JP2009171022A - Phased array antenna - Google Patents

Abstract

There is provided a phased array antenna using an antenna element that faces a satellite at an elevation angle lower than the zenith (an elevation angle is less than 90 degrees).
A phased array antenna in which element antennas having two main beams are arranged on the same plane on a hemisphere, or a dipole antenna and a reflector, and the distance between the reflector and the dipole antenna is 0.35λ. A phased array antenna in which element antennas of 0.55λ are arranged on the same plane, or a phased array antenna in which element antennas having two main beams and parasitic elements are alternately arranged on a hemisphere.
[Selection] Figure 3

Description

  The present invention relates to a phased array antenna.

  Conventionally, as a phased array antenna using a dipole antenna with a reflector as an element antenna, there is an antenna that uses a radar. In this case, since the application is radar, the main beam direction of the antenna needs to be perpendicular to the array antenna surface, and an electronic beam scan of about ± 45 degrees is usually performed with respect to the array surface.

On the other hand, as a phased array antenna for a satellite communication mobile body, an antenna using a microstrip antenna as an element antenna has been reported for the purpose of use in the L-band band (Non-patent Document 1).
Further, Non-Patent Documents 2 to 4 shown below have been announced due to the necessity of recent mobile satellite communications.

IEICE Transactions, B-II, Vol. J72-B-II, No.7, pp. 323-329, 1989, Title: Electronic scanning antenna for on-board satellite communications, Authors: Nishikawa Kunoshi, Sato Kazuo, Yoshitoshi Fujimoto, Affiliation: Toyota Central Research Institute, Ltd. IEICE Transactions, B, Vol. J89-B, No. 9, pp. 1696-1704, 2006, Title: Electronic scanning characteristics of a simple satellite tracking array antenna, Authors: Kenichi Kaneko, Norimitsu Tanaka, Toyoaki Takahashi, Koichi Ito, Affiliation: Chiba University IEEE Antennas and Propagation Magazine, Vol. 33, No. 3, pp. 33-41 (Chapter 6 of pp. 37-38, Planar microstrip Yagi array), June 1991, Title: Microstrip Antenna Development at JPL, Author: John Huang, Affiliation: Jet Propulsion Laboratory IEEE Transactions on Antennas and Propagation, Vol. 55, No. 6, pp. 1883-1887, June 2007, Title: A Novel Planar Switched Parasitic Array Antenna With Steered Conical Pattern, Authors: WH Chen, JW Sun, X. Wang, ZH Feng, FL Chen, Y. Furuya, and A. Kuramoto, Affiliation: Tsinghua University and NEC YRP Center

  As described above, various types of phased array antennas have been developed and studied for the purpose of radar or satellite communications. However, what is common to these phased array antennas is the maximum radiation directivity of the element antennas used as array antennas. The radiation direction is perpendicular to the antenna surface (see FIG. 1).

  This is because the phased array antenna was originally researched and developed for the purpose of radar for military use, and its basic technology is a technology intended for radar. That is, the directivity of the element antenna is a technique using an antenna element having only one beam on the hemisphere. Therefore, in a phased array antenna that can perform beam scanning only along the beam width of the element antenna, ± 45 at most. The beam scanning can only be performed to a certain degree. Therefore, communication between a communication satellite that is stationary on the equator and a mobile object such as an automobile or a train that travels on the ground (mobile satellite communication) is limited to some countries (equator. Except for countries directly below), there is a drawback that the antenna height is high, but in order to ensure high-quality communication, the array antenna is tilted toward the satellite, and in that state beam scanning or antenna is fixed, Or it was satisfied with insufficient quality communication with a phased array antenna using a planar antenna to make the antenna thinner.

  To deal with this problem, it is sufficient to use an element antenna with the main beam of the element antenna pointing in the direction of the satellite. However, among experts in this field, this technique deteriorates the radiation level in the direction of 90 ° elevation. However, since the beam of the element antenna is split into two as shown in Fig. 2, it is assumed that one beam cannot be made when a phased array antenna is used. There has been no example of configuring a phased array antenna using.

  In addition, in the phased array antenna, it is necessary to attach a phase shifter for changing the feeding phase to each antenna element for electronic beam scanning. However, since this phase shifter is expensive, as described above, some Although research on such a phased array antenna has been made, the fact is that it has not been put into practical use.

  The present invention has been made to solve the above-described problems, and the main beam of the element antenna used so far does not face the zenith direction with respect to the element, but the elevation angle is lower than the zenith (the elevation angle is less than 90 degrees). ) To provide a phased array antenna using antenna elements facing the satellite.

  Furthermore, in the antenna of the present invention, one of the objects is to provide an inexpensive phased array antenna by thinning out the feeding elements instead of feeding all the antenna elements in order to reduce the number of expensive phase shifters. It is said.

In order to solve the above problems, the present invention provides, for example, the following inventions.
(Invention 1)
A phased array antenna in which element antennas having two main beams are arranged on the same plane on a hemisphere.
(Invention 2)
A phased array antenna in which element antennas, each of which is composed of a dipole antenna and a reflector, and whose distance between the reflector and the dipole antenna is 0.35λ to 0.55λ are arranged on the same plane.

  The element antennas of the inventions 1 and 2 are antennas that do not radiate in the direction perpendicular to the element antenna, that is, the zenith direction, and have two maximum radiation directions in a conical shape (see FIG. 2). It is characterized by having a beam. The “conical shape” indicates a portion where the “thickness” is thick in the right direction and the left direction of the donut in FIG. 2.

  Furthermore, when this element antenna is used as a phased array antenna, it is a major feature that has never been seen before, which has a main beam with a lower elevation angle (elevation angle <90 degrees) than the zenith direction (elevation angle 90 degrees). (See Figure 3).

(Invention 3)
A phased array antenna in which element antennas with two main beams and parasitic elements are arranged alternately on a hemisphere.
With such a configuration, thinning-out power feeding can be performed, so that an expensive phase shifter can be reduced and the price can be further reduced.

  As described above, since the antenna of the present invention is a phased array antenna composed of element antennas having a conical radiation characteristic, it is desirable to communicate with a geostationary satellite stationary on the equator from Japan. When satellite communication is performed when the satellite is not in the zenith direction, the antenna gain in the high angle direction is particularly high compared to the phased array antenna using the conventional element antenna, so that communication of good communication quality can be provided. Thus, it is possible to reduce the size of the antenna, and thus the antenna price can be reduced.

  Further, since the antenna of the present invention can perform thinning power feeding, an expensive phase shifter can be reduced and the cost can be further reduced.

  In the following description, the feature of the present invention “having a main beam having a lower elevation angle (elevation angle <90 degrees) than the zenith direction (elevation angle 90 degrees)” is further embodied, and a geostationary satellite on the equator is viewed. An explanation will be made focusing on an antenna having an elevation angle of 30 to 60 degrees.

FIG. 4 shows a saddle configuration of a phased array antenna according to an embodiment of the present invention.
The antenna includes an array antenna unit 401 in which a large number of element antennas are arranged, and a power feeding circuit unit 403 including a phase shifter necessary for beam scanning in each of the elements.

  As the element antenna, a normally used half-wave dipole antenna is used and arranged on a flat reflector. The arrangement may be a square arrangement in which each of the four element antennas forms a quadrangle, or may be a triangle arrangement in which the three element antennas form a triangle.

  In this case, the distance between the reflector and the element antenna is not λ / 4 which forms a single beam used in radar or the like, but does not radiate in the zenith direction of the antenna as shown in FIG. It is preferable that it is the distance which shows. If element antennas having such distances are arranged to constitute a phased array antenna, an antenna having an elevation angle when viewing a stationary satellite on the equator and an elevation angle in the direction of 30 to 60 degrees can be obtained as will be described later.

  According to the calculation, the antenna height at which this characteristic can be obtained at an elevation angle of 30 to 60 degrees when viewing a geostationary satellite on the equator from Japan is 0.35λ to 0.55λ, and at this antenna height, a phased array antenna is used. The beam scannable angle of ± 15 degrees or more with respect to the maximum radiation direction is obtained, and the elevation angle of 30 degrees to 60 degrees necessary for tracking the satellite from within the country can be satisfied.

  When the antenna height is 0.35λ, the elevation angle of 30 degrees, the antenna, regardless of the parameters of the other antennas (interval distance between element antennas, feeding phase difference between element antennas, etc.) When high = 0.55λ, it can be said that the elevation angle is 60 degrees regardless of the parameters of other antennas. In other words, when it is an array, it changes by 2 to 3 ° precisely due to the influence of mutual coupling. However, since this difference cannot be discriminated even by a person skilled in the art engaged in antennas even if it is measured, it is not a problem.

  Incidentally, when the antenna height is 0.45λ to 0.52λ, the maximum radiation direction is substantially 45 degrees from the zenith at the antenna height.

  Furthermore, in this case, when this antenna is arranged as an element antenna to form a phased array antenna, and the beam is scanned in the desired satellite direction as seen from the country by phase control, as shown in FIG. The number of main beams is one, and a beam similar to that of a conventional phased array antenna formed by an element antenna having one main beam in a hemisphere is formed. That is, it is possible to obtain a phased array antenna having a predetermined azimuth angle and an elevation angle smaller than 90 degrees.

  In this case, the “azimuth angle” can be changed by changing the feeding phase to each element.

  At this time, the antenna gain is 60 degrees or more (elevation angle 30), although a gain decrease of about 2 dB is observed when scanning at an angle of about 30 degrees from the zenith direction (elevation angle 60 degrees) as shown in FIG. When scanning at a high angle (less than or equal to degrees), for example, at 63 degrees, the antenna of the present invention has an advantage that the antenna gain is 7 dB or more higher than the conventional antenna. (An angle of about 30 degrees = an elevation angle of 60 degrees, 60 degrees or more = an elevation angle of 30 degrees or less)

  Therefore, for example, it is very effective for countries such as Scandinavia that require scanning at a higher angle outside Japan. The effect becomes more remarkable as the number of elements required for the arrangement increases.

  As a dipole antenna element of this configuration, an antenna element that has knowledge of antenna engineering is usually designed including dimensions and the like. Therefore, the antenna may be constituted by a linear conductor, or a dipole antenna may be designed using a generally used high frequency dielectric substrate.

  As an example of the array antenna, a dipole antenna with a reflector having a height h = 0.48λ, a radius α = 0.0007λ of the dipole element (11), and a length L = 0.474λ of the dipole element (11) is shown in FIG. As described above, the triangular array 19-element array antenna is used, and the distances dx and dy between the dipole elements (11) in the x-axis direction and the y-axis direction are dx = 0, 55λ, dy = 0.476λ, and the reflector (12 FIG. 7A shows the simulation result of the H-plane beam scanning characteristic when) is 5λ × 5λ.

  FIG. 7A shows the main beam angle of the array antenna with respect to the phase shift amount. By setting the phase shift amount to 67.5 to 157.5 degrees, the radiation angle of the main beam in the direction of the communication satellite is 30 to 60 degrees. The beam is scanned.

  FIG. 7B shows the gain of the array antenna with respect to the amount of phase shift. The gain is low from the zenith direction where communication is not performed in mobile satellite communication to the vicinity of the radiation angle of 20 degrees, but near the radiation angle of 26 to 64 degrees. The gain is high and the gain is stable.

The array antenna of the first embodiment can also be expressed as follows.
A plane reflector,
A single half-wave dipole antenna disposed on the planar reflector with a height h = 0.48λ.
An antenna comprising:
A dipole antenna with a reflector, characterized in that the main beam angle on the magnetic field surface is 30 to 60 degrees, and an array antenna in which a plurality of the element antennas are arranged,
H = 0.48λ,
Element radius α = 0.0007λ of the half-wave dipole antenna;
The dipole element length L = 0.474λ,
The size of the reflecting plate is a rectangle of 5λ × 5λ,
age,
When the array antenna is viewed from the vertical direction on the reflector, the longitudinal directions of the individual dipole antennas are arranged in parallel to each other in the X-axis direction,
The dipole antenna is arranged in order of three, four, five, four, three in order in the Y-axis direction perpendicular to the vertical direction and perpendicular to the X-axis,
The X coordinate of the center in the longitudinal direction of one central dipole antenna of the three, five, and three dipole antennas coincides,
The X coordinate of the center in the longitudinal direction of one central dipole antenna of the four or four dipole antennas coincides,
The X coordinate of the center in the longitudinal direction of each of the three, five, and three dipole antennas coincides with the X coordinate of the center of the gap between the elements of the four and four dipole antennas,
Distance dx = 0.5λ between adjacent dipole antenna centers in the X-axis direction,
The distance dy = 0.476λ between adjacent dipole antenna centers in the Y-axis direction,
Total number of elements = 19,
The center of gravity of the 19-element dipole antenna group coincides with the center of gravity of the rectangular reflector,
The amount of phase shift between adjacent antennas = 67.5-157.5 degrees,
Accordingly, the main beam is scanned in a range of radiation angle = 30 to 60 degrees.
Phased array antenna.

  Furthermore, the antenna of the present invention may have a structure including an element that does not supply power without supplying power to all the arranged antenna elements, that is, a thinning power supply method. At this time, when the antenna of the present invention is fed to all antenna elements, substantially the same antenna characteristics can be obtained.

According to the experiment and calculation results, the elements to be thinned are in accordance with the following basic conditions.
(1) Feeding elements and parasitic elements are alternately arranged.
(2) However, for several percent, a feeding element or a parasitic element may be continuous.
(3) The direction of the main beam at that time is determined by the following equation.

θ = sin ⁻¹ (φ / kd) (Formula 1)

Where θ is the direction of the main beam, k is the wave number, ψ is the phase difference between the feeding elements for beam scanning in the desired θ direction, and d is not the distance between the elements including the normally considered parasitic elements. , The distance between elements of the feeding element.
Λ is a wavelength.

Next, a description will be given of the case where thinning power feeding is performed.
FIG. 8 shows an embodiment of an antenna when thinning power feeding is performed.
This antenna is composed of a reflecting plate 1, a feeding element antenna 2, and a parasitic element antenna 3.

  In FIG. 8, the heights of the feeding element and the parasitic element from the reflecting plate are equally 0.48λ. According to the calculation, the height of the parasitic element does not necessarily have to be equal to the height of the feed element, and the characteristics are equal to or higher than the half of the height of the feed antenna element to 1.5 times the height. Is obtained.

  The number of elements is a 25-element array of 5 elements in the vertical direction and 5 elements in the horizontal direction. Further, the size of the reflecting plate is determined by the number of elements conventionally employed in the array antenna, and in this example, the size of the reflecting plate is approximately 3.3λ.

The distance between the antenna elements is 0.55λ including the parasitic elements, and the arrangement method is a so-called square arrangement in which the antenna elements are arranged in the same straight line in both the vertical and horizontal directions. In this case, the arrangement method may be a rectangular arrangement or a triangular arrangement that is usually used to improve the sidelobe characteristics in the 45-degree direction in the arrangement plane, which is a problem with the phased array antenna.
FIG. 9 shows measured values of directivity characteristics during beam scanning of this antenna.

In addition, the invention which concerns on the specific example of Example 2 can also be expressed as follows.

A plane reflector,
A single fed half-wave dipole antenna disposed on the planar reflector with a spacing of height h = 0.48λ, and
An antenna comprising a single parasitic half-wavelength dipole antenna disposed on the plane reflector plate with a height h = 0.48λ to 0.72λ.
The size of the reflecting plate is a rectangle of 3.3λ × 3.3λ,
age,
When the array antenna is viewed from the vertical direction on the reflector, the longitudinal directions of the individual feed and parasitic dipole antennas are parallel to each other and arranged in the X-axis direction at equal intervals of 0.55λ,
Five power supply dipoles, five power supply dipoles, five power supply dipoles, five in order at equal intervals of 0.55λ in the Y axis direction orthogonal to the vertical direction and orthogonal to the X axis There are 5 parasitic dipoles, 5 feeding dipoles,
Total number of elements = 25,
The center of gravity of the 25-element dipole antenna group coincides with the center of gravity of the rectangular reflector,
The amount of phase shift between adjacent antennas = ψ degrees,
By
When wave number = k, d = 1.1λ,
The main beam is scanned with a radiation angle θ = sin ⁻¹ (ψ / kd).
Phased array antenna.

  The present invention can be used for an electronic tracking antenna that is equipped with a moving body that travels on land such as an automobile or a train, and that is used for transmitting or receiving communication or broadcasting via a satellite. It is not limited to.

Radiation directivity of an element antenna used as a conventional array antenna. Radiation directivity of the antenna according to the embodiment of the present invention, which does not substantially radiate in the direction perpendicular to the element antenna, that is, the zenith direction and has two maximum radiation directions in a conical shape. When the element antenna of FIG. 2 is used as a phased array antenna, the radiation directivity of a phased array antenna having a main beam with an elevation angle (elevation angle <90 degrees) lower than the zenith direction (elevation angle 90 degrees). 1 is a schematic configuration of a phased array antenna according to an embodiment of the present invention. Comparison of the gain (◆) of an array antenna using an element antenna with h = 0.25λ and the gain (■) of an array antenna using an element antenna with h = 0.48λ Dipole array antenna with triangular array 19-element reflector. Beam scanning characteristics of a dipole array antenna with a triangular array 19-element reflector with a height h = 0.48λ (the main beam angle of the array antenna with respect to the amount of phase shift). Beam scanning characteristics of a dipole array antenna with a triangular array 19-element reflector with a height h = 0.48λ (array antenna gain with respect to phase shift amount) An example of an antenna in the case of thinning power feeding Measured value of directivity during beam scanning of antenna in FIG.

Explanation of symbols

401 Array antenna unit 403 Feed circuit unit

Claims (3)

  A phased array antenna in which element antennas having two main beams are arranged on the same plane on a hemisphere.   A phased array antenna in which element antennas, each of which is composed of a dipole antenna and a reflector, and whose distance between the reflector and the dipole antenna is 0.35λ to 0.55λ are arranged on the same plane.   A phased array antenna in which element antennas with two main beams and parasitic elements are arranged alternately on a hemisphere.