Ground planes for reducing multipath reception by antennas
An antenna system for a global navigation satellite system reference base station is disclosed. The antenna system includes an antenna positioned above a high capacitive impedance surface (HCIS) ground plane. Over a specific range of the lateral dimension of the HCIS ground plane and the height of the antenna above the HCIS ground plane, a high level of multipath suppression and high sensitivity for low-elevated satellites can be simultaneously maintained. The HCIS ground plane can be fabricated as a flat conducting plate with an array of conducting elements such as pins, pins with expanded tips, or mushroom structures. Alternatively, the HCIS can be fabricated as a flat conducting plate with a concentric series of choke rings. The antenna system can provide a positioning accuracy of +/−1 mm, an order of magnitude improvement over previous designs.
1. An antenna system configured to receive circularly polarized electromagnetic radiation from a plurality of satellites in a global navigation satellite system, the antenna system comprising:
a high capacitive impedance surface ground plane having a characteristic lateral dimension; and
an antenna positioned at a height above the high capacitive impedance surface ground plane;
wherein:
a down/up ratio of the antenna in a nadir direction has a maximum value;
the characteristic lateral dimension has a value such that a down/up ratio of the antenna system at an elevation angle has a maximum value; and
the height has a value such that an antenna pattern level of the antenna system at the elevation angle has a minimum value; and
wherein the elevation angle is 12 degrees;
wherein the characteristic lateral dimension is selected according to the formula
DU
12
(
L
)
=
20
log
[
3
(
L
λ
+
2.45
)
-
1.28
]
in
dB
,
wherein:
λ represents a wavelength of the electromagnetic radiation;
L represents the characteristic lateral dimension; and
DU 12 (L) represents the maximum value of the down/up ratio of the antenna system at the elevation angle of 12 degrees; and
wherein the height is selected according to the formula
F +12 ( h )=20 log [0.438 h/λ+ 0.064] in dB,
wherein:
h represents the height; and
F +12 (h) represents the minimum value of the antenna pattern level at the elevation angle of +12 degrees.
2. The antenna system of claim 1 wherein
the maximum value is about −12 dB to about −15 dB.
3. The antenna system of claim 1 , wherein:
the elevation angle is about 12 degrees;
the maximum value of the down/up ratio of the antenna system at the elevation angle is about −20 dB; and
the minimum value of the antenna pattern level at the elevation angle is about −12 dB to about −14 dB.
4. The antenna system of claim 1 , wherein:
the electromagnetic radiation has a frequency ranging from a first frequency to a second frequency, wherein the second frequency is higher than the first frequency; and
λ corresponds to the first frequency.
5. The antenna system of claim 1 , wherein:
the value of L is greater than or equal to about 5λ; and
the value of h is about 0.25λ to about 0.6λ.
6. The antenna system of claim 5 , wherein:
the electromagnetic radiation has a frequency ranging from a first frequency to a second frequency, wherein the second frequency is higher than the first frequency; and
λ corresponds to the first frequency.
7. The antenna system of claim 1 , wherein the high capacitive impedance surface ground plane comprises:
a flat conducting plate; and
an array of conducting elements electrically connected to the flat conducting plate and oriented orthogonal to the flat conducting plate.
8. The antenna system of claim 7 , wherein the array of conducting elements comprises an array of conducting pins.
9. The antenna system of claim 8 , wherein a height of a conducting pin in the array of conducting pins has a value of about 0.255λ to about 0.260λ, wherein λ represents a wavelength of the electromagnetic radiation.
10. The antenna system of claim 9 , wherein:
the electromagnetic radiation has a frequency ranging from a first frequency to a second frequency, wherein the second frequency is higher than the first frequency; and
λ corresponds to the first frequency.
11. The antenna system of claim 7 , wherein the array of conducting elements comprises an array of conducting pins with expanded tips.
12. The antenna system of claim 7 , wherein the array of conducting elements comprises an array of mushroom structures, wherein a height of a mushroom structure in the array of mushroom structures has a maximum value of about 0.1λ to about 0.15λ, wherein λ represents a wavelength of the electromagnetic radiation.
13. The antenna system of claim 12 , wherein:
the electromagnetic radiation has a frequency ranging from a first frequency to a second frequency, wherein the second frequency is higher than the first frequency; and
λ corresponds to the first frequency.
14. The antenna system of claim 1 , wherein the high capacitive impedance ground plane comprises:
a flat conducting plate; and
an array of conducting choke rings electrically connected to the flat conducting ground plane and oriented orthogonal to the flat conducting ground plane.