Forward Transmission Coefficient Research Articles

Small signal and noise analysis of T-gate HEMT with polarization doped buffer for LNAs

Small signal behavior and RF noise performance of T-gate InAlN/GaN HEMT with polarization doped buffer (PDB-HEMT) have been examined in this paper and compared to conventional HEMTs at GHz frequency range. Enhancement mode operation is possible in the PDB-HEMT device, which has a recessed T-gate structure with a gate length of 10 nm and delivers the threshold voltage (Vth) of 0.9 V and a high transconductance of 1.55 S/mm. This study examines the auto/cross-correlation factor, minimum noise figure, reflection/transmission coefficients, noise conductance, and optimal noise resistance and reactance. The enhanced transconductance of PDB-HEMT has resulted in a considerable increase in the forward transmission coefficient and a decrease in the input/output reflection coefficient compared to traditional HEMTs. It has also been shown that the PDB- HEMT has a lower noise figure and noise conductance than the GaN buffer HEMT by 57% and 20%, respectively. This research demonstrates that the T-gate polarization doped buffer (PDB-HEMT) structure is an excellent choice for Low Noise Amplifiers (LNA) operating at higher frequencies.

Design of an optical diode based on conical refraction in biaxial crystals

Propagation of light beam along the optical axis of a biaxial crystal results in conical intensity distribution with an azimuthally varying polarization. Such variation of the polarization vector is utilized for the design of an optical diode in which the biaxial crystal with appropriate length is placed between two angularly adjusted polarizers. Our simulation results reveal that a significant difference in forward and backward transmission coefficients could be obtained by adjusting the crystal length as well as the optical wavelength.

A Systematic Transmission Line Model for the Analysis of Self-Resonant Structures Within Multi-Layer Dielectric Media

This paper introduces a transmission line model analysis for dielectric-loaded self-resonant structures (SRSs). Equivalent circuit models, besides their fast computational time, usually offer some insights into the underlying physics of the electromagnetic structures, hence simplifying and improving the design and optimization criteria of these structures. A systematic approach for deriving impedance expressions of SRS on and within multi-layer dielectric media is presented. The process of extracting equivalent circuit parameters from impedance expressions is explained. The trends of equivalent circuit parameters are studied with different dielectric medium properties and various angles of incidence for an SRS with multiple resonant states highlighting the effect of changing the physical and electrical dimensions on the equivalent circuit parameters. The transmission line model responses are compared to full-wave simulation results, and model accuracy is assessed using the mean absolute error criteria. Furthermore, a new simplified method for calculating the forward transmission coefficient of an SRS within multi-layer media is proposed. This expression offers fundamental insights into the factors contributing to the $S_{21}$ response. Finally, experimental measurements for SRS embedded in a multi-layer dielectric media inside a waveguide is conducted and compared to the equivalent model with very good agreement.

Electron transport analysis in positional isomers - A DFT-NEGF approach

Molecular electronics is believed to be the possible solution to the problem of miniaturization of conventional silicon-based electronics. Since various quantum effects occur in this regime, it is vital to understand the transport properties of organic molecules. The electron transport properties of 4,6‐dibromobenzene‐1,3‐dithiol; 2,4‐dibromobenzene‐1,3‐dithiol and 2,5-dibromobenzene-1,3-dithiol molecules was analyzed using Density Functional Theory (DFT) with Non-Equilibrium Green's Function (NEGF). The density of states at zero bias of all these molecules more or less resemble the same nearby Fermi region. While increasing the bias, the bias window gets opened and the available density of states nearby Fermi region changes and produce nonlinearity in the current flow. The projected density of states was calculated to get an insight into the molecular contribution in electron transport. At higher bias, the dissimilarity between the forward and reverse bias transmission coefficient was observed. Due to this, rectification was present in these molecular junctions. Out of these molecular junctions, 2,4‐dibromobenzene‐1,3‐dithiol shows higher rectification ratio than 4,6-dibromobenzene-1,3-dithiol and 2,5-dibromobenzene‐1,3‐dithiol molecules.

A 79GHz Adaptive Gain Low Noise Amplifier for Radar Receivers

This paper presents an Adaptive Gain 79GHz Low Noise Amplifier (LNA) suitable for Radars applications. The circuit schematic is a two stage LNA consists of Differential cascode configuration followed by a simple common source amplifier with an Adaptive Biasing (ADB) circuit. Adaptive biasing is a three- stage common source amplifier to decrease output voltage as input power increases. The circuit is simulated in 180nm CMOS technology and the simulation results have proved that the circuit operates at the center frequency 79GHz with adaptive biasing for adaptive gain. The gain analysis shows a decrease of 35-30dB with an increase in input power -50 to 0 dB. At 79GHz the circuit has achieved the input reflection coefficient (S11) of -24.7dB, reverse isolation (S12) of -3 dB, forward transmission coefficient (S21) of -2.97dB and output reflection coefficient (S22) of -5.62 dB with the reduced noise figure of 0.9 dB and a power consumption of 236 mW.

One to 40 GHz ultra‐wideband RF MEMS direct‐contact switch based on GaAs MMIC technique

This study presents a 1–40 GHz ultra-wideband radio frequency (RF) micro-electro-mechanical systems (MEMS) direct-contact switch based on a GaAs microwave monolithic integrated circuit (MMIC) process. The proposed switch utilises an inline cantilever membrane and a pull-in electrode to achieve ‘off’ and ‘on’ states. It has been manufactured by micro-machining, which is completely compatible with the GaAs MMIC process. An equivalent distributed parameter circuit model of the switch is established to analyse the microwave performances. The measured S-parameters show that the isolation (S21) in the ‘off’ state is better than 22.5 dB from 1 to 40 GHz. In the ‘on’ state, the input reflection coefficient (S11) is less than −20.9 dB and the forward transmission coefficient (S21) is better than −0.25 dB over the complete band. In addition, the measured pull-in voltage is ∼17.5 V. The measured maximum power handling capacity is 36.5 dBm. A lifetime of 2.4 × 107 switching cycles is also verified by this design. The whole structure is designed with the purpose of expanding its working bandwidth and achieving higher microwave performances over current state of art.

Intrinsic Properties of Metamaterial Slab in Wireless Power Transfer for Efficiency Improvement of Wireless Communication Systems

Metamaterial (MTM) slabs, realized using Split Ring Resonators (SRR’s) to enhance efficiency of Wireless Power Transfer (WPT) systems is discussed here. A detailed study of intrinsic properties obtained by simulation of the actual MTM slab is presented. An improvement in the wavelength to unit cell size of 813, at a low operating frequency of 5680 kHz is shown. Forward transmission coefficients (S₂₁) for with and without MTM slab cases are compared. In this low frequency regime, with simulated S-parameters an efficiency of ~ 68% is achieved by placing the MTM slab closer to receiver coil than the transmitter coil.

Multiport RF MEMS switch for satellite payload applications

Design, fabrication and characterization of a novel RF switch is proposed in this paper. The multiport RF MEMS switch provides a single input multiple output novel topology suitable for satellite payload applications. A single ETA is used to switch the device from one mode to another. When a voltage difference is applied across the electrode pads of ETA, and depending on the configuration, the actuator actuates forward or backward in plane producing either a quad or dual output respectively. The reflection loss and insertion loss are improved effectively. Measurement results show that in `dual mode’ position, the input reflection coefficient (S 11) is less than − 50 dB with the forward transmission coefficient (S 21) better than − 2 dB at 0–15 GHz. At ‘quad mode’, position, the input reflection coefficient (S 11) is less than − 55 dB with the forward transmission coefficient (S 21) better than − 4 dB at 0–15 GHz. The larger than 50 dB over 0–15 GHz isolation realized in both modes of operation ensures dual and quad mode outputs without information loss. The actuation voltage is reduced to 4.5 V. The measured power handling capability can reach up to 35 dBm while the power consumption of the switch is 50 mW. This compact RF MEMS capacitive switch possesses excellent performances in terms of low insertion loss, high isolation, low power and high power handling capability.

Transmission characteristics of multi‐walled carbon nanotube‐based through‐silicon vias considering temperature effects

In this study, a simplified temperature-dependent expression of electron mean free path (MFP) is proposed first. Then, the electrical model of multi-walled carbon nanotube bundle-based through-silicon vias (MWCNTB-TSVs) is established considering the temperature effects of the MFP, metal-oxide-semiconductor capacitance, substrate conductance and number of conducting channels of MWCNT. Based on this model, the propagation constant, forward transmission coefficient S 21 and crosstalk at different temperatures are calculated. By analysing the phase constant, the zero dispersion transmission condition is obtained. According to this condition, the guidelines on how to select the substrate in different level integrations are proposed. Furthermore, a concise formula for the equivalent conductivity of MWCNTB is proposed. Moreover, the minimum diameter of MWCNTB-TSV whose attenuation is less than that of copper-filled TSV has been deduced.

High-Gain Graphene Transistors with a Thin AlOx Top-Gate Oxide

The high-frequency performance of transistors is usually assessed by speed and gain figures of merit, such as the maximum oscillation frequency fmax, cutoff frequency fT, ratio fmax/fT, forward transmission coefficient S21, and open-circuit voltage gain Av. All these figures of merit must be as large as possible for transistors to be useful in practical electronics applications. Here we demonstrate high-performance graphene field-effect transistors (GFETs) with a thin AlOx gate dielectric which outperform previous state-of-the-art GFETs: we obtained fmax/fT > 3, Av > 30 dB, and S21 = 12.5 dB (at 10 MHz and depending on the transistor geometry) from S-parameter measurements. A dc characterization of GFETs in ambient conditions reveals good current saturation and relatively large transconductance ~600 S/m. The realized GFETs offer the prospect of using graphene in a much wider range of electronic applications which require substantial gain.

Ka‐band RF MEMS capacitive switch with low loss, high isolation, long‐term reliability and high power handling based on GaAs MMIC technology

This study presents a Ka-band radio frequency (RF) micro electro mechanical systems (MEMS) capacitive switch with low loss, high isolation, long-term reliability and high power handling based on GaAs microwave monolithic integrated circuit (MMIC) technology. In this design, a T-matching structure is employed to realise impendence matching at ‘up-state’ by modifying the dimensions of centre signal line. Thus, the reflection loss and insertion loss are improved effectively. Measurement results show that in ‘up-state’ position, the input reflection coefficient (S11) is less than −20.4 dB with the forward transmission coefficient (S21) of better than −0.27 dB at Ka-band (27–40 GHz). At ‘down-state’, the switch is designed in a state of self-resonance to obtain high isolation. The measured isolation is better than 20 dB over Ka-band and can reach 35 dB at its self-resonant frequency of 35 GHz. The measured actuation voltage is about 36 V. The measured lifetime is at least 5.76 × 107 cycles. The measured power handling capability can reach up to 39 dBm. The proposed compact RF MEMS capacitive switch possesses excellent performances in terms of low insertion loss, high isolation, long lifetime and high power handling capability.

Wideband Modeling and Characterization of Differential Through-Silicon Vias for 3-D ICs

This paper presents the wideband modeling and analysis of differential through-silicon vias (D-TSVs) in 3-D ICs. An equivalent-circuit model of the ground–signal–signal–ground-type D-TSVs is given and validated against a commercial full-wave electromagnetic simulation tool. The common- and differential-mode impedances are extracted using the partial-element equivalent-circuit method, while the admittances are calculated analytically, with the MOS effects considered and treated appropriately. The circuit model can also be used for studying the differential annular TSVs (ATSVs). It is shown that the ATSVs are more suitable for transmitting differential signals in comparison with the cylindrical TSVs. Based on the equivalent-circuit model, the characteristic impedances and the forward transmission coefficients of the D-TSVs made of Cu and carbon nanotubes are characterized and compared under different settings of frequencies and temperatures.

Alternating current-driven microwave loss modulation in a fluxonic metamaterial

We introduce a fluxonic metamaterial on the basis of nanopatterned superconducting Nb microstrips and employ it for modulation and synthesis of quantized loss levels in the lower GHz range by a sine-wave quasistatic ac drive. The nanopatterns are uniaxial nanogrooves with identical and different slope steepness, which induce a pinning potential of the washboard type for Abrikosov vortices. For the fundamental matching field, when the location of vortex rows geometrically matches the nanogrooves, the following effects are observed: The forward transmission coefficient S21(f) of the microstrips can be controllably modulated within a range of about 3 dB by the ac. For the sample with symmetric grooves, depending on the choice of the operation point in the current-voltage curve, the shape and the duty cycle of the output signal can be tuned. For the sample with asymmetric grooves, depending on the ac amplitude, a sine-to-triangular or a sine-to-rectangular pulse shape conversion is observed. The possibility of synthesizing quantized loss levels by a serial connection of the two samples with different nanopatterns is exemplified and can be used for the development of multilevel excess-loss-based fluxonic devices.

Flexible use

With the growth of the Internet Of Things, significant resources are being put into the development of smart garments. Ideally, the systems in these garments should be fully flexible to allow greater comfort and a wider range of applications. Now, a team jointly from Loughborough University (UK) and the National Centre of Scientific Research “Demokritos” (Greece) have developed an all-textile flexible method of connecting textile transmission lines. The method is designed to allow easy connection, although currently requires clamps to keep the connection stable In wearable communication systems currently in operation, rigid connectors such as coaxial SMA connectors are used to connect antennas to the electronic systems required to operate them. These rigid parts can make wearable technology uncomfortable and more prone to damage. With this in mind, the team previously investigated connection methods that could eliminate the need for such rigid connections. Of the methods investigated, complementary overlap (CO) emerged as the most promising. In this method two identical striplines are overlapped (as show in the images). This time, the team has investigated issues related to the structural modification of CO and to the fabrication of a connector. To optimise the connector the team had to investigate fabrication issues such as materials and structure. Felt was used as the dielectric substrate and Nora-Dell fabric as the conductive textile. Through experiments the team found, out of the three adhesives investigated (a universal adhesive, Hemming-web and sewing using non-conductive thread), that Hemming-web gave the best performance. The team also discovered that extending the ground planes on the longest side decreased the effect of structural discontinuities on the forward transmission coefficient. “A noticeable advantage is the power transmission performance improvement (+3 dB) by the structural modification of the textile stripline interconnection method. The insertion losses of our flexible interconnection are less than 1.8 dB, which means that more than 66% of the inserted power is transmitted” Mr Tsolis, the corresponding author for the team, informed us. “Remaining challenges are to find a way of making the connector stable and flexible at the same time. This means that when the interconnection happens it needs to be stable and also flexible in terms of ease in connecting and disconnecting the transmission lines.” To keep the individual stripline parts of the CO firmly connected the team had to use clamps, as a stable measurement setup was required to evaluate the power transmission via measurements. “We believe that in terms of a final wearable realisation conductive Velcro or magnets could be used instead of clamps. The use of Velcro seems like a feasible solution for wearable and flexible systems. We plan to further investigate the implementation of supporting the proposed connection by using Velcro” said Tsolis. In the short term, the team plan to use this technology to advance their own research into wearable technologies. So far they have been continuing their work into this technology through simulations and measurements as part of the larger activities of their laboratory, which focuses on the design and analysis of wearable communication systems and related technologies. The complementary overlap method was tested against a straight transmission line made from the same materials In the long term, the team believe that the new method will increase the flexibility of wearable communication systems, and lead to the production of technologies such as garments with integrated textile striplines using flexible connectors to connect to antennas as needed. Such garments could be used in hospitals, monitoring the condition of patients and automatically informing the staff of any emergencies. When asked about the future of this sort of technology, Tsolis and the team have high expectations. “We believe that there will be a rapid explosion in the wearable antennas and electronics technology. We predict that this technology is the future of smart garments and furthermore the future of our daily lives. We would like to see, and would be very happy to witness “state-of-the-art” garments that will be capable of supporting health monitors, entertainment and sports training equipment. A smart garment could be an assistant, a doctor, a trainer etc. to every human's life.”

Dual cut-off direct current-tunable microwave low-pass filter on superconducting Nb microstrips with asymmetric nanogrooves

We present a dual cut-off, dc-tunable low-pass microwave filter on a superconducting Nb microstrip with uniaxial asymmetric nanogrooves. The frequency response of the device was measured in the range 300 KHz–14 GHz at different temperatures, magnetic fields, and dc values. The microwave loss is most effectively reduced when the Abrikosov vortex lattice spatially matches the underlying washboard pinning landscape. The forward transmission coefficient S21(f) of the microstrip has a dc-tunable cut-off frequency fd which notably changes under dc bias reversal, due to the two different slope steepnesses of the pinning landscape. The device's operation principle relies upon a crossover from the weakly dissipative response of vortices at low frequencies when they are driven over the grooves, to the strongly dissipative response at high frequencies when the vortices are oscillating within one groove. The filter's cut-off frequency is the vortex depinning frequency tunable by the dc bias as it diminishes the pinning effect induced by the nanopattern. The reported results unveil an advanced microwave functionality of superconducting films with asymmetric (ratchet) pinning landscapes and are relevant for tuning the microwave loss in superconducting planar transmission lines.

CORRELATION BETWEEN SIMULATIONS AND REAL MEASUREMENTS OF MICROSTRIP FILTERS BASED ON LTCC IN HIGH FREQUENCY AREA

The aim of this paper lies in comparison of two CAD (Computer aided Design) software (Ansoft Designer from Ansys and HyperLynx 3D EM Designer from Mentor Graphics) and real measurements of designed and fabricated filters. Both software tools belong to the group of the most used tools for design and simulation of different structures. These structures are made by transmission lines of a few kinds (microstrip, stripline, slotline, etc.) and they substitute common elements in HF (High Frequency) area. This paper presents 3 various microstrip filters based on LTCC (Low Temperature Co-fired Ceramic) dielectric material GreenTape 951. Low pass (LP), band pass (BP) and band stop (BS) filters for UWB (Ultra Wide-Band) sensor systems were designed, simulated, fabricated and measured. Measured results and simulations (S21 – forward transmission coefficient) are plotted in joint graphs where divergences are observed and depicted.

Magnetically Tunable Ferrite-Loaded Half-Mode Substrate Integrated Waveguide

A magnetically tunable ferrite-loaded half-mode substrate integrated waveguide (HMSIW) is presented. To achieve the magnetic tuning, a planar Yttrium Iron Garnet (YIG) slab is loaded along the metalized wall of the HMSIW, where the concentration of the magnetic field is strongest. Static (DC) magnetic bias is applied on the ferrite slab transversely to the direction of propagation. Measured phases of forward and reverse transmission coefficients show the non-reciprocal behavior of this transmission line. Measured results illustrating the comparison between a single ferrite slab-loaded SIW and a HMSIW are presented. As an application example, a two-dimensionally tunable bandpass filter (BPF) operating at X-band is proposed and studied. By controlling the value of loaded lumped capacitors and the applied magnetic bias, a bandwidth tunable BPF is demonstrated.

Regimes of flux transport at microwave frequencies in nanostructured high-Tcfilms

We report on combined dc and microwave electronic measurements of magnetic flux transport in micron and submicron-patterned high-${T}_{c}$ films. In a given temperature regime below the superconducting transition temperature ${T}_{c}$, the current-driven flux transport is restricted to flux motion guided by the submicron patterns. Via frequency-dependent measurements of the forward transmission coefficient ${S}_{21}$ it is demonstrated that the mechanism of the guided flux transport depends on the microwave frequency and the geometrical size of the superconducting structures. At low frequencies, flux is transported via Abrikosov vortices leading to additional microwave losses. Above a geometrically defined frequency, a different mechanism seems to be responsible for flux transport that does not contribute to the microwave losses and most likely represents a phase-slip type mechanism. The limiting vortex velocity obtained from the frequency dependence of the microwave properties agrees with the Larking-Ovchinnikov critical vortex velocity that is determined via dc pulse measurements. In spite of the change of mechanism, guidance of flux persists in these nanopatterns up to high frequencies of several GHz.

Electromagnetic Compatibility-Oriented Study on Through Silicon Single-Walled Carbon Nanotube Bundle Via (TS-SWCNTBV) Arrays

Electromagnetic compatibility-oriented study is performed for accurately characterizing through silicon single-walled carbon nanotube bundle via (TS-SWCNTBV) array in this paper. Based on the modified equivalent lumped-element circuit model of a pair of TS-SWCNTBVs, its forward transmission coefficient, in comparison with copper- and tungsten-based TSVs, is investigated for different metallic fractions of the SWCNTs, with quantum effects treated appropriately. The 3-D transmission-line method (TLM) is further employed for studying mutual couplings in three, four, and nine TS-SWCNTBV arrays, respectively, where the effects of their geometrical and physical parameters on the effective capacitance and conductance are examined in detail. Also, transient coupling noises in different arrays excited by a clock signal, respectively, are predicted and compared, which are useful for the design of high density TS-SWCNTBV arrays with better signal transmission performance.

Flux transport in nanostructured high-Tc films at microwave frequencies

The understanding of flux transport in micro- and nanostructured superconducting systems that are exposed to an electromagnetic field at microwave frequencies is of interest for basic aspects of vortex matter and for potential application of superconductivity in fluxonic devices. We report on the combination of dc and microwave electronic measurements on submicron-patterned high-Tc films. The frequency dependence of the forward transmission coefficient S21 indicates that the mechanism of flux transport depends on the velocity of vortices. At low frequencies, flux transport via Abrikosov vortices is present leading to additional microwave losses. Above a geometrically defined frequency, a different, loss-free mechanism seems to be responsible for flux transport. This mechanism most likely represents a phase-slip type of mechanism. The limiting vortex velocity obtained from the frequencies dependence of the microwave properties agrees with the Larkin–Ovchinnikov critical vortex velocity determined via dc pulse measurements. In spite of the change of mechanism, guidance of flux persists in these nano-patterns up to high frequencies.