Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
1999-09-10
2003-04-08
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S7810CA
Reexamination Certificate
active
06545645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of reflector antennas, and more particularly, to a compact reflector antenna which includes a frequency selective subreflector to provide a plurality of antenna patterns from a single reflector antenna.
2. Description of the Prior Art
Reflector antennas are frequently used on spacecraft to provide communication links with the ground or other spacecraft's. A single spacecraft will typically house multiple antennas to provide multiple communication links. These multiple antennas on a single spacecraft typically operate at different frequencies and are used for uplink and downlink communications with the earth.
Referring to
FIGS. 1 & 2
, one method of providing multiple frequencies and multiple communication capabilities on a single spacecraft is to utilize a frequency sensitive structure
10
, also known as a dichroic structure, as the subreflector
10
in a cassegrain type reflector antenna
12
. A cassegrain type reflector antenna
12
has a main reflector
14
and a smaller subreflector
10
. The dichroic subreflector
10
is hyperbolic in shape and has two focal points
16
,
17
one located on each side of the subreflector
10
. The subreflector
10
is placed between the main reflector
12
and the focal point
18
of the main reflector
12
with the convex side
20
of the subreflector
10
facing the main reflector
14
. The focal point
16
on the concave side
22
of the subreflector
10
is placed at the focal point
18
of the main reflector
14
, and, a downlink feed
24
, radiating a downlink RF signal at a first frequency, depicted by the lines marked
26
, is placed at the focal points
16
,
18
. The dichroic subreflector
10
is configured to pass the downlink RF signal
26
through the subreflector
10
so that the downlink RF signal
26
will be incident on the main reflector
14
which generates therefrom a downlink antenna pattern at the first frequency.
An uplink feed
28
, radiating an uplink RF signal, depicted by the lines marked
30
, at an uplink frequency, is placed at the focal point
17
of the convex side
20
of the subreflector
10
. The dichroic subreflector
10
is configured to reflect the uplink RF signal
30
and redirect it towards the main reflector
14
such that the uplink RF signal
30
will be incident on the main reflector
14
which generates therefrom an uplink antenna pattern at the uplink frequency. In this way, a single reflector
14
can provide antenna patterns at two separate frequencies.
The uplink and downlink RF signals are typically generated by electronics
34
which are positioned near the reflector
14
. To provide the uplink and downlink RF signals to the uplink
28
and downlink
24
feeds typically requires waveguides
32
,
36
coupled between the electronics compartment
34
and the uplink
28
and downlink
24
feeds. This antenna
12
requires a long waveguide run
32
from the electronics package
34
to the downlink feed
24
which is lossy, causes design difficulties in the antenna
12
by increasing the structural, temperature and EMI/EMC protection needed by the antenna
12
. It also increases manufacturing costs, volume and size required by the antenna
12
as well as the weight of the antenna.
A need exists to have a single reflector antenna having reduced cost, size, volume and weight which provides multiple antenna patterns at different frequencies.
SUMMARY OF THE INVENTION
The aforementioned need in the prior art is satisfied by this invention, which provides a multi-pattern reflector antenna for generating first and second antenna patterns from first and second RF signals having first and second frequencies of operation respectively. A multi-pattern reflector antenna, in accord with the invention, comprises a reflector having a focal point, first and second subreflectors and first and second feeds. The first and second subreflectors are positioned to image the focal point of the reflector at first and second preselected locations respectively.
The first and second subreflectors partially overlap each other with the overlapping portion of the first subreflector configured to be a frequency selective structure which reflects RF signals having the first frequency of operation and passes RF signals having the second frequency of operation. The second subreflector is configured to reflect RF signals having the second frequency of operation.
The first and second feeds are positioned at the first and second preselected locations respectively and are configured to operate at the first and second frequencies of operation respectively. The first and second feeds are configured to radiate the first and second RF signals respectively.
The first RF signal is incident upon and reflected by the first subreflector which is configured to redirect the first reflected RF signal towards the reflector. The second RF signal passes through the overlapping portion of the first subreflector and is incident upon the second subreflector which is configured to redirect the second RF signal towards the reflector.
The reflector is configured to generate first and second antenna patterns from the first and second reflected RF signals respectively.
In a first aspect, the multi-pattern antenna is configured so that the feeds are more proximate the reflector than the subreflectors.
REFERENCES:
patent: 4342036 (1982-07-01), Scott et al.
patent: 4701765 (1987-10-01), Arduini et al.
patent: 5130718 (1992-07-01), Wu
patent: 5373302 (1994-12-01), Wu
patent: 5576721 (1996-11-01), Hwang et al.
patent: 54114065 (1979-09-01), None
Ueno, K., et al,“Low-Loss Ka-Band Frequency Selective Subreflector,”Jun. 20, 1991, Electronic Letters, IEE Stevenage, GB, vol. 27, No. 13, p. 1155.
Honma, S., et al.,“Performance Measurement of Frequency Selective Reflector Using Planar Near-Field Techniques,”Jun. 18, 1995, IEEE Antennas and Propagation Society International Symposium Digest, vol. 3, pp. 1663-1666.
Pelton, Edward L., et al.,“Scattering from Periodic Arrays of Crossed Dipoles,”May 1979, IEEE Transactions on Antennas and Propagation, vol. AP-27, No. 3, pp. 323-330.
Clinger James
Thousand Connie M.
TRW Inc.
Wong Don
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