Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
1999-02-24
2001-04-17
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S7000MS, C343S767000
Reexamination Certificate
active
06219002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to antenna, and more particularly, to a planar antenna.
2. Description of the Related Art
In general, an antenna is a special electric circuit used in connection with a high frequency circuit. A transmitting antenna efficiently converts the electric power of the high frequency circuit into wave energy and radiates the converted wave energy into free space. A receiving antenna efficiently converts the energy of an input wave into electric power and transmits it to the electric circuit. The antenna operates as an energy converter between the electric circuit wave and the radio wave. The size and shape of the antenna is appropriately designed so as to improve conversion efficiency.
The beam pattern of the antenna is important in determining the channel characteristic in a high speed radio communication system.
FIG. 1
shows the beam pattern of an antenna provided for indoor high speed mobile radio communication. A base antenna
100
on a ceiling has a wide beam width
110
. An antenna
130
attached to a user terminal
120
has a directional beam characteristic
140
. Antennas for indoor high speed mobile communication use circular polarization in order to reduce the occurrence of a multipath fading phenomenon.
An antenna having the directional beam characteristic required for a receiving-end antenna can be easily realized using an array antenna. However, it is very difficult to realize a circularly polarized antenna having a wide beam angle such as that required for a base antenna. If a base antenna radiation pattern has a bowl shaped beam characteristic in which the antenna gain in the middle is low, the strength of the received electric field is uniform regardless of the position of a user. Therefore, it is possible to remarkably relax restrictions on the linear characteristics of RF transmitting and receiving ends, to easily realize an RF system, and considerably reduce manufacturing expenses.
In general, the planar antenna comprised of a dielectric and a conductor induces current to the surface of a conductor put on the dielectric or a slot and radiates electromagnetic wave energy into free space. The planar antenna occupies a small space since it can be attached to the surface of a terminal or a wall. It is possible to easily construct the array antenna using the planar antenna. Also, the manufacturing price of the planar antenna is low since it can be mass-produced. However, an undesired surface wave mode is generated other than a radiation mode since a dielectric layer is used. Accordingly, the efficiency of planar antenna is low. In the planar antenna, the wave is radiated into free space when current flows on the surface of the conductor and there exists a surface wave proceeding along the surface of the dielectric. The number of surface wave modes is proportional to the thickness of the dielectric layer. A minimum of one surface wave modes exists. The thickness of the dielectric layer should be reduced in order to suppress the number of surface wave modes. Only one mode (which cannot be removed) is generated when the thickness is reduced to no more than ¼ of the radio wavelength in the dielectric. Accordingly, loss is minimized. In practice, however, since the wavelength is several mms in a millimetric wave bandwidth, the dielectric layer is so thin that it can be easily broken when it is manufactured.
FIG. 2A
shows a micro-strip patch antenna which is widely used as a planar antenna. The micro-strip patch antenna is comprised of dielectric
20
, a conductor
24
located under the dielectric
20
, and a micro strip line
22
for feeding the current.
FIG. 2B
shows an example of a planar antenna using a multiple dielectric layer, which is comprised of the multiple dielectric layer
220
, a conductor plate
210
positioned on the multiple dielectric layer including a ring slot
200
, dielectric
240
positioned on the conductor plate
210
, and a feeder unit
230
for feeding current to the ring slot
200
.
In general, in the case of obtaining a circular polarization characteristic using the micro-strip patch antenna, it is very difficult to obtain an excellent axial ratio with respect to a wide angle. Also, the cross polarization characteristic is not good. Also, when the frequency is no less than the millimetric wave bandwidth, the planar antenna becomes so small that the dielectric is difficult to make and is easily broken by a slight shock.
A planar antenna formed by stacking various layers of dielectric having a thickness of ¼ wavelength was once provided in order to make a thick and efficient planar antenna. In such a planar antenna, it is possible to increase the gain when the dielectric layers are stacked in an order in which the dielectric constants of the respective layers are high-low-high. However, it is not easy to make a multiple dielectric layer for a high millimetric wave bandwidth. That is because parasitic effects generated on the contact surface of different materials deteriorate the performance of the antenna when the antenna is not very precisely manufactured. Also, the performance may be affected if the antenna is twisted due to a change in temperature or compression.
It is possible to increase the gain by attaching an oval dielectric lens in the high millimetric wave bandwidth. However, the method is used in an extremely specialized field such as radio astronomy due to large expenses for precisely processing the lens and technological difficulties.
FIG. 3
shows a ring-slot antenna, which comprises a conductor plate
300
, dielectric
310
under the conductor plate
300
, and a slot
320
for radiating the radio wave. The ring-slot antenna is a uniplanar radiation device which replaces the micro-strip antenna in a millimetric wave frequency bandwidth. It can be easily manufactured even for a high frequency. The ring-slot antenna can employ various feeding methods such as a micro strip transmission line and a coplanar waveguide (CPW). It is possible to easily realize an antenna having a dual polarization characteristic with the ring-slot antenna. However, it is not easy to obtain the circular polarization characteristic at a wide angle though the above antenna is used. Since a ground surface exists on the same surface as the antenna, undesired backward radiation often occurs. A method of feeding to the ring-slot from two points with an angle difference of 90° is used for realizing the dual polarization. In this case, the beam pattern is directional and asymmetrical. Also, it is difficult to obtain a desired axial ratio characteristic.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a planar antenna by which it is possible to obtain a bowl shaped beam characteristic and to obtain a circular polarization characteristic having a wide angle by feeding current to four micro strip transmission lines and using a ring-slot as a radiation device.
It is another object of the present invention to provide a planar antenna using multiple dielectric layers into which an air layer having a small dielectric constant has been inserted in order to increase the antenna gain.
Accordingly, to achieve the above objects, there is provided a planar antenna comprising a conductor plate for radiating radio waves to free space, an upper dielectric layer attached to the upper side of the conductor plate, a feeder unit attached to the upper surface of the upper dielectric layer for feeding current for the wave radiation of the conductor plate, and a plurality of dielectric layers attached to the lower side of the conductor plate and including at least one air layer.
The lower dielectric layer has a higher dielectric constant than the upper dielectric layer.
The air layer preferably has a dielectric constant equal to or less than that of the upper and lower dielectric layers of the air layer. The air layer can be formed by inserting columns between two dielectric layers constructing the plurality of lower dielectric layers. The thickness of the air l
Burns Doane Swecker & Mathis L.L.P.
Phan Tho
Samsung Electronics Co,. Ltd.
Wong Don
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