In this letter, a flexible two-section transmission-line transformer with single-band operation is introduced to transform complex source impedance to real load impedance. Two characteristic impedances and their electrical lengths of two-section transmission-lines are derived in closed form. From the newly derived design equations, once the complex source impedance and real load impedance are determined, two characteristic impedances of two-section transmission-lines can be selected arbitrary, then their electrical lengths are calculated automatically. Several simulated examples show that: by using the proposed design equations, there are different group of design parameters for a given condition, the circuit size could be much more compact than those in the previous work, meanwhile, 20 dB bandwidth can be maintained, and harmonic suppression could also be improved. Experimental circuit shows that: circuit size is shrunk to 38.6%, and its harmonic suppression has been improved over 15 dB.
2017 by The Institute of Electronics, Information and Communication Engineers