Broadband Phase Modulator with a Branch Line Coupler - Transformer

The paper presents a way and results of the computer aided optimization of the phase modulators to attain almost flat phase shift about the centre frequency. the modulator consists of the branch line coupler-transformer and of PIN diodes. There are many parameters of the circuit, namely structure and transformation coefficient of the coupler, lengths and characteristic impedances of the lines with diodes which oan be adjusted to attain optimum characteristics of the modulator. A program of the analysis and synthesis using the matrix techniques has been developed. Computs, tion results have shown that one can made the phase modulator for 180 and 90 degrees phase shifts with the deviation not greater than 2 degrees in the 15 per cent operating frequency band. Experimental results have shown a good agreement with the developed theory.