The balanced modulator topology requires a total of four couplers, one each for the input and output and one within each single-stage branch.
The balanced modulator using reflection-type attenuators is an extremely robust technique that provides perfect BPSK performance with negligible design effort.
Although in a balanced modulator it is possible to remove the amplitude and phase errors caused by the parasitics of the cold-pHEMT, the resulting circuit would in theory be double the size of the original single-stage design.
The balanced modulator configuration employs two reflection-type single-ended modulators in a push-pull fashion, which can be combined by employing a pair of 3 dB, 90 [degrees] couplers.
If the two cold-FET terminations in each branch were fed with complementary but otherwise identical baseband control signals, the resulting balanced modulator would produce near-perfect amplitude and phase balance.
The overall voltage transmission coefficient of the balanced modulator is given by
Hence, with two single-stage modulators connected in tandem to realize the balanced modulator, the total voltage reflection coefficient of the circuit is expressed as