JPH0797730B2 - Monopulse microstrip antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a monopulse microstrip antenna that forms sum and difference patterns for monopulses.

(Prior Art) A conventional microstrip antenna for monopulse is
As shown in FIG. 8, by arranging at least four radiating elements 11 on the same plane and synthesizing these outputs by four or more hybrids 12 and terminators 13, etc., X-Z
An in-plane difference pattern ΔX-Z, a Y-Z difference pattern ΔY-Z, and a sum pattern Σ are obtained.

However, in the conventional monopulse microstrip antenna as described above, four or more radiating elements and hybrids are required, the configuration thereof is complicated, phase matching is difficult, and its adjustment is difficult. It was

(Problems to be Solved by the Invention) This invention was made to improve the problem that the conventional antenna has a complicated structure and difficult phase matching, and has a small number of parts and a simple structure. An object is to provide a monopulse microstrip antenna that can be easily aligned.

[Configuration of the Invention] (Means for Solving the Problems) The monopulse microstrip antenna according to the present invention is excited in the lowest order mode from the first feeding point and forms a sum pattern used for so-called monopulse angle measurement. And a first radiating element that is located on one side of the first radiating element via a dielectric or air and serves as a ground conductor of the first radiating element and is wider than the first radiating element. Is formed and is excited from the second and third feeding points in a lowest-order next higher-order mode different from the lowest-order mode,
A second radiating element forming a difference pattern used for so-called monopulse angle measurement, and a second radiating element located on the opposite side of the first radiating element with a dielectric or air, The ground conductor of the radiating element, which is wider than the second radiating element, and the first to third feeding points formed on the first and second radiating elements. A power feeding means for feeding power, the first and second power feeding points are arranged at different positions on the first axis, and the third power feeding point is arranged at the center position of the second radiating element. As described above, on an axis inclined by 45 ° from a second axis orthogonal to the first axis,
It is characterized in that it is arranged at the same distance as the distance from the intersection to the second feeding point.

(Operation) In the monopulse microstrip antenna having the above configuration, the first radiating element excited in the lowest order mode and the second radiating element excited in the lowest next mode are stacked in a stack, It is possible to take the sum pattern from the first radiating element and the difference pattern from the second radiating element without the use of a special hybrid.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 shows the configuration, and FIG. 1 (a) is a top view,
(B) The figure is a side view. In the figure, 21 is the first radiating element that resonates in TM110 mode, 22 is the second radiating element that is a ground conductor plate for the first radiating element 21 and resonates in TM210 mode, and 23 is the second radiating element 22. To the ground conductor plate, 24-26 are first to third feeding coaxial lines, A is a first feeding point for exciting the first radiating element, and B and C are second radiating elements 22 respectively. Are the second and third feeding points for exciting.

The first and second radiating elements 21 and 22 are opposed to each other with a distance t1 therebetween, and a layer of the dielectric ε1 is formed between them. The second radiating element 22 and the ground conductor plate 23 are opposed to each other with a space t2 therebetween, and a layer of the dielectric ε2 is formed between them. The first and second radiating elements 21 and 22 have diameters a1 and a2, respectively.
They are formed in a disk shape with (a1 <a2) and face each other so that their central axes (Z-axis direction) are the same. The ground conductor plate 23 is formed wider than the second radiating element 22 and is provided so as to face the second radiating element 22.
It is penetrated so that it does not face 21 near the center.

The first feeding point A is provided on the X axis at a position where the first radiating element 21 and the ground conductor plate 23 do not overlap each other. At the first feeding point A, the center conductor of the first feeding coaxial line 24 is connected to the first radiating element 21, and the outer conductor is connected to the second radiating element 22. The second feeding point B is provided on the X axis at a position where the first radiating element 21 and the second radiating element 22 do not overlap each other. At this second feeding point B, the second feeding coaxial line
The center conductor of 25 is connected to the second radiating element 22, and the outer conductor is connected to the ground conductor plate 23. The third feeding point C is X at a position where the first radiating element 21 and the second radiating element 22 do not overlap each other.
It is provided at a position inclined by 45 ° from the axis in the Y-axis direction. At this third feeding point C, the central conductor of the third feeding coaxial line 26 is connected to the second radiating element 22, and the outer conductor is the ground conductor plate 23.
It is connected to the.

The operation of the above configuration will be described below.

First, the first radiating element 21 is caused to resonate in the TM110 mode, and the second radiating element 22 is caused to resonate in the TM210 mode. The radius a ₁ of the first radiating element 21 that resonates in the TM ₁₁₀ mode is Can be approximated by The radius a ₂ of the second radiating element 22 that resonates in the TM ₂₁₀ mode is Can be approximated by This is based on the literature (K. Hirasaw
a, et el. “Analysis, Design, and Measurement of Small
and Low-Profile Antennas "Norwood, MA.; Artech Hous
e, 1992.) and the like.

However, x _mn0 is the n-th solution that satisfies J _m ′ (x _mn0 ) = 0 when the Bessel function of the first kind m-th order is represented by J _m (x), and the TM ₁₁₀ mode and TM ₂₁₀ mode Can be approximated by x ₁₁₀ ≈1.841 x ₂₁₀ ≈3.054, respectively.

Further, f ₀ is the design frequency, and ε _r is the relative permittivity of the medium between the radiating element conductor and the ground conductor plate. Further, ε ₀ and μ ₀ are the permittivity and transmittance of free space, respectively, and ε ₀ = {1 / (36π)} × 10 ^-9 [F / m] μ ₀ = 4π × 10 ^-7 [H / m].

At this time, the TM110 mode current flows through the first radiating element 21 as indicated by the arrow in FIG. 2 due to the feeding at the first feeding point A. Therefore, it is possible to obtain the sum pattern Σ of monopulses as shown in FIG. 3, for example, through the first feeding coaxial line 24 without using a hybrid. In FIG. 3, (a) is a sum pattern in the XZ plane (E plane), and (b) is a sum pattern in the YZ plane (H plane).

On the other hand, in the second radiating element 22, the TM210 mode current flows as indicated by the arrow in FIG. 4 due to the feeding at the second feeding point B. Therefore, without using the hybrid, the second
Through the feeding coaxial line 25, the difference pattern ΔX− in the XZ plane in the TM210 mode in the monopulse as shown in FIG. 5 can be obtained.

Further, in the second radiating element 22, the TM210 mode current flows as indicated by the arrow in FIG. 6 due to the feeding of the third feeding point C. Therefore, without using a hybrid, through the third feeding coaxial line 26, for example, in the Y-mode by the TM210 mode in the monopulse as shown in FIG.
A difference pattern ΔY−Z in the Z plane can be obtained.

That is, a microstrip antenna with a circular radiating element conductor is generally called a circular microstrip antenna, and a resonance mode called TM _mn0 mode is excited in the area sandwiched between the radiating element conductor and the ground conductor plate. It The electric field component of this mode is Can be expressed as Here, V _mn0 is a coefficient determined from boundary conditions, and t is the thickness of the region sandwiched between the radiating element conductor and the ground conductor plate. Further, φ _mn0 is an eigenfunction corresponding to a resonance mode that can exist in the resonance region sandwiched between the radiating element conductor and the ground conductor plate, and in the case of a circular microstrip antenna, Is replaced by However, And φ ₀ represents the φ coordinate of the feeding point.

In this case, the current distribution on the surface of the radiating element conductor facing the ground conductor plate is Can be expressed as However, ω is an angular frequency. Therefore, the current distribution for the TM ₁₁₀ mode with m = 1 and n = 1 is φ ₀ = 0 when its feed point is chosen to be point A on the X axis.
And becomes as shown in FIG. Also, the current distribution for the TM ₂₁₀ mode is as shown in FIG. 4 when the feeding point is also selected at the point B on the X axis.

Now, paying attention to the current distribution for the TM ₂₁₀ mode, it can be seen that by selecting the position of the feeding point at point C in FIG. 1, φ ₀ = 45 °, and the current distribution shown in FIG. 6 is obtained. What should be noted here is that there is no correlation between this current distribution and the current distribution shown in FIG. This means that there is high isolation between both feed points, and the radiation pattern based on these current distributions constitutes the sum pattern and difference pattern required for monopulse angle measurement. is there.

From the Huygens principle, the radiated magnetic field corresponding to this current distribution is Is asked. However, the integral of the above equation represents the area on the open side surface of the radiating element of the microstrip antenna,
′ Represents the outward unit normal vector on the same side. Further, is a unit vector in the Z-axis direction, and r represents the distance from the wave source to the observation point with respect to the radiated electric field. Furthermore, k ₀
Is a propagation constant in free space, and can be expressed as k ₀ = 2π / λ ₀ when the wavelength with respect to the design frequency is represented by λ ₀ . From the equation (7), the radiated electric field can be expressed as _mn0 = 120π _mn0 × (8). Based on this result, TM with m = 1 and n = 1
_{When the} radiated electric field based on the ₁₁₀ mode is obtained, when the feeding point is selected at the point A on the X-axis, φ ₀ = 0 ° is set and the result becomes as shown in FIG. 3, which corresponds to the Σ pattern of the monopulse angle measurement. You can see that it is directional. Also,
When the radiated electric field based on the TM ₂₁₀ mode is obtained, when the feeding point is selected at the point B on the X-axis, φ ₀ = 0 ° is set to obtain the one shown in FIG. 5, and the Δ pattern in the XZ plane is obtained. It can be seen that the directivity is equivalent to. On the other hand, when selecting point C, by setting φ ₀ = 45 °, it becomes that shown in FIG. 7, and it can be seen that the directivity corresponds to the Δ pattern in the YZ plane.

Therefore, the monopulse microstrip antenna configured as described above does not require a hybrid and further does not require complicated work such as phase matching, so that the number of parts is small, the structure is simple, and the phase matching is easy. is there.

In the above embodiment, the circular microstrip antenna is described as an example for convenience, but the TM ₁₁₀ mode in this case is a so-called basic mode and the TM ₂₁₀ mode is a so-called higher order mode. The point is that the use of the lowest-order mode and the lowest-order next-order mode is a feature of the present invention, and does not depend on the shape of the radiating element conductor.

For example, for a rectangular microstrip antenna, TM
_The radiated electric field based on the ₀₁₀ mode or the TM ₁₀₀ mode has a directivity corresponding to the Σ pattern, and the radiated electric field based on the TM ₁₁₀ mode has a Δ pattern in the XZ plane and a Δ pattern in the YZ plane. The directivity corresponds to the pattern. The dielectric layers ε1 and ε2 may have the same relative permittivity and thickness, or may be air. Further, the size and shape of the substrates 21 to 23 may be arbitrary as long as they are larger than the radiating element conductors thereon.

[Advantages of the Invention] As described above, according to the present invention, it is possible to provide a monopulse microstrip antenna having a small number of parts, a simple configuration, and easy phase matching.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a monopulse microstrip antenna according to the present invention, FIGS. 2 to 7 are views for explaining the operation of the same embodiment, and FIG. 8 is a view of a conventional antenna. It is a block diagram which shows a structure. 11 ... Radiating element, 12 ... Hybrid, 13 ... Terminator,
21,22 ... Radiating element, 23 ... Ground conductor plate, 24-26 ... Coaxial line for feeding, AC ... Feeding point.

Claims (1)

[Claims] 1. A first radiating element which is excited in the lowest order mode from a first feeding point and forms a sum pattern used for so-called monopulse angle measurement, and a dielectric on one side of the first radiating element. Alternatively, it is located through the air, serves as a ground conductor of the first radiating element, and is formed wider than the first radiating element, and second,
A second radiating element that is excited by a lowest order next higher order mode different from the lowest order mode from a third feeding point and forms a difference pattern used for so-called monopulse angle measurement; and A ground conductor which is located on the side of the radiating element opposite to the first radiating element via a dielectric or air and serves as a ground conductor of the second radiating element and is formed wider than the second radiating element. A plate, and first to third layers formed on the first and second radiating elements
Power feeding means for feeding power to the power feeding point, the first and second power feeding points are arranged at different positions on the first axis, and the third power feeding point is the second radiating element. 45 from the second axis that passes through the center position of and is orthogonal to the first axis.
A monopulse microstrip antenna characterized in that it is arranged at the same distance as the distance from the intersection to the second feeding point on the tilted axis.