Phase radiation pattern. The concept of the phase center of the antenna. Methods for reducing the level of side lobes in emitter systems Deriving an expression for dn lar

Main lobe width and side lobe level

The width of the pattern (main lobe) determines the degree of concentration of the emitted electromagnetic energy. DN width is the angle between two directions within the main lobe in which the amplitude of the electromagnetic field strength is 0.707 levels from the maximum value (or 0.5 levels from the maximum power density value). The width of the bottom line is indicated as follows:

2i is the width of the pattern in terms of power at the level of 0.5;

2i - width of the pattern in terms of tension at the level of 0.707.

The index E or H denotes the width of the pattern in the corresponding plane: 2i, 2i. A level of 0.5 in power corresponds to a level of 0.707 in field strength or a level of 3 dB on a logarithmic scale:

It is convenient to experimentally determine the width of the pattern using a graph, for example, as shown in Figure 11.

Figure 11

The level of the side lobes of the pattern determines the degree of spurious radiation of the electromagnetic field by the antenna. It affects the quality of electromagnetic compatibility with nearby radio-electronic systems.

The relative side-lobe level is the ratio of the field strength amplitude in the direction of the maximum of the first side lobe to the field strength amplitude in the direction of the maximum of the main lobe (Figure 12):

Figure 12

This level is expressed in absolute units, or in decibels:

Directional coefficient and gain of the transmitting antenna

Directional coefficient (DC) quantitatively characterizes the directional properties of a real antenna in comparison with a reference omnidirectional (isotropic) antenna with a spherical pattern:

KND is a number showing how many times the power flux density P (u, q) of a real (directional) antenna is greater than the power flux density P (u, q) of a reference (non-directional) antenna for the same direction and at the same distance, provided that the radiation powers of the antennas are the same:

Taking (25) into account, we can obtain:

The gain factor (GC) of an antenna is a parameter that takes into account not only the focusing properties of the antenna, but also its ability to convert one type of energy into another.

KU- this is a number showing how many times the power flux density P (u, c) of a real (directional) antenna is greater than the power flux density PE (u, c) of a reference (non-directional) antenna for the same direction and at the same distance, provided that the powers supplied to the antennas are the same.

The gain can be expressed in terms of efficiency:

where is the antenna efficiency. In practice, the antenna gain is used in the direction of maximum radiation.

Phase radiation pattern. The concept of the antenna phase center

Phase radiation pattern is the dependence of the phase of the electromagnetic field emitted by the antenna on the angular coordinates.

Since in the far zone of the antenna the field vectors E and H are in phase, the phase pattern is equally related to the electrical and magnetic components of the EMF emitted by the antenna. The phase pattern is designated as follows: Ш = Ш (u, ц) at r = const.

If W (u, q) = const at r = const, then this means that the antenna forms the phase front of the wave in the form of a sphere. The center of this sphere, where the origin of the coordinate system is located, is called the phase center of the antenna (PCA). It should be noted that not all antennas have a phase center.

For antennas that have a phase center and a multi-lobe amplitude pattern with clear zeros between them, the field phase in adjacent lobes differs by p (180°). The relationship between the amplitude and phase radiation patterns of the same antenna is illustrated in Figure 13.

Figure 13 - Amplitude and phase patterns

The direction of propagation of electromagnetic waves and the position of its phase front at each point in space are mutually perpendicular.

Reducing the level of side lobes of mirror antennas by positioning metal strips in the aperture

Akiki D, Biayneh V., Nassar E., Harmush A,

University of Notre Dame, Tripoli, Lebanon

Introduction

In a world of increasing mobility, there is a growing need for people to connect and access information, regardless of where the information is located or the individual. From these considerations, it is impossible to deny that telecommunications, namely the transmission of signals over distances, is an urgent need. The demands for wireless communication systems to be so perfect and ubiquitous mean that increasingly more efficient systems need to be developed. When improving a system, a key initial step is to improve the antennas, which are the core element of current and future wireless communication systems. At this stage, by improving the quality of the antenna parameters we will understand a decrease in the level of its side lobes of its radiation pattern. Reducing the level of side lobes, naturally, should not affect the main lobe of the diagram. Reducing the sidelobe level is desirable because for antennas used as receives, the sidelobes make the system more vulnerable to stray signals. In transmitting antennas, side lobes reduce information security, since the signal may be received by an unwanted receiving party. The main difficulty is that the higher the sidelobe level, the higher the probability of interference in the direction of the sidelobe with the highest level. In addition, increased sidelobe levels mean that signal power is dissipated unnecessarily. Much research has been done (see, for example, ), but the purpose of this article is to review the “strip positioning” method, which has proven to be simple, effective and low cost. Any parabolic antenna

can be developed or even modified using this method (Fig. 1) to reduce interference between antennas.

However, the conductive strips must be very precisely positioned to achieve sidelobe reduction. In this paper, the "strip positioning" method is tested through experiment.

Description of the task

The problem is formulated as follows. For a particular parabolic antenna (Fig. 1), it is necessary to reduce the level of the first side lobe. The antenna radiation pattern is nothing more than the Fourier transform of the antenna aperture excitation function.

In Fig. Figure 2 shows two diagrams of a parabolic antenna - without stripes (solid line) and with stripes (line shown with *), illustrating the fact that when stripes are used, the level of the first side lobe decreases, but at the same time the level of the main lobe also decreases, and the level also changes the remaining petals. This shows that the position of the stripes is very critical. It is necessary to position the strips in such a way that the width of the main lobe at half power or the antenna gain does not change noticeably. The level of the rear lobe should also not change noticeably. The increase in the level of the remaining petals is not so significant, since the level of these petals is usually much easier to reduce than the level of the first side lobes. However, this increase should be moderate. Let us also remember that Fig. 2 is illustrative.

For the above reasons, when using the "strip positioning" method, the following must be kept in mind: the strips must be metal in order to fully reflect the electric field. In this case, the position of the stripes can be clearly determined. Currently, side lobe level measurements

Rice. 2. Antenna radiation pattern without stripes (solid)

and with stripes (

Rice. 3. Theoretical normalized radiation pattern in dB

two methods are used - theoretical and experimental. Both methods complement each other, but since our evidence is based on a comparison of experimental diagrams of antennas without breakdowns and with stripes, in this case we will use the experimental method.

A. Theoretical method. This method consists of:

Finding the theoretical radiation pattern (RP) of the antenna under test,

Measurements of the side lobes of this pattern.

The pattern can be taken from the technical documentation of the antenna, or can be calculated, for example, using the Ma1!ab program or using any other suitable program using known relationships for the field.

The P2P-23-YHA mirror parabolic antenna was used as the antenna under test. The theoretical value of the DP was obtained using the formula for a circular aperture with uniform excitation:

]ka2E0e іkg Jl (ka 8Іпв)

Measurements and calculations were performed in the E-plane. In Fig. Figure 3 shows the normalized radiation pattern in the polar coordinate system.

B. Experimental method. In the experimental method two antennas must be used:

The receiving antenna under test,

Transmitting antenna.

The pattern of the antenna under test is determined by rotating it and fixing the field level with the required accuracy. To improve accuracy, it is preferable to perform readings in decibels.

B. Adjusting the level of side lobes. By definition, the first side petals are those closest to the main petal. To fix their position, it is necessary to measure the angle in degrees or radians between the direction of the main radiation and the direction of the maximum radiation of the first left or right lobe. The directions of the left and right side lobes should be the same due to the symmetry of the pattern, but in an experimental pattern this may not be the case. Next, you also need to determine the width of the side lobes. It can be defined as the difference between the pattern zeros to the left and right of the side lobe. Here one should also expect symmetry, but only theoretically. In Fig. Figure 5 shows experimental data on determining the side lobe parameters.

As a result of a series of measurements, the position of the strips for the P2P-23-YXA antenna was determined, which are determined by the distance (1.20-1.36)^ from the axis of symmetry of the antenna to the strip.

After determining the side lobe parameters, the position of the stripes is determined. The corresponding calculations are performed for both theoretical and experimental patterns using the same method, described below and illustrated in Fig. 6.

Constant d is the distance from the axis of symmetry of the parabolic antenna to the strip located on the surface of the aperture of the parabolic mirror, determined by the following relationship:

„d<Ф = ъ,

where d is the experimentally measured distance from the point of symmetry on the surface of the mirror to the strip (Fig. 5); 0 - the angle between the direction of the main radiation and the direction of the maximum of the side lobe found experimentally.

The range of C values is found by the relationship: c! = O/dv

for values of 0 corresponding to the beginning and end of the side lobe (corresponding to the zeros of the pattern).

After determining the range C, this range is divided into a number of values, from which the optimal value is experimentally selected

Rice. 4. Experimental setup

Rice. 5. Experimental determination of side lobe parameters Fig. 6. Strip positioning method

Results

Several positions of the strips were tested. When moving the strips away from the main lobe, but within the found range C, the results improved. In Fig. Figure 7 shows two patterns without stripes and with stripes, demonstrating a clear decrease in the level of side lobes.

In table Table 1 shows comparative parameters of the pattern in terms of the level of the side lobes, directivity and width of the main lobe.

Conclusion

Reduction in the level of side lobes when using strips - by 23 dB (level of side lobes of an antenna without strips -

12.43 dB). The width of the main petal remains almost unchanged. The method discussed is very flexible, since it can be applied to any antenna.

However, a certain difficulty is the influence of multipath distortions associated with the influence of the ground and surrounding objects on the pattern, which leads to a change in the level of the side lobes up to 22 dB.

The method discussed is simple, inexpensive and can be completed in a short time. In the following we will try to add additional stripes in different positions and examine the absorption stripes. In addition, work will be carried out on the theoretical analysis of the problem using the method of geometric diffraction theory.

Far field radiation pattern of the antenna P2F- 23-NXA linear magnitude - polar plot

Rice. 7. DN antenna P2F-23-NXA without stripes and with stripes

Antenna comparison parameters

Side lobe level

Theoretical pattern (program Ma11a) pattern according to technical documentation 18 dB 15 dB

Measured pattern without stripes 12.43 dB

Measured pattern with stripes With multipath Without multipath

Main lobe width in degrees D D, dB

Theoretical DN (program Ma^ab) 16,161.45 22.07

DN for technical documentation 16,161.45 22.07

Measured pattern without stripes 14,210.475 23.23

Measured pattern with stripes 14,210.475 23.23

Literature

1. Balanis. C Antenna Theory. 3rd Ed. Wiley 2005.

2. IEEE standard test procedures for antennas IEEE Std. 149 - 1965.

3. http://www.thefreedictionary.com/lobe

4. Searle AD., Humphrey AT. Low sidelobe reflector antenna design. Antennas and Propagation, Tenth International Conference on (Conf. Publ. No. 436) Volume 1, 14-17 April 1997 Page(s):17 - 20 vol.1. Retrieved on January 26, 2008 from IEEE databases.

5. Schrank H. Low sidelobe reflector antennas. Antennas and Propagation Society Newsletter, IEEE Volume 27, Issue 2, April 1985 Page(s):5 - 16. Retrieved on January 26, 2008 from IEEE databases.

6. Satoh T. shizuo Endo, Matsunaka N., Betsudan Si, Katagi T, Ebisui T. Sidelobe level reduction by improvement of strut shape. Antennas and Propagation, IEEE Transactions on Volume 32, Issue 7, Jul 1984 Page(s):698 - 705. Retrieved on January 26, 2008 from IEEE databases.

7. D. C Jenn and W. V. T. Rusch. "Low sidelobe reflector design using resistive surfaces," in IEEE Antennas Propagat., Soc./URSI Int. Symp. Dig., vol. I, May

1990, p. 152. Retrieved on January 26, 2008 from IEEE databases.

8. D. C Jenn and W. V. T. Rusch. "Low sidelobe reflector synthesis and design using resistive surfaces," IEEE Trans. Antennas Propagat., vol. 39, p. 1372, Sept.

1991. Retrieved on January 26, 2008 from IEEE databases.

9. Monk A.D., and Cjamlcoals P.J.B. Adaptive null formation with a reconfigurable reflector antenna, IEEE Proc. H, 1995, 142, (3), pp. 220-224. Retrieved on January 26, 2008 from IEEE databases.

10. Lam P., Shung-Wu Lee, Lang K, Chang D. Sidelobe reduction of a parabolic reflector with auxiliary reflectors. Antennas and Propagation, IEEE Transactions on. Volume 35, Issue 12, Dec 1987 Page(s):1367-1374. Retrieved on January 26, 2008 from IEEE databases.

GOST R 50867-96

Group E58

STATE STANDARD OF THE RUSSIAN FEDERATION

ANTENNAS FOR RADIO RELAY COMMUNICATION LINES

Classification and general technical requirements

Antennas of microwave telecommunication lines.
Classification and main technical requirements

OKS 33.060.20
OKSTU 6577

Date of introduction 1997-01-01

Preface

1 DEVELOPED AND INTRODUCED by the Ministry of Communications of the Russian Federation

2 ADOPTED AND ENTERED INTO EFFECT by Resolution of the State Standard of Russia dated March 21, 1996 N 193

3 INTRODUCED FOR THE FIRST TIME

1 AREA OF APPLICATION

This standard applies to radio relay line (RRL) antennas designed for receiving (transmitting) electromagnetic energy in the frequency ranges allocated for RRL.

The standard establishes general technical requirements for the range of electrical parameters and the design of RRL antennas, and defines methods for measuring electrical parameters.

2 REGULATORY REFERENCES

3 DEFINITIONS

For the purposes of this standard, the following terms and corresponding definitions apply.

3.1 OPERATING FREQUENCY RANGE - a band limited by the upper and lower operating frequencies, within which the specified electrical parameters of the antenna remain unchanged or change within acceptable limits.

3.2 PROTECTIVE ACTION - a decrease in the signal received by the antenna from the direction opposite to the main one or in a certain specified sector of angles, compared to the same signal received in the main direction.

3.3 GUARANTEED DIRECTIONAL DIAGRAM - the envelope of the peak values of the lobes of the real radiation pattern.

Note - It is allowed to exceed the level of the guaranteed radiation pattern by no more than 3 dB and by no more than 10% of the side lobe peaks of the actual radiation pattern.

3.4 RELATIVE PROTECTIVE ACTION - protective effect reduced to the radiation level of an isotropic antenna.

3.5 Other terms are in accordance with GOST 24375.

4 CLASSIFICATION

4.1 Based on the number of mirrors used in the circuit, antennas are divided into single-mirror, consisting of a main mirror and a feed, double-mirror, consisting of a main and auxiliary mirrors and a feed, and multi-mirror, consisting of a main and two or more auxiliary mirrors and a feed.

4.2. Based on the location of the feed, antennas are divided into axisymmetric, when the feed system is located along the focal axis in the center of the antenna aperture, and non-axisymmetric (with a remote feed), when the feed system is shifted relative to the center of the antenna aperture.

4.3 Based on the number of operating bands, antennas are divided into single-, dual- and multi-band.

4.4 Based on quality indicators (mainly in terms of noise immunity), antennas, in accordance with the international classification, are divided into three main categories - standard, high-quality and ultra-high-quality.

Note - In addition to the main categories listed, there are categories of antennas that are improved in one of the parameters.

4.5. Based on the number of operating polarizations, antennas are divided into single-polarization, operating on one polarization, and dual-polarization, operating on two polarizations.

4.6 Based on the number of operating directions, antennas are divided into single-beam, operating in one direction, and angularly spaced, operating in two or more directions.

5 TECHNICAL REQUIREMENTS

5.1 General requirements

Antennas must comply with the requirements of this standard and the specifications for the specific antenna type.

5.2 Electrical requirements

5.2.1 When developing, constructing and manufacturing antennas, the following electrical parameters must be standardized:

- operating frequency range;

- polarization characteristics;

- gain;

- indicator of matching of the antenna with the feeder path;

- width of the main lobe at half power level;

- width of the main lobe at zeros or at level minus 15 or minus 20 dB;

- level of the first side lobe;

- protective effect;

- the level of cross-polarization maxima or the maximum level of cross-polarization radiation in a given spatial sector of angles near the direction of the main radiation;

- level of lateral radiation in a circular or specified sector of angles.

Note - The specified parameters are subject to control during certification tests of antennas.

5.2.2 The operating range of a specific RRL antenna must correspond to the operating range of the radio relay communication system in which the antenna is to operate*.
______________
* The operating range of the radio relay communication system is established in accordance with the International Radio Communications Regulations, the Russian table of distribution of frequency bands between services and the relevant decisions of the State Committee for Radio Frequencies of Russia.

The operating band width of the operating range is limited by the lower and upper frequencies.

5.2.3 Polarization of RRL antennas must be linear, horizontal and/or vertical.

Note - If necessary, operation on rotating polarization is acceptable.

5.2.4 The antenna gain must be set at one (middle) or three (extreme and middle) frequencies of the operating range or in the form of the minimum permissible value within the entire operating range, separated, if necessary, by polarization.

The gain must be specified in decibels.

5.2.5 The indicator of antenna matching with the feeder path must be specified by the voltage standing wave ratio (VSWR) in the form of the maximum permissible value within the operating range, separated, if necessary, by polarization.

Note - It is possible to set the matching indicator in the form of a reflection coefficient.

5.2.6 The width of the main lobe at half power level should be set at one (middle) or three (extreme and middle) frequencies of the operating range, separated, if necessary, by plane and polarization.

Note - If necessary, set the width of the main lobe and the zeros or the level of minus 15 or minus 20 dB.

5.2.7 The level of the first side lobe should be specified as the maximum permissible value within the operating range, separated, if necessary, by plane and polarization.

5.2.8 The protective effect of the antenna must be specified as the minimum permissible value within the operating range, separated, if necessary, by plane and polarization.

5.2.9 The level of cross-polarization maxima or the level of cross-polarization radiation in a given spatial sector of angles near the direction of the main radiation should be specified as the maximum permissible value within the operating range, separated, if necessary, by plane and polarization.

5.2.10 The level of lateral radiation must be specified in the form of guaranteed patterns (main and cross-polarization) simultaneously for both polarizations or with separation by polarizations in the horizontal or horizontal and vertical, or in several of the most characteristic planes.

5.2.11 The level of the first side lobe, the level of cross-polarization maxima (or the level of cross-polarization radiation in a given spatial sector of angles near the direction of the main radiation) and the level of side radiation are specified in decibels relative to the level of radiation in the main direction.

5.2.12 Separation of parameters by planes (the main ones are horizontal and vertical) and polarizations (planes and ) is used in the case when the difference in the values of the parameters exceeds the specified accuracy.

5.2.13 In addition to the main parameters specified in 5.2.1, derived parameters can be set - the coefficient of utilization of the opening surface and the relative protective effect.

5.2.14 When additional elements are included in the antenna - waveguide transitions, bends, weatherproof shelter, etc., affecting the electrical parameters, the value of each of the electrical parameters must be set taking into account their influence, if these elements form an integral part of the antenna , if, depending on the inclusion of additional elements, there are several versions of the antenna, then the values of all or only the parameters dependent on the antenna version must be indicated separately for each version.

5.2.15 Standards for the electrical parameters of antennas are determined when designing specific radio relay communication systems, depending on the length of RRL spans, propagation conditions and parameters of the equipment used (transmitter power, receiver sensitivity, etc.), purpose of communication systems (backbone, zone), number of channels (multi-channel or few-channel), the method of modulation used (analog or digital), electromagnetic compatibility requirements, etc. and are indicated in the technical specifications for a specific type of antenna.

5.2.16 Approximate values of the main parameters of antennas used in RRL are given in Appendix A.

5.2.17 General requirements for measurements of antenna parameters are set out in Appendix B.

5.3 Design requirements

5.3.1 The antenna design must include a mirror, a feeder and elements for attaching the antenna to the supporting structure.

Note - The antenna may include a stand and an adjustment device.

5.3.2 The weight and overall dimensions of the antenna should be minimized.

5.3.3 The direction of the waveguide output of the feed (horizontal, vertical, inclined) must be set depending on the design parameters of the system as a whole.

5.3.4 The output of the feeder must have a standard size and connector that ensures connection with the corresponding elements of the feeder path or radio relay equipment. The requirements for the output of the feed are established in the technical specifications for a particular type of antenna.

5.3.5 The waveguide path of the feed, if necessary, must be sealed and tested at excess air pressure specified in the technical specifications for a particular type of antenna.

5.3.6 The design of the antenna must ensure mechanical strength and standards for electrical parameters established in the technical specifications when operating the antenna in specified climatic regions at a given installation height.

5.3.7 The antenna must maintain the electrical parameters specified by the technical specifications and must not have mechanical damage after transportation tests determined by the technical specifications for a specific type of antenna.

5.3.8 The service life of the antenna, unless otherwise specified by special conditions, must be at least 20 years.

5.3.9 Requirements for marking and packaging must be specified in the technical specifications for a specific type of antenna.

5.3.10 The antenna design must be provided with a load-catching hole for lifting, lowering and holding it suspended during installation and repair work.

5.3.11 In the design of non-axisymmetric antennas, it is advisable to provide for the possibility of their visual adjustment.

5.3.12 Elements of the antenna structure must not have sharp edges, corners or surfaces that pose a source of danger, except as specified in the design documentation.

5.3.13 The antenna design must provide convenient access to elements that require special monitoring or replacement during operation.

5.3.14 The maximum permissible antenna installation height is determined depending on the requirements of the system in which it must operate.

5.3.15 In the absence of special requirements, antennas must be designed to operate in V wind, IV snow and ice regions at ambient temperatures from minus 50 to +50 °C and humidity 100% at a temperature of +25 °C.

5.4 Requirements for electromagnetic compatibility, environmental safety and electrical safety

5.4.1 The level of lateral radiation of newly developed, modernized and purchased abroad antennas, which determines the electromagnetic compatibility of communication systems, must comply with the requirements given in Appendix B.

5.4.2 Requirements for environmental safety and electrical safety are determined by the technical specifications for radio relay equipment of a particular type.

APPENDIX A (for reference). ESTIMATED VALUES OF THE MAIN PARAMETERS OF ANTENNAS CURRENTLY USED IN RRL

APPENDIX A
(informative)

A.1 The gain of RRL antennas ranges from 20 to 50 dB.

Note - If necessary, antennas with both lower and higher gain values can be used.

A.2 The VSWR of antennas used for operation in high-capacity backbone radio relay systems and in systems with an extended waveguide path ranges from 1.04 to 1.08.

The VSWR of antennas used for operation in zone systems and systems that do not have an extended waveguide path (the equipment is directly connected to the antenna input) ranges from 1.15 to 1.4.

Note - It is advisable to use antennas with low VSWR values, incl. and below the specified lower limits.

A.3 The width of the main lobe at the half-power level of single-beam highly directional RRL antennas ranges from fractions of a degree to several degrees.

A.4 The level of lateral radiation of RRL antennas corresponds to the reference radiation patterns given in Appendix B.

A.5 The relative protective effect of standard antennas is from 0 to 10 dB, high-quality - from 10 to 20 dB, ultra-high-quality - from 20 to 40 dB.

Note - It is advisable to use antennas with a higher protective effect.

A.6 The first side lobe level is from minus 15 to minus 30 dB.

Note - It is advisable to use antennas with a low level of the first side lobe, incl. and below the specified lower limit.

A.7 The level of cross-polarization maxima (or the level of cross-polarization radiation in a given spatial sector of angles near the direction of the main radiation) ranges from minus 15 to minus 30 dB, and when operating simultaneously on two polarizations - from minus 30 to minus 35 dB.

Note - It is advisable to use antennas with low cross-polarization peaks.

A.8 The coefficient of utilization of the opening surface of RRL antennas ranges from 0.4 to 0.7 (from 40 to 70%).

Note - It is advisable to use antennas with a high utilization factor, incl. and more than the upper limit specified above.

APPENDIX B (recommended). GENERAL REQUIREMENTS FOR MEASUREMENTS OF ANTENNA PARAMETERS

B.1 Antenna measurements are carried out at a specially equipped test site or in anechoic chambers coated with a special absorbing material. The location and method of measurements are chosen taking into account the required accuracy in determining the values of the measured parameters in the operating frequency range.

B.2 When making measurements, unless specifically stated in the technical specifications for an antenna of a particular type, standard measurement circuits and standard measuring equipment must be used to ensure the necessary accuracy of the measured values in the operating frequency range.

B.3 Examples of typical schemes for measuring radiation patterns and gain are shown in Figures B.1-B.3.

Note - It is allowed to use other circuits and methods for measuring electrical parameters that ensure the measurement accuracy specified by the technical specifications for an antenna of a particular type.

B.4 The following parameters are subject to direct measurement:

- gain;

- standing wave ratio;

- directional patterns (main and cross-polarization).

Figure B.1 - Block diagram of measuring radiation patterns (measuring

Broadcast

1 - generator; 2, 8 - high-frequency cable; 3, 7, 9 - coaxial-waveguide transition; 4 - ferrite valve; 5 - measuring (polarization) attenuator; 6 - decoupling attenuator; 10 - waveguide transition from round to rectangular cross-section; 11 - auxiliary (transmitting) antenna.

Reception

12 - antenna under test; 13 - waveguide transition from round to rectangular cross-section; 14 - coaxial-waveguide transition; 15 - high-frequency cable; 16 - measuring receiver; 17, 19 - low-frequency cable; 18 - amplifier; 20 - recorder.

Notes

Figure B.1 - Block diagram of measuring radiation patterns (measuring
attenuators are located on the transmission)

Figure B.2 - Block diagram of radiation pattern measurement (measuring attenuators are located at the reception)

Broadcast

1 - generator; 2 - high-frequency cable; 3 - coaxial-waveguide transition; 4 - waveguide transition from round to rectangular cross-section; 5 - auxiliary (transmitting) antenna.

Reception

6 - antenna under test; 7 - waveguide transition from round to rectangular cross-section; 8, 10 - decoupling attenuator; 9 - measuring (polarization) attenuator; 11 - detector section; 12, 14 - low-frequency cable; 13 - low-frequency amplifier; 15 - recorder.

Notes

1 When using a waveguide path with flexible waveguide inserts and transmitting and receiving equipment with waveguide inputs (outputs), high-frequency and coaxial-waveguide transitions are excluded from the circuit.

2 If the waveguide output of the feed has a rectangular cross-section, waveguide transitions from round to rectangular cross-section are not used.

Figure B.2 - Block diagram of measuring radiation patterns (measuring
attenuators are located at the reception)

Figure B.Z - Block diagram of gain measurement (measuring attenuators are located on the transmission)

Broadcast

12 - antenna under test; 13, 15 - waveguide transition from round to rectangular cross-section; 14 - measuring (reference) antenna; 16 - decoupling attenuator; 17 - measuring section; 18 - low-frequency cable; 19 - low-frequency amplifier.

Notes

2 If the waveguide output of the feed has a rectangular cross-section, waveguide transitions from round to rectangular cross-section are not used.

Figure B.Z - Block diagram of gain measurement (measuring
attenuators are located on the transmission)

B.5 Based on the main radiation patterns, the width of the main lobe is determined at half power level and at zeros (or at a level of minus 15 or minus 20 dB), the level of the first side lobe, the level of side radiation and guaranteed radiation patterns at the main polarization.

B.6 Using cross-polarization radiation patterns, the level of cross-polarization maxima and/or the level of cross-polarization radiation in a given spatial sector of angles near the direction of the main radiation, the level of lateral radiation and guaranteed cross-polarization radiation patterns are determined.

B.7 The following parameters are indirectly determined:

- protective effect;

- coefficient of utilization of the opening surface;

- relative protective effect.

B.8 The scope of measurements is determined by the technical specifications for a particular type of antenna.

B.9 Methods for measuring antennas of specific types must be specified in the technical specifications for the antenna of a specific type.

APPENDIX B (recommended). REFERENCE DIRECTIVE DIAGRAMS OF ANTENNAS FOR LINE OF VISIBILITY RADIO RELAY SYSTEMS

B.1 Reference radiation patterns in accordance with the Recommendation* are used in the absence of real radiation patterns to resolve electromagnetic compatibility issues, namely:

- during a preliminary study of issues of eliminating sources of interference in the coordination zone;

- when reusing radio frequencies in a radio relay network, when the same radio frequencies can be repeatedly used either in areas significantly distant from each other, or in sections of lines diverging from one station in different directions, or in one area using cross-polarization.
______________
* As the ITU Assembly changes Recommendation 699, newer editions of it should be used, taking into account the latest developments in the field of antenna design and construction after 1994.

B.2 Reference radiation patterns are envelopes of the peaks of the lobes of real radiation patterns of the most typical and most frequently used (at the time of adoption of the last edition of the above recommendation) antennas of line-of-sight radio relay systems, while it is assumed that a small percentage of the peaks of the side lobes of real radiation patterns may exceed level limited by the reference diagram.

B.3 Reference radiation patterns cannot serve as a maximum permissible value for developers and potential consumers, limiting the level of lateral radiation from below or above, however, they can be a guideline for them when assessing the quality of newly developed or purchased antenna equipment relative to a certain average world level.

B.4 To increase throughput, it is advisable to use antennas with better (compared to reference) radiation patterns.

Note - It is also possible to use antennas with worse radiation patterns (in this case, when solving issues of electromagnetic compatibility, only real radiation patterns should be used).

B.5 In accordance with the decision of the ITU Radiocommunication Assembly (Recommendation), in the absence of specific antenna pattern information, the reference patterns below should be used in the frequency range 1-40 GHz.

B.5.1 In the case where the ratio of the diameter of the radio relay antenna to the operating wavelength is , the expression should be used

where is the gain relative to the isotropically radiating antenna;

- angle of deviation from the axis;

- gain of the main lobe relative to the isotropically radiating antenna, dB;

and - antenna diameter and wavelength, expressed in the same units;

- gain of the first lobe

The width of the pattern (main lobe) determines the degree of concentration of the emitted electromagnetic energy.

The width of the pattern is the angle between two directions and within the main lobe, in which the amplitude of the electromagnetic field strength is a level of 0.707 from the maximum value (or a level of 0.5 from the maximum power density value).

The width of the pattern is designated as follows: 2θ 0.5 is the width of the pattern in terms of power at the level of 0.5; 2θ 0.707 - width of the pattern according to the intensity at the level of 0.707.

The index E or H shown above means the width of the pattern in the corresponding plane: , . A level of 0.5 in power corresponds to a level of 0.707 in field strength or a level of 3 dB on a logarithmic scale:

The beam width of the same antenna, represented by field strength, power or logarithmic scale and measured at the corresponding levels, will be the same:

Experimentally, the width of the pattern can be easily found from the graph of the pattern depicted in one or another coordinate system, for example, as shown in the figure.

The level of the side lobes of the pattern determines the degree of spurious radiation of the electromagnetic field by the antenna. It affects the secrecy of the operation of a radio-technical device and the quality of electromagnetic compatibility with nearby radio-electronic systems.

Relative sidelobe level is the ratio of the field strength amplitude in the direction of the sidelobe maximum to the field strength amplitude in the direction of the main lobe maximum:

In practice, this level is expressed in absolute units, or in decibels. The level of the first side lobe is of greatest interest. Sometimes they operate with the average level of side lobes.

4. Directional coefficient and gain of the transmitting antenna.

The directional coefficient quantitatively characterizes the directional properties of real antennas in comparison with a reference antenna, which is a completely omnidirectional (isotropic) emitter with a spherical pattern:

The efficiency factor is a number showing how many times the power flux density P(θ,φ) of a real (directional) antenna is greater than the power flux density

PE (θ,φ) of the reference (omnidirectional) antenna for the same direction and at the same distance, provided that the radiation powers of the antennas are the same:

Taking into account (1) we can obtain:

where D 0 is the directivity in the direction of maximum radiation.

In practice, when talking about antenna efficiency, we mean a value that is completely determined by the antenna radiation pattern:

In engineering calculations, an approximate empirical formula is used that relates the directivity factor to the width of the antenna pattern in the main planes:

Since in practice it is difficult to determine the radiation power of an antenna (and even more so to fulfill the condition of equality of the radiation powers of the reference and real antennas), the concept of antenna gain is introduced, which takes into account not only the focusing properties of the antenna, but also its ability to convert one type of energy into another .

This is expressed in the fact that in a definition similar to the efficiency factor, the condition changes, and it is obvious that the efficiency of the reference antenna is equal to unity:

where P A is the power supplied to the antenna.

Then the directional coefficient is expressed through the directional coefficient as follows:

where η A is the antenna efficiency.

In practice, G 0 is used - the antenna gain in the direction of maximum radiation.

5. Phase radiation pattern. The concept of the phase center of the antenna.

The phase radiation pattern is the dependence of the phase of the electromagnetic field emitted by the antenna on the angular coordinates. Since in the far zone of the antenna the field vectors E and H are in phase, the phase pattern is equally related to the electrical and magnetic components of the EMF emitted by the antenna. FDN is designated as follows:

Ψ = Ψ (θ,φ) for r = const.

If Ψ (θ,φ) at r = const, then this means that the antenna forms the phase front of the wave in the form of a sphere. The center of this sphere, where the origin of the coordinate system is located, is called the phase center of the antenna (PCA). Not all antennas have a phase center.

For antennas that have a phase center and a multi-lobe amplitude pattern with clear zeros between them, the field phase in adjacent lobes differs by (180 0). The relationship between the amplitude and phase radiation patterns of the same antenna is illustrated by the following figure.

Since the direction of propagation of electromagnetic waves and the position of its phase front are mutually perpendicular at each point in space, by measuring the position of the phase front of the wave, it is possible to indirectly determine the direction to the radiation source (direction finding by phase methods).

Let the current distribution along the length of the antenna be constant:

Real antennas (for example, slot waveguides) or printed antenna arrays often have exactly this current distribution. Let's calculate the radiation pattern of such an antenna:

Now let's build a normalized pattern:

(4.1.)

Rice. 4.3 Radiation pattern of a linear antenna with uniform current distribution

The following areas can be distinguished in this radiation pattern:

1) The main lobe is the section of the radiation pattern where the field is maximum.

2) Side petals.

The following figure shows the radiation pattern in the polar coordinate system, in which
has a more visual appearance (Fig. 4.4).

Rice. 4.4 Radiation pattern of a linear antenna with uniform current distribution in a polar coordinate system

A quantitative assessment of the antenna directivity is usually considered to be the width of the main lobe of the antenna, which is determined either by a level of -3 dB from the maximum or by zero points. Let's determine the width of the main lobe based on the level of zeros. Here we can approximately assume that for highly directional antennas:
. The condition for the system multiplier to be equal to zero can be approximately written as follows:

Considering that
, the last condition can be rewritten this way:

For large values of the electrical length of the antenna (for small values of the half-width of the main lobe of the antenna), taking into account the fact that the sine of the small argument is approximately equal to the value of the argument, the last relation can be rewritten as:

From where we finally get the relationship connecting the width of the main lobe and the size of the antenna in fractions of the wavelength:

An important conclusion follows from the last relationship: for a common-mode linear antenna at a fixed wavelength, increasing the antenna length leads to a narrowing of the radiation pattern.

Let's estimate the level of side lobes in this antenna. From relation (4.1) we can obtain the condition for the angular position of the first (maximum) side lobe:

(-13 dB)

It turns out that in this case the level of the side lobes does not depend on the antenna length and frequency, but is determined only by the type of amplitude current distribution. To reduce the UBL, one should abandon the accepted type of amplitude distribution (uniform distribution), and move to a distribution that decreases towards the edges of the antenna.

5. Linear antenna array

5.1. Deriving the expression for day lar

Expression 4.2. allows you to easily move from the field of a linear continuous antenna system to the field of a discrete antenna array. To do this, it is enough to specify the current distribution under the integral sign in the form of a lattice function (a set of delta functions) with weights corresponding to the excitation amplitudes of the elements and the corresponding coordinates. In this case, the result is the antenna array radiation pattern as a discrete Fourier transform. Master's students are left to implement this approach independently as an exercise.

6. Synthesis of afr on a given day.

6.1. Historical review, features of antenna synthesis problems.

Often, to ensure the correct operation of radio systems, special requirements are imposed on the antenna devices that are part of them. Therefore, designing antennas with specified characteristics is one of the most important tasks.

Basically, the requirements are imposed on the radiation pattern (DP) of the antenna device and are very diverse: a specific shape of the main lobe of the pattern may be required (for example, in the form of a sector and cosecant), a certain level of side lobes, a dip in a given direction or in a given range of angles. The section of antenna theory devoted to solving these problems is called antenna synthesis theory.

In most cases, an exact solution to the synthesis problem has not been found and we can talk about approximate methods. Such problems have been studied for quite a long time and many methods and techniques have been found. Methods for solving antenna synthesis problems are also subject to certain requirements: speed; sustainability, i.e. low sensitivity to minor changes in parameters (frequency, antenna sizes, etc.); practical feasibility. The simplest methods are considered: partial diagrams and the Fourier integral. The first method is based on the analogy of the Fourier transform and the connection between the amplitude-phase distribution and the pattern; the second method is based on the expansion of the pattern series into basis functions (partial patterns). Often, the solutions obtained by these methods are difficult to apply in practice (antennas have poor instrumentation characteristics, the amplitude-phase distribution (APD) is difficult to implement, the solution is unstable). Methods are considered that allow taking into account restrictions on PRA and avoiding the so-called. "overdirectional effect".

Separately, it is worth highlighting the problems of mixed synthesis, the most important of which is the problem of phase synthesis, i.e. finding the phase distribution for a given amplitude, leading to the required pattern. The relevance of phase synthesis problems can be explained by the widespread use of phased antenna arrays (PAA). Methods for solving such problems are described in, and.