Frequency Agile Filters Research Articles

A new frequency agile filter structure employing CDTA for positioning systems and secure communications

Multi-standard transceivers are more useful than the other classical transceivers. The flexibility of the multi-standard transceivers allow all pre-defined protocols to sense without redesign the t...

CMOS implementations of VDTA based frequency agile filters for encrypted communications

In this study, two different voltage mode frequency agile filters employing voltage differencing trans-conductance amplifier (VDTA) are designed for encrypted communications. The agility of the designed frequency agile filters are supported by only switching transistors instead of feedback systems in the conventional designs. The proposed frequency agile filters are implemented by CMOS technology to benefit from easy and cheaper manufacturing of CMOS circuits. One of the designed frequency agile filter is realized by changing gm (trans-conductance) and the other is realized by varying capacitance. The MOS capacitor technique is used instead of conventional capacitors in the second frequency agile filter structure. The CMOS performance of designed frequency agile filter realized with VDTA is compared with the recently recommended frequency agile filter structure realized with Bi-CMOS technology. The performance parameters of the VDTA and agile filter structures are summarized and the suitability of the filters for different applications are given. The designed filter can be easily operated up to 1 GHz. In this study, HAVEQUICK operating UHF band between 225 and 400 MHz is selected as the essential application of the designed filters. Moreover, proposed structures are laid-out. To prove the performance of the designed frequency agile filters, post-layout simulations with Monte Carlo and corner analyses are performed as well. AMS 0.18 µm parameters are used for the CMOS realization of the designed frequency agile filter.

New Current-Mode Class 1 Frequency-Agile Filter for Multi Protocol GPS Application

Recently, due to their cost, accuracy, and integrability of conventional current-mode (CM) on-chip integrated filters working in radio frequency region, frequency-agile filters (FAFs) have started taking great interest in multi-standard transceivers, encrypted communication, cognitive radio, software defined radio structures, and global positioning system applications. By following the most recent trend in the literature, this paper proposes the first class 1 CM FAF using high-performance analog building block so-called positive-type electronically controllable second-generation current conveyor (ECCII+), two resistors, and two grounded capacitors. The theory and the proposed 2nd-order CM FAF are supported by both regular and post-layout simulations performed using CADENCE Spectre tool with TSMC 0.18 µm level-49 CMOS technology process BSIM3v3 parameters. Furthermore, corner and Monte-Carlo analyses are given to prove the accuracy of centre frequency of the CM FAF. DOI: http://dx.doi.org/10.5755/j01.eee.21.5.13323

Design of CDTA and VDTA Based Frequency Agile Filters

This paper presents frequency agile filters based on current difference transconductance amplifier (CDTA) and voltage difference transconductance amplifier (VDTA). The proposed agile filter configurations employ grounded passive components and hence are suitable for integration. Extensive SPICE simulations using 0.25 μm TSMC CMOS technology model parameters are carried out for functional verification. The proposed configurations are compared in terms of performance parameters such as power dissipation, signal to noise ratio (SNR), and maximum output noise voltage.

Encrypted communications: towards very low consumption frequency-hopping active filters

The principal techniques of coding used for secure encrypted communications are first indicated. Then, after a brief recall of the essential points of frequency-agile filters, a second order frequency-hopping bandpass filter operating in current mode and implemented with CCCII is introduced. It necessitates six CCCII only and uses an improved multiple feedback loop connected in such a way that all of its frequency-agile filters of classes 0, 1, 2 and 3 are available. This very low consumption active filter so offers the advantage to have four central frequencies selected digitally for each value of its bias current. Validation results in 0.25 μm SiGe BiCMOS technology are given. They highlight the new perspectives for encrypted communications to be expected from this approach.

Ultra-high suppression microwave photonic bandstop filters

A bandstop radio frequency (RF) filter can enhance the capabilities of RF communication systems by removing unwanted signal components such as distortion, or interference. In modern cognitive radio systems, frequency agile filters are desired to block interferers with dynamically changing frequencies and powers. These filters should be tunable over a broad frequency range, and they should be capable of suppressing very strong signals with a high resolution. To simultaneously meet these requirements with traditional RF filters are highly challenging. Microwave photonic (MWP), a technology that primary deals with the generation, distribution, and processing of high speed RF signals using photonic techniques and components, is promising for creating frequency agile RF filters. However, traditional MWP filters are lacking the high resolution and peak suppression exhibited by state-of-the-art RF electrical filters. We recently introduced a new class of MWP notch filter which is free from this limitation. This scheme allowed the creation of anomalously high suppression MWP notch filter from virtually any kind of optical resonance, irrespective of its type (gain or absorption), or its magnitude. This enabled, for the first time, simultaneous optimization of the MWP filter resolution, peak attenuation, and frequency tuning range. In this paper, we present the analysis of notch filter response creation using the novel sideband processing technique. We then show the applicability of this technique to a wide range of optical filters. We compare simulated and experimental results of the notch filter response created using three types of optical filter commonly used in MWP signal processing, namely stimulated Brillouin scattering (SBS), an integrated optical ring resonator (ORR), and a phase-shifted fiber Bragg-grating (FBG).

Guest editorial: Introduction to the special issue on selected papers from the ELECO’2011 conference

Welcome to the Special Issue on Selected Papers from the ELECO-2011 Conference!, the seventh International Conference on Electrical and Electronics Engineering, held 1–4 December 2011, in Bursa-Turkey. ELECO conferences are organized at international level in odd numbered years and as national conferences in even numbered years. As such ELECO-2011 is the seventh international conference, with participants coming from various countries, presenting papers from the rich spectrum of electrical and electronics engineering discipline. ELECO-2011 is jointly organized by Uludag University, Bursa; Istanbul Technical University (ITU) and the Chamber of Turkish Electrical Engineers (EMO), Bursa Section. The IEEE-Turkey Section and The Scientific and Technological Research Council of Turkey (TUBITAK) are co-sponsors of ELECO-2011. We are grateful to them for their contributions. Considering the broad scope of the technical program, it was probably the largest electrical and electronics engineering conference ever held in Turkey. The scope of the conference covers topics ranging over electric power systems, electrical machines and drives, power electronics, high voltage techniques, electrical materials, electronics, circuits and systems, signal processing, electromagnetics, antennas and propagation, microwave theory, communication systems, mechatronics, control theory, control applications, automation systems, robotics and intelligent control systems. This year 288 papers have been submitted for presentation and 166 papers have been accepted. If we look at the contributions with respect to geographical point of view, it is seen that ELECO’2011 contributions are coming from 19 different countries. Selected papers from previous international ELECO Conferences were invited to be published in extended form in special ELECO issues of international journals, under peer review. Two special ELECO issues appeared in the journal Analog Integrated Circuits and Signal Processing containing selected papers from ELECO’2001 and ELECO’2007. Furthermore, four special ELECO issues appeared in the journal TJEECS: Turkish Journal of Electrical Engineering and Computer Sciences where selected papers from ELECO’2003, 2005, 2007 and 2009 were published in extended form, respectively. This Special Issue on Selected Papers from ELECO’2011 contains extended versions of ten papers presented at the conference. Two papers are selected from invited talks given by world-known scientists during the conference. The other eight are chosen from regular submitted manuscripts. The paper by Yahya Lakys and Alain Fabre entitled ‘‘Multistandard Transceivers: State of the Art and a New Versatile Implementation for Fully Active Frequency Agile Filters’’ was presented at ELECO-2011 as an invited paper. In this paper various architectures of transceivers for current standards are firstly compared, different possibilities to achieve multi-standard transceivers are also recalled and compared. It is demonstrated that the second generation current controlled conveyor operating in current mode is perfectly suitable for the realization of frequency-agile filters. A S. Ozoguz (&) H. H. Kuntman Faculty of Electrical Electronics Engineering, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey e-mail: ozoguz@itu.edu.tr

Multistandard transceivers: state of the art and a new versatile implementation for fully active frequency agile filters

The various architectures of transceivers for current standards are firstly compared. Different possibilities to achieve multi-standard transceivers are also recalled and compared. We demonstrate that ease of realization and flexibility evolve in opposite directions. The advantages and drawbacks of reconfigurable active filters are indicated. We demonstrate that the second generation current controlled conveyor operating in current mode is perfectly suitable for the realization of frequency-agile filters. After a brief recall of the essential points of agile filters, a second order frequency agile bandpass filter operating in current mode is implemented with CCCII+. It has four central frequencies whose values could be selected digitally. The validation results show that its tuning ratio n = f 0max /f 0min is equal to 5.1 with f 0max = 1.22GHz.

Cognitive and encrypted communications: state of the art and a new approach for frequency-agile filters

Several communication techniques are investigated in the first part of this paper: software radio, cognitive radio and encrypted communications. State of the art of research on agile and reconfigurable filters, passive as well as active, necessary for transceivers is then made and various tables for comparison are given. In the third part, a new theory for a 2^{nd}-order frequency-agile filter is introduced. The center frequency of the filter is proportional to the gain of a feedback amplifier and thus can be tuned over a wide frequency range. This new theory is thereafter generalized to the n^{th}-class leading to a center frequency proportional to (A)^{n/2}. Simulation results of band pass agile filters in current mode and made from second-generation current controlled conveyors (CCCII+) in 0.25 \mu m SiGe BiCMOS technology are given for n = 1 and n = 2. These simulation results along with results of measurements carried out on the fabricated filters entirely confirm the new approach. They also highlight the improvements to be expected for cognitive and encrypted communications.

Improved Dielectric Properties of Low-Temperature-Sintered (Ba,Sr)TiO3-Based Ceramics by Ge Substitution

Multilayer microwave dielectric materials with low sintering temperature are required for microwave phase shifters, filters, and true-time delay devices. We investigated the sintering and dielectric properties of (Ba0.6Sr0.4)(Ti1-xGex)O3 (BSTG; 0.05≤x≤0.3) ceramics. As the Ge concentration was increased, the lattice constant of BSTG ceramics decreased, and Ba2Ge2TiO8, which is the liquid phase at low temperature, was formed. Ba2Ge2TiO8 liquid phase may increase the sintering density. The effect of Ge substitution is the decrease in the sintering temperature from over 1400 to 1150 °C in BST system ferroelectric ceramics. With increasing Ge concentration, the dielectric constant decreased from 2190 to 530, and the dielectric loss decreased up to 0.001 (at 1 MHz) with sintering at 1150 °C for 2 h. When Ge was substituted at 0.05 and 0.1 mol of Ti in the BST at 1150 °C, the dielectric constant, dielectric loss, tunability, Curie temperature, and figure of merit were 2184 and 1529, 0.002 and 0.001, 27 and 23%, -11 and -18 °C, and 135 and 230, respectively. These compositions show microwave dielectric properties comparable to those of (Ba0.5Sr0.5)TiO3 ferroelectrics, which are the important materials for tunable devices such as varactors, phase shifters, and frequency agile filters.

Low-Loss Frequency-Agile Bandpass Filters With Controllable Bandwidth and Suppressed Second Harmonic

This paper presents a novel approach to design frequency-agile bandpass filters with constant absolute bandwidth and passband shape, as well as a suppressed second harmonic. A novel mixed electric and magnetic coupling scheme is proposed to control the coupling coefficient variation. Theoretical analysis indicates that it is able to achieve desired coupling coefficients between the proposed resonators at various frequencies so as to obtain constant absolute bandwidth. Moreover, this half-wavelength resonator has a Q higher than the quarter- and half-wavelength counterparts, thus resulting in low insertion loss. A filter of this type is designed to validate the proposed idea. To remove the spurious responses of the filter, a method is then introduced to suppress the second harmonic without degrading the passband performance. For demonstration, two frequency-agile filters with 60- and 80-MHz constant absolute bandwidth are implemented with the frequency tuning range from 680 to 1000 MHz. Comparisons of experimental and simulated results are presented to verify the theoretical predications.

A $\hbox{Pb}(\hbox{Zr}_{0.55}\hbox{Ti}_{0.45}) \hbox{O}_{3}$-Transduced Fully Differential Mechanically Coupled Frequency Agile Filter

This letter reports on the performances of a frequency-tunable lead-zirconate-titanate-transduced fully differential mechanically coupled high-overtone width-extensional filter. The demonstrated electric field tuning provides channel agility and bandwidth adjustability for the incorporation of analog spectral processors in modern radio receiver architectures. We designed and experimentally characterized the higher overtone frequency response of a fully differential width-extensional filter. The filter demonstrates a center frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fC</i> ) tuning range of 7 MHz at 260 MHz and an adjustable bandwidth from 3 to 6.3 MHz while maintaining a maximum frequency shift due to hysteresis effects below 0.14% and a stopband rejection floor of -60 dB.

Improved Figure of Merit of (Ba,Sr)TiO3-Based Ceramics by Sn Substitution

The dielectric properties of (Ba0.6Sr0.4)(Ti1-xSnx)O3 (0 ≤x ≤0.3) ceramics were investigated. Single-phase specimens having a cubic perovskite structure could be obtained. As Sn concentration increased, dielectric loss decreased untill a composition of x = 0.15 and slightly increased as Sn concentration increased further. The diffused phase transition appeared owing to substitution of Sn ions. When Sn was substituted at 0.1 mol in (Ba0.6Sr0.4)TiO3 at 1400 °C, the dielectric constant, dielectric loss, tunability, Curie point, and figure of merit (FOM) were 1400, 0.0027, 18%, -40 °C, and 67, respectively. These compositions show excellent dielectric properties than those of (Ba0.5Sr0.5)TiO3 ferroelectrics, which are limelight materials for tunable devices such as varactors, phase shifters, and frequency agile filters.

Improvement of dielectric loss of (Ba,Sr)(Ti,Zr)O 3 ferroelectrics for tunable devices

(Ba 0.6Sr 0.4)(Ti 1− x Zr x )O 3 (0.05 ≤ x ≤ 0.3) ferroelectric materials have cubic perovskite structure and show paraelectric properties at room temperature. Curie point shifted to a negative value as increasing Zr content in (Ba 0.6Sr 0.4)(Ti 1− x Zr x )O 3 system. When Zr substituted 0.1 mol, the dielectric constant, dielectric loss, tunability, Curie point and FOM were 4500, 0.0005, 63%, −1.6 °C and 1260, respectively. This composition shows excellent microwave dielectric properties than those of (Ba 0.6Sr 0.4)TiO 3 ferroelectrics, which are limelight materials for tunable devices such as varactors, phase shifters and frequency agile filters, etc.

Superconducting microwave filter systems for cellular telephone base stations

In the second decade following the discovery of high-temperature superconductivity (HTS), wireless communications has emerged as the earliest large commercial market. The enormous growth of the wireless industry coupled with its increasing technology demands has created a significant opportunity for HTS technology in wireless base stations. These systems combine high-performance HTS RF filters with cryocooled semiconductor preamplifiers to offer enhanced sensitivity to improve signal reception and exceptional selectivity to reject interfering signals. There are now thousands of installed HTS systems and the prospects are good for widespread future deployment. This paper discusses the underlying technologies that support HTS wireless applications, based upon the characteristic microwave properties of HTS thin films and substrates. HTS filter design technology has been under development for a decade and has gained a fair measure of maturity in terms of design tools, simulation techniques, and available topologies. The need for extremely narrow-band filters, highly selective filters, frequency-agile filters, and very compact filter designs has led to many technology advances. On the system level, comparable advances in cryocooler technology and cryopackaging have enabled the development of a broadly deployable technology. We discuss industry trends and the methodologies and results of simulations and real-world measurements of HTS filter systems.

Frequency Agile Filters Based on SrTiO 3 /YBa 2 Cu 3 O 7 Heterostructures Grown by PLD on LaAlO 3 Substrates

Passive devices using high temperature superconductors are already going to be implemented in electronics for passive filtering in telecommunications. To avoid the frequency jamming not only in terrestrial and satellite communications but also in the radar frequency ranges, filter agility is essential to undertake further development. We will discuss here the interest of using SrTiO 3 as tunable oxide for agile devices and present our last results on voltage agile microwave resonator fabricated from YBa 2 Cu 3 O 7 /SrTiO 3 heterostructures. A strong correlation is found between Q 0 or agility and the tetragonal distortion of the SrTiO 3 layer. The resonator performance is markedly increased by associating growth parameter optimization and ex situ annealing of SrTiO 3 layer prior to the YBa 2 Cu 3 O 7 deposition. Annealed samples exhibit almost voltage independent losses of about 5 2 10 m 3 at 6 GHz and 77 K, with l r at 1200 showing a variation of S 50% at 10 5 V/m.

Frequency Agile Optical Filters using Nanoscopic Polymer Dispersed Liquid Crystals

ABSTRACTThe ability to realise frequency agile filters has always been a major goal of materials and device scientists. Polymer dispersed liquid crystal materials (PDLCs), in which the droplets are deliberately produced with dimensions smaller than the Rayleigh limit for optical scatter, provide a means of realising this goal. At visible wavelengths the material has the appearance of a phase-homogeneous medium both with and without applied electric field. Refractive indices are an average of those of the liquid crystal and those of its host and can be described on the basis of effective medium approximations using orientationally averaged values for the randomly aligned LC material for the ambient state. On application of electric field, the individual liquid crystal molecules align with a resulting reduction in the effective index of the medium. Extensive studies of the variation of process parameters and their effect on the morphology of the composite have enabled field induced changes in refractive index in excess of 0.05 to be achieved without recourse to the use of polarisers and with little or no hysteresis effects. At wavelengths associated with WDM devices for telecommunication applications, the degree of scatter loss is negligible. Design trade-offs have been assessed for candidate tunable WDM filters based on resonant cavity devices.