Antenna assembly for an RFID reader

1. An antenna assembly for a radio frequency identification (RFID) reader, the antenna assembly comprising:

a support member having an inner surface and an opposing outer surface;

a first bifilar helical antenna element wound about a first helical axis extending from the outer surface of the support member, wherein the first helical axis is exclusive to the first helical antenna element;

a first control terminal on the support member, electrically connected with the first bifilar helical antenna element;

a second bifilar helical antenna element wound about a second helical axis extending from the outer surface of the support member, wherein the second helical axis is exclusive to the second helical antenna element;

a second control terminal on the support member, electrically connected with the second bifilar helical antenna element;

a first plurality of additional bifilar helical antenna elements wound about respective helical axes extending from the outer surface at the primary radius from the center of the outer surface; and

a second plurality of additional bifilar helical antenna elements wound about respective helical axes extending from the outer surface at the secondary radius from the center of the outer surface,

wherein:

the first helical axis extends from the outer surface at a primary radius from a center of the outer surface;

the second helical axis extends from the outer surface at a secondary radius from the center of the outer surface;

the secondary radius is greater than the primary radius;

the first bifilar helical antenna element and the first plurality of additional bifilar helical antenna elements are arranged in a primary ring about the center of the outer surface;

the second bifilar helical antenna element and the second plurality of additional bifilar helical antenna elements are arranged in a secondary ring about the center of the outer surface; and

the bifilar helical antenna elements of the primary ring have a primary height greater than a secondary height of the bifilar helical antenna elements of the secondary ring.

2. The antenna assembly of claim 1 , wherein the outer surface is planar, and wherein the first and second helical axes are perpendicular to the outer surface.

3. The antenna assembly of claim 1 , wherein the first and second control terminals are disposed on the inner surface of the support member; the antenna assembly further comprising:

a first electrical conduit extending through the support member from the first control terminal to the first bifilar helical antenna element; and

a second electrical conduit extending through the support member from the second control terminal to the second bifilar helical antenna element.

4. The antenna assembly of claim 1 , wherein the secondary ring consists of eight bifilar helical antenna elements.

5. The antenna assembly of claim 1 , wherein the primary ring consists of six bifilar helical antenna elements.

6. The antenna assembly of claim 1 , further comprising:

a first mast extending from the outer surface of the support member along the first helical axis, to support the first bifilar helical antenna element; and

a second mast extending from the outer surface of the support member along the second helical axis, to support the second bifilar helical antenna element.

7. The antenna assembly of claim 6 , wherein the first and second masts are cylindrical.

8. The antenna assembly of claim 1 , wherein each first bifilar helical antenna element includes (i) a first volute wound from a first base through 180 degrees to a first summit, and (ii) a second volute wound from a second base opposite the first base, through 180 degrees to a second summit, and (iii) a short connecting the first summit and the second summit.

9. A radio frequency identification (RFID) reader, comprising:

an antenna assembly including:

a support member having an inner surface and an opposing outer surface;

a first bifilar helical antenna element wound about a first helical axis extending from the outer surface of the support member, wherein the first helical axis is exclusive to the first helical antenna element;

a first control terminal on the support member, electrically connected with the first bifilar helical antenna element;

a second bifilar helical antenna element wound about a second helical axis extending from the outer surface of the support member, wherein the second helical axis is exclusive to the second helical antenna element; and

a second control terminal on the support member, electrically connected with the second bifilar helical antenna element;

a transceiver connected to the first and second control terminals;

a controller connected to the transceiver, and configured to transmit data to the transceiver for emission via the antenna assembly;

a first plurality of additional bifilar helical antenna elements wound about respective helical axes extending from the outer surface at the primary radius from the center of the outer surface; and

a second plurality of additional bifilar helical antenna elements wound about respective helical axes extending from the outer surface at the secondary radius from the center of the outer surface,

wherein:

the first helical axis extends from the outer surface at a primary radius from a center of the outer surface;

the second helical axis extends from the outer surface at a secondary radius from the center of the outer surface;

the secondary radius is greater than the primary radius;

the first bifilar helical antenna element and the first plurality of additional bifilar helical antenna elements are arranged in a primary ring about the center of the outer surface;

the second bifilar helical antenna element and the second plurality of additional bifilar helical antenna elements are arranged in a secondary ring about the center of the outer surface; and

the bifilar helical antenna elements of the primary ring have a primary height greater than a secondary height of the bifilar helical antenna elements of the secondary ring.