Dual frequency coaxial feed assembly

A dual frequency feed assembly employing a pair of coaxial circular wave guide cavities, each with respective probe. The higher frequency cavity, e.g. Ku band, is located within the lower frequency, e.g. C band cavity. A common motor is used to drive the two probes which have a common axis A. The lower frequency probe is coupled through the rear wall of the assembly to a rectangular waveguide. The higher frequency probe is also coupled through the rear wall of the assembly but via a coaxial line which is diverted from the axis A to exit beside the lower frequency waveguide. The two rectangular waveguides and the drive motor for the probes are all mounted on the rear of the assembly. In one embodiment of the invention the coaxial line extends from its probe to a housing on the body containing a signal processing circuit board. Connection to that board is made directly eliminating the need for any waveguide transmission line. In other embodiments of the invention, electronic switches, for example, ferrite switches are used in place of rotating probes. The probes may then be fixed and their coaxial lines fixed as well.

BACKGROUND OF THE INVENTION 
With the advent of two predominant frequency bands for reception of 
satellite repeater television communication, the Ku band and the C band 
significant advances have been needed in feed horn assembly designs. It 
has been the desire to develop truly coaxial feed assemblies and this I 
have achieved in my co-pending application, Ser. No. 105,135, now U.S. 
Pat. No. 4,903,037. In that dual frequency feed, a pair of cavities or 
open-ended circular waveguides are located coaxially with the Ku band 
cavity located inside of the C band cavity. A rotatable probe is located 
in each cavity and they are coupled together for simultaneous rotation 
from a common drive source with the drive shaft preferably entering from 
the rear of the C band cavity. 
The coupling of the Ku band probe has presented some difficulty since its 
normal exit direction through the rear of the C band cavity would place it 
in direct interference with the C band probe. I avoided this problem with 
my co-pending application by the use of a radically extending coaxial 
line. Other approaches to coaxial dual frequency feed assemblies are 
illustrated in the following U.S. Patent: 
______________________________________ 
U.S. Pat. No. 
Inventor Issued 
______________________________________ 
4,740,795 John M. Seavey April 26, 1988 
______________________________________ 
The foregoing constitute, a rather complex structure, both mechanically and 
electrically. Single frequency band feeds with the signal from the probes 
being extracted from the rear of the feed are illustrated in the 
following: 
______________________________________ 
U.S. Pat. No. 
Inventor Issued 
______________________________________ 
4,528,528 E. P. Augustin 
July 9, 1985 
4,414,516 H. T. Howard November 8, 1983 
4,554,553 F. Grim November 19, 1985 
4,504,836 J. M. Seavey March 12, 1985 
______________________________________ 
A single frequency band system does not encounter the problem of mechanical 
and electrical interference between the probes and their coaxial lines. 
BRIEF DESCRIPTION OF THE INVENTION 
I have found that in addition to the method of extracting received signals 
from the Ku band probe via the side wall of the C band cavity or out the 
front face of the assembly as I proposed in my earlier application, 
referenced above, that it is possible for the Ku band signal to be 
extracted at the rear. Such an extraction was not practical when using a C 
band probe of a three sided rectangular shape as is disclosed in U.S. Pat. 
No. 4,414,516 to A. T. Howard or an L shaped probe of the type disclosed 
in U.S. Pat. No. 4,528,528 to E. P. Augustin because each of these include 
a portion of the probe which sweeps around the interior of the C band 
cavity with insufficient clearance for rear exit of the probe. 
I have determined that it is possible to have a axial rear exit conductor 
from the Ku band cavity which is diverted sidewardly and rearwardly to 
exit through the rear wall of the C band cavity when used in combination 
with a C band probe of a hook shaped as disclosed in U.S. Pat. No. 
2,880,399 to E. J. Murphy. In this combination the Ku band probe is 
coupled by a slip coupling to its output conductor and is affixed to the 
body or a portion of the body defining the Ku band cavity. A member 
extends from the C band probe root and engages the Ku band body or the 
rotating portion thereof to cause a rotation of the Ku band probe with 
rotation of the C band probe. This allows a single motor to drive both 
probes as is accomplished in my invention U.S. patent application, 
referenced above. In this case the rear of the feed assembly includes a C 
band waveguide section, a Ku band waveguide section and a drive motor all 
in non-interfering positions. 
I have also discovered that it is possible to use ferrite switching devices 
for either one or both of the frequency bands with respective pickup 
probes located coaxially within their respective cavities and provide 
electronic rather than mechanical switching of polarization within each 
cavity. 
In another embodiment of this invention I have provided for direct feeding 
of signals from the coaxial lines to an integrated circuit board without 
the need of a waveguide and its needed transform and inherent losses.

DETAILED DESCRIPTION OF THE INVENTION 
Now referring to FIGS. 1-3, a dual frequency feed assembly, generally 
designated 10, may be seen therein with a C band waveguide 11 with its 
flange 12 located at the rear face of the assembly. The front face of the 
assembly shows a pair of annular rings 13 and 14 which ar coaxial with C 
band circular waveguide or cavity 15. Coaxially located within C band 
cavity 15 is a Ku band circular waveguide or cavity 16 with its associated 
probe 20. 
Concealed behind the Ku band cavity 16 is the C band probe which may best 
be seen in FIGS. 3 and 5. A radially extending wall 21 of the assembly 10 
is preferably integral with the side walls 22, the rings 13 and 14 and 
with a rear extension 23 appearing in FIGS. 3, 4 and 5. The extension 23 
defines the major length of the C band cavity 15. A rear flange 24 which 
may be seen in FIGS. 3 and 5 provides: 
a) A closure for the rear C band cavity; 
b) A mounting hole 25 for a bearing 26 for the C band probe; as well as, 
c) A mounting structure for: 
1. A drive motor 30; 
2. The C band waveguide 11 of FIGS. 1 and 5; and 
3. The Ku band waveguide 50 of FIGS. 3, 4 and 5. 
Now referring specifically to FIG. 3, it may be seen there that the C band 
cavity 15 is substantially larger in diameter and greater in length than 
the Ku band cavity 20, as is to be expected, since C band frequency range 
is lower namely 3.7-4.2 GHz and the Ku band is in the optional 10.95-11.7 
GHz range and 11.7-12.2 GHz mandatory range. As illustrated in FIG. 3 the 
Ku band probe 20 is located at the rear of the Ku band cavity and exposed 
to electromagnetic energy entering through the aperture 20a of cavity 20. 
The probe 20 is mechanically secured to rear flange 40 of the Ku band 
cavity 20 for rotation with the Ku band cavity within the front 
bearing/spacer 41 which maintains the Ku band cavity coaxially along axis 
A within the C band cavity 15. The bearing/spacer 41 is preferably of 
dielectric electromagnetic energy transparent material and may be in disc 
form as shown in FIG. 3 or on the form of a spider with three or more legs 
as illustrated in FIG. 5. 
The Ku band cavity 20 is secured at its end wall 40 to an eccentric support 
and rotating shaft 42 including an axial section 42A which is coaxial with 
the axis A and with the bearing 26 so that rotation of the drive shaft 
associated with drive motor 30 produces simultaneous rotation of the C 
band probe 17 the shaft 42 and rotation of the Ku band cavity 20 and its 
cavity 16 and its probe 20. The probe 20 is coupled through slip joint 43 
to a coaxial line 44 which includes an angle portion 44A which extends 
towards the edge of the C band cavity while maintaining clearance from the 
C band probe 17 regardless of its orientation. The rear straight portion 
44R of the coaxial line 44 extends through the rear face of the rear 
flange 24 through the wall of the Ku band waveguide section 50 at the rear 
of the entire sampling and includes a probe 44P in coupling relationship 
with the Ku band waveguide section 50. The C band probe 17 extends into 
the C band waveguide 11 for coupling energy from the C band probe 17 which 
arrives at the C band aperture 15A. In FIG. 3 the extreme opposite 
position of the C band probe and the drive 44 are indicated by dashed 
lines. It should be noted that there is no interference between the C band 
probe and the coaxial line 44. This allows all of the mechanical 
components used to extract energy from the drive, as well as the drive 
motor 30, to be located at the rear of the assembly 10. This may be 
clearly seen. 
As best seen in FIGS. 4 and 5, the ends of the C band wave guide 11 and Ku 
band waveguide generally abut while the motor drive 30 is secured to the 
outer wall of the wave guide 11. The drive motor or its gearbox 30 are 
aligned with axis A in a simple effective assembly. This is all 
accomplished since energy detected by both probes 17 and 20 is extracted 
through the rear of the assembly 10. 
Now referring specifically to FIG. 6, it may be seen therein that another 
form of switching of the higher (e.g. Ku band) polarization without a 
rotating probe is possible. This totally eliminates rotational 
interference between the assembly elements. When no physical rotation is 
encountered, a sidewall signal extraction becomes more practical. In FIG. 
6, a Ku band aperture is formed by tube 101 which encloses a signal 
receiving probe 102 surrounded by ferrite polarization rotator 103 with 
its coil through which direct current produces a polarization reversing 
field in the ferrite 103. Control signals are applied to the ferrite 103 
coil via leads 104. Behind the probe 102 is rectangular waveguide 105 into 
which either vertical or horizontally polarized signals at the aperture of 
tube 101 are introduced. In certain cases, tuning of the rectangular 
waveguide may be necessary and a tuning probe 107, may be used in 
accordance with well known practice in the waveguide art. 
A Ku band probe 106 extends into the rectangular waveguide 105 and extracts 
the detected Ku band signal for transmission over coaxial line 108 to the 
signal utilization device for the signal(unshown). The Ku band assembly 
and ferrite rotator are supported in the C band cavity 111 by dielectric 
ring 109. Signals received at probe 102 are introduced into the 
rectangular waveguide 105 at the probe's inner or transmitting end 110. As 
in the foregoing embodiments, the Ku band assembly is all coaxially 
located in the C band circular waveguide 111. The C band probe 33 is 
rotated by drive 113, similar to the previously described embodiments. 
Carrying this concept of ferrite switching in dual frequency band coaxial 
assemblies one step farther, the dual frequency feed assembly may employ 
ferrite switching for both the higher frequency and lower frequency 
probes. Such an arrangement is illustrated in FIG. 7 in which the same 
reference numbers are applied to the corresponding elements of FIG. 6. In 
addition to the higher frequency band cavity with its ferrite switch 103, 
the assembly includes a lower frequency, C band probe 102A and ferrite 
switch 103A with a lead 104A extending into a rectangular waveguide 105A. 
Signals received at the probe 102A are introduced into the rectangular 
waveguide 105A at the probe's inner or transmitting end 110A. 
One other aspect of this invention is illustrated in FIG. 8 as an alternate 
high frequency signal conductor arrangement. The embodiment is based upon 
the dual frequency version of my copending patent application Ser. No. 
105,135, now U.S. Pat. No. 4,903,037. FIG. 2, to which reference is now 
made and the specification thereof is hereby incorporated by reference. 
For ease of understanding of this embodiment as well, the same reference 
numerals used in the previous embodiments are used in this figure of the 
drawing. 
The dual frequency feed assembly 10 includes a main body 10A with a pair of 
encircling rings 13 and 14 surrounding the C band aperture 15 of the C 
band circular waveguide or cavity. A Ku band cavity with its aperture 20A 
is supported in the C band cavity by harp 60 for rotation with the C band 
probe 17 under the control of drive 30. C band signals detected by the C 
band probe 17 are extracted by introduction into waveguide 11 as the probe 
extension extends through the waveguide 11 through thermal isolator 61 
with its integral bearing portion 61A between the waveguide 11 and the 
drive 30 which preferably is a miniature d. c. motor and reduction gear 
contained within a housing mounted on the assembly 10. 
Of particular importance with respect to this embodiment is the fact that a 
coaxial line 30 which extends into signal transfer relationship with the 
Ku band probe 20 contained within the aperture 20 A, extends out of the Ku 
band cavity, through a wall of the C band cavity and into a housing 62 
which is made up of two housing parts, an inner housing part 63 and an 
outer housing 64 which contain a signal processing circuit board 65 
carrying the required integrated circuits for signal processing. The 
coaxial line 30 connects directly to the circuit contained in board 65 so 
no waveguide transformation is required. Signal processing for the Ku band 
is conducted directly on the feed assembly 10 itself. This significantly 
reduces the cost and adds to the reliability of the system. The line 30 is 
coupled to the probe 20 via a rotating joint in the Ku band cavity so that 
rotation of the Ku band probe 20 by the drive 30 through the harp 60 
allows the line 30 to be fixed. The housing 62 is sealed against the 
elements by gasket 66 and includes a suitable weathertight connector 
(unshown in the drawing) for conducting the processed signal from the 
assembly 10 in accordance with well known practices in the electronics 
art. The connector and cable will be selected depending upon the 
frequency, bandwidth and shielding requirements of the signal after its 
processing on the board 65. 
Each of the foregoing embodiments constitute important refinements in the 
dual frequency feed assembly of my copending application Ser. No. 105,135, 
now U.S. Pat. No. 4,903,037. The refinements maintain the basic principle 
of that invention while adding to its adaptability and utility. 
The foregoing constitute the best mode known by the applicant for carrying 
out this invention however, the specific embodiments disclosed are 
illustrative of the principle of the invention and are not limiting in its 
scope. To the contrary, it is recognized that one of ordinary skill in the 
art, given this teaching, may make variations in the structure or 
compositions without departing from the spirit and scope of this 
invention. Its scope is defined by the following claims including the 
protection offered by the doctrine of equivalents.