Average Return Loss Research Articles

Modified Square Fractal Antenna for Multiband Application

Antennas with low profile, compact size, multiband are in great insist in modern telecommunication system. Fractal antennas are simple, lightweight and compact. A compact fractal antenna derived from Sierpinski triangle concept, but in different modern way by rotating the square in tiny degrees, then migrated the new square with the old one to create a new antenna with 70 × 70 mm2 substrate scale. In this paper, a new model antenna was researched for application that requires multiband and wide range of frequencies from 1 GHz to 10 GHz, with 10 frequency responses with VSWR bandwidth nearly less than 1.8 for all these frequencies, and with average return loss bandwidth almost -15 dB.

10–25 GHz frequency reconfigurable MEMS 5-bit phase shifter using push–pull actuator based toggle mechanism

This paper presents a frequency tunable 5-bit true-time-delay digital phase shifter using radio frequency microelectromechanical system (RF MEMS) technology. The phase shifter is based on the distributed MEMS transmission line (DMTL) concept utilizing a MEMS varactor. The main source of frequency tuning in this work is a bridge actuation mechanism followed by capacitance variation. Two stages of actuation mechanisms (push and pull) are used to achieve a 2:1 tuning ratio. Accurate control of the actuation voltage between the pull to push stages contributes differential phase shift over the band of interest. The functional behavior of the push–pull actuation over the phase shifter application is theoretically established, experimentally investigated and validated with simulation. The phase shifter is fabricated monolithically using a gold based surface micromachining process on an alumina substrate. The individual primary phase-bits (11.25°/22.5°/45°/90°/180°) that are the fundamental building blocks of the complete 5-bit phase shifter are designed, fabricated and experimentally characterized from 10–25 GHz for specific applications. Finally, the complete 5-bit phase shifter demonstrates an average phase error of 4.32°, 2.8°, 1° and 1.58°, an average insertion loss of 3.76, 4.1, 4.2 and 4.84 dB and an average return loss of 11.7, 12, 14 and 11.8 dB at 10, 12, 17.2 and 25 GHz, respectively. To the best of the authors’ knowledge, this is the first reported band tunable stand alone 5-bit phase shifter in the literature which can work over the large spectrum for different applications. The total area of the 5-bit phase shifter is 15.6 mm2. Furthermore, the cold-switched reliability of the unit cell and the complete 5-bit MEMS phase shifter are extensively investigated and presented.

COPLANAR-PGL TRANSITIONS ON HIGH RESISTIVITY SILICON SUBSTRATE IN THE 57-64 GHZ BAND AND INFLUENCE OF THE PROBE STATION ON THE PERFORMANCES

We present Coplanar-Planar Goubau Line (PGL) transitions designed on high-resistivity Silicon to characterize a PGL using microwave probing. These transitions are optimized in the 57{ 64GHz frequency band to present excellent electrical performances despite the fleld disturbance of the measurement setup. As the transitions are positioned on a probe station chuck, a glass substrate is added between the transition under test and the metallic chuck to minimize the disturbance. 3-D full- wave electromagnetic fleld simulations performed on a commercial software and on-wafer measurements show almost comparable results in term of scattering matrix parameters. Low losses are attained with a measured average transmission parameter of 2.5dB at 60GHz for a length of 8mm of a back-to-back structure with the transitions at the extremities. The measured average insertion loss and return loss per transition are better than 1.36dB and 11dB, respectively, with a bandwidth greater than 7% at 60GHz for a length of 1mm (about a half of the wavelength at 60GHz).

A 15–40-GHz Frequency Reconfigurable RF MEMS Phase Shifter

This paper presents a novel frequency reconfigurable phase shifter using the RF microelectromechanical systems (MEMS) technology. The phase shifter is based on the triple-stub circuit topology composed of three stubs that are connected by two transmission lines that are all implemented as distributed MEMS transmission lines. The insertion phase of the circuit is controlled by changing the electrical lengths of the stubs and the connecting transmission lines, while having ideally zero reflection coefficient at all times. The phase shifter has theoretically no specific limits on the frequency; in other words, it can be reconfigured to work at any frequency between 15-40 GHz, with adjustable phase steps, while providing a constant time delay within a 2%-3% instantaneous bandwidth around any selected center frequency in the above-mentioned band. The phase shifter is fabricated monolithically using a surface micromachining process on a quartz substrate and occupies 10.8 mm × 5.9 mm. Measurement results show that the phase shifter has average phase error of 1.6 °, 3.7 °, and 4.7 °, average insertion loss of 3.1, 5, and 8.2 dB and average return loss of 19.3, 15.8, and 13.7 dB at 15, 30, and 40 GHz, respectively. To the best of our knowledge, this paper demonstrates the first phase shifter in the literature that can work at any given frequency in a targeted band with adjustable phase steps.

Physical Contact Connection Between SC Connector and Raw Cleaved SM-Fiber End

We achieve a physical contact (PC) connection by using simple butt jointing between an SC connector and a raw cleaved single-mode (SM) fiber end without index matching material. We show that there are two requirements for a cleaved fiber endface for PC connection. One is that the fiber endface inclination is less than 0.6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , and the other is that there is no mist on the endface. The cleaving condition is also discussed to allow us to consistently obtain an appropriate endface. A crack depth of less than 5 μm and a bending radius of 100 mm before breaking are the optimum values in the conventional fiber cleaving process. The average insertion and return losses are 0.14 and 51.1 dB, respectively, and these values are similar to those for a conventional SC connector.

Design approach for return-loss optimisation of multi-stage millimetre-wave microelectromechanical systems dielectric-block phase shifters

This study reports on the radiofrequency (RF) performance optimisation of a novel multi-stage microelectromechanical system (MEMS) dielectric-block phase-shifter concept. The objective is to minimise the average return loss for all possible operation states of a multi-stage phase shifter, without substantially compromising the overall insertion loss or in phase-shift performance. The optimisation method presented in this study is generally applicable to any type of multi-stage RF MEMS devices that are operated in all possible state combinations of the different stages. The return loss is optimized for a seven-stage MEMS dielectric-block phase shifter by adjusting the individual distances between the phase shifter stages, for the nominal frequency of 75 GHz as well as for 500 MHz and 1 GHz bandwidth. A total of seven different designs following different optimisation approaches are investigated by simulations and measurements of fabricated devices. The best concept was found for exponentially increasing distances between the stages that takes into account the proper actuation sequence for all possible phase-shift combinations. As compared with a non-optimised device previously published by the authors, the design offering the best compromise between return loss and insertion loss, achieved by this optimisation method, results in a significant return loss improvement of 11.8 dB (simulated) and 6.98 dB (measured), whereas compromising the insertion loss by only 0.75 dB (simulated) and 0.92 dB (measured). In contrast to that all other investigated concepts, including intuitive optimisation methods such as λ/4 distances or optimisation of equidistant concepts result in a much smaller or no return-loss improvement and some even in a drastic worsening of the insertion loss.

A terahertz broadband 3dB directional coupler based on bridged PPDW

In this paper, a novel broadband 3 dB directional coupler with very flat coupling based on bridged parallel plate dielectric waveguide (PPDW) is proposed and demonstrated. In the uniform coupling section, a bridge structure between the two PPDWs is employed to obtain accurate coupling value and achieve a broadband coupling. It is found that this new type of coupling structure exhibits excellent performance at terahertz frequencies. In order to achieve strong isolation between the adjacent ports and reduce the power reflection in all ports, two quarter-circle bend arms are introduced as the curved transition sections to connect the uniform coupling section. For this bridged coupler, it only needs the value of the uniform coupling length as short as 400 μm to achieve a broadband 3 dB coupling. In this case, the coupler's average return loss is greater than 28 dB, average isolation is better than 27 dB and average coupler loss is only 0.9 dB, over a percentage bandwidth of 12.5% at 1 THz. Compared to the conventional PPDW coupler, the bridged PPDW coupler shows significantly greater bandwidth (about 4.2 times), compact and mechanically stable with a much shorter uniform coupling length (reduced about 61%), which may have potential applications for terahertz integrated circuits and systems.

Waveguide-Slot Array Antenna Designs for Low-Average-Sidelobe Specifications

This paper discusses the design, analysis, and development of waveguide-fed planar slot arrays to achieve low-average-sidelobe specifications, as may arise in radiometer applications. Such antennas may be required to meet strict average sidelobe levels in different angular regions, and low average return loss over a specified bandwidth. In addition to Elliott's design technique, we used a Moment-Method analysis program, Ansoft's HFSS code, and results of tolerance studies using Monte Carlo simulations to meet the design objectives. Comparisons of simulated results and experimental results are also presented.

Wang-Shaped Patch Antenna for Wireless Communications

A novel Wang-shaped patch antenna with a small aperture is presented in this letter. Stable radiation patterns and cross-polarization levels of -20 dB are achieved at a wide operational bandwidth of 1.7-2.5 GHz. Average gain, return loss, and efficiency are measured as 6.5 dBi, ≥ 15 dB, and > 80%, respectively, across the bandwidth. The antenna can serve simultaneously most of the modern wireless communication standards.

Polishing of fiber optic connectors

The polishing characteristics of end faces of fiber optic connectors consisting of the combined structure of silica inlaid zirconia were investigated using a connector polisher and polishing papers with different abrasive types and grit sizes. The geometrical quality was measured using optical interferometry and fiber optical microscopy. The quality parameters included fiber and ferrule surface roughness, end face morphology, fiber height, radius of curvature, and apex offset. The optical performance was eval uated in terms of return and insertion losses using a loss tester. The surface roughness smaller than 20 nm R a in the fiber area, the fiber heights smaller than 75 nm, the end face curvature radii of about 20–50 mm, and the apex offsets smaller than 100 μm were obtained in a polishing cycle of 1 min. The corresponding average return and insertion losses of −48 and 0.15 dB, respectively, were also achieved. The polishing efficiency was raised by at least 30% compared to the commercially applied processes. Finally, the polishing mechanisms of the fiber optic connectors were investigated regarding material response to abrasive machining.

Effects of bottom electrodes on the orientation of AlN films and the frequency responses of resonators in AlN-based FBARs

Effects of bottom electrode materials, included in film bulk acoustic resonators (FBARs), on the orientation of piezoelectric AlN thin films and the frequency response characteristics of AlN-resonators are investigated. AlN films are deposited using RF reactive sputtering on various bottom metals, such as Al, Cu, Ti and Mo. Measurements of X-ray diffraction, field-emission scanning electron microscopy and atomic force microscopy show that the AlN film deposited on the Mo electrode exhibits highly desirable properties, namely, a texture coefficient value of ∼93%, crystallite size of ∼40 nm and surface roughness of ∼8.5 nm. The AlN film deposited on the Mo electrode reveals a relatively dense and well-textured columnar structure with fairly uniform grains, while the films deposited on the other electrode metals exhibit a granular type of structure with mixed small and large grains. FBAR devices employing an Al (top)/AlN/metal (bottom)/Si configuration were also fabricated and their frequency response characteristics ( S 11) were measured. The resonator using the Mo electrode was found to have a superior performance (average return loss ⩾10 dB at 3 GHz). It is concluded that the positive role of the Mo electrode in achieving the high-quality AlN films and the high-performance FBAR devices may be attributed to the smaller lattice mismatch as well as the similarity of the thermal expansion coefficient between the deposited AlN film and the Mo electrode substrate.

Effects of bottom electrodes on the orientation of AlN films and the frequency responses of resonators in AlN-based FBARs

Effects of bottom electrode materials, included in film bulk acoustic resonators (FBARs), on the orientation of piezoelectric AlN thin films and the frequency response characteristics of AlN-resonators are investigated. AlN films are deposited using RF reactive sputtering on various bottom metals, such as Al, Cu, Ti and Mo. Measurements of X-ray diffraction, field-emission scanning electron microscopy and atomic force microscopy show that the AlN film deposited on the Mo electrode exhibits highly desirable properties, namely, a texture coefficient value of ∼93%, crystallite size of ∼40 nm and surface roughness of ∼8.5 nm. The AlN film deposited on the Mo electrode reveals a relatively dense and well-textured columnar structure with fairly uniform grains, while the films deposited on the other electrode metals exhibit a granular type of structure with mixed small and large grains. FBAR devices employing an Al (top)/AlN/metal (bottom)/Si configuration were also fabricated and their frequency response characteristics (S11) were measured. The resonator using the Mo electrode was found to have a superior performance (average return loss ⩾10 dB at 3 GHz). It is concluded that the positive role of the Mo electrode in achieving the high-quality AlN films and the high-performance FBAR devices may be attributed to the smaller lattice mismatch as well as the similarity of the thermal expansion coefficient between the deposited AlN film and the Mo electrode substrate.

Micro/meso ultra precision grinding of fibre optic connectors

The present paper reports on the development of a micro/meso grinding technology using inclined resin bond diamond cup wheels for machining spherical end faces of fibre optic connectors. The ground spherical end faces obtained using the wheel of grit size of 4 μm have an average roughness ( R a) value of ∼7 nm in the fibre area and a profile error of below 0.4 μm. The corresponding average return and insertion losses are ∼55 and 0.1 dB, respectively. The results are competitive to those obtained from the polishing process that is currently used in industries. Furthermore, this study has revealed the relationships between the ground surface quality characterized by roughness and profile accuracy and the optic performance evaluated by insertion and return losses.

PLC connector with PLC-fiber physical contact for multichannel receptacle PLC modules for optical circuit board integration

We describe a novel waveguide-fiber connector, namely, the planar lightwave circuit (PLC) connector, designed to realize a receptacle interface in PLC-based optical modules for economical optical circuit board integration. This connector can provide stable high-density multiple connection between a PLC and single-mode fibers. Moreover, this connector is inexpensive to produce because it utilizes physical contact (PC) connection between a PLC and fibers by employing the elastic force generated by the fibers themselves rather than by a ferrule and spring. We fabricated a duplex PLC connector and a multiple PLC connector for an optical transceiver module and multichannel optical modules, respectively, and successfully obtained low average connection losses of 0.2 and 0.33 dB, and high average return losses of 43 and 43 dB, respectively. In addition, we confirmed that the connectors had sufficient environmental durability. We also realized 2- and 34-channel receptacle interfaces in the transceiver module and a thermooptic switch module by equipping the modules with the duplex connector and three of the multiple connectors.

A 2-bit RF MEMS phase shifter in a thick-film BGA ceramic package

The development of a thick-film hermetic BGA package for a radio-frequency (RF) microelectromechanical systems (MEMS) 2-bit phase shifter is presented. The measured packaged MEMS phase shifter average in-band insertion loss was 1.14 dB with an average return loss of 15.9 dB. The package transition insertion loss was less than 0.1 dB per transition with excellent agreement between simulated and measured results. It was also demonstrated that the RF MEMS phase shift performance could be improved to obtain a phase error of less than 3.3 degrees. The first reported measurements of the average rise and fall times associated with a MEMS circuit (in this case a 2-bit phase shifter) were 26 and 70 /spl mu/s, respectively. The advent of packaged RF MEMS phase shifters will reduce the cost (both design and building) of future phase arrays.

Injection molded plastic multifiber connector realizing physical contact with fiber elasticity

We have proposed and demonstrated a fiber physical contact connector. This connector aligns multiple bare fibers in microholes individually and realizes physical contact by using the buckling force of the fibers themselves. The prototype is injection molded plastic and has a size of 7/spl times/24/spl times/3 mm for 8 fibers at a 0.25-mm pitch. The average insertion and return losses for single-mode fibers are under 0.2 dB and over 60 dB. These losses are stable in environmental tests.

PLC connector with fibre physical contact

A novel planar lightwave circuit (PLC) connector utilising physical contact (PC) between bare fibres and waveguides was developed. This connector allows the use of PLC-based optical modules without fibre pigtails. The fabricated connectors successfully realised average connection and return losses of 0.25 and 43 dB, respectively.

Advanced physical contact technology for optical connectors

An advanced low-reflection PC (physical contact) optical connector with an average return loss of 46 dB has been realized while maintaining a reliability as high as that of conventional PC optical connectors. The high return loss and reliability of the APC have been achieved by suppressing damaged layer generation and by reducing fiber withdrawal from the ferrule endface. Slight variations in the damaged layer significantly affect the return loss and distribution of the APC connector, because the refractive index of the layer is very close to that of silica fiber core.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Novel coplanar waveguide to slotline transition on high resistivity silicon

Two novel coplanar waveguide (CPW) to slotline transitions have been fabricated and tested on high resistivity silicon. The first transition uses an air bridge to couple RF power from the CPW line to the slotline and has the entire circuit on the top side of the wafer. In the second transition, the grounded CPW line and the slotline are on opposite sides of the wafer and are coupled electromagnetically. The measured average intersection loss and return loss per transition are better than 1.5 and 10 dB, respectively, with a bandwidth greater than 30 percent at C-band frequencies.

Miniature optical connector with small zirconia ferrule

The problems and design targets related to miniaturizing an optical connector are described, and the results of optical characteristic measurements after a trial fabrication are presented. Miniaturized optical connectors using 1.25-mm-diameter ferrules have been developed. They are smaller and have a higher packaging density than conventional optical connectors. Ferrule pitch is 1/2, plug volume is 2/5, and cross-sectional area is 2/5 that of the SC connector. Excellent optical performance, an average insertion loss of 0.04 dB, and an average return loss of 50.1 dB have been achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>