Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
1999-09-15
2001-08-28
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S772000, C333S02100R
Reexamination Certificate
active
06281855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a monopulse antenna apparatus and antenna structure configured by using a single horn.
2. Description of the Prior Art
As a conventional tracking method used in a tracking radar apparatus, a beam switching method or a sequential lobing, and a monopulse method are known. The monopulse method is capable of detecting an angle error by using a single pulse and a four-horn monopulse method is considered to be typical.
Antenna to which the four-horn monopulse method is applied is exemplarily disclosed in Japanese Laid-open publication 59-99804, entitled “monopulse horn antenna apparatus”. Japanese Laid-open publication 59-8409, entitled “monopulse antenna” also discloses an antenna of this kind. The monopulse horn antenna apparatus excites or forms, at an aperture of the antenna, a TE
10
mode wave (TE stands for transverse electric) for at least a sum beam, and a TE
20
mode wave for a differential mode, as described in a paragraph of “Claims of the Invention” of the specification. In the monopulse horn antenna apparatus, a plurality of horn antennas which can form monopulse beams in the H plane, are arranged in the E plane. For that purpose, a plurality of partitions made of a metallic plate, are inserted into each of these horn antennas in the direction of the H plane, thus forming monopulse beams in both the E plane and H plane.
The above-mentioned monopulse antenna is provided by improving characteristics of each primary horn in a multi-horn configuration. More specifically, the monopulse antenna has an aperture configured by four primary horns, in which a radiation-direction controlling board with a crisscross shape consisting of a metallic conductor plate, is arranged in parallel with the axis of the antenna, so as to increase the total directivity of the antenna.
Referring to
FIGS. 14
to
16
, a well-known monopulse antenna adopting a four-horn configuration will be described.
FIG. 14
shows a structure of a conventional monopulse antenna of four-horn type, which comprises a main reflector
101
, a subreflector
102
, a horn
103
consisting of four horns, and a comparator (amplitude comparator)
104
for obtaining sum signals and difference signals which will be described later.
FIG. 15
is a perspective view of the horn
103
which is divided or partitioned into four horns, shown as horns A, B, C and D.
FIG. 16
is a block diagram of the comparator
104
, showing its internal structure.
The comparator as shown in
FIG. 16
has hybrid circuits
105
to
108
such as a magic T and the like, for deriving sum signals and difference signals from the four horns. It should be noted that the sum of signals is shown by &Sgr; and the difference of signals is depicted as &Dgr;. Specifically, the comparator
104
produces a sum-signal output &Sgr;
111
, denoted by A+B+C+D, and similarly provides a sum-signal output &Sgr;
113
, given by ((A+C)−(B+D)).
The comparator
104
also produces a difference-signal output &Dgr;A
Z
112
denoted by ((A+B)−(C+D)), which is an error signal with respect to the horizontal direction (in the direction associated with the angle of depression). Furthermore, a difference-signal output &Dgr;E
1
110
expressed by ((A+D)−(B+C)) is provided by the comparator
104
, which is an error signal with respect to the vertical direction (in the direction associated with the angle of elevation).
FIG. 17
is a structure of a higher-mode monopulse antenna using a conventional single horn, which is described, for example, in “Handbook of Antenna Engineering” edited by Institute of Telecommunications Engineers, Ohm Publications, a paragraph 9.6.3 (1980). This antenna comprises a main reflector
201
, a subreflector
202
, a higher-mode detector
204
connected to a single horn
203
, and a reference signal detector
205
.
The higher-mode detector
204
is, say, a TM
10
(TM indicates transverse magnetic) mode detector and produces &Dgr;A
Z
+j&Dgr;E
1
as an error signal
207
. Note that j indicates the signal phase is shifted in 90°. The reference signal detector
205
comprises, for example, a waveguide with a taper, a circular polarization/linear polarization converter, a circular waveguide (TE
11
)/rectangular waveguide (TE
10
) converter and the like, which are not shown in the figure.
However, the previously described conventional four-horn type monopulse antenna requires four independent horns or four-partitioned horns, which makes the antenna apparatus itself larger in size and brings disadvantages from a cost perspective. Even if the antenna apparatus can be miniaturized, there is a problem that leakage power from the subreflector becomes large and performance of the antenna is deteriorated accordingly.
With respect to the higher-mode monopulse antenna utilizing a conventional single horn, a higher-mode detector generally comprises a mode coupler of multi-aperture type and a combining circuit consisting of a waveguide for coupling outputs from the mode coupler. This kind of monopulse antenna also raises a problem that the antenna apparatus becomes larger in size.
SUMMARY OF THE INVENTION
The present invention aims to solve the problems mentioned above. It is a primary object of this invention to provide a monopulse antenna apparatus and antenna structure capable of preventing antenna performance from deteriorating and of holding down the cost of the apparatus.
It is another object of the present invention to provide a monopulse antenna apparatus and antenna structure which make the apparatus itself small in size.
According to one aspect of the invention, the objects of the invention are achieved by a monopulse antenna apparatus using a single horn, comprising electromagnetic field generating means for generating the electromagnetic field inside of said single horn; and polarization means for causing polarization of distributions of said electromagnetic field to at least four locations which are symmetrical about the axis of said horn.
It is preferable that the apparatus further comprising means for deriving an angular error signal, based on horizontally polarized waves and/or vertically polarized waves generated by said polarization.
It is also preferable that said electromagnetic field generating means is a waveguide and said polarization means consists of four dielectric lines which are symmetrically arranged along the axis of said horn and separated with each other in the angle of 90 degrees, said dielectric lines being excited by said waveguide.
It is preferable that said electromagnetic field generating means is a coaxial cavity and said polarization means consists of four metallic lines which are symmetrically arranged along the axis of said horn and separated with each other in the angle of 90 degrees, said metallic lines forming a central conductor of said coaxial cavity and being excited by said cavity.
According to another aspect of the invention, the objects of the invention are achieved by a monopulse antenna apparatus having a single horn which comprises a main waveguide and at least four subwaveguides, wherein said single horn has at least four openings in its wall which are symmetrically arranged in the circumferential direction of the horn, and each of said subwaveguides is placed on the outer surface of the horn to cover each of said openings, whereby said four subwaveguides and said main waveguide are spatially communicated with each other through said openings, and an angular error signal is obtained based on a signal derived from said subwaveguides.
According to still another aspect of the invention, the objects of the invention are achieved by an antenna structure using a single horn, comprising at least four electromagnetic field generation members arranged in the inner side of said single horn to be symmetrical about the axis of said horn; electromagnetic field polarization members, one end of which is fixed on the end wall of said electromagnetic field generation member located in
Ho Tan
Mitsubishi Denki & Kabushiki Kaisha
Rothwell Figg Ernst & Manbeck
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