A 77 GHz SiGe sub-harmonic balanced mixer

A novel SiGe 77 GHz sub-harmonic balanced mixer is presented with a goal to push the technology to its limit [SiGe2-RF transistor (f/sub T/=80 GHz)]. This new topology uses a compact input network not only to achieve high isolation between the LO and RF ports, but also to result in excellent 2LO-RF isolation. The measured results demonstrate a conversion gain of 0.7 dB at 77 GHz with an LO power of 10 dBm at 38 GHz, LO-RF isolation better than 30 dB, 2LO-RF isolation of 25 dB, and a P/sub 1dB/ of -8 dBm. The mixer core consumes 4.4 mA at 5 V. The circuit demonstrates that SiGe sub-harmonic mixers have comparable performance with GaAs designs, at a fraction of the cost.     

Micromachined devices for wireless communications

An overview of recent progress in the research and development of micromachined devices for use in wireless communication subsystems is presented. Among the specific devices described are tunable micromachined capacitors, integrated high-Q inductors, micromachined low-loss microwave and millimeter-wave filters, low-loss micromechanical switches, microscale vibrating mechanical resonators with Q's in the tens of thousands, and miniature antennas for millimeter-wave applications. Specific applications are reviewed for each of these components with emphasis on methods for miniaturization and performance enhancement of existing and further wireless transceivers     

Tuning in to RF MEMS

RF MEMS technology was initially developed as a replacement for GaAs HEMT switches and p-i-n diodes for low-loss switching networks and X-band to mm-wave phase shifters. However, we have found that its very low loss properties (high device Q), its simple microwave circuit model and zero power consumption, its high power (voltage/current) handling capabilities, and its very low distortion properties, all make it the ideal tuning device for reconfigurable filters, antennas and impedance matching networks. In fact, reconfigurable networks are currently being funded at the same level-if not higher-than RF MEMS phase shifters, and in our opinion, are much more challenging for high-Q designs.     

"Window" laryngoplasty: a new combined laser endoscopic and open technique for conservation surgery

Endoscopic laser resection of early laryngeal carcinoma is an increasingly used treatment modality; however, the limited exposure achieved and the alteration of vocal function are still major problems. A new surgical procedure, "window" laryngoplasty, has been devised and tested in an in vivo study in 6 canines with 50 days' survival. The right vocal cord was incised endoscopically with the carbon dioxide laser, and the en bloc specimen with adjacent thyroid cartilage was removed through a window approach made in the thyroid cartilage. A sternohyoid muscle flap based superiorly was inserted into the cartilaginous window to reconstruct a pseudocord with coverage of either mucosa or fascia. A diode laser soldering technique was used to secure the mucosal graft in place. Epithelial transplantation can be accomplished externally with precise endoscopic guidance for reliable placement of the pseudocord. The results show that the new technique, a combination of endoscopic and open approaches, may be a better treatment choice than standard vertical partial laryngectomy in selected patients. Advantages of this technique include adequate en bloc resection, including adjacent cartilage for pathologic evaluation, preservation of the integrity of most of the laryngeal framework, avoidance of tracheotomy, and better functional results.     

Millimeter-wave Fermi tapered slot antennas on micromachinedsilicon substrates

This paper presents 90 GHz Fermi-type tapered slot antennas (TSA) on a micromachined 100 μm thick silicon substrate (ϵ_r=11.7) and for comparison purposes, 90 GHz Fermi-type TSA on 150 μm thick quartz substrate (ϵ_r=3.78). A 100 μm thick wafer is chosen because it is compatible with 90-100 GHz low-noise amplifier circuits on GaAs-InP substrates. The effective thickness of the substrate was reduced by selectively micromachining holes in the silicon wafer using deep reactive ion etching (deep RIE). The radiation patterns of the micromachined antennas were significantly better than the nonmicromachined version and had similar radiation patterns to the quartz design. The etched hole diameter was changed from 300 to 750 μm with minor effect on the radiation patterns. This shows that the predominant reason for the improved patterns lies in the reduced effective dielectric constant and not in substrate-mode suppression effects. This type of antenna is well suited for millimeter-wave imaging arrays     

Switchable low-loss RF MEMS Ka-band frequency-selective surface

A switchable frequency-selective surface (FSS) was developed at 30 GHz using RF microelectromechanical systems (MEMS) switches on a 500-/spl mu/m-thick glass substrate. The 3-in-diameter FSS is composed of 909 unit cells and 3636 MEMS bridges with a yield of 99.5%. The single-pole FSS shows a transmission loss of 2.0 dB and a -3-dB bandwidth of 3.2 GHz at a resonant frequency of 30.2 GHz with the MEMS bridges in the up-state position. The -1-dB bandwidth is 1.6 GHz. When the MEMS bridges are actuated to the down-state position, an insertion loss of 27.5 dB is measured. Theory and experiment agree quite well. The power handling is limited to approximately 25 W with passive air cooling and >150 W with active air cooling due to the increased temperature of the overall circuit resulting from the transmission loss (for continuous-wave operation with the assumed maximum allowable temperature of 80/spl deg/C), or 370 W-3.5 kW due to self-actuation of the RF MEMS bridges (for pulsed incident power). Experimental results validate that 20 W of continuous-wave power can be transferred by the RF MEMS FSS with no change in the frequency response. This is the first demonstration of a switched low-loss FSS at Ka-band frequencies.     

W-band CPW RF MEMS circuits on quartz substrates

This paper presents W-band coplanar waveguide RF microelectromechanical system (MEMS) capacitive shunt switches with very low insertion loss (-0.2 to -0.5 dB) and high-isolation (/spl les/ -30 dB) over the entire W-band frequency range. It is shown that full-wave electromagnetic modeling using Sonnet can predict the performance of RF MEMS switches up to 120 GHz. Also presented are W-band 0/spl deg//90/spl deg/ and 0/spl deg//180/spl deg/ switched-line phase shifters with very good insertion loss (1.75 dB/bit at 90 GHz) and a wide bandwidth of operation (75-100 GHz). These circuits are the first demonstration of RF MEMS digital-type phase shifters at W-band frequencies and they outperform their solid-state counterparts by a large margin.     

Distributed 2- and 3-bit W-band MEMS phase shifters on glass substrates

This paper presents state-of-the-art RF microelectromechanical (MEMS) phase shifters at 75-110 GHz based on the distributed microelectromechanical transmission-line (DMTL) concept. A 3-bit DMTL phase shifter, fabricated on a glass substrate using MEMS switches and coplanar-waveguide lines, results in an average loss of 2.7 dB at 78 GHz (0.9 dB/bit). The measured figure-of-merit performance is 93/spl deg//dB-100/spl deg//dB (equivalent to 0.9 dB/bit) of loss at 75-110 GHz. The associated phase error is /spl plusmn/3/spl deg/ (rms phase error is 1.56/spl deg/) and the reflection loss is below -10 dB over all eight states. A 2-bit phase shifter is also demonstrated with comparable performance to the 3-bit design. It is seen that the phase shifter can be accurately modeled using a combination of full-wave electromagnetic and microwave circuit analysis, thereby making the design quite easy up to 110 GHz. These results represent the best phase-shifter performance to date using any technology at W-band frequencies. Careful analysis indicates that the 75-110-GHz figure-of-merit performance becomes 150/spl deg//dB-200/spl deg//dB, and the 3-bit average insertion loss improves to 1.8-2.1 dB if the phase shifter is fabricated on quartz substrates.     

A 24-GHz high-gain Yagi-Uda antenna array

A compact 24-GHz Yagi-Uda antenna has been developed using standard design tables and simple scaling to take into account the added capacitance due to the supporting dielectric substrate. The antenna results in a directivity of 9.3 dB, a front-to-back ratio of 11 dB, and a bandwidth of 2.5-3%. The Yagi-Uda antenna has been implemented in an 11-beam system using a planar array and a 2-inch Teflon spherical lens. The measured patterns show a 22 dB gain beam, a cross-polarization level of -24 dB, and a crossover level of -6 dB. The design method presented in this paper is quite straightforward, and can be used to develop low-, medium-, and even high-gain endfire Yagi-Uda antennas.     

Mode conversion at GCPW-to-microstrip-line transitions

Mode conversion at the transition between grounded coplanar waveguide (GCPW) and microstrip line is demonstrated. Experimental results show the effect of overmoding in a conductor-backed coplanar waveguide on the transition behavior. A simple micromachining solution is used to cancel the parasitic modes triggered by the transition in the GCPW feed line. This results in an insertion loss of 0.3 dB and a return loss better than -18 dB from 75 to 110 GHz. The transition can prove very useful for millimeter-wave packaging and interconnects