Showing papers on "Return loss published in 2001"
TL;DR: In this paper, a planar platform is developed in which the microstrip line and rectangular waveguide are fully integrated on the same substrate, and they are interconnected via a simple taper.
Abstract: Usually transitions from microstrip line to rectangular waveguide are made with three-dimensional complex mounting structures. In this paper, a new planar platform is developed in which the microstrip line and rectangular waveguide are fully integrated on the same substrate, and they are interconnected via a simple taper. Our experiments at 28 GHz show that an effective bandwidth of 12% at 20 dB return loss is obtained with an in-band insertion loss better than 0.3 dB. The new transition allows a complete integration of waveguide components on substrate with MICs and MMICs.
1,631 citations
20 May 2001
TL;DR: In this paper, a planar platform is developed in which a coplanar waveguide and a rectangular waveguide are fully integrated on the same substrate, and they are interconnected via a simple transition.
Abstract: Usual transitions between planar circuit and rectangular waveguide make use of 3-D complex mounting structures. Such an integration requires costly high precision mechanical alignment, In this paper, a new planar platform is developed in which a coplanar waveguide (CPW) and a rectangular waveguide are fully integrated on the same substrate, and they are interconnected via a simple transition. They can be built with a standard PCB process. Our experiments at 28 GHz show that an effective bandwidth of 7% at 15 dB return loss can easily be achieved. The CPW-to-waveguide transition allows for a complete integration of waveguide components on substrate with active components such as MMIC.
208 citations
TL;DR: In this paper, a detailed investigation of flip-chip interconnects up to W-band frequencies is presented, where different test structures were fabricated and measured to determine the electromagnetic characteristics of flipchip multichip modules, such as detuning, reflection at the interconnect, and parasitic coupling.
Abstract: A detailed investigation of flip-chip interconnects up to W-band frequencies is presented in this paper. In a coplanar 50-/spl Omega/ environment, different test structures were fabricated and measured to determine the electromagnetic characteristics of flip-chip multichip modules, such as detuning, reflection at the interconnect, and parasitic coupling. Electromagnetic simulation is used to explain the details behind the measured results. Key to high return loss at the interconnect is a small bump-pad area. Applying simple compensation structures, the frequency range of operation can be further extended. It is shown that a return loss beyond 20 dB in the frequency range up to 80 GHz is achievable along with excellent reproducibility. Measurements on detuning and isolation are also presented.
148 citations
TL;DR: In this article, a three-port microstrip multifrequency diplexer is proposed to take 10, 12, 19, and 21 GHz into port 1 and to separate 10 and 19 GHz to port 2 and 12 and 28 GHz to part 3 with minimal dispersion.
Abstract: This paper introduces a three-port microstrip multifrequency diplexer used in a phased-array transceiver system that employs band-stop filters with open-circuited stubs for band selection and separation. The diplexer is designed to take 10, 12, 19, and 21 GHz into port 1 and to separate 10 and 19 GHz to port 2 and 12 and 21 GHz to part 3 with minimal dispersion. The insertion loss for each frequency varies from 0.4 to 3.4 db and the return loss is better than 10 dB. The isolation between channels at the four frequencies is greater than 50 dB. Each passband created between adjacent stopbands has a bandwidth over 1 GHz. The microstrip diplexer is designed using periodic stubs that collectively have the advantages of low insertion loss, high isolation and rejection, wide-band performance on each channel, and easy fabrication. This type of diplexer has many applications in multifrequency transceivers for communication systems.
106 citations
TL;DR: In this paper, the authors describe the development and performance of a wideband dual linear polarization microstrip antenna array used in the Danish high-resolution airborne multifrequency polarimetric synthetic aperture radar, EMISAR.
Abstract: This paper describes the development and performance of a wideband dual linear polarization microstrip antenna array used in the Danish high-resolution airborne multifrequency polarimetric synthetic aperture radar, EMISAR. The antenna was designed for an operating frequency of 1.25 GHz/spl plusmn/50 MHz and was built as an array of 8/spl times/2 probe-fed stacked microstrip patches. The feeding network is constructed in microstrip and is capable of handling 6 kW of peak input-power at an altitude of 45000 ft (unpressurized). The impedance bandwidth (return loss better than -14 dB) of the antenna is 10%, the isolation between the horizontal and the vertical ports of the array is 50 dB and the cross-polarization suppression is 40 dB. A new design principle for simultaneously achieving very low cross-polarization and low side lobes in dual linear polarization antenna arrays has been applied.
103 citations
Patent•
13 Sep 2001
TL;DR: In this article, a multilevel and space-filling ground-plane design is proposed to control the return loss, bandwidth, gain, radiation efficiency, and frequency performance of an antenna system.
Abstract: An antenna system includes one or more conductive elements acting as radiating elements, and a multilevel or space-filling ground-plane, wherein said ground-plane has a particular geometry which affects the operating characteristics of the antenna. The return loss, bandwidth, gain, radiation efficiency, and frequency performance can be controlled through multilevel and space-filling ground-plane design. Also, said ground-plane can be reduced compared to those of antennas with solid ground-planes.
85 citations
TL;DR: In this paper, a coplanar stripline (CPS)-to-microstrip line was developed for wideband coplanars with a simple structure for the ease of fabrication with low cost.
Abstract: A wideband coplanar stripline (CPS)-to-microstrip line was developed. The transition has a simple structure for the ease of fabrication with low cost. The measured performance of two back-to-back transitions exhibits an insertion loss of less than 3 dB and a return loss of better than 10 dB over a bandwidth from 1.3 GHz to 13.3 GHz (1:10.2). For narrower bandwidth, an insertion loss of less than 1 dB with a return loss of better than 10 dB was achieved from 1.4 GHz to 7.3 GHz (1:5.2).
78 citations
20 May 2001
TL;DR: In this paper, the authors describe the design and measured performance of a duplexer based on film bulk acoustic resonators (FBARs) for the 1900 MHz PCS cellular phone market.
Abstract: We will describe the design and measured performance of a duplexer based on film bulk acoustic resonators (FBARs) for the 1900 MHz PCS cellular phone market. Typical specifications for the duplexer require the Tx filter to attenuate frequencies in the Rx band by >40 dB while maintaining a worst-case insertion loss of 3.5 dB over the Tx band. VSWR must be better than 2.2 in the pass-band (8.5 dB return loss). The Rx filter must attenuate the Tx frequencies by >50 dB while maintaining a worst-case insertion loss of 4.2 dB in the Rx band. Again, VSWR must be better than 2.2.
76 citations
TL;DR: In this article, a new type of interconnect is developed that significantly extends the bandwidth of fixed-length bond-wire interconnects between microwave circuits, which is treated as a five-stage low-pass filter where basic filter theory is used to develop an interconnect prototype.
Abstract: A new type of interconnect has been developed that significantly extends the bandwidth of fixed-length bond-wire interconnects between microwave circuits. This interconnect maximizes bond-wire length, as well as landing pad size while simultaneously extending the cutoff frequency of the interconnect. The bond-wire interconnect is treated as a five-stage low-pass filter where basic filter theory is used to develop an interconnect prototype. Microstrip interconnects are designed using electromagnetic simulators, which match a specific low-pass filter response on a 5-mil thick (127 /spl mu/m) glass substrates. The measurements indicate a return loss greater than 12 dB and an insertion loss from 0.0 to 0.3 dB from DC to 80 GHz using two 17-mil-long (432 /spl mu/m) 1-mil-diameter (25 /spl mu/m) ball bonds with a tolerance of /spl plusmn/2 mil (50 /spl mu/m). For comparison, an uncompensated interconnect with two 17-mil-long (432 /spl mu/m) bond wires has 1-dB insertion loss and 10-dB return loss at 40 GHz and continues to degrade at higher frequencies.
76 citations
Journal Article•
TL;DR: In this paper, a coplanar stripline (CPS)-to-microstrip line was developed for wideband coplanars with a simple structure for the ease of fabrication with low cost.
Abstract: A wideband coplanar stripline (CPS)-to-microstrip line was developed. The transition has a simple structure for the ease of fabrication with low cost. The measured performance of two back-to-back transitions exhibits an insertion loss of less than 3 dB and a return loss of better than 10 dB over a bandwidth from 1.3 GHz to 13.3 GHz (1: 10.2). For narrower bandwidth, an insertion loss of less than 1 dB with a return loss of better than 10 dB was achieved from 1.4 GHz to 7.3 GHz (1: 5.2).
67 citations
20 May 2001
TL;DR: In this paper, an antenna switch/filter module integrating GSM/DCS/PCS diplexer functions and Rx/Tx antenna switching on a low temperature co-fired ceramic (LTCC) substrate is presented.
Abstract: This paper presents the results of an antenna switch/filter module integrating GSM/DCS/PCS diplexer functions and Rx/Tx antenna switching on a low temperature co-fired ceramic (LTCC) substrate. Although the RF front-end module (FEM) was configured for dual-band (GSM/DCS) applications, the high pass filter function was designed to operate in the PCS band as well. Harmonic filtering was included in the diplexer design, which reduced the filtering requirements for the power amplifier. The 50-ohm in/out FEM utilized GaAs PHEMT switches and associated bias passives surface mounted on the LTCC substrate. S-parameter characterization of the FEM demonstrated excellent insertion and return loss characteristics. For GSM, the return and insertion losses measured at 912 MHz were better than 28 dB and less than 1.7 dB, respectively. Similarly, for DCS applications, the return and insertion losses at 1.77 GHz were better than 19 dB and less than 1.5 dB, respectively. In both cases, the design approach yielded excellent agreement between measured and simulated results.
20 May 2001
TL;DR: In this paper, a coplanar waveguide (CPW) to microstrip transition is presented, and the authors show that a bandwidth of 13 GHz with less than -25 dB return loss can be achieved.
Abstract: A new design of a coplanar waveguide (CPW) to microstrip transition is presented. Simulation using the high frequency simulator software (HFSS) shows that a bandwidth of 13 GHz with less than -25 dB return loss can be achieved. The transition was fabricated and characterized. Experimentally, the S/sub 11/ of two back to back conductor backed CPW to microstrip transitions on InP substrate is better than -12 dB up to 14 GHz. For alumina substrate the S/sub 11/ was less than -15 dB up to 25 GHz.
TL;DR: In this article, a new approach to designing a handset antenna for satellite applications is reported, based on precise control of the phasing between two bifilar helices, giving accurate resonant frequency position and radiation pattern volute.
Abstract: A new approach to designing a handset antenna for satellite applications is reported. It is based on precise control of the phasing between two bifilar helices, giving accurate resonant frequency position and radiation pattern volute. Results show an antenna with a gain of -2 dBi, 19 dB discrimination between the right and left hand circular polarisations and an axial ratio less than 1 dB. The front-to-back ratio is 24 dB. A return loss of 14.6 dB is also measured.
TL;DR: In this article, a stacked, dual-frequency microstrip planar inverted-F antenna (DF-PIFA) was proposed for mobile telephone handsets that can concurrently work in two frequency bands, viz., those associated with the GSM and DCS 1800 systems operating at 0.9 GHz and 1.8 GHz.
Abstract: We describe a stacked, dual-frequency microstrip planar inverted-F antenna (DF-PIFA) for mobile telephone handsets that can concurrently work in two frequency-bands, viz., those associated with the GSM and DCS 1800 systems operating at 0.9 GHz and 1.8 GHz, respectively. The proposed microstrip DF-PIFA is fed by a coaxial line, as opposed to two separated feed lines used in the conventional design. The design is carried out in a systematic manner and involves two steps. We begin with an initial configuration of the PIFA that is based on a standard design for a microstrip patch antenna fed by a coaxial line and is derived from an empirical approximation in conjunction with a transmission line model. Next, we employ a computer-aided design (CAD) tool, based on the nonuniform finite-difference time-domain (NU-FDTD) Maxwell solver, to optimize the performance characteristics of the DF-PIFA, including the return loss, the matching of the input impedance, and the far-field radiation patterns.
TL;DR: In this article, a broadband microstrip to coplanar waveguide (CPW) transition is proposed based on vertical resonant coupling between the microstrip and CPW, which does not require via holes, wire bonds, or air bridges.
Abstract: A broadband microstrip to coplanar waveguide (CPW) transition is proposed. The design is based on vertical resonant coupling between the microstrip and CPW. The transition does not require via holes, wire bonds, or air bridges. The design of the transitions at C band shows good agreement with return loss better than -15 dB over 2.8-7.5 GHz. The new transition has the advantages of broad bandwidth and easy fabrication.
01 Jan 2001
TL;DR: In this article, a low-cost cavity backed coplanar-waveguide with a spiral antenna was proposed to cover a 9:1 bandwidth with a return loss better than 10 dB from 04 to 38 GHz.
Abstract: This article discusses a low-cost cavity backed coplanar-waveguide to coplanarstrip fed logarithmic uniplanar spiral antenna that covers a 9:1 bandwidth with a return loss better than 10 dB from 04 to 38 GHz The IE3D computer program is used to predict the performance of the spiral antenna in terms of radiation pattern and input impedance The obtained numerical results are in good agreement with the experimental data The spiral antenna radiates from an active region that is a frequency-dependent part of the structure The rotation of the radiation pattern as a function of frequency will also be discussed
TL;DR: In this article, two feeding designs for achieving dual orthogonal linear polarization operations of dielectric resonator (DR) antennas fed by microstrip lines are demonstrated, and the microstrip feedlines can be placed directly under the DR or conformal to the surface of the DR.
Abstract: Two feeding designs for achieving dual orthogonal linear polarization operations of dielectric resonator (DR) antennas fed by microstrip lines are demonstrated. The microstrip feedlines can be placed directly under the DR or conformal to the surface of the DR. Good dual-polarization excitation can be obtained for the two feeding designs. Experimental results for the return loss, isolation between two feeding ports, and radiation patterns are presented and discussed. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 222–223, 2001.
TL;DR: In this paper, the authors explored the development of a new class of broadband antenna in which TE/sub 0/surface-wave is used as the primary source of free space radiation, which can be designed to operate over a broad bandwidth, be extremely compact, and can be easily integrated with MIC and MMIC technology.
Abstract: This letter explores the development of a new class of broadband antenna in which TE/sub 0/ surface-wave is used as the primary source of free space radiation. We demonstrate that antennas based on this concept can be designed to operate over a broad bandwidth, be extremely compact, and can be easily integrated with MIC and MMIC technology. Measurement of return loss and radiation pattern characteristics of the antenna described in this letter indicate a 47% operating bandwidth, covering a large part of the frequency spectrum assigned for U.S. as well as European high-speed wireless local area network (WLAN) applications, making it ideal for integration with WLAN modules.
TL;DR: In this paper, a dual-polarized microstrip antenna capable of achieving a wide bandwidth, high isolation, low crosspolarisation levels and low backward radiation levels is presented.
Abstract: A dual-polarised microstrip antenna capable of achieving a wide bandwidth, a high isolation, low cross-polarisation levels and low backward radiation levels is presented The H-shaped coupling aperture is used For wide bandwidth and easy integration with active circuits, it uses the aperture-coupled stacked microstrip square patches Measured return loss exhibits a bandwidth of over 209% and isolation is better than 36 dB over the bandwidth Cross-polarisation levels and the front-to-back ratio are better than –22 and 21 dB, respectively
01 Sep 2001
TL;DR: In this paper, a reduced size branch-line coupler has been implemented and demonstrated in a 4×4 Butler Matrix beamforming network operating at 1.7-2.0 GHz.
Abstract: This paper presents a reduced size quadrature branch-line coupler that has achieved size reduction by approximately up to 80% without having to compromise performance. This design is realized on a low cost substrate (FR4, 0.50mm, ?r = 4.4), yields an excellent return loss (?49.0dB) and coupling loss (?3.30 ~ ?3.50dB) characteristics at 1.8GHz. The practical application of this novel reduced size branch-line coupler has been implemented and demonstrated in a 4×4 Butler Matrix beam-forming network operating at 1.7-2.0GHz.
TL;DR: In this paper, a 12-pole quasi-elliptic filter with 0.5% fractional bandwidth at 1.775 GHz has been designed using meander-line microstrip resonators and manufactured on a double-sided YBCO film on a LaAlO/sub 3/ substrate.
Abstract: The compact meander-shape configuration of planar resonators is suggested for applications in narrowband filters with quasi-elliptic characteristic. The quasi-elliptic frequency response with two transmission zeroes at the edges of the passband is provided by the specific symmetry of the coupled resonators and is controlled by an appropriate choice of the resonator dimensions and the couplings between the resonators. The 12-pole quasi-elliptic filter with 0.5% fractional bandwidth at 1.775 GHz has been designed using meander-line microstrip resonators and manufactured on a double-sided YBCO film on a LaAlO/sub 3/ substrate. The filter exhibited the in-band insertion loss less than 0.5 dB at T=60 K, the return loss of 20 dB, the out-of-band rejection better than 75 dB, and 40 dB/MHz slope of the characteristic.
Patent•
21 Apr 2001
TL;DR: In this paper, a probe-fed rectangular patch antenna with a pair of wide slits is proposed, which can have an impedance bandwidth of about 24% (determined from 10-dB return loss).
Abstract: A new broadband design of a probe-fed rectangular patch antenna with a pair of wide slits is proposed. The proposed design is with an air or foam substrate. Experimental results show that simply by inserting a pair of wide slits at one of the radiating edges of the rectangular patch, good impedance matching for a wide range of operating frequencies can easily be achieved for the proposed antenna. With an air substrate of thickness about 8% of the wavelength of the center operating frequency, the proposed probe-fed patch antenna can have an impedance bandwidth of about 24% (determined from 10-dB return loss). For the operating frequencies within the impedance bandwidth, good radiation characteristics are also observed, and the peak antenna gain obtained is about 7.2 dBi.
01 Jun 2001
TL;DR: In this article, a novel four-beam dual-polarized microstrip antenna array at the 10 GHz band is presented, where two Butler matrix microstrip circuits corresponding to two orthogonal polarisations can be located on different substrate layers and integrated with a patch array.
Abstract: A novel four-beam dual-polarised microstrip antenna array at the 10 GHz band is presented. By using a multilayered structure and multiport slot-coupled microstrip lines, two Butler matrix microstrip circuits corresponding to two orthogonal polarisations can be located on different substrate layers (above and below the ground plane) and integrated with a patch array. The antenna has eight input ports corresponding to two orthogonal polarisations and four beams. The theoretical design is based on the finite-difference time-domain (FDTD) method. The measured return loss and isolation characteristics exceed 10 and 23 dB, respectively, in the 9.7-10.3 GHz band. The radiation pattern is close to an ideal Butler pattern and the cross-polarisation level is lower than -18 dB in the beams. Details of the antenna and its characteristics are presented.
20 May 2001
TL;DR: In this paper, a wideband coplanar waveguide (CPW) DC-26 GHz MEMS absorptive switch on silicon substrate is presented, which utilizes novel DC-contact series and shunt fixed-fixed beam MEMS switches with "dimples" at the contact area for improved contact resistance.
Abstract: The design and performance of a wideband coplanar waveguide (CPW) DC-26 GHz MEMS absorptive switch on silicon substrate is presented. The absorptive switch utilizes novel DC-contact series and shunt fixed-fixed beam MEMS switches with 'dimples' at the contact area for improved contact resistance. An insertion loss of 0.5 dB or better is achieved from DC-26 GHz. The isolation is -40 dB at 5 GHz, -35 dB at 10 GHz and -25 dB at 26 GHz. These switches are useful in applications where good return loss is required in the isolation state.
08 Jul 2001
TL;DR: In this paper, two identical parasitic patches next to the resonant edges of the main patch were introduced to widen the narrow bandwidth of the newly suggested coplanar patch antennas, achieving an impedance bandwidth of about 8.0 dB and stable radiation patterns.
Abstract: We have presented simulation and experimental results of wideband coplanar waveguide fed coplanar patch antennas. The antennas were developed to widen the narrow bandwidth of the newly suggested coplanar patch antennas. This was achieved by introducing two identical parasitic patches next to the resonant edges of the main patch. Simulation was done by a commercial package. Antennas operating at 10 GHz were designed and fabricated. The return loss, radiation patterns and gain of the antennas were measured. An impedance bandwidth (return loss <-10 dB) of about 8.0 % and stable radiation patterns were observed, and the gain of the antennas were about 9.0 dBi. Design procedures and the experience of using the antennas have been discussed.
TL;DR: In this paper, a reactively sputtered aluminum nitride (AlN) piezoelectric film and its application for a film bulk acoustic resonator (FBAR) device are presented.
Abstract: In this article, a reactively sputtered aluminum nitride (AlN) piezoelectric film and its application for a film bulk acoustic resonator (FBAR) device are presented. The FBAR is composed of an AlN film sandwiched between top aluminum (Al) and bottom gold (Au) electrodes and an acoustic reflector block of SiO2/W stacked multilayers. Both the top and bottom electrodes are connected by a transmission line. The insertion loss (S21) and return loss (S11) were 6.1 and 37.19 dB, respectively. Using the empirical definition technique, the series resonance frequency (fs) and parallel resonance frequency (fp) were found to be 1.976 and 2.005 GHz, respectively. Based on these findings, the effective electromechanical coupling coefficient (Keff2) and the quality factor (Q) were also obtained as 3.53% and 4261, respectively.
TL;DR: In this paper, an integrated-circuit sampling down-converter with an internal pulse generator, local oscillator (LO), and an IF amplifier is presented, which exhibits a good linearity and low harmonic levels.
Abstract: In this paper, we report on the development of a new integrated-circuit sampling down-converter having its own pulse generator, local oscillator (LO), and IF amplifier. The internal pulse generator uses a step recovery diode together with a unique ultra-wide-band hybrid junction to generate sub-nanosecond balanced pulses for gating the sampling diodes. The down-converter exhibits a conversion gain from 12 to 15.5 dB over an RF frequency of 0.01-3 GHz with 10-MHz LO and sampling pulses of about 100 ps. Return loss at the RF port is better than 15 dB over this RF bandwidth. The down-converter exhibits a good linearity and low harmonic levels. This down-converter employs a coplanar waveguide and slot line to make the entire circuit uniplanar and is, thus, suitable for low-cost production. In addition, if has an internal pulse generator, LO, and IF amplifier, making it a compact receiver subsystem, which can readily be used in many microwave systems.
TL;DR: In this paper, the design, integration, and measurement of quadrature couplers integrated in a multilayer thin-film multichip-module technology are discussed.
Abstract: In this paper, the design, integration, and measurement of quadrature couplers integrated in a multilayer thin-film multichip-module technology are discussed. We have investigated four- and six-finger coplanar-waveguide (CPW) Lange couplers and a coupler based on reentrant sections. Three methods for the design of CPW Lange couplers are compared for the first time. The method of Paolino consistently results in the best performance. The four-finger Lange coupler results in a -3.2+/-0.2-dB coupling bandwidth from 10.8 to 14.9 GHz, with a return loss better than -18 dB and an isolation better than -20 dB. The six-finger Lange coupler results in a -3.2+/-0.5-dB coupling bandwidth from 9.5 to 17 GHz, with a return loss and isolation better than -16 dB. The coupler using reentrant sections results in a -3.4+/-1.1-dB coupling bandwidth from 6.9 to 18.8 GHz with a return loss and isolation better than -21 dB. It is shown that CPW Lange couplers are not sensitive to planarization effects, while for the design of couplers using reentrant sections, the effect should be taken into account. The Lange couplers have the additional advantage that they are easier to design, have a lower insertion loss, and can be very well predicted using method-of-moments simulations.
TL;DR: In this paper, a dual-polarized aperture-coupled microstrip antenna with a wide bandwidth, high isolation, low crosspolarisation levels and low backward radiation levels is presented.
Abstract: A dual-polarised aperture-coupled microstrip antenna with a wide bandwidth, a high isolation, low cross-polarisation levels and low backward radiation levels is presented. The square patch is fed at two corners via H-shaped apertures. The measured return loss exhibits a bandwidth of over 24.4% and the isolation is better than 30 dB over the bandwidth. The cross-polarisation levels and the front-to-back ratio are better than -23 and 22 dB, respectively.
12 Sep 2001
TL;DR: In this paper, a silicon micromachined on-wafer packaging scheme for RF MEMS switches is proposed that has excellent performance at K-band with an insertion loss of 0.1 dB and return loss of 32 dB at 20 GHz along with a 55% bandwidth of operation.
Abstract: A silicon micromachined on-wafer packaging scheme for RF MEMS switches is proposed that has excellent performance at K-band. The designed RF transition has an insertion loss of 0.1 dB and a return loss of 32 dB at 20 GHz along with a 55% bandwidth of operation. A novel fabrication technique previously presented is utilized for patterning the RF interconnects inside micromachined silicon cavities. The fabrication process is designed so as to be completely compatible with the MEMS switch process, hence allowing the parallel fabrication of all the components on one wafer. The on-wafer packages require no external wiring to achieve signal propagation and thus have potential for lower loss and better performance at higher frequencies.