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Analyzing Stub Matching with Reflection Coefficients
Walter Maxwell wrote in
: Summarizing reflection coefficient values at stub point with stub in place: Line coefficients: voltage 0.5 at +120°, current -60° (y = 1 + j1.1547) Stub coefficients: voltage 0.5 at -120°, current +60° (y = 1 - j1.1547) Resultant coefficients: voltage 0.5 at 180°, current 0.5 at 0° WRONG Resultant coefficients: voltage 1.0 at 180°, current 1.0 at 0° CORRECT Walt, Though admittance or impedance at a point on the mismatched line are calculated from the underlying Zo and the reflection coefficient corrected for line loss, they are easier to work in than the raw reflection coefficient. It is easier to explain why the stub is located at a position where Yn'=1 +jB than where Gamma=0.5120 (assuming lossless line). It is relatively obvious that where Yn'=1+jB, a shunt reactance of -jB from a s/c or o/c stub will leave Yn=1 which is the matched condition. Re your worked solution (above), I agree that the normalised admittance looking into 30deg of line with load 16.667+j0 is about 1-j1.1547 (not the different sign). I make the normalised admittance looking into the stub about 0+j1.15 (and the reflection coefficient about 0.5-98, how do you get 1+j1.15? The addition of the two normalised admittances 1-j1.15 + 0+j1.15 gives 1 +j0 which is the matched condition. The design is correct, the stub results in a match at the stub connection point (irrespective of what is connected on the source side of the point), but I can't understand your maths above (allowing for the sign error that I think you have made). Is the reflection coefficient explanation a clearer explanation than using admittances? Owen BTW, my line loss calculator solutions (http://www.vk1od.net/tl/tllc.php) for Belden 8262 RG58 (you said RG53, but you probably meant RG58) a (Note some symbols arent supported by plain ascii and appear as '?'.) Load to Stub connection: Parameters Transmission Line Belden 8262 (RG-58C/U) Code B8262 Data source Belden Frequency 16.000 MHz Length 1.030 metres Zload 16.67+j0.00 ? Yload 0.059999+j0.000000 ? Results Zo 50.00-j0.54 ? Velocity Factor 0.660 Length 29.97 ?, 0.083 ? Line Loss (matched) 0.059 dB Line Loss 0.149 dB Efficiency 96.63% Zin 22.12+j24.55 ? Yin 0.020258-j0.022480 ? Gamma, rho, theta, VSWR (source end) -2.44e-1+j4.29e-1, 0.493, 119.6?, 2.950 Gamma, rho, theta, VSWR (load end) -5.00e-1+j4.03e-3, 0.500, 179.5?, 3.000 ? 6.54e-3+j5.08e-1 k1, k2 1.30e-5, 2.95e-10 Loss model source data lowest frequency 1.000 MHz Correlation coefficient (r) 0.999884 Stub: Parameters Transmission Line Belden 8262 (RG-58C/U) Code B8262 Data source Belden Frequency 16.000 MHz Length 1.685 metres Zload 100000000.00+j0.00 ? Yload 0.000000+j0.000000 ? Results Zo 50.00-j0.54 ? Velocity Factor 0.660 Length 49.02 ?, 0.136 ? Line Loss (matched) 0.096 dB Line Loss 40.574 dB Efficiency 0.01% Zin 0.50-j43.44 ? Yin 0.000265+j0.023019 ? Gamma, rho, theta, VSWR (source end) -1.37e-1-j9.69e-1, 0.978, - 98.0?, 90.720 Gamma, rho, theta, VSWR (load end) 1.00e+0+j1.07e-8, 1.000, 0.0?, inf ? 6.54e-3+j5.08e-1 k1, k2 1.30e-5, 2.95e-10 Loss model source data lowest frequency 1.000 MHz Correlation coefficient (r) 0.999884 |
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