A Photogenerated Silicon Plasma Waveguide Switch and Variable Attenuator for Millimeter-Wave Applications

This paper reports the design, fabrication, and measurement of a millimeter-wave solid-state ?pi-match waveguide switch using bulk silicon micromachining. A photogenerated plasma within a silicon post is utilized as the switching element within the waveguide channel. Not only does this isolate the switch bias network from the RF signal path, but allows for tuning of the OFF-state isolation with increasing optical power for application as a variable attenuator. A measured OFF-state isolation greater than 25 dB up to 40 GHz is reported, with a measured extracted ON-state insertion loss of 0.52 dB at 35 GHz, and less than 0.88 dB across the entire band from 30-40 GHz. The proposed switch illustrates the significant potential for photogenerated silicon plasma switching of high-performance bulk micromachined millimeter-wave waveguides.

A Photogenerated Silicon Plasma Waveguide Switch and Variable Attenuator for Millimeter-Wave Applications

This paper reports the design, fabrication, and measurement of a millimeter-wave solid-state ?pi-match waveguide switch using bulk silicon micromachining. A photogenerated plasma within a silicon post is utilized as the switching element within the waveguide channel. Not only does this isolate the switch bias network from the RF signal path, but allows for tuning of the OFF-state isolation with increasing optical power for application as a variable attenuator. A measured OFF-state isolation greater than 25 dB up to 40 GHz is reported, with a measured extracted ON-state insertion loss of 0.52 dB at 35 GHz, and less than 0.88 dB across the entire band from 30-40 GHz. The proposed switch illustrates the significant potential for photogenerated silicon plasma switching of high-performance bulk micromachined millimeter-wave waveguides.

A tuneable rat-race coupler for full duplex communications

Full duplex (FD) could potentially double wireless communications capacity by allowing simultaneous transmission and reception on the same frequency channel. A single antenna architecture is proposed here based on a modified rat-race coupler to couple the transmit and receive paths to the antenna while providing a degree of isolation. To allow the self-interference cancellation (SiC) to be maximized, the rat-race coupler was made tuneable. This compensated for both the limited isolation of the rat race and self-interference caused by antenna mismatch. Tuneable operation was achieved by removing the fourth port of the rat race and inserting a variable attenuator and variable phase shifter into the loop. In simulation with a 50 Ω load on the antenna port, better than −65 dB narrowband SiC was achieved over the whole 2.45 GHz industrial, scientific and medical (ISM) band. Inserting the S-parameters of a commercially available sleeve dipole antenna into the simulation, better than −57 dB narrowband SiC could be tuned over the whole band. Practically, better than −58 dB narrowband tuneable SiC was achieved with a practical antenna. When excited with a 20 MHz Wi-Fi signal, −42 dB average SiC could be achieved with the antenna.