Abstract: Based on structures in feeder line, two critical factors including resonance and higher mode, which affect bandwidth characteristics of feeder line, are analyzed. By measuring time-domain impedance and S parameters over the range of pulse frequency spectrum, their effect are studied in detail and validated experimentally. The testing results indicate that periodic impedance non-uniformity of feeder line is processed by Fourier transform and can be decomposed into two harmonic components which lead to resonance peaks on voltage standing wave ratio curve. The discontinuous structures in feeder line can excite TE11 and TE21 higher modes which cause loss peaks on transmission loss curve. The －3 dB bandwidth of feeder line is determined by resonance peak that the first harmonic component generates, but it can still match the main lobe width of pulse frequency spectrum. Finally, according to test results, the corresponding improvement measures are put forward to subsequent design optimization of feeder line.