High frequency transmission characteristic of co-planar film transformer fabricated on flexible polyamide film

A co-planar film transformer has been fabricated on a flexible polyamide film. The transmission characteristic of this transformer was measured in the frequency range of 10 MHz to 1300 MHz. A transmission over 90% was obtained around 400 MHz and 800 MHz and that between 300 MHz and 900 MHz was over -6 dB (50%). At low frequency, a thin film transformer can be represented by a concentrated parameter circuit composed of three elements, inductance, capacitance and resistance. On the other hand, at high frequency, the thin film transformer must be treated as a distributed constant circuit. It was shown that the measured transmission characteristics below 1 GHz could be explained by a calculation using distributed parameter circuit theory.