Spiral antenna for distributed wireless communications systems
An antenna for wireless communication comprises a dielectric substrate having a first side and an opposite second side. A first major arm having a first modified log-spiral spiral pattern is disposed on the first side of the dielectric substrate. A second major arm having a second modified log-spiral pattern is disposed on the second side of the dielectric substrate, wherein the first and second major arms are formed from a conductive material. A connector coupling is disposed at a center of the modified log-spiral patterns, the connector coupling having a first portion coupled to the first major arm and a second portion coupled to the second major arm. The antenna is self-complementary. The antenna can achieve a return loss better than 10 dB over a broadband range.
1. A wideband, balun-free antenna for wireless communication, comprising:
a dielectric substrate having a first surface and an opposite second surface;
a first major arm having a first modified log-spiral pattern disposed on the first surface of the dielectric substrate, wherein the first major arm is formed from a combination of first and second minor arms each having a log-spiral pattern shape and each having the same area;
a second major arm having a second modified log-spiral pattern disposed on the second surface of the dielectric substrate, wherein the second major arm is formed from a combination of first and second minor arms each having a log-spiral pattern shape and each having the same area, wherein the first and second major arms are formed from a conductive material, wherein each major arm comprises a log-spiral arm having a first spiral line defined in part by equation (1)
r=r 0 e at Eq. (1);
where r is the radial distance from the origin, a is the expansion rate of the spiral, and r 0 is the radius at the origin; and
a second spiral line, defined in part by equation (2),
{
x
(
t
)
=
r
0
e
at
cos
(
ω
t
)
y
(
t
)
=
r
0
e
at
sin
(
ω
t
)
Eq
.
(
2
)
where equation (2) is multiplied by a constant K=e −aθ , where ω is the radian speed and θ is the angle with the x axis;
a coaxial receptacle positioned at a center of the modified log-spiral patterns including having a main body mounting portion mountable to one of major arms and a center pin configured to pass through the dielectric substrate and connect to the other major arm, and wherein the antenna is self-complementary such that a total surface area of the major arms equals a total surface area of adjacent dielectric regions; and
wherein the antenna does not include a balun and wherein the antenna has a bandwidth extending from about 400 MHz to about 6 GHz.
2. The antenna of claim 1 , wherein the antenna has scale invariance.
3. The antenna of claim 1 , wherein each second minor arm is oriented such that it is rotated about 112 degrees from a position 180 degrees from its corresponding first minor arm.
4. The antenna of claim 1 , wherein the first and second minor arms each include a semi-circular end cap formed on an end portion thereof.
5. The antenna of claim 1 , wherein the antenna has an impedance of 50 ohms.
6. The antenna of claim 1 , wherein the first and second major arms are substantially non-overlapping.
7. The antenna of claim 1 , further including a housing to support the dielectric substrate, the housing having a low profile cover.
8. The antenna of claim 7 , further including a support plate mountable to a wall, ceiling or other mounting surface.
9. The antenna of claim 8 , wherein one side of the support plate includes an adhesive backing.
10. The antenna of claim 1 , wherein “a” has a value of from about 0.4 to about 0.8; θ has a value of from about 1.0 to about 1.3 (radian); and ω has a value of from about 1.1 to about 1.8 (radian).
11. The antenna of claim 10 , wherein a=0.59, θ=1.15, ω=1.5 (radian), and the spiral has 1.5 turns.
12. A directional antenna comprising the antenna of claim 1 , wherein the antenna is disposed in a housing, further comprising a metal backing plate disposed in proximity to and spaced apart from one side of the housing.
13. The directional antenna of claim 12 , further comprising an absorber material, wherein the metal backing plate is disposed between the absorber and one side of the housing.
14. A wideband, balun-free antenna for wireless communication, comprising:
a first major arm having a first modified log-spiral spiral pattern defining a first plane, wherein the first major arm is formed from a combination of first and second minor arms each having a log-spiral pattern shape and each having the same area;
a second major arm having a second modified log-spiral pattern defining a second plane, wherein the first and second major arms are formed from a conductive material, wherein the second major arm is formed from a combination of first and second minor arms each having a log-spiral pattern shape and each having the same area, wherein each major arm comprises a log-spiral arm having a first spiral line defined in part by equation (1)
r=r 0 e at Eq. (1);
where r is the radial distance from the origin, a is the expansion rate of the spiral, and r 0 is the radius at the origin; and
a second spiral line, defined in part by equation (2),
{
x
(
t
)
=
r
0
e
at
cos
(
ω
t
)
y
(
t
)
=
r
0
e
at
sin
(
ω
t
)
Eq
.
(
2
)
where equation (2) is multiplied by a constant K=e −aθ , where ω is the radian speed and θ is the angle with the x axis;
a coaxial receptacle positioned at a center of the modified log-spiral patterns including having a main body mounting portion mountable to one of major arms and a center pin configured to connect to the other major arm, wherein the major arms are spaced by an air gap, and wherein the arms are substantially non-overlapping; and
wherein the antenna does not include a balun, has an impedance of 50 ohms and has a bandwidth extending from about 400 MHz to about 6 GHz.