JP3306844B2 - Diversity antenna - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity antenna suitable for a simple base station antenna used in mobile communication using, for example, a micro cell.

[0002]

2. Description of the Related Art In conventional mobile communication using a micro cell, two base station antennas are provided in order to perform diversity on the base station side. Actually, due to installation restrictions, a height diversity antenna in which two antennas are integrated vertically and a space diversity antenna in which two antennas are arranged horizontally apart from each other depending on the installation location Used. In addition, as an antenna installed at a high position such as a building roof, in order to reduce interference from a horizontal direction, which is a problem in that case, the antenna has a tilt beam in which the direction of a main beam in a vertical plane is tilted downward. Diversity antennas have also been used.

FIGS. 6 and 7 show these conventional antennas. FIG. 6A shows two antennas 6-1 and 6-.
Antenna 6-1 in the case of height diversity antenna integrated spaced apart by a distance D 2 up and down, the distance d ₁
And two radiating elements 6-3 arranged one above the other,
Similarly antenna 6-2 are two intervals d ₁ of the radiating element 6
4 is provided. These antennas 6-1 and 6-2 are of equal gain, that is, the same antenna is used. At the lower end of the lower antenna 6-2, input / output connectors 6-5 and 6-6 connected to the radiating elements 6-3 and 6-4 are attached.

FIG. 6B shows a case of a space diversity antenna in which two antennas 6-1 and 6-2 are arranged in parallel in a horizontal direction at a distance D, and FIG. 7 is a diagram showing two antennas 6-1 and 6-2. , Two radiating elements 6-3 and two radiating elements 6-4.
Is a phase difference excitation, and the direction of the main beam in the vertical plane is tilted downward. In both FIG. 6B and FIG. 7, the antennas 6-1 and 6-2 are the same as in FIG. 6A.

In general, when these antennas are used, there is a direction in which a radiation electric field becomes zero periodically in directions other than the main beam as the distance from the main beam increases. However, in a conventional cellular system such as a mobile phone and a cellular phone in an urban area, since the propagation environment is multi-wave propagation, even in a direction (angle) where the radiated electric field of the antenna becomes zero, scattering from surrounding buildings. The wave did not produce an insensitive area (an area where the received electric field was below the allowable level).

[0006]

However, in mobile communication using microcells, the propagation environment is dominated by line-of-sight propagation, so that there is almost no effect due to multiple waves and the direction in which the radiated electric field of the antenna becomes zero. Thus, a dead area is generated. That is, as shown in FIG. 8, an antenna 12 is mounted on the roof of a building 11, and the direction of a main beam (main lobe) 13 of the antenna 12 is slightly downward with respect to the horizontal direction. The direction of the edge of the area 14, that is, the direction of the cell edge 15 in the microcell mobile communication, indicates that the directivity of the antenna 12 is such that a side lobe is generated periodically and angularly with respect to the main beam 13 in a vertical plane. One side lobe 16 is generated downward from the main beam 13, a null direction exists between the main beam 13 and the first side lobe 16, and an insensitive area 17 is generated.

On the other hand, if the conventional technique is used, the reception level on the moving side can be made uniform by using an array antenna having directivity, for example, beam shaped into a cosecant square shape or the like. However, the array antenna having this shaped beam has the disadvantage that the amplitude and phase of the radiating element need to be set to predetermined values, and it is difficult to adjust at the time of manufacture compared to an array antenna of equal amplitude and equal phase excitation. is there. Further, in order to improve the beam formability, it is necessary to increase the number of elements of the antenna, and there is a disadvantage that the antenna length is increased and the gain is limited.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a diversity antenna which is relatively narrow, such as a microcell, and which does not generate an insensitive area with a relatively simple configuration when transmission and reception are performed mainly by direct waves only.

[0009]

According to the first aspect of the present invention, two array antennas having different values of the product of the number of elements and the element spacing are arranged vertically or horizontally in parallel and separated by a distance D. The excitation phases of the adjacent radiating elements in the antenna are set to be substantially the same. Then, the number of radiating elements of the two antennas and the radiating element spacing product N ₁ d ₁ and N
The ratio of ₂ d _{2 is, N 2 d 2 / N 1} d 1 = 2m / (2m + 1) ( where m is a natural number) is set to.

According to the second aspect of the present invention, two array antennas having different values of the product of the number of elements and the element spacing are arranged vertically or horizontally in parallel at a distance D, and adjacent radiating elements in each antenna. Are set to approximately (360 / N ₁ ) ° and (360 / N ₂ ) ° (where N ₁ and N ₂ are the number of elements). In the invention of claim 3, characterized in that in the invention of claim 2, the two radiating elements number and radiating element spacing of the antenna product N ₁ d ₁ and N
The ratio of ₂ d _{2 is, N 2 d 2 / N 1} d 1 = 2 (m + 1) / (2m + 3) ( where m is a natural number) is set to.

According to the fourth aspect of the present invention, the first and second aspects are provided.
Alternatively, in the third aspect of the present invention, an antenna having a unidirectional directivity in a horizontal plane is used.

[0012]

[Action] Generally, the direction theta _m of equal amplitude excitation was array antenna sidelobes, the direction of the null (null) theta
_n is given by the following equation.・ Side lobe direction: θ _m θ _m = sin ^-1 {(λ / (2πd)) [((2m + 1) π / N) + φ _O ]} (1) ・ Null direction: θ _n θ _n = sin ^-1 {(λ / (2πd)) [(2mπ / N) + φ _o ]} (2) where d is the radiating element interval, N is the number of radiating elements, λ is the wavelength, and φ _O is between adjacent radiating elements. And m is a natural number. Expression (1) is an approximate expression.

Now, the number of elements of the two array antennas is N ₁
And N ₂ , and the element spacing d ₁ and d ₂ , the number of elements N
_{It is} considered that the direction θ _m of the side lobe of the array antenna having the radiating element spacing d ₁ at ₁ matches the null direction θ _n of the array antenna having the radiating element spacing d ₂ at the number of elements N ₂ .
At this time, the ratio between the radiating element intervals d ₁ and d ₂ is given by the following equation. d ₂ / d ₁ = {(2mπ / N ₂ ) + φ _O } / {(2m + 1) π / N ₁ ) + φ _O } (3) Here, when in-phase excitation is performed, the following equation can be rewritten. N ₂ d ₂ / N ₁ d ₁ = 2 m / (2m + 1) (4) When the first null is directed in the horizontal direction to reduce interference, the following equation can be rewritten.

N ₂ d ₂ / N ₁ d ₁ = 2 (m + 1) / (2m + 3) (5) In the present invention, the relations given by equations (3) to (5) are obtained. In other words, the product N ₁ d ₁ and N ₂ d ₂ of the above formula (4) of the two Areante radiating element number and the radiation element spacing of Na constituting the diversity antenna or (5)
Set to the ratio given by At this time, the direction of the m-th side lobe of the array antenna with the number of elements N ₁ and the radiating element spacing d ₁ and the direction of the m-th null of the array antenna with the number of elements N ₂ and the radiating element spacing d ₂ are Matches. As a result, the direction in which the radiated electric field of one array antenna becomes zero is different from the direction in which the radiated electric field of the other array antenna becomes zero, and the dead area in the microcell (when the received electric field is below the allowable level) Area) can be eliminated.

At this time, the radiation level in the cell edge direction, which determines the cell size, is almost the same for both array antennas, and can be regarded as an equal gain antenna.
The characteristics (particularly, the diversity gain) as the diversity antenna maintain the same characteristics as those of the conventional diversity antenna. In addition, in the antenna of the present invention, in a region close to the base station, the side lobe direction of one array antenna becomes the null direction of the other array antenna, and the two array antennas have the directional diversity operation. A higher performance diversity antenna can be realized.

At the same time, the excitation phases of the adjacent radiating elements in the two array antennas are almost (360 /
By setting the phase difference to (N ₁ ) ° and (360 / N ₂ ) °, a null can be provided in the horizontal plane, and the effect of reducing the influence of the interference wave from the horizontal plane can be obtained.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention, and portions corresponding to those in FIG. FIG.
In this case, the array antenna 6-1 has N ₁ of equal amplitude and in-phase excitation.
= A two radiating elements 6-3, the radiating element spacing d ₁
Is a array antenna 6-2 is equal amplitude, the radiating element spacing d ₂ consists N ₂ = 2 radiating elements 6-4 that phase excitation, the antennas 6-1 and 6-2 by the interval D in the vertical They are placed apart. Here, the ratio between the radiating element intervals d ₁ and d ₂ is selected according to the relationship given by equation (4).

FIG. 2 shows the radiation directivity in the vertical plane of the diversity antenna shown in FIG. Here, N ₁ = N ₂ = 6
And The solid curve 2-1 shows the characteristics of the array antenna 6-1, and the dotted curve 2-2 shows the characteristics of the array antenna 6-2. Here, the radiation element interval d ₁ is 0.9 wavelength,
m = 2. Assuming that m = 2, therefore, according to equation (4), d ₂ is 0.72 wavelength, and the direction 2-3 of the second side lobe of the upper array antenna 6-1 is 2-3.
And the second null direction 2- of the lower array antenna 6-2.
4 are almost the same. Thus, the direction in which the radiated electric field of one array antenna does not become zero and the direction in which the radiated electric field of the other array antenna becomes zero can be set, and the dead area in the microcell (the received electric field becomes lower than the allowable level) Area) can be eliminated.

At this time, the feed loss to the upper array antenna 6-1 is larger than the feed loss to the lower array antenna 6-2, and the loss difference is the upper and lower array antennas 6-1.
The two array antennas 6-1 and 6-2 cancel out the gain difference of 1 and 6-2, and become antennas of almost equal gain. That radiating element spacing d ₁ is a larger than d _2, Aru gain of the upper antenna array 6-1 is larger than the gain of the array antenna 6-2. Therefore, the radiation level in the cell edge direction that determines the cell size is two array antennas 6 −
1, it is approximately equal to as 6-2, characteristics as diversity antenna (particularly, diversity gain) maintains the same characteristics as the conventional diversity antenna.
In addition, in the antenna of this embodiment, in an area close to the base station, two array antennas 6-1 and 6-2 are used.
Since the radiation directivities other than the main beam are alternated in the vertical plane, a higher performance diversity antenna having both directional diversity operations can be realized.

FIG. 3 shows a second embodiment of the present invention. In this case, the shape is the same as that of the embodiment of FIG. 1, but in this embodiment, the excitation phase difference φ _O between the adjacent radiating elements 6-3 is set to (360 / N ₁ ) °. The excitation phase difference φ _O between 6-4 is selected to be (360 / N ₂ ) °.
At this time, both of the two array antennas 6-1 and 6-2
One of the first nulls of each radiation characteristic in the vertical plane of the radiating element 6-3 (6-4) can be directed in a direction perpendicular to the antenna arrangement direction, and the array antennas 6-1 and 6-2 are installed vertically. Then, a beam tilt antenna having a null in the horizontal direction can be realized. Thereby, the influence of the interference wave coming from the horizontal plane can be reduced.

Here, the ratio of the products N ₁ d ₁ and N ₂ d ₂ of the number of radiating elements and the spacing between the radiating elements of the beam tilt antenna having a null in the horizontal direction is selected according to the relationship given by equation (5). . FIG. 4 shows the radiation directivity of the beam tilt diversity antenna having a null in the horizontal direction shown in FIG. Here, N ₁ = a N ₂ = 6, the radiating element spacing d ₁ 0.9 wavelength, m = 2, thus d ₂ from equation (5)
Is about 0.77 wavelength. As shown in FIG. 2, by assuming that m = 2, the direction of the second null of the first array and the second side lobe of the upper array antenna 6-1 on the opposite side to the main lobe, The direction of the second null of the lower array antenna 6-2 substantially matches. Thus, the direction in which the radiated electric field of one array antenna does not become zero and the direction in which the radiated electric field of the other array antenna becomes zero can be set, and the dead area in the microcell (the received electric field becomes lower than the allowable level) Area) can be eliminated.

At this time, as in the first embodiment, the feed loss to the upper array antenna 6-1 is larger than the feed loss to the lower array antenna 6-2, and the loss difference is d.
₁ > d ₂ based on the upper and lower array antennas 6-1 and 6
2 and the two array antennas 6-1,
6-2 is an antenna having almost equal gain. Therefore, the radiation level in the cell edge direction that determines the cell size is substantially the same value for the two array antennas 6-1 and 6-2, and the characteristics (particularly, the diversity gain) as the diversity antenna are different from those of the conventional diversity antenna. Similar characteristics are maintained. In addition to this,
In the area close to the base station, two array antennas 6
Since the radiation directivities other than -1, 6-2 main beams can be alternated, a higher performance diversity antenna having both directional diversity operations can be realized. At this time, since one of the first nulls on both sides of the main beam is in the horizontal direction, the influence of the interference wave from the horizontal direction can be reduced.

FIG. 5 is similar to FIG. 4, but shows the radiation directivity of the beam tilt diversity antenna with a null in the horizontal direction shown in FIG. 3, where, unlike the FIG. 4, N ₁ And N ₂ are different. In Figure 5, the number of elements N ₁ 6, the number of elements N ₂ and 5, a radiating element spacing d ₁ 0.9 wavelength, m = 2, therefore d ₂ from equation (5) about 0.
The wavelength is 93. 2 and 4, assuming that m = 2, the direction of the second side lobe of the upper array antenna 6-1 and the second null of the lower array antenna 6-2 are assumed. The direction is almost the same.
Thus, the direction in which the radiated electric field of one array antenna does not become zero and the direction in which the radiated electric field of the other array antenna becomes zero can be set, and the dead area in the microcell (the received electric field becomes lower than the allowable level) Area) can be eliminated.

At this time, similarly to the above-described embodiment, the power supply loss to the upper array antenna 6-1 is larger than the power supply loss to the lower array antenna 6-2, and the loss difference is d.
₁ > d ₂ based on the upper and lower array antennas 6-1 and 6
2 and the two array antennas 6-1,
6-2 is an antenna having almost equal gain. Therefore, the radiation level in the cell edge direction that determines the cell size is substantially the same value for the two array antennas 6-1 and 6-2, and the characteristics (particularly, the diversity gain) as the diversity antenna are different from those of the conventional diversity antenna. Similar characteristics are maintained. In addition to this,
In the area close to the base station, two array antennas 6
Since radiation directivities other than -1, 6-2 main beams can be alternated, a higher performance diversity antenna having both directivity diversity operations can be realized. At this time, since one of the first nulls on both sides of the main beam is in the horizontal direction, the influence of the interference wave from the horizontal direction can be reduced.

As described in the section of the means for solving the problems in each of the above embodiments, the equation (1) for giving the direction θ _m of the side lobe of the array antenna is approximate, and Is not strictly correct. To this strictly correct, numerically it is necessary to obtain the direction theta _m sidelobes. Also, the above equation is
Are those at the time of equal amplitude excitation, also at unequal amplitude excitation, strictly speaking, it is necessary to determine the direction theta _m of numerically sidelobe. However, in each case, approximately, the above method is sufficient.

In each of the above calculation examples, an antenna having an omnidirectional directivity in the horizontal plane has been described. However, a similar effect can be obtained when the directivity in the horizontal plane is bidirectional or unidirectional. It goes without saying that this is the same as in the above-described embodiment. Radiation elements 6-3 and 6 to make an omnidirectional antenna
-4 is a dipole antenna, for example, the radiating elements 6-3 and 6-4 are bi-directional, and the radiating elements 6-6 and 6-4 are, for example, a parallel plate type printed antenna or a slot antenna. 3, 6-4 may be, for example, microstrip antennas.

In the above description, when m = 2, the second side lobe direction of one array antenna coincides with the second null direction of the other array antenna. The null direction may be matched, or the third sublobe direction may be matched with the third null direction by setting m = 3. When m is increased, a deviation occurs between the first side lobe, the second side lobe, and the other first null direction and second null direction. From this point, m is usually 1, 2, 3
It is made either of Also, in the above description, the present invention arranges two array antennas vertically, but similarly to the conventional antenna shown in FIG. 5B, two vertical array antennas are horizontally separated, that is, provided side by side, The products N ₁ d ₁ and N ₂ d of the number of radiating elements and the spacing between the radiating elements
₂ may be different from each other, and may further satisfy Expression (3), and may satisfy Expression (4) or Expression (5) as necessary. The radiating elements 6-3 and 6-4 are practically about 2 to 10, preferably about 5 or 6.

[0028]

As described in detail above, according to the present invention, while having the same function as the conventional diversity antenna, in a relatively small area such as a microcell, which is close to the base station, There is an advantage that it is possible to realize a high-performance diversity antenna that combines the operation of the directional diversity, eliminates the dead area, has a simple configuration, and is easy to adjust.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the invention of claim 1;

FIG. 2 is a view showing radiation directivity in a vertical plane of the diversity antenna of the embodiment shown in FIG. 1;

FIG. 3 is a diagram showing an embodiment of the invention of claim 2;

FIG. 4 is a view showing radiation directivity in a vertical plane of the diversity antenna of the embodiment shown in FIG. 3;

FIG. 5 is a view showing the radiation directivity in the vertical plane of the diversity antenna with other parameters of the embodiment shown in FIG. 3;

FIG. 6 shows a diversity antenna according to the prior art;
A is a height diversity antenna in which two antennas are vertically arranged at an interval D, and B is a space diversity antenna in which two antennas are arranged in parallel in the horizontal direction (left and right) at an interval D. is there.

FIG. 7 is a diagram showing a conventional diversity antenna having a tilt beam in which the direction of a main beam in a vertical plane is tilted downward.

FIG. 8 is a diagram illustrating a state in which a dead area is generated in a microcell based on antenna directivity.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-308222 (JP, A) JP-A-57-26932 (JP, A) JP-A-59-144205 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01Q 3/00-3/46 H01Q 21/00-25/04

Claims (4)

(57) [Claims] 1. A first array antenna in which N ₁ (N ₁ is an integer of 2 or more) radiating elements are vertically arranged in multiple stages, and a N ₂ element (N ₂ is an integer of 2 or more) radiating element. In a diversity antenna in which second array antennas arranged in multiple stages in the vertical direction are arranged vertically or horizontally, the number of radiation elements of the first and second array antennas and radiation
The product of element spacings N ₁ d ₁ and N ₂ d ₂ is set so that N ₂ d ₂ / N ₁ d ₁ = 2 m / (2m + 1): m is a natural number , and diversity antenna excitation phase of each adjacent radiating element is characterized in that it is set to the same phase in the array antenna. 2. A first array antenna in which N ₁ (N ₁ is an integer of 2 or more) radiating elements are vertically arranged in multiple stages, and a N ₂ element (N ₂ is an integer of 2 or more) radiating element. In a diversity antenna in which second array antennas arranged in multiple stages in the vertical direction are arranged vertically or horizontally, the products N ₁ d ₁ and N ₁ of the number of radiating elements and the spacing of the radiating elements of the first and second array antennas Unlike ₂ d ₂ from each other, and said first and second excitation phase of the radiating element adjacent the array antenna each (360 / N ₁₎ ° and (360 / N ₂₎ is set to the phase difference ° A diversity antenna. 3. The products N ₁ d ₁ and N ₂ d _{2 of the} number of radiating elements and the spacing between the radiating elements of the first and second array antennas.
_{There, N 2 d 2 / N 1} d 1 = 2 (m + 1) / (2m + 3): m is diversity antenna according to claim 2, characterized in that it is set to meet the natural number relationship. 4. A diversity antenna as claimed in any one of claims 1 to 3 horizontal plane directivity of the first and second array antenna characterized in that it is a unidirectional.