Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1999-04-30
2001-08-28
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S374000, C342S377000, C333S139000, C333S164000
Reexamination Certificate
active
06281838
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to phased array antenna phase shifters and more particularly to a select-line, base-3 phase shifter using micro electro mechanical system (MEMS) technology.
2. Description of the Related Art
Phased array antennas comprise multiple radiating elements whose transmission signals combine during operation to yield superior results over a single element antenna. The transmission signals of the multiple radiating elements are typically phased and summed during transmission to yield a synthesized transmission beam. The resulting transmission beam contains the combined power of all the multiple radiating elements and provides a single agile and inertialess beam that is useful in many applications, including radar and communication.
During operation of a phased array antenna, it is useful to steer the phased array transmission beam. Often the steering of the transmission beam is implemented by mechanical means using a gimbaled system to physically turn the phased array antenna. The transmission beam can also be steered electronically while keeping the phased array antenna in a fixed position. This is accomplished by electronically manipulating the phase of the transmission signal of each individual radiating element in the phased array antenna. The beam of a phased array antenna may be steered to an desired angle by applying a linearly progressive phase increment, or shift, from radiating element to radiating element. Electronic beam steering has advantages over a mechanically actuated system, greater reliability, more effective beam synthesizing and greater adaptation to hostile environments.
FIG. 1
is a simplified diagram of one row of a conventional phased array antenna
10
utilizing electronic beam steering, a complete planar phased array antenna having a number of such rows. Each radiating element
12
of the phased array antenna
10
has its own phase shifter
14
. An input line
16
carrying a transmission signal is coupled to each phase shifter
14
, which imparts a respective predetermined phase shift to the transmission signal as it passes through that phase shifter
14
. The phase shifted transmission signals are then coupled to respective radiating elements
12
for transmission. Various types of phase shifters
14
have been developed, including switched-line phase shifters, reflection-line phase shifters and loaded-line phase shifters. The present invention is directed to an improvement over conventional switched-line phase shifters.
Present binary switched-line phase shifters are discussed in Skolnik, Radar Handbook, Second Edition (1990), pp. 7.63-7.68 and in U.S. Pat. No. 4,649,393 to Rittenbach. Present phase shifters have one or more serial connected stages, each stage having two delay lines of different length. As a transmission signal is passed through the respective phase shifter
14
, it passes through each of the serially connected stages. One of the delay lines within each stage carries the transmission signal as it passes through the stages of the phase shifter. A phase shift is imparted to the transmission signal by a time delay which the transmission signal experiences as it passes through the delay line within each stage. The total phase shift is the accumulation of the individual time delays within each stage of the phase shifter.
FIG. 2
is a diagram of the conventional prior art base-2 phase shifter
14
having six serially connected stages
22
a-f
with two delay lines
24
a,
24
b
per stage.
FIG. 2
further illustrates the phase shift that can be imparted by each of the stages
26
a-f.
In switched-line phase shifting, one delay line in each stage is dedicated to zero phase shift or zero time delay. For instance, in stage one delay line
24
b
is dedicated to zero phase shift. The zero phase shift delay lines in each stage allows the transmission signal to pass through each stage and the entire phase shifter without a phase shift, if desired. In prior art phase shifter
14
half of the delay lines are dedicated to zero phase shift. The greater percentage of delay lines dedicated to zero phase shift results in fewer lines dedicated to imparting phase shifts and a corresponding reduction in phase shift resolution.
The desired delay line within each stage is activated for carrying the transmission signal by closing the appropriate switches at the input and output of the desired delay line. The switch closing is generally controlled by a microprocessor over electrical control lines with either parallel or serial access to the switches. The switches could also be controlled by other modalities such as optical control.
The prior art switches include PIN diode switches and FET transistor switches. It is well known that switches of this type suffer from insertion loss dominated by the resistive loss of the signal line. Furthermore, switches characteristically reflect signals during transmission, causing signal distortion. As the transmission signal passes through each stage of the phase shifter, the transmission signal experiences loss and signal distortion from the switches within the stages. The greater the number of stages the greater the resulting loss and distortion.
SUMMARY OF THE INVENTION
The present invention provides a superior method and device for switched-line phased array antenna phase shifting, utilizing more delay lines per stage (preferably three as opposed to two). The additional delay lines per stage, provides greater phase shifting resolution using the same number of switches and reduces the transmission signal loss and distortion. A switching technology with superior insertion loss and isolation characteristics is also used.
In the preferred embodiment, a base-3 rather that base-2 selection of delay lines per stage is used. Using the same number of switches as in the past, the number of stages can be reduced. For instance, the base-3 implementation of 12 delay lines uses four stages while the prior base-2 implementation uses six stages. With the base-3 implementation, the transmission signal need only encounter four stages and eight switches during transmission as opposed to the prior art six stages and twelve switches. Thus, the loss and distortion experienced by the transmission signal is significantly reduced.
A base-3 selection of delay lines also provides for greater phase shifting resolution. In the present invention, one delay line per stage is dedicated to zero phase shift for a total of one third of the delay lines of the entire phase shifter delay lines dedicated to zero phase shift. Two thirds of the delay lines are used to impart phase shift on the transmission signal. By dedicating a greater percentage of delay lines to phase shifting, the shifting can occur in smaller increments. This allows for a greater resolution in phase shifting while using the same number of delay lines and switches as the prior art.
The base-3 selection of transmission lines can be implemented using conventional switches including PIN diode and FET transistor switches. In the preferred embodiment, the switches within each phase shifter are fabricated using micro electro mechanical system (MEMS) technology, providing superior isolation and insertion loss characteristics. Each switch comprises a micro fabricated, miniature electro mechanical RF switch capable of handling signal frequencies greater than a Ghz while maintaining minimal insertion loss in the “ON” state and excellent electric isolation in the “OFF” state. Each MEMS switch is formed on a semi-insulating substrate and includes a cantilever arm that is affixed to the substrate and extends over a ground line, and a gapped signal line formed by metal microstrips on the substrate. An electrical contact is formed on the bottom of the cantilever arm positioned above and facing the gap in the signal line. A top electrode on the cantilever arm forms a capacitor structure above the ground line on the substrate. The switch is actuated by application of a voltage to the top electrode. With voltage applied, electrostatic force
Gregory Bernarr E.
Koppel & Jacobs
Rockwell Science Center LLC
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