Gallium nitride high electron mobility transistors (GaN HEMTs) were developed for millimeter-wave high power amplifier applications. The device with a gate length of 80 nm and an InAlN barrier layer exhibited high drain current of more than 1.2 A/mm and high breakdown voltage of 73 V. A cut-off frequency f_T of 113 GHz and maximum oscillation frequency f_max of 230 GHz were achieved. The output power density reached 1 W/mm with a linear gain of 6.4 dB at load-pull measurements at 90 GHz. And we extracted equivalent circuit model parameters of the millimeter-wave InAlN/GaN HEMT and showed that the model was useful in simulating the millimeter-wave power performance. Also, we report a preliminary constant bias stress test result.

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This paper presents an experimental investigation on the RF characteristics of a 3W-class cryogenically-cooled receiver amplifier employing a gallium-nitride high electron mobility transistor (GaN HEMT) with a blue light for mobile base stations. In general, a cryogenically-cooled receiver amplifier using a GaN HEMT exhibits unstable DC characteristics similar to those found in the current collapse phenomenon because the GaN HEMT loses thermal energy at cryogenic temperatures. The fabricated cryogenically-cooled receiver amplifier achieves stable DC characteristics by injecting blue light into the GaN HEMT instead of thermal energy. Experimental results show that the amplifier achieves fine stable DC characteristics for deviation in the drain-source current from 42% to 5% and RF characteristics for a maximum power added efficiency from 58% to 68% without and with the blue light at 60 K. The fabricated amplifier is effective in reducing the power consumption at cryogenic temperatures. To the best of our knowledge, this paper is the first report regarding RF characteristics of a cryogenically-cooled receiver amplifier using a blue light for mobile base stations.

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This paper describes the design method of a broadband CMOS stacked power amplifier using harmonic control over wide bandwidths in a 0.11 μm standard CMOS process. The high-efficiency can be obtained over wide bandwidths by designing a load impedance circuit as purely reactive as possible to the harmonics with broadband fundamental matching, which is based on continuous Class-F mode of operation. Furthermore, the stacked topology overcomes the low breakdown voltage limit of CMOS transistor and increases output impedance. With a 5-V supply and a fixed matching circuitry, the suggested power amplifier (PA) achieves a saturated output power of over 26.7 dBm and a drain efficiency of over 38% from 1.6 GHz to 2.2 GHz. In W-CDMA modulation signal measurements, the PA generates linear power and power added efficiency of over 23.5 dBm and 33% (@ACLR =-33 dBc).

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We proposed a through-hole based transformer between microstrip line and post-wall waveguide (PWW). The transformer is based on a through-hole which is electrically separated from top and bottom broad walls of a waveguide by ring-shaped spaces. The proposed transformer shows a considerable merit compared with a conventional one based on blind-via in terms of fabrication and cost because it can be realized by through-holes in general printed-circuit-board technology. We selected liquid crystal polymer (LCP) as the material of substrates because of its lower dielectric loss and easy fabrication. The transformer was fabricated and measured. The loss associated with the mode conversion is estimated to be around 0.32 dB, and the bandwidth for a reflection smaller than -15 dB is 8 GHz, i.e., from 59 to 67 GHz.

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Realization of a planar dual-band fork three-way power divider (PDBF3PD) with Cheng's equivalent structure is discussed. The Cheng's structure consists of two open-circuited stubs and a transmission line, and the characteristic impedances tend to be high. As a result, the realizable range of frequency ratios of upper frequency to lower frequency is limited in a narrow area. In this paper, an impedance scale factor is proposed to transform characteristic impedances into a realizable range and to facilitate the design of PDBF3PDs. Theoretical considerations are verified using a simulator of ADS2008U and by an experiment.

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This paper proposes a compact three-mode H-shaped resonator bandpass filter fed by antiparallel coupled input/output lines. To investigate the resonant behavior of the H-shaped resonator, even/odd-mode resonance conditions of the resonator are first derived analytically. The multimode resonances of the H-shaped resonator filter are modeled by a multipath circuit formed with resonance paths. Moreover, a direct source/load coupling path is connected in parallel, of which the value shows a frequency dependency because of the antiparallel coupled feeding lines, thereby generating four transmission zeros (TZs) greater than the number of a theoretical limitation. The H-shaped resonator bandpass filter is synthesized, developed, and tested, showing a third-order passband response with four TZs located near the passband, and a wide stopband property.

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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.

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Underfill materials are used in a packaging of millimeter wave IC. However, there are few reports for dielectric properties of underfill materials in millimeter wave region. A cut-off circular waveguide method is one of a powerful technique to evaluate precisely complex permittivity in millimeter wave region. This method may be useful not only for low-loss materials, but also for mid-loss ones with loss tangent of 10^-2 order. In this paper, an evaluation technique based on the cut-off circular waveguide method is presented to measure mid-loss underfill materials. As a result, the relative permittivity ε_r and the loss tangent tanδ are in the range of 2.8∼3.4 and (1.0∼1.6)×10^-2, respectively. Also, the measurement precision is 2.3% for ε_r ≅ 3 and 40% for tanδ ≅ 10^-2.

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This paper proposes a sector base station antenna for mobile wireless communication systems employing multiple woodpile metamaterial reflectors and a multiband radiator that establishes the same beamwidth in the horizontal plane for more than two frequency bands. Electromagnetic Band Gap (EBG) characteristics of each metamaterial reflector can be controlled through structural parameters of the woodpile reflector, e.g., the rod width and rod spacing. As an example of the proposed antenna, a design for a triple-frequency-band antenna that radiates at 800 MHz, 2 GHz, and 4 GHz is shown. The algorithm used to adjust the beamwidth of the proposed antenna is newly introduced and adjusts the beamwidth to be the same for each band using the rod width of the woodpile. A prototype of the proposed antenna has the approximately 90^° beamwidth in the horizontal plane at the three frequencies, and the measurement results agree well with the electromagnetic field simulation results.

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A simple, low reflection, and highly-efficient pilot-plant scale microwave irradiation reactor for woody biomass pretreatment was fabricated. Pretreatment is an essential process for effective bioethanol production.The fabricated reactor consists of 8 microwave irradiators which are attached to a metal pipe. The woody biomass mixture which contains water and organic acid flows through the metal pipe and is heated by microwaves at a total power of 12 kW. To design the microwave irradiators, we used a 3D Finite Element Method (FEM) simulator, which was based on the measured complex permittivity data of the woody biomass mixture.The simulation results showed that the reflection coefficient |S₁₁| from the reactor was less than -30 dB when the woody biomass mixture temperature was between 30^°C and 90^°C.Finally, we experimentally confirmed that the fabricated irradiation reactor yielded a microwave absorption efficiency of 79%.

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This paper presents a 24×24 MIMO channel sounder that has been developed based on a scalable fully parallel MIMO architecture. It can be flexibly configured with 3 sub-transmitters and 3 sub-receivers, each of which consists of 8 RF ports. This flexibility allows the measurement for both purposes of double directional and multi-link MIMO channel measurements. Implementation issues related to the multi-link operation on the fully parallel architecture were successfully solved by appropriate system design and applying several calibration techniques. The performance of the developed system was validated by extensive test experiments. Finally, a multi-link channel measurement example in an indoor environment was presented demonstrating the capability of the proposed system.

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This paper addresses a noise matching problem for MIMO receiver with mutual coupling in the presence of signal and antenna noise coupling. The matching network in this paper is designed to maximize the system's ergodic capacity by means of minimizing the noise figure matrix.For reducing RF circuit complexity, low noise matching design without crossover elements of the matching circuit is derived for compact symmetrical 2×2 MIMO receiver system with mutually coupled antenna.Numerical simulation verifies our analytical results and demonstrates the superiority of the proposed matching method among feasible ones.The paper furthermore investigates the lossy matching circuit with the corresponding circuit parameters in a specific condition and the effect of practical matching circuit.

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This paper presents a printed circuit board (PCB) integrated multi-layered strip line tandem coupler, which used simple compensating ground through-hole (GTH) elements. The GTH elements on one end of the coupled line can generate additional capacitance between the signal line and the ground, which effectively compensates for the parasitic capacitance around the crossed signal lines on the opposite end of the coupled line. It has been experimentally demonstrated that the proposed coupler fabricated for the X-band is effective to improve both the reflection and the isolation characteristics.

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We have improved a compact model for the injection-enhancedinsulated-gate bipolar transistor for inverter circuit simulation. The holeaccumulation of floating-base region and potential change are modeled. It turned out that negative capacitance which occurs by floating-base region has the dependence of frequency. It is necessary to consider the frequency dependence of the total gate capacitance for transient simulation. We analyzed the relationship between negative gate capacitance and current rise rate at the switch turn-on timing and device structure. The development model simulation result is well reproduced I_c and V_ce of measurement data, and the switching loss calculation accuracy is improved.

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This paper proposes low-power voltage-mode/current-mode hybrid circuits to realize an arbitrary two-variable logic function and a full-adder function. The voltage and current mode can be selected for low-power operations at low and high frequency, respectively, according to speed requirement. An nMOS pass transistor network is shared to realize voltage switching and current steering for the voltage- and current-mode operations, respectively, which leads to high utilization of the hardware resources. As a result, when the operating frequency is more than 1.15 GHz, the current mode of the hybrid logic circuit is more power-efficient than the voltage mode. Otherwise, the voltage mode is more power-efficient. The power consumption of the hybrid two-variable logic circuit is lower than that of the conventional two-input look-up table (LUT) using CMOS transmission gates, when the operating frequency is more than 800 MHz. The delay and area of the hybrid two-variable logic circuit are increased by only 7% and 13%, respectively

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In the theory of periodic gratings, there is no methodto make up a numerical solution that satisfies thereciprocity so far. On the basis of the shadow theory, however, this paper proposes a new method to obtain a numerical solution that satisfies the reciprocity. The shadow thoery states that, bythe reciprocity, the mth order scattering factor is an even function with respect to a symmetricalaxis depending on the order m of diffraction. However, a scattering factor obtained numerically becomesan even function only approximately, but not accurately.It can be decomposed to even and odd components,where an odd component represents an error with respect to the reciprocity and can be removed by the average filter. Using even components, a numerical solution that satisfies the reciprocity is obtained. Numerical examples are givenfor the diffraction of a transverse magnetic (TM) plane wave by a very rough periodic surface with perfect conductivity. It is then found that, by use ofthe average filter, the energy error is much reduced in some case.

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