JPH0480561B2 - - Google Patents

Description

Claim 1: An antenna system to be installed on an aircraft to fit the shape of the aircraft in order to generate an electronically scanned main radiation lobe, comprising: (a) a plurality of Yagi antennas that do not overlap each other; Each Yagi antenna is composed of a plurality of parallel linear element conductors extending along the direction of the linear arrangement. including an exciter, a reflector and a waveguide,
Each of the exciter, reflector, and waveguide has a length shorter than the center spacing of each of the Yagi antennas, and each of the Yagi antennas has the direction of the linear arrangement as the X axis, and the direction of the linear arrangement as the X axis. The endfire direction is the Z axis, and the direction perpendicular to the X axis and the Z axis is the Y axis, and in the X-Z plane and the Y-Z plane, respectively,
Free space half-width Bx and
By, and a linear array of the plurality of Yagi antennas configured to radiate electromagnetic waves having a maximum gain in free space in the endfire direction of the Yagi antennas, and (b) an antenna consisting of the linear array of the Yagi antennas. While maintaining the main lobe half width in the Y-Z plane of the entire system equal to approximately By, the main lobe in the X-Z plane is
variable phase for controlling the signal phase and amplitude of each Yagi antenna to electronically scan over an angular range of 90° or more with an expanded mutual coupling effect between the Yagi antennas; and variable amplitude means.

2. The antenna system according to claim 1, wherein the distance between the Yagi antennas is approximately 0.55λ.

3. An antenna system according to claim 1, characterized in that Bx is approximately 42°.

4. The antenna system according to claim 1, wherein the main lobe half width of the system in the Y plane is approximately 48 degrees.

5. An antenna system as claimed in claim 1, characterized in that the antenna system includes means for mounting each of the Yagi antennas on the wing of an aircraft to match the shape of the wing.

6. The antenna system comprises (a) a pair of side-lucking antennas, and (b) the side-lutzing antenna and the electronic scanning antenna system are installed on the aircraft in a manner that conforms to the shape of the aircraft, thereby achieving a wide azimuth. Antenna system according to claim 1, characterized in that it includes means for achieving angular coverage.

7 configuring two antenna systems including a second electronically scanned antenna system similar to said antenna system, wherein said means for said airframe compatible equipment further comprises said two antenna systems with their Z axes extending in opposite directions; 7. The antenna system according to claim 6, further comprising antenna mounting means for mounting the antenna in a positional relationship in which the Y-axes extend in parallel and in the same direction.

8. Claim 6, characterized in that the means for fitting the aircraft is configured to fit the electronically scanned antenna system within the main wing of the aircraft. Antenna system as described in section.

9. Claim 9, characterized in that said antenna mounting means is configured to mount said two antenna systems within the main wing and horizontal stabilizer of said aircraft, respectively, to fit their shapes. Antenna system according to item 7.

10. The antenna system according to claim 9, wherein the side-lucking antenna is mounted on the fuselage of an aircraft so as to conform to the shape of the aircraft.

11. The antenna system according to claim 1, wherein the reflector in each of the Yagi antennas is made of a common reflecting member.

12. The antenna system of claim 1, wherein each of the Yagi antennas includes non-conductive support means for supporting the exciter, reflector and waveguide in a fixed positional relationship with respect to each other. .

13. The antenna system of claim 1, wherein the exciter, reflector, and waveguide in each Yagi antenna are separated from each other by a distance of approximately 0.25λ.

BACKGROUND OF THE INVENTION The present invention relates to antennas, and more particularly to electronically scanned antenna systems having a linear array of vertical elements (endfire elements). A “vertical element” means that its maximum gain is in the “vertical axis direction”, that is, in the arrangement direction of the element conductors such as exciters, reflectors, waveguides, etc. arranged in parallel to constitute the vertical element (so-called end-of-axis direction). is defined as such an element obtained along the eye direction).

Electronically scanned linear arrays of simple elements are well known in the art. Such element arrays are generally characterized by relatively low gain and broad vertical directivity characteristics. Vertical element arrays in which scanning is performed mechanically by rotating the entire element array are also well known. These element arrays are often required to be installed in a manner that is compatible with the aircraft, that is, in an arrangement that fits within the aircraft's air oil (main wings and horizontal stabilizers), but this is currently not fully satisfied. It's not a thing.

Although various antenna element arrangements are well known, US Pat. No. 2,236,393 (Beck et al.) discloses a broadband vertical antenna array. Additionally, U.S. Patent No.
No. 3,182,330 (Blume) discloses an antenna array with non-uniform spacing between individual elements. Additionally, U.S. Pat. No. 2,425,887 (Lindenblad) discloses a vertical antenna array in which all elements are energized with equal voltages in proper phase. US Pat. No. 3,258,774 (Kinsey) discloses a series-fed phased antenna array. Reference should also be made to US Pat. No. 3,509,577 (Kinsey). U.S. Patent No. 2419562 (Kandoian)
discloses a binomial array that forms a cloverleaf pattern with high directionality. A typical Yagi antenna is U.S. Patent No. 3,466,655 (Mayes et al.)
It is described in.

Furthermore, in known antenna arrays, mutual coupling relationships between element antennas are generally recognized as disadvantageous, and consideration is given to minimizing their effects. In contrast, the present invention utilizes mutual coupling relationships to improve antenna performance. "Mutual coupling" as used herein means that the radiation waves from the arrayed element antennas interfere with each other, changing the original radiation lobe, and forming composite radiation lobes of different shapes.

In this case, the vertical axis (endfire direction) of the Yagi antenna, which is a typical vertical element, is the Z axis,
If the "conductor" axis of the exciter, reflector, waveguide, etc. made up of straight conductors that make up the element antenna is the X axis, and the axis perpendicular to the X axis and the Z axis is the Y axis, then the Yagi antenna will be placed on a horizontal plane. Although it is well known as a device that generates a high-density radiation beam with sharp directivity in the (X-Z plane) and vertical plane (Y-Z plane), it is still unclear what the antenna characteristics will be when arrayed. It wasn't. Therefore,
In conventional practice, it has been thought that configuring a so-called array antenna in which a large number of element antennas are arranged would be disadvantageous for wide-angle electronic scanning.
In general, the limit of the directional scanning angle of an array antenna is the array element directivity (the directivity of that one element when only one element is activated and all other elements are non-reflective terminated). ) is determined by the practical width (angular range) of the antenna element, and this width is said to become narrower as the mutual coupling between element antennas becomes stronger and as the number of elements increases. Contrary to conventional methods, the present invention advantageously realizes a multi-element array for wide-angle scanning by utilizing the effect of mutual coupling between element antennas, which was unknown with respect to Yagi antennas, and thereby enables electronic scanning. It is designed to widen the array element directivity in a plane where a

One object of the invention is to produce a beam of radiation having a high gain as a whole antenna array and a narrow vertical angular range, and the radiation beam itself having a narrow horizontal angular range is electronically scanned through a wide horizontal angular range. An object of the present invention is to provide an antenna array that can be obtained.

Another object of the present invention is to provide a very small vertically directional device preferably arranged on or in the plane of the airfoil plane (wing surface) of the aircraft, such as the leading edge of the main wing and the trailing edge of the horizontal stabilizer. An object of the present invention is to provide an antenna array having an angular width.
A suitable radome (abbreviation for radome, electrically transparent aerodynamic cover), which is an integral part of the airfoil, is formed at the leading edge of these main wings.

Yet another object of the present invention is to provide an antenna array with high gain and widened array element directivity to extend the angular range over which the antenna main lobe is electronically scanned.

A specific purpose of the above is to widen the narrow array element directivity in an array of vertical elements.

Another object of the present invention is to widen the array element directivity of a vertical element arrangement only in one plane, that is, in the horizontal plane.

In summary, the present invention utilizes mutual coupling between closely spaced Yagi antennas, expands the array element directivity pattern of each Yagi antenna, and attempts to electronically steer the entire antenna array in azimuth (in the horizontal plane). It is something to do.

Other objects, configurations, and advantages of the present invention will become apparent from the detailed description given below with reference to the drawings.

SUMMARY OF THE INVENTION Briefly, the present invention is an electronically scanned antenna system having a linear array of vertical elements, wherein the vertical elements have a center-to-center spacing of no more than 0.9λ, preferably about 0.55L, greater than the width of each element antenna. They are spaced apart by λ in the lateral direction, thereby increasing their mutual coupling effect and increasing the in-plane ((X-Z plane)
The scanning range of the directivity angle of the radiation signal is expanded. Upper limit of center spacing is 0.9λ
The reason for this restriction is that the mutual coupling between the element antennas weakens and the angle of the radiation beam with respect to the vertical axis cannot be made very large. Furthermore, in order to utilize mutual coupling, it is better to have a short center spacing, but if the lower limit is not greater than the width of the element antenna, that is, the length of the element conductor, the ends of the conductors will overlap. Therefore, the lower limit of the center-to-center spacing is theoretically 0.5λ, considering the typical length of the preferred element conductor (i.e., the width of the element antenna) of 0.5λ; , the preferred spacing above
0.55λ is derived.

The term "electronic scanning" is used to include adjusting the excitation coefficients (eg, phase and amplitude) of individual element arrays according to the desired direction of beam generation.

It has been well known that an antenna beam heads in a direction perpendicular to a wavefront (a plane in which the amplitude is continuous with the same phase at each time, which is synonymous with a wavefront). In phase scanning of an antenna array, by individually controlling the excitation phase of each radiating element, a wavefront of the same phase that is formed as a whole (as will be described later,
In FIG. 4, the inclined line making an angle θ ₀ with the antenna array is adjusted to steer a beam with this in-phase wavefront. To allow rapid scanning, a phase shifter is electronically driven to adjust the phase between 0 and 2πrad. Although such electronic scanning is perhaps the most commonly used method, other means may be employed to similarly alter the in-phase wavefronts of the element array to effect beam steering. Control of the excitation coefficient of an array of elements is commonly known as an "antenna feed" and is used to make the amplitude and phase of the signal independent of each other between the individual elements of the antenna array.
or all means for controlling in a dependent manner and means for dividing or combining them.

Figure 6 shows multiple Yagi antennas (element conductor length
The array element directivity pattern when antennas (0.5λ) are arranged with a center spacing of 0.55λ and the free space directivity pattern of the same Yagi antenna arranged singly are shown by solid lines and broken lines, respectively. As is clear from this figure, the azimuth range (direction angle range in the horizontal plane) of the array element directivity pattern is significantly expanded compared to that of a single Yagi antenna.

Of course, the degree of expansion of the angular range is thought to depend not only on the spacing between antenna centers, but also on the number of waveguides and their spacing, but the directivity of a single Yagi antenna is sharp. If so, it is clear that the angular range expanded by the multiple array will be a sharp expansion, and will be smaller than that of a standard Yagi antenna array.

DETAILED DESCRIPTION OF EMBODIMENTS FIG. 1 shows an antenna 1 constructed in accordance with the present invention.
0 is abbreviated. Antenna 10 includes a linear array of vertical elements 12 electronically coupled to element drive circuitry 14, commonly known as an antenna feed.

Each vertical element 12 is sequentially extended laterally over a distance slightly longer than the width of the element antenna to approximately 0.9λ, preferably approximately
Having centers spaced apart by a distance D of 0.55λ enhances the mutual coupling effect between elements 12;
As a result, an enlarged element pattern of the main beam within the array plane as shown by the solid line range drawn in the center of FIG. 1 can be obtained without structural difficulty. The length L of each element 12 is approximately 1.25λ.

Referring to FIG. 2, a Yagi antenna 12A is shown as a vertical element used in the antenna array of the present invention. As is well known, an array of Yagi antenna elements consists of a driving element or projector plus at least two additional elements. Yagi antenna 1
2A has six conductor elements 16, 18, 20, 22,
24 and 26. Such a multi-element array is known as a six-element beam. Each element has a diameter of about 0.01λ and a length of about 0.5λ.

6 elements 16, 18, 20, 22, 24 and 26
The distance between adjacent elements is about 0.25λ, and they are arranged in parallel along the same line of sight (horizontal axis). This 0.25λ distance between element conductors provides good impedance matching as well as smooth and broad array element directivity. This is desirable and important in electronic scanning systems applying the present invention. 6 elements 16, 18, 20, 2
2, 24 and 26 are supported by a pair of non-conductive Plexiglas (trademark) supports 28 and 30. For example, elements 16, 18, 20, 2
2, 24 and 26, their supports 28 and 3
This is achieved by inserting it into a hole formed in 0. Supports 28 and 30 support elements 16, 18, 2
0, 22, 24 and 26 from each other and has the further advantage of being substantially transparent to emitted electromagnetic waves.

Element 16 is a reflector, element 18 is an exciter, and elements 20, 22, 24 and 26 are waveguides.
A coaxial cable 32 is electrically coupled to exciter 18 and adapted to provide a signal thereto.
The radiator 16 and the waveguides 20-26 interact in a conventional manner to provide increased gain and unidirectionality to the radiation pattern from the exciter. When the element 12A is placed alone, the free space half-width is Bx=42° in the E plane, that is, the X-Z plane (see Figure 2),
In the H plane, that is, the Y-Z plane, By=48° as shown in FIG. 2A.

Referring to Figure 3, 10 in the format shown in Figure 2.
vertical elements 12A to 12J are common reflectors 1
6A, about 0.5-0.9λ from each other, preferably about
They are arranged close to each other in the lateral direction with a center spacing of 0.55λ, thereby enhancing the mutual coupling effect. In other words, the distance between the element antennas is 0.55λ
This makes the radiated electric field intensity distribution of the arrayed element antenna the broadest and flattest when the element antenna is excited by the hook-type dipole driver. The benefit of making this distribution wider and flatter is that it can cover a wider azimuthal angle in the horizontal plane with minimal loss of antenna gain, and with mutual coupling between such elemental antennas, “ It is called "extended mutual coupling". Also,
An additional benefit is that this 0.55λ spacing minimizes variation in antenna drive point impedance so as to provide constant impedance matching as a function of scan angle. According to such an arrangement, the composite directivity of the arrangement, that is, the angular range in the horizontal plane over which the antenna main lobe is electronically scanned, is ±21 for a single vertical element 12A, as indicated by the solid line range in FIG. , i.e. from 42°, can be expanded to angles greater than 90° in this arrangement 10A. (This aspect is as shown for the schematic antenna array 10 of FIG. 1.)
In the case of a single vertical element 12A, a narrow vertical plane (H-plane) of ±24°, or 48°, shown in FIG. 2A.
The directional characteristics are maintained even in this ten array 10A. Thus, the effect of arranging the vertical elements 12A in close proximity to each other in the linear array 10A is to expand the width of the element directivity in the horizontal plane (E plane) of the array 10A, while maintaining the narrow vertical plane (H plane) directivity characteristic.

The E-plane directivity characteristic of the vertical element expanded in the array can be confirmed as follows. That is, the elements 12A to 12D and 12F to 12J are at the ground potential 36 in the element array 10A.
34A through 34D, and 34F through 34J.
terminating impedance 34A to 34D, and 3
4F to 34J are selected to match the antenna driving point impedance to the antenna scanning angle of 0° (Z-axis direction) in the E plane. Matching here refers to making the impedance (antenna driving point impedance) that each Yagi antenna embodies (for received waves or radiated waves) at a certain frequency equal to each other at a scanning angle of 0° in the E plane. It is.
In the embodiment shown in FIG.
J is 50Ω. Element 12E is monitored by meter 38. That is, the meter measures the power received by element 12E at a sufficient distance from array 10A, i.e., when used as a receiving device for signals transmitted from a remotely located electromagnetic emitter (not shown). It is something.
When array 10A is rotated together at an angle with respect to the radiator, the power measured at meter 38 will vary depending on the element directivity within the array of elements 12E. This method of directivity measurement is well known in the art. Furthermore, the element directivity in the array measured in this manner can be made as a function of angle when all elements 12A to 12J are used for beamforming by applying drive circuit connections as described below. It is also well known that the gain of the array 10A is approximately proportional to the gain of the array 10A.

Array 10A operates as follows with reference to FIG. A coupling and drive circuit 40 is supplied with transmit signals by feed means (not shown), and this circuit 40 divides the signals to the individual elements 42 of the array 44 (a total of N transporters 46). In this case, in the horizontal plane (in the X-Z plane)
Regarding the angle θ ₀ of the wavefront shown by the above-mentioned inclined line with respect to the antenna array line (X-axis), φ=2π/λ Ssinθ ₀ (where λ is the wavelength and S is the element spacing (center to center). ), the phase of the transporter 46 connected to each antenna is advanced (during transmission) or delayed (during reception) one after another in the order of the opening direction of θ ₀ . Requires non-uniform amplitude for each antenna element, resulting in relatively low antenna sidelobes (commonly known as amplitude slope)
The coupling and drive circuit 40 effectively provides such a distribution.

Since the antenna array 10A and its feed mechanism are bidirectional linear passive elements and obey the exchange law, their characteristics remain unchanged even when they are used in receive mode.

Referring to FIG. 5, aircraft 48 is equipped with antenna arrays 10B, 10C and 10D located within wing leading edges 50 and 52 and horizontal stabilizer 54 in accordance with the present invention. According to this configuration, by electronically scanning arrays 10B, 10C and 10D, and conventional side-looking antennas 56 and 58 mounted on opposite sides of fuselage 60, a 360° can obtain an azimuth range of . In other words, the main wing antenna arrays 10B and 10C move forward ±45° (90°), respectively.
An omnidirectional type that covers ±45° (90°) to the left and right sides by the side Lutzking antennas 56 and 58, and ±45° (90°) to the rear by the horizontal stabilizer antenna array 10D. becomes. Such an arrangement has the advantage of eliminating the need for the fuselage 60 to be equipped with a large radome that must be mechanically rotated to provide the same 360° azimuthal range.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a linear arrangement of vertical elements constructed in accordance with the present invention; FIG. 2 is a perspective view showing a Yagi antenna vertical element in a linear arrangement of the invention;
Figure 2A is a beam profile diagram of the same element in the vertical plane;
FIG.
Figure 5 is a plan view showing a linear array of vertical elements similar to Figure 3 scanned at an angle θ ₀ ; Figure 5 shows a linear array of vertical elements installed in accordance with the invention; Figure 6 is a partially cutaway perspective view of the aircraft, and Figure 6 shows the array element directivity pattern when multiple Yagi antennas (element conductor length 0.5λ) are arranged with a center spacing of 0.55λ, and when they are arranged individually. FIG. 4 is a pattern diagram showing the free space directivity patterns of the same Yagi antenna with solid lines and broken lines, respectively.

10,10A...Antenna array, 12,12A
~12J...Element antenna, 16...Anti-radiator, 1
8... Exciter, 20, 22, 24, 26... Wave director, 28, 30... Support body.