Multiple RF-/DC-Line Crossovers in Multilayer Millimeter Wave Circuits

We investigated the propagation losses and the characteristic impedances Z/sub L/ of coplanar waveguides (CPWs) and microstrip lines (MSLs) on a planar lightwave circuit (PLC)-platform formed on a silica/silicon substrate. The loss of the CPWs was 2.7 dB/cm at 10 GHz on the PLC-platform with 30 /spl mu/m thick silica layer. Thus, a cm-order circuit of this CPW is difficult to fabricate in the 10 Gb/s module. This is because the silicon substrate has a large loss tangent (tan /spl delta/). On the other hand, the loss of the MSLs, where a ground plane shielded the high loss silicon substrate, could be improved to 0.9 dB/cm at 10 GHz with 30 /spl mu/m thick polyimide. These lower loss MSLs on a PLC-platform can be applied to module operation at 10 Gb/s. Furthermore they have the advantage that they are suitable for application to array device circuits or circuits in a module where several devices are integrated because unlike CPWs the ground planes are not divided by signal lines or DC bias lines. The structure of CPWs and MSLs on a PLC-platform with a Z/sub L/ of 50 /spl Omega/ was also studied in detail.

This paper newly proposes that coupling between a coplanar waveguide (CPW) and a TE/sub 01/spl gamma//mode dielectric resonator (DR) can be realized for a parallel resonant characteristic as the DR coupled with a microstrip line. Coupling characteristics have been investigated by placing the DR on a special support above the CPW and by moving the DR away from the center of a slot of the CPW to the ground plane. FEM simulation (HFSS) results in terms of S-parameters agree well with measurement results. Finally, loaded Q values of the DR coupled with a CPW are compared with those of the DR coupled with a microstrip line. The comparison demonstrates that a DR coupled with a CPW has slightly higher loaded Q than that coupled with a microstrip line has.

To find the optimal driving voltage and bandwidth for electro-optic polymer-waveguide-based directional couplers, four electrode structures are investigated. They are the microstrip line (MSL), the asymmetric coplanar waveguide with ground (ACWG), the coplanar waveguide with ground (CPWG), and the edge-coupled microstrip line (CMSL). UV15:Polymethyl methacrylate/dispersed-red 1:UV11-3-based directional couplers are evaluated. The CPWG and the ACWG have almost the same driving voltages, which are about twice the driving voltage of the CMSL. The MSL has the largest driving voltage, which is 20 to 25% higher than the diving voltages of the CPWG and ACWG. Simulation results further conclude that the MSL has the largest bandwidth, and its bandwidth is about 1.6 times that of the bandwidth of the CMSL, which has the narrowest bandwidth. The bandwidths of the ACWG and CPWG are 1.4 and 1.2 times that of the CMSL, respectively. The driving voltages for the four different devices are experimentally confirmed.

It is expected that the superior high‐frequency characteristics, such as low loss and low dispersion, of superconducting oxides are applied to microwave circuits. However, low‐loss superconducting oxide films can only be fabricated on limited types of substrate materials using present technologies. Therefore, the dielectric constant, dielectric loss, and thickness of substrate materials place severe limitations on the circuit design and the propagation characteristics.This paper discusses the attenuation constants, characteristic impedances, and wiring density of three fundamental planar transmission lines, namely, stripline, microstrip line, and coplanar waveguide fabricated on substrate materials MgO and LaAlO3. This discussion is based on the TEM and quasi‐TEM analysis procedures. The thin films with low surface resistances have been fabricated on MgO and LaAlO3. It is concluded that the microstrip line is suitable for fabricating a low‐loss transmission line and the coplanar waveguide on a low dielectric constant substrate is suitable for high‐density wirings.Also measured were the characteristics of the half‐wave transmission line resonators of these three transmission line configurations, which are made of EuBa2Cu3Ox thin films on an MgO substrate. The attenuation constant of 50 Ω, 50‐μm wide coplanar waveguide is 9.7 × 10−3 Np/m (8.4 × 10−2 dB/m) at 3.9 GHz and 28 K. This value is two orders of magnitude lower than that of the copper transmission line.

Two printed wide-slot antennas with square patches within an arc-shape slot are proposed in this letter. They are fed by a coplanar waveguide (CPW) and a microstrip line with almost the same performances. Their impedance bandwidths for $ S_11leq -10~ dB$ are enhanced largely to more than 158%. The radiation patterns are given at 2, 6, and 10 GHz.

In modern radar systems, often planar transmission lines, such as stripline, microstrip line or coplanar waveguides are used to distribute signals between different components. In this paper we present a way to realize low-loss distribution with embedded waveguides by radiating laterally from an MMIC housed in an eWLB package into a waveguide. In this work, the waveguide is made half of a 3d-part and the other half is realized as cavity in a low cost non RF printed circuit board. For a proof of concept study, the chip was replaced by a differential microstrip line back-to-back structure. Different manufacturing tolerances and their impact on the performance will be shown. A prototype was built, measured and compared to the simulation results. It will be shown that the splitted PCB-waveguide channel has a loss of 0.11 dB/cm and that the transition from PCB-waveguide to differential microstrip line will lead to an insertion loss of 2.55 dB.

High performance coplanar waveguides (CPWs) on GaN membrane technology for AlGaN/GaN high electron mobility transistors (HEMTs) grown on low-resistivity (LR) Si substrates have been demonstrated in this work. The developed CPW technology shows a remarkable improvement in RF losses when the lossy Si beneath CPW structures is removed, resulting in comparable RF performance to that of CPW realized on high-resistivity (HR) Si and semi-insulating (SI) SiC substrates, with similar AlGaN/GaN top epitaxial layers. Experimental results, first to be reported, demonstrate transmission losses ( $S_{21}$ ) of 0.47 dB and $Q$ -factor of 20.77 for the CPW on GaN membrane technology, compared to $S_{21}$ of 2.95 dB and $Q$ -factor of 4.51 for the CPW on GaN-on-LR Si, at 40 GHz. Furthermore, the influence of substrate parasitics on RF performance of CPW on GaN-based HEMTs grown on various substrates was studied and analyzed by the extraction of transmission line parameters for frequencies up to 40 GHz. These findings offer viable integrated GaN-based HEMTs on LR Si technology suitable for high-power and high-temperature system applications at RF and millimeter-wave frequencies, when used in conjunction with high thermal coefficient materials such as diamond and AIN.

A design theory is described for coupling between microstrip line and image guide through small coupling holes in a common ground plane. A five-slot Chebyshev coupler is designed based on coupling through a rectangular slot. The theoretical results are compared with experimental results.

In this paper, propagation characteristics of even-symmetric hybrid modes in a waveguide-shielded microstrip line with the presence of the resistive films affixed to the two sides of the center strip is investigated. The method of lines with modifications concerning the inhomogeneity of the surface between the air and substrate layers is used for analysis. After a validity check of the analysis by considering two special structures, i.e., a microstrip line (R/sub m/=/spl infin/) and a coplanar waveguide (R/sub m/=0), the resistance R/sub m/ and the width W/sub m/ of the film are varied to see the influence on the propagation and attenuation constants of the dominant mode as well as the higher-order (parasitic) modes. Optimal combinations of the resistance and the width are found so that the resistive film has the largest attenuating effect on the higher-order modes but has no interference with the dominant one. >

In this paper, coplanar waveguide (CPW) method is proposed for identifying the surface wave band-gap of mushroom-like EBG structure. Two lines are cut off from the complete ground plane of the EBG structure and the defected ground plane can be viewed as a coplanar waveguide with characteristic impedance of 50 Ohm. The other layer of the EBG structure is not changed. The surface wave band-gap range can be obtained from the transmission curve of CPW in two cases: EBG inserted and no EBG inserted. Furthermore, the electric field distribution within and beyond the stop-band are studied. And we also investigate the influence of EBG rows on the band-gap. The results extracted from CPW method agrees very weD with that of TEM waveguide model. Compared to the most used experimental method, suspended microstrip line method, the CPW method is a one-layer structure which leads to be low-cost, easy-made and more effective. Both simulated and experimental results verify the effectiveness of the CPW method. Therefore, the CPW method can be applied for identifying the surface wave band-gap of EBG structure much more effectively in engineering applications.

Planar Beam-forming Antenna Array for 60-GHz Broadband Communication

A broadband high-gain periodic endfire antenna is presented in this article. The broadband is achieved by using a planar out-of-phase power divider with ultra-wideband performance and periodic dipole elements. The device uses two substrates with a common ground plane. A coupling between two microstrip lines on the top and bottom substrate layers through a slot in the common ground plane, and a transition from two microstrip lines to a parallel stripline are used to achieve an ultra-wideband operation. The gain enhancement is achieved by loading with an I-shape resonator (ISR) structure in the endfire direction. The effect of the I-shape unit cell structure on the gain enhancement is investigated. Both the ISR-loaded antenna and unloaded one are fabricated to verify the predictions. The measurements show that ISR-loaded antenna presents gain of about 7 dB-10 dB in the whole working band (3 GHz-11 GHz), which is about 2 dB-3.5 dB more than the unloaded one. The proposed antenna can be using in wireless communication systems for its advantages of broad bandwidth and high-gain.

A broadband high gain endfire antenna is presented in this paper. Broad bandwidth is realized by using a planar out-of-phase power divider with ultra-wideband performance and periodic dipole elements. The device uses two substrates with a common ground plane. A coupling between two microstrip lines on the top and bottom substrate layers through a slot in the common ground plane , and a transition from two microstrip lines to a parallel stripline are used to achieve an ultra-wideband operation. The gain enhancement is achieved by loading split-ring resonator (SRR) structure in the endfire direction. The effect of the SRR-shape unit structure on the gain enhancement is investigated. Both SRR-loaded antenna and unloaded one are fabricated to verify the predications. The measurements show that SRR-loaded antenna presents gain of about 7dB-10dB in the whole working band (3.5GHz-11GHz) ,which is about 2dB-4.5dB more than the unloaded one. This antenna can be used in wireless communication systems for its advantages of the broad bandwidth and high gain.

Vertical-cavity surface-emitting lasers with vertically integrated electro-absorption modulators (EAM-VCSELs) potentially can reach higher modulation bandwidths than directly current-modulated VCSELs. The aforementioned device modulation capabilities are, however, currently restricted by their electrical contact parasitics. It, thus, becomes critical to optimize their access line to improve performance. In this paper, we numerically and experimentally demonstrate that a microstrip (MS) access line using a planarized benzocyclobutene (BCB) layer exhibits improved high-frequency characteristics compared to the coplanar waveguide (CPW) access line used to-date, since it reduces the losses induced by the doped substrates. We also use this opportunity to introduce an innovative technique for BCB layer planarization, which is not only compatible with the EAM-VCSEL double-mesa structure, but is also independent of the device pitch. The resulting BCB layer dielectric permittivity and losses are measured up to 100 GHz, and a side-by-side comparison of the electrical response of three-electrodes MS and CPW access lines is subsequently carried out. Finally, using the measured pad and access line RF responses and the EAM modulation characteristics, the devices with MS access are shown to be no longer limited by their electrode parasitics, but by the modulator internal impedance.

A structure consisting of dielectric-loaded feed lines (such as surface-wave lines similar to Goubau lines) and below-cutoff air-filled cavities can be used to form essentially L-C sections. The capacitance is due to electric-field coupling from the feed-line dielectric medium into the below-cutoff section. The inductance results from combining the inductors in the inductive tee equivalent circuit for such below-cutoff sections. Dielectric loading is used to shorten the guide wavelength at the input to the evanescent section, increasing the effective input inductance. The dielectrically loaded feed lines can comprise microstrip, coplanar waveguide (CPW), coplanar stripline (CPS), Goubau lines (surface-wave structures), waveguide, etc. The resulting resonant elements are usable at frequencies below 1 GHz, with small dimensions. If connected to the common ground plane, these L-C sections act as a transmission zero. If "floated," i.e., connected in the "hot" line rather than to the ground plane, the sections form bandpass circuits (transmission poles). The air-filled below-cutoff sections (evanescent mode) are placed in a supporting low dielectric-constant medium (air, Teflon, or similar) with the open end in proximity to the dielectric portion of the feed line and are, thus, termed "suspended." The individual L-C sections can be coupled together using microstrip, surface-wave line, CPW, CPS, finline, waveguide, or lumped elements. Such combinations can be chosen to implement Chebychev, Butterworth, quasi-elliptic, etc. responses.