The inductance of the full wave wire equivalent, the lumped component radiator element, equates to an inductance at the lowest frequency of operation of a value of:
full wave length * inductance of wire per metre : (300/0·136) * 300nH = 660uH of inductance as a coil of wire.
The impedance match tuning of the 50Ω stub tuning are as follows with the calculated SWR matching values.
The lower end of the 50Ω stub tuning circuit must not be ground to earth, it must stay free of any grounding connection, while only the top end positioned to the 50Ω terminal connection, need only be connected to the tuning stub circuit.
In many regards, the 50Ω stub tuning circuit can be referred by other means as a counter-poise antenna load of a 50Ω impedance.
Text Box
10 Cshunt= 4700E-12
20 Lcoil = 100E-6
30 PRINT
40 PRINT
50
60
70
80 PRINT TAB(15);"LF / MF vertical antenna stub tuning Trapped"
90 PRINT TAB(15);"Cshunt = ";Cshunt/1E-12;"pF";" Lcoil = ";Lcoil/1E-6;"nH "
100 REM PRINT TAB(15);"leg_B = ";segments_B;"m"
110 PRINT
120 PRINT TAB(15);"performance spec's"
130 PRINT
140
150
160
170 FOR f = 0.35 TO 0.38 STEP 0.005
180 PROC_sums
190 NEXT
200 PRINT
210 FOR f = 0.47 TO 0.48 STEP 0.001
220 PROC_sums
230 NEXT
240 PRINT
250
260 PRINT
270
280
290 REM *CHDIR C:\Users\alastair\Pictures\antenna designs
300 REM *SCREENSAVE 50omh_mobile_phone_antenna.bmp 1,1,2000,1100
310
320 END
330
340
350
360 DEFPROC_sums
370 Xc=1/(2*PI*f*1E6*Cshunt)
380 Xl = (2*PI*f*1E6*Lcoil)
390
400 Trap_effect = ((Xc*Xl)/(Xc+Xl))
410
420 L_trap_effect_inductance = Trap_effect / (2*PI*f*1E6)
430
440 L_antenna_inductance = L_trap_effect_inductance
450
460 resonant_length = L_trap_effect_inductance/(0.3E-6)
470
480 wave_length = L_trap_effect_inductance * 2 * PI * f * 1E6
490
500 SWR_imped = (wave_length)/50
510
520 PRINT TAB(15);" freq = ";f*1000;"KHz";TAB(32)"eqiv. stub = ";INT(resonant_length * 100)/100;" m";TAB(59);"coax line = ";INT(50*SWR_imped*10)/10;" ohms";TAB(88);" SWR = ";INT(SWR_imped * 100)/100
530
540 ENDPROC
550