榎原 晃

In this paper we have proposed a five-way power divider using unequal LC-ladder dividers. The LC-ladder divider is a compact power divider based on the Wilkinson power divider to solve size problem at a low frequency band (UHF) used by IoT devices. According to the circuit analysis, the proposed circuit can realize 67.5% bandwidth and flat transmission characteristics. In order to confirm actual operation of the divider, we have carried out electromagnetic analysis and measurement.

This paper deals with an unequal power divider with two matching frequencies by using LC-ladder circuits. This circuit that is constructed based on the Wilkinson power divider, consists of 9 elements. This circuit can achieve the same or wider bandwidth as the original one by holding the two matching frequencies close together. In order to confirm the practicality in IoT, the design center frequency is set to 920 MHz, and its actual measurement is carried out after circuit pattern design and analysis.

We designed and evaluated 1×2 and 2×2 optical couplers using multimode interference (MMI) optical waveguides of Ti-diffused LiNbO3. A Mach-Zehnder electrooptic modulator (MZM) designed using those two MMI couplers as an optical power splitter and combiner was fabricated. Optical intensity modulation was achieved with a 50 dB extinction ratio. And the experimental results showed that the 2 ×2 MMI optical coupler could provide nearly equal power division with a 90° phase difference as a 90° hybrid. Next, we applied the MZM structure to the single sideband (SSB) modulation. 10 GHz microwave signals of 90° phase difference were fed to the modulation electrodes on the two arms of the MZM. The SSB modulation operation was confirmed from output light spectra, and the sideband suppression ratio of 39 dB was observed by miner adjustment of the optical phase bias.

A Mach-Zehnder optical modulator with the tunable multimode interference coupler was fabricated using Ti-diffused LiNbO3. The modulation extinction ratio could be voltage controlled to maximize up to 50 dB by tuning the coupler. Optical single-sideband modulation was also achieved with a sideband suppression ratio of more than 30 dB.

We propose a new design of an electro-optic full adder by using coupled Si microring resonators for highly dense integration. The device size is significantly reduced by using doubly coupled microring resonators as a power divider. A newly designed crossing waveguide is included in the device. Our design reduces the optical waveguide footprint to approximately 60 μm × 100 μm per bit. Numerical analysis of the full adder operation shows the effectiveness and feasibility of our proposed electro-optic full adder.

In the paper, improvement of the efficiency for the Rectenna (Rectifier + Antenna) is described. The rectifier circuit in this research promotes further improvement in efficiency and expansion of the power range by using the passive path switching method that can be shifted according to the frequency band. In the previous research, the circuit was configured by using the conventional branch-line coupler as a power divider, however the conversion efficiency on the low power region was not so good. Therefore, in this research, the circuit is configured by using the doubly asymmetrical branch-line coupler to widen the impedance difference at the output ports. As a result, it was confirmed by using an electromagnetic simulation (AWR AXIEM) that the conversion efficiency at low power region was improved up to 65.8%, which was about twice that of the conventional one. In addition, it is verified experimentally as well as analyzed.

We analyzed the optical properties of optical couplers based on multimode interference (MMI) in titanium-diffused LiNbO3 (Ti:LN) waveguides using the beam propagation method (BPM) with refractive index distributions by Ti diffusion. From these results, we designed and fabricated 2 × 2 MMI couplers operating at 1.55μm wavelength using Ti:LN waveguides. An optical power splitting ratio of 0.53:0.47 (0.52 dB power deviation from equal split) and an insertion loss of less than 1.5 dB were observed with a coupler consisting of an MMI waveguide 50μm wide and 2.12 mm long. Electrical tuning of the power splitting ratio by the electro-optic effect of LiNbO3 was also considered. The electrodes were formed directly on the MMI waveguide section of the coupler and the power splitting ratios were controlled almost in proportion to the voltage applied to the electrode and a deviation of about 1 dB (0.56:0.44) of the power splitting ratio from an equal split could be adjusted to zero by applying a voltage of −6.1 V.

In this paper, a 180-degree rat-race hybrid which consists of short transmission lines less than quarter wavelength with shunt capacitors at both ends and an ideal phase inverter is described. We show the possibility of realizing a compact and wideband 180-degree rat-race hybrid that is about 1/10 smaller than the conventional rat-race hybrid and has twice the operating band by an electromagnetic simulation with a uniplanar structure at 28 GHz band used for 5G applications.

Optical couplers based on Multi-mode interference (MMI) were considered using Ti-diffused LiNbO3 (Ti:LN) waveguides. Properties of MMI waveguides of Ti:LN were analyzed using the beam propagation method. An optical 90-degree hybrid of the MMI structure was designed and fabricated with the Ti:LN waveguides. We experimentally confirmed that the MMI coupler could operate as a 90-degree hybrid using the MMI waveguide part of 50 μm width and 2.13 mm length.

A new structure of the electro-optic modulator to compensate the third-order intermodulation distortion (IMD3) is introduced. The modulator includes two Mach-Zehnder modulators (MZMs) operating with frequency chirp and the two modulated outputs are combined with an adequate phase difference. We revealed by theoretical analysis and numerical calculations that the IMD3 components in the receiver output could be selectively suppressed when the two MZMs operate with chirp parameters of opposite signs to each other. Spectral power of the IMD3 components in the proposed modulator was more than 15 dB lower than that in a normal Mach-Zehnder modulator at modulation index between 0.15 and 0.25 rad. The IMD3 compensation properties of the proposed modulator was experimentally confirmed by using a dual parallel Mach-Zehnder modulator (DPMZM) structure. We designed and fabricated the modulator with the single-chip structure and the single-input operation by integrating with 180. hybrid coupler on the modulator substrate. Modulation signals were applied to each modulation electrode by the 180. hybrid coupler to set the chirp parameters of two MZMs of the DPMZM. The properties of the fabricated modulator were measured by using 10 GHz two-tone signals. The performance of the IMD3 compensation agreed with that in the calculation. It was confirmed that the IMD3 compensation could be realized even by the fabricated modulator structure.

In this paper, a four-way lumped-element power divider with in-phase output using LC-ladder circuits is described. We propose a four-way LC-ladder divider composed of 2-section LC-ladder circuits between input and output ports, and their output ports are connected through external circuits composed of an LC-ladder circuit and a series LR circuit to obtain satisfactory isolations. By designing the divider based on even-/odd-mode analysis techniques and a complex conjugate impedance matching theorem, the proposed four-way LC-ladder divider can achieve dual-band operation. To confirm the validity of the design method, the divider is designed and fabricated at a center frequency of 300MHz. As results of simulation and experiment, broadband characteristics with a relative bandwidth of about 43% can be obtained. Furthermore, measurement results of the fabricated power divider indicate low reflection, high isolation and extremely flat power division, and good agreement with simulation results.

In this paper, we describe branch-line couplers (BLCs) with broadband characteristics over relative bandwidths of 50% in X-band. The proposed couplers consist of a conventional BLC and external matching networks composed of two-stage open-circuited coupled transmission lines and an impedance step between the coupled lines. By utilizing the equivalent admittance approach to the proposed coupler, the wideband characteristics of the desired relative bandwidth can be obtained in the X-band. In addition, it is confirmed that the relative bandwidth is 50.5% in the electromagnetic simulation. Furthermore, prototype experiments are also conducted, and the validity of this design annroach is verified from these results.

This paper treats a rat-race circuit which plays com-bining/dividing of a microwave signal, and shows size-reduction and band-broadening design methods of the uniplanar circuit utilizing shunt capacitors and a crossover-type phase inverter. The designed circuit simultaneously realizes compact size and broadband characteristics. Next, we simulate the designed uniplanar rat-race circuit by using a commercial electromagnetic simulator in order to verify the design procedure and show broadband characteristics and flat couplings. Finally, experimental verification of the circuit at a center frequency of 2.4GHz is also described.

We designed and fabricated an electro-optic modulator for optically compensating the nonlinear distortion. The single-chip structure and the single-input operation were realized by integrating a microwave 180-degree hybrid on the DPMZM substrate.

Screen printing technology using silver nanoparticle ink with high conductivity attracts attention as a technology for fabricating low-loss transmission lines in high frequency band such as millimeter-wave band. Its effectiveness has been confirmed in millimeter-wave band exceeding 100 GHz [1]. This paper describes a 180-degree rat-race circuit (RRC) utilizing composite a right-/left-handed transmission line (CRLH-TL) composed of lumped elements at 76 GHz band in order to confirm the reliability of circuit components by utilizing the screen printing technology. The proposed RRC consists of three right-handed transmission lines (RH-TLs) and a CRLH-TL. Conventionally, it has also been the mainstream to use chip elements for these lumped elements, however the proposed circuit consists of only transmission lines without them. For 76 GHz band, the designed -10 dB RRC with the CRLH-TL can realize compact size and practical characteristics. Effectiveness of the design method was confirmed by using a commercially electromagnetic field simulator (ANSYS HFSS).

This paper describes design of a substrate integrated waveguide (SIW) slot antenna for microwave liquid heating. It is well known that the SIW characteristics are similar to dielectric-filled waveguides. A proposed microwave heating system heats liquid by radiation microwave from slots that are arranged on upper surface of the SIW. From result of designing the SIW slot antenna using a commercial electromagnetic simulator (ANSYS HFSS), a reflection characteristic of -20dB or less at a center frequency of 2.45GHz is realized. Measurement result of a fabricated SIW slot antenna is good agreement with the simulation result.

© 2019 Optical Society of America We designed a universal linear circuit by using microring resonators instead of conventional Mach-Zehnder interferometers and phase shifters. We illustrated that the footprint of the universal linear circuit can be drastically reduced (∼ 1/10). In addition, power consumption can also be reduced by using the sensitivity of the phase change in the vicinity of the resonant peak. Furthermore, as an important example of the application for optical communication, MIMO compensation operation is numerically demonstrated by our proposed universal linear circuit. The proposed design can be adapted to other experimentally reported devices, which will accelerate the integration of the universal linear circuit.

A new electro-optic modulator for compensating the nonlinear distortion is proposed. The third-order intermodulation distortion (IMD3) induced in the receiver output are optically suppressed by using two Mach-Zehnder modulators (MZMs) connected in parallel and operating with chirp-parameters of the opposite signs to each other. The performance of the IMD3 compensation was estimated by the numerical calculations. We made an experiment to confirm the IMD3 compensation operation by using 10 GHz two-tone microwave signals and a 1.55 μm light source. The modulator was constituted by a dual-parallel Mach-Zehnder modulator (DPMZM). The chirp parameters of MZMs of the DPMZM were set to +0.5 and -0.5, respectively. It was observed by the measurement that the IMD3 components in the receiver output were suppressed by more than 20 dB compared to those for the conventional single-MZM operation in a range of modulation index below 0.25π rad. These experimental results agree well with the numerical calculation ones.

This paper describes wideband three-way Wilkinson power dividers using LC-ladder circuits. The proposed dividers consist of multi-section LC-ladder circuits between input and output ports, and their output ports are connected each other through external circuits composed of series RL circuits. By connecting the appropriate external circuits in accordance with the number of LC-ladder circuits, the proposed dividers can be realized extremely wideband operation. In order to verify the design procedure, wideband three-way Wilkinson power dividers are simulated and fabricated at VHF-band. As results of simulation and experiment, we can obtain broadband characteristics with a relative bandwidth of over 60%, which are near agreement with the theoretical results.

Copyright © 2018 The Institute of Electronics, Information and Communication Engineers. This paper presents a lumped-element Wilkinson power divider (WPD) using LC-ladder circuits composed of a capacitor and an inductor, and a series LR/CR circuit. The proposed WPD has only seven elements. As a result of designing the divider based on an even/odd mode analysis technique, we theoretically show that broadband WPDs can be realized compared to lumped-element WPDs composed of II/T-networks and an isolation resistor. By designing the WPD to match at two operating frequencies, the relative bandwidth of about 42% can be obtained. This value is larger than that of the conventional WPD based on the distributed circuit theory. Electromagnetic simulation and experiment are performed to verify the design procedure for the lumped-element WPD designed at a center frequency of 922.5MHz, and good agreement with both is shown.

© 2018 Wiley Periodicals, Inc. This article describes rat-race circuits (RRCs) in which a pair of ring-lines have parallel lines of ±180-degree difference for electrical length to realize the RRC with very loose coupling such as −10 dB or less. The proposed RRCs with parallel ring-lines realize a coupling factor of −10 dB and −20 dB by using moderate characteristic impedance lines with a view point of fabrication tolerance for general PCB technologies. We confirm the validity of this circuit construction and design method using a commercial electromagnetic simulator and decide the circuit pattern for fabrication at a center frequency of 2.45 GHz. The fabricated RRCs with parallel ring-lines realize the desired coupling factors and in-/out-of-phase outputs, and the measurement results of scattering parameters for −10 dB and −20 dB RRCs are in good agreement with the simulation results.

A new electro-optic modulator for compensating the nonlinear distortion is proposed. The third-order intermodulation distortion (IMD3) in receiver output is optically suppressed by the frequency-chirp modulation in the dual-parallel Mach-Zehnder modulator (DPMZM) structure. All of optical branches of the DPMZM are symmetric. The performance was analyzed by numerical calculations. First, we made an experiment to confirm the performance using a DPMZM with a microwave hybrid coupler for applying 10GHz two-tone signals to each electrode of the DPMZM. The chirp parameters of two Mach-Zehnder modulators (MZMs) of the DPMZM were set to opposite signs to each other, +1 and -1. It is seen from the experiment that the intensity ratio of IMD3 to signal in the receiver output was less than -58dB at modulation indices below 0.55 (0.175 €) rad and that the minimum of the ratio was less than -80dB at around 0.5 (0.16π) rad. In contrast, for a conventional single-MZM the ratio was less than -27dB below 0.55rad modulation indices. These experimental results agreed well with the calculation ones. Next, we designed and fabricated the modulator of the single-chip structure and the single-input operation for smallsizing and simple operation. The microwave rat-race circuit (RR), which operates as a 180° hybrid coupler, was designed on a Lithium Niobate (LN) substrate at 10GHz and was integrated with modulation electrodes of the DPMZM. The RR and modulation electrodes were formed with a gold thin film pattern at a time. The IMD3 suppression operation was confirmed for the fabricated modulator as well.

This letter describes a design method for multiband Wilkinson power dividers (WPDs) utilizing multisection LC-ladder circuits. The design method is inspired by even- and odd-mode analysis techniques and an L-section matching network. Two trial dividers, which operate with dual-band/triband, were fabricated at a 300-MHz band. The measured relative bandwidths of these dividers were more than 45% and 60%, and their insertion losses were less than 1 dB. The sizes of these WPDs were 17.0 x 13.3 mm(2) and 22.0 x 14.3 mm(2), respectively. The measurement results for the fabricated dividers were in good agreement with theoretical results and the dividers show multiband characteristics.

This paper describes a novel rat-race circuit with very loose coupling less than -10dB utilizing parallel ring-lines composed of a quarter wavelength transmission line and a short-circuited quarter wavelength coupled one. For a conventional rat-race circuit, the minimum coupling factor is limited by the highest impedance of the ring-line which can be manufactured by a general PCB technology. The proposed rat-race circuit with parallel ring-lines can be realized the circuit with a very loose coupling factor of less than -10dB. By using the proposed structure, we can successfully design the compact rat-race circuit with a coupling factor of -20dB. The validity of this design procedure is confirmed by carrying out electromagnetic simulation and experiment. The fabricated -20dB rat-race circuit is actually realized -33dB reflection, -40dB isolation, and -21dB coupling at a center frequency of 4GHz, respectively.

<p>In this paper, we propose a design method of compact multi-way Wilkinson power divider with a multiband operation for size reduction and band broadening. The proposed divider consists of multisection LC-ladder circuits in the division arms and isolation circuits between the output ports. To validate design procedures, we fabricated a trial divider at VHF band. The circuit layout of the trial divider was decided by using an electromagnetic simulator (Sonnet EM). Because the proposed divider consists of lumped element circuits, we can realize great miniaturization of a circuit area compared to that of the conventional Wilkinson power divider. The circuit size of the trial divider is 35 mm square. The measurement results for the trial divider by using a vector network analyzer indicates a relative bandwidth of about 60% under -17 dB reflection, flat power division within ±0.1 dB, and very low phase imbalances under 1.0 degree over the wide frequency range.</p>

This paper describes a lumped-element 5-way Wilkinson power divider with broadband characteristics. The circuit contains multi-section LC-ladder circuits between input and output ports, and each output port is connected through series RLC circuits. By designing the divider based on multi-section matching transformer and L-section matching network techniques, the proposed 5-way divider can achieve broadband characteristics. In order to verify the design procedure, the proposed divider was designed and fabricated at a center frequency of 300MHz. The fabricated divider exhibited broadband characteristics with a relative bandwidth of about 75%.

The rat-race (RR) circuit, which operates as a 180-degree hybrid, with an asymmetric power split ratio was integrated with the dual electrode type electro-optic modulator on the same substrate. Thereby, frequency chirp modulation with a compact configuration was realized. The RR circuit was designed with 4.5:1 power split ratio on a z-cut LiNbO3 substrate. The operation of the modulator was confirmed by observing the output light spectra. Moreover, the chirp parameter was directly measured by using the chromic dispersion of the optical fiber, whrere the power penalty of detected modulation signals transmitted through optical fiber was observed as a function of the fiber distance. The chirp parameter of the modulated light at 10 GHz was confirmrd to be 0.47 by the measuremrnt.

An electro-optic (EO) modulator integrated with the microwave planar circuit directly formed on a LiNbO3 (LN) substrate for low frequency-chirp performance and compact configuration is introduced. Frequency chirp of EO intensity modulators was investigated and a dualelectrode Mach-Zehnder (MZ) modulator combined with a microwave ratrace (RR) circuit was considered for the low-chirp modulation. The RR circuit, which operates as a 180-degree hybrid, was designed on a z-cut LN substrate to create two modulation signals of the same amplitude in anti-phase with each other from a single input signal. Output ports of the RR were connected to the modulation electrodes on the substrate. The two signals of the equal amplitude drive two phase modulation parts of the modulator so that the symmetric interference are realized to obtain intensity modulation of low frequency-chirp. The modulator was designed and fabricated on a single LN substrate for around 10 GHz modulation frequencies and 1550 nm light wavelength. The chirp parameters were measured to be less than 0.2 in the frequency range between 8 and 12 GHz. By compensating imbalance of the light power splitting in the waveguide MZ interferometer the chirp could be reduced even more.

Optical single sideband (SSB) modulation with theMach- Zehnder (MZ) interferometer was realized by integrating the modulation electrode with the branch-line coupler (BLC) as a 90-degree hybrid onto the modulator substrate. In this paper, BLCs of the microsrtip-line structure were miniaturized on modulator substrates, LiNbO3 (LN), to realize more compact optical SSB modulators. We introduced two techniques of miniaturizing the BLC, one is using periodically installed open-circuited stabs and the other is installing series capacitors. Compared with a conventional pattern of the BLC, an area of the miniaturized BLC by using periodically installed open-circuited stubs was reduced to about 50%, and that by installing series capacitors was done to about 60%. The operation of these miniaturized BLCs was experimentally confirmed as the 90-degree hybrid at around 10GHz. Output ports of each miniaturized BLC were directly connected with the modulation electrode on the modulator substrate. Thereby, we fabricated two types of compact SSB modulators for 1550nm light wavelength. In the experiments, the optical SSB modulation was successfully confirmed by the output light spectra and the sideband suppression ratio of more than 30dB were observed.

This paper presents a compact multiple-port power divider with a Substrate Integrated Waveguide (SIW) structure. The proposed divider consists of several cascaded-connected directional couplers inserted a number of metallic posts within the SIW with suitable coupling coefficients and a right-angled corner, and realizes an equal power division in a same direction by using honeycomb structures which consist of a large number of small-size holes vertically installed between the directional couplers as phase shifters. By optimizing the circuit dimensions of directional couplers and the right-angle corner at a operating frequency of 17GHz based on the H-plane planar circuit approach [1], a good performance of an equal power division within ±0.3dB unbalance and 20dB return loss can be obtained with a relative bandwidth of about 2%. The 5-way SIW power divider which the circuit patter is decided by electromagnetic simulations is fabricated on a dielectric substrate to verify the design procedure. Measurement results of the fabricated divider are nearly agreement with the simulation results.

Optical single sideband (SSB) modulation can be realized by using a Mach-Zehnder (MZ) interferometer with the branch-line coupler (BC) circuit as a 90 degree hybrid. In this paper, a miniaturized configuration of the BC circuit with installed series capacitors of the inter-digital structure was designed onto an electro-optic (EO) crystal, LiNbO3, substrate. Compared with a conventional BC, an area of the miniaturized BC was reduced by about 60% and the operation as the 90 degree hybrid was confirmed at around 10 GHz. The BC circuit directly connected with modulation electrodes was designated onto an EO modulator substrate for a single input type optical SSB modulator with a compact configuration. In the experiment, the modulator was fabricated and the optical SSB signal with the sideband suppression ratio of more than 30 dB was observed using light-waves of the 1550 nm region.

The branch-line coupler (BC) circuit of miniaturized configuration using periodically installed open circuit stabs was designed onto an electro-optic (EO) crystal, LiNbO3, substrate at 10 GHz. The operation as the 90 degree hybrid was confirmed at around the center frequency by the experiment. By using this BC circuit as the signal power divider, we proposed a compact EO single sideband (SSB) modulator. The SSB modulator was designated and fabricated for 1550 nm light wavelength. In the experiment, the optical SSB signal with the sideband suppression ratio of about 30 dB was observed.

In this paper, we consider a parallel ring-line rat-race circuit realized by replacing some parts of the ring-lines with composite right-/left-handed transmission lines (CRLH-TLs). For a conventional rat-race circuit, the minimum coupling factor is limited by the highest impedance of the ring-lines that can be manufactured by general printed circuit board (PCB) technologies. However, the coupling factor of the parallel ring-line type rat-race circuit proposed in this paper is determined by the difference between the admittances of the parallel ring-lines. As a result of designing parallel ring-line rat-race circuits having coupling factors of -20 and -30 dB for an operation frequency of 4 GHz, the proposed rat-race circuit realizes broadband characteristics of about 35.5% according to the numerical results for the -20 dB circuit. Furthermore, broadband characteristics including reflection, isolation, and couplings can be maintained for the fabricated -20 dB rat-race circuit up to an input power of 40 dBm.

This paper treats parallel ring-line rat-race circuits with very loose coupling utilizing composite right-/left-handed transmission lines (CRLH-TLs). We have already reported the parallel ring-line rat-race circuits composed of four CRLH-TLs and two right-handed transmission lines (RH-TLs), and successfully designed -20dB rat-race circuits with broadband characteristics. In this paper, to reduce the number of CRLH-TLs we propose the parallel ring-line rat-race circuit composed of two CRLH-TLs with electrical length of -90 degrees and four RH-TLs with 90 degrees. As a result of designing the circuit at 4GHz, a relative bandwidth of about 27% can be obtained for the -20dB rat-race circuit. Furthermore, high power durability for the trial -20dB circuit has been also demonstrated.

An electro-optic (EO) modulator integrated with the microwave planar circuit directly prepared onto a LiNbO3 substrate for low chirp performance and compact configuration is introduced. A microwave rat-race (RR) circuit, which operates as the 180-degree hybrid, is designed on a z-cut LiNbO3 substrate to create two modulation signals of the same amplitude in anti-phase with each other from a single-input signal. Output ports of the RR were connected to the modulation electrodes on the substrate. The two signals drive two phase modulation parts of dual-electrode Mach-Zehnder modulator so that the symmetric interference are realized to obtain low-chirp intensity modulated light signals. The modulator was designed and fabricated for around 10 GHz modulation frequencies and 1550 nm light wavelength. The chirp parameters were measured to be less than 0.2 in the frequency range between 8 and 12 GHz. By compensating the unbalance of the light power splitting the chirp could be significantly reduced.

近年のワイヤレス情報通信技術の進歩に伴い,マイクロ波回路素子には小型・広帯域化など高性能化に加え,高耐電力性も要求されている.本論文では,マイクロ波信号を同相/逆相で分配するラットレース回路を取り上げ,位相進みの特性を有するCRLH線路を利用した回路構成で,4GHz帯動作での小型且つ広帯域化の検討を行っている.また,耐電力性を考慮した構成での提案回路構成法の妥当性を市販電磁界シミュレータによる数値解析と試作実験により解析的,実験的に動作を確認するとともに,試作回路の耐電力性についても検討を行っている.

Optical single-sideband (SSB) modulation is theoretically realised by applying two modulation signals with a 90° phase difference to the dual-electrode type electro-optic (EO) modulator. A branch-line coupler (BC) as the microwave 90° hybrid was directly prepared on the EO modulator substrate, LiNbO 3 , to create two modulation signals from a single input signal. Output ports of the BC were connected to the modulation electrodes on the substrate. Thereby, an EO optical SSB modulator was realised with a single-tip and a smallsized configuration. The SSB modulator was designed and fabricated for around 10 GHz modulation frequency and 1550 nm light wavelength. The optical SSB modulation operation with a sideband suppression ratio of more than 20 dB was confirmed by the experiment. © The Institution of Engineering and Technology 2013.

This paper presents a compact wideband rat-race hybrid composed of composite right/left-handed transmission lines (CRLH-TLs). Using CRLH-TLs with phase delays of -90 degrees and a right-handed transmission line (RH-TL) with 90 degrees at a design frequency, a relative bandwidth of about 36 % can be obtained at the design frequency of 4 GHz. Furthermore, size reduction of about 60 % can be simultaneously achieved compared with a conventional rat-race hybrid utilizing only RH-TLs based on a distributed circuit theory. The validity of this design procedure has been demonstrated by em-simulations and experiments. Moreover, a trial rat-race hybrid can maintain wideband characteristics and no variation of insertion losses up to 20 dBm input power. © 2013 IEEE.

This paper considers band-broadening design methods for branch-line and rat-race hybrids such as 90- and 180-degree hybrids. For the 90-degree hybrid, utilizing external matching networks composed of coupled-transmission lines, broadband characteristics with a relative bandwidth of over 40% can be obtained for a 3 dB hybrid designed for operation at 3 GHz based on the equivalent admittance approach. For the 180-degree hybrid, a rat-race hybrid in which right-handed transmission lines are replaced with composite right-/lefthanded transmission lines also realizes broadband characteristics. The validity of these design procedures has been demonstrated by electromagnetic simulations and experiments. © IEICE 2013.

The heating effect by microwave irradiation for the ecologic system was investigated by using cubic phantoms and plants. For the accurate evaluation, the irradiation was performed in the hollow wave guide. The relation between the microwave absorption and surface temperature increase by the microwave heating were theoretically estimated by the principle of heat transfer. These results were also confirmed by the experiment performed with 2.45GHz microwave irradiation. The absorption coefficient of the cubic phantom with sides 30mm long in the 109.2mm~54.6mm hollow wave guide was measured to be about 0.38 at 2.45GHz. The surface temperature increase of the cubic phantom by the irradiation of 2W microwave was around 18 degree, which is agree with the calculation in error of about 20%. Some kinds of vegetables were also used in the irradiation experiment and observed the surface temperature increase by the heating effect. © 2012 IEEE.