BACKGROUND OF THE INVENTION
Field of the Invention
[0001] 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.
Description of the Prior Art
[0002] Generally, frequencies mainly used in mobile radio communications are in the range
of 150∼900MHz. Recently, according to the rapidly increasing demand therefore, frequencies
of a pseudo-microwave band in the range of 1∼3GHz are also used.
[0003] In applying the pseudo-microwave band to the mobile radio communications, personal
communication service (PCS) has already used a frequency range of 1.7∼1.8GHz, and
next-generation mobile radio communication systems such as GMPCS (1.6GHz), IMT2000
(2GHz), etc., will also use the pseudo-microwave band to enable communications through
all places of the world.
[0004] 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.
[0005] 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.
[0006] Meanwhile, a typical microstrip antenna has a structure in which radiation patches
having a resonance length of λ/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 miniaturization
of the antenna to be difficult.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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.
[0017] Specifically, according to the QMSA of FIG. 1, a dielectric 22 and the radiation
patch 23 are successively attached to the ground patch 21 of λg (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 be λg/4 to have a fixed frequency
range.
[0018] 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 (εr=2.4), Teflon (εr=2.5),
or epoxy-fiberglass (er=3.7) can be used as the dielectric 22.
[0019] FIG. 3 shows the variation of the gain ratio according to the variation of Gz in
FIG. 2. In FIG. 3, 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.
[0020] 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 = 7.67cm, Gz = 2.79cm, the width W of the radiation patch 23 = 3cm,
the width t of the dielectric 22 = 0.12cm, and dielectric constant εr = 2.5 (Teflon).
[0021] Meanwhile, when the standing-wave distribution is positioned near its minimum point
in a complicated city environment, the transmission/reception sensitivity of the electric
field antenna deteriorates due to the diffraction, reflection, etc., of the signal,
and this causes the communication to be disturbed.
[0022] Accordingly, the current radio equipment or system uses a spatial diversity, directional
diversity, polarized diversity, etc. Meanwhile, two or more antennas may be installed
to solve the low reception sensitivity caused by a multipath.
[0023] Meanwhile, according to the PMSA (not illustrated) which is a modified microstrip
antenna, two radiation open surfaces are formed on both sides of a radiation patch,
a short-circuited post is connected to a ground patch and the radiation patch through
a dielectric instead of a short-circuited end of the QMSA antenna, and a feed line
is located at a predetermined distance from the short-circuited post. Though the PMSA
has two open surfaces, the radiation pattern thereof is substantially similar to that
of the QMSA.
[0024] Also, according to the WMSA (not illustrated) which is a modified microstrip antenna,
a slit is formed at a predetermined distance from the radiation patch of the QMSA
to have a reactance component, and thus the length of the radiation patch can be shortened.
According to the FVMSA (not illustrated), the resonance frequency of the QMSA can
be electronically changed in accordance with the change of the reactance load value.
[0025] However, the conventional modified microstrip antennas, i.e., the QMSA, PMSA, WMSA,
and FVMSA have drawbacks in that if the ground patch is determined to be small, the
radiation open surfaces become narrow, and their gains are rather attenuated, so that
they cannot become small-sized. Also, if they are used for portable radio equipment,
the field strength thereof deteriorates due to walls of a building and various metals
in the building, and the receiving sensitivity deteriorates due to the multipath interference.
[0026] US-A-5781158 discloses a microstrip antenna having a dielectric element sandwiched
between a radiation patch arrangement and a ground plate, the patch arrangement comprising
first and second radiation patches with a slot between them.
SUMMARY OF THE INVENTION
[0027] It is an object of the present invention to solve the problems involved in the related
art, and to provide a microstrip antenna which can greatly miniaturize its size without
attenuation of its gain and without limiting the range of lines of electric force
between a ground patch and radiation patches, and which can have a wide bandwidth
by implementing a greater gain on a capacity-loaded side rather than the ground patch.
[0028] According to a first aspect of the invention, there is provided a microstrip antenna
comprising a dielectric element sandwiched between a radiation patch arrangement and
a ground patch, the ground patch including first and second ground plates connected
by a bridge plate, the radiation patch arrangement comprising a first radiation patch,
connected to the first ground plate, and a second radiation patch, connected to the
second ground plate, arranged so as to form a radiation slot between the first and
second radiation patches; and further comprising a feed line connected to one of the
radiation patches characterised in that the width of the bridge plate is smaller than
the width of the first and second ground plates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The above object, other features and advantages of the present invention will become
more apparent by describing the preferred embodiment thereof with reference to the
accompanying drawings, in which:
FIG. 1 is a side view illustrating a general microstrip antenna;
FIG. 2 is a perspective view illustrating the structure of a conventional QMSA antenna;
FIG. 3 is a graph illustrating the gain relationship with respect to Gz in FIG. 2;
FIG. 4 is a graph illustrating the gain relationship with respect to the whole length
L of the antenna of FIG. 2;
FIG. 5 is a graph illustrating the gain relationship with respect to the width W of
the radiation patch 23 of FIG. 2;
FIG. 6 is a view illustrating the radiation characteristics in XY, YZ, and ZX directions;
FIG. 7 is a perspective view illustrating the structure of the microstrip antenna
according to the present invention;
FIG. 8 is a plane view illustrating the structure of the microstrip antenna according
to the present invention;
FIG. 9 is a bottom view illustrating the structure of the microstrip antenna according
to the present invention;
FIG. 10 is a side view illustrating the structure of the microstrip antenna according
to the present invention;
FIG. 11 is a perspective view looking from the bottom of the microstrip antenna according
to the present invention;
FIG. 12 is a graph illustrating the return loss with respect to the frequency of the
microstrip antenna according to the present invention;
FIG. 13 is a graph illustrating the standing-wave ratio with respect to the frequency
of the microstrip antenna according to the present invention;
FIG. 14 is a Smith chart explaining the microstrip antenna according to the present
invention; and
FIG. 15 is a view of the radiation pattern explaining the microstrip antenna according
to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The construction and operation of the present invention will be explained in detail
with reference to the accompanying drawings.
[0031] FIG. 7 is a perspective view illustrating the structure of the microstrip antenna
according to the present invention.
[0032] The microstrip antenna according to the present invention includes a dielectric 50
laminated on a ground patch 40 as shown in FIG. 7. On the upper surface of the dielectric
50, a left radiation patch 61 is positioned in such a way that it is short-circuited
with one end of the ground patch 40, and a right radiation patch 62 is positioned
in such a way that it is short-circuited with the other end of the ground patch 40.
A gap is provided between the left and right radiation patches (They are apart from
each other at a spacing of 0.5mm, and the gap is referred to as a radiation slot 70).
[0033] The microstrip antenna made of such a radiation slot 70 is capable of loading the
capacity between the left radiation patch 61 and the right radiation patch 62, such
that the formation of the line of electric force is not limited, causing the antenna
to be more easily miniaturized. The gain on the capacity-loaded side is increased
more than that on the ground patch 40, such that it has a radiation pattern with a
larger gain, thereby being preferably used as an antenna in the service band of PCS.
[0034] Specifically, the microstrip antenna 100 has a gain which is increased by 1 to 1.76
dB on the capacity-loaded side relative to the ground patch 40, and has a radiation
pattern with a maximum electric field of 2dB which is larger than that of the prior
dipole antenna, thereby being preferably used in various wireless devices.
[0035] Also, with the microstrip antenna 100 of the present invention, the thickness H1
of the dielectric 50 and the width of the capacity-loaded side can be adjusted to
increase or reduce the bandwidth and the gain, and the point position of the feed
line 30 can be variably adjusted to eliminate the fringe effect of the feed point
of the feed line, thereby overcoming actively the indefinite distribution of the feed
line.
[0036] FIG. 8 is a plane view illustrating the structure of the microstrip antenna according
to the present invention.
[0037] The microstrip antenna 100 of FIG. 8 according to the present invention is an example
wherein, when the whole length ℓ 1 is 25mm, the length ℓ 2 of the left patch 61 is
14.5mm, and the length 4 of the right patch 62 is 10mm, taking into consideration
the width of the radiation slot 70, namely, the length 3, corresponding to 0.5mm,
and wherein the width W1 is 15mm.
[0038] FIG. 9 is a bottom view illustrating the structure of the microstrip antenna according
to the present invention.
[0039] As shown in FIG. 9, the ground patch 40 serving as the ground of the microstrip antenna
provides a feed line point on which a feed line 30 is positioned. The central conductor
of the feed line 30 extends towards the width center of the right radiation patch
62 adjacent to the radiation slot 70 via the ground patch 40 and the dielectric 50.
The outer conductor of the feed line 30 is connected to the ground patch 40. The feed
line 30 is spaced apart and separated from each of the left and right radiation patches
61 and 62 in a state in which the dielectric 50 is interposed therebetween. By virtue
of the dielectric 50, the feed line 30 is electronically coupled to each of the left
and right radiation patches 61 and 62.
[0040] The ground patch 40 includes a right triangle ground plate 41 having an area extending
from the core conductor of the feed line 30 to both corners of the dielectric 50 at
which the right radiation patch 62 is short-circuited. The ground patch 40 also includes
a connecting plate 42 extending from the core conductor of the feed line 30 towards
the left radiation patch 61, and a left ground plate 43 covering the under surface
of the dielectric 50.
[0041] As shown in FIG. 9, since both sides of the connecting plate 42 of the ground patch
40, to which the feed line 30 is connected, are opened, the current distribution of
both sides becomes zero, and the voltage distribution becomes maximum. Preferably,
if the whole length of the microstrip antenna 100 is 25mm, the length ℓ 5 of the right
ground plate 41 is 5mm, the length ℓ 6 of the connecting plate 42 is 6mm, and the
length ℓ 7 of the left ground plate 43 is 14mm. Additionally, if the whole length
1 of the microstrip antenna 100 is 15mm, it is preferable to design the microstrip
antenna 1'00 such that the core conductor of the feed line 30 is connected at a point
of 7.5mm distance from an end of the dielectric 50, that is, the center of the width
of the dielectric 50, and that the width W2 of the connecting plate 42 is 2mm. Also,
the whole thickness H1 of the microstrip antenna 100 is 3.2mm, as shown in FIG. 10.
[0042] The microstrip antenna 100 according to the above embodiment of the present invention
comprises the ground patch 40 with both sides being opened by taking the connecting
plate as a standard line, thereby providing inherent characteristics which will be
explained below. In order to maintain those inherent characteristics, the ground patch
40 has to be mounted apart from, for example, the printed circuit board of a portable
mobile terminal (wireless telephone) to which the microstrip antenna 100 is applied.
[0043] FIG. 10 is a side view illustrating the structure of the microstrip antenna according
to the present invention.
[0044] In the case that the ground patch 40 is directly mounted on the printed circuit board
of the portable mobile terminal, since it is meaningless that both sides are opened
by taking the connecting plate 42 as a base line, the ground patch 40 is bent from
the center of the left radiation patch 61 to the left ground plate 43 through the
side of the dielectric 50, and has a bent mounting piece 80 to provide a height H2
apart from the printed circuit board. The mounting piece 80 maintains the condition
of the microstrip antenna 100 apart from the printed circuit board of the mobile terminal,
for example the apart height of 3mm, so that the function of the ground patch 40 can
be effected at a maximum.
[0045] Preferably, the length T1 of the mounting piece 80 mounted on the upper surface of
the left radiation patch 61 and the lower surface of the left ground plate 43 is 3mm,
respectively, and its width S1 is 8mm, the bent width S2 is 2mm, and its length T2
is 2.7mm.
[0046] With the above mentioned construction, the microstrip antenna 100 of the present
invention is used as a transmission/reception antenna of a flying object such as a
rocket, missile, airplane, etc., and may 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.
[0047] An explanation will now be given of the embodiment in which the microstrip antenna
of the present invention is applied to a portable mobile terminal.
[0048] A dipole antenna, a Yagi antenna, or the like is used in the portable mobile terminal.
The dipole antenna is a resonance antenna of a half wavelength and has a characteristic
of all directional radiation, such that it is used for an antenna of a mobile terminal
in cellular communication and a service antenna of a small relay. The Yagi antenna
is made of a laminated dipole antenna to enhance directional gain and is used for
an antenna of a small relay.
[0049] Additionally, the microstrip antenna 100 is used for a personal mobile communication
service using a cellular phone and personal communication service, a wireless local
looped service, future public land mobile telecommunication system, and variable wireless
communication comprising satellite communication to transmit and receive the signal
between the base station and the mobile terminal.
[0050] Meanwhile, since the prior microstrip laminated antenna is a resonance antenna, it
has drawbacks in that it has a very narrow bandwidth of frequency and a low gain.
Accordingly, a great number of sheets of patches must be laminated or arrayed. This
results in an increase in the size and thickness of the antenna. For this reason,
it is difficult for the prior antenna to be mounted on personal mobile terminals,
mobile communication repeaters, wireless communication equipment or the like.
[0051] The microstrip antenna according to the present invention 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
can be minimized in 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.
[0052] FIG. 12 is a graph illustrating the return loss with respect to the frequency of
the microstrip antenna according to the present invention.
[0053] It will be noted from FIG. 12 that in the microstrip antenna according to the present
invention, its service band is in the range of 1,750 to 1,870MHz, and its bandwidth
is above 120MHz (above about 160MHz), so that it can be more easily adapted to the
personal communication service.
[0054] Specifically, the microstrip antenna according to the present invention shows that
since the reflecting loss in the range of 1,750 to 1,870MHz is -10dB, the loss value
to the reflecting current is very preferable. Further, its bandwidth is maintained
widely on the order of 120MHz.
[0055] FIG. 13 is a graph illustrating the standing-wave ratio with respect to the frequency
of the microstrip antenna according to the present invention, in which the maximum
standing-wave ratio to the resonance impedance of 50Ω in a frequency band of personal
communication service is 1:1.06 to 1.76.
[0056] Supposing that the ideal standing-wave ratio is 1 in the microstrip antenna, at marker
1 the standing-wave ratio is 1.768 and the frequency is 1.75000GHz, at marker 2 the
standing-wave ratio is 1.1613 and the frequency is 1.78000GHz, at marker 3 the standing-wave
ratio is 1.4269 and the frequency is 1.84000GHz, and at marker 4 the standing-wave
ratio is 1.80664 and the frequency is 1.87000GHz. Accordingly, the standing-wave ratio
to the resonance impedance of 50Ω in the bandwidth of 0.12GHz is preferably realized.
[0057] Further, the gain of the microstrip antenna 100 of the present invention should be
effectively achieved for the transmission/reception with the base station or the relay
station. As the result of a measurement for radiated gain conducted in a room in which
electromagnetic waves are not reflected, it can be found that a gain of 0.5 to 1.3dB
is obtained in all directions.
[0058] FIG. 14 is a Smith chart explaining the microstrip antenna according to the present
invention.
[0059] Supposing that the resonance impedance is 50Ω in the frequency band of the personal
communication service, at marker 1 the impedance is 33.660Ω and the frequency is 1.75000GHz,
at marker 2 the impedance is 44.160Ω and the frequency is 1.78000GHz, at marker 3
the impedance is 59.616Ω and the frequency is 1.84000GHz, and at marker 4 the impedance
is 47.846Ω and the frequency is 1.87000GHz. Accordingly, the resonance impedance in
the bandwidth of 0.12GHz is realized in a range of 34 to 60Ω, and, in particular,
the resonance impedance in the markers 1 and 2 is nearly 50Ω.
[0060] FIG. 15 is a view of the radiation pattern explaining the microstrip antenna according
to the present invention.
[0061] The microstrip antenna according to the present invention realizes an omni-direction
pattern as shown in FIG. 15, thereby solving the directional problem.
[0062] It will be noted that Y axis shows an amplitude value as dB, a line A shows 1.74GHz,
a line B shows 1.78GHz, a line C shows 1.8GHz, a line D shows 1.84GHz, and a line
E shows 1.87GHz, thereby achieving the omni-directional pattern.
[0063] With the above mentioned constitution, because a leak current does not flow in the
outer conductor of the feed line 30, it is not necessary to provide a matching circuit
in the portable wireless system. Further, since it is made by loading its capacity,
the electric line of power between the ground patch 40, the right radiation patch
62 and the left radiation patch 61 is not limited, thereby making its size small without
diminishing its gain.
[0064] Because the left radiation patch 61 and the right radiation patch 62 are divided
by the radiation slot 70 to cause the entire radiation patch to have an electric field
of the same phase, it is possible to solve the low reception sensitivity.
[0065] Specifically, the microstrip antenna 100 has a gain which is increased by 1 to 1.76
dB on the capacity-loaded side relative to the ground patch 40, and has a radiation
pattern with a maximum electric field of 2dB larger than that of the prior dipole
antenna, so that it can be effectively used as an antenna for bands of PCS services
[0066] Also, with the microstrip antenna 100 of the present invention, the thickness H1
of the dielectric 50 and the width of the capacity-loaded side can be adjusted to
increase or reduce its bandwidth gain, and the feed point of the feed line 30 can
be variably adjusted to eliminate occurrence of a fringe effect at the feed point
of the feed line, thereby effectively overcoming the indefinite distribution of the
feed line.
[0067] Also, an increase in gain occurs at the capacity-loaded part rather than at the ground
patch 40. As a result, the microstrip antenna 100 of the present invention can have
a radiation pattern of larger gain.
[0068] The microstrip antenna of the present invention is used as a transmission/reception
antenna of a flying object such as a rocket, missile, airplane, etc., and may be designed
on the substrate together with solid-state modules such as an oscillator, amplifying
circuit, variable attenuator, switch, modulator, mixer, phase shifter, etc. Additionally,
the microstrip antenna is used for a personal mobile communication service using a
cellular phone and personal communication service, a wireless local looped service,
future public land mobile telecommunication system, and variable wireless communication
comprising satellite communication to transmit and receive the signal between the
base station and the mobile terminal.