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Artificial Lines
Figure 138 shows these four combinations for any electrical length θ of line section in degrees. It is assumed in this figure that the line operates at a single frequency and is terminated in a pure resistance equal in value to the line characteristic impedance Z_{0}. Figure 139 is the vector diagram for a leading phase shift pisection line of 90° electrical length. Proportions of L and C are somewhat different in these line sections than in wave filters.
To obtain approximately constant time delay over a range of frequencies, several constantK lowpass filter sections may be used, each having a cutoff frequency high enough so that the phase shift is proportional to frequency. The time delay per section is then θ/2πf at any frequency in the range, and θ = 2πf√(LC), where 8 is the phase shift in radians, L is the inductance per section, and C is the capacitance per section. In Fig. 139, E_{R} = E_{s}. If the section were terminated in impedance higher than Z_{0}, E_{R} > E_{s}. The line section is then a kind of transformer, although the ratio E_{R}/E_{S} varies with frequency. Ninetydegree line sections are often used at high frequencies to obtain transformation of voltage.


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