N. S. Barker

A W-band dielectric-lens-based integrated monopulse radar receiver

An integrated monopulse receiver has been developed for tracking applications at W-band frequencies. The receiver is based on dielectric-lens-supported, coplanar-waveguide-fed slot-ring antennas integrated with uniplanar subharmonic mixers. The design center frequency is 94 GHz and the IF bandwidth is 2-4 GHz. The measured DSB conversion losses of the individual receiver channels range from 14.4 to 14.7 dB at an LO frequency of 45.0 GHz and an IF of 1.4 GHz. This includes the lens reflection and absorption losses, backside radiation, RF feedline loss, mixer conversion loss, and IF distribution loss. Excellent monopulse patterns are achieved with better than 45 dB difference pattern nulls using IF monopulse processing. This translates to sub-milliradian angular accuracy for a 24 mm aperture. Better than 25 dB nulls are possible over a 600 MHz bandwidth.

A reconfigurable RF MEMS based double slug impedance tuner

A reconfigurable double-slug impedance tuner has been developed based on a distributed RF-MEMS transmission line (DMTL). The fabricated device shows very good tuning operation from 10-30 GHz with a capacitance ratio of 2.5:1 resulting in uniform coverage of the Smith chart with a maximum VSWR of 4:1. The simulated and measured results are presented in the paper.

Terahertz micromachined on-wafer probes: Repeatability and robustness

Although progress has been made in the development of submillimeter-wave monolithic integrated circuits, the evaluation of these circuits still relies on test fixtures, which makes testing expensive and time consuming. Based on a W-band prototype, a micromachined on-wafer probe covering frequencies 500–750 GHz is built to simplify submillimeter-wave integrated circuits testing. This paper demonstrates the repeatability and the robustness of this terahertz micromachined on-wafer probe.

SU-8 micromachining process for millimeter and submillimeter-wave waveguide circuit fabrication

This paper presents a fabrication technique that utilizes a combination of photolithography and mechanical lapping to achieve a micromachining process to overcome the limitations of conventional machining for realization of millimeter and submillimeter waveguide components. The fabrication process for the waveguide sections begins with spin cleaning a silicon wafer. The SU-8 micromachined part will be assembled to the flange and measurements will be taken of the waveguide sections to characterize the micromachined waveguides.

A comparison of the Gaussian coupling efficiency for three types of terahertz horn antennas

The performance of a diagonal, conical and octagonal horn antenna at 1.6 THz are compared in terms of antenna patterns and Gaussian coupling efficiency. The conical horn was created by laser-machining, the diagonal horn by milling, and the octagonal horn by SU-8 based micromachining.

Vertical RF Transition with Mechanical Fit for Three-Dimensional Heterogeneous Integration

This paper presents the design, simulation and measurement of a vertical interconnect with mechanical fit for three-dimensional heterogeneous integration. The mechanical fit is a strategy employing interlocking SU-8 structures to transition between flip-chip style stacked chips through vertical CPW transmission lines. The mechanical fit is introduced in this paper to reduce flip-chip alignment difficulty and increase the reliability of the interconnects. This paper also describes a process for using pre-fabricated active ICs in a mechanical fit vertical configuration. Experimental results show excellent RF performance up to 50 GHz, with extremely low insertion loss (better than 0.25 dB at 40 GHz per transition). The transitions have been fabricated and tested for 380 ¿m-thick silicon substrates with passive components and experiments are being conducted on active components.

A W-Band RF-MEMS Sliding Termination for Six-Port Reflectometer Calibration

This paper presents the implementation of a W-band RF-MEMS sliding termination for use in calibrating a six-port network analyzer. This sliding termination is based on the distributed MEMS transmission line (DMTL) phase shifter. A novel through-the-substrate biasing technique is introduced for the microstrip phase shifter. This technique is based on a quarter-wavelength open stub acting as both an RF short as well as a capacitor in series with the MEMS bridge capacitance. Because of the series capacitor, the bridge capacitance ratio has been increased from 1.2 to 1.35. The measured results demonstrate from 82deg phase shift at 75 GHz to 205.6deg phase shift at 110 GHz

Characterization of submillimeter-wave Schottky diodes in the 500–750 GHz band using micromachined on-wafer probes

For the first time, direct measurement and characterization of planar Schottky diodes using micromachined on-wafer probes operating from 500 to 750 GHz is described. The Schottky diodes are fabricated on a GaAs substrate and integrated into a coplanar waveguide to allow direct measurement of the device calibrated scattering parameters using CPW probes. The measurements are used to establish and verify equivalent circuit models and parasitics for submillimeter-wave diodes that, previously, were based solely on simulation or scaling of measurements done at microwave frequencies.

Micromachined probes for characterization of submillimeter-wave on-wafer components

Terahertz components and devices are typically interfaced with measurement instrumentation and characterized using fixtures equipped with waveguide flanges or antennas. Such fixtures are known to introduce significant uncertainty and error in measurements. It is preferable to characterize such devices in-situ, where the device under test can be measured on-wafer, prior to dicing and separately from the circuit housing to which it is ultimately affixed. This is commonly done in the RF and millimeter-wave region with a probe station equipped with coplanar launchers. Commercial coplanar waveguide probes have generally been available to the WR-2.2 band (325—500 GHz) but few options currently exist for on-wafer measurements above these frequencies. This paper describes recent work at the University of Virginia and Dominion Microprobes, Inc. to extend on-wafer measurement capabilities to terahertz frequencies through the design and implementation of coplanar probes based on silicon micromachining. At present micromachined on-wafer probes operating to WR1.2 (600 to 900 GHz) have been demonstrated and exhibit typical insertion losses lower than 7 dB with return loss of 15 dB or greater over a full waveguide band.