1、- CCIR RECMN*Lb2-3 92 W 4855232 0539LB5 T97 =. Rec. 162-3 255 3A b: Antennas characteristics RECOMMENDATION 162-3* USE OF DIRECTIONAL TRANSMI“ING ANTENNAS IN THE FIXED SERVICE OPERATING IN BANDS BELOW ABOUT 30 MHz (Question 15019) (1953-1956-1966-1970-1992) The CCIR, considering a) that there is ser
2、ious congestion in the fixed service bands between 4 and 28 ME; b) that occupancy of the radio-frequency spectrum is represented, not only by occupancy in bandwidth and time, but also by the spatial distribution of the radiated power: cl that radiation outside the directions necessary for the servic
3、e can be effectively reduced by the use of directional antennas; 4 that Articles 5, 18 and 19 of the Radio Regulations would seem to justify explicit requirements for the use of directional antennas in these bands: e) that the Panel of Experts, in Recommendation No. 13 of its Final Report, Geneva, 1
4、963, advocates the use of directional antennas for transmission and reception in the fured service; 0 that the request by the Panel of Experts in Recommendation No. 38 of its Final Report, and the urgent question of the FRB, Question 150/9, ask for specification of reasonable standards of directivit
5、y for antennas in the various types of radio services in the bands between 4 and 28 MHz, with due regard to economy of cost; that the adoption of minimum standards for directional antennas would contribute to the solution of frequency sharing problems: h) that antenna performance materially better t
6、han these minimum standards is attainable at economic cost using modern techniques, recommends that the following definitions should be used in specing the performance of directional antennas: 1. 1. 1 Direc tiviy, Go * * In a given direction, 4n times the ratio of the intensity of radiation (power p
7、er unit solid angle (steradian), in that direction, to the total power radiated by the antenna. 1.2 Service sector, S The horizontal sector containing the main beam of the antenna radiation and including the direction required for service. It is very close to twice the angular width of the main beam
8、 measured to the half-power (-3 dB) points. * This Recommendation should be brought to the attention of the IFRB. This text concludes the studies of Question 150/9. See No. 154 of the Radio Regulations for a definition of power gain. * COPYRIGHT International Telecommunications Union/ITU Radiocommun
9、icationsLicensed by Information Handling ServicesCCIR RECMN*Lb2-3 92 W Y855212 05L91b 923 = 256 Ree. 162-3 1.3 Interference sector, I The horizontal sector outside the main beam Io = 360“ -So 1.4 Minimum standard antenna The antenna having the specified minimum characteristics as regards directivity
10、 and service sector at its operating frequency or frequencies. 1.5 Economic standard antenna The antenna having the specified characteristics as regards directivity and service sector at its operating frequency or frequencies which are justifiable on economic grounds (i.e. by savings in the cost of
11、providing a given transmitter output power). 1.6 Antenna directivity factor, M* The ratio of the power flux-density in the wanted direction to the average value of power flux-density at crests in the antenna directivity pattern in the interference sector. This is equivalent to the average improvemen
12、t in signal-to-interference ratio achieved by using the actual antenna in place of an isotropic radiator in free space; 2. that the minimum standard antenna should have a directivity factor given by: M = 0.1fz f being the operating frequency in MHz; 3. that the economic standard antenna should have
13、a directivity factor given by: M = 0.25f2 4. that, for a radiated power of 5 kW or greater, the directivity factor, M, of the antenna used should be equal to or greater than that of the minimum standard antenna; 5. that, for a radiated power of 10 kW or greater, antennas having performances not wors
14、e than that of the economic standard antenna should be used to the extent practicable; 6. that, for transmitter powers below 5 kW, the power flux-density in the interference sector should not exceed that radiated in this sector from the minimum standard antenna with a total radiated power of 5 kW; 7
15、. that, in the interests of reducing the effects of interference, the directivity factor, M, of the receiving antenna should be equal to or greater than that of the minimum standard antenna and should, as far as practicable, attain that of the economic standard antenna. Furthermore, when calculated
16、gains, based on constant-current formulae, are used to determine the M-factor, adjustment should be made to ailow for the current decay along the actual antenna. Methods of making these adjustments are described in Annex 1. No preferred polarization or type of antenna is established. Horizontal pola
17、rization offers better ground reflection characteristics and, for receiving, some reduction of interference due to man-made noise. Where reflection over sea water or over earth of very high conductivity takes place, the use of vertical polarization can enhance the low-angle performance needed for lo
18、ng paths. This important consideration is reflected in the computation of M, which includes a weighting factor lO/A, where A is the vertical angle of optimum radiation. There is no requirement for the transmitting and receiving antennas to have the same polarization characteristics because of the ra
19、ndomization of the polarization in the ionospheric transmission process. * The derivation cf the directivity factor for any given antenna is explained in Annex 1 I COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesCCIR RECMN*Lb2-3 92 m 4
20、855212 0517187 BbT m 10 15 20 Rec. 162-3 257 10 16.6 39 25 20.4 25 22.5 18.3 32 57 22.1 21 40 19.4 28 100 23.3 18 The M-factors chosen are largely based upon the measured performance of typical rhombic antennas and typical antenna-arrays. The radiation characteristics of single rhombic antennas in t
21、he interference zone are, in general, somewhat inferior to other types of antenna (e.g. half-wave antenna arrays), a fact which is reflected in the M-factor. Provided the parameters are correctly chosen, the performance of antennas of differing types possessing the same M-factor is comparable; 8. th
22、at Annex 1 should be referred to for the values of directivity and service sector; 9. that Annex 2 should be referred to for a detailed explanation of directional antennas; 10, that Annex 3 should be referred to for a description of directional arrays with aperiodic reflector. ANNEX1 Values of direc
23、tivity and service sector The values of directivity and service sector appropriate to the specified values of M for the minimum standard antenna and the economic standard antenna respectively are given in the following Table 1: TABLE 1 I Minimum standard antenn Economic standard antenn: 5 I 2.5 I 13
24、.8 I 54 I 6.25 I 17.5 I 3F1 The antenna gain relative to a half-wave dipole above earth may be obtained by subtracting 8 dB from the value of GO. It should be noted that the S value is the minimum bound at the directivity specified and has been derived on the assumption that at least 40% of the tota
25、l power is radiated in the main beam (a value appropriate to many rhombic antennas). Where (as is commonly the case) the (power) gain of the antenna (No. 154 of the Radio Regulations) is known, a suitable adjustment should be made to account for the efficiency of the antenna in deriving the directiv
26、ity. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services258 CCIR RECNN*362-3 72 4855232 0537LB 7Tb Rec. 162-3 ANNEX 2 Use of directional antennas in the bands 4 to 28 MHz 1. Introduction This Annex discusses the problem of specifying reas
27、onable standards for the directivity of antennas in the various types of radio service, and for various distances, in the bands between 4 and 28 MHz with due regard to economy of cost. It is mainly concerned with point-to-point circuits longer than 4000 km but, with suitable modifications, could be
28、applied to shorter range circuits. The technique discussed requires a knowledge of the gain of the antenna under consideration and the angular widths in zenith and azimuth of its main beam of radiation. With this information a directivity factor is derived which, used in conjunction with certain oth
29、er factors, for example, transmitter power and provision cost, may be used to assess the suitability of an antenna for any particular application. 2. Proposition An antenna possessing a given directivity which radiates all its power in a single beam could be regarded as having the best attainable pe
30、rformance of its class. Communication systems using such antennas for emission and reception could operate on a common frequency with a given spatial distribution without risk of mutual interference, the only condition being that each receiving antenna should “see” only the wanted transmitting anten
31、na. With such an ideal arrangement the number of systems sharing the same frequency would increase as a function of the gain of the antennas because of their smaller angular beamwidth. By making certain simplifying but justifiable assumptions, it can be shown that to a high degree of approximation t
32、here is a fixed relationship between the directivity (relative to an isotropic radiator) and the angular widths of this single beam (to the null) as follows: (00 and cpo are the horizontal and vertical angular widths respectively, in radians and P, PO are the total powers radiated from the ideal ant
33、enna and the isotropic radiator respectively to produce the same field in the desired direction). Practical antennas fall some way short of this ideal in that a proportion of the power is radiated (or received) in directions other than in the main beam. If the directivity of such an antenna is G and
34、 the widths of its main beam are 00, cpo, then from equation (i), the power radiated in the main beam: If this represents a fraction q of the total radiated power, or COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesCCIR RECMN*362-3 92
35、4855232 0539387 632 = Rec. 162-3 259 Thus, from the measured or computed characteristics of an antenna it is possible to determine its radiation efficiency, i.e. the fraction of the total radiated power that is directed in the main beam. The power radiated outside the main beam of a transmitting ant
36、enna which is liable to set up interfering signals is given by: If this were distributed evenly over the residual hemisphere outside the lunar arc 80 the average power flux would be: Since the maximum flux in the main beam is Pd47c, one can write: Maximum useful signal power flux Average interfering
37、 signal power flux G (27c - eo) (1 - q) 47c - As is well known, the spatial distribution of flux outside the main beam will vary widely and values considerably in excess of the average will be found. It would seem appropriate to express this as a probability distribution in such a way that its effec
38、t in degrading the signal-to-interference ratio appears as a term in the directivity factor of the antenna. To do this would require a knowledge of the minor beam flux distributions of a large sample of practical antennas and because insufficient information of this nature is available an alternativ
39、e approach must be adopted, The method used is to derive an antenna directivity factor based on the assumption that all the misdirected power appears as a number of equi-amplitude secondary beams and to apply an adjusmient when individual secondary beam amplitudes are likely to be significant to a p
40、articular problem e.g. frequency sharing studies. If the same power distribution (cosine-squared) as that assumed for the main beam is used then, for the secondary beams: -l2=Zz- 2n2 - 3.36 (5.3 dB) and one can then write: G (2 - eo) - Maximum useful signal power flux Maximum interfering signal powe
41、r flux (1 - q) 4n x 3.36 One further modification to the formula is necessary to take account of what has been called the “propagation match” of the antenna: various studies have shown that for long distances (4000 km), circuit performance improves as the vertical angle of the main beam maximum of t
42、he antenna is reduced. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesCCIR RECNN*Lb2-3 92 m 4855212 0539190 354 260 Rec. 162-3 A weighting factor (appropriate for vertical launching angles between about 5 and 25”) ailows for this effe
43、ct and the equation for the antenna directivity factor becomes: G (2.n - eo) 10 (1 -4) 4.n x 3.36 M= and expressing eo, cpo in degrees: G (360 - 00) M= 241.9 Am (1 - 4) (7) where: GI eo cpo = 176600 G : directivity of antenna expressed relative to an isotropic radiator (expressed as a ratio unless o
44、therwise stated) 80 : horizontal angular width of main beam (degrees) (to first minimum points) cpo : vertical angular width of main beam (degrees) (to first minimum points) Am : vertical angle of main beam maximum (degrees). For distances less than 4 O00 km, this factor may be omitted and instead t
45、he height of the antenna chosen to match the propagation conditions over the route. 3. Determination of directivity When the measured characteristics of antennas are available, particularly the (power) gain and angular beamwidths, calculation of the figure of merit, M, is straightforward provided th
46、e power efficiency of the antenna is known. In many instances, however, it will be necessary to evaluate paper designs and special care is needed in the case of the rhombic antenna. Although the angular dimensions of the main beam and the vertical angle of the main beam maximum can be predicted with
47、 sufficient accuracy by a calculation which assumes constant current in the antenna wires, the gain so calculated is generally optimistic and must be corrected before it can be used in the M factor formula. This correction may be considered in two parts. 3.1 Adjustment for power dissipation in the t
48、ermination, Ct This is, in effect, a conversion from measured (power) gain to directivity and is given for various configurations in Figs. la) and 3a). 3.2 Adjustment of current decay along the antenna, Cd This adjustment is necessary to convert (power) gain calculated from constant correct formulae
49、 to a value more nearly in conformity with the measured values on actual antennas and is given, for the same configurations, in Figs. lb) and 3b). For convenience these curves are combined in Figs. 2 and 4, which enables the calculated (power) gain to be converted directly to directivity. The full-line portions of these curves represent the normal design range. All the curves are derived from measurements made on the power efficiencies of rhombic antennas in which a linearly tapered current decay dong the antennas was assumed. The antennas were of 3-wire cons
