Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2001-06-08
2003-06-03
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S783000, C343S786000
Reexamination Certificate
active
06573873
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to stepped horn antennas, and particularly to stepped horn antennas usable at disparate frequencies.
BACKGROUND OF THE INVENTION
Spacecraft-based communication systems often operate at disparate frequencies, as for example at 3.7-to-4.2 (3.95) GHz for downlink transmission and 5.925-to-6.425 (6.2) GHz for uplink transmission. At the spacecraft, transmission takes place at the lower frequency, and reception at the higher frequency. Because of the long transmission path lengths in satellite-based operation, and the resultant losses, it is common to use high-gain antennas at the spacecraft. Reflector-type antennas are widely used for both transmission and reception in satellite communication, because a relatively large radiating aperture can be achieved with a simple and lightweight structure. These reflector-type antennas require a feed antenna, as known in the art. Feed antennas for use with reflectors are not different from antennas used for other purposes, but their aperture distributions are tailored to produce the desired aperture distribution over the face of the reflector.
The tailoring of the aperture distribution of a reflector-type antenna by adjusting the nature of the feed antenna often requires a feed structure including a plurality of horn antennas, each of which is itself tailored to produce a portion of the aperture distribution. These several horn antennas add unwanted weight to the antenna portion of the spacecraft. As known to those involved in spacecraft, the cost of boosting or launching a mass to orbit is very great, and the on-station value of an operating communication satellite is large. Every measure is normally exerted to reduce the weight of all structures of a spacecraft, so that additional expendable propellant can be on-loaded, which allows more on-station time for the spacecraft. For this purpose, the number of reflector feed horns, and the size of each feed horn, should be kept to a minimum, commensurate with achieving appropriate radiation efficiency as measured by spillover of feed energy beyond the edges of the reflector(s).
In an antenna which uses a reflector and a plurality of feed horns to produce multiple overlapping beams on the Earth's surface, the spacing or overlapping of the beams (the angular separation of the beams) depends, at least in part, on the spacing between feed horns. Close beam spacing, in turn, requires close spacing of the feed horns, to the point at which the horns may actually touch, at which point closer spacing is not possible. In order to achieve closer angular beam spacing, the horns themselves must be small, so that their phase centers may be placed closer together. While horn apertures can always be made smaller, small size is generally correlated with low gain and a large beamwidth. However, the large beamwidth tends to create “spillover” losses, in which the feed-horn energy is not intercepted by the reflector.
In
FIGS. 1
a
and
1
b
, a horn antenna
10
includes a metallic or conductive horn portion
12
defining an upper plate or wall
14
u
and a lower or bottom plate or wall
14
b
. In the embodiment of
FIGS. 1
a
and
1
b
, the plates
14
a
and
14
b
extend parallel to each other, separated in a radiating-end or phasing region
16
by a left vertical plate or wall
18
l
and right vertical plate or wall
18
r
, and separated in a feed-end region
20
by a left vertical plate or wall
22
l
and a right vertical plate or wall
22
r
. The walls
14
u
,
14
b
,
18
l
and
18
r
together define a rectangular radiating aperture
26
, and the walls
14
u
,
14
b
,
22
l
, and
22
r
together define a rectangular waveguide feed aperture. The direction of the electric field of the horn antenna
10
in normal operation is illustrated by arrow e, having terminations or ends at upper plate
14
u
and at lower plate
14
b.
Those skilled in the arts of antennas know that the term “feed” and “radiating” are used in respect of antennas for historic reasons rather than as accurate descriptors, since the antenna is a transducer between guided energy and unguided or radiated energy, and the transduction operates in both directions of propagation. Thus, in a transmitting mode of operation, energy to be transmitted may be applied to the feed port, and is ideally all radiated from the radiating aperture, whereas in a receiving mode of operation, unguided energy is intercepted by the “radiating” aperture and is transduced to the “feed” port.
As illustrated in
FIGS. 1
a
and
1
b
, upper wall
14
u
and lower wall
14
b
extend from feed aperture
24
to radiating aperture
26
without a step, whereas a step in dimension exists at a plane
28
lying between radiating-end or phasing portion
16
and feed-end portion
20
. A pair of vertically disposed electrically conductive walls
24
l
and
24
r
are disposed coincident with plane
28
, and are in conductive contact with the ends of the vertical walls. More particularly, a vertical wall
24
l
is connected to that portion of wall
18
l
remote from radiating aperture
26
and to that portion of vertical wall
22
l
remote from feed aperture
24
. Similarly, a vertical wall
24
r
is connected to that portion of wall
18
r
remote from radiating aperture
26
and to that portion of vertical wall
22
r
remote from feed aperture
24
.
The specification of the electric field direction identifies the various conductive walls of metallic horn
12
as being either in the Electric (E) plane or in the magnetic (H) plane. In particular, those electrically conductive plates on which the electric field lines terminate (when they are straight) are the E-plane walls, and correspond to walls or plates
14
u
and
14
b
. Those electrically conductive walls which are parallel to straight electric field lines are designated as H plane walls. Thus, walls
18
l
,
22
l
, and
24
l
, and walls
18
r
,
22
r
, and
24
r
, are all H-plane walls.
Stepped horns are known in the art, and are described, for example, in U.S. Pat. No. 4,757,326, issued Jul. 12, 1988 in the name of Profera, Jr. As described therein, a step transition in the H-plane dimensions of the horn set up TE
3,0
waveguide mode (equivalent to the LSE
3,0
mode) which interacts with the principal TE
1,0
mode (equivalent to the LSE
1,0
mode) to linearize the electric field amplitude distribution in the radiating aperture, for thereby increasing the effective aperture in the H plane. The TE
3,0
mode must be in-phase with the TE
1,0
mode near the H-plane walls of the horn in order to linearize the distribution, and if it should be out-of-phase, the amplitude distribution would be such as to reduce the effective aperture of the horn. The axial length of the phasing portion
16
of the antenna
12
is selected to provide the proper phasing of the TE
3,0
mode relative to the TE
1,0
at the radiating aperture
26
.
Improved spacecraft antennas are desired.
SUMMARY OF THE INVENTION
A horn antenna according to an aspect of the invention includes an electrically conductive first waveguide portion defining a rectangular waveguide feed aperture and a second rectangular aperture which is larger than the feed aperture, at least in the H plane. The horn includes an electrically conductive rectangular second waveguide portion defining a radiating aperture and a second aperture. The second aperture of the second waveguide portion is larger than the second aperture of the first waveguide portion in the H plane, and the second aperture of the second waveguide portion is identical in dimension to the second aperture of the first waveguide portion in the E plane. The second apertures of the first and second waveguide portions are juxtaposed with corresponding polarizations, thereby defining an H-plane step in dimension, but not an E-plane step. The horn further includes electrically conductive means or walls coupling the walls of the first and second waveguide portions at the H-plane step, to thereby define continuous H-plane walls extending from the feed to the radiating apertures. The horn
Lockheed Martin Corporation
Morris LLP Duane
Wimer Michael C.
LandOfFree
Stepped horn with dielectric loading does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Stepped horn with dielectric loading, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Stepped horn with dielectric loading will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3104420