in  FIG. 3 . The third pin group  102   c  may be rotated axially approximately 22.5° from the second pin group  102   b . The third pin group  102   c  may include two pins rotated axially approximately 22.5°. One pin of the third pin group  102   c  may be at the same angle as one pin of the second pin group  102   b  and may be hidden by the second pin group  102   b  when the feed  100  is viewed on end as in  FIG. 3 . The fourth pin group  102   d  may be rotated axially approximately 22.5° from the third pin group  102   c . The fourth pin group  102   d  may include two pins rotated axially approximately 22.5°. One pin of the fourth pin group  102   d  may be at the same angle as one pin of the third pin group  102   d  and may be hidden by the third pin group  102   d  when the feed  100  is viewed on end as in  FIG. 3 . The 22.5° rotation in the pin groups  102   a - 102   d  may provide a 90° rotation in the polarization of the signal. For example, an input signal with vertical polarization may be rotated 90° and output with horizontal polarization. Alternatively, an input signal with horizontal polarization may be rotated 90° and output with vertical polarization. 
     As shown in  FIG. 3 , the first pair of capacitive tuning probes  104   a  may be rotated approximately 90° from one pin of the first pin group  102   a , or 112.5° from the other pin of the first pin group  102   a . The second pair of capacitive tuning probes  104   b  may be rotated approximately 90° from one pin of the second pin group  102   b , or 112.5° from the other pin of the second pin group  102   b . The third pair of capacitive tuning probes  104   c  may be rotated approximately 90° from one pin of the third pin group  102   c , or 112.5° from the other pin of the third pin group  102   c . The fourth pair of capacitive tuning probes  104   d  may be rotated approximately 90° from one pin of the fourth pin group  102   d , or 112.5° from the other pin of the fourth pin group  102   d . The four pairs of capacitive tuning probes  104   a - 104   d  may extend outside of the wall  101  of the feed  100  to allow for adjustment of the tuning probes. The four pairs of capacitive tuning probes  104   a - 104   d  may improve the bandwidth of the feed  100  by cancelling an inductive mismatch caused by the polarization rotation of the four pin groups  102   a - 102   d.    
     It is noted that while four pin groups with approximately 22.5° rotation between adjacent pin groups is illustrated, other numbers of pins and rotations may be used as well. For example, five pin groups with 18° of rotation between adjacent pin groups may be used that are spaced apart along the length of the waveguide by about one fifth of the wavelength. Any combination of the number of pins and the desired polarization rotation may be selected along with a spacing that leads to a length of less than one wavelength. The number and spacing of the associated capacitive probes will be selected to correspond to the number and position of the pins. 
     Although the various exemplary embodiments have been described in detail with particular reference to certain exemplary aspects thereof, it should be understood that the invention is capable of other embodiments and its details are capable of modifications in various obvious respects. As is readily apparent to those skilled in the art, variations and modifications can be affected while remaining within the spirit and scope of the invention. Accordingly, the foregoing disclosure, description, and figures are for illustrative purposes only and do not in any way limit the invention, which is defined only by the claims.