Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2000-06-23
2002-03-19
Phan, Tho (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S846000, C343S848000
Reexamination Certificate
active
06359589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microstrip antenna. In particular, the present invention relates to a microstrip antenna which can minimize leakage current by separately arraying a left radiation patch and a right radiation patch on an upper surface of a dielectric so that they have an electric field of the same phase, and which can minimize its size and thus can be built in various kinds of wireless communication equipment such as portable mobile terminals by improving its standing-wave ratio and gain so that it has a wide bandwidth.
2. Description of the Prior Art
Generally, frequencies mainly used in mobile radio communications are in the range of 150~900 MHz. Recently, according to the rapidly increasing demand therefore, frequencies of a pseudo-microwave band in the range of 1~3 GHz are also used.
In applying the pseudo-microwave band to the mobile radio communications, personal communication service (PCS) has already used a frequency range of 1.7~1.8 GHz, and next-generation mobile radio communication systems such as GMPCS (1.6 GHz), IMT2000 (2 GHz), etc., will also use the pseudo-microwave band to enable communications through all places of the world.
As portable telephones become small-sized and high-graded by their rapid development, the importance of their antennas have been naturally highlighted, and as an example, a microstrip antenna has been presented as the subject of special research in this field.
Typically, the microstrip antenna has a better efficiency as a dielectric constant becomes lower, and a substrate becomes thicker. Also, since the microstrip antenna has a low efficiency in case of using a low frequency, but has a high efficiency in case of using a high frequency, it can be considered as the very antenna that can satisfy the limited condition of miniaturization that the portable telephone pursues.
Meanwhile, a typical microstrip antenna has a structure in which radiation patches having a resonance length of &lgr;/2 are attached on a wide ground patch, and has the form of an array. Between the patches on the left and right sides of a feed point and the ground patch are formed lines of electric force. If the ground patch is short on the left and right sides of the feed point, this limits the formation of the lines of electric force, and thus lowers the gain of the antenna, causing the of miniaturization of the antenna to be difficult.
The microstrip antenna has a simple structure in which a dielectric is formed on the ground patch, and rectangular or circular radiation patches are attached on the upper surface of the dielectric, and thus it has drawbacks in that it has a narrow bandwidth and a low efficiency. However, it has advantages in that it can be manufactured at a low cost with a small size and a light weight, and thus it is suitable to mass production.
Also, since it can be wound on various devices and components with a predetermined form due to its free banding characteristic and can be easily attached to an object moving at a high speed, it has been widely used as a transmission/reception antenna of a flying object such as a rocket, missile, airplane, etc.
In addition, the microstrip antenna can be designed on a circuit board together with solid-state modules such as an oscillator, amplifying circuit, variable attenuator, switch, modulator, mixer, phase shifter, etc.
The microstrip antenna as described above may be designed so as to have one or two feed points and circular or rectangular radiation patches in a satellite communication system that requires circularly polarized waves. Also, it can be used for a Doppler radar, radio altimeter, remote missile measuring device, weapon, environmental machine and its remote sensor, transmission element of a composite antenna, remote control receiver, radiator for biomedicine, etc.
As a result, with the rapid spread of mobile communication terminals such as telephones for vehicles, pocket bells, cordless telephones, etc., due to the rapid development of information processing, the equipment for such mobile communications becomes small-sized, and this demands that the antenna thereof also to become small-sized.
FIG. 1
is a side view illustrating a general microstrip antenna. Referring to
FIG. 1
, the general microstrip antenna has a radiation patch
1
both ends of which are open, and thus the current distribution of which is 0 and the voltage distribution of which is a maximum value. A feed position is determined as the ratio of the current distribution value to the voltage distribution value in accordance with the resistance value of a feed line
2
.
Also, lines of electric force,
3
and
5
, can be considered to be divided into a vertical component and a horizontal component, respectively. The vertical components are cancelled due to their opposite phase to each other, and the horizontal components exist in array due to their same phase.
If the length of the ground patch
6
in the microstrip antenna is determined to be short, the range where the lines of electric force,
3
and
5
, exert is limited, and this results in attenuation of the gain. Thus, shortening the ground patch
6
cannot achieve the miniaturization of the antenna.
Generally, the microstrip antenna is a unit of a VHF/UHF band, and is required to have a compact and light-weighted structure. As the presently developed microstrip antenna, a quarter-wavelength microstrip antenna (QMSA), post-loading microstrip antenna (PMSA), window-attached microstrip antenna (WMSA), frequency-variable microstrip antenna (FVMSA), etc., exist. The PMSA, WMSA, and FVMSA are provided by partially modifying the QMSA, and thus basically have similar radiation patterns to one another.
FIG. 2
is a perspective view illustrating the structure of a conventional QMSA. Referring to
FIG. 2
, according to the conventional QMSA, a radiation patch
23
and a ground patch
21
are constructed so that they have an identical width W, and the ground patch
21
extends in a direction opposite to a radiation opening
22
to provide a small-sized antenna that can be mounted in a limited space of a small-sized radio device.
Specifically, according to the QMSA of
FIG. 2
, a dielectric
22
and the radiation patch
23
are successively attached to the ground patch
21
of &lgr;g (guide wavelength)/2, one end of the ground patch
21
is short-circuited to the radiation patch
23
, and the length of the radiation patch
23
is determined to to be &lgr;g/4 to have a fixed frequency range.
Also, an outer conductor of a feed line
24
is grounded to the ground patch
21
, and an inner conductor (center conductor) of the feed line
24
is connected to the radiation patch
23
through the ground patch
21
and the dielectric
22
(Japanese Electronic Information Society, Vol. J71-B, 1988.11.). Typically, polyethylene (&egr;r=2.4), Teflon (&egr;r=2.5), or epoxy-fiberglass (&egr;r=3.7) can be used as the dielectric
22
.
FIG. 3
shows the variation of the gain ratio according to the variation of Gz in FIG.
2
. In
FIG. 2
, 0 (dB) represents the gain of a basic half-wavelength dipole antenna. Gz plays a very important role for determining the increasing rate of radiation.
FIG. 4
shows the variation rate of gain according to the whole length L of the antenna of
FIG. 2
, and
FIG. 5
shows the gain ratio to the width W of the radiation patch
23
of FIG.
2
.
FIG. 6
shows the measured radiation property of the QMSA of FIG.
2
. In
FIG. 6
, (A), (B), (C) represent an XY plane, YZ plane, and ZX plane, respectively. As shown in
FIG. 6
, it can be recognized that the QMSA of
FIG. 2
is an electric field antenna having the radiation patterns in all propagation directions. The radiation characteristics of the QMSA are obtained by determining parameters of the antenna as the whole length L of the antenna=7.67 cm, Gz=2.79 cm, the width W of the radiation patch
23
=3 cm, the width t of the dielectric
22
=0.12 cm, and dielectric constant &egr;r=2.5 (Teflon).
Meanwhile, w
Clinger James
Kosan Information and Technologies Co., Ltd.
Phan Tho
Snell & Wilmer
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