Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
2002-11-08
2004-08-31
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C455S562100
Reexamination Certificate
active
06784838
ABSTRACT:
TECHNICAL FIELD
The present invention relates to phased array antenna systems, such as radar, and more particularly relates to a beam former that generates encoded control signals that drive the antenna elements of a phased array to receive multiple beams while allowing a filter to detect coding parameters contained in the control signals to separate the multiple beams from a combined signal received from the antenna.
BACKGROUND OF THE INVENTION
Phased array antenna systems, such as those used for radar systems, take advantage of the phase differential that occurs according to the direction of coherent propagating energy. For example, in a simple array of two closely spaced antenna elements lying in a plane and both facing forward, an incoming signal coming straight from the forward direction would be received at the same time at both elements, resulting in signals at each element having the same phase, which are referred to as “in-phase.” But if the energy approaches the elements at an angle, the two elements receive the energy at different times, resulting in a phase differential or “shift” between the two signals. This is similar to ocean waves arriving at a beach. If the wave comes straight in to shore, the wave washes upon the beach at the same time along the beach. If the wave is coming in at an angle relative to the beach, however, it arrives first in one spot and then progressively arrives down the beach at later times.
A similar phenomenon is at work in phased array antenna systems. Since the propagating electromagnetic energy reaches the nearest antenna element first, the direction of the incoming energy can be determined by detecting the phase differential. Similarly, a directional “beam” may be formed by collecting the signals from the antenna elements with coordinated phase delays, which causes the received energy to add up constructively in a desired beam direction while partially or completely canceling out in all other directions. It is common to steer a coherent beam created in this manner by controlling programmable phase and gain control devices at each antenna element in a coordinated manner. For example, a single beam formed by a phased array may be controlled to periodically sweep across the antenna's angular coverage, to track a detected target, to sweep or track while avoiding a known signal, or to achieve other objectives. This conventional single-beam steering system uses a single controllable phase and gain control device for each antenna element, a single beam forming combiner, and a beam steering computer to create and control the beam.
It is also conventional to use a phased array antenna system to simultaneously receive multiple beams having different pointing directions. For example, rather than steering one beam to sweep across the antenna's angular coverage, as described above, the phased array may be controlled to divide the antenna's angular coverage into multiple beams to monitor the entire operational volume simultaneously. This may be thought of as causing the antenna to “look” in many different directions at the same time. This is accomplished conventionally by dividing the signal received at each antenna element into separate channels using separate phase and gain control devices at each antenna element for each desired beam. In addition, a separate beam forming combiner is typically required to assemble each beam from the signals received for the corresponding beam from each antenna element. In other words, the multiple beams are conventionally formed by providing separate sets of antenna hardware for each beam, which generally multiplies the required number of antenna hardware elements, including phase and gain control devices and beam forming combiners, by the number of desired beams. This may be considered a “brute force” design technique due to the heavy dependence on antenna hardware to generate the desired beams.
In a typical target acquisition radar, for example, the phased array antenna may include 1,000 antenna elements that are used to form 100 independently controlled beams. In this case, each of the 1,000 antenna elements requires 100 different simultaneous phase and gain settings to form the 100 different beams. This is conventionally accomplished by providing each of the 1,000 antenna elements with 100 different phase and gain devices, one corresponding to each beam. The signals for each beam received from the various antenna elements are then combined in a separate beam forming combiner to create 100 different beams, each having a component received from each antenna element. This conventional approach requires 100,000 phase and gain devices and 100 beam forming combiners, which typically results in a system that is exorbitantly expensive, complex to construct, large in size, and heavy. Any one or more of these penalties may be critical for a particular application.
To save against these penalties, the beams may be set in advance by fixed phase and gain control devices, which cannot be changed without changing the antenna hardware. This option, of course, limits the flexibility of the system. Alternatively, the antenna may include programmable control hardware that can be reprogrammed to create different beam sets, which may involve defining the number of beams, their pointing directions, and the shapes of their antenna patterns. However, this approach may be prohibitively expensive because it requires separate programmable phase and gain control devices for each antenna element, for each desired beam. For the antenna in the previous example, this would require 100,000 programmable phase and gain control devices. The number of beams or antenna elements may be reduced, but performance is sacrificed with these alternatives.
In addition, a conventional single-beam radar system typically includes a single phase and gain device for each antenna element, a single beam forming combiner, and a Doppler filter. In many such cases, the beam forming network produces a sum and two difference beams for mono-pulse operation. Upgrading such a system to receive multiple beams in the conventional manner, as described above, would require multiplying the number of phase and gain control devices at each antenna element by the number of desired beams, and adding a separate beam forming combiner and Doppler filter for each desired beam. Again, size, weight or cost constraints may ultimately limit the number of beams that can be accommodated in the upgrade. The design penalties would be minimized, of course, if multiple beams could be produced while requiring only a single phase and gain control device for each antenna element and a single combiner and Doppler filter for all of the beams. But such systems are not presently available.
Accordingly, a need exists for improved methods and systems for receiving multiple beams with a phased array antenna system. A further need exists for methods and systems for upgrading existing single-beam phased array antenna systems to receive multiple beams. In particular, a need exists for phased array antenna systems that can receive multiple beams without relying on multiple phase and gain control devices for each antenna element, and without dedicating separate beam formers for each beam.
SUMMARY OF THE INVENTION
The present invention meet the needs described above in a phased array antenna system that uses an intelligent beam former to drives the antenna array to receive multiple beams using a single programmable phase and gain control device for each antenna element and a single combiner and beam former for all of the beams. The intelligent beam former encodes each beam, combines the encoded beams into a combined signal, and then separates the multiple beams from the combined signal. For example, the beams may be code division multiplexed using orthogonal codes, and the beams may be decoded to separate the beams using an orthogonal code filter, such as a conventional CDMA filter. Alternatively, the beams may be frequency coded and decoded to separate the beams with a frequency filter. In a
EMS Technologies Inc.
Issing Gregory C.
Mehrman Michael J.
Mehrman Law Office PC
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