Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-05-04
2001-09-18
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
Reexamination Certificate
active
06292143
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to patch antennas and, more particularly, to a multi-mode broadband patch antenna that selects the parameters of a radiator so that it operates in an odd-order mode generating a broadside beam and provides tuning by providing a ferroelectric film sandwiched between a substrate and the radiator and by applying a dc field between the radiator and ground plane.
BACKGROUND OF THE INVENTION
Microstrip antennas comprise a radiator element commonly referred to as a patch. Microstrip patch antennas are highly desirable for aerospace applications because they are lightweight, conformal, and inexpensive since they can be produced using conventional lithographic methods. These microstrip patch antennas are becoming increasingly important because of the proliferation of low Earth orbiting communications and remote sensing satellites that generally demand phased array antenna systems advantageously comprised of microstrip patch antennas. Microstrip patch antennas are known and some of which are described in U.S. Pat. Nos. 5,315,753; 5,448,252; 5,561,435; 5,589,845; 5,694,134; 5,777,581; 5,818,391; 5,838,282; and 5,870,057, all of which are herein incorporated by reference. The patch geometry can be square, rectangular, a disk or an annular ring. A major drawback of microstrip antennas is their inherently narrow instantaneous bandwidth, typically 1% or so. Intuitively obvious approaches to enhance bandwidth, such as the use of extremely low permittivity substrates or thick substrates are typically met with an undesirable increase in antenna size or the generation of surface waves that degrade the efficiency of the antennas.
Several approaches are known to increase patch antenna bandwidth. For example, stacked patches have been used to generate dual resonant frequencies. In this approach, a bottom patch is covered with a dielectric layer that serves as the substrate for a top patch. The bottom patch serves as a ground plane for the top patch. Bancroft in a technical article “Accurate Design of Dual-Band Antennas,” Microwaves & RF, September, 1988, pp. 113-118, herein incorporated by reference, describes such a bottom patch covered with a dielectric layer and operating at 9 and 11 GHz, a difference of about 20%. Another approach is to use varactor diodes to modify the resonant frequency and is described in a technical article “Active Patch Antenna Element with Diode Tuning,” of P. Haskins, P. Hall, and J. Dahele, Electronics Letters, Vol. 27, No. 20, September, 1991, pp. 1846-1847, which is herein incorporated by reference. Haskins et al integrated a diode with a multilayer patch and obtained a 4% tuning range. Navarro and Chang in a technical article “Broadband Electronically Tunable IC Active Radiating Elements and Power Combiners,” Microwave Journal, October, 1992, pp. 87-101, herein incorporated by reference, integrated a varactor with a notch antenna and achieved tuning from 8.9 to 10.2 GHz, a range of about 14%. Kiely, Washington, and Bernhard in a technical article “Design and Development of Smart Microstrip Patch Antennas,” Journal of Smart Materials and Structures, Vol. 7. pp. 792-800, 1998, herein incorporated by reference, arranged a patch above a parasitic element and varied the separation therebetween by using piezoelectric actuators to shift the frequency. Rainville and Harackiewicz in a technical article IEEE Micro Guided Wave Lett., Vol. 12, no. 2, pp. 483-485, 1992, herein incorporated by reference, describe a patch fabricated on a ferrite film. The application of an in-plane magnetic field onto this ferrite film advantageously tuned the resonant frequency of a cross-polarized field, but not the co-polarized field. The tuning range was 5.86 to 6.03 GHz, about 3%. Although each of these efforts further advanced the art, it is desired that further improvement be made to further increase patch antenna bandwidth so as to enhance their application to both the military and commercial endeavors. Commercial and military applications include low cost tracking terminals to advantageously complement the forthcoming wideband low Earth orbiting satellite constellations and stealthy communications and radar systems.
OBJECTS OF THE INVENTION
It is the primary object of the present invention to provide for a patch antenna having a bandwidth that is maintained about a selectable frequency and which can be tuned over a relatively broad frequency range.
It is another object of the present invention to provide for a broadband patch antenna that can be used for reception at a selected individual frequency, such as 19 GHz, and transmission at another individually selected frequency, such as 29 GHz.
It is still another object of the present invention to provide for a broadband patch antenna that may be fabricated in a relatively inexpensive manner, such as by using conventional photolithography similar to that use for semiconductors and printed circuits.
It is a further object of the present invention to provide for a broadband patch antenna having an odd-order mode of operation generating a broadband beam, and also allowing for tuning by applying a dc voltage between the radiating element and ground plane.
It is a still further object of the present invention to provide a ferroelectric film having a dielectric constant which is a function of the voltage applied across the film so as to modify the dielectric constant and correspondingly adjust the apparent electrical length of the broadband patch antenna.
SUMMARY OF THE INVENTION
This invention is directed to a broadband patch antenna that can transmit or receive at two essentially independent frequencies, while at the same time has tuning capabilities to vary the selected frequency over a predetermined frequency range.
A tunable microstrip patch antenna element is provided and comprises a ground plane comprised of a conductive material, a substrate comprised of a dielectric or semiconductive material which is mounted on the ground plane, a radiator, and a ferroelectric film. The radiator has an apparent electrical dimension and has parameters that are selected so as to operate in a fundamental mode at an odd-order common denominator of desired operating frequencies. The radiator has a circuit for connecting to means for generating a dc electric field between the radiator and the ground plane. The ferroelectric material is placed on the substrate, and in cooperation with the substrate, is deterministic of the apparent dimension of the radiator.
REFERENCES:
patent: 5315753 (1994-05-01), Jensen
patent: 5448252 (1995-09-01), Ali
patent: 5561435 (1996-10-01), Nalbandian
patent: 5589845 (1996-12-01), Yandrofski
patent: 5694134 (1997-12-01), Barnes
patent: 5777581 (1998-07-01), Lilly
patent: 5818391 (1998-10-01), Lee
patent: 5838282 (1998-11-01), Lalezari
patent: 5870057 (1999-02-01), Evans
Bancroft, Randy: “Accurate Design of Dual-Band Antennas”, Microwaves and RF, Sep. 1988, pp. 113-118.
Haskins, P. et al: “Active Patch Antenna Element with Diode Tuning”, Electronics Letters, vol. 27, No. 20, Sep. 1991, pp. 1846-1847.
Navarro, Julio & Chang, Kai: “Broadband Electronically tunable IC Active Radiating Elements and Power Combiners”, Microwave Journal, Oct. 1992, pp. 87-101.
Keily, Edward & Washington, Gregory, & Bernhard, Jennifer: “Design and Development of Smart Microstrip Patch Antennas”, Journal of Smart Materials and Structures, vol. 7, 1998, pp.792-800.
Rainville, P.J. & Harackiewicz, F.J.: IEEE Micro Guided Wave letters, vol. 12, No. 2, 1992, pp. 483-485, “Magnetic Tuning of a Microstrip Patch Antenna Fabricated on a Ferrite Film”.
Stone Kent N.
The United States of America as represented by the Administrator
Wimer Michael C.
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