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A Quasi Yagi antenna is presented that provides off-axis radiation when backed by a metal reflector. The off-axis radiation pattern is achieved by an increase in the substrate thickness beneath the antenna elements. At 2.4 GHz the antenna demonstrated a bandwidth of 190 MHz, beam tilt towards the end tire direction ([theta] = 42[degrees]), maximum gain of 4.5 dB, anda radiation efficiency of 87%. The results of a study on bandwidth, gain and radiation pattern versus substrate thickness ate presented herein. To the best of the authors' knowledge previous realization of this antenna over a ground plane has not been investigated. Index Terms--Beam steering, end tire, metal backing, Quasi Yagi.

In this paper, design equations for true-time-delay microelectromechanical (MEM) phase shifters comprised of impedance-matched slow-wave unit cells are presented. The input to these equations requires only the specification of the maximum frequency of operation ([f.sub.max]) and substrate dielectric constant ([[member of].sub.[tau]]). The basis of the design methodology is to maximize the phase shift versus insertion loss performance. Experimental data for three 1-bit devices that are 11.44-mm long ([f.sub.max] = 12 GHz), 4.6-mm long ([f.sub.max] = 50 GHz), and 3.12-mm long ([f.sub.max] : 110 GHz) shows a maximum phase deviation of 3% compared to predicted performance, with [S.sub.11] less than -19 dB from 1 to 110 GHz. The worst case insertion loss is 0.9 dB for [f.sub.max] = 12 GHz, 1.16 dB for [f.sub.max] = 50 GHz, and 2.65 dB for [f.sub.max] = 110 GHz. The MEM beams are actuated using high-resistance SiCr bias lines with typical actuation voltage around 30-45 V. Index Terms--Microelectromechanical systems (MEMS), phase shifter, RF MEMS, true time delay (TTD).

A true-time-delay multibit microelectromechanical systems (MEMS) phase-shifter topology based on impedance-matched slow-wave coplanar-waveguide sections on a 500-[micro]m-thick quartz substrate is presented. A semilumped model for the unit cell is derived and its equivalent-circuit parameters are extracted from measurement and electromagnetic simulation data. This unit cell model can be cascaded to accurately predict N-section phase-shifter performance. Experimental data for a 4.6-mm-long 4-bit device shows a maximum phase error of 5.5[degrees] and [S.sub.11] less than -21 dB from 1 to 50 GHz with worst case [S.sub.21] less than -1.2 dB. In a second design, the slow-wave phase shifter was additionally loaded with MEMS capacitors to result in a phase shift of 257[degrees]/dB at 50 GHz, while keeping [S.sub.11] below -19 dB (with [S.sub.21] < -1.9 dB). The beams are actuated using high-resistance SiCr bias lines with typical actuation voltage around 30-45 V. Index Terms--Loaded transmission line, micromechanical systems (MEMS), phase shifter, RF MEMS.

This paper presents a 10-GHz cross-coupled bandpass filter integrated onto low-resistivity silicon. The filter is fabricated on a quartz substrate and then mounted onto the silicon using benzocyclobutene and inverted microstrip interconnects. The approach enables the integration of low-loss distributed microwave components onto CMOS-grade Si substrates while occupying a small effective footprint on the silicon. Experimental and theoretical results are given for 10-GHz filters integrated onto a 10-[ohm] * cm silicon substrate. Index Terms--Cross-coupled, low-resistivity silicon (LRS), microwave filters, three-dimensional (3-D) integration.

As a means of increasing the awareness of the sensing sciences among undergraduates, a novel design course has been developed by the Tennessee Technological University and the University of South Florida. Students study, design, fabricate, and test a wireless-based sensor system that relays data over a radio-frequency link for centralized processing. Weekly seminars on applicable topics in telecommunication, signal processing, and microwave systems originate from either university, using interactive Internet conferencing. Students from both schools form design teams to develop subsystems that are integrated to complete the project, thereby necessitating collaboration across teams and universities. Student evaluations of the first two offerings (Spring 2000/2001) were excellent. Index Terms--Communication systems, design course, distance learning, microwave systems, multiuniversity, sensor systems.

This paper describes micromachined, membrane-supported low-pass and bandpass filters which are suitable for microwave and millimeter-wave (mm-wave) application. The designs are realized in coplanar-waveguide (CPW) form using short- and open-end series stubs with integrated metal-insulator-metal (MIM) capacitors, and are compact in lateral and longitudinal dimensions. A computationally efficient analysis has been developed for the design and characterization of the filters. The technique is based on a quasi-static coupled-line (CL) treatment of the series stubs, and uses normal mode impedance parameters, which are calculated with the spectral-domain approach (SDA). Due to the broad TEM-bandwidth of the membrane-supported transmission lines, the method can accurately predict filter responses well into the rejection band. To demonstrate the above claims, the measured and simulated S-parameters of a 0.3 mm x 2.2 mm low-pass filter with a cutoff frequency at 17 GHz, and a second passband at 115 GHz, are presented. The new approach is also used in the design of bandpass filters which exhibit 1.5-2-dB insertion loss and bandwidths around 10%. Index Terms - Coplanar waveguide, coupled lines, filters, micromachining, millimeter wave.

A new noncontacting waveguide backshort has recently been developed for millimeter- and submillimeter-wave frequencies. The design consists of a metal bar with rectangular holes cut into it, which is covered with a dielectric layer to form a snug fit with the broadwalls of a waveguide. It is mechanically rugged and can be readily fabricated for frequencies from 1-1000 GHz. This paper presents a technique for the theoretical characterization of the backshort, using an approach that combines the mode-matching method and a set of coupled space-domain integral equations. The convergence characteristics of the analysis are included, along with a set of general design guidelines.

Several millimeter-wave passive components have been fabricated using the microshield transmission line geometry, and their performance is presented herein. Microshield is a quasi-planar, half-shielded design which uses a thin dielectric membrane (1.5 [[micro]meter]) to support the conducting lines. This approach provides a nearly homogeneous, air-filled environment and thus allows extremely broad-band TEM operation. This paper examines the conductor loss and effective dielectric constant of microshield lines and presents results on transitions to conventional coplanar waveguide, right-angle bends, different stub configurations, and lowpass and bandpass filters. Experimental data is provided along with numerical results derived from an integral equation method. The microshield line is shown to be very suitable for high performance millimeter- and submillimeter-wave applications.

Coplanar striplines and waveguides capable of supporting ultra-high-frequency pulses over many millimeters of propagation length have been fabricated on low-permittivity substrates, including a durable 1.4-[[micro]meter]-thick membrane. These transmission lines were characterized using broadband pulses from a novel in situ optoelectronic test-signal generator together with an electro-optic probe tip and an optically-based sampling technique. Pulse-propagation characteristics fur the coplanar lines on the low-permittivity substrates have been compared in both the time and frequency domains with the transmission behavior of lines on GaAs substrates. A semi-empirical model has also been used to simulate the experimental results with good agreement, helping to indicate the origin of the distortion mechanisms involved. In addition, for the coplanar waveguide structures, waveforms corresponding to the even and odd modes have been individually resolved in the time domain for lines fabricated on the GaAs and membrane substrates.

This article reviews recent developments in Si micromachining, as it applies to the design of millimeter- and sub-millimeter-wave circuits. Advances in semiconductor-processing techniques have made it possible to create monolithic geometries which are not bound to the surface of the water. These use a third dimension, to provide shapes and exhibit electrical functions, which are not possible through standard microstrip or coplanar-waveguide technologies. A variety of recently developed circuits are presented herein, which demonstrate the numerous capabilities micromachining offers to the circuit and antenna designer.