JPH0666578B2 - Omnidirectional microstrip antenna - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a collinear antenna for a mobile radio base station on land.
The present invention relates to an omnidirectional microstrip antenna suitable for a basic radiating element of an antenna.

2. Related Art FIG. 20 is a perspective view showing an example of a conventional microstrip antenna. 11 is a substrate made of a dielectric material that is sufficiently thin compared to the wavelength, and 12 is a rectangular conductor provided in the center of the surface of the substrate 11. A radiating element, 13 is a ribbon-shaped conductor, and 14 is a substrate
A ground conductor provided on the back surface of 11 and 15 are coaxial power supply terminals, the outer conductor of which is connected to the ground conductor 14 and the inner conductor of which is connected to the ribbon-shaped conductor 13.

When excitation is performed in the fundamental mode via the microstrip line composed of the feeding terminal 15, the ribbon-shaped conductor 13, and the ground conductor 14, the required length a of the radiating element 12 is the relative permittivity εr of the substrate 11 and the radiation wavelength. Is λ, And the feeding point, that is, the radiating element 12 and the ribbon-shaped conductor 13
When the upper edge facing the lower edge of the radiating element 12 including the connection point with is short-circuited to the ground conductor 14, the radiating element 12
The required length a of Becomes

The basic characteristics of this microstrip antenna are that the feeding point of the radiating element 12 serves as a wave source, and the upper edge portion symmetrical to the feeding point with respect to the center point of the radiating element 12 serves as a wave source.
Since the electromagnetic waves radiated from these two wave sources are combined, assuming that the substrate 11 has a uniform relative permittivity and the substrate 11 is a flat plate, both the radiated electric field surface and the magnetic field surface have directivity only in the front direction. Have.

With the center of the radiating element 12 in FIG. 20 as the origin of coordinates, the length direction of the radiating element 12 is the X-axis direction, the width direction is the Y-axis direction, and the plate surface of the substrate 11 is as shown by the solid lines with arrows. An example of the directivity of the YZ plane, that is, the directivity of the magnetic field plane when the orthogonal direction is the Z-axis direction is shown in Fig. 21. As is clear from the figure, the half-width is approximately 80 °. is there.

An example of the directivity of the XZ plane, that is, the directivity of the electric field plane is shown below.
As shown in Fig. 22, the full width at half maximum is approximately 76 °.

In addition, the impedance characteristic of this microstrip antenna has a large Q and a narrow specific band because the antenna is composed of an unbalanced plane circuit resonator.

FIG. 23 is a diagram showing an example of the relationship between the radiation frequency and the return loss when the relative permittivity εr of the substrate 11 in the antenna shown in FIG. 20 is selected as 3.6. The horizontal axis represents frequency and the vertical axis represents It is return loss (dB), but as is clear from the figure,
When the return loss is 10 dB (voltage standing wave ratio VSWR ≈ 1.9), the bandwidth is about 2.5%.

FIG. 24 is a diagram showing an example of a microstrip antenna conventionally proposed and implemented in order to make the directivity in the horizontal plane omnidirectional, and FIG. 25 is a developed view of the main part thereof, in both figures, Reference numeral 16 is a bullet-shaped support, 17 is a flexible base made of a dielectric, and 18 is a radiating element made of a ribbon-shaped conductor, which is provided on the surface of the base 17. 19 is a power supply line.

Problems to be Solved by the Invention An antenna for a mobile radio base station on land is required to be vertically polarized and omnidirectional in the horizontal plane, and especially when it is used for both transmission and reception. , The conventional microstrip antenna shown in FIG. 20 is not suitable as an antenna for a mobile radio base station on land because it is required that the relative bandwidth reaches approximately 10%.

The antenna shown in FIGS. 24 and 25 is omnidirectional in the YZ plane, but not only is the shape and structure large and complex,
Since the radiating element 18 is basically an unbalanced plane circuit resonator, it has a narrow frequency characteristic and is not suitable as an antenna for a mobile radio base station on the ground.

Means for Solving the Problems The present invention realizes a microstrip antenna in which a cylindrical secondary radiating element is provided on the outer periphery of a primary radiating element made of a metal film deposited on the surface of a dielectric substrate. This aims to eliminate the drawbacks of the conventional antenna.

Action The antenna of the present invention configured as described above is small, exhibits omnidirectionality in the horizontal plane, and has a very small change in impedance characteristic over a wide band.

Embodiment FIG. 1 is a front view showing an embodiment of the present invention, FIG. 2 is a side view, FIG. 3 is a rear view, FIG. 4 is a plan view, and FIG. 6 is a side view of the main part, and in each figure, 1
Is a dielectric substrate which is thinner than the radiation wavelength, 2 is a primary radiation element made of a rectangular conductor provided on the surface of the substrate 1, and 3 is the substrate 1
The upper end of the ribbon-shaped conductor is provided on the surface of the first radiating element 2. 4 is an impedance matching element formed by widening the middle portion of the ribbon-shaped conductor 3 over an appropriate length, 5 is a ground conductor provided on the back surface of the substrate 1, 6 is a feeding terminal, for example, coaxial The terminal conductor is connected to the ribbon-shaped conductor 3, and the outer conductor is connected to the ground conductor 5.

The primary radiating element 2, the ribbon-shaped conductor 3, the impedance matching element 4, the grounding conductor 5 and the like are formed by a copper foil or the like adhered to the front surface or the back surface of the substrate 1 by a printed wiring method or a means such as vapor deposition. .

Reference numeral 7 denotes a secondary radiating element, which is composed of a cylindrical conductor with both ends open, and has its central axis substantially aligned with the central axis of the primary radiating element 2 in the longitudinal direction. And the inner diameter of the secondary radiating element 7 is made appropriate so that the primary radiating element 2, the ribbon-shaped conductor 3, the ground conductor 5 and the like do not come into contact with the secondary radiating element 7. is there.

8 ₁ to 8 ₄ is a support made of dielectric, respectively, for example the shape of the cross section is semicircular, the fitting concave portion of the substrate 1 provided in a flat responsible sidewalls, the support body 8 ₁ and 8 ₂ secondary The radiating element 7 is mounted on the upper end thereof, the supports 8 ₃ and 8 ₄ are mounted on the lower end of the secondary radiating element 7, and the substrate 1 is sandwiched between the fitting recesses of the supports 8 _{1 to} 8 _4. , Supports 8 _{1 to} 8 ₄ and secondary radiating element 7
Allowed to fixation with appropriate adhesive or the like and between the support 8 ₁ to 8 ₄ and the substrate 1 with.

Without providing a fitting recess in the flat responsible sidewalls of the support 8 ₁ to 8 _4, it may be caused to sandwich the substrate 1 in the state of flat responsible sidewalls.

Although the drawing shows the case where the contour shape of the primary radiating element 2 as viewed from the front is formed into a rectangle, it may be formed into a circular shape or an elliptical shape, or the secondary radiating element 7 may have a cross-sectional shape. The present invention can be implemented by forming the shape into any shape such as an ellipse, a square or a rectangle in addition to the circle.

Supports 8 _{1 to} 8 ₄ depending on the shape of the cross section of the secondary radiating element 7
Needless to say, the shape of each cross section is determined.

Further, instead of forming the primary radiating element 7 with a tubular shape made of a conductive plate, it is formed with a mesh-shaped or lattice-shaped conductor, or a printed wiring method, vapor deposition, or the like is performed on the outer or inner surface of the substrate made of a tubular dielectric. You may form with the copper foil etc. which were made to adhere by the method of.

FIG. 7 to FIG. 9 are views for explaining the structure and operating principle of the antenna of the present invention, the reference numerals in each drawing are the same as those in FIGS. 1 to 6, and the solid line with an arrow indicates the electric field distribution. , The broken lines show the current distributions, respectively.

The required length a of the primary radiating element 2 in the case of exciting the primary radiating element 2 in the microstrip antenna of the present invention in the fundamental mode is approximately given that the relative permittivity of the substrate 1 is εr and the radiation wavelength is λ. This is the same as the conventional microstrip antenna shown in FIG.

In the present invention, the axial length of the secondary radiating element 7 is appropriately selected to be shorter than 1/2 of the radiating wavelength in terms of electrical length, but the secondary radiating element 7 has a relative dielectric constant of the substrate 1 as compared with that of the primary radiating element 2. As described above, even if the secondary radiating element 7 is formed by using a copper foil or the like adhered to the surface of the cylindrical dielectric body, as described above, By using a material having an appropriate relative permittivity, the actual axial length of the secondary radiating element 7 can be made longer than the actual length of the primary radiating element 2 in the longitudinal direction. As shown in FIG. 9, both radiating elements can be arranged so as to cover the primary radiating element 2 with the cylindrical side wall of the secondary radiating element 7.

Hereinafter, for convenience of description, a plane that includes a point d ₇ on the side wall corresponding to ½ of the axial length of the secondary radiating element 7 and is orthogonal to the cylinder axis, and a center point d _{2 in} the longitudinal direction of the primary radiating element ₂ are A case where both radiating elements are arranged so as to coincide with each other will be described.

Points c in FIGS. 7 to 9 are ribbon-shaped conductors 3,
At a connection point between the feeding line formed by the microstrip line including the substrate 1 and the ground conductor 5 and the microstrip antenna including the primary radiating element 2, the substrate 1 and the ground conductor 5, that is, at the feeding point, the feeding point c is When the microstrip antenna is excited via the primary radiation element 2, the current distribution based on the electric field generated in the discontinuous portion in the longitudinal direction of the primary radiation element 2 is as shown in FIG.
At the maximum in the longitudinal direction of the center point d _2, becomes symmetrical about the _two points d, it becomes zero at the both end portions of the primary radiation element 2.

Focusing on the electric field vector in the substrate 1 among the electric field distributions that cause such a current distribution, the vector on the left side of the drawing from the point d ₂ is the ground conductor 5 to the ribbon-shaped conductor 3 and the primary radiation element 2. upward vector directed to, in a downward vector directed to the grounding conductor 5 right vector from the primary radiating element 2 from d ₂ points, the vector at a position symmetrical about the _two points d, are equal to each other size, The phases are opposite to each other.

The portion composed of the primary radiating element 2, the substrate 1 and the ground conductor 5 also functions as a microstrip line, and
The length of the primary radiation element 2 is almost Since the d ₂ point is the center point in the longitudinal direction of the primary radiating element 2, the potential difference between the d ₂ point of the primary radiating element 2 and the d ₅ point of the ground conductor 5 corresponding to this d ₂ point is It becomes zero. Therefore, without a current also flows in short-circuiting the _two points and d ₅ points d, not electrically to produce any problem.

As shown in FIG. 8, a discontinuity in the longitudinal direction of the primary radiating element 2, that is, an electric field generated at each end of the primary radiating element 2 induces an electric field in the secondary radiating element 7. The electric fields generated at both ends of the element 2 have the same magnitude of electric field vectors at symmetrical positions with respect to the longitudinal center point d ₂ of the primary radiating element 2, and the phases are opposite to each other. The potential difference between the longitudinal center point d _{2 of the} radiating element 2 and the point d ₅ on the ground conductor 5 corresponding to this d ₂ point becomes zero, and the primary radiating element 2
Similarly, the voltage is maximized at both ends of the electric field vector, and the magnitudes of the electric field vectors at the positions symmetrical to each other about the point d ₇ that is half the axial length of the secondary radiating element 7 are equal to each other, and the phases are equal to each other. Since the voltages are opposite to each other and the voltage across the secondary radiating element 7 is maximum and becomes zero at the center point d ₇ , currents shown by broken lines are distributed on the inner surface and the outer surface of the secondary radiating element 7.

Also in this case, not come current flows even if there is a short _5-point d at the center point d ₂ and the ground conductor 5 of the primary radiation element 2, it does not cause problems in the electrical.

If the outer diameter of the secondary radiating element 7 is appropriately made smaller than the radiating wavelength, an electric field generated in the primary radiating element 2 causes an induction electric field in the entire circumferential direction at both ends of the secondary radiating element 7. As shown in FIG. 9, a current distribution similar to that shown in FIG. 8 is generated over the entire circumferential surface of the side wall of the secondary radiating element 7.

Therefore, an arbitrary point on the line of intersection between the side surface of the secondary radiating element 7 and the side wall orthogonal to the cylinder axis including the d ₇ point, and the center point d ₂ of the longitudinal direction of the primary radiating element 2 and Ground conductor 5
'S d ₅ points, both current maximum, because the zero voltage, the without current also flows by short-circuiting any point, does not cause problems in the electrical.

The secondary radiating element 7 in the antenna of the present invention is composed of one cylindrical conductor and has a mechanically different structure from the dipole antenna composed of two radiating elements, but is shown by a broken line in FIG. As apparent from the current distribution, it is electrically 1/2
It is equivalent to a wavelength dipole antenna.

In a normal dipole antenna, when the outer diameter of the line forming the radiating element is extremely small, the directivity in the vertical plane (electric field plane) can be obtained by forming the total length of the dipole antenna at half the radiation wavelength. , The electric field can be maximized in the horizontal direction. That is, it is possible to make the doughnut-shaped directivity having an 8-shaped cross section.

However, as the outer diameter of the radiating element forming the dipole antenna becomes larger, the total length of the antenna is appropriately shortened from ½ of the radiating wavelength, so that the directivity of the donut shape with the cross section 8 as described above is obtained. It is well known that is obtained.

Although the secondary radiating element 7 in the present invention is different from the normal dipole antenna as described above, the outer diameter of the cylindrical conductor is appropriately determined and the axial length is set to the radiating wavelength within a range smaller than the radiating wavelength. It is possible to exhibit the same directivity as that of a normal dipole antenna by forming it appropriately shorter than 1/2 of the above.

That is, the analysis results described with reference to FIGS. 7 to 9 are:
It was obtained by determining the outer diameter and the axial length of the secondary radiating element 7 as described above, and the secondary radiation was obtained from the analysis result and the directivity of the antenna of the present invention shown in FIGS. 18 and 19 described later. It can be seen that the element 7 is electrically equivalent to a normal dipole antenna.

FIG. 10 is an equivalent circuit diagram of the antenna of the present invention, where L ₂ and C ₂ are the effective inductance and effective capacitance of the primary radiating element 2, and L ₇
And C ₇ are the effective inductance and the effective capacitance of the secondary radiating element, C ₂₇ is the electric field coupling capacitance between the primary radiating element 2 and the secondary radiating element 7, Rr is the radiation resistance that contributes to the radiation of electromagnetic waves, and T _f is the feeding point. is there.

The width b of the primary radiating element 2 is changed, the central axes of the substrate 1 and the secondary radiating element 7 are shifted, or the substrate 1 is formed into a curved surface having an appropriate curvature, or the cross section of the secondary radiating element 7 is changed. The size of the electric field coupling capacitance C ₂₇ can be changed by changing the shape to, for example, an elliptical shape or a rectangular shape,
The frequency characteristic of the return loss can be changed by changing the size of the electric field coupling capacitance C ₂₇ .

In the first invention described with reference to FIGS. 1 to 10, the length a of the primary radiating element 2 is substantially equal to By forming in and exciting in the fundamental mode, it has achieved the purpose of realizing an omnidirectional microstrip antenna suitable for the basic radiating element of a collinear antenna for mobile radio base stations on land, As described with reference to FIGS. 7 to 9, the center point of the primary radiating element 2
Even if d ₂ and the ground conductor 5 are short-circuited, no electrical problem will occur. Therefore, as shown in FIG. 11 at the midpoint in the longitudinal direction of the primary radiating element 2 shown in FIGS. As shown in the front view with some cutouts, the primary radiating element 2 and the ground conductor 5 are short-circuited via a short-circuit pin or through holes 9 _{1 to} 9 ₃ and the primary radiating element part above is removed from this short-circuited portion However, the present invention can be implemented.

In this embodiment, the excitation to the secondary radiating element 7 is equivalent to the voltage feeding to one end of the secondary radiating element 7, and operates equivalently to the half-wavelength dipole antenna.

FIG. 12 is a front view showing another embodiment of the present invention, Fig. 13 is a side view, reference numeral 1 is a common dielectric substrate, 2 ₁ and 2 ₂ in the primary radiating element, the substrate 1 Are provided at appropriate intervals in the longitudinal direction. 3 is a ribbon-shaped conductor, 4 ₁ and 4 ₂ are impedance matching elements, 5 is a ground conductor provided on the back surface of the substrate 1, 7 ₁ and 7 ₂ are secondary radiating elements, and primary radiating elements 2 ₁ and 2 _{2 respectively.} It is provided on each outer circumference.

Also in this embodiment, the primary radiation element 2 ₁ and the secondary radiating element
₁ to 6 show the electrical and mechanical constitutional relationship with 7 ₁ and the electrical and mechanical constitutional relationship between the primary radiating element 2 ₂ and the secondary radiating element 7 ₂ .
The electrical and mechanical structural relationship between the primary radiating element 2 and the secondary radiating element 7 in the embodiment described above is exactly the same.

In this embodiment, the primary radiating elements 2 ₁ and 2 ₂ are fed in series via a feeding line formed by a microstrip line composed of a ribbon-shaped conductor 3 and a ground conductor 5.

As shown in the front view in FIG. 14, a ribbon-shaped conductor 3 forming a main power supply line and a ribbon-shaped conductor forming a branch power supply line
3 ₁ and 3 ₂ are provided also be configured to perform parallel feed can be used to practice the present invention.

Above has been illustrated the case of forming the feed line with a microstrip line composed of the grounding conductor 5 provided on the back of the ribbon-shaped conductor 3, 3 ₁ and 3 ₂ and the substrate 1 which is provided on the surface of the substrate 1, the micro The feed line may be formed by using a balanced line instead of the strip line, and instead of using the surface of the substrate 1 instead of forming the microstrip line or the balanced line by a metal coating applied to the front and back surfaces of the substrate 1. The power supply line may be formed only on the back side.

Also, as shown in the front view in FIG. 15 and the side view in FIG. 16,
Whether the coaxial feeder 10 provided on the back side of the substrate 1 and the ribbon-shaped conductor 3 provided on the front side of the substrate 1 form a main feeder line, and the ribbon-shaped conductors 3 ₁ and 3 ₂ form a branched feeder line. ,
All the feeder lines may be formed by coaxial lines.

When a coaxial line is used, it is desirable to connect the outer conductor of the coaxial line to the ground conductor 5 in order to reduce the influence on the radiation characteristics.

12 to 16 exemplify a case where two sets of the primary radiating element and the secondary radiating element are provided on a common dielectric substrate.
The present invention can also be implemented by providing two or more arbitrary plural sets of primary radiating elements and secondary radiating elements.

Although not shown in FIGS. 11 to 16, a support is interposed between the substrate and the secondary radiating element to hold the secondary radiating element at a required position, and other reference numerals in each drawing. The configuration and the like are similar to those of the embodiment shown in FIGS. 1 to 6.

In the second invention described with reference to FIGS. 12 to 16, by providing a plurality of sets of primary radiating elements and secondary radiating elements, the directivity in the direction of the radiated electric field is improved as in the case of a conventionally known array antenna. At the same time, the same purpose as that of the first invention can be achieved.

The microstrip antenna of the present invention is small and lightweight,
It has a simple structure and can exhibit omnidirectional radiation characteristics over a wide band, and is suitable for a basic radiation element of a collinear antenna for a mobile radio base station on land.

FIG. 17 shows the antenna of the present invention shown in FIGS. 1 to 6, in which the length a of the primary radiating element 2 is 0.261λ, the width W of the ground conductor 5 is 0.075λ, and the thickness of the substrate 1 is 0.005λ. , The relative permittivity εr is 3.6, the axial length L of the secondary radiating element 7 is 0.377λ, and the outer diameter of the secondary radiating element 7 is 0.087λ, and the width b of the primary radiating element 2 is changed. Shows the measured value of the change in the frequency characteristic of the return loss in the case of the following. The horizontal width is the frequency, the vertical axis is the return loss (dB), and the curve b ₁ is the width b of the primary radiating element 2 is 0.058λ. If the curve b ₂
Is 0.046λ, the curve b ₃ is 0.035λ, and the curve b ₄ is 0.023λ.

As is clear from the figure, by increasing the width b of the primary radiating element 2, the return loss tends to be large and the band width tends to be wide. At b = 0.058λ, the return loss is 10 dB, and the relative bandwidth is At 12%, b = 0.035λ, the return loss is 26 dB,
The bandwidth is 4% and can be adjusted according to the purpose of use.

Figure 18 shows the width of the primary radiating element 2 in the prototype as 0.
046λ, all other mechanical dimensions and relative permittivities are made the same, and the center of the primary radiating element 2 in FIGS. 1 to 6 is used as the coordinate origin, and as shown by the solid line with an arrow, the primary The radiating element 2 has an X axis in the length direction and a Y direction in the width direction.
The measured values of the directivity in the YZ plane when the Z axis is taken in the direction orthogonal to the axis and the plate surface of the substrate 1, respectively, and as shown in the figure, it exhibits extremely good non-directionality. .

FIG. 19 is an actual measurement value of the directivity on the XZ plane in the prototype described above, and it is clear from the figure that the directivity has an 8-shape similar to the half-wavelength dipole antenna.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of the present invention, FIG. 2 is a side view, FIG. 3 is a rear view, FIG. 4 is a plan view, FIG. 5 is a front view of essential parts, and FIG. Is a side view of the main part, FIGS. 7 to 9 are diagrams for explaining the operating principle of the antenna of the present invention, FIG. 10 is an equivalent circuit diagram of the antenna of the present invention, and FIG. FIG. 12 is a front view having a partially cutaway portion showing the embodiment of FIG.
FIGS. 14 and 15 are front views showing another embodiment of the present invention, FIGS. 13 and 16 are side views, and FIGS. 17 to 19 are
The figure which shows an example of the characteristic of the antenna of this invention, FIG. 20 is a perspective view which shows an example of the conventional antenna, FIGS.
FIG. 24 is a diagram showing an example of characteristics of a conventional antenna, FIG. 24 is a diagram showing another example of the conventional antenna, and FIG. 25 is a developed view of a main part thereof, where 1: dielectric substrate, 2, 2 ₁ And 2 ₂ : primary radiating element,
3,3 ₁ and 3 ₂ : Ribbon-shaped conductor, 4, 4 ₁ and 4 ₂ : Impedance matching element, 5: Grounding conductor, 6: Feeding terminal, 7, 7 ₁ and 7 ₂ : Secondary radiating element, 8 ₁ To 8 ₄ : Support, 9 _{1 to} 9 ₃ : Short-circuit pin, 1
0: coaxial line, 11: dielectric substrate, 12: radiating element, 13: ribbon-shaped conductor, 14: ground conductor, 15: power supply terminal, 16: bullet-shaped support, 17: flexible base made of dielectric , 18: radiating element, 19:
It is a power supply line.

Claims (2)

[Claims] 1. A primary radiating element made of a metal coating deposited on the surface of a dielectric substrate, which is thinner than the radiation wavelength, a grounding conductor made of the metal coating deposited on the back of the dielectric substrate, The power supply line connected to the primary radiating element, the axial length is shorter than 1/2 of the radiation wavelength, and both ends are open,
The outer diameter is made of a tubular conductor having a smaller diameter than the radiation wavelength, the tubular axis is parallel to the radiation electric field direction of the primary radiating element, the tubular side wall covers the primary radiating element, and the tubular side wall is An omnidirectional microstrip antenna comprising: the primary radiating element, the ground conductor, and a secondary radiating element provided on the outer periphery of the primary radiating element so as not to come into contact with the feeder. 2. A common dielectric substrate having a thin and long shape, which is thinner than a radiation wavelength, and a surface of the common dielectric substrate, which is attached at appropriate intervals in the longitudinal direction of the common dielectric substrate. A plurality of primary radiating elements made of a metallic coating, a common ground conductor made of a metallic coating deposited on the back surface of the common dielectric substrate, and a feed line connected to the plurality of primary radiating elements And each axial length is shorter than ½ of the emission wavelength, each end is open, and each outer diameter is smaller than the emission wavelength. Of the plurality of primary radiating elements, each tubular side wall is parallel to the radiation electric field direction of each corresponding primary radiating element, and covers each corresponding primary radiating element among the plurality of primary radiating elements. Of the plurality of primary radiating elements, each corresponding primary radiating element, the A plurality of secondary radiating elements separately provided on the outer circumference of each of the plurality of primary radiating elements so as not to come into contact with a common ground conductor and the feeder line. Directional microstrip antenna.