Communications: radio wave antennas – Antennas – Including magnetic material
Reexamination Certificate
2000-06-16
2001-12-25
Phan, T. (Department: 2821)
Communications: radio wave antennas
Antennas
Including magnetic material
C343S7000MS, C343S909000, C333S161000
Reexamination Certificate
active
06333719
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to microwave antenna and, in particular, is directed to a tunable ferroelectric stacked antenna with enhanced bandwidth and gain.
BACKGROUND OF THE INVENTION
Tunable antennas with different operating frequency bands have received increasing attention recently. However, most of them use diodes or shorting pins to achieve tuning performance. This additional circuitry adds protrusion and complexity to the circuit structure that impedes the capability of these antennas to operate in a high temperature, conformal and rugged environment.
The use of ferroelectric materials in phase shifters is disclosed in “Ceramic Phase Shifters for Electronically Steerable Antenna Systems”, Varadan et al., Microwave Journal, January 1992, pages 116-126. Some different configurations also appear in U.S. Pat. No. 5,561,407 and U.S. Pat. No. 5,307,033, both issued to Koscica et. al. The use of ferroelectric tunable resonators in filter circuits appears in U.S. Pat. No. 5,617,104 to Das. Ferroelectric materials have also been described for use in electronic phased scanning periodic arrays. For example, such arrays are described in U.S. Pat. No. 5,589,845 to Yandrofski et al., U.S. Pat. No. 5,729,239 to Rao and U.S. Pat. No. 5,557,286 to Varadan et. al. In such arrays, electrical scanning of an RF energy beam pattern is the main concern.
The common dielectric constant values for barium strontium titanate materials used in the systems disclosed in U.S. Pat. No. 5,427,988 to Sengupta et al. and U.S. Pat. No. 5,557,286 to Varadan et al. are relatively high for typical antenna applications. The challenges and difficulties to produce a low dielectric constant material with good electrical properties for antenna applications has been highlighted in “Ferroelectric Materials For Phased Array Applications”, Rao et. al., “IEEE Antennas & Propagation Society International Symposium”, volume. 4, pages. 2284-2287, 1997. In trying to produce a low dielectric substrate, electrical inhomogeneity, low tunability and poor loss tangent performance are the commonly associated drawbacks. As a result, most of these ferroelectric antennas are realized on a high dielectric constant substrate.
Microstrip antennas with high permittivity substrates suffer from poor efficiency due to the energy loss associated with the excitation of surface wave modes. It has been found that for a single layer ferroelectric antenna with dielectric constant of around 16, the radiating output power from the antenna is lower than the power supplied to the input port. Parasitically coupled antennas may be used to increase the gain, but for these antennas, the performance is optimized at a certain discrete frequency only.
Accordingly, there is a need for a compact antenna that is electrically tunable. There is also a need for such an antenna with a substantial bandwidth and gain.
SUMMARY OF THE INVENTION
The present invention provides an antenna structure, which operates in a continuous tunable mode, which exhibits resonance at different tunable frequency bands and at the same time has a substantial bandwidth and enhanced radiation efficiency.
The antenna of the invention has a stacked assembly that includes a ferroelectric substrate that carries on one face thereof an electrically ground plane and on its opposite face an electrically conductive patch serving as an active feeder-resonator. A second dielectric layer is supported above the ferroelectric substrate. A parasitic radiator patch is disposed on top of the second dielectric layer. The resonant frequency of the stacked antenna assembly varies with the value of a DC voltage applied across the ferroelectric substrate. The tunable ferroelectric substrate has the advantage of being conformal and yet achieving the goal of a frequency hopping microwave communication system.
An aspect of the invention is an air gap between the ferroelectric substrate and the second dielectric layer. The air gap space provides two important useful features for the antenna structure. First, it enhances the gain of the antenna structure. Second, it allows wire connections to the feeder resonator for the coupling of the bias voltage thereto. The air gap also serves to enhance an electromagnetic coupling of electrical energy from the feeder resonator to the parasitic radiator.
In accordance with another aspect of the invention, a DC bias pad is positioned along the centerline of the feeder resonator. The centerline lies on the symmetry plane that bisects the feeder resonator patch into two equal halves. DC voltage is then applied via a DC block to the bias pad.
Another aspect of the invention is a cascaded of multi-stage feed network is designed and optimized on the ferroelectric tunable substrate. The tunable feed network provides a frequency variable impedance matching function for the antenna structure over different frequency bands.
REFERENCES:
patent: 5307033 (1994-04-01), Koscica et al.
patent: 5427988 (1995-06-01), Sengupta et al.
patent: 5557286 (1996-09-01), Varadan et al.
patent: 5561407 (1996-10-01), Koscica et al.
patent: 5589845 (1996-12-01), Yandrofski et al.
patent: 5617104 (1997-04-01), Das
patent: 5729239 (1998-03-01), Rao
patent: 6049726 (2000-04-01), Gruenwald et al.
patent: 6160524 (2000-12-01), Wilber
“Ceramic Phase Shifters for Electronically Steerable Antenna Systems” by Varadan et al., 1992, pps. 5 pages, Microwave Journal, pp. 116-126.
“Ferroelectric Materials for Phased Array Applications”, IEEE Antennas & Propogation Society International Symposium, vol. 4, pp. 2284-2287, 1997.
Teo Peng Thian
Varadan Vijay K.
Ohlandt Greeley Ruggiero & Perle L.L.P.
Phan T.
The Penn State Research Foundation
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