Passive RF Research Articles

Dual-antenna system composed of patch array and open-ended waveguide for eliminating blindness of wireless communications

In mobile communications in urban area, it is a significant problem that blind spots of in the narrow street are caused by high buildings. In this research, a new dual-antenna system is proposed, including a receiving and a reradiating antenna and feeding networks to realize a broad-angle beam control. An equivalent bistatic radar cross section (BRCS) is deduced to evaluate the antenna performance. The main advantage of this design over ordinary reflectarray antenna as a passive RF booster is its flexible beam control capabilities.

Post-CMOS Compatible Micromachining Technique for On-Chip Passive RF Filter Circuits

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper reports on a post-CMOS compatible micromachining technology for passive RF circuit integration. The micromachining technology combines the formation of high-performance microelectromechanical systems solenoid inductors and metal—insulator—metal (MIM) capacitors by using a post-CMOS process on standard CMOS substrate. Utilizing this process, novel on-chip 3-D configured RF filters for 5 GHz band are integrated on-chip. Two types of compact filters are designed and fabricated, with the layout size of the bandpass filter as 0.65<formula formulatype="inline"> <tex Notation="TeX">$\,\times\,$</tex></formula>0.67 <formula formulatype="inline"><tex Notation="TeX">${\rm mm}^{ 2}$</tex></formula> and that of the low-pass filter as 0.77<formula formulatype="inline"><tex Notation="TeX">$\,{ \times }\,$</tex></formula>1.25 <formula formulatype="inline"><tex Notation="TeX">${\rm mm}^{ 2}$</tex></formula>. From the measurement results, the fifth-order low-pass filter shows less than 1.06 dB insertion loss up to 5 GHz and <formula formulatype="inline"><tex Notation="TeX">${-}{\rm 1.5}~{\rm dB}$</tex></formula> cutoff frequency at 5.3 GHz. The bandpass filter is a second-order coupled-resonator type, with measured 4.3 dB minimum insertion loss and better than 13 dB return loss in the pass band. Both simulation and shock testing results have shown that the filters are almost free of influence from environmental vibration and shock. From the measured results in various temperatures, the bandpass filters were found to show lower loss under low temperatures, while the passband shift is negligible in the various temperatures. Together with the fabricated filters, the developed micromachining technique has demonstrated the potential of on-chip integration and miniaturization of passive RF circuits. </para>

Optimized Porous Si Microplate Technology for On-Chip Local RF Isolation

In this paper, we present an optimized porous Si (PS) microplate technology for use as a local substrate for the on-chip integration of RF passives. The substrate used is a heavily doped p-type Si wafer with a resistivity of 0.005 Omegamiddotcm, which shows similar RF response to the p/p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> epiwafers, commonly used by complementary metal-oxide-semiconductor industry. Broadband electrical characterization of the microplates in the frequency range from dc up to 20 GHz was performed by integrating on them coplanar waveguides and using them to characterize RF losses in the composite PS/Si substrate material. We show that the porous material has a complex permittivity epsiv = 3.05(1 + i0.029), which is much superior to that obtained by the authors for PS grown on a p-type substrate. The effect of the thickness of the PS membrane on the RF isolation was also examined.

Optimum ASK Modulation Scheme for Passive RFID Tags Under Antenna Mismatch Conditions

We propose optimized ON/OFF states of the backscattered amplitude shift keying (ASK) modulator for the passive RF identification (RFID) tags. This takes into account both the reader receiver sensitivity and tag antenna mismatch conditions. Based on the analysis of the power transfer between the passive RFID tag and reader, we derived the optimum configuration of the ASK modulator. It maximizes the harvestable power to enhance the identification range between the tag and reader. The performance of the proposed modulator configuration was superior to the conventional scheme. We also developed an optimization procedure of the modulator for a given receiver sensitivity of the reader and various antenna mismatch conditions of the tag.

The RFID Technology for Neurosciences: Feasibility of Limbs' Monitoring in Sleep Diseases

This contribution investigates the feasibility of the passive UHF RF identification technology for the wireless monitoring of human body movements in some common sleep disorders by means of passive tags equipped with inertial switches. Electromagnetic and mechanical models as well as preliminary experimentations are introduced to analyze all the significant issues concerning the required power, the tag antenna design, the read distance, and the expected biosignals collected by the interrogation device.

Electronic Beam-Steering IC for Multimode and Multiband RFID

The performance of an RF identification (RFID) system can be limited by the static radiation pattern of a reader or interrogator. In this paper, a novel and low-power CMOS chip has been designed to enable beam steering for the RFID interrogator. This is suitable for the RFID system, operating from 900-MHz to 2.4-GHz bands, which uses passive and active RF tags. Our solution does not change the basic transceiver design in order to minimize the cost of the system. The chip has been implemented in 130-nm CMOS. It can provide up to eight time shifted signals to feed the multiple RF synthesizers in a phased array. This is suitable for the RFID reader, which requires multibands and multimodes, covering ISO-18000-6, Electronic Product Code, and IEEE 802.11b/g standards. The size of this die is 1.2 mm2 and it consumes only 10 mA. It can provide multiple delayed signals with 5-ps resolution. This will translate to a 2deg scanned angle at 2.4-GHz band. Measured results for the integrated circuit and phased arrays will be provided.

Complete Link Budgets for Backscatter-Radio and RFID Systems

Backscatter radio - wireless communication by modulating signals scattered from a transponder (RF tag) - is fundamentally different from conventional radio because it involves two distinct links: the power-up link for powering passive RF tags, and the backscatter link for describing backscatter communication. Because of severe power constraints on the RF tag, a thorough knowledge of the backscatter channel is necessary to maximize backscatter-radio and radio-frequency identification (RFID) system performance. This article presents four link budgets that account for the major propagation mechanisms of the backscatter channel, along with a detailed discussion of each. Use of the link budgets is demonstrated by a practical UHF RFID portal example. The benefits of future 5.8 GHz multi-antenna backscatter-radio systems are shown. An intuitive analogy for understanding the antenna polarization of RF tag systems is presented.

A Hierarchical Electromagnetic-Circuit Technique for Statistical Analysis of RF Circuits in the Spectral Domain

Spectral domain statistical analysis of RF circuits, combining a circuit simulator, which models the circuit part and a full-wave field solver, which models the passive elements, is presented in this paper. This paper first illustrates the importance of the knowledge of correlation information in accurately modeling the probability density functions (PDFs) of eventual objective functions using a simple transmission line paradigm. Next, this paper looks at the statistical study of on-chip RF passives using the spiral inductor as an example. It is shown that larger process variations necessitate modeling by means of a quadratic response surface to preserve accuracy. This results in nonindependent non-Gaussian nonclosed-form PDFs for the equivalent-circuit parameters of the passives. This paper then proposes a hierarchical technique to perform statistical analysis of RF circuits based on y-parameter representation for the circuit and the passive element parts. The proposed technique obviates the need for optimization steps to derive the equivalent-circuit parameters for the electromagnetic objects and the need to compute the correlation matrix between the circuit equivalent elements, while maintaining accuracy. The proposed approach is illustrated for the statistical analysis of an RF amplifier and its differential version operating at 15.78 GHz. PDFs of various quantities of interest are derived and yield measures are computed.

Modeling and analysis of power extraction circuits for passive UHF RFID applications

Modeling and analysis of far field power extraction circuits for passive UHF RF identification (RFID) applications are presented. A mathematical model is derived to predict the complex nonlinear performance of UHF voltage multiplier using Schottky diodes. To reduce the complexity of the proposed model, a simple linear approximation for Schottky diode is introduced. Measurement results show considerable agreement with the values calculated by the proposed model. With the derived model, optimization on stage number for voltage multiplier to achieve maximum power conversion efficiency is discussed. Furthermore, according to the Bode–Fano criterion and the proposed model, a limitation on maximum power up range for passive UHF RFID power extraction circuits is also studied.

Conformal Magnetic Composite RFID for Wearable RF and Bio-Monitoring Applications

This paper introduces for the first time a novel flexible magnetic composite material for RF identification (RFID) and wearable RF antennas. First, one conformal RFID tag working at 480 MHz is designed and fabricated as a benchmarking prototype and the miniaturization concept is verified. Then, the impact of the material is thoroughly investigated using a hybrid method involving electromagnetic and statistical tools. Two separate statistical experiments are performed, one for the analysis of the impact of the relative permittivity and permeability of the proposed material and the other for the evaluation of the impact of the dielectric and magnetic loss on the antenna performance. Finally, the effect of the bending of the antenna is investigated, both on the S-parameters and on the radiation pattern. The successful implementation of the flexible magnetic composite material enables the significant miniaturization of RF passives and antennas in UHF frequency bands, especially when conformal modules that can be easily fine-tuned are required in critical biomedical and pharmaceutical applications.

Investigation of the impact of magnetic permeability and loss of magnetic composite materials on RFID miniaturization for conformal medical applications

AbstractThe successful implementation of a flexible magnetic composite material has enabled the investigation of the potential impact on RFID (radio frequency identification) and RF passives miniaturization, considering both material/fabrication properties and geometric design parameters. The benchmarking structure is a short‐circuited quarter‐wavelength rectangular patch antenna for RFID UHF band (400–930 MHz). The antenna is electromagnetically modeled in HFSS full wave EM (electromagnetic) software and optimized using statistical tools, and it is found that the permeability of a practical magnetic composite can enable miniaturization by a factor larger than 3, something that could be replicated for other large‐size RF passives, such as integrated inductors. The impact of the magnetic loss of the composite on the miniaturized antenna performance is also evaluated and the material is reformulated to meet the loss requirements. Then a real RFID tag is implemented for 480 MHz frequency band and good performance of the miniaturized antenna is proven both in planar and conformal configurations. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Differential Colpitts VCO for Enhancing Transceiver Performance in Specified UHF Mobile RFID Environment Conditions

In this paper, we introduce a differential Colpitts voltage-controlled oscillator (VCO), performing a signal oscillation with low phase noise. The proposed VCO is a part of our RF integrated circuit (IC) transceiver design project; some transceiver components are also introduced. VCO performance is verified both in simulation and practical measurement using the proposed RF IC transceiver, communicating with a commercial passive UHF RF identification tag in a small-scale area. The measured phase-noise level at the frequency divider output port is nearly -106 and -135 dBc/Hz at 40-kHz and 1-MHz offset, respectively. A good figure-of-merit of 1.93 dB is obtained. The paper also highlights some important components [e.g., phase-locked loop, low-noise amplifier, dc offset canceller (DCOC)], and their performance. We configure the reader system, which consists of the proposed transceiver on board and a patch antenna, to use frequency hopping in 15 channels at a 200-kHz interval. The transceiver power amplifier supports 22 dBm of power. Configuring the interrogation range to 1 m, we measure received backscatters at the DCOC output port (the regenerated tag data level is 8 mV). Finally, we verify satisfactory states of the tag data process in the receiver.

Analysis on Control of the Bunch Length by Passive Harmonic RF Cavities in Storage Rings

Analysis on Control of the Bunch Length by Passive Harmonic RF Cavities in Storage Rings

RF characterization and isolation properties of mesoporous Si by on-chip coplanar waveguide measurements

We report on the broadband electrical characterization of thick mesoporous silicon layers used as RF microplates for on-chip integration of high-Q passive devices in a CMOS-compatible process. To measure the RF losses of the microplate we have fabricated several designs of Coplanar Waveguides (CPWs), for form-factors relevant to the sizes of on-chip passive RF devices, on thick mesoporous Si layers (RF microplates) of various thicknesses, and we compared the results with those obtained from similar CPWs integrated directly on the p-type Si substrate. For maximum measurement sensitivity of the loss, the CPWs were designed to be very good transmission lines matched to 50Ω port impedances. We also characterized the grown mesoporous Si by performing electromagnetic simulations of the structure and identifying the measured and simulated S-parameters over a broadband frequency region, for the appropriate simulator input of complex permittivity. The measured results show that, for CPW features commensurate with the scale of on-chip RF passive devices, a 50-μm-thick mesoporous Si layer on the Si substrate reduces the losses to 1/6th–1/4th of the values corresponding to a p-type Si substrate, showing that mesoporous Si is an excellent material for CMOS-compatible on-chip integration of high-Q passive devices.

Wireless switch for implantable medical devices based on passive RF receiver

A wireless switch designated for battery-supplied implantable medical devices is designed and verified based on a passive RF receiver. The switch employs wireless energy recovery and wireless identification, and consumes zero standby power. Unlike the commonly used dry reed switch, the proposed switch features high tolerance to noise and disturbance, as well as compatibility with integrated circuits. The proposed wireless switch circuit has been implemented using 0.18 µm CMOS technology, and verified in a wireless capsule endoscope prototype system.

Quasi-Static Derived Physically Expressive Circuit Model for Lossy Integrated RF Passives

This paper presents a novel approach for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">deriving</i> a physically meaningful circuit model for integrated RF lossy passives such as spiral inductors on a silicon substrate. The approach starts from a quasi-static partial element equivalent circuit (PEEC) model. The concept of complex inductance and capacitance is introduced to uniformly deal with the conductor and dielectric losses. Basic Y- Delta network transformation is used to ldquoabsorbrdquo the insignificant internal nodes of the original PEEC network and to reduce the order of the circuit model. The physically expressive circuit model given here can be very concise while preserving the major physical meanings and attributes of the original circuit layout. A low-temperature co-fired ceramic bandpass filter and two practical inductors fabricated using a 0.18-mum CMOS process are studied by the model to demonstrate the validity of this new approach. Furthermore, the stability condition of the model is also discussed.

A Portable Low-Power Harmonic Radar System and Conformal Tag for Insect Tracking

Harmonic radar systems provide an effective modality for tracking insect behavior. This letter presents a harmonic radar system proposed to track the migration of the Emerald Ash Borer (EAB). The system offers a unique combination of portability, low power and small tag design. It is comprised of a compact radar unit and a passive RF tag for mounting on the insect. The radar unit transmits a 5.96 GHz signal and detects at the 11.812 GHz band. A prototype of the radar unit was built and tested, and a new small tag was designed for the application. The new tag offers improved harmonic conversion efficiency and much smaller size as compared to previous harmonic radar systems for tracking insects. Unlike RFID detectors whose sensitivity allows detection up to a few meters, the developed radar can detect a tagged insect up to 58 m (190 ft).

Wireless RF Identification System Based on SAW

The passive RF identification system is discussed in this paper. The system uses the surface acoustic wave (SAW) as an identification tag and works at ISM-915 MHz. The system adopts a pair of passive dispersive SAW filters for pulse expansion and compression in order to improve antijamming performance and degrade the severe requirement for sensitivity of a wideband receiver. Then, the structure of the SAW tag, the principle of transmitter and receiver, and the DSP subsystem are discussed. Finally, testing results are demonstrated.

A Wideband ΔΣ Digital-RF Modulator for High Data Rate Transmitters

A wideband software-defined digital-RF modulator targeting Gb/s data rates is presented. The modulator consists of a 2.625-GS/s digital DeltaSigma modulator, a 5.25-GHz direct digital-RF converter, and a fourth-order auto-tuned passive LC RF bandpass filter. The architecture removes high dynamic range analog circuits from the baseband signal path, replacing them with high-speed digital circuits to take advantage of digital CMOS scaling. The integration of the digital-RF converter with an RF bandpass reconstruction filter eliminates spurious signals and noise associated with direct digital-RF conversion. An efficient passgate adder circuit lowers the power consumption of the high-speed digital processing and a quadrature digital-IF approach is employed to reduce LO feedthrough and image spurs. The digital-RF modulator is software programmable to support variable bandwidths, adaptive modulation schemes, and multi-channel operation within a frequency band. A prototype IC built in 0.13-mum CMOS demonstrates a data rate of 1.2 Gb/s using OFDM modulation in a bandwidth of 200 MHz centered at 5.25 GHz. In-band LO and image spurs are less than -59 dBc without requiring calibration. The modulator consumes 187 mW and occupies a die area of 0.72 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Tunable Permittivity of Polymer Composites through Incremental Blending of Raw and Functionalized Single-Wall Carbon Nanotubes

A method is reported for controlling the permittivity of single-wall carbon nanotube (SWNT) polymer composites based on variations in the amount of raw and functionalized SWNTs (f-SWNTs) that are incorporated. The total weight percent of SWNTs included in the composites remains constant at 0.5%. Measurements were taken at a frequency range of 1-1000 MHz. The magnitude of the real permittivity varied between 20 and 3.3, decreasing as higher fractions of f-SWNTs are added. This type of control over the permittivity is important for applications including passive RF antenna structures, electromagnetic interference mitigation, and other radio frequency applications.