A new overlay coupler for direct digital modulator in GaAs HBT

A new overlay coupler has been realized at millimeter-wave frequency with an area that is less than one-half that of the Lange coupler. It was used to construct a binary phase-shift keying (BPSK) modulator, employing balanced reflection topology, in which the HBTs acted as switches. It was shown that the BPSK modulator could be modulated at 1 Gb/s at 28 GHz.