ITU-R BS 80-3-1990 Transmitting antennas in HF broadcasting《高频(HF)广播的发射天线》.pdf
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1、CCIR VOLUME*X-1 90 W YB55212 050395b b 78 Rec. 80-3 RECOMMENDATION 80-3 * TRANSMITTING ANTENNAS IN HF BROADCASTING The CCIR, (Question 44/10, Study Programme 44H/10) (1951 -1 978-1986-1990) CONSIDERING (a) that a directional transmitting antenna should be used whenever appropriate, both to obtain ad
2、equate coverage of an intended service area and to minimize unwanted radiation, and potential interference, elsewhere; (6) that the design and installation of a wide variety of directional HF antenna types of improved performance are feasible using current technology; (c) (d) given in Part 1 of Anne
3、x I to Recommendation 705;- (e) antennas is given in Part 2 of Annex I to Recommendation 705, that directional transmitting antennas can radiate significant power in unwanted directions; that comprehensive and detailed information on the theoretical radiation characteristics of HF antennas is that i
4、nformation regarding the differences between the theoretical and practical performance of HF UNANIMOUSLY RECOMMENDS 1. antenna; that Annex I and Annex II should be used to give guidance on the choice of a suitable HF transmitting 2. that side-lobe radiation should be maintained at the lowest practic
5、al value; 3. that in practical operating conditions, for purposes of calculating interference, the field strength in other azimuths at angles of elevation corresponding. to those of the main lobe, cannot be assumed to be less than 222.mV/m at a distance of 1 km for 1 kW of power supplied to the ante
6、nna, in the case of high gain antennas. A lower value of interfering field strength may need to be considered in the case of low gain antennas. 4. that Annex I to Recommendation 705 should be used as a source for more detailed information. Note - The World Administrative Radio Conference for the Pla
7、nning of HF Bands Allocated to the Broad- casting Service (WARC HFBC(l), Geneva, 1987 has adopted for use, calculated values of minimum radiation which in some cases are lower than that given above (see Annex II). ANNEX I* 1. The use of non-directional and directional antennas In HF broadcasting the
8、 antenna is the means by which the radio-frequency energy is directed towards the required service area. The selection of the right type of antenna will enhance the signal in this area, while reducing radiation in unwanted directions. This will protect other users of the radio-frequency spectrum ope
9、rating on the same channel or adjacent channels in another service area. The use of directional antennas with well defined radiation patterns is thus recommended as far as possible. * Since the content of Reports 32-5 and 1062 have been modified and annexed to this Recommendation as Annexes I and II
10、, respectively, Reports 32-5 (Dubrovnik, 1986) and 1062 (Dubrovnik, 1986) are hereby deleted. Nomenclature is explained in Annex I to Recommendation 705 and in Annex II to the present Recommendation. * COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Ha
11、ndling ServicesRec. 80-3 79 Non-directional antennas can be used when the transmitter is located within the required service area. In this case the required service area as seen by the transmitter extends over an azimuthal angle greater than 180“. Directional antennas serve a double purpose. The fir
12、st is to prevent interference to other users of the spectrum by means of their directivity. The second is to provide sufficient field-strength for satisfactory reception by means of their power gains. A chart in Fig. 1 gives some. general guidelines for the choice of optimum antennas for a given typ
13、e of service according to the required distance range. Two different categories are considered: short distance and medium/long-distance services. A short distance service is understood here to have a range of up to about 2000 km. The corresponding area can be covered with either a non-directional or
14、 a directional antenna whose beamwidth can be selected according to, the sector to be served. In the case of directional antennas, both horizontal dipole curtain and logarithmic-periodic antennas can be employed. Medium and long distance services can be considered to reach distances greater than app
15、roximately 2000 km. Such coverage can be provided by antennas whose main lobe elevation angle is small (6“-13“) and whose horizontal beamwidth - depending on the area to be served - is either wide between 65“ and 95“ (generally 70“) or narrow between 30“ and 45“ (generally 35“). The value of the fie
16、ld strength in the reception area is influenced by the radiation characteristics of the antenna, which depends upon the type of array. Antennas of extremely narrow horizontal and vertical beamwidth should nor be used because variations of the ionosphere could change the location of the coverage area
17、. Although rhombic antennas are used for broadcasting, their use should be discouraged because of the size and number of their sidelobes, which could create unnecessary interference. 2. Reduction of subsidiary lobes For the purpose of avoiding interference in frequency sharing, the reduction of subs
18、idiary lobes in high-frequency broadcasting directional antenna systems is of utmost importance. This interference is generally caused by the radiation pattern of the transmitting antenna having subsidiary lobes in unwanted directions, or by scatter of the energy of the main lobe, due to propagation
19、 anomalies. Reduction in intensity of the subsidiary lobes is possible by correct antenna design, while the propagation scatter in unwanted directions presents a complex problem, and its effect should be treated statistically. HF curtain antennas constructed of horizontal dipole elements are made un
20、idirectional by the addition of a reflector screen. This screen can be comprised of either: - an identical array of dipoles tuned to provide an optimum front-to-back ratio over the range of operating frequencies. In general no power is applied to this type of reflector, which is known as either a “t
21、uned dipole“ or a “parasitic“ reflector; or - a screen consisting of horizontal wires which act as an untuned.reflector. This type of reflector is known as an “aperiodic screen“. The maximum slew values obtained in practice for different antenna types are given in Table I of - Annex II. While slewin
22、g does not appreciably affect the horizontal width of the main lobe of radiation, it does increase its asymmetry and at the same time produces a principal subsidiary lobe of considerable intensity. In slewing, the gain of main lobe decreases with the increase of the slewing angle and side lobe radia
23、tion increases. As a consequence the field strength created by the side lobes will substantially increase. . Practical experience in the Peoples Republic of China has confirmed the possibility of obtaining satisfactory slewing by using the value of current phase differences determined by a successiv
24、e approximation method of calculation CCIR, 1986-9Oal. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesCCIR VOLUIE*X-II 90 W 4855232 0503758 T W 80 Rec. 80-3 I I I I antenna Narrow I Log. periodic antenna single plane 0.65 Q 7 0.8 17“
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