Multi-resonant, high-impedance electromagnetic surfaces

• US 6,512,494 B1
• Filed: 10/04/2000
• Issued: 01/28/2003
• Est. Priority Date: 10/04/2000
• Status: Expired due to Fees

• Current Assignee: Wemtec Inc.
• Original Assignee: E-Tenna Corporation
• Inventors: McKinzie, William E. III, Diaz, Rodolfo E.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Dinh, Trinh Vo
• Application Number:
  US09/678,128
• Time in Patent Office: 846 Days
• Field of Search: H01/Q 1.502, 343/909, 343/700.MS, 343/770, 343/767, 343/748, 343/788, 343/842, 343/866, 343/911.R
• US Class Current: 343/909
• CPC Class Codes: H01Q 15/008 said selective devices having Sievenpipers' mushroom elements
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
• CPC Class Codes: H01Q 9/0442 with particular tuning means

Abstract

An artificial magnetic conductor is resonant at multiple resonance frequencies. The artificial magnetic conductor is characterized by an effective media model which includes a first layer and a second layer. Each layer has a layer tensor permittivity and a layer tensor permeability having non-zero elements on the main tensor diagonal only.

Claims

1. An artificial magnetic conductor (AMC), the AMC characterized by an effective media model comprising:

a first layer and a second layer, each layer having a layer tensor permittivity and a layer tensor permeability, each said layer tensor permittivity and each said layer tensor permeability having non-zero elements on a main diagonal only, x and y tensor directions being in-plane with each respective layer and z tensor direction being normal to each layer the first layer including a specific arrangement of conducting and dielectric regions chosen to produce, resonance at predetermined multiple frequencies which are not necessarily harmonically related.

2. The AMC of claim 1 wherein the first layer and the second layer are electrically thin relative to the free space wavelength of the resonance frequencies.

3. The AMC of claim 2 wherein the first layer has a thickness t and the second layer has a thickness h and wherein h<

λ

/10 and t<

λ

/10, wherein λ

corresponds to the free space wavelength of the resonance frequencies.

4. The AMC of claim 1 wherein the second layer is characterized by a periodic rodded media including rods having longitudinal axes parallel to the z tensor direction within a host medium.

5. The AMC of claim 4 wherein the permittivities of the second layer in the x tensor direction and the y tensor direction are independent of frequency.

6. The AMC of claim 5 wherein the permittivities of the second layer in the x tensor direction and the y tensor direction are within 5% of the host medium dielectric value.

7. The AMC of claim 4 wherein the permittivity of the second layer in the z tensor direction is negative at the multiple resonance frequencies.

8. The AMC of claim 4 further comprising a conductive ground plane electrically coupled with one end of each of the rods.

9. The AMC of claim 8 wherein the second layer comprises:

a periodic array of rods disposed within the host medium, each rod having a predetermined cross section having dimensions small relative to the free space wavelength of the resonance frequencies.

10. The AMC of claim 1 wherein the first layer is characterized by transverse permittivities in the y tensor direction and the x tensor direction which are variable with frequency and which exhibit one or more Lorentz resonances.

11. The AMC of claim 10 wherein the transverse permittivity in the y tensor direction is substantially equal to the transverse permittivity in the x tensor direction.

12. The AMC of claim 10 wherein the transverse permittivity in the y tensor direction does not equal the transverse permittivity in the x tensor direction to produce an anisotropic high impedance surface.

13. The AMC of claim 10 wherein the one or more Lorentz resonances fall between the multiple resonant frequencies of the AMC.

14. The AMC of claim 10 wherein the transverse permittivity of the first layer is modeled by ${\varepsilon }_{}$

1

t=Y

(ω

)jω

ɛ

0

t

where Y(ω

) is an admittance function described by Foster'"'"'s second canonical form for a one port circuit, $Y<br><br>\left(\mathrm{\omega <br><br>}\right)=\mathrm{j\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>C_{\mathrm{\infty <br><br>}}+\frac{1}{\mathrm{j\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>L_o}+\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>\frac{1}{R_n+\mathrm{j\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>L_n+\frac{1}{\mathrm{j\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>C_n}},$

where j is the imaginary operator, ω

is radian frequency, ε

_o is the permittivity of free space, C_∞

is the asymptotic limit on transverse capacitance of the first layer as ω

approaches an infinite value, L_o is the asymptotic limit on shunt inductance of the model as ω

approaches 0, R_n is a branch resistance, L_n is a branch inductance and C_n is a branch capacitance.

15. The AMC of claim 14 wherein the poles of Y(ω

) correspond to Lorentz resonances in transverse permittivities in the x and y tensor directions.

16. The AMC of claim 14 where in the number of the multiple resonance frequencies of the AMC is one more than the number of poles of Y(ω

).

17. The AMC of claim 10 wherein the first layer is characterized by a normal permittivity in the z tensor direction which is substantially constant with frequency and substantially equal to 1.

18. The AMC of claim 10 wherein the normal permeability of the first layer is modeled by ${\mu }_{}$

1

z=Z

(ω

)jω

μ

0

t

where Z(ω

) is an impedance function described by Foster'"'"'s first canonical form for a one port circuit, $Z<br><br>\left(\mathrm{\omega <br><br>}\right)=\mathrm{j\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>L_{\mathrm{\infty <br><br>}}+\frac{1}{\mathrm{j\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>C_o}+\underset{n=1}{\overset{N}{\sum <br><br>}}<br><br>\frac{1}{G_n+\mathrm{j\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>C_n+\frac{1}{\mathrm{j\omega <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>L_n}},$

where ω

is radian frequency, L_∞

is the asymptotic limit on series inductance of the model as ω

approaches an infinite value, C_o is the asymptotic limit on the circuit capacitance as ω

approaches 0, G_n is a conductance, C_n is a capacitance, and L_n is an inductance for an nth antiresonant circuit.

19. The AMC of claim 18 wherein poles of Z(ω

) are Lorentz resonances in normal permeability of the first layer in the z tensor direction.

20. The AMC of claim 1 wherein the multiple resonance frequencies of the AMC satisfy the equation ${\varepsilon }_{}$

1

t=1ω

2

μ

2

t

μ

0

ɛ

0

ht,

where ε

_1t is the transverse permittivity of the first layer, μ

_2t is the transverse permeability of the second layer, ω

=2π

f is radian frequency, and t and h are thicknesses of the first layer and the second layer, respectively.

21. The AMC of claim 20 wherein the multiple resonance frequencies of the AMC further satisfy the relation ${\varepsilon }_{}$

1

t=Y

(ω

)jω

ɛ

0

t.

22. The AMC of claim 21 wherein intersections of the equations ${\varepsilon }_{}$

1

t=1ω

2

μ

2

t

μ

0

ɛ

0

ht

 



and

 



ɛ

1

t=Y

(ω

)jω

ɛ

0

t

define the multiple resonant frequencies where AMC reflection phase goes to zero.

23. An artificial magnetic conductor operable over at least a first high-impedance frequency band and a second high-impedance frequency band as a high-impedance surface, the artificial magnetic conductor being defined by an effective media model comprising:

a spacer layer; and

a frequency selective surface (FSS) disposed adjacent the spacer layer and having a transverse permittivity so, defined by ${\mathrm{\varepsilon <br><br>}}_{1<br><br>x}={\mathrm{\varepsilon <br><br>}}_{1<br><br>y}=\frac{Y<br><br>\left(\mathrm{\omega <br><br>}\right)}{{\mathrm{j\omega <br><br>\varepsilon <br><br>}}_0<br><br>t},$

 

wherein Y(ω

) is a frequency dependent admittance function for the frequency selective surface, j is the imaginary operator, ω

corresponds to angular frequency, ε

₀ is the permittivity of free space, and t corresponds to thickness of the frequency selective surface.

24. The artificial magnetic conductor of claim 23 wherein the FSS layer has a normal permeability μ

_1z ${\mathrm{\mu <br><br>}}_{1<br><br>z}=\frac{Z<br><br>\left(\mathrm{\omega <br><br>}\right)}{{\mathrm{j\omega <br><br>\mu <br><br>}}_0<br><br>t},$

wherein Z(ω

) is a frequency dependent impedance function, j is the imaginary operator, ω

corresponds to angular frequency, μ

₀ is the permeability of free space, and t corresponds to thickness of the frequency selective surface.

25. The artificial magnetic conductor of claim 24 wherein the spacer layer and the frequency selective surface each are defined by a permittivity tensor ${\varepsilon }_{}$

i=ɛ

0

(ɛ

it000ɛ

it000ɛ

in),

where i=1 for the frequency selective surface and i=2 for the spacer layer.

26. The artificial magnetic conductor of claim 23 wherein the spacer layer and the frequency selective surface each are defined by a permeability tensor ${\mu }_{}$

i=μ

0

(μ

it000μ

it000μ

in),

where i=1 for the frequency selective surface and i=2 for the spacer layer.

27. The artificial magnetic conductor of claim 23 wherein the transverse permittivity has one or more Lorentz resonances at predetermined frequencies located between the first high-impedance frequency band and the second high-impedance frequency band of the artificial magnetic conductor.

28. The artificial magnetic conductor of claim 23 further comprising:

an array of artificial magnetic molecules including

a first planar array of conductive loops; and

a second planar array of conductive loops spaced a distance t from the first planar array of conductive loops, each loop of the second planar array overlapping one or more loops of the first planar array.

29. An artificial magnetic conductor (AMC) resonant with a substantially zero degree reflection phase over two or more AMC resonant frequency bands, the artificial magnetic conductor comprising:

a spacer layer including an array of metal posts extending through the spacer layer; and

a frequency selective surface (FSS) disposed on the spacer layer in which the frequency selective surface comprises specific geometric arrangements of metal and dielectric regions, wherein such regions have been designed to exhibit one or more Lorentz resonances in the presence of electromagnetic waves at predetermined frequencies different from the two or more AMC resonant frequency bands.

30. The artificial magnetic conductor of claim 29 wherein the frequency selective surface has an in-plane permittivity having one or more Lorentz resonances at the predetermined frequencies.

31. The artificial magnetic conductor of claim 30 wherein the frequency selective surface has a frequency variable normal permeability.

32. The artificial magnetic conductor of claim 31 wherein the frequency selective surface has a normal permeability having one or more Lorentz resonances at the predetermined frequencies.

33. The artificial magnetic conductor of claim 29 wherein the AMC resonant frequency bands of zero degree reflection phase are not harmonically related.

34. The artificial magnetic conductor of claim 29 further comprising:

a conductive ground plane adjacent the spacer layer and electrically contacting the array of metal posts.

35. The artificial magnetic conductor of claim 29 wherein the frequency selective surface has a frequency dependent in-plane permittivity.

36. The artificial magnetic conductor of claim 35 wherein frequency dependence of the in-plane permittivity is independent of frequency dependence of the normal permeability.

37. The artificial magnetic conductor of claim 36 wherein the predetermined reflection phase resonant frequencies are not harmonically related, and wherein the lowest two reflection phase resonant frequencies are spaced to have a ratio less than 3:

1.

38. The artificial magnetic conductor of claim 29 wherein the frequency selective surface exhibits capacitive coupling between elements of the frequency selective surface.

39. The artificial magnetic conductor of claim 29 wherein the frequency selective surface comprises a plurality of conductive layers.

40. The artificial magnetic conductor of claim 39 wherein the plurality of layers exhibit a strong capacitive coupling between each layer such that a low frequency limit of relative transverse permittivity for the FSS is at least 10.