Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
2001-03-19
2002-05-14
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S770000, C343S872000, C342S374000
Reexamination Certificate
active
06388631
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to phased array antennas and, more specifically, to reconfigurable wideband phased array antennas capable of generating multiple beams for multiple functions.
BACKGROUND OF THE INVENTION
Defense and commercial electronic systems such as radar surveillance, terrestrial and satellite communications, navigation, identification, and electronic counter measures are often deployed on a single structure such as a ship, aircraft, satellite or building. These systems usually operate at different frequency bands in the electromagnetic spectrum. To support multiple band, multiple function operations, several single discrete antennas are usually installed on separate antenna platforms, which often compete for space on the structure that carries them. Additional antenna platforms add extra weight, occupy volume, and can cause electromagnetic compatibility, radar cross section, and observation problems.
There is a need to operate antenna apertures at close proximity to each other at different frequencies and with different functions, without detrimentally affecting antenna operation. It is often desired to have multiple band, wide scan, and multiple channel capabilities in a single platform. A typical architecture for providing multiple band, multiple function capabilities in a single platform is shown in FIG.
1
. The antenna platform
100
comprises multiple antenna cells
110
A . . . N
, where each cell consists of a radiating element
116
A . . . N
, a transmission line
114
A . . . N
that couples RF energy to the radiating element
116
A . . . N
, and a radiating control element
112
A . . . N
, such as a phase shifter, transmit and receive (T/R) module, or other devices that control the RF energy radiated from each radiating element
116
A . . . N
. Each antenna cell
110
A . . . N
is coupled to a separate transmit or receive function
10
A . . . N
. Each transmit or receive function
10
A . . . N
is an independent process of amplitude, phase, and/or frequency. For example, one function may the transmission of a satellite communication signal at 2 GHz, while another function may be the receipt of a radar signal at 10 GHz. The antenna platform
100
may comprise a planar array that contains several of the antenna cells
10
A . . . N
latticed in two dimensions, with each cell
110
A . . . N
acting collectively to produce a far field beam related to the overall desired functional properties.
An antenna platform may use a different density of antenna cells occupying the same lattice space for different transmit or receive functions. For example, a high frequency function, such as a radar operating at 10 GHz, may use several antenna cells to provide for precision beam steering, while a low frequency function, such as a communication channel operating at 2 GHz, may use fewer antenna cells due to its lower wavelength. The use of different densities of antenna cells for different functions is sometimes referred to as array thinning. Each transmit or receive function may require a unique lattice spacing to optimize radiation performance, such as to provide grating lobe free scanning, or to optimize beam width synthesis. At lower frequencies, phase control over fewer radiating elements is required to achieve grating lobe free scanning, since only elements spaced more than a half wavelength apart must be controlled.
FIG. 2
illustrates a planar array
200
where different densities of antenna cells
210
A
,
210
B
,
210
C
are used for three different antenna functions,
10
A
,
10
B
,
10
C
. In
FIG. 2
, a specific area of the planar array
200
, a first function
10
A
uses four antenna cells
210
A
, while a second function
10
B
uses only two radiating elements
210
B
, while a third function
10
C
uses only a single antenna cell
210
C
. Each antenna cell
210
A
,
210
B
,
210
C
still contains a radiating element
216
A
,
216
B
,
216
C
, a transmission line
214
A
,
214
B
,
214
C
, and a radiating control element
212
A
,
212
B
,
212
C
.
Note that thinning the array reduces the number of elements required in the planar array. For example, if a planar array uses sixteen antenna cells for each function, and the array services three functions, a total of forty-eight antenna cells are required for the array. This also means that forty-eight radiating elements, transmission lines, and radiating control elements are also required. However, if the array thinning illustrated in
FIG. 2
is used, fewer antenna cells and thus fewer antenna components are required. For example, in
FIG. 2
, if the first function
10
A
uses a total of sixteen antenna cells
210
A
to achieve the desired performance, sixteen radiating elements
216
A
, transmission lines
214
A
, and radiating control elements
212
A
are required. However, the second function
10
B
will require only half as many antenna cells
210
B
, so it requires only eight radiating elements
216
B
, transmission lines
214
B
, and radiating control elements
212
B
. Finally, the third function
10
C
requires one-quarter as many antenna cells
210
C
as the first function
10
A
, so it requires only four radiating elements
216
C
, transmission lines
214
C
, and radiating control elements
212
C
. Hence, the array thinning shown in
FIG. 2
provides a significant reduction in the number of components.
Antenna cells of a thinned planar array can be interleaved in a single array as shown in FIG.
2
. However, if the radiating elements are in close proximity to each other, the RF energy from an antenna cell supporting one function is likely to couple to another antenna cell and reduce the performance of the array. One approach to reduce the coupling of RF energy is to switch the unused cells, as shown in FIG.
3
. In
FIG. 3
, each antenna cell
310
A,B,C
in the planar array
300
consists of a radiating control element
312
A,B,C
an RF switch
318
A,B,C
, a transmission line
314
A,B,C
, and a radiating element
316
A,B,C
. However, simply disconnecting an unused cell
310
A,B,C
with the RF switch
318
A,B,C
, is not desired because the finite length of open circuit transmission lines
314
A,B,C
tends to add spurious impedance to the array
300
, or losses can occur when the switches
318
A,B,C
are terminated in loads.
The prior art discloses many techniques for addressing the interleaving problems discussed above without the use of switches. Provencher et al. in U.S. Pat. No. 3,623,111, Bowen et al. in U.S. Pat. No. 4,772,890, Chu et al. in U.S. Pat. No. 5,557,291, and Mott et al. in U.S. Pat. No. 5,461,391 disclose examples of multiple band arrays that do not use switches to provide operation at multiple frequency bands. These arrays generally use radiating elements configured to radiate radio frequency energy at a specific frequency band. Dissipation of the active ports is minimized by reducing the coupling of energy into adjacent inactive radiating elements. Because the adjacent elements in an interleaved aperture can re-radiate spurious signals with an amplitude and phase varying over frequency, thus interfering with the radiation of the desired signal, the apertures within these arrays are usually cross-polarized from one another or widely spaced in frequency to avoid mutual coupling errors. However, these design choices limit the flexibility of the array.
The prior art also discloses reusing radiating elements at lower frequency bands by coupling the radiating elements with the transmit or receive function with an RF combiner
460
, such as a coupler, diplexer, or switch, as shown in FIG.
4
.
FIG. 4
shows an antenna array
400
where three transmit or receive functions
10
A,B,C
are coupled to separate radiating control elements
420
A,B,C
. However, the outputs of the radiating control elements
420
A,B,C
are multiplexed to the minimum number of radiating elements
440
required to support a specific function
10
A,B,C
by using RF combiners
460
. In the example depicted in
FIG. 4
, one function
10
A
requires four radiating elements
440
, so th
Lee Jar J.
Livingston Stan W.
Loo Robert Y.
Schaffner James H.
Ho Tan
HRL Laboratories LLC
Ladas & Parry
LandOfFree
Reconfigurable interleaved phased array antenna does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Reconfigurable interleaved phased array antenna, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reconfigurable interleaved phased array antenna will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2824312