Multi-mode patch antenna system and method of forming and steering a spatial null

• US 6,252,553 B1
• Filed: 01/05/2000
• Issued: 06/26/2001
• Est. Priority Date: 01/05/2000
• Status: Expired due to Term

• Current Assignee: Mitre Corporation
• Original Assignee: Mitre Corporation
• Inventors: Solomon, Moise N.
• Primary Examiner(s): PHAN, THO GIA
• Application Number:
  US09/478,221
• Time in Patent Office: 538 Days
• Field of Search: H01/Q.138, H01/Q 2.106, 343/700.MS, 343/846, 343/778, 343/829, 343/830, 343/850, 343/852
• US Class Current: 343/700.0MS
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40
• CPC Class Codes: H01Q 9/0442 with particular tuning means
• CPC Class Codes: H01Q 9/045 with particular feeding means for circular polarisation H01Q9/0428

Abstract

A hand-held antenna specifically for GPS applications is provided which includes a microstrip patch antenna having a ground board, a single radiating patch spaced from the ground board and a resonant cavity defined between the ground board and the single radiating patch. Feed points are provided, one in the geometrical center of the radiating patch, and one, two, or four equidistantly spaced from the central feed point and disposed at 90° angular intervals. A feed network couples fundamental modes of excitation to the side feed points on the patch and a higher mode of excitation to the central feed point. Amplitude and phase controllers are provided in the feed network for amplitude and phase shifting between the fundamental and higher order modes of excitation in order to steer a spatial null in azimuth and elevation.

Claims

1. An antenna system, comprising:

a patch antenna, including;

a ground plane,

a single radiating patch installed in spaced relationship to said ground plane and extending substantially parallel thereto,

a dielectric filled resonant cavity located between said ground plane and said single radiating patch,

a central feed point disposed at the geometric center of said single radiating patch, and

at least one first side feed point on said single radiating patch disposed a predetermined distance from said central feed point; and

a feed network, coupled to said central and said at least one first side feed point,

said feed network including;

a first path for coupling at least a first fundamental mode of excitation to said at least one first side feed point,

a second path for coupling a higher order mode of excitation to said central feed point to generate a top-loaded monopole radiation pattern, and

means for controlling an amplitude and phase relationship between said at least first fundamental mode of excitation and said higher order mode of excitation, thereby creating a radiation pattern of said patch antenna having a directionally adjustable spatial null.

2. The antenna system of claim 1, further comprising:

a second side feed point on said single radiating patch, said second side feed point being spaced from said central feed point by a distance substantially equal to said predetermined distance, whereby imaginary lines extend between said central feed point and each of said first and second side feed points being orthogonal each with respect to the other;

said first path of said feed network further coupling a second fundamental mode of excitation to said second side feed point;

said first and said second fundamental modes of excitation being phase shifted by substantially 90°

, thereby creating a circularly polarized radiation pattern of said patch antenna.

3. The antenna system of claim 2, including a Global Positioning System (GPS) receiver or wireless communications receiver, whereby a signal received by said patch antenna propagates from said central and said first and second side feed points through said feed network towards said GPS receiver.

4. The antenna system of claim 2, wherein said fundamental modes of excitation and said higher-order mode of excitation are respectively coupled to said side feed points and central feed point simultaneously, thereby creating said radiation pattern of said patch antenna, said radiation pattern constituting a combination of a circularly polarized radiation pattern and said top loaded monopole radiation pattern.

5. The antenna system of claim 2, wherein said first path of said feed network includes:

a first arm coupled at a first end thereof to said first side feed point,

a second arm coupled at one end thereof to said second side feed point,

a 90°

phase shifter coupled to either one of said first and second arms between said first end thereof and a second end thereof, and first combiner means coupled between said second end of said first arm and a second end of said first arm and a second end of said second arm,

a first line having first and second ends, coupled at said first end thereof to an output of said first combiner means;

said second path of said feed network includes a second line having first and second ends thereof coupled at said first end thereof to said central feed point;

amplitude control means for controlling signal amplitudes, said amplitude control means coupled in either one of said first and second lines between said first and second ends thereof;

phase control means for controlling signal phases coupled to either one of said first and second lines between said first and second ends thereof;

second combiner means coupled between said second ends of said first and second lines for combining output signals of said first and second paths of said feed network; and

a third line coupled to an output of said second combiner means for receiving a combined output signal from said feed network and providing said combined output signal to a global positioning system receiver.

6. The antenna system of claim 5, wherein said phase control means controls location of the spatial null in azimuth.

7. The antenna system of claim 5, wherein said amplitude control means controls location of the spatial null in elevation.

8. The antenna system of claim 1, wherein each of said first and second paths of said feed network further includes at least one feed probe and at least one transmission line terminating in said feed probe, said at least one feed probe protruding through said ground plane towards said single radiating patch for direct electrical contact with a respective one of said side and central feed points thereon, and said feed probe extending through said dielectric filled resonant cavity for injecting and extracting energy therefrom.

9. The antenna system of claim 1, further including four side feed points equidistantly spaced from said central feed point and arranged on said single radiating patch at 90°

mutual angular disposition therebetween.

10. The antenna system of claim 9, wherein each pair of adjacent side feed points of said four side feed points is fed with fundamental modes of excitation, phase shifted substantially 90°

each with respect to the other.

11. A method of forming a radiation pattern having a spatial null of an antenna for a GPS (global positioning system) receiver, comprising the steps of:

providing a patch antenna including;

a ground board,

a single radiating patch spaced from said ground board,

a dielectric filled resonant cavity defined between said single radiating patch and said ground board,

a central feed point defined in the geometrical center of said single radiating patch, and

first and second side feed points on said single radiating patch substantially equidistantly spaced from said central feed point and disposed in angular orthogonal relationship therebetween;

providing a feed network, comprising;

a first path connected to said first and second side feed points, and

a second path connected to said central feed point;

coupling first and second 90°

phase shifted fundamental modes of excitation to said first and second side feed points through said first path, and simultaneously coupling a higher order mode of excitation to said central feed point, thereby creating a radiation pattern having a spatial null;

amplitude shifting said fundamental modes of excitation with respect to said higher-order mode of excitation, thereby steering said spatial null in elevation; and

phase shifting said fundamental modes of excitation with respect to said higher-order mode of excitation, thereby steering the spatial null in azimuth.