Four-port patch antenna

Details Four-port patch antenna Four-port patch antenna

2001-08-22

2003-04-15

Le, Hoanganh (Department: 2821)

Communications: radio wave antennas

Antennas

Microstrip

C343S846000

Reexamination Certificate

active

06549166

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to phased array antenna systems. More specifically, but without limitation thereto, the present invention relates to a patch antenna for a phased array antenna system for radiating a circularly polarized wave over a wide frequency band.
A typical phased array antenna used, for example, in code division multiple access (CDMA) communications systems, consists of many array elements arranged in a two-dimensional aperture. An array element commonly used in these phased array antennas has a conductive area or “patch” on one side of a patch substrate made of a dielectric material and a pattern of slots formed in an electrically conductive ground plane on the opposite side of the patch substrate. A hybrid network couples radio frequency signals capacitively to the slots in the ground plane through a feed substrate made of a dielectric material facing the side of the ground plane opposite to the patch substrate. Array elements having this structure are called patch antennas.
A two-port patch antenna element is typically used for dual-band and dual polarization applications. A two-port patch antenna has two input ports or excitation ports. When the first port is driven by a radio frequency signal, the TM-01 mode is excited (for a rectangular patch). When the second port is driven by a radio frequency signal, the TM-10 mode is excited. The TM-01 and the TM-10 modes are mutually orthogonal, and the resonant frequencies may be controlled independently, for example, by changing the length and width of the patch. The polarizations of the TM-01 and the TM-10 modes are also mutually orthogonal.
A disadvantage of two-port patch antennas is that when the first port is driven, not only is the TM-01 mode excited, but also the TM-02, TM-03, etc. modes. The TM-02 mode introduces asymmetry in the radiation pattern of the patch antenna, resulting in axial ratio degradation at angles from the boresight direction.
Another disadvantage of two-port patch antennas besides poor axial ratio performance over a wide frequency band is significant return loss, or reflected power, at the input.
SUMMARY OF THE INVENTION
The present invention advantageously addresses the problems above as well as other problems by providing a patch antenna that has four ports for circular polarization that suppress the TM-02 mode, resulting in a radiation pattern that is symmetric. The axial ratio performance is consequently superior to that of two-port patch antennas.
In one embodiment, the present invention may be characterized as a patch antenna that includes a patch made of an electrically conductive material, a patch substrate coupled to the patch wherein the patch substrate is made of a dielectric material, a ground plane coupled to the patch substrate wherein the ground plane is made of an electrically conductive material having at least four slots formed therein, a feed substrate coupled to the ground plane wherein the feed substrate is made of a dielectric material, and a hybrid network coupled to the feed substrate that includes a right hand circularly polarized port, a left hand circularly polarized port, and two matched terminated ports.
In another embodiment, the present invention may be characterized as a phased array antenna for a communications system that includes an array of patch antennas wherein each patch antenna includes a patch made of an electrically conductive material, a patch substrate coupled to the patch wherein the patch substrate is made of an electrically insulating material, a ground plane coupled to the patch substrate wherein the ground plane is made of an electrically conductive material having at least four slots formed therein, a feed substrate coupled to the ground plane wherein the feed substrate is made of a dielectric material, and a hybrid network coupled to the feed substrate that includes a right hand circularly polarized port, a left hand circularly polarized port, and two matched terminated ports.


REFERENCES:
patent: 4903033 (1990-02-01), Tsao et al.
patent: 5043738 (1991-08-01), Shapiro et al.
patent: 5124713 (1992-06-01), Mayes et al.
patent: 5223848 (1993-06-01), Rammos et al.
patent: 5241321 (1993-08-01), Tsao
patent: 5880694 (1999-03-01), Wang et al.

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