Communications: radio wave antennas – Antennas – Microstrip
Reexamination Certificate
2002-12-23
2004-06-22
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Microstrip
C343S846000
Reexamination Certificate
active
06753817
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-element planar array antenna which comprises a plurality of antenna elements arranged on a two-dimensional plane, and more particularly, to a multi-element planar array antenna which improves the polarization characteristics to facilitate the utilization of polarization components, and can be readily reconfigured into an active antenna by mounting a semiconductor device, IC (integrated) and the like thereon.
2. Description of the Related Arts
Planar antennas are widely used in for example, radio communications and satellite broadcasting in a microwave band and a millimeter band. Planar antennas are classified into a microstrip line type, a slot line type, and the like. Generally, the microstrip line planar antenna is often used because of a simple structure in a feed system, better radiation characteristics, and the like.
In recent years, a so-called multi-element array structure using a plurality of antenna elements has been employed with the intention of improving the antenna gains which is a challenge for the microstrip line planar antenna. As is well known, electromagnetic radiations include polarization components such as horizontal and vertical linear polarizations, and right-handed and left-handed circular polarizations. Many antennas making use of such polarization characteristics are widely used with the intention of sharing an antenna for transmission and reception, effectively utilizing the frequency resources, suppressing interference between transmission and reception, and the like.
FIGS. 1A
to
1
D are plan views respectively illustrating exemplary configurations of conventional planar antennas. Out of these planar antennas, those illustrated in
FIGS. 1A
,
1
B and
1
C are microstrip line planar antennas, while that illustrated in
FIG. 1C
is a slot line planar antenna. Each of these figures illustrates an exemplary configuration of a planar antenna having single antenna element
1
for producing a linear or a circular polarization.
The planar antenna illustrated in
FIG. 1A
is a microstrip line planar antenna for linear polarization which comprises square antenna element (i.e., circuit conductor)
1
and feed line
2
on one principal surface of substrate
3
made, for example, of a dielectric material. A ground conductor is disposed substantially over the entirety of the other principal surface of substrate
3
. In this planar antenna, the antenna frequency (i.e., resonant frequency) is determined by the shape of antenna element
1
, the dielectric coefficient of substrate
3
, and the like. Also, in this planar antenna, a polarization plane of linear polarization for transmission and reception is set by a feeding direction in which feed line
2
is connected. Specifically, as indicated by arrows, a vertical polarization component can be transmitted and received when antenna element
1
is fed in the vertical direction (up-to-down direction in the figure), while a horizontal polarization component can be transmitted and received when antenna element
1
is fed in the horizontal direction (left-to-right direction in the figure).
The planar antenna illustrated in
FIG. 1B
is a microstrip line planar antenna having square antenna element
1
on one principal surface of substrate
3
, similar to the one illustrated in
FIG. 1A
, but differs in that antenna element
1
is fed at two points so that it is adapted for use with a circular polarization. Specifically, feed line
2
is branched into two in the middle such that one of the branch lines is used as a vertical feed line while the other is used as a horizontal feed line. The vertical and horizontal feed lines differ in the electric length from each other by one-quarter wavelength. As a result, a vertical polarization component is out of phase from a horizontal polarization component by 90 degrees (&pgr;/2), so that these polarization components are combined into a circular polarization. Consequently, the resulting planar antenna is capable of transmitting and receiving a circular polarization. It should be noted that the planar antennas illustrated in
FIGS. 1A and 1B
each utilize a degeneration mode in antenna element
1
.
The planar antenna illustrated in
FIG. 1C
is a microstrip line planar antenna for circular polarization, in which degeneration is released in antenna element
1
to feed antenna element
1
at one point. In this planar antenna, portions of antenna element
1
in a set of diagonal directions are cut away to release the degeneration so that resonance modes in two directions (vertical and horizontal directions) are out of phase by 90 degrees from each other at the operating frequency of the antenna, thereby providing the capabilities to transmit and receive a circular polarization.
FIG. 1D
illustrates a slot line planar antenna for use with a circular polarization which releases degeneration in an antenna element. This planar antenna comprises antenna element
21
having a slot line instead of an antenna element in a microstrip line planar antenna. Antenna element
21
is rectangular in shape and released from the degeneration, thereby constituting a resonator at the antenna frequency. When antenna element
21
is fed at one corner thereof, resonance modes in the two directions are out of phase by 90 degrees from each other, similar to the foregoing, thereby providing the capabilities to transmit and receive a circular polarization.
The conventional microstrip line type and slot line type planar antennas described above can be shared for a horizontal polarization and a vertical polarization, and transmit and receive the circular polarization when they are provided with a single antenna element alone. However, these conventional planar antennas are problematic in configuring a multi-element planar array antenna comprised of a plurality of antenna elements arranged in a two-dimensional plane while maintaining the above functions of the planar antenna having a single antenna element.
Specifically, any of the planar antennas of the types illustrated in
FIGS. 1A
to
1
D encounters difficulties, when it is configured as a multi-element array, in implementing connections of the feed line to respective antenna elements, i.e., a feeder circuit on the plane. For this reason, a multi-layer substrate, for example, should be used to implement a feeder circuit, in which case difficult designing is obliged for ensuring the same line lengths, for example, from a feed point, due to a requirement of exciting the respective antenna elements in phase.
Further, when the configuration illustrated in
FIG. 1B
is used for a circular polarization antenna, a phase difference feeder circuit is required for each antenna element for giving a phase difference of &pgr;/2. In addition, the planar antenna illustrated in
FIG. 1C
suffers from a narrow operating frequency range on principles. The planar antenna illustrated in
FIG. 1D
is similar in that it encounters difficulties in double use of both vertical and horizontal polarization components, and an adaptation for a two-dimensional planar array antenna using a circular polarization component.
As described above, the conventional planar antennas, whichever one is concerned, generally have a problem in the double use of polarizations, and the adaptation for a two-dimensional planar array antenna using a circular polarization component.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a multi-element planar array antenna which has a two-dimensional array structure that can use polarization components together and use a circular polarization.
The inventors diligently investigated the configuration of planar antennas, and perceived the transmission characteristics and line structures of microstrip lines and slot lines formed on both sides of a substrate made of a dielectric material or the like, and particularly perceived features of an anti-phase serial branch from the slot line to the microstrip line, and a circuit in which microstrip line
Aikawa Masayoshi
Asamura Fumio
Nishiyama Eisuke
Oita Takeo
Katten Muchin Zavis & Rosenman
Nihon Dempa Kogyo Co. Ltd.
Tran Chuc
Wong Don
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