Bandpass filters with broad bandwidth (up to 70%), very wide upper stopband (nearest spurious passband occurs up to five times of passband center frequency (f0)), good stopband rejection performance (better than -30-40 dB in the whole stopband region), and matching with the conventional low cost printed circuit board process with low dielectric constant substrates are proposed in this paper. The proposed filters are designed using parallel-coupled vertically installed planar stepped-impedance resonators (VIPSIRs), which adopt the inherent nature of very tight coupling of VIP coupled line and extremely high impedance of VIP line. The extremely tightly coupled line enables the proposed filters having very wide passband and the extremely high impedance of VIP line leads to extremely large low-to-high impedance ratio that pushes the nearest spurious passband up to 5f0. Both VIP coupled line and VIP high impedance line are analyzed and characterized by the design charts. The design procedures based on the design charts are verified by several experimental examples. The measured results agree very well with the simulated ones.

One method for achieving high-speed waveform digitizing uses time-interleaved A-D Converters (ADCs). It is known that, in this method, using multiple ADCs enables sampling at a rate higher than the sampling rate of the ADC being used. Degradation of the dynamic range, however, results from such factors as phase error in the sampling clock applied to the ADC, and mismatched frequency characteristics among the individual ADCs. This paper describes a method for correcting these mismatches using a digital signal processing (DSP) technique. This method can be applied to any number of interleaved ADCs, and it does not require any additional hardware; good correction and improved accuracy can be obtained simply by adding a little to the computing overhead.

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.

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.

Characteristics of a class of stepped-impedance resonators (SIRs) which is loaded with two dielectric rods, are investigated by a Finite-Difference Time-Domain (FDTD) method. Dielectric rods to be inserted between a strip conductor and the ground plane have higher relative permittivity than that of the substrate. When a tapped half-wavelength (λ/2) microstrip resonator is loaded with two dielectric rods, the electric length of a loaded λ/2 resonator becomes longer than λ/2, which makes its fundamental resonant frequency () to be generated on the region lower than that of an unloaded λ/2 resonator (fr) and its first spurious response (fsp1) is generated on the region higher than 2. Therefore, to shift back to fr, the resonator's length is to be reduced, and this, in turns, suppress the spurious responses. Then, the resonant characteristics of an SIR employing the proposed method has also been investigated, and it is found that this is capable of suppressing the spurious responses in wideband together with an attenuation pole in the stopband, and of further reducing the resonator's length. Therefore, wide exploitation of the presented method can be expected in the filter design based on the LTCC technique.

In a partially coupled-line bandpass filter (BPF), a combination of two microstrip line resonators which are partially coupled, are considered, where one resonator is half-wavelength (λ/2)-long, and another whose one end is grounded, is only quarter-wavelength (λ/4)-long. Therefore, the length of a coupled-line section can be varied based on the position of the grounding end, and five conditions of the movable coupling length have been simulated which will greatly influence the spurious responses of a BPF. This property is numerically investigated in this paper. The analysis shows that, based on the grounding position, this method is capable of realizing the improved out-of-band characteristics by locating the multiple attenuation poles in the stopband and improved spurious responses up to five times of the center frequency (5f0). A few empirical models of BPF are fabricated, and the numerical results are ensured by comparing with the experimental results.

This paper presents a new method to improve the resonant characteristics of a microstrip resonator. The improved characteristics have been achieved by inserting two dielectric rods between strip conductor and the ground plane. Dielectric rods to be inserted have higher relative permittivity than that of the substrate. Therefore, it is suitable to realize by Low-Temperature Cofired Ceramics (LTCC) technique. Several model of microstrip resonators employing the proposed method are analyzed by a Finite-Difference Time-Domain (FDTD) method, and their resonant characteristics are discussed. One of the advantages of the proposed method is that an attenuation pole (fl or fh) in each side of the fundamental resonant frequency (fr) and improved-spurious responses can be realized together by a capacitive-coupling tapped resonator loaded with dielectric rods. The proposed method is also effective to achieve sharp skirt characteristics and wide stopband of a direct-coupling tapped resonator which can be used either as a wideband lowpass filter or a band-elimination filter. Another interesting feature of the analyzed resonators is that about 60% reduction in resonator's length has been obtained compared to a basic half-wavelength (λ/2) microstrip resonator. Therefore, wide exploitation of the proposed method can be expected in the filter design based on the LTCC technique.

This paper focuses on the realization of low spurious responses by various bandpass filters (BPFs) using open-ended λ/2 resonators. The first part of this paper gives the resonance characteristics of the open-ended λ/2 resonators when the excitation methods are chosen. Secondly, various BPFs obtained with our methodology are provided. For constructing the BPF, (1) point-coupled resonators, (2) comb-line resonators, (3) quasi comb-line resonators and (4) parallel-coupled resonators are used. It is verified that the presented BPFs can be used to obtain low spurious responses both theoretically and experimentally.

Segmentation of a dielectric resonator enables one to control its spurious property. When a dielectric plate is divided into some planar pieces, the effective permittivity does not change appreciably along the divided plane, while it decreases quite an amount perpendicular to it. This anisotropy is useful for shifting the resonant frequencies of unwanted modes of a dielectric resonator. Since its eigen modes have their own electric field distribution, segmentation of a resonator along the electric line of force of a certain mode will not affect its resonant frequency. When the type of segmentation is changed, we can select the wanted mode, and thus control the resonant frequencies of the unwanted modes. Calculated results with an EM field simulator and experimental results of controlling the resonant frequency are shown for divided dielectric resonators.

Microwave Power Transmission (MPT) technology is one of the most essential parts for Solar Power Station/Satellite (SPS). We study on application of magnetrons as DC-RF converters for the MPT transmitting system. Magnetrons cost much cheaper, have much higher DC-RF efficiency over 70% and much lighter system weight per 1 watt RF output than semiconductor amplifiers although they have wider bandwidth of the fundamental frequency and spurious noises in various frequencies. Spurious noises are radiated from the transmitting system and interfere in the other communication systems both in space and on the Earth. The objective of this study is the improvement of the spurious noises generated from magnetrons. Experimentally, magnetrons driven by DC stabilized power supply had not only narrower bandwidth of the fundamental frequency but also lower spurious noise levels when filament current is turned off than when it is turned on. Some spurious noises are probably caused by the intermodulation between the low frequency spurious noises, which frequency is below 1 GHz, and the fundamental or the harmonics. We also verified that the harmonics levels of the measured magnetron in our measurement system were below -70 dBc, which are comparable to or better than those of some semiconductor amplifiers, and that the harmonics were not improved greatly when the filament current was turned off because the source of the harmonics is the distortion of the fundamental.

A design methodology of bandpass filters (BPFs) using λ/4 resonators for improving out-of-band characteristics is proposed. Firstly, the basic characteristics of various λ/4 resonators are examined. In this study, we focus on four types of λ/4 resonators, i.e., (1) direct-coupled λ/4 resonator, (2) loaded-element λ/4 resonator, (3) tapped λ/4 resonator and (4) loaded-element tapped λ/4 resonator. Secondly, the application examples of BPFs with improved out-of-band characteristics are provided. We examine the improvement of filter characteristics, i.e., sharp skirt characteristics and low spurious responses. The results of this study lead us to the conclusion that the methodology is very useful for improving the out-of-band characteristics of the BPFs using the λ/4 resonators.

In mobile computing environments, a problem may exist between loss recovery mechanisms employed by the TCP (transmission control protocol) and RLP (radio link protocol). It is because that local retransmissions performed by the RLP could interfere with the TCP end-to-end error recovery when there are long and correlated packet losses due to bursty channel errors. That is, a spurious timeout would occur at the transport layer. In this paper, a new method is proposed to effectively suppress the occurrence of TCP spurious timeouts. In this new method a small number of ACKs (acknowledgements) is buffered at the base station prior to the emergence of every bad state period in the wireless channel, and these ACKs are henceforth released by the base station one at a time to reset the TCP sender's retransmission timer. Comprehensive comparisons between the proposed method and a baseline method are conducted through simulations to show that the improvement in throughput performance can be as large as 22%.

Two novel linearization processes in electro-absorption-modulator (EAM) are proposed and demonstrated. These two modulation schemes are used to compensate the nonlinear component of the EAM by controlling the DC bias voltages of the each EAM separately. The simulations on the nonlinearity of EAM and linearization process are performed in both time and frequency domains. From a serially cascaded modulation simulation, a reduction of 16 dB in IMD3, 45 dB in IMD5 and the following increase of 15 dB in linear dynamic rage (LDR) are achieved. In dual-parallel modulation experiment at 8 GHz, a reduction of 23 dB in IMD3 and the following increase of 15.1 dB in LDR of are achieved compared to those of a single EAM operation.

This letter presents a low spurious frequency setting algorithm for a triple tuned type PLL synthesizer driven by a DDS. The triple tuned PLL synthesizer is based on a single PLL configuration with two variable frequency dividers. The DDS is employed for a reference source of the PLL. The proposed algorithm determines appropriate frequency tuning values of the DDS frequency and the division ratios of two frequency dividers. The division ratios are selected to achieve a desired output frequency while the low spurious condition of the DDS has been maintained. A 5 to 10 GHz synthesizer with frequency step of 500 kHz demonstrated spurious level below -46 dBc with improvement of 13 dB.

A simple method for improving out-of-band characteristics of a planar microwave filter is proposed. We clarify the close relationship among 'tap connection,' 'attenuation pole' and 'spurious responses' in filter design, theoretically and experimentally. Firstly, the basic characteristics of the resonator depending on the excitation method are examined. We show that skirt characteristics can be improved and spurious responses can be suppressed by using the tap connection technique. Secondly, the application examples of bandpass filters (BPFs) on the basis of the resonator with our principle are provided. It is confirmed that the resonator depending on the excitation method is useful for improving out-of-band characteristics of the planar microwave filter.

A K-band MMIC subharmonically pumped mixer integrating local oscillator (LO) amplifier has been developed. For up-converter application, it is necessary to reduce the leakage of second harmonic component of LO frequency to RF port, which is generated by nonlinear operation of LO amplifier. A quasi-lumped short-circuited stub using microstrip structure has been successfully applied to the MMIC mixer to enhance 2fLO-suppression. We propose a new configuration of a quasi-lumped short-circuited stub, which reduces the influence of parasitic elements of via-holes. The developed MMIC has a one-stage LO amplifier and it has shown about 10 dB-improvement of 2fLO-suppression compared to conventional configuration using a quarter-wavelength short-circuited stub.

The aim of this study is to examine the effectiveness of various open-ended resonators. According to the required filter responses, the application to microwave filters based on presented open-ended resonators is systematically examined as well. First, the resonance property of the basic open-ended resonator is discussed based on even-and odd-mode analysis. The intrinsic property of a tapped open-ended resonator is also discussed here. Second, the basic properties of a stepped impedance resonator (SIR) and a loaded-element resonator are examined theoretically for improvement of spurious responses and the dual-passband response. The basic operations of these resonators are also explained based on even- and odd-mode analysis. Examples for filter applications based on presented resonators are also provided. We found that the intrinsic properties of the open-ended resonators are very useful for practical filter responses.

A novel K-band MMIC frequency doubler has been developed using resistive series feedback circuit. The doubler exhibits much better D/U ratio, smaller output power variation against ambient temperature and lower power consumption than those of the conventional single-ended doubler. This paper presents the simulation results on the effect of the resistive series feedback by harmonic balance methods. To obtain practical and accurate simulation results, newly developed gate charge model for Cgs and Cgd is introduced. The fabricated result of the proposed MMIC is also demonstrated.

A very low spurious frequency doubler for wireless communication systems is proposed. The key to this technique is to change the input signal into a rectangular wave, which effectively suppresses the fundamental frequency and the odd harmonic components. The desired to undesired signal ratio (D/U) is better than 50 dBc at the desired output frequency of 1.1 GHz. The proposed doubler eliminates the need for the band-pass filters which occupy a large part of the radio frequency (RF) module. High order multipliers easily are fabricated with this method. In this paper, a quadrupler is also described.

Basic characteristics of a short-ended coplanar waveguide (CPW) resonator of good spurious suppression property is studied. The resonator is loaded with open tubs at its middle position and makes a fully planar structure. The length of the resonator is shortened almost by half and the first spurious resonance goes up to more than 3 times of the fundamental resonant frequency without degradation of unloaded Q(Q0). The origin and property of spurious response is thoroughly investigated to show the advantage and the limit of this configuration. The external Q(Qe) and fundamental resonant frequency of the resonator are also clarified theoretically and experimentally. Using those result, a bandpass filter (BPF) is designed on the basis of the narrow band approximation is realized and its transmission characteristics are examined theoretically and experimentally. The spurious suppression characteristics have been realized by the present filter in accordance with the expectation.