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Planar ferro-electric phase shifter
| Details |
Inventors: Babbitt, Richard W.; Drach, William C.; Koscica, Thomas E.;
Assignee: The United States of America as represented by the Secretary of the Army (Washington, DC)
Primary Examiner: Pascal; Robert J.
Assistant Examiner: Neyzari; Ali
Attorney, Agent or Firm: Zelenka; Michael, Anderson; William H.
A planar ferro-electric phase shifter which is compatible with commonly-u microwave transmission media to include microstrip, inverted microstrip, and slot line. The ferro-electric material, Ba.sub.x Sr.sub.1-x TiO.sub.3, which has a high dielectric-constant, is the phase shifting element. In the microstrip embodiment, the microstrip circuit consists of a ferro-electric element interposed between a conductor line and a ground plane. A DC voltage is applied between the conductor line and the ground plane, thereby controlling the dielectric constant of the ferro-electric material. The dielectric constant of the ferro-electric element in turn controls the speed of the microwave signal, which causes a phase shift. Microwave energy is prevented from entering the DC supply by either a high-impedance, low pass filter, or by an inductive coil. DC voltage is blocked from traveling through the microstrip circuit by a capacitive high-voltage DC bias blocking circuit in the ground plane. |
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DETAILED DESCRIPTION The first general purpose of this invention is to provide a novel planar ferro-electric phase shifter which is compatible with commonly-used microwave transmission media to include microstrip, inverted microstrip, and slot line.
The ferro-electric element which induces the phase shift is Ba.
sub.
x Sr.
sub.
1-x TiO.
sub.
3 the properties of which have been described in more detail above.
The term ferro-electric element means an element fabricated from material that possesses an extremely high dielectric constant.
In the case of Ba.
sub.
x Sr.
sub.
1-x TiO.
sub.
3, the dielectric constant ranges from 200 to 5,000 depending on the Ba, Sr, and Tio.
sub.
3 composition ratio.
Ba.
sub.
x Sr.
sub.
1-x TiO.
sub.
3 is an amorphous, rigid ceramic solid prepared using standard ceramic processing techniques.
Its amorphous nature causes it to not have a preferred axis at zero volts, i.
e.
, at zero volts the dielectric constant is uniform in all directions.
Under voltage, the dielectric constant of the ferro-electric element is reduced along the direction of the electric field caused by the applied voltage.
The ferro-electric element, of course, has dielectric constants in the x, y, and z axes; under voltage, the dielectric constants along directions perpendicular to the electric field caused by the applied voltage remain unchanged.
In the microstrip embodiment, the microstrip circuit consists of a ferro-electric element interposed between a conductor line and a ground plane.
The microwave signal passes through an impedance transformer which matches the microwave signal into the ferro-electric element, thereby reducing signal reflection.
The microwave signal emerges from the transformer and travels through the ferro-electric element between the conductor line and the ground plane.
A DC voltage is applied between the conductor line and the ground plane, thereby controlling the dielectric constant of the ferro-electric material.
The dependency between the dielectric constant and the applied voltage is an inverse square root relationship, i
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MEMS 
