International Conference on Antenna Theory and Techniques, 17-21 September, 2007, Sevastopol, Ukraine pp. 332-334

978-1-4244-1584-7/07/$25.00©2007 IEEE

ADAPTIVE ARRAY OF BASE STATION OF MOBILE COMMUNICATION

Shirokov I. B., Durmanov M. A. and Chertkov V. E.

Sevastopol National Technical University, Sevastopol, Ukraine E-mail: Shirokov@stel.sebastopol.ua

Abstract The adaptive antenna’s system is discussed. The one of three sectors is taken into

account. The antenna’s pattern has three main lobes. The mutual placing of these lobes determines the signal strength from different direction. The array consists of three elements. The elements are turned each from another on certain angle. The bi-nary law of phase discretes is considered.

Keywords: Adaptive array, phase shifter, antenna’s pattern, side lobe, main lobe.

1. INTRODUCTION Adaptive or intellectual antenna's systems now have found wide application in the field of telecommunica-tion. The using of new technology of adaptive anten-nas allows to base station to cover the larger area, that in a consequence should reduce necessary amount of base stations. Furthermore, this technology allows to reduce the power consumption of the mobile terminal by decrease of its output power, without change of a cover zone of base station. Especially it is useful when the subscriber terminal is located on a boundary of base station zone.

The presented paper is devoted to analysis and de-sign of adaptive antenna’s system of small amount of elements. The main goal of paper is the optimization of mutual placing of antenna elements and optimiza-tion of control law of phase shifting.

The algorithm of control of the antenna pattern is discussed in a paper.

2. THE APPROACH TO A PROBLEM As it is well known, stationary antennas of base sta-tions are not capable to turn in accordance all of mo-bile phones that are connected to base station. Therefore, there was necessary to create such antenna system in which the electronic management of an-tenna pattern would be realized.

The multi-beam pattern can be created by the intro-duction of a number of elements of radiation. Thus, for the control with the beam it is suggested an idea of re-placement of antenna of each sector of base station with system of three elements, so, we’ll receive phased array.

In this case, at the certain geometrical arrangement of radiations elements, and also at the certain phase shift between excitation signals, the changing of a array pattern of base stations is obviously possible.

The main task of presented design is not only form-ing the single beam of array which is rotated with subscriber terminal moving. It is proposed to form the multi-beam pattern of array, the gain in a different direction of a multi-beam pattern is chosen in accor-dance with placing of groups of subscribers.

Obviously, required pattern of any array it can be obtained with setting of certain distribution of ampli-tudes and phases of excitation signals. That is true for multi-element array, the number of elements of which can reach hundreds and thousands.

From the other hand, the changing of amplitude distribution is wrong way, such distribution can be realized with only attenuation of excitation signals. The power of communication link can be only de-creased in this case.

In a presented paper it is suggested to use only three antenna elements without any amplitude distri-bution. The only phase distribution of excitation sig-nals it is proposed. Necessary phasing of the antennas is realized with controlled discrete phase shifters. Thus, by the entering of certain phase shift in each excitation signal it is possible to achieve of increasing of radiation in one or in two directions and accord-ingly achieve of decreasing of radiation in another. It will allow us to generate optimum array pattern, which depends on a location of the subscribe termi-nals in a service zone of base station.

It is possible to obtain such patterns of base station array if the antenna elements are turned each with re-spect to another on a certain angle. The amount of this angle depends on value of service sector, beam width of each antenna element in horizontal plane, spacing between elements and phase shift discrete. Evidently, the discrete of phase shift must correspond to binary law. So, for the 120º service sector of base station array these parameters were optimized. The element spacing was one wave length and the angle of turn of neighbor elements from central one were + 15º and – 15º.

Adaptive Array of Base Station of Mobile Communication

International Conference on Antenna Theory and Techniques, 17-21 September, 2007, Sevastopol, Ukraine 333

For the further analysis we must represent the de-sign of antenna system. The block diagram of the base station array is presented on Fig. 1.

The base station array consists of three radiating elements А1, А2, А3, three phase shifters PS1, PS2, PS3, the controlling device and power divider. As radiating element it is used the flat panel antenna Kathrein 742 215.

These elements are placed on distance of wave-length λ from each other and extreme ones are un-wrapped in a horizontal plane on 15° to the left and to the right accordingly.

The phase shifters are four-section each. It is conven-ient to make this phase shifter with the hybrid bridge circuit and p-i-n diodes commutation. The step of phase shifters it is defined by the number of section and the binary law and from equation (1) it is equal to 22.5°. 2 /2nϕ πΔ = , (1)

where n is number of section of the phase shifter. The divider of power provides equal distribution of

power between three flat panel antennas. No addi-tional demands to power divider are not required.

Further, for array beam forming, it is necessary to de-fine the antenna element characteristics. The flat panel Kathrein 742 215 has the following characteristics:

1) frequency band is 1710…1880 MHz; 2) ½ of beam width in a horizontal plane are:

• at a level – 3 dB — -3 dB 67Θ = ° ;

• at a level – 10 dB — -10 dB 125Θ = ° .

The approximated analytical expression of antenna pattern in a horizontal plane is:

0.5

( ) exp 1, 38ELE⎡ ⎤⎛ ⎞Θ ⎟⎜⎢ ⎥⎟Θ = − ⎜ ⎟⎢ ⎥⎜ ⎟⎟⎜Θ⎝ ⎠⎢ ⎥⎣ ⎦

, (2)

where 0.5Θ is a beam width at level – 3 dB. On Fig. 2 it is presented the pattern of Kathrein

742 215 in horizontal plane.

For composition of resulting pattern of system of antennas it is necessary to fulfill the following calcu-lation. Let's write down analytical expression for cal-culation resulting pattern of a three-element array:

( )

( )

( )

1

21

1

31

1

SUM EL

sin( )

EL

2 sin( )2

EL

1( )

3

,

j

jkdkd

jkdkd

E E eb

E e

E e

ψ

ψ

ψ

γ

γ

⎛ ⎞⎟⎜ ⎟⎜⋅ − Θ ⎟⎜ ⎟⎟⎜⎜ ⎟⎝ ⎠

⎛ ⎞⎟⎜ ⎟⎜⋅ ⋅ − Θ ⎟⎜ ⎟⎟⎜⎜ ⎟⎝ ⎠

⎡⎢Θ = Θ− ⋅ +⎢⋅ ⎢⎣

+ Θ ⋅ +

⎤⎥+ Θ+ ⋅ ⎥⎥⎦

(3)

where: b is normalizing factor; γ is an angle of turn of elements, concerning a plane of their arrangement; 1ψ , 2ψ , 3ψ — it is artificial entered phase shifts by

controlled phase shifters on the first, second and third elements accordingly; k propagation constant.

The first and third elements are wrapped on a fixed corner γ to the left and to the right accordingly. It is necessary to keep the required width of service sector, and also for reduction of side lobes.

Thus, changing the phases of signals of excitation, we shall compose the various characteristic array patterns.

Let's consider a variant when the maximal radiation is concentrated in one of "extreme" directions (Fig. 3). This solution is fulfilled when there are set phase distribution: 1 247.5ψ = ° , 2 67.5ψ = ° , 3 0ψ = ° (case of "001"). From Fig. 3 it is shown, that insignificant lateral

radiation, on a level equal to the fifth part of the main beam takes place. Beams of the first and second sec-tors have been suppressed for 25 and 35 percent ac-cordingly, that allows us to judge redistribution of the power aside the third element in this case.

Further we’ll consider distribution of a maximum of an orientation only in a mainstream (Fig. 4). This solution is fulfilled when there are set phase distribu-tion: 1 0ψ = ° , 2 67.5ψ = ° , 3 0ψ = ° (case of "010").

For this case it is received good redistribution of energy of radiation between elements: the suppressed

Fig. 1. The Block diagram of base station array.

Fig. 2. The pattern of Kathrein 742 215.

Shirokov I. B., Durmanov M. A. and Chertkov V. E.

334 International Conference on Antenna Theory and Techniques, 17-21 September, 2007, Sevastopol, Ukraine

levels of the first and third beams do not exceed a level 0.6 from the normalized value. Side lobes have bidirectional character, their level does not exceed a quarter from the main beam.

Now we’ll consider the pattern for a case that is opposite to the previous one. Here we obtain the dis-tribution of energy between extreme directions of radiation (Fig. 5). This solution is fulfilled when there are set phase distribution: 1 0ψ = ° , 2 135ψ = ° ,

3 0ψ = ° (case of "101"). The most successful variant of calculations. Ideal distribution between the first and third elements, a level of the second element does not exceed a level 0.7. Side lobes at all do not reach a level 0.15 and their influence is negligible.

And at last for a generality of a presentation we’ll consider uniform distribution of a maximum of an orientation on three directions (Fig. 6). This solution is fulfilled when there are set phase distribution: 1 0ψ = ° , 2 112.5ψ = ° , 3 0ψ = ° (case of "111").

Distribution between the first and third elements equal and maximal, a level of a beam of the second element within the limits of 0.9. The level of side lobes does not exceed 0.2. The given distribution can be counted as the basic one.

4. CONCLUSION So, it was presented the possibility of beam forming of base station array. The beam forming is obtained with the only phase distribution of excitation signals and without any amplitude attenuation. So, the ener-getic of communication link is not reduced.

The algorithm of functioning of adaptive array of base station assume the analysis of the level of receiv-ing signal from different subscriber terminals. So, substituting different phase distribution, we’ll choose those pattern, when the number of receiving signals with low level is minimal.

Fig. 3. Array pattern for a case of "001".

Fig. 4. Array pattern for a case "010".

Fig. 5. Array pattern for a case of "101".

Fig. 6. Array pattern for a case "111".