Microwave Circuit Applications Research Articles

Preparation and properties of silica filled PTFE flexible laminates for microwave circuit applications

Micron and nano size silica fillers are incorporated in the PTFE matrix to prepare flexible composite substrates. A proprietary process comprising of sigma mixing, extrusion, calendering followed by hot pressing (SMECH process) has been employed to obtain nearly isotropic and dimensionally stable filled PTFE substrates. Theoretical modeling has been employed to predict the effective dielectric constant of the composite system and validated the results with experimental data. The distribution of particulate filler in the PTFE matrix has been studied using scanning electron microscopy. The linear coefficient of thermal expansion and ultimate tensile strength of the composite systems with respect to filler loading have been found out. Dielectric properties of the composite substrates at X-band frequency (8.2–12.4 GHz) are measured using waveguide cavity perturbation technique. Moisture absorption of fused silica filled substrates is found out conforming to IPC-TM-650 2.6.2.

Rutile filled PTFE composites for flexible microwave substrate applications

Rutile filled PTFE composite substrates were fabricated for microwave circuit applications. Morphology of the composites and dispersion of filler in the polymer matrix were studied using Scanning Electron Microscopic technique. Microwave dielectric properties of filled composites were measured by waveguide cavity perturbation technique using Vector Network Analyzer. Different theoretical modeling approaches were used to predict the dielectric constant of PTFE composites with respect to filler loading. The temperature coefficient of dielectric constant ( τ ε ′ r ) was measured in the 0–100 °C temperature range. Moisture absorption properties were measured as per IPC-TM-650 2.6.2 standards. Universal testing machine was used to evaluate the tensile properties. Flexible laminates having dielectric constant 10.2 with loss tangent 0.0022 was realized in the PTFE/rutile composites at X-band frequency region.

Microwave Properties of Ferromagnetic Nanowires and Applications to Tunable Devices

Microwave devices as circulators or tunable filters demand nowadays small size and broad bandwidth. Ferromagnetic nanowired membranes are ideal candidates for this purpose. This paper focuses on the dielectric properties of such substrates, as influenced by the ferromagnetic nature of nanowires and their filling factor. Two particular cases are considered: a membrane filled up to its top with nanowires, forming a one-layer substrate, and a membrane filled up to a certain percentage of its height with nanowires, forming a two-layer substrate. The models proposed in this paper for each case take the inductive and gyromagnetic effects in the wires into account. They predict for the one-layer case a magnetodielectric behavior which is tunable by applying an external magnetic field. The effect is no longer visible for the two-layer topology corresponding to microwave circuit applications.

DC Performance and Low Frequency Noise in n-MOSFETs using Self-Aligned Poly-Si/SiGe Gate

The characterization of an n-MOS transistor with poly-Si/SiGe Gate fabricated with the CMOS process entirely developed in the Center for Semiconductor Components (CCS) at UNICAMP is presented. The Gate layer was grown by vertical LPCVD at 800 {degree sign}C. The resultant transistor has a channel region with oxide thickness of 30 nm and self-aligned thick S/D region. The DC and Gm characteristics of poly-Si/SiGe n-MOS transistor are reported. The turn-on in the I-V characteristics increases and at a drain-to-source bias VDS of +0.1 V nMOSFETs with 3 µm gate length had peak transconductance (µS) increased as well, compared with conventional n-MOS with poly-Si gate. The Gm characteristics and low frequency noise 1/f of the n-MOS transistors are studied using devices sizes with width of 20 µm and several lengths. Promising devices for RF and microwave circuit applications, show low 1/f and high values of transconductance.

A novel compact microstrip bandpass filter using folded stepped impedance resonators

AbstractA folded quarter‐wavelength stepped impedance resonator (SIR) is proposed with a largely reduced size. A bandpass filter with center frequency of 1.85 GHz using the SIRs is designed, fabricated, and measured. This compact filter covers an area less than 10 mm × 10 mm, which makes it suitable for compact and high‐performance microwave circuit applications. © Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1864–1867, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23476

Design Considerations of Miniaturized Least Dispersive Periodic Slow-Wave Structures

Slow-wave structures using distributed periodic inductive and capacitive loadings have found many microwave circuit applications as left-handed (bandpass) or right-handed (low-pass) transmission lines. A large slow-wave factor (SWF) could result in a much smaller passive component, but also a much lower bandgap (cutoff) frequency and a larger dispersion. This paper addresses the issues and the design tradeoff between the SWF, group delay (dispersion), and the cutoff frequency of a right-handed (low-pass) quasi-lumped transmission line. A new two-layer transmission line structure using 3-D substrate metallization with an SWF of 5.8 is designed. A prototype of a 3-GHz branch-line coupler with a 70% size reduction using such a transmission line structure is fabricated and tested.

Microfabrication of solenoid-type RF SMD chip inductors with an Al2O3 core

We investigated micron size, high-performance, and solenoid-type radio-frequency surface-mounted device (SMD) chip inductors with a low-loss Al 2 O 3 core for a GHz drive microwave circuit application. Copper coils with a diameter of 27 μm were used and the chip inductors fabricated in this study are 0.86 × 0.46 × 0.45 mm 3 . The high-frequency characteristics of the inductance ( L ), quality factor ( Q ), and impedance ( Z ) of the developed inductors were measured using a RF impedance/material analyzer (HP4291B with HP16193A test fixture). The developed inductors have a self-resonant frequency of 3.7–5.2 GHz and exhibit L of 15–34 nH. The inductors have Q of 38–49 over the frequency ranges of 900 MHz–1.7 GHz. The calculated data obtained from the equivalent circuit and the derived equation of Q described the high-frequency data of L , Q , and Z of the inductors developed quite well.

Nickel nanowires for planer microwave circuit applications and characterization

The dynamic properties of uniform one-dimensional arrays of high aspect ratio nickel nanowires have been studied by ferromagnetic resonance (FMR) technique at 24GHz. The fundamental magnetic parameters such as spontaneous magnetization, gyromagnetic ratio (γ), and magnetic anisotropies of the nanowires are derived from the angular variation of resonance field Hr(θH) positions. The effective fields of the nanowire system were observed to decrease with increasing length of the nanowires. Further, the use of nanowires as a tunable stop-band notch filter in a coplanar waveguide geometry has been assessed. The stop-band frequency (fr) is observed to be tunable up to 14GHz with an applied field (H) of up to 4kOe. The kink in the fr(H) data gives the measure of the effective field (Heff) of the nanowire system. The theoretical fitting of fr(H) data to resonance relation yields values of Heff and γ which are a little higher than the conventional FMR results.

A Sandwich Like EBGs With Three Different Materials and Its Defect Modes

A sandwich-like Electromagnetic Bandgap Structure (EBGs) with three different materials-BiNbO4, Alumina and Teflon-is proposed, and the defect modes are studied. Compared with the traditional EBGs made of two materials, this novel configuration can provide more excellent characteristics, which bandwidth is up to 69.5% of the central frequency from 6.98 GHz to 14.42 GHz, and the ripples in the stopband and passband are almost suppressed perfectly. It also provides more means to introduce defect modes. Meanwhile the EBGs periodicity is just 1 mm, rather smaller relative to the working wavelength. All these advantages over ordinary EBGs configuration indicate extensively potential applications in microwave devices and circuits.

Anisotropic Periodic Assemblies and Metamaterials for Applications to Antennas and Microwave Devices

SUMMARY Basic microwave properties of magnetic photonic (MPC) and degenerate band edge (DBE) crystals are investigated mathematically and experimentally. Two dimensional and three dimensional models are considered demonstrating the very high sensitivity and field growth associated with these crystals. A major part of the paper deals with the development of realistic anisotropic periodic structures using a combination of layers constructed from thin film frequency selective surfaces, alumina, titanate and calcium vanadium garnet (CVG) materials. Measurements for antenna applications demonstrate and validate the theoretical performance of the MPC and DBE crystals. The latter part of the paper will present an exciting and promising development relating to microwave circuit applications. Specifically, a novel dual-line printed circuit is presented to emulate propagation in anisotropic media. As such, the MPC and DBE phenomena can be realized using very simple printed circuits (coupled lines). Lastly, physically small printed antennas and arrays based on the coupled transmission lines are presented.

Dual-Gate E/E- and E/D-Mode AlGaAs/InGaAs pHEMTs for Microwave Circuit Applications

In this paper, we developed dual-gate enhancement/enhancement-mode (E/E-mode) and enhancement/depletion-mode (E/D-mode) AlGaAs/InGaAs pHEMTs for high-voltage and high-power device applications. These dual-gate devices had a higher breakdown voltage (Vbr) and maximum oscillation frequency (fmax). This could be obtained because there were two depletion regions, and the total electrical field was shared between the two regions, leading to lower output conductance (go) and lower gate-to-drain capacitance (Cgd). The dual-gate device can be operated at a higher drain-to-source voltage (Vds), resulting in better linear gain and output power performance, as compared to a conventional single-gate E-mode GaAs pHEMT device. The maximum oscillation frequency obtained using the dual-gate E/E-mode device increased from 78 to 123 GHz. When operated at 2.4 GHz, the maximum RF output power of the single-gate E-mode and dual-gate E/D-mode devices increased from 636 to 810 mW/mm, respectively. We also produced a 2.4-GHz high-gain and high-power density two-stage power amplifier using dual-gate E/E and E/D-mode transistors. A linear gain of 40 dB and a maximum output power of 24 dBm were obtained.

Calculations of return loss of bonding wires fabricated on a test board by FDTD method

AbstractReturn losses of bonding wires fabricated on a test board for RF and microwave circuit applications are studied by the finite‐difference time‐domain (FDTD) method. Simulation results of return losses obtained by the FDTD method are presented and compared with those obtained by the HFSS software and measurements at frequencies of 0.04–6 GHz. It is found that simulation results calculated by the FDTD method make a good agreement with those obtained by the HFSS software. Results of the FDTD method are also further validated by the measurement data. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1603–1606, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22546

Novel Planer Microwave Circuit Applications and Characterization of Ni Nanowires

ABSTRACTArrays of Ni nanorods were electrodeposited into alumina oxide templates with various lengths (11-50 micro meter) and fixed pore diameter (150 nm). The magnetization behavior of these rods were investigated with ferromagnetic resonance (FMR) techniques; fixed frequency (conventional FMR) and swept frequency (Network Analyzer FMR). Both resonance spectra indicate the presence of strong dipolar interaction between the nanorods. The fundamental magnetic parameters like spontaneous magnetization, gyromagnetic ratio, and magnetic anisotropies of the nanorods were derived from the angular variation of resonance field data. Further, the use of nanorods as a tunable stop-band notch-filter in a coplanar waveguide geometry has been assessed. The stop-band frequency (fr) is observed to be tunable up to 24 GHz with an applied field (H) of up to 6 kOe. The theoretical fitting of fr(H)data to resonance relation yield values of effective field (Heff) and gyromagnetic ratio, which are a little higher than the conventional FMR results.

Comprehensive Characterization of In0.45Al0.55As ∕ In0.5Ga0.5As ∕ InxAl1 − xAs Metamorphic High-Electron-Mobility Transistors on GaAs Substrates

An metamorphic high-electron-mobility transistor (MHEMT) with an inverse-step metamorphic buffer, grown by molecular beam epitaxy on substrate, is presented. A typical gate-length MHEMT has a drain current density of and a peak extrinsic transconductance of . High-frequency scattering parameter measurements yield a unity current gain cutoff frequency of as well as a maximum frequency oscillation . High two-terminal and three-terminal breakdown voltages are achieved mainly because of the high bandgap of the Schottky layer and the large conduction-band discontinuity at the heterojunction. The large-signal power performance and noise characteristics are measured. Experimental results on the temperature-dependence study of the saturation drain current density, the extrinsic transconductance, the leakage current, the off-state breakdown voltage, and the threshold voltage are presented. The shift of the device at elevated temperatures is as small as . All of the experimental results confirm the exceptional potential of the MHEMT in microwave circuit and high-temperature applications.

A microstrip resonator filter using sandwich structure

We present results for a compact, multiple gap and multiple pass band microstrip resonator filter. The microstrip resonator filter, consisting of a sandwich substrate with a metallic fractal pattern, shows multiple gaps from 40 MHz to 10 GHz. The transmission characteristics of the microstrip resonator filter show multiple pass bands and stop bands for electromagnetic waves over the microwave frequency range. Experimental observations are in good agreement with the results of finite difference time domain (FDTD) simulations. These properties can be useful in the application in compact microwave circuits, microwave filters, and microwave switches.

Return loss of three types of arching bond wire structures for RF and microwave circuit applications

AbstractThe S‐parameters of a gold wire bonded in air to two microstrip lines are validated by measurements and HFSS software simulations at frequencies of 0.04–6 GHz. From simulation results and measurement data, it is found that an arching bond wire with a smaller arc angle can minimize the return loss. From simulations, it is also found that the return loss can be improved, and operation frequency shifts can be achieved by using multiple wires placed in parallel in bond wire arrays. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1701–1704, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21807

Concentric Ring-Shaped Defected Ground Structures for Microstrip Applications

A new defected ground structure (DGS) consisting of concentric circular rings in different configurations is experimentally studied to examine the stopband characteristics. Unlike previous DGS designs, a metallic shielding is introduced at the back of the DGS to suppress any leakage or radiation, and this would be advantageous for microwave circuit applications. A wide stopband is demonstrated with a set of prototypes designed for X-band. Its application to suppressing mutual coupling in microstrip patch arrays is demonstrated

Electrical Modeling of Ferroelectric Tunable Microwave Components and Circuits

Ba(1−x)Sr x TiO 3 (BST) is currently being investigated for applications in tunable microwave devices and circuits. Our group has demonstrated several working ferroelectric tunable microwave circuits in collaboration with NASA Glenn Research center in the past several years. Current work is underway in optimizing the ferroelectric thin-films properties at microwave frequencies, in collaboration with Air Force Research Laboratories. Ferroelectric tunable filters, couplers, and phase shifters have been demonstrated in the past using two-layered microstrip or coplanar waveguide configuration. Accurate electrical modeling of ferroelectric tunable components and circuits will be presented in detail in this work. With known material properties such as dielectric tunability, capacitance vs voltage, and Q values over a wide frequency range, one could model any circuit and estimate the circuit's performance over a wide frequency range. Electrical models can be developed that predict the frequency tunability, and the effect of the dielectric tunability on various circuit parameters. For example, in the tunable filters, the effect of dielectric tunability of the ferroelectric thin-film on the filter's passband insertion loss, return loss, bandwidth, and frequency shift could be assessed using a simple lumped element circuit models. We have also developed models for MEMS capacitive shunt switches using BST thin-film as a dielectric layer for phase shifter applications.

A wideband EBG structure with 1D compact microstrip resonant cell

This paper presents the design of novel 1D compact microstrip resonant cells (CMRC). Several thin line arrays in the 50Ω microstrip line with special configurations are fabricated without the requirement of any additional process. Three cells of the proposed structure can provide a wide stopband of −10 dB from 12.7 to 35.9 GHz and −30 dB from 13.8 to 35.9 GHz, respectively. This novel CMRC structure can be used for various compact and wideband microwave-circuit applications. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 45: 386–387, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20831

Strained Si HFETs for microwave applications: state-of-the-art and further approaches

This paper reviews the RF and noise performance of strained Si heterostructure field-effect transistors. For SiGe n-HFETs the high RF figures of merit f T=90 GHz, f MAX=188 GHz and noise performance NF MIN =0.3 dB at 2.5 GHz demonstrate the capabilities of these devices for microwave circuit applications. Recently some IC demonstrators have been successfully implemented. Strained Si HFETs fabricated on thick SiGe virtual substrates have been traditionally employed as a vehicle of study. Nevertheless these thick relaxed buffers involve some decisive disadvantages: Reduction of the wafer throughput, non-acceptable surface topology if implemented in mixed technologies like CMOS, and, in particular, self-heating due to low thermal conductivity of SiGe alloys compared to Si. In order to overcome these drawbacks several approaches to reduce the buffer thickness have been very recently developed. In this paper the RF and low frequency noise performance of SiGe HFETs prepared on very thin virtual substrates are reported. The potentialities of these technologies have not yet reached their limits. One can expect a great improvement by combining a proper device shrinking with very thin virtual substrates. These heterosystems could become the backbone of strained silicon devices towards microwave applications.