Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
2001-04-19
2003-01-21
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S7000MS, C343S769000
Reexamination Certificate
active
06509880
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to an integrated planar printed antenna and, more particularly, to a compact, integrated planar printed antenna that includes a metalization layer formed on a dielectric slab and voids extending through the slab that control the effective dielectric constant of the slab across the antenna aperture to reduce or eliminate surface waves and/or standing waves in the slab to increase antenna performance.
2. Discussion of the Related Art
Current wireless communications systems, including radio frequency systems, global positioning systems (GPS), cellular telephone systems, personal communications systems (PCS), etc., typically require broadband antennas that are compact in size, low in weight and inexpensive to produce. Currently, radio frequency systems use the 20-400 MHz range, GPS use the 1-1.5 GHz range, cellular telephone systems use the 900 MHz range, and PCS use the 1800-2000 MHz range. The antennas receive and transmit electromagnetic signals at the frequency band of interest associated with the particular communications system in an effective manner to satisfy the required transmission and reception functions. Different communications systems require different antenna optimization parameters and design concerns to satisfy the performance expectations of the system.
The antennas necessary for the above-mentioned communications systems pose unique problems when implemented on a moving vehicle. The transmission and reception of electromagnetic waves into and out of a vehicle for different communications systems is generally accomplished through several antennas usually in the form of metallic masts protruding from the vehicle's body. However, mast antennas have significant drawbacks in this type of environment. In a typical design, the linear dimensions of a monopole mast antenna are directly proportional to the operational wavelength A of the system, and are usually a quarter wavelength for high performance purposes. Thus, at the lower end of the frequency spectrum, the size of a high-efficiency antenna becomes prohibitively large. For example, a monopole mast antenna used in the 800 MHz range should be around 10 cm long. Current military wireless communications systems use HF/UHFNHF frequency bands, in addition to cellular telephone systems, GPS and PCS. For military communications in the 20 MHz range, the size of a high performance antenna is in the 4 m range. For military vehicles, mast antennas increase the vehicle's radar visibility, and thus reduce its survivability.
Further, when using multiple antennas to satisfy several communication systems, electromagnetic interference (EMI) between the antennas may become a problem. If the antennas are formed on a common substrate, the antenna signals tend to couple to each other and deteriorate the system's performance and signal-to-noise ratio. Thus, the design of multifunction antennas for military and commercial vehicles tends to pose major challenges with regard to the antenna size, radiation efficiency, fabrication costs, as well as other concerns.
To obviate the drawbacks of mast antennas, it is known in the art to employ planar antennas, including slot, microstrip, and aperture type designs, all well known in the art for a variety of communications applications in the above-mentioned frequency bands, primarily due to the simplicity, conformability, low manufacturing costs and the availability of design and analysis software for such antenna designs.
FIG. 1
shows a perspective view of a planar slot ring antenna
10
depicting this type of design, and is intended to represent all types of planar antenna designs. The ring antenna
10
includes a substrate
12
and a conductive metalized layer
14
printed on a top surface of the substrate
12
. The layer
14
is patterned by a known patterning process to etch out a ring
16
, and define a circular center antenna element
18
and an outside antenna element
20
on opposite sides of the ring
16
. The antenna elements
18
and
20
are excited and generate currents by received electromagnetic radiation for reception purposes, or by a suitable transmission signal for transmission purposes, that create an electromagnetic field across the ring
16
. A signal generator
22
is shown electrically connected to an antenna feed element
24
patterned on an opposite side of the substrate
12
from the layer
14
. The signal generator
22
generates the signal for transmission purposes and receives the signal for reception purposes.
The antenna
10
is a slot antenna because no conductive plane is provided opposite to the layer
14
. This allows the antenna
10
to operate with a relatively wide operational bandwidth compared to a metal backed antenna configuration. However, the absence of a metallic ground plane results in radiation into both sides of the antenna, hence, bidirectional operation. In order to direct the radiation into one side of the antenna (unidirectionally), a high dielectric constant superstrate can be employed.
FIG. 2
shows a cross-sectional view of the antenna
10
where a superstrate
26
having a high constant &egr;
r
has been positioned on the layer
14
, opposite to the substrate
12
, to direct the radiation through the substrate
26
. The higher the dielectric constant &egr;
r
of the superstrate
26
, the more directional the antenna
10
.
In addition to providing unidirectionality, a high dielectric constant superstrate leads to antenna size reduction. The linear dimensions of planar antennas are directly proportional to the operational wavelength of the system. The transmission wavelength &lgr; of electromagnetic radiation propagating through a medium is determined by the relationship:
λ
=
C
f
∈
r
(
1
)
where C is the speed of light, f is the frequency of the radiation and &egr;
r
is the relative dielectric constant or relative permittivity of the medium. For air, &egr;
r
=1. In this context, the dielectric constant &egr;
r
and the index of refraction n can be used interchangeably, since &egr;
r
=n
2
. To significantly reduce the size of the antenna
10
for miniaturization purposes at a particular operational wavelength, it is known to position the superstrate
26
adjacent the layer
14
and make the superstrate
26
out of a high dielectric constant material, so that when the electromagnetic radiation travels through the superstrate
26
, the wavelength is decreased in accordance with equation (1). This is because the guided wavelength along the antenna elements
18
and
20
is inversely proportional to the square root of the effective dielectric constant &egr;
eff
, which in turn is related to the relative dielectric constant &egr;
r
of the superstrate
26
. The exact relationship depends on the particular geometry of the elements of the antenna
10
. The dimensions of the antenna
10
would be well known to those skilled in the art for particular frequency bands of interest. By continually increasing the dielectric constant &egr;
r
, the size of the antenna
10
can be further reduced for operation at a particular frequency band.
The use of a high dielectric constant superstrate is highly effective in reducing the size of the antenna so that it is practical for many high and low frequency communications applications. However, the use of high dielectric constant superstrates has a major drawback. It is known that planar antenna designs that employ high index substrates or superstrates have a significantly degraded performance due to the generation of surface waves and resonant or standing waves within the substrate or superstrate. These waves are generated because electromagnetic waves are reflected by dielectric interfaces, and are eventually trapped in the substrate
12
or superstrate
26
in the form of surface waves. The trapped waves carry a large amount of electromagnetic power along the interface and significantly reduce the radiated power from the antenna
10
. The power carried by the excited surfac
Katehi Linda P. B.
Ozdemir Tayfun
Sabet Kazem F
Sarabandi Kamal
EMAG Technologies, Inc.
Ho Tan
Miller, Esq. John A.
Warn, Burgess & Hoffman, P.C.
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