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Automatic bandwidth adjustment can be included in iterative approximation procedures for transformed-variable synthesis of lossless doubly terminated filters. With a modified algorithm, the bandwidth and loss-pole frequencies are simultaneously adjusted to meet exactly the prescribed stopband requirements. The potential acceptability of a filter configuration is immediately determined by whether or not the resulting bandwidth meets or exceeds the required minimum bandwidth. Existing pole-placer routines are easily modified using auxiliary transformed variables for the bandwidth and the loss-pole frequencies. Applications of this technique to low-pass, bandpass, and narrow-bandpass filters are described, with examples of low-pass and narrow-bandpass filter approximation.