This application is related to Japanese Patent Application No. 2008-198297 filed on Jul. 31, 2008, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a microstrip array antenna including a dielectric substrate, which is usable as a transmitting antenna or a receiving antenna of various radio wave sensors such as a vehicle-mounted radar.
2. Description of Related Art
A microstrip array antenna constituted of strip conductors formed on a dielectric substrate is becoming widely used as a transmitting/receiving antenna of various radio wave sensors including a vehicle mounted-radar such as an adaptive cruise control system for its advantages of slimness, low cost and high productivity.
Meanwhile, since a microstrip line has a large transmission loss at high frequency, there has been a problem that it is difficult to embody a microstrip array antenna having a high gain at high frequency. Accordingly, it is proposed to use a series-feed microstrip array antenna in spite of its design complexity instead of a parallel-feed microstrip array antenna widely used for its design simplicity. For example, refer to Japanese Patent Application Laid-open No. 2001-44752.
Each of the radiating antenna elements 101, 102, 103, disposed on one side edge (on the upper side edge in
Input power fed to the feeding strip line 120 from an input end (leftward end in
To achieve desired directivity by use of such a series-feed microstrip array antenna, each of the radiating antenna elements has to be designed independently, because the series-feed microstrip array antenna is excited by traveling wave, and accordingly the coupling factor differs from one radiating antenna element to another. The coupling factors of the radiating antenna elements can be controlled by adjusting the element widths thereof.
For example, when all the radiating antenna elements are formed to have the same shape and size so that they have the same coupling factor, the power radiated from the antenna decreases toward the terminal end, because the input power inputted from the input end decreases toward the terminal end.
It is possible that all the radiating antenna elements have the same radiation factor if the radiating antenna element closer to the input end has a smaller element width to have a smaller radiation factor, and the radiating antenna element closer to the terminal end has a larger element width to have a larger radiation factor, as is the case with the microstrip array antenna 100 shown in
As exemplified above, conventional series-feed microstrip array antennas are configured such that each of the radiating antenna elements has an adjusted element width to have a desired coupling factor.
However, since the adjustable range of the coupling factor of each radiating antenna element having such a configuration is relatively narrow, there has been a problem that desired antenna characteristics (desired directivity, for example) cannot be achieved in some cases.
In addition, when the element width is increased to achieve a large coupling factor, since a high frequency current flowing in each radiating antenna element along its lateral direction increases, a radio wave emitted in the direction crossing the direction in which a main polarized wave is emitted (the longitudinal direction of the radiating antenna elements) increases. This causes a problem that the radiation level of a polarized wave emitted in the crossing direction increases.
Furthermore, since each radiating antenna element is directly connected to the feeding strip line, it is difficult to achieve impedance matching for each radiating antenna element, and accordingly, it is difficult for each radiating antenna element to exhibit a desired reflection characteristic.
The present invention provides a microstrip array antenna comprising:
a dielectric substrate formed with a conductive ground plate at a back surface thereof; and
the strip conductors including a linear main feeding strip line, and a plurality of array elements connected to the main feeding strip line, the array elements being disposed at least one of both sides of the main feeding strip line at a predetermined interval along a longitudinal direction of the main feeding strip line,
each of the array elements including a sub-feeding strip line connected to the main feeding strip line, a rectangular radiating antenna element connected to a terminal end of the sub-feeding strip line, and a stub connected to the sub-feeding strip line,
the stub being disposed between a connecting position between the main feeding strip line and the sub-feeding strip line and a connecting position between the sub-feeding strip line and the radiating antenna element.
The present invention also provides a microstrip array antenna comprising:
a dielectric substrate formed with a conductive ground plate at a back surface thereof; and
the strip conductors including a linear main feeding strip line, and at least one array element disposed at each of both sides of the main feeding strip line, the array element being connected to the main feeding strip line,
the array element including a sub-feeding strip line connected to the main feeding strip line, a rectangular radiating antenna element connected to a terminal end of the sub-feeding strip line, and a stub connected to the sub-feeding strip line,
the stub being disposed between a connecting position between the main feeding strip line and the sub-feeding strip line and a connecting position between the sub-feeding strip line and the radiating antenna element.
According to the present invention, there is provided a microstrip array antenna in which undesired cross-polarized components are suppressed, and reflection is reduced to achieve a desired coupling factor at each of its array elements.
Other advantages and features of the invention will become apparent from the following description including the drawings and claims.
In the accompanying drawings:
The microstrip array antenna 1 is constituted of strip conductors formed on a front surface of a dielectric substrate 2 formed with a conductive ground plate 3 at its back surface. As shown in
In more detail, the array elements A1a, A1b and A1c are connected to a first side edge 4a (one of two side edges of the main feeding strip line 4) at a predetermined interval therebetween. This predetermined interval is equal to the wavelength λg of a radio wave propagating the strip conductors at an operating frequency (76.5 GHz in this embodiment). Hereinafter, this wavelength is referred to as a waveguide wavelength. The other array elements A2a, A2b and A2c are connected to a second side edge 4b (the other of the two side edges of the main feeding strip line 4) at the predetermined interval equal to the waveguide wavelength λg therebetween.
The array elements A1a, A1b and A1c and the array elements A2a, A2b and A2c are shifted in their positions in the longitudinal direction of the main feeding strip line 4 by approximately λg/2.
The array element A1a which is the closest of the array elements connected to the first side edge 4a of the main feeding strip line 4 to the input end is constituted of a sub-feeding strip line 12a connected to the main feeding strip line 4, a rectangular radiating antenna element 11a connected to the terminal end of the sub-feeding strip line 12a, and a stub 13a connected to a predetermined middle portion of the sub-feeding strip line 12a.
Likewise, the array element A1b, which is the second closest of the array elements connected to the first side edge 4a of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 12b, a rectangular radiating antenna element 11b and a stub 13b. The array element A1c, which is the third closest of the array elements connected to the first side edge 4a of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 12c, a rectangular radiating antenna element 11c and a stub 13c. The array element A2a, which is the closest of the array elements connected to the second side edge 4b of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 22a, a rectangular radiating antenna element 21a and a stub 23a. The array element A2b which is the second closest of the array elements connected to the second side edge 4b of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 22b, a rectangular radiating antenna element 21b and a stub 23b. The array element A2c, which is third closest of the array elements connected to the second side edge 4b of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 22c, a rectangular radiating antenna element 21c and a stub 23c.
The input power fed to the main feeding strip line 4 from the input end (the leftward end in
A matching terminal element 5 is provided in the terminal end of the main feeding strip line 4 to absorb the remaining power. However, in order to radiate power efficiently from the microstrip array antenna 1, the terminal end may be provided with a radiating antenna element instead of the matching terminal element 5.
Next, the structures of the array elements are explained. Since the array elements A1a, A1b, A1c, A2a, A2b and A2c have the same shape and size, only the array element A1a closest of the array elements connected to the first side edge 4a of the main feeding strip line 4 to the input end is explained with reference to
As shown in
The sub-feeding strip line 12a is provided with the stub 13a of a length of Ls extending from the bent portion of the sub-feeding strip line 12a at an angle of approximately 45 degrees with respect to the longitudinal direction of the main feeding strip line 4. The stub 13a is formed to extend from the first line section of the sub-feeding strip line 12a in the same direction as the longitudinal direction of the first line section. Accordingly, the first line section and the stub 13a can be assumed to constitute a straight strip line.
The terminal end of the sub-feeding strip line 12a (the end portion of the second line section) is connected with the radiating antenna element 11a. The length Le of the radiating antenna element 11a is equal to approximately half the waveguide wavelength (λg/2).
The radiating antenna element 11a is formed in a rectangular shape having a length of Le smaller than its width of We. The sub-feeding strip line 12a is connected to a feeding point 14a on a longer side edge of the radiating antenna element 11a. This feeding point 14a is set at a predetermined position between the center portion and one end portion of the longer side of the radiating antenna element 11a.
The impedance of the rectangular radiating antenna element 11a is lower at its longer side edge than at its shorter side on the whole. In the longer side edge, the impedance is substantially 0 at its center portion, while the impedance is high at its end portions. Accordingly, the feeding point 14a is set at a position between the center portion and one end portion of the longer side edge of the radiating antenna element 11a, and the sub-feeding strip line 12a is connected to this feeding point 14a, so that impedance matching can be achieved easily. For example, when the characteristic impedance of the sub-feeding strip line 12a is 50Ω, the sub-feeding strip line 12a is connected to a point of the longer side of the radiating antenna element 11a where the impedance is 50Ω as the feeding point 14a.
The radiating antenna element 11a is disposed such that the longitudinal direction thereof is in parallel with the longitudinal direction of the stub 13a. That is, the longitudinal direction of each of the radiating antenna element 11a and the stub 13a forms an angle of approximately 45 degrees with the longitudinal direction of the main feeding strip line 4.
Since the array element A1a has the structure where the stub 13a is connected to the bent portion of the sub-feeding strip line 12a, a current flows through this stub 13a causing radio wave to be radiated also from the stub 13a. Although the radiation from the stub 13a is minute compared to the radiation from the radiating antenna element 11a, it is unnecessary radiation, and is undesirable intrinsically because it affects the radiation from the radiating antenna element 11a.
However, if the direction of the electric field radiated from the stub 13a is the same as the direction of the electric field radiated from the radiating antenna element 11a, the radiation from the stub 13a can be effectively used.
Accordingly, in this embodiment, the radiating antenna element 11a and the stub 13a are disposed parallel to each other. In this case, since the currents respectively flowing through the stub 13a and the radiating antenna element 11a are parallel to each other, the directions of the electric fields radiated respectively from the radiating antenna element 11a and the stub 13a are the same with each other. Hence, the stub 13 can be used not only for impedance matching but also as a radiating antenna element.
The array element A1a has the configuration in which one of the contour edges of the radiating antenna element 11a as a field-emission edge line 110a and a field-emission edge line 130a of the stub 13a are on the same straight line.
As explained above, since the radiating antenna element 11a and the stub 13a are disposed such that both their longitudinal directions are inclined by an angle of approximately 45 degrees with respect to the longitudinal direction of the main feeding strip line 4, both their field-emission edge lines 110a and 130a are inclined by an angle of approximately −135 degrees with respect to the longitudinal direction of the main feeding strip line 4.
In this embodiment, the radiating antenna element 11a is connected to the main feeding strip line 4 not directly but through a matching strip line constituted of the sub-feeding strip line 12a and the stub 13a. This makes it possible to achieve impedance matching for reducing reflection, because the position at which the sub-feeding strip line 12a is connected to the radiating antenna element 11a, and the length, shape and connecting position of the stub 13a can be determined arbitrarily.
In addition, the provision of the matching strip line enables controlling the coupling factor between the main feeding strip line 4 and the array element A1a, which is equal to the to some extent, because the size of the stub 13a can be determined arbitrarily, for example.
Here, the coupling factor is a factor which indicates how much portion of the input power propagating through the main feeding strip line is supplied to the array element. That is, the coupling factor=(input power−transmitting amount of input power−reflecting amount of input power)/input power. Accordingly the amount of radiation at the array element=ratio between radiated power and incident power into array antenna. Hence, by controlling the coupling factor, the radiation factor can be controlled.
As shown in
The other array elements A1b and A1c connected to the first side edge 4a of the main feeding strip line 4 have the same structure as the array element A1a shown in
In other words, the longitudinal directions of the radiating antenna elements 21a, 21b and 21c and the longitudinal directions of the stubs 23a, 23b and 23c of the array elements A2a, A2b and A2c are all inclined by an angle of approximately −135 degrees with respect to the longitudinal direction of the main feeding strip line 4.
Hence, in the microstrip array antenna 1 of this embodiment, the longitudinal directions of radiating antenna elements 11a, 11b, 11c, 21a, 21b and 21c and the stubs 13a, 13b, 13c, 23a, 23b and 23c of the array elements A1a, A1b, A1c, A2a, A2b and A2c connected to the first side edge 4a or the second side edge 4b of the main feeding strip line 4 are parallel to one another.
Furthermore, in the microstrip array antenna 1 of this embodiment, the radiating antenna elements 11a, 11b and 11c of the array elements A1a, A1b and A1c connected to the first side edge 4a of the main feeding strip line 4 do not have the same width. The radiating antenna element closer to the input end has a smaller width We. Accordingly, the radiating antenna element 11a which is the closest to the input end has the smallest width We, and the radiating antenna element 11c closest to the terminal end has the largest width We.
The above also applies to radiating antenna elements 21a, 21b and 21c of the array elements A2a, A2b and A2c connected to the second side edge 4b of the main feeding strip line 4.
The reason why the widths of the radiating antenna elements are varied depending on their connecting positions to main feeding strip line 4 is to make the radiation factors of the array elements A1a, A1b, A1c, A2a, A2b and A2c the same with one another.
Since the level of the input power propagating through the main feeding strip line 4 is larger at a position closer to the input end, to make the radiation factors of the array elements A1a, A1b, A1c, A2a, A2b and A2c the same one another, the width We of the radiating antenna element closer to the input end has to be smaller to make its coupling factor smaller. On the other hand, the width We of the radiating antenna element more distant from the input end has to be larger to make its coupling factor larger.
Although the widths of the radiating antenna elements are determined in order that radiation factors of the array elements Ala, A1b, A1c, A2a, A2b and A2c are equal to one another in this embodiment, they may be determined depending on specification and characteristics required of the microstrip array antenna 1.
This is because the excitation amplitude to be achieved at each of the radiating antenna elements should be determined depending on the directivity characteristic required of the microstrip array antenna 1, and the width We of each of the radiating antenna elements is determined to achieve the determined excitation amplitude.
Next, various characteristics of the array element A1a shown in
First, the coupling characteristics of the invention structure and the conventional structure are explained with reference to
In the conventional structure, to achieve a coupling factor larger than 30%, the element width has to be larger than 1 mm. As the element width is increased, the current flowing in the direction crossing the longitudinal direction of the radiating antenna element (main polarization component) increases, other than the current flowing in this longitudinal direction (cross-polarization component), and accordingly, the radiation level of the cross-polarized wave increases. Therefore, when taking account of the influence of the cross-polarized wave, the coupling factor of the conventional structure is limited to the order of 20%. Accordingly, it has been difficult to provide a radiating antenna element having a coupling factor larger than 30%.
On the other hand, in the invention structure, to achieve a coupling factor of 30% for example, the element width is required only to be larger than 0.7 mm. According to the invention structure, it is possible to achieve a sufficiently large coupling factor without substantially increasing the radiation level of the cross-polarized wave.
Next, the polarization characteristics of the invention structure and the conventional structure are explained with reference to
As seen from
The reason is that since the width We of the radiating antenna element can be made smaller in the invention structure than in the conventional structure, the component of a current other than the current flowing in the direction of the main polarization component can be made small compared to the conventional structure. Hence, according to the invention structure, the level of the cross-polarized wave can be substantially reduced, making the width We of the radiating antenna element small compared to that in the conventional structure, while achieving the same characteristic as the conventional structure for the main polarized wave.
Next, the reflection and transmission characteristics of the invention structure and the conventional structure are explained with reference to
As seen form
On the other hand, the reflection coefficient S11 drops at the operating frequency of 76.5 GHz much deeper in the invention structure than in the conventional structure. At the operating frequency, the reflection coefficient S11 drops down to −16.1 dB in the conventional structure, while it drops as low as −50.4 dB in the invention structure.
This is because the radiating antenna element is directly connected to the main feeding strip line in the conventional structure, while the radiating antenna element is connected to the main feeding strip line through the matching strip line in the invention structure. Connecting the radiating antenna element to the main feeding strip line through the matching strip line makes it easy to achieve impedance matching to reduce the reflection.
Next, the horizontal directivity (relative amplitude) of the microstrip array antenna 1 shown in
As seen from
This is because the array elements A1a, A1b, A1c, A2a, A2b and A2c constituting the microstrip array antenna 1 can be designed and fabricated precisely to achieve desired characteristics. Since the coupling factors can be controlled precisely, while achieving impedance matching and suppressing the cross-polarized component, the microstrip array antenna 1 can achieve high performance and high directivity.
Next, some relationships between the size parameters of the array elements A1a, A1b, A1c, A2a, A2b and A2c and the characteristics of the microstrip array antenna 1 are explained with reference to
As shown in
On the other hand, when the stub length Ls is varied, both the resonance frequency and the level of the reflection coefficient S11 are varied. In this embodiment, since the operating frequency is 76.5 GHz, the stub length Ls is set to 0.67 mm. If the stub length Ls is increased, the resonance frequency shifts to the lower side, and the reflection coefficient S11 increases on the whole, and if it is reduced, the resonance frequency shifts to the higher side, and the reflection coefficient S11 increases on the whole.
Next, the relationship between the field-emission edge line of the radiating antenna element and that of the stub, and the relationship between the stub length Ls and the characteristics of the radiating antenna element (particularly, the variation of the characteristics of the array element A1a depending on the relationship between the field-emission edge line of the stub 13a and that of the radiating antenna element 11a) are explained with reference to
As described above, the characteristics of the array element Ala vary depending on the element length Le of the radiating antenna element 11a and the stub length Ls of the stub 13a. As explained below, when the field-emission edge line 110a of the radiating antenna element 11a and the field-emission edge line 130a of the stub 13a are one the same straight line, the characteristics of the array element A1a such as the coupling factor and reflection characteristic become favorable.
As seen from
On the other hand, as seen from
The first embodiment described above provides the following advantages. The microstrip array antenna 1 has the structure in which each radiating antenna element is connected to the main feeding strip line 4 not directly but through the matching strip line. Accordingly, it is easy to achieve impedance matching to reduce the reflection factor of each of the array elements A1a, A1b, A1c, A2a, A2b and A2c.
The provision of the matching strip line enables controlling the coupling factor of each of the array elements A1a, A1b, A1c, A2a, A2b and A2c to some extent by adjusting the element lengths We of the radiating antenna elements 11a, 11b, 11c, 21a, 21b and 21c, and the size of the matching strip line (mainly, the stub length Ls). This enables each array element to have a large coupling factor by appropriately designing the matching strip line without increasing the element widths We. This means that a desired coupling factor can be achieved while suppressing the undesired cross-polarized components from the array elements A1a, A1b, A1c, A2a, A2b and A2c, and reducing the reflection at each of these array elements. Accordingly, the microstrip array antenna 1 of this embodiment can have a desired directivity and a high efficiency.
In this embodiment, each of the array elements A1a, A1b, A1c, A2a, A2b and A2c is connected with the sub-feeding strip line at the predetermined position between the center and the end of the longer side of its rectangular radiating antenna element. This enables achieving impedance matching with ease.
In this embodiment, each of the array elements A1a, A1b, A1c, A2a, A2b and A2c is formed such that the radiating antenna element is in parallel to the longitudinal direction of the stub so that the direction of the electric field radiated from the radiating antenna element coincides with the direction of the electric field radiated from the stub. Accordingly, in this embodiment, since the radiation component from the stub, which is conventionally an undesired component, can be effectively used together with the main polarized component from the radiating antenna element, the radiation efficiency of the entire array element can be improved.
In this embodiment, since the array elements A1a, A1b, A1c, A2a, A2b and A2c constituting the microstrip array antenna 1 are so configured that the longitudinal directions of the radiating antenna elements 11a, 11b, 11c, 21a, 21b and 21c, and the stubs 13a, 13b, 13c, 23a, 23b and 23c are all parallel, the microstrip array antenna 1 has a high radiation ability and a high receiving sensitivity.
Furthermore, since the radiating antenna elements 11a, 11b, 11c, 21a, 21b and 21c and the stubs 13a, 13b, 13c, 23a, 23b and 23c are all formed with an angle of approximately 45 degrees (or approximately −135 degrees) with respect to the longitudinal direction of the main feeding strip line 4, it is possible that the microstrip array antenna 1 has planes of polarization inclined by 45 degrees (or approximately −135 degrees).
Next, a microstrip array antenna 30 according to a second embodiment of the invention is described with respect to
The microstrip array antenna 30 according to the second embodiment of the invention has a structure in which array elements A3a, A3b, A3c, A4a, A4b and A4c are connected to either side edge of the main feeding strip line 4. The number of the array elements connected to the main feeding strip line 4 and the connection interval are the same like the first embodiment.
The array element A3a, which is the closest of the array elements connected to the first side edge 4a of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 32a connected to the main feeding strip line 4, a rectangular radiating antenna element 31a connected to the terminal end of the sub-feeding strip line 32a, and a stub 33a connected to a predetermined middle portion of the sub-feeding strip line 32a.
Likewise, the array element A3b, which is the second closest of the array elements connected to the first side edge 4a of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 32b, a rectangular radiating antenna element 31b and a stub 33b. The array element A3c, which is the third closest of the array elements connected to the first side edge 4a of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 32c, a rectangular radiating antenna element 31c and a stub 33c. The array element A4a, which is the closest of the array elements connected to the second side edge 4b of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 42a, a rectangular radiating antenna element 41a and a stub 43a. The array element A4b, which is the second closest of the array elements connected to the second side edge 4b of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 42b, a rectangular radiating antenna element 41b and a stub 43b. The array element A4c, which is third closest of the array elements connected to the second side edge 4b of the main feeding strip line 4 to the input end, is constituted of a sub-feeding strip line 42c, a rectangular radiating antenna element 41c and a stub 43c.
Next, the structures of the array elements are explained. Since the array elements A3a, A3b, A3c, A4a, A4b and A4c have the same shape, only the array element A3a which is the closest of the array elements connected to the first side edge 4a of the main feeding strip line 4 is explained with reference to
As shown in
The radiating antenna element 31a is formed in a rectangular shape so as to have the length Le smaller than its width We. The sub-feeding strip line 32a is connected to a feeding point 34a on a longer side of the radiating antenna element 31a. This feeding point 34a is set at a predetermined position between the center portion and one end portion of the longer side of the radiating antenna element 31a.
The radiating antenna element 31a is disposed such that its longitudinal direction is in parallel with the longitudinal direction of the stub 33a. That is, the longitudinal directions of both the radiating antenna element 11a and the stub 13a are parallel to the longitudinal direction of the main feeding strip line 4. Accordingly, the radiation from the stub 33a can be used as an effective radiation component as in the case of the first embodiment.
Also, like the first embodiment, the array element A3a is configured such that one of the contour edges of the radiating antenna element 31a as a field-emission edge line 310a and a field-emission edge line 330a of the stub 33a are on the same straight line.
Compared with the characteristics of the array element of the first embodiment shown in
The other array elements A3b and A3c connected to the first side edge 4a of the main feeding strip line 4 and the array elements A4a, A4b and A4c connected to the second side edge 4b of the main feeding strip line 4 have the same structure as the array element A3a shown in
That is, the array elements A3a, A3b, A3c, A4a, A4b and A4c constituting the microstrip array antenna 30 are so configured that the longitudinal directions of the radiating antenna elements 31a, 31b, 31c, 41a, 41b and 41c, and the stubs 33a, 33b, 33c, 43a, 43b and 43c are all parallel to one another.
Next, some relationships between the size parameters of the array elements A3a, A3b, A3c, A4a, A4b and A4c and the characteristics of the microstrip array antenna 30 are explained with reference to
As shown in
On the other hand, when the stub length Ls is varied, both the resonance frequency and the reflection coefficient S11 are varied as shown in
As shown in
The second embodiment described above provides the following advantages. The microstrip array antenna 30 has the structure in which each radiating antenna element is connected to the main feeding strip line 4 not directly but through the matching strip line. Accordingly, impedance matching can be achieved easily to reduce the reflection factor of each of the array elements A3a, A3b, A3c, A4a, A4b and A4c.
The provision of the matching strip line enables controlling the coupling factor of each of the array elements to some extent by adjusting the element lengths We and the size of the matching strip line (mainly, the stub length Ls). This enables each of the array elements to have a large coupling factor by appropriately designing the matching strip line without increasing the element widths We. This means that a desired coupling factor can be achieved, while suppressing the undesired cross-polarized components, and reducing the reflection from each of these array elements.
Also in this embodiment, each of the array elements A3a, A3b, A3c, A4a, A4b and 42c is formed such that the longitudinal direction of the radiating antenna element is parallel to the longitudinal direction of the stub so that the direction of the electric field radiated from the radiating antenna element coincides with the direction of the electric field radiated from the stub. Accordingly, also in this embodiment, since the radiation component from the stub, which is conventionally an undesired component, can be effectively used together with the main polarized component from the radiating antenna element, the radiation efficiency of the entire array element can be improved.
It is a matter of course that various modifications can be made to the above described embodiments as described below.
Although the present invention has been described by way of the first and second embodiments having the structures shown in
For example, the present invention also provides a microstrip array antenna 50 shown in
The array element A5a is constituted of an L-shaped sub-feeding strip line 52a extending from the main feeding strip line 4 with an angle of approximately 90 degrees with respect to the longitudinal direction of the main feeding line 4, a rectangular radiating antenna element 51a having the element length Ls equal to λg/2 and connected to the terminal end of the sub-feeding strip line 52a, and a stub 53a extending from a bent portion of the sub-feeding strip line 52a in the direction crossing the longitudinal direction of the main feeding strip line 4. The longitudinal directions of the radiating antenna element 51a and the stub 53a are parallel to each other.
The microstrip array antenna 50 having the structure shown in
The microstrip array antennas of the above described embodiments have the structure in which the main feeding strip line 4 is connected with the array elements at both side edges thereof. However, the main feeding strip line 4 may be connected with the array elements at only one of the first side edge 4a and the second side edge 4b as shown in
Furthermore, the main feeding strip line 4 may be connected with only one array element at each side edge thereof as shown in
Then number of array elements to be connected to each side edge of the main feeding strip line 4 is determined depending on a required directivity etc. However, it should be noticed that to achieve a high directivity, it is preferable that the main feeding strip line 4 is connected with array elements at not only one side edge thereof but at both side edges thereof, as explained below with reference to
Since the lengths of the radiating antenna elements and the intervals at which the array elements are connected to the main feeding strip line should be determined depending on the characteristics required of the entire microstrip array antenna in relation to the waveguide wavelength λg, they may be n times (n being an integer larger than 1) those described in the embodiments. Also in this case, each radiating antenna element can radiate radia wave most efficiently.
The above explained preferred embodiments are exemplary of the invention of the present application which is described solely by the claims appended below. It should be understood that modifications of the preferred embodiments may be made as would occur to one of skill in the art.
Number | Date | Country | Kind |
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2008-198297 | Jul 2008 | JP | national |