The half-wave symmetric dipole

Размещено на http://www.allbest.ru/

Introduction

The present a term paper is devoted to calculation of low-noise one-optical-type parabolic antennas which find broad application in space and radio relay communication links, and also in a radio astronomy. The specifics of satellite communication consisting in the big extent of routes between the artificial satellites of Earth (ASE) and the terrestrial stations (TS), the considerable weakening of radio signals on these trasses impose serious requirements to a design and parameters of optical-type antennas. Decrease in influence of external hindrances (radiation of Earth, land radio services and other radio engineering systems) requires increase of noise immunity of antennas and decrease in level of side lobes.

Sufficient simplicity and ease of a design, possibility of formation of the most various directional diagrams, high к.п.д., small noise temperature - here the main advantages of optical-type antennas causing their broad application in the modern radio systems.

The purpose of this term paper is development by students of a technique of projection of optical-type parabolic antennas: determination of their key electrodynamic parameters and design calculation.

In a term paper definition of a radiation field of the parabolic antenna is made by an aperture method, widely applicable at projection of optical-type antennas. The technical parameters set for projection of the antenna are specified according to Regulations of a radio communication [5] and meet the practical requirements to the modern systems of a radio communication. The optical-type antennas designed according to the given parameters can be applied in satellite and radio relay communication links: NERA, Pasolink, Radian; small stations for a telephony and data transmission (VSAT); systems of a satellite television broadcasting (Eutelsat, Tack, Telecom IIA, B, Tele-X, TVSat-2, etc.).



Task

The explanatory note of 20-25 sheets of the hand-written text which enter:

a) title page;

b) requirement specification;

c) calculation of geometrical and electrodynamic parameters of an irradiator and paraboloid proceeding from the greatest relation signal/noise;

d) calculation of spatial structure of the directional diagram (DD) of the parabolic antenna;

e) calculation of noise temperatures of antenna system;

e) calculation of key parameters of the antenna: coefficient of a directional effect (CDE), intensification coefficient (IC), efficiency (E);

g) design calculation of the antenna.

Graphic part into which enter:

a) amplitude DN of an irradiator across the field in a polar frame in the planes E and H;

b) amplitude DN of the parabolic antenna to a field in a rectangular frame in the planes E and H;

c) distribution of amplitude of a field in a mirror aperture;

d) design drawing of the antenna.

Given data for option 95:

antenna parabolic focal diagram

Table 1 - Working frequency of f, GHz

Penultimate figure of the record book	Year
1	2	3	4	5	6	7	8	9	0
1.0	1.2	1.4	1.6	1.8	2.0	4.0	6.0	8.0	0.0	even
1.1	1.3	1.5	1.7	1.9	2.1	2.5	3.0	4.5	5.0	odd

Table 2 - DN width at the level of half power 2н0,5, mrad

Last figure of the record book	Year
DN width	1	2	3	4	5	6	7	8	9	0
2н0,5	43	46	39	53	57	61	65	67	72	76	even
2Е0,5	48	51	54	58	62	66	70	72	77	81	even
2н0,5	48	51	54	58	62	66	70	57	77	81	odd
2Е0,5	53	56	59	63	67	71	75	72	82	86	odd

Table 3 - Irradiator type

First letter of a surname of the student, even year	Irradiator type	First letter of a surname of a student, odd year
Ю, А, Г, В, Я, Ы	Half-wave dipole with a counterreflector in the form of a core	А, Ж, Н, У, Щ
Э, Д, Б, Е, Л, К	Half-wave dipole with a disk counterreflector	Б, З, О, Ф, Э, К
М, О, Ж, З, И, Ч	Loud-hailer pyramidal	В, И, П, Х, Ю, Г
Н, П, Р, У, Ф	Open end of a rectangular wave guide	Д, Л, С, Р, Ч, Ы
Т, Х, С, Ц, Ш, Щ	Loud-hailer conic	Е, М, Т, Ш, Я, Ц

Table 4 - Level of side petals [dB]

Last figure of the record book	Year
1	2	3	4	5	6	7	8	9	0
-15	-16	-17	-18	-19	-20	-21	-22	-23	-24	even
-19	-20	-21	-22	-23	-24	-25	-26	-27	-28	odd

Table 5 - Average brightness temperature of a palate Tnsr, оК

Penultimate figure of the record book	Year
1	2	3	4	5	6	7	8	9	0
5	6	7	9	10	11	12	13	14	15	Even
15	13	12	11	10	9	8	7	6	5	odd

Table 6 - Temperature of noise of the receiver Tpr, оК

Last figure of the record book	Year
1	2	3	4	5	6	7	8	9	0
2000	1900	1800	1700	2300	1600	1500	1400	2100	2200	even
2300	2200	2100	2000	1900	1800	1700	1600	1500	1300	odd

Table 7 - Length of the feeding lф line, m

Penultimate figure of the record book	Year
1	2	3	4	5	6	7	8	9	0
5	6	7	10	8	15	13	12	14	11	even
6	10	14	8	7	11	15	5	12	13	odd



1 Solution

е0=10-9/(36?р)=8.842?10-12 F/m

м0=4?р?10-7=1.257?10-6

щ=2рf

щ=13.188?109 rad

Feeder choice. Determination of noise temperature of the feeding highway Тф and efficiency

Determination of noise temperature of the feeding highway Тф and efficiency is made on formulas

Тф=67оlф=67

where - damping factor of a transmission line [dB/m];

B/m

lф - length of the feeding line [m].

Тф=Т0(1-КПД) => КПД =1-(5.52013/290)

where Т0=2900 К.

Calculation of noise temperature of antenna system is carried out on formulas

Та= Тф+КПДТнср+КПДТ0(1-1+ 1u)=5,52013+0.981

where u=(0.02 - 0.03) - the coefficient considering "transfusion" of part of power of an irradiator through edges of a mirror

1=1-cosn+10=1- cos2+1(64)=0.915,

0=2*arctg(R0/2f0)=64

R0/f0=1.25

N=6 - is defined by irradiator type.

T=Tа+Tпр = 43.749+2000=2043.749K.

Determination of diameter of a opening

Optical-type antenna - the directional antenna containing primary radiator (further in the text an irradiator) and an antenna reflector in the form of a metal surface (mirror) [2]. The parabolic optical-type antenna is presented in figure 4.1.

Drawing 1-Reflecting parabolic antenna

In case of evenly exited opening of a parabolic mirror DN width approximately is defined [3]

20.5 1.02*R0 (4.1)

where 20.5 - directional diagram width at the level of half power, it is mrad.;

wavelength (accepted) antenna emitted radio signal;

R0 - reflector aperture radius (figure 4.1).

However it is not possible to achieve the uniform exaltation of a opening practically. It is known [3] that KND of an optical-type antenna has the greatest size in case amplitude of a stimulating field on the edge of a opening makes not less than one third of field amplitude in the center of a opening.

Nonuniform exaltation of reflector aperture leads to some expansion of the main petal of DN as the efficient area of a opening decreases. Besides, it must be kept in mind that most often directional diagrams of optical-type antennas do not possess a rotational symmetry (the majority of radiators form osenesimmetrichny directional diagrams), i.e. width of the main petal in the planes E and H is various. In the majority of practical cases it involves the following change of expression (4.1) [4]

2Н0.5 1.2*R0 (4.2)

2Е0.5 1.3*R0

From the system of equations R0

where 2Н0.5 , 2Е0.5 - DN width respectively in the plane N and E.

Because in a task for a term paper there are data on directional diagram width in both planes, from expressions (4.2) and (4.3) it is possible to determine diameter of a opening dp = 2 R0, and, it is necessary to choose the greatest from the received two values of diameter.

Determination corner of a opening and focal distance of an optical-type antenna

Depending on placement of an irradiator concerning a mirror it is possible to receive this or that value of KND. At the particular optimum relation of R0/f0 KND the greatest. This results from the fact that the amount of loss energy depends on a form of a directional diagram of an irradiator and on R0/f0 relation. At decrease of the relation of R0/f0 from optimum KND decreases as the part of the energy missing mirrors increases. On the other hand, the increase in this relation also leads to decrease of KND in connection with more strong rejection of the distribution law of exaltation from the uniform (figure 4.2); best value of R0/f0 is determined by the approximated normalized directional diagram of an irradiator (approximation by function of a look F() = cosn/2(), where n defines degree of elongation of DN of an irradiator). For various types of irradiators of value n are provided in table 4.1.Т а б л

Table 4.1

Irradiator type	n	R0/f0
1 The vibrator with a counterreflector in the form of a core	2	1.25...1.43	0.83
2 The vibrator with a counterreflector in the form of a disk	4	1.0...1.25	0.82
3 The funnel-shaped, etc. irradiators	6	0.8...1.0	0.81

Figure 2 - Options of placement of an irradiator

From the point of view of optimization of geometry of the antenna on the maximal relation signal/noise it is necessary to make the following calculation.

Sensitivity of is defined by a formula =S23КПД',

where the first four coefficients do not depend from 0, а ' determining

where Т1 =Тпр+Т0(1-КПД)+КПДТнср,

S- mirror aperture area.

S=12.9*6.5=83.85

'=4.5*10^-4

g=0.882

To the maximum the function constructed graphically (0) the reflector aperture corner (a step of change of a corner of a opening is defined 0 not less 1о).

The focal distance of f can be calculated on the basis of the following ratio:

0 = 2 arctg(R0/2f0)=64

Thus, the geometrical sizes of a mirror are defined.

The half-wave symmetric dipole with a counterreflector in the form of a disk

The phase center of the vibrator with a counterreflector in the form of a disk lies between the vibrator and a counterreflector slightly closer to the last. Usually counterreflectors are carried out in the form of disks by diameter 2d = (0.7 ... 0.8), thus DN has a form, the close to the chart to a rotational symmetry. The distance between the vibrator and a counterreflector gets out the close to a quarter of a wavelength, and vibrator length - to a half of a wavelength (2l /2).

The directional diagram of such irradiator in E planes pays off on a formula[11]

These formulas are fair for E and H less

The half-wave symmetric dipole with a counterreflector in the form of a core

The design of such irradiator is presented in figure 5.2. Here vibrator also half-wave 2l /2. The distance of d gets out in the range 0,1<d/< 0,25 , and counterreflector length 2a (1.05-1.1) 2l.

In this case DN are described by the following analytical expressions.

In Е plane

Figure 5.2 - The symmetric vibrator with a counterreflector in the form of a core

in Н plane

where the relation of amplitudes of currents in passive and fissile vibrators;

arctg - arctg phase shift between these currents;

- wave number.

Determination of active R12 and reactive X12 components of the relative resistance, and also the fissile R22 making resistance of radiation of a counterreflector are determined by schedules (figure 5.3) [4].

Figure 3 - Dependences of resistance of dipole irradiators on geometrical parameters.

Necessary size X22 it can be provided with connection of a jet loop and is defined from a condition =/2.

Calculation of a space directional diagram and determination of parameters of the parabolic antenna

Engineering calculation of space DN of the parabolic antenna is often reduced to definition of DN of an ideal round synphasic platform with a nonuniform distribution of strength of a stimulating field. In this case distribution of strength of a stimulating field, generally is defined by irradiator DN in the corresponding plane. Expression for the normalized DN of the optical-type parabolic antenna thus has an appearance [1, 2]

где J1,J2 - цилиндрические функции Бесселя первого и второго порядка;

k1 = = cos2(0/2)Fобл(0)- the coefficient showing in how many time amplitude of a stimulating field on the edge of a opening is less than amplitude in the center of a opening in the corresponding plane taking into account distinctions of distances from an irradiator to the center of a mirror and to edge of a mirror;

Eкр, Emax - weeding amplitudes on the edge and in the center opening.

To execute calculation of DN on the COMPUTER.

Approximately the coefficient of a directional effect of an optical-type antenna is defined by expression [1].

where S - are of opening

- resultant capacity factor of a surface.

Taking into account that efficiency of an optical-type antenna about 0,9, it is possible to calculate its intensification coefficient.

Precise determination of parameters of the antenna.

Surface capacity factor

Ки=g 1 2 3

where 2=(1-2 u)2

3=exp(-d2)



а/2R - accuracy of realization of a profile of a mirror (it is routine in limits 0,410-3- 10-5).

Efficiency area of antenna

Sэфф=R2Kи.

Directive factor

D=(2R/)2g123.

Antenna gain

G=КПДD.

Constructive calculation of the antenna

Calculation of a profile of a mirror

Mirror antennas have the greatest KND at inphase excitement of a opening (the flat phase front of a wave). The parabolic profile of a mirror provides identical lengths of electric ways from the irradiator established in focus of a paraboloid of rotation to each point of the plane of a opening (property of a parabola). In polar system of coordinates the parabola is described by the equation:

cos(64))=2.64*109

where - polar coordinates, f focal length.

In this case is changing from 0 to 0.

Mirror design choice

For the purpose of reduction of weight and wind loadings the surface of a mirror is often carried out punched or mesh (figure 7.1).



Figure 7.1. Design of mirror choice

At such design of a mirror the part of energy filters through it, forming the return undesirable radiation. Value of coefficient of passing in the opposite direction is admissible

where Pобр , Pпад - radiation power in the opposite direction and falling on a mirror, respectively. For the punched reflector diameter of openings has to be less 0,2 at the total area of openings no more than 0,5... 0,6 all areas of a mirror.

The two-linear grid works well at distance between conductors less 0,1 and diameter of wires not less 0,01.

Definition of admissions on production accuracy

Inaccuracy of production of a mirror causes not phase synchronism of a field in an opening. Phase distortions of a field in a mirror opening are admissible no more /4. Thus reduction of coefficient of strengthening of the antenna doesn't exceed several percent [3].

Let the surface of a paraboloid have some roughnesses (ledges and deepenings). The greatest deviation from an ideal surface in the direction we will designate through (figure 7.2).

Figure 7.2 - Admissions on the accuracy of production of a mirror

Way of the beam reflected from roughness in a place of the greatest deviation from, changes thus at a size cos, and the corresponding shift of phases will make size 1+cos), and he shouldn't exceed size /4, from here we receive

.

The analysis of the received expression for shows that near the center of a paraboloid (=0) necessary accuracy of production of a mirror the highest. Here the greatest deviation from an ideal surface shouldn't surpass size /16, at an edge of a paraboloid of the requirement to accuracy turn out the smallest.

Accuracy of installation of an irradiator is also defined by norms on the greatest admissible phase distortions of a field in a opening [6]. Let the phase center of an irradiator be displaced on x (figure 7.3).

Then lengths of ways of beams from the phase center increase to a opening. The greatest lengthening of a way happens at the beams falling on mirror top. This lengthening of ways at small shifts can be defined approximately as x сos . Then change of a phase will make size

where - the phase distortions arising because of inaccuracy of installation of an irradiator in the center and on the edge of a opening, respectively. This size shouldn't exceed 4, from here we receive that:

.Размещено на http://www.allbest.ru/

Thus, with increase in a corner of a opening the accuracy and installation of an irradiator in focus increases.

Figure 7.3 - Admissions on the accuracy of installation of an irradiator Conclusion

At the solution of settlement pf term paper, we determined parameters sufficient simplicity and ease of a design, possibility of formation of the most various directional diagrams, high к.п.д., small noise temperature - here the main advantages of optical-type antennas causing their broad application in the modern radio systems.

According to the obtained data the technical parameters set for projection of the antenna are specified according to Regulations of a radio communication [5] and meet the practical requirements to the modern systems of a radio communication. The optical-type antennas designed according to the given parameters can be applied in satellite. Optical-type antenna - the directional antenna containing primary radiator (further in the text an irradiator) and an antenna reflector in the form of a metal [2].

List of literature

1. Yerokhin G. A., etc. Antenna-feeder devices and distribution of radio waves. - M.:goryachy liniya-Telecom, 2004. - 496 pages.

2. Frolov O. Antennas for terrestrial stations of satellites of a radio communication. - M.: The higher school, 2000. - 376 pages.

3. Kocherzhevsky G. M., Yerokhin G. A., Kozyrev N. D. Antenna-feeder devices. - M.:Radio and communication, 1989. - 352 pages.

4. Hop V. F., Chaplin A.F., Shumlyansky I.I. Antennas and microwave ovens devices. - Kiev: Vishcha school, 1990. - 232 pages.

5. Regulations of a radio communication. T. 1. - M.: Radio and communication, 1995.-509 pages.

6. Satellite communication and a broadcasting / Under the editorship of the Cantor L.A. - M.: Radio and communication, 1997. - 526 pages.

Размещено на Allbest.ru

...