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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.

In this paper, simple lumped-element power dividers with 9 elements that can be matched at arbitrary two frequencies are described. About those circuits, assuming that the ratio of two frequencies is 4, we design and analyze the dividers that operate in the UHF/SHF bands used in IoT and 5G (sub6 band). The effectiveness of the proposed dividers has been confirmed by fabricating and measuring a prototype circuit.

In this paper, a design method of a semi-lumped-element power divider with dual-band characteristics in UHF/SHF bands is presented. The circuit configuration has the Wilkinson power divider composed of only nine lumped-element components. The design is performed by even-/odd-mode analysis techniques and an impedance matching theory. In order to validate this approach a proposed divider at a center frequency of 920 MHz has been simulated and fabricated. To implement the ideal circuit model, some structures of spiral/meander transmission lines are used as inductors in consideration with high frequency compatible and size reduction. The simulation and experimental results are agreed very well. Over the 45.9% relative bandwidth from 0.80 to 1.28 GHz, return losses of input/output ports are better than 18 dB, maximum power division is -3.40 dB, and phase ripple is about ±2.6°. Finally, good performances of this proposed power divider are experimentally validated, showing the advantages of low cost, small size, and easy fabrication, etc. Also, it presents an excellent candidate for dividing microwave signal in microwave systems of UHF/SHF bands.

Optical couplers based on Multi-mode interference (MMI) were considered using Ti-diffused LiNbO 3 (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.

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.

This paper describes broadband branch-line couplers (BLCs)with arbitrary coupling factors at Ka-band. The coupler has open-/short-circuited coupled transmission lines as external matching networks and a pair of branch-lines. Electromagnetic simulations for designed broadband couplers with coupling factors from −3 dB to −30 dB based on the equivalent admittance approach are carried out to verify the band-broadening design method.

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).

In this paper we describe broadband branch-line couplers with very loose coupling at X-band. The proposed branch-line couplers consist of short-/open-circuited coupled-transmission lines as a pair of branch-lines and external matching networks. As a result of designing broadband couplers with a coupling factor of −20 dB based on the equivalent admittance approach, the desired coupling factor is obtained. In addition, the coupler has broadband characteristics with a relative bandwidth of 43.1% by an electromagnetic simulation. Then, fabrication and experiment of the designed coupler are carried out, and the effectiveness of this design method is confirmed experimentally.

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.

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 design of a substrate integrated waveguide (SIW) slot antenna for microwave liquid heating. It is well known that the SIW characteristics are similar to dielectricfilled 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.

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.

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, where 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 confirmed to be 0.47 by the measurement.

This paper describes a novel lumped-element Wilkinson power divider using LC-ladder circuits. The proposed divider consists of parallel multi-section LC-ladder circuits and combined ones, and a resistor connected between two output ports. As a result of designing the divider based on an even-/odd-mode analysis technique, broadband dividers with relative bandwidths of over 100 % are realized. The designed lumped-element Wilkinson power dividers are fabricated at P-band and lower frequency, and those circuit patterns are decided by utilizing an electromagnetic simulator. The measurement results of fabricated dividers are good agreement with theoretical results and show broadband low reflection of input/output ports, isolation between the output ports, and very flat coupling.

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 in- stalled series capacitors of the inter-digital structure was de- signed 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 de- gree 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.

This paper describes a design of microstrip rectangular disk quadrature directional couplers on the basis of a modified eigenfunction expansion method with consideration of frequency dependences of an effective width and an effective relative permittivity of a microstrip disk circuit. Using this approximate method, we can optimize the disk configuration of directional couplers in a reasonable computational time. The validity of the design method is examined by comparison with the numerical results by the FDTD method, Article, Microwave Conference Proceedings, 1997. APMC '97, 1997 Asia-Pacific

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.

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.

This paper suggests a substrate integrated waveguide in honeycomb structure consisting of a number of small holes (air-filled posts) drilled vertically and entirely through both plating-conductor layers of the substrate (HCSIW), and shows a design method of an SIW right-angle corner as an example of its applications. First, the propagation constant of an HCSIW is derived from the simulation results of a commercial em-simulator (HFSS), and then its effective dielectric constant (e r eff) and transmission loss are discussed. It is shown that the e r eff is approximately determined from the ratio of all the cross-section area of the air-filled posts to the remainder dielectric one, and the transmission loss is comparable with that of a common SIW. Next, the SIW right-angle corner is designed by arranging appropriately honeycomb structure. Experimental verification for the designed right-angle corner is also shown.

This paper treats an active circulator operating at frequency region of 17GHz to 21.5GHz. Proposed active circulator is composed of three amplifiers which consist of FETs mounted at fin-line circuits in rectangular waveguides, and three waveguide-type directional couplers using a dielectric block and taper structures at the side walls of each directional coupler. The feature of this circulator is no requirement of ferrite materials. As a measurement result of the trial circulator, about 40dB isolations and 0.1dB forward insertion losses can be obtained with the frequency range of 17.0 to 21.5 GHz. Amplifiers used in this research are available for 10 to 20dBm input power.

This paper proposes a PTFE-filled waveguide cruciform coupler with air-filled posts. Directivity and matched state of the coupler can be realized by “holes” in the dielectric material. The difference of dielectric constant is positively used in designing. First, the design method based on the planar circuit approach is described. Then, the PTFE-filled waveguide cruciform 3dB coupler is designed at Q-Band. Next, the cruciform 3dB coupler is fabricated using the SR (synchrotron radiation) etching process of PTFE, sputter deposition of metal, and electroplating. The measurement results of the fabricated cruciform 3dB coupler are shown.

A metallic waveguide is one of effective media for millimeter- and submillimeter-waves because of the advantage of low-loss. This paper describes trial fabrication of a PTFE-filled waveguide bandpass filter (BPF) with the use of the SR (synchrotron radiation) direct etching process of PTFE, sputter deposition of metal, and electroplating. PTFE is known as a difficult material to process at high precision. However, it has been reported that PTFE microstructures can be fabricated by the direct exposure to SR. In this paper, an iris-coupled waveguide BPF with 5-stage Chebyshev response is designed at Q-band, and the fabrication procedure for the PTFE-filled waveguide BPF is described. The measurement results of the fabricated BPF are shown.

This paper describes a constitution method of a novel TE 10 -TE 20 mode transducer utilizing an H-plane right-angled corner composed of a standard waveguide and an over-moded one. By placing several metallic posts in the corner junction for both good mode-conversion and low return loss, and optimizing their positions and diameters by the use of the H-plane planar circuit approach together with the short-circuiting method of fictitious ports, a compact and easy-to-fabricate mode transducer is realized. Next, an out-of-phase power divider is designed by utilizing this mode transducer, and relatively wide-band characteristics are obtained for both power-split balance and 180° phase difference. Finally, the validity of the design result is confirmed by experiments.

This paper treats a novel lumped-element quadrature Wilkinson power divider. The proposed divider consists of a parallel LC-ladder circuit, a series RL circuit connected though two output ports, and phase shifters consisting of II/T networks. Under this construction broadband characteristics with a relative bandwidth of 33.4%can be obtained in comparison with lumped-element Wilkinson power dividers using II/T networks. Verification of this design method is also shown by EM simulation and experiment.

In this paper, we propose in/reverse-phase Wilkinson power dividers with unequal power-split ratio using lumped-element circuits. Although unequal Wilkinson power dividers using the defected ground structure (DGS) have been reported, impedance mismatch between DGS lines and conventional microstrip lines, and radiation may become problems. The proposed divider consists of parallel pi /T-networks and LC-ladder circuits. The designed reversed- phase divider with a power-split ratio of 4 has a practical property of a relative bandwidth of about 14 %. The validity of this design procedure is also shown by EM-simulations and experiments.

A compact H-plane waveguide cruciform coupler using metallic posts has recently been proposed. It consists of two rectangular waveguides crossing each other at right-angles, two metallic posts arranged on a diagonal line of the cross region for producing directional properties, and one metallic post inserted for matching at each waveguide port. Generally, it is known that any lossless reciprocal 4-port circuit with two-fold symmetry can constitute 90-degree directional coupler, if the four ports are completely matched. In this work, a design of the cruciform hybrid coupler using dielectric posts instead of metallic posts is attempted [3]. The analysis and the design are performed based on the H-plane planar circuit approach for short-circuited boundary segments with the use of the segmentation method. It is shown that good frequency characteristics with fractional bandwidths of about 10% can be realized for the X-band waveguides. The validity of the design results is confirmed by an EM-simulator (Ansoft HFSS) and an experiment.

Conventional rectangular metallic waveguides are seldom used at frequencies higher than twice the cutoff frequency because of higher mode propagation. Single-mode propagation is available for a metallic waveguide using two arrayed dielectric rods. Although coaxial-waveguide converters are generally used for the introduction of electromagnetic wave to metallic waveguides, impedances cannot be matched by only one converter, because of the narrow bandwidth. Accordingly a frequency multiplexer or demultiplexer that connects to two coaxial-waveguide converter is necessary for impedance matching in each frequency range. S-parameters for three waveguide ports were calculated using Ansoft's HFSS. Although the frequency width for the reflection coefficient of each port is not so wide, port isolation is above 20 dB from 14 GHz to 17.5 GHz between two output ports.

This paper treats a rat-race circuit with loose coupling using parallel ring-lines. The minimum coupling factor of a conventional rat-race circuit is limited by the highest impedance of ring-lines that can be manufactured. The proposed rat-race circuits with parallel ring-lines can be realized couplers with loose coupling factors of less than -10 dB by reducing the difference between two admittances of parallel ring-lines. The circuit with a coupling factor of -20 dB can be successfully designed. Finally, verification of this design method can be also shown by using electromagnetic simulator and experiment.

This paper describes compact H-plane right-angled corners with a couple of matching metallic posts with axis parallel to the electric field of a TE 10 mode. Some corners are successfully designed by properly arranging the posts in their square elbow region. Corners with one or two posts can be matched at an arbitrary center frequency over a certain bandwidth. Furthermore, it is shown that the bandwidth of an optimized corner with three metallic posts covers a full X-band or more with very low return loss better than 40 dB. The above corners are designed using the H-plane planar circuit approach because of the planar structure in the H-plane. The validities of the design concept and procedures are confirmed by em-simulations (HFSS), and the wideband corner with three posts is verified experimentally also.

This paper presents a new technique for suppressing the spurious response of parallel-coupled microstrip bandpass filters at twice the design frequency. Floating conductors loaded into periodic slots on the inner edges of each coupled section are employed to compensate the difference between evenand odd-mode phase velocities. This technique is marked by maintenance of planar structure and ease of design due to the symmetrical coupled line section. The designed filter has a satisfactory suppression level of about 40 dB and a symmetrical frequency response of the pass band. The validity of the design concept is confirmed both numerically and experimentally.

This paper suggests a novel cruciform substrate- integrated waveguide quadrature 3-dB hybrid, and shows the frequency characteristics of hybrids designed at various center frequencies using the H-plane planar circuit approach. As a result, relatively flat coupling properties are realized in a compact structure.

This paper presents design methods of 3-dB branch- line couplers operating at two arbitrary frequencies and the centre of them. After a brief survey of the equivalent admittance approach, two types of external matching networks for tri-band operation are proposed. One consists of a two-section impedance transformer and a shunt stub; the other two series stubs and an impedance transformer. Then, two tri-band/broadband couplers are designed using these matching networks; the former is constructed in microstrip line and the latter in CPW. The design techniques are verified by em-simulations and experiments.

A metallic waveguide with dual in-line dielectric rods can propagate electromagnetic waves more than two times higher than the cutoff frequency region without higher modes. This type of waveguide, however, requires many rods with a high dielectric constant such as 29.5. Sintered alumina, with a dielectric constant around 9, may be more suitable for dielectric rods, as it is a popular material for use in microwave systems. Attenuation constants for alumina and for a high dielectric constant material were calculated using the finite-difference time-domain method and compared. Although the attenuation constant for alumina is higher than that of the high dielectric constant material due to its high loss tangent, it is not so high to make it practicable.

This paper treats a novel Wilkinson power divider operating at two arbitrary different frequencies. The proposed divider consists of two-section transmission lines and a series RLC circuit connected between two output ports. The circuit parameters for a dual-frequency operation are derived by the even/odd mode analysis. Equal power split, complete matching, and good isolation between two output ports are demonstrated. Finally, verification of this design concept is shown by using an electromagnetic simulator.

We investigate a design method of multi-stage, multi-way microstrip power dividers to construct a compact low-loss power divider with number of outputs. First, we describe an integration design technique of multi-way power dividers founded on the planar circuit approach in combination with segmentation method, and design broadband 3- and 4-way power dividers. Next, we successfully design a 9-way power divider consisting of 3-way dividers of two-stage structure using a similar technique. As a result, the fractional bandwidths of nearly 90%, 100%, and 85% are obtained, respectively. The validity of these design results is confirmed by HFSS and an experiment.

We have presented a new type of photonic crystal (PC) waveguide in our previous report. The waveguide has a low propagation loss at millimeter wave frequencies compared with an NRD (nonradiative dielectric waveguide) guide, but the PC material is difficult to obtain since a relatively high dielectric constant is required. Therefore, this paper presents another low loss PC waveguide constructed of sintered alumina with a dielectric constant of 8.9 which is easy to obtain. Though the loss of the PC guide is twice larger than that of the previous PC waveguide, its loss is less than that of an NRD guide and the bending loss is reasonable.