A novel wideband bandpass filter with improved stopband characteristics is presented in this paper. Dual-mode square ring resonator is used in the proposed filter. New formulas based on the even- and odd-mode analysis are derived to facilitate the design of transmission zeros of the square ring resonator. A short-circuited stub and a piece of aperture-enhanced parallel-coupled lines are introduced to the input and output of the resonator to lower the passband return loss and widen the stopband of the filter significantly. The filter has a 50% fractional bandwidth, is compact in configuration, and shows remarkably improved performance compared with previously reported filters of the same kind. The measured filtering response shows a good agreement with the simulated result.

A novel structure of bandpass filter using NRD guide E-plane resonators is proposed. The NRD guide E-plane resonator is constructed by inserting metal foils in the E-plane of NRD guide. Simulation, fabrication and handling of the filter are very easy because each resonator is separated by simple metal foils. Chebyshev response bandpass filters are designed based on the theory of direct-coupled resonator filters and fabricated at 60 GHz. Simulated and measured filter performances agreed well with the design specifications. Insertion losses of the fabricated filters were found to be around 0.3 dB for 3-pole filter and 0.5 dB for 5-pole bandpass filter, respectively.

The Evolutionary Electronics refers to the design method of electronic circuits with the help of Evolutionary Algorithms. Over the years huge experience has been accumulated and tremendous results have been achieved in this field. Two obvious tendencies are prevailing in the area over designers to improve the performance of Evolutionary Algorithms. First of all, as with any solution-search-algorithm, the designers try to reduce the potential solution space in order to reach the optimum solution faster, putting some constrains onto search algorithm as well as onto potential solutions. At the same time, the second tendency of unconstraining the Evolutionary Algorithms in its search gives unpredictable breakthroughs in results. Enabling the evolution to optimize with more experimental parameters devoted to drive the evolution and adjusted previously manually, is one of an example where such kind of unconstraining takes place. The evolution with the maximum freedom of search can be addressed as unconstrained evolution. The unconstrained evolution has already been applied in the past towards the design of digital circuits, and extraordinary results have been obtained, including generation of circuits with smaller number of electronic components. Recently, the similar method has been introduced by authors of this paper towards the design of analogue circuits. The new algorithm has produced promising results in terms of quality of the circuits evolved and evolutionary resources required. It differed from constrained method by its simplicity and represented one of the first attempts to apply Evolutionary Strategy towards the analogue circuit design. In this paper both conventional constrained evolution and newly developed unconstrained evolution in analogue domain are compared in detail on the example of "LC" low-pass filter design. The unconstrained evolution demonstrates the superior behaviour over the constrained one and exceeds by quality of results the best filter evolved previously by 240%. The experimental results are presented along with detailed analysis. Also, the obtained results are compared in details with low-pass filters designed previously.

In 2004, Tsuji and Shimizu proposed a one-time password authentication protocol, named 2GR (Two-Gene-Relation password authentication protocol). The design goal of the 2GR protocol is to eliminate the stolen-verifier attack on SAS-2 (Simple And Secure password authentication protocol, ver.2) and the theft attack on ROSI (RObust and SImple password authentication protocol). Tsuji and Shimizu claimed that in the 2GR an attacker who has stolen the verifiers from the server cannot impersonate a legitimate user. This paper, however, will point out that the 2GR protocol is still vulnerable to an impersonation attack, in which any attacker can, without stealing the verifiers, masquerade as a legitimate user.

This paper proposes a new microstrip stepped-impedance resonator (SIR) used for bandpass filters with reduced size and improved stopband characteristics. A comprehensive treatment of both ends of the resonator with loaded triangular and rectangular microstrips is described. The design concept is demonstrated by two filter examples including four-resonator parallel-coupled Chebyshev bandpass and compact four-resonator cross-coupled elliptic-type filters. These filters are not only compact size due to the slow-wave effect, but also have a wider upper stopband resulting from the resonator bandstop characteristic. The filter designs are described in details. The simulated and experimental results are demonstrated and discussed.

This paper overviews the history of a class of varactor tuned bandpass filters. Since the miniaturization as well as the high performance of the tunable bandpass filters is required for the next generation mobile communication systems, the discussion is focused on the various planar type tunable filters including active configurations. Brief design concepts of various tunable filter configurations as well as their characteristics are discussed.

A novel linear transconductor using translinear cells is proposed. It consists of a voltage follower, a resistor, and a current follower. SPICE simulations using an 8 GHz bipolar transistor-array parameter show that the linear transconductor with a transconductance of 1 mS exhibits a linearity error of less than 0.75% over an input voltage range of 1 V for a supply voltage of 2.0 V. The temperature coefficient of the transconductance is less than 124 ppm/. The -3-dB frequency of the transconductance is more than 4.5 GHz. Applying the linear transconductor as a building block, the design of a bandpass filter with center frequency of 85 MHz and Q-factor of 80 is presented.

This paper presents a methodology based on congruent transformation for distributed interconnects described by state-space time-delays system. The proposed approach is to obtain the passive reduced order of linear time-delays system. The unified formulations are used to satisfy the passive preservation. The details of the mathematical proof and a couple of validation examples are given in this paper.

This letter proposes a compact multi-layered bandpass filter exhibiting left-handed and right-handed behaviors in its passband. This filter has a greatly expanded passband from 1.61 GHz to 4.16 GHz (88.4% bandwidth) with a maximum ripple of 1.2 dB and well-suppressed out-of-passbands with transmission zeros at 1.15 GHz and 4.52 GHz. The physical mechanisms are studied with FEM-based full-wave simulations, equivalent circuit analysis and careful experiments.

A compact open-loop resonator bandpass filter is presented to suppress the spurious passband using compensated compact microstrip resonant cell (C-CMRC) feeding structure. Based on the inherently compact and stopband characteristics of the C-CMRC feeding, the proposed filters shows a better spurious rejection performance than the only open-loop resonator filter. The suppression is -57.4 dB, -49.5 dB, and -43.9 dB at the 2nd, 3rd and 4th harmonic signal separately. All the performance of proposed filters have been verified by the measured results.

This investigation proposes a modified equivalent circuit of single complementary split-ring resonator (CSRR) in planar transmission media and a dual-mode ring bandpass filter (BPF) that uses periodic CSRRs to suppress the spurious response. The proposed modified equivalent circuit consists of lumped elements that can be easily extracted from the measured S parameters. The proposed dual-mode ring BPF has exhibits a wide stopband characteristic owing to the bandgap resonant characteristic of CSRRs in the harmonic frequency of the dual-mode ring BPF. Good agreement with EM simulation and measurement is demonstrated.

In AlGaN/GaN high electron mobility transistors (HEMTs), Si3N4 passivation film brings effective improvements in the current collapse phenomenon, however, the suppression of this phenomenon in a high voltage operation can not be achieved in only the Si3N4 deposition process. In order to solve this problem, we have demonstrated an NH3-plasma surface pretreatment in the chamber of plasma enhanced chemical vapor deposition (PE-CVD) just before Si3N4 deposition process. We found that the optimized NH3-plasma pretreatment could improve the current collapse as compared with only the Si3N4 deposition and an excessive pretreatment made it worse adversely in AlGaN/GaN-HEMTs. It was confirmed by Auger electron spectroscopy (AES) analysis that the optimized NH3-plasma pretreatment decreased the carbon contamination such as hydrocarbon on the AlGaN surface and the excessive pretreatment degraded the stoicheiometric composition of AlGaN surface.

Ultrahigh-speed continuous-tine delta-sigma modulators (DSMs) have been designed by using a fully-differential comparator consisting of resonant-tunneling diodes (RTDs) and HEMTs. Continuous-time lowpass and bandpass filters using HEMTs have also been incorporated to obtain lowpass- and bandpass-type DSMs, respectively. Circuit simulation assuming 0.1-µm InP-based HEMT and RTD technology has revealed a successful operation of the 2nd-order lowpass DSM at a sampling frequency of 20 GHz. The clock frequency was 10 GHz because of the double sampling function of the present comparator. The 2nd-order bandpass DSM has also been designed with a center frequency of 3 GHz. These results clearly show high potential of the present delta-sigma modulators.

This paper presents high-performance millimeter-wave passive devices using MEMS technology. The purpose of this paper is to show the possibility of MEMS technology as an enabling technology for millimeter-waves. The loss and cost issues, which have been the inherent barrier for commercialization of mm-waves, can be solved by RF MEMS technology. Successful demonstrations of MEMS technology for mm-waves include novel CPW transmission lines, digital impedance tuners, analog tunable band-pass filters, reconfigurable low-pass filters, V-band digital distributed phase shifters and 2-D mechanical beam-steering antennas. All these circuits were implemented for 30-65 GHz frequency range, and show the state-of-the-art performance, which is beyond the limit set by the conventional technology.

A second-order CMOS continuous-time bandpass filter with a tuneable 4-12 MHz center frequency (fc) is presented. The Design has been done by using a new second-order block which is based on Gm-C method. This Gm-C filter achieves a dynamic range of 30 dB for 1% IM3, and Q equal to 58 at 12 MHz, while dissipating only 10.5 mW from 3.3 V power supply in 0.35 µm CMOS process. The on-chip indirect automatic tuning circuit uses a phase-locked loop which sets filter center frequency to an external reference clock.

Recently, Yoon et al. exhibited the vulnerability of the smart-card-equipped password based authentication protocol proposed by Chien et al. to the Denning-Sacco attack. Furthermore, they also pointed out that the protocol does not provide the perfect forward secrecy. Accordingly, they presented an enhanced protocol to strengthen the security. This letter, however, demonstrates an interleaving attack on the Yoon et al.'s improved protocol and also discusses how to defend the protocol from the attack presented here.

This paper discusses the design and performance of on-chip passive components of transmission lines (TR) and inductors. First, the measurement technique of on chip passives is discussed. A transmission line that can be used for Gbps signal propagation on Si CMOS is examined. As a high density transmission line structure of diagonal-pair differential TR line is described. Also, a circuit and TR line is introduced for above 10 Gbps signal propagation. The on-chip inductor which is a key passive component in RF application of Si CMOS technology is discussed. We examine some on-chip inductors that have been developed in our group: small area inductor, high performance inductor using WL-CSP (Wafer-Level Chip-Size-Packaging) technology. Finally, a wide tuning range LC-VCO using a variable inductor for RF reconfigurable circuit is introduced.

This paper proposes a parallel coupled microstrip bandpass filter (BPF) with ring Electromagnetic Bandgap (EBG) cells on the middle layer for spurious suppression. The ring EBG cells of the middle layer add a good stopband-rejection mode to the second harmonics of the parallel coupled microstrip BPF with suppression of over -50 dB, without affecting the center frequency and insertion loss of the original designed BPF. The design of ring EBG cells is presented and verified by the experimented results.

This paper presents a design procedure of multilayer single-input/single-output dual-band filters of small size fabricated in high-permittivity LTCC (Low Temperature Co-fired Ceramic) substrates. The present dual-band filter, with pass bands of 950 MHz and 1.9 GHz, consists of two single-band filters each one of which has a matching circuit for controlling the input impedance in the pass band of the counterpart. Discussed first in this paper is a dual-band filter that has the matching circuit connected to the single-band filters externally. Then, a dual-band filter with the matching circuit embedded in its body is investigated together with metallization patterns of the matching elements. Presented finally is a very small single-input/single-output dual-band filter suitable for dual-band wireless communication systems.

This paper proposes a new architecture for multibit complex bandpass ΔΣAD modulators with built-in Switched-Capacitor (SC) circuits for application to Low-IF receivers such as used for Bluetooth and WLAN. In the realization of complex bandpass ΔΣAD modulators, we face the following problems: (i) SNR of AD converter is deteriorated by mismatches between internal analog I and Q paths. (ii) Layout design becomes complicated because of signal lines crossing by complex filter and feedback from DAC for I and Q paths in the complex modulator, and this increases required chip area. We propose a new structure for a complex bandpass ΔΣAD modulator which can be completely divided into two paths without layout crossing, and solves the problems mentioned above. The two parts of signal paths and circuits in the modulator are changed for I and Q while CLK is changed for High/Low by adding multiplexers. Symmetric circuits are used for I and Q paths at a certain timing, and they are switched by multiplexers to those used for Q and I paths at another timing. Therefore the influence from mismatches between I and Q paths is reduced by dynamic matching. As a result, the modulator is divided into two separate parts without crossing signal lines between I and Q paths and its layout design can be greatly simplified compared with conventional modulators. We have conducted MATLAB simulations to confirm the effectiveness of the proposed structure.