Finite Ground Coplanar Waveguide Research Articles

A Novel Partly Shielded Finite Ground CPW Low Pass Filter

A novel partly shielded-finite ground coplanar waveguide (PS-FGCPW) low pass filter has been designed. The device consists of a PS-FGCPW loaded with metal stubs at periodic positions of the signal line. The width of the metal stubs has a sinusoidal variation as the function of the position along the signal line. By properly choosing the position and dimension of the loaded stubs, a wide stop band, more than four times the pass bandwidth, is obtained through the suppression of spurious frequencies inherent to the distributed structures. The prototype also exhibits very sharp cutoff, very low insertion loss in the passband, slow-wave effect and high isolation performance.

Wide-Band Impedance Characteristics of Finite-Ground Uniform and Stepped Coplanar Waveguides

Using the extended Heinrich equations for computing the per-unit-length resistance and inductance of coplanar waveguides (CPWs), we have studied the wide-band impedance characteristics of various finite-ground uniform and stepped CPWs. Finite-ground CPWs are frequently used in the design of CPW-based microwave and millimeter-wave devices. For various physical parameters, in particular the metallization thickness and its conductivity, we examined both resistance and inductance over a wide frequency range. Our work can serve as a basis for further study of the energy dissipation of the devices in the excitation of a high-power pulse.

A New Approach of Lateral RF MEMS Switch

This paper presents a novel lateral series microwave switch fabricated on a silicon-on-insulator (SOI) substrate with a finite ground coplanar waveguide (FGCPW) configuration which is laterally actuated by the electrostatic force. The switch is built with a cantilever beam in the direction of the signal line and a fixed electrode is located opposite the cantilever beam. The mechanical structures are fabricated using SOI deep reactive ion etching (DRIE) and shadow mask technology. The fabricated lateral RF MEMS switch has an isolation of 16 dB at 20 GHz. The insertion loss of the switch is 1 dB and return loss is 15 dB at 20 GHz. The threshold voltage is 19.2 V and switching time is 30 μs.

Crosstalk Between Finite Ground Coplanar Waveguides Over Polyimide Layers for 3-D MMICs on Si Substrates

Finite-ground coplanar (FGC) waveguide lines on top of polyimide layers are frequently used to construct three-dimensional Si-SiGe monolithic microwave/millimeter-wave integrated circuits on silicon substrates. Requirements for high-density, low-cost, and compact RF front ends on silicon can lead, however, to high crosstalk between FGC lines and overall circuit performance degradation. This paper presents theoretical and experimental results and associated design guidelines for FGC line coupling on both highand low-resistivity silicon wafers with a polyimide overlay. It is shown that a gap as small as 6 /spl mu/m between two adjacent FGC lines can reduce crosstalk by at least 10 dB, that the nature of the coupling mechanism is not the same as with microstrip lines on polyimide layers, and that the coupling is not dependent on the Si resistivity. With careful layout design, isolation values of better than -30 dB can be achieved up to very high frequencies (50 GHz).

Isolation in three-dimensional integrated circuits

The necessity for high-density integrated-circuit (IC) design makes the issue of circuit isolation a critical one. In multilayer structures, surface waves excited by planar discontinuities induce parasitic currents on adjoining interconnects, therefore, causing a parasitic coupling, which becomes a limiting factor as density increases and size reduces. This paper presents a study of those proximity effects on interconnect geometry for X- and W-bands. Various configurations of finite ground microstrip lines, finite ground coplanar (FGC) waveguides, and transitions have been analyzed for silicon and Duroid substrates. The results included in this paper illustrate the implications of parasitic coupling associated with interconnects printed in parallel or perpendicular configurations, lines located in close proximity to open-end discontinuities, vias etched near FGC lines, and finally vertical transitions through wafers. Theoretical and experimental results, in terms of reduced isolation, are provided, showing the advantages of the use of FGC lines over conventional microstrip lines since, in the cases investigated, they offer 8 dB higher isolation. Additionally, open-end effects are demonstrated to increase coupling by as much as 6 dB, while vertical transitions through wafers cause a parasitic coupling in the order of 3 dB. The results presented in this study can be employed in order to reduce parasitic interference between interconnects.

Monolithic Wilkinson power divider on CMOS grade silicon with a polyimide interface layer for antenna distribution networks

Using an optimized finite ground coplanar waveguide layout on a CMOS grade silicon wafer with a 20 /spl mu/m thick polyimide interface layer and embedded passives, a Wilkinson power divider is built. The measured characteristics show an insertion loss of only 0.57 dB at 12.5 GHz and better than 15 dB return loss and isolation.

A 60-GHz uniplanar MMIC 4× subharmonic mixer

A uniplanar GaAs monolithic microwave integrated circuit /spl times/4 subharmonic mixer (SHM) has been fabricated for 60-GHz-band applications using an antiparallel diode pair in finite ground coplanar (FGC) waveguide technology. This mixer is designed to operate at an RF of 58.5-60.5 GHz, an IF of 1.5-2.5 GHz, and an LO frequency of 14-14.5 GHz. FGC transmission-line structures used in the mixer implementation were fully characterized using full-wave electromagnetic simulations and on-wafer measurements. Of several mixer configurations tested, the best results show a maximum conversion loss of 13.2 dB over the specified frequency range with a minimum local-oscillator power of 3 dBm. The minimum upper sideband conversion loss is 11.3 dB at an RF of 58.5 GHz and an IF of 2.5 GHz. This represents excellent performance for a 4/spl times/ SHM operating at 60 GHz.

Finite ground coplanar waveguide (FGC) low loss, low coupling 90-degree crossover junctions

Microwave and millimeter-wave integrated circuits and RF distribution networks often require two transmission lines to cross over each other. In this paper, experimental measurements and three-dimensional (3-D) finite difference time domain analysis are used to thoroughly characterize coplanar waveguide (CPW) and finite ground coplanar waveguide (FGC) 90-degree crossover junctions. It is shown that FGC crossover junctions have approximately 15 dB lower coupling than CPW crossover junctions. Furthermore, it is shown that the FGC junctions do not excite the parasitic slotline mode, whereas, the CPW junctions do excite the slotline mode. The results presented indicate that the FGC crossover junction is easier to implement and has better characteristics than the CPW crossover junction.

W-band micromachined circuit combining networks

In circuit-combining networks, low-loss interconnecting transmission lines are pivotal in reducing excess loss. Micromachined finite ground coplanar waveguides are used in this study as low-loss interconnects showing significant improvements in line loss while maintaining 50-/spl Omega/ characteristic impedance. Wilkinson power dividers, reactive tee junctions, and right-angle bends are combined with micromachined interconnects in 1:2, 1:4, and 1:8 power-dividing networks and show measured loss reduction of 0.3-1.0 dB depending on circuit type and size from 85 to 95 GHz.

A CPW T-resonator technique for electrical characterization of microwave substrates

An impedance independent method is proposed using a finite ground coplanar waveguide (CPW) T-resonator to electrically characterize microwave materials. Silicon-based CPW T-resonators are designed and measured, with calibrated data agreeing well with other methods up to 30 GHz. Uncalibrated measurements produce dielectric constant and attenuation results within 3.7% and 25%, respectively, of those obtained with calibration. Hence, the CPW T-resonator can be used to provide rapid and accurate characterization of microwave substrates with unknown dielectric properties.

Characterization of finite-ground CPW reactive series-connected elements for innovative design of uniplanar M(H)MICs

A variety of finite-ground coplanar waveguide (FGCPW) reactive series-connected capacitive and inductive elements are extensively studied and characterized as equivalent-circuit models that include complex parasitic effects caused by finite-ground widths. These models are developed by implementing a numerical calibration procedure called short-open calibration, which is used to extract characteristic parameters of the circuit model from full-wave method-of-moments calculations. The proposed model is generally described as an equivalent series admittance (Y/sub g/) or impedance (Z/sub g/) together with a pair of shunt admittances (Y/sub p/) for FGCPW series-connected structures. With the new scheme, the FGCPW elements of interest behave like lossless lumped elements at low-frequency range, consisting of a series capacitance or inductance, as well as two shunt capacitances. As frequency increases, however, Y/sub g/ and Z/sub g/ exhibit a frequency-related dispersion and also a lossy resonance behavior, which stand for some added inductive or capacitive coupling effect caused by the extent of finite-ground width. On the other hand, unbounded radiation effect, considered in this model, appears too strong to be ignored around resonance. Theoretical and experimental results that compare very well with each other are shown for interesting electrical behaviors of finite-ground structures. An innovative uniplanar three-stage bandstop filter is designed and measured on the basis of its simplified equivalent-circuit model.

Finite-ground coplanar-waveguide branch-line couplers

Two branch-line (BL) couplers based on finite-ground coplanar-waveguide (FGCPW) structures are proposed. The first one uses the bended structure to reduce the size of the normal quarter-wavelength two-arm BL coupler. The second one improves the bandwidth by adding external compensated networks, which are also folded for size reduction. In this study, the performances of these BL couplers are examined, theoretically and experimentally.

Impact of light illumination and passivation layer on silicon finite-ground coplanar-waveguide transmission-line properties

The modeling of silicon finite-ground coplanar-waveguide (FGCPW) transmission lines is presented in this paper. It is shown that the effective substrate conductivity increases in the presence of illumination and in the presence of a passivation layer in the slot regions independently. As a result, the losses of trenched FGCPW are lower than conventional FGCPW transmission lines. The strong dependence of the substrate conductivity on illumination suggests that optically controlled attenuators can be implemented with FGCPW transmission lines exhibiting practically no phase change between the different attenuation states. A new contrast ratio for optically controlled transmission lines is derived.

Full-wave CAD-based design of a finite ground CPW directional filter

Full-wave CAD-based design of a finite ground CPW directional filter

W-band InP HEMT MMICs using finite-ground coplanar waveguide (FGCPW) design

In this paper, we report on the development of W-band monolithic microwave integrated circuit (MMIC) power amplifiers using 0.1-/spl mu/m AlInAs/GaInAs/InP high electron mobility transistor (HEMT) technology and finite-ground coplanar waveguide (FGCPW) designs. In the device modeling, the Angelov nonlinear HEMT model was employed to predict the large signal performance of the device, and the results were validated by using state-of-the-art vector load-pull measurements. A two-stage single-ended W-band FGCPW MMIC using a 150-/spl mu/m-wide HEMT as the driver and a 250-/spl mu/m-wide HEMT for the output stage was designed, fabricated, and tested. The MMIC amplifier demonstrates a maximum output power of 18.6 dBm with 18.2% power-added efficiency and 10.6 dB associated gain at 94 GHz. This result is the best output power to date reported from an InP-based MMIC using FGCPW design at this frequency.

Si-micromachined coplanar waveguides for use in high-frequency circuits

This paper describes the development and characterization of a new class of Si-micromachined lines and circuit components for operation between 2-110 GHz. In these lines, which are a finite-ground coplanar-waveguide (FGC) type, Si micromachining is used to remove the dielectric material from the aperture regions in an effort to reduce dispersion and minimize propagation loss. Measured results have shown a considerable loss reduction to levels that compare favorably with those of membrane lines and rectangular waveguides. Micromachined FGC lines have been used to develop V- and W-band bandpass filters. The W-band micromachined FGC filter has shown a 0.8-dB improvement in insertion loss at 94 GHz over a conventional FGC line. This approach offers an excellent alternative to the membrane technology, exhibiting very low loss, no dispersion, and mode-free operation without using membranes to support the interconnect structure.