Micromachined Plastic Millimeter-wave Radar Components

Iris filters are natural extension of plastic rectangular waveguides by building irises separated at half-wavelength to form resonant cavities that are coupled together using window openings in the irises. Several plastic, five-cavity iris filters have been designed, constructed and tested for operation at 95GHz. Fabricated filters have been tested with a bandwidth of 3.5GHz centered at 95.4GHz, a minimum insertion loss of 1.22dB, a return loss better than 10dB, and out-of-band rejection better than 60dB. The next technology advancement aims at tunable iris filters and phase shifters. This is accomplished by introducing deformable diaphragms to perturb the volume of the resonant cavities. The disturbance of the electric field lines of the resonant modes changes the effective capacitance of the LC tank, and consequently the resonant frequency. For membranes with size of 1.6mm in diameter, a total of 2.59GHz change in center frequency has been achieved when the membrane deflects from –50μm to +150μm. The deflections of the membranes also add time delay on the propagating waves to realize a phase shifter, a key element in phased-array antennas. Measurements of the phase of propagating waves show total phase shift of 110º has been accomplished for the membrane deflection between -50μm to +150μm with the addition of 1.11dB in insertion loss. Finally, a plastic horn antenna has been demonstrated using a 3D self-aligned embossing technique for a pyramidal horn antenna geometry fed with a rectangular waveguide. Alignment is achieved using built-in keys and key slots with a misalignment error of 25μm.  Measurements show a total directivity of 17.33dB, a 10dB beamwidth between 75.5-101.7GHz, and an impedance match better than 17.5dB at 95GHz.