Compact multi-band antenna
A multi-band antenna is disclosed that can operate in two different frequency bands through two different modes of operation. It can operate as a radio antenna for coupling energy into or out of a radio signal in a radio frequency band; or it can operate as a magnetic antenna for coupling energy into or out of a magnetic signal in a lower frequency band. A radio signal is a signal consisting of an electromagnetic wave; a magnetic signal is a signal consisting of a magnetic field. The multi-band antenna achieves the two modes of operation in a compact volume of space comparable to the volume of space occupied by an equivalent single-band antenna.
1. A dual-frequency antenna comprising:
a flat magnetic coil physically adapted for efficient antenna coupling with magnetically-coupled energy at a first frequency;
wherein the shape of the coil is also physically adapted for efficient antenna coupling with electromagnetic energy at a second frequency;
wherein the flat magnetic coil comprises multiple coil layers; and
wherein coil loops in one coil layer are in a shifted position, relative to coil loops in an adjacent layer, such that the capacitance between adjacent coil loops is large enough to present a low impedance at the second frequency.
2. A dual-frequency antenna comprising:
a flat magnetic coil physically adapted for efficient antenna coupling with magnetically-coupled energy at a first frequency;
wherein the shape of the coil is also physically adapted for efficient antenna coupling with electromagnetic energy at a second frequency;
wherein the flat magnetic coil comprises at least one coil layer, and at least one other layer that comprises a conductive strip; and
wherein the conductive strip is physically arranged such that the conductive strip is capacitively coupled with a plurality of coil loops.
3. A method for making a dual-frequency antenna, the method comprising:
(i) designing an antenna for efficient coupling with electromagnetic energy at a first frequency, wherein the antenna design is based on one or more sheets of electrically conductive material;
(ii) replacing, in the antenna design, at least part of one of the one or more sheets with a flat magnetic coil; and
(iii) providing a first input-output port coupled with the magnetic energy at the first frequency, and a second input-output port coupled with the electromagnetic energy at the second frequency;
wherein the flat magnetic coil is designed with coil loops in one coil layer that are placed in a shifted position, relative to coil loops in an adjacent layer, such that the capacitance between adjacent coil loops is large enough to present a low impedance at the second frequency.
4. A method for making a dual-frequency antenna, the method comprising:
(i) designing an antenna for efficient coupling with electromagnetic energy at a first frequency, wherein the antenna design is based on one or more sheets of electrically conductive material; and
(ii) replacing, in the antenna design, at least part of one of the one or more sheets with a flat magnetic coil;
wherein the flat magnetic oil is designed so as to provide efficient coupling with magnetic energy at a second frequency;
wherein the flat magnetic coil is designed with at least one coil layer, and at least one other layer that comprises a conductive strip; and
wherein the conductive strip is physically arranged such that the conductive strip is capacitively coupled with a plurality of coil loops.