Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-01-05
2001-06-26
Phan, Tho G (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S850000
Reexamination Certificate
active
06252553
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a single element, multi-mode patch antenna system capable of forming a spatial null, and more particularly, to a patch antenna system which uses fundamental and higher order modes within a single microstrip patch radiator which is capable of forming a spatial null in the vicinity of the horizon where a jamming or interference threat is the greatest. More in particular, the present invention relates to an antenna system for GPS application which is provided with a feed network for uniquely feeding a single microstrip patch radiator for forming a spatial null and steering the created spatial null in azimuth and elevation thereof.
DESCRIPTION OF THE PRIOR ART
Hand held GPS receivers have revolutionized navigation in many areas. However, current military hand held receivers are vulnerable to jamming, both intentional and unintentional. For GPS applications, the receiving antenna pattern is necessarily hemispherical which further increases its vulnerability to jamming. Adaptive antennas and associated receiver electronics do exist, generally however, they rely on antenna arrays which are physically large for practical hand held use. Small arrays of two elements may be used to steer a single null in azimuth and elevation by combining their received signals with suitable amplitude and phase weighting. A miniature single element GPS receiving antenna for hand-held application capable of forming and steering a spatial null in azimuth and elevation has therefore become a need in navigation, military, and commercial areas of application.
Antennas have evolved in a wide variety of types, sizes, and degrees of complexity. For many military and commercial communication systems, such as Global Positioning Systems (GPS), as well as microstrip or patch antennas which have been widely used due to their lightweight, low cost, and low profile characteristics. Typically, a patch antenna includes a ground plane and a rectangular or circular patch radiator stacked on the ground plane and separated therefrom by a dielectric substrate or an air filled cavity.
In this form, the patch antenna constitutes essentially a pair of resonant dipoles formed by two opposite edges of the patch. The patch is of such dimension that either pair of adjacent sides can serve as halfway radiators, or the resonant dipole edges may be from approximately a quarter wavelength to a full wavelength long.
The GPS antenna receives satellite signals from a multiplicity of satellites located virtually anywhere overhead from horizon to horizon. It has been found that the circular polarization of the satellite signals is necessary and desirable. Thus, the incoming satellite signal has a right hand circular polarization. The GPS antenna system is also required to have circular polarization to exclude the dependence of the received signal amplitude on azimuth and elevation angle of the incoming satellite signal, i.e., to exclude polarization mismatch effects.
Additionally and in conjunction with the requirement for circular polarization of the GPS receiver antenna, a broad bandwidth is needed for receiving GPS signals.
The prior art discloses a number of Patents on microstrip patch antennas with circular polarization and broad bandwidth. For example, U.S. Pat. No. 5,319,378 describes a multi-band microstrip antenna capable of dual frequency operation. The antenna comprises a microstrip having a thin rectangular metal strip that is supported above a conductive ground plane by two dielectric layers which are separated by an air gap or other lower dielectric constant material. The antenna feed is a coaxial transmission line that provides a mechanism for coupling the antenna to an external circuit. The spaced dielectric layer and the air gap produces higher order modes in addition to the lower order mode, which causes dual frequencies of operation. This system is, however, susceptible to jamming.
U.S. Pat. No. 5,003,318 discloses a dual frequency microstrip patch antenna with capacitively coupled feed utilizing a stacked arrangement of circular radiating patches separated by a layer of dielectric for receiving signals transmitted by the GPS satellite. The upper stacked patches are further separated by another layer of dielectric from a pair of separated ground planes. A modal shorting pin extends between the patches and ground planes, and the patches are fed through a pair of feed pins by a backward wave feed network.
The shorting or modal pin in the center of each patch forces the antenna element into the TM01 mode. This modal pin connects the center of each radiating patch to the ground plane. When the upper patch is resonant, it uses the lower patch as a ground plane. The lower patch operates against the upper ground plane and acts nearly independently of the upper element. The antenna is fed through the two feed pins which are oriented at right angles to each other to excite orthogonal mode and are 90° out of phase to achieve circular polarization. The bandwidth of the antenna is increased by increasing the thickness of the dielectric material between the radiating patches.
As stated in the '318 Patent, the antenna enjoys increased bandwidth including a wider frequency operating range, and a wider operating range for a prescribed antenna gain which permits its use with a GPS system. Additionally, this prior art includes an adaptive nulling processor for interference rejection. The wider bandwidth permits the processor to develop deep nulls over a wide frequency range as is necessary for this system. The specifics of the adaptive nulling arrangement are not however described in the Patent. However, the stacked arrangement of a pair of ground boards and two patches with a plurality of dielectrical spacers therebetween is highly complex and is labor intensive in the manufacture of the system. The antenna limits itself to circularly shaped radiating patches and denies any other contours for radiating patches of the antenna.
U.S. Pat. No. 5,712,641 discloses an interference cancellation system for global positioning satellite receivers in which the orthogonally polarized components of the composite received signal are separated by the receiving antenna arrangement and adjusted in the polarization feed adaptor network between the antenna and GPS receiver to optimally cancel components.
The antenna and installation arrangement creates a polarization filter relative to interference sources which changes their apparent polarization orientation and support adaptive discrimination based on dissimilar polarization characteristics relative to the desired signals. The orthogonally received signal components from the GPS satellite and from interference sources are combined to adaptively create cross-polarization nulls that try to attenuate interference sources while slightly modifying the GPS received signal.
The orthogonal components of the received environment signal are filtered, amplified, and transmitted from the antenna system to the nulling system in each GPS band using separate cables. In the case of the L2 bypass configuration, the right hand circular polarization signal may be developed at the antenna entrance. A sample of the interference signal in each band of the GPS channel is detected and processed to identify interference conditions wherein control signals are produced that are applied to the adaptive antenna circuit in each band of interest that controls the effective tilt angle and ellipticity of the combined antenna system.
The effective polarization property of the antenna system is controlled so as to cross polarize or mismatch the antenna to the interference source and thus null or suppress the interference signal in the channel containing the GPS signal. However, this prior art system does not suggest using the fundamental TM010 and the TM001 mode and the higher order mode in the single patch antenna system in order to create a radiation pattern having a special null in the desired direction. Additionally, it does not suggest weighting the amplitude and phase betwe
Phan Tho G
Rosenberg , Klein & Lee
The Mitre Corporation
LandOfFree
Multi-mode patch antenna system and method of forming and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multi-mode patch antenna system and method of forming and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multi-mode patch antenna system and method of forming and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2435135