Fast-wave resonant antenna with stratified grounding planes

Details Fast-wave resonant antenna with stratified grounding planes Fast-wave resonant antenna with stratified grounding planes

1999-01-29

2001-05-29

Wong, Don (Department: 2821)

Communications: radio wave antennas

Antennas

Microstrip

C343S772000, C343S829000

Reexamination Certificate

active

06239749

ABSTRACT:

BACKGROUND OF THE PRESENT INVENTION
The present invention relates to a fast-wave resonator with stratified grounding planes, particularly to a small size fast-wave resonant antenna with stratified grounding planes which can be installed by surface mounting technology (SMT).
The hidden antenna is receiving more attention with the widespread use of mobile phones. Since the hidden antenna is small in size, it can be arranged into an RF circuit by surface mounting technology, thereby increasing its accuracy and thus improving the quality of the mobile phone.
A patch metal strip is used in a conventional hidden antenna.
FIG. 1
shows a patch antenna wherein the medium substrate
11
is located on the grounding plane
12
and the patch
13
is located at the center of the upper surface of the medium substrate
11
. Signals can be fed into the antenna from the feed line
14
. Such configuration is commonly used in various active antennas.
FIG. 2
shows another kind of patch antenna. The difference between FIG.
2
and
FIG. 1
is that the feed line
15
of
FIG. 2
is extended along the upper surface of the medium substrate
11
and extended downward along the edge through the via hole of the substrate. Such configuration is used to make a surface mounting antenna.
FIG. 3
shows still another kind of conventional patch antenna which is similar to the patch antenna shown in FIG.
1
. The main difference is that the signals are fed into the patch antenna via a probe or a coaxial line. It is obvious that connecting such kind of antenna with other microwave circuits using SMT technology may not be appropriate since a coaxial line needs a microwave connector to connect to an external coaxial cable.
According to a prior research result, the resonant frequency of the metal strip antenna is inversely proportional to {square root over (∈
r
+L )}(∈
r
being the relative permittivity). Under this restriction, dielectric materials with relative permittivity exceeding 20 are usually necessary for the miniaturized metal strip antennas depicted in
FIG. 1
to FIG.
3
. Moreover, it is known that limited dimension of the grounding plane greatly influences the performance of the metal strip antenna. Therefore, the dimension of the grounding plane should be greater than that of the patch so that the metal strip can work properly.
Besides, a hidden dielectric antenna used in a general integrated circuit can be designed by utilizing the resonance phenomena of the dielectric materials and coupling energy to a medium resonator via a metal strip or a slot line. However, dielectric materials with high relative permittivity are usually adopted in this kind of dielectric antenna because its size is also inversely proportional to {square root over (∈
r
+L )}.
Observe the simplified model of a monopole antenna depicted in FIG.
4
(
a
), the length of the monopole antenna
42
on the housing of the mobile phone
41
is one-fourth the length of free-space wavelength. FIG.
4
(
b
) shows a simplified model of a helix antenna, which is also used in mobile phones. The total length of this kind of helix antenna
43
is quite near to the free-space wavelength &lgr;
0
, therefore, it is obvious that both these kinds of antennas are not suitable to be used as hidden antennas in mobile phones. Besides, these two kinds of antennas use their housing as the grounding plane. The dimension of the grounding plane is always large, approximately 2&lgr;
0
2
in general design (&lgr;
0
being free-space wavelength). The dimension of the grounding plane of the antenna is becoming smaller and smaller for downsizing of the mobile phones, thereby influencing the performance of the antenna.
SUMMARY OF THE PRESENT INVENTION
In view of the above, the present invention discloses a specially designed miniature antenna which utilizes a bound mode and a fast-wave leaky mode co-existing in a suspended metal strip. The respective modal currents and transverse electric field (magnetic field) of the bound mode and fast-wave leaky mode are very similar in the neighborhood of the metal strip. Therefore, a fast-wave resonant antenna with stratified grounding planes can be designed according to the resonance phenomena of the fast-wave leaky mode.
This antenna comprises a fast-wave resonator and a stratified and via grounding device, wherein the fast-wave resonator consists of a medium substrate which is cuboid in shape and a suspended metal strip cohering to the surface of the cuboid substrate. The shape of the cohering metal strip is determined based on the radiation field pattern required, and the cohering metal strip is compacted (i.e., confined) within a small range or area of the substrate surface. Signals are fed in from one end of the metal strip and the other end of the metal strip is open.
The grounding device is located below the fast-wave resonator. The grounding device is cuboid in shape and provided with a plurality of via holes, the via holes being rectangular and/or circular in shape, i.e., the via holes having at least one of the following shapes: (a) a rectangular shape, and (b) a circular shape, and the number and size of the rectangular and/or circular via holes being determined according to a grounding area required to provide a desired or predetermined structural strength.
Since the metal strip is confined within a small area of the substrate surface, while the grounding device provides a considerable area for grounding in a limited space, the size of the antenna can be reduced substantially. Moreover, this antenna can be directly installed in a printed circuit board (PCB) by using the surface mounting technology. In particular, the antenna in accordance with the present invention does not require dielectric materials with high relative permittivity, the dielectric materials with a relative permittivity between 2 and 5 are appropriate.


REFERENCES:
patent: 5453754 (1995-09-01), Fray
patent: 5703600 (1997-12-01), Burrell et al.
patent: 5796367 (1998-08-01), Andersson
patent: 5963181 (1999-10-01), Abe
patent: 5966097 (1999-10-01), Fukasawa et al.

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