Miniaturized antennas based on negative permittivity materials
View Patent ↗An antenna comprises a resonator and a waveguide. The resonator comprises at least one body having a negative effective electrical permittivity or a negative magnetic permeability when a resonance is excited therein by electromagnetic radiation lying in some portion of the microwave spectrum. A termination of the waveguide is situated adjacent the resonator. The resonator is conformed such that at the resonance, there is efficient coupling between the resonator and the waveguide.
1. An apparatus comprising an antenna for operation in a range of frequencies including a resonant frequency f res of the antenna associated with a vacuum wavelength λ res of electromagnetic radiation, the antenna comprising:
a) at least one resonator of the kind in which a patterned structure, or a shaped material of negative electric permittivity or magnetic permeability, has maximum spatial extent less than one-half λ res and is effective, at least at f res , for:
i) supporting a resonance, and
ii) coupling to an external radiation field such that the resonant scattering cross-section of the resonator is at least about 0.3λ res 2 for at least one incident polarization and direction of electromagnetic radiation; and
b) a transmission line coupled to the resonator such that when the resonator is driven at f res by a driving signal in the transmission line, such portion of the driving signal as reflects back into the transmission line does so with a return loss of at least 10 dB.
2. The apparatus of claim 1 , wherein the transmission line comprises at least two conductors and has an end proximate the resonator, and one of said conductors terminates in a stub which extends beyond the end of the transmission line and lies adjacent the resonator.
3. The apparatus of claim 2 , wherein the transmission line has a center conductor and a ground conductor coaxial with the center conductor, the stub is continuous with the center conductor, and the stub and the transmission line lie on opposing sides of a planar conductive region that extends substantially perpendicularly to the transmission line and is electrically continuous with the ground conductor.
4. The apparatus of claim 3 , wherein the resonator comprises a toral body aligned coaxially with the stub.
5. The apparatus of claim 2 , wherein the transmission line is disposed on a planar surface.
6. The apparatus of claim 5 , wherein the transmission line comprises a center conductor disposed between two ground conductors, and the stub is continuous with the center conductor.
7. The apparatus of claim 6 , wherein the resonator comprises at least one metallization pattern disposed on a planar surface.
8. The apparatus of claim 7 , wherein the metallization pattern comprises at least one pair of resonant structures disposed symmetrically about the stub.
9. The apparatus of claim 7 , wherein at least one said metallization pattern is coplanar with the transmission line.
10. The apparatus of claim 7 , wherein the resonator comprises a stack of two or more metallization patterns occupying different planes.
11. The apparatus of claim 7 , wherein at least one said metallization pattern comprises a ring-shaped structure.
12. The apparatus of claim 1 , further comprising a ground plate situated adjacent the resonator, and wherein:
the transmission line is a coaxial cable having an inner and an outer conductor, and the outer conductor is electrically continuous with the ground plate;
the coaxial cable and the resonator lie on opposite sides of the ground plate;
proximate the resonator, the coaxial cable is terminated by a stub which is continuous with the inner conductor, said stub projecting through and beyond the ground plate such that at least a portion of the stub lies adjacent the resonator.
13. The apparatus of claim 12 , wherein the extent of the stub beyond the ground plate is less than λ res .
14. The apparatus of claim 13 , wherein the extent of the stub beyond the ground plate is less than one-fourteenth of λ res .
15. The apparatus of claim 1 , wherein the resonator has negative electrical permittivity when excited at the resonant frequency.
16. The apparatus of claim 1 , further comprising a source of radiofrequency signals for transmission, said source coupled to the transmission line so as to excite the antenna via said transmission line.
17. The apparatus of claim 1 , further comprising a radiofrequency receiver circuit coupled to the transmission line so as to receive radiofrequency signals from the antenna via said transmission line.