Abstract
Two-wire helix 1 : 1 transformers are often used to reverse the polarity of short pulses or to drive push-pull amplifiers by single-ended generators.
This type of transformers are also used in balanced detection. Therefore it is desirable that their available bandwidth be as broard as possible.
The transmission of signal through a transformer is considered as a combination of the balanced and the unbalanced transmissions. And, since any transformer has a finite winding length, the end effect in the balanced transmission and the resonance in the unbalanced transmission have to be taken into consideration. These phenomena deteriorate the higher frequency responses of the transformer.
The authors thought out the following two methods in order to construct trans-formers free from these deteriorations, 1) Winding the paired wire on a bobbin having a groove angle of 30°-45°. 2) Setting a disc screen at each end of the windings on a cylindrical bobbin.
It is confirmed by the measurement of insertion loss and phase vs. frequency characteristics that the 1 : 1 transformer having a bandwidth of several hundred megahertz can be realized using cylindrical as well as troidal structures.
