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第二章 简单的线天线. 2.1 水平对称天线. 在通信、电视或其它无线电系统中,常使用水平天线 (Horizontal Antenna) 。水平架设天线的优点是: ( 1 )架设和馈电方便,阻抗可调; ( 2 )地面电导率对水平天线方向性的影响较垂直天线的小; ( 3 )可减小干扰对接收的影响。因为水平对称天线辐射水平极化波,而工业干扰大多为垂直极化波,故可以减少干扰对接收的影响,这对短波通信是有实际意义的。. 天线的结构、结构参数、架设方法 天线的电参数,及其特点 天线的用途及尺寸选取方法 天线的优缺点 天线的改进方法. 第二章 简单的线天线. - PowerPoint PPT Presentation
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(Horizontal Antenna)1232.1
2.12.1.1 (Horizontal Symmetrical Dipole)36mm23m/4
211 l=12m22m1000H=10m60044m2H+2l64m0.390300km
1. 212-1
213213214213
213213214214
1
212=0xOz=0213, fxOz(,=0)=|1-oskl||2sin(kHsin)| (214) xOz1174
1fxOz(,=0)=|1-coskl||2sin(kHsin)| (214) (1)H/l/H/ (2)H/=0 (3)H/0.25H/0.3=90=60900300km
(4)H/>0.3H/m1m1172m100H
0(5),
2 213: f1()215216l/=0.25l/=0.50
215216l/=0.25l/=0.50215 l/=0.25216 l/=0.5
(1) H/ (2)l/,l/,l/0.7=0,l/0.7 (3)cossin215 l/=0.25216 l/=0.5
(1) (2)H/0.3,,0300km (3) (4)=0l/0.7
2. ,217217 l=20mH=6m
3. ,f(m1,)m1 2 15;Rrf(m1,)RrRr=R11-R12R11R122H218H>/2l/H 218 D~l/
(2) l/Al/0.1219l0.2 l0.2max (2110)219 K~l/ 0.2maxl0.7min (2111) ,230MHz210MHz,2l=222m1030MHz2l=212m
2) H
300km,H=(0.10.3)815m m10216H r
2.1.2 64m210222=64m4mm1k350
1.75ma
(Cage Antenna)21106835mm13m250400 2110
34m ae:
abna2mmb1.5mn8ae0.85m64m353.6
2111a2111b354637434(2111(a)) 2111 (a)(b)
211221132114 2112 2113 2114
2.1.3 V20 1l/=0.635Dmax=3.296 l=90202115V(Vee Dipole) V1.4,Im;l;r; 12
V
2116 V ,V2116V=0V12
2116 V l/ 202optl/2opt0.5l/3.0V,V20VV2opt
0.5V 3V 2l,123 4LPDA
1. 2.1.4
2. (1):,
(2)(3)
1. 112VHF48.5~223MHz1368UHF470958MHz
888()
2. (Turnstile Antenna) 211790
A2119kr E=E1+E2=Asin(t+-kr) (2120) 21182120kr 2120t=08E882118a
5%2118b
8
2118
3. VHF(Batty Wing Antenna)2119EE2120EE2119
AEEDCBADA150/2
2121 11.12025% 2 3 2121
75
2.2 H/,(Vertical Antenna)221(Monopole Antenna)
221
H(HH) 1 2Q 3Pin=RinI2in/2Uin=Iin(Rin+jXin)jIinXin f/f02f
5: H1%
5.1. 225(TopLoading)226 225 226
H226(a)226(b)CaZ0H: ,H;ah0=h+h 1/5~3/10h(0.1~0.2)h 226
(h+h)/ h/2h/2
,zI0he
5.2.Induction Coil 227 227 1/31/2hh
5.3. 2280.20.5m151503mm h/=300m15mA6.5%,1203mm90m93.3% 2290.51m380.150.2 228 229
2.2.2 T T 1. T T2210TT lhhTh/0.15T2211 2210 T 2211 T
THT22122212 T 2.22139.22214a30602214(b)
3. L22152216 Tl
2216
1l2217(a)hhl2217(b)
2217 l,h l,h l,h l,h
2lH2217c3lH221822 17(d)2217 2218 hl l,h l,h
HEEz2219(a)122219(b) EEz Ez 2219
2.2.3 Helical Whip Antenna 22202/32220
(Helical Antenna)DD/2221D/0.46
N2222EDE 2222 lsin90 AR
2.2.4 VHF/4(Elevatedfeed Whip Antenna)
2223 (a)(b)(c) 2223
2223 (a)(b)(c)
2223 (a)(b)(c)
2223 (a)(b)(c) 2223(c)10
2223 (a)(b)(c) 3076MHz3m30MHz0.376MHz0.77
2.2.5 (Biconical Antenna)22242224
2225 1. (Discone Antenna)19452225 VHFUHF51501.5 DCminCminSS=0.3CminD=0.7Cmaxh=30Cmin=L/22L1.571291
HE2226
2226
22272227
2. 2228(Sleeve Monopole)2228aL+L/2
2228
, L/L=2.2541,221
221
2231 (Opensleeve Antenna)2231310MHz510MHz,501.8
2.3 C=2b0.2 ,
Im
l
a
f=0
2.3.1 1231(Small Loop Antenna)231 ISRl:
ab
D=1.5
As the current is along the x direction,b is the length of the block, and w c is the equivalent cross-sectionsl area with w as its width and c as its thickness
231/25 10
/2/42300MHzNN2(NNINE1N2P1) N ,Rp;R0,
232b=/25a=10-4410-45.7107(S/m)f=100MHz8Rp/R0=0.38 888
232R'r Rre Q
232
2.3.2 1. J.E.Storer,233231=2ln(2b/a)ab
233 kb=0.1,kb=0.2 kb,kb=0.20.030.04kb=1=0180=90270
C2b=23 1231 A,r-1
R
RA2311A yOz90kb=1 ,J0J202xOz0180
2312 ;yOz: f()=cosJ0(sin)+J2(sin) (2317) xOz: f()=J0(sin)-J2(sin) (2318) 234 234 (a)yOz(b)xOz0.27
235 (a)(b)236 0kb=2b/=C/2.5 C()2Xin=2ln(2b/a) 9 kb>1(kb=18100 236z
2. 237(0.30.5),0.52L4L6L2381234
237 238 (a)2L(b)4L(c)6L
kb1100239a0.272L239b,,
239 2L(a)(b)
2L4L6L2310a2310bH=0.252L4L6L2310c
2310 (a)(b)(c)
1.05161.1202.3.3 ()(Loaded Circular Loop Antenna)2311VHF
2311
RLZ0 kb2312a=2ln(2b/a)bRL3259.4300kbkb2003002312 (a)(b)
kb1,2311kb>1,C/,C/min1 1 2311
8.6.1 Surface resistanceLet the electric field intensity in a good conductor be Neglecting the displacement current density in a good conductor, the total current is The average power dissipated per unit volume is
Comparing (6.68)and (6.69),we obtain the resistance of the block asAs the current is along the x direction,b is the length of the block, and w c is the equivalent cross-sectionsl area with w as its width and c as its thicknessThe skin resistance() or surface resistance() is defined as the resistance of a plane conductor of unit length (b=1),unit width(w=1),and thickness c
As the current is along the x direction,b is the length of the block, and w c is the equivalent cross-sectionsl area with w as its width and c as its thickness
Although we have computed the skin resistance on the basis that a plane wave is propagating through a flat block,(8.71)can also be used to obtain an approximate value of the skin resistance for a cylindrical conductor.when the current is along the length of a cylindrical conductor of radius a such that a> c ,the skin resistance per unit length is
2.4 P91YagiUdaantenna (YagiUda Antenna)Uda1926Yagi1927241() 241 241
242 (a)2(b)2a212();b212()1.(Director)(Reflector)1.1
242 (a)2(b)2a=0E=1.5E1,=180E=0.5E1,122 211/2E2E1
2.4.1
2.4.2 244 ?24412l122l2dI2,I22
U1=I1Z11+I2Z12U2=I1Z21+I2Z22 =0m(2l1,2l2)d
241 2l1/=0.475
3.(Multiple Element Antenna) 246a246 (a)(b)E (c)H(d)
24112132zz246bcd2lr=0.52l0=0.472l1=2l2=2l3=2l4=0.43dr=0.25d1=d2=d3=0.302a=0.0052EH246 (a)(b)E (c)H(d)
2470.150.0025247 N=3N=41dB78N=9N=100.2dB
2.4.2 242EH
242
1. 70()U(5075)2 ,2
2. MoM248L(244)248,HEHE248L/>220.5L/
248 20.5~L/
HE(242)242249
249
3. 2410L/10, 90%1, G=DD 2452410 D~L/
4. 5. S210% d/
X2411X 2411 X(a)(b)X
2412aIM1=IM2IM=IM1+IM2=2IM1 ,Rr,70 IM1IM
=1PinPr246247IM=2IM14
,DDD=(0.01~0.03) K
4.9
:zz
0z
11, ZLZ0
2 (1)ZLZ0l ZinZG ZGZ0(2) Z*GZin
c
,,,.,,...,,.1 ? ?
22.1 l/4 l/4 l/4 I40I4 I4I4=0I1I3
2.2 (l/4 )Z0 l/4 ,4I4I44I4I1I2I2I4I4I4I1
2.3 UU2
UZA2ZA1475ZA475300AA
2.4.5 (Loop Element YagiUda Antenna)2421 3.2dB100 2421
brdr 1d=(0.1~0.3)kb=0.9 2kbd0.3dkb=0.7d0.15dd
3HE, 4kb0=1.1kbr=1.05dr=0.1kb1 1200MHz1.22520dB
2.4.6 2060-20dB-30dB 1.(Back Fire Antenna) T24 22T13dB3dB
24 22
/22dB8dB
1530dB,
2.(Short Back Fire Antenna) 24230.40.62W=/4~/2
8.517dB1/10
2423
2.12.32.42.72.82.102.122.13123