1. Field of the Invention
The present invention relates to methods and apparatuses to obtain variable power level distribution through a corporate power divider network. The present invention relates to monolithic thin film power dividers. The present invention relates to an actively balanced power division technique suitable for RF signals in the millimeter wave spectrum.
2. Description of Related Art
Multiple polarization antennas are typically implemented through a conjunction of either electrical or mechanical switching, electrical or mechanical attenuation, electrical or mechanical phase shifting, and dedicated transmission line routing definitions. Attenuators reduce the RF efficiency by “throwing away” RF power to achieve the desired power balance between the orthogonal ports.
In the field of wireless base station antenna systems, U.S. Pat. No. 6,864,837 discloses an antenna having a beam steering circuit including variable power divider and a multi-beam beam forming network. FIG. 3 illustrates a conceptual view of the prior art variable power divider. The variable power divider preferably uses a single adjustable control element 34, typically a microstrip wiper arm, to divide the input voltage signal into the voltage drive signals V1 and V2, which have complementary amplitude over the range of voltage amplitude division. In FIG. 3, “A” represents the 50% division point. The power division varies smoothly between position “C”, in which 100% power goes to V1, to “B”, in which zero power goes to V1.
The adjustable control element 34 operates by swinging along the transmission line arc in order to alter the relative lengths of transmission lines between the single input port and the two input ports to the hybrid combiner stage. The voltage drive signals V1 and V2 provide input signals to the multi-beam forming network, which is typically configured as an orthogonal two-by-four beam forming network or a four-by-four Butler matrix. The beam forming network outputs beam driving signals that each include a component from each of the voltage drive signals V1 and V2. As the induced relative phase differences combine within the multi-beam beam forming network, a desired power distribution balance is achieved. However, because of the mechanical operation of the adjustable control element, the beam steering circuit is limited to low frequency applications.
Piezoelectric materials include a subgroup consisting of pyroelectric materials, which in turn include ferroelectric materials. A ferroelectric crystal is a crystal which belongs to the pyroelectric family (i.e., shows a spontaneous electric polarization), and whose direction of spontaneous polarization can be reversed by applying an electric field. When the electric field is removed, the polarization still remains. To eliminate the polarization, an external opposite electric field is required.
An antiferroelectric crystal is a crystal whose structure can be considered as being composed of two sublattices polarizing spontaneously in antiparallel directions at least in one projection, and whose ferroelectric phase can be induced by applying an electric field. Subsequently, in antiferroelectrics, the induced phase transition is observed as a double hysteresis loop. Also, above a certain temperature, ferroelectricity in most ferroelectric materials will disappear and transition to paraelectric.
Furthermore, the spontaneous polarization in ferroelectrics or the sublattice polarization in antiferroelectrics can be regarded as a structural perturbation on a nonpolarized crystal. The non-perturbed crystal structure can be considered as a paraelectric structure. The paraelectric structure can be realized by making the ferroelectric polarization or the sublattice polarization equal to zero. The phase having a paraelectric structure is called a paraelectric phase.
Ferroelectricity and antiferroelectricity are also based on the dielectric behavior of the crystal. A change in the dielectric constant induced by applying an electric field causes a change in the effective electrical length of the device.
U.S. Pat. No. 6,875,369 to Tidrow et al., dated Apr. 5, 2005, discloses examples of ferroelectric/paraelectric materials. In particular, Tidrow discloses materials derived from Barium-Strontium-Titanate (Ba1-xSrxTiO3 “BST”).
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