Different from distributed baluns, active baluns have group delay variations in the lower bands related to inherent internal capacitances and resistance in transistors. A negative group delay (NGD) circuit is employed as a compensator of group delay variation for an ultra-wideband (UWB) active balun. First, three-cell NGD circuit is inserted into a simple active balun circuit for realizing both group delay compensation and return loss improvement. The simulated results show a group delay variation of 4.8 ps and an input return loss of above 11.5 dB in the UWB band (3.1-10.6 GHz). Then, a pair of one-cell NGD circuits is added to reduce the remaining group delay variation (3.4 ps in simulation). The circuit with the NGD circuits was fabricated on an InGaP/GaAs HBT MMIC substrate. The measured results achieved a group delay variation of 7.7 ps, a gain variation of 0.5 dB, an input return loss of greater than 10 dB, and an output return loss of larger than 8.1 dB in the UWB band.

A microwave power amplifier with independently biased InGaP/GaAs HBTs is proposed, and its superior performance is confirmed. Using harmonic balance simulation, the optimal bias conditions for an amplifier with two independently biased InGaP/GaAs HBTs were investigated with the aim of achieving high-efficiency low-distortion performance. A 1.9-GHz-band cascode power amplifier was designed and fabricated. Power efficiencies and third-order intermodulation distortions (IMD3) for the fabricated amplifier were estimated. The collector bias voltage of the first stage transistor mainly affects power-added efficiency (PAE). The base bias current of the first-stage HBT mainly affects IMD3 characteristics, and that of the second-stage HBT mainly affects PAE. The proposed amplifier shows superior performance when compared to a conventional cascode amplifier. The amplifier achieved a maximum PAE of 68.0% with an output power of 14.8dBm, and IMD3 better than -35dBc with a PAE of 25.1%, for a maximum output power of 10.25dBm at 1.9GHz. A PAE of more than 60% was achieved from 1.87 to 1.98GHz.

Analytical expression of transmission for the orbital angular momentum (OAM) communication using loop antenna arrays and paraboloids is derived to achieve a communication distance of 100 m. With the field distribution of the single “transformed OAM mode” radiated by a loop antenna, the collimated field by the transmitting paraboloid and its diffracted field are analytically derived. Effects of frequencies, sizes of paraboloids, and shifts of transmitting and receiving arrays from the focal planes are included. With the diffracted field distribution on the focal plane of the receiving paraboloid, transmission between the transmitting and receiving loop antennas is analytically estimated. It is shown that the transmission between the antennas with different OAM modes is null, but the transmission between the antennas with the same mode can be reduced. To clarify the mechanism of the reduction, factors of the reduction are quantitatively defined, and the explicit formulae are derived. Based on the analytical results, numerical estimation for a communication distance of 100 m is demonstrated, where the frequency, the focal length, and the size of the paraboloid are 150 GHz, 50 cm and 100 cm, respectively. Where both arrays are located on each focal plane, the transmission for the signal is more than -7.78 dB for eight kinds of OAM modes. The transmission is the least for the highest-order mode. The transmission loss is shown to be mitigated by optimizing the shifts of transmitting and receiving arrays from their focal planes. The loss is made almost even by exploiting the tradeoff of the improvement for the mode orders. The transmission is improved by 5.98 dB, to be more than -1.80 dB, by optimizing the shifts of the arrays.

An InGaP/GaAs HBT MMIC amplifier with an active balun has been developed for ultra-wideband radio systems (UWB). The MMIC was designed to drive a self-complementary antenna with a balanced mode, where an input impedance is 60π ohms. The MMIC consists of a common mode negative feed back ultra-wideband amplifier circuit, an active balun circuit, and a high impedance drive circuit. The developed amplifier provides a 3-dB gain roll-off bandwidth from 2.4 GHz to 10.8 GHz with a 14.1-dB linear power gain, and a linear power output up to 3 dBm. The developed amplifier with the active balun provides a 3-dB gain roll-off bandwidth from 2.3 GHz to 8.6 GHz with a 21.3-dB power gain in a balanced mode, and a linear power output up to 0.6 dBm. The measured total group delay is less than 32 psec. Output signals at the balanced output terminals of the MMIC were kept inverted with a steep pulse shape for an impulse input signal of 57-psec pulse width.

Extremely compact harmonic tuning circuits for class-F amplifiers are realized using composite right-/left-handed (CRLH) transmission line stubs. The proposed circuits take up only a small fraction of the amplifier circuit area and yet are capable of treating four harmonics up to the 5th with a single stub or double stub configuration. This has become possible by using the negative order resonance modes of the CRLH TL, allowing for flexible and simultaneous control of many harmonics by engineering the dispersion relation of the stub line. The CRLH harmonic tuning stubs for 2-GHz amplifiers were realized using surface mounting chip capacitors, whereas the stub for 4-GHz amplifiers was fabricated based fully on microstrip-line technology. The fabricated 2-GHz and 4-GHz GaN HEMT class-F amplifiers exhibited peak drain efficiency and peak PAE of more than 83% and 74%, respectively.

An inter-modulation distortion (IMD) compensation method for thermal memory effect using a multistage RC-ladder circuit has been proposed. The IMD caused by the thermal memory effect on an InGaP/GaAs HBT amplifier was compensated for by inserting a multistage RC-ladder circuit in the base bias circuit of the amplifier. Since heat flux owing to self-heating in the transistor can be approximated with a multistage thermal RC-ladder circuit, the canceling of IMD by an additional electrical memory effect generated from the RC-ladder circuit is predicted. The memory effects cause asymmetrical characteristics between upper and lower IMD. The IMD caused by the memory effects is expressed as a vector sum of each origin. By adjusting an electrical reactance characteristic for sub-harmonics affected by the thermal memory effect in the amplifier circuit, the asymmetric characteristic is symmetrized. The parameters of the RC-ladder circuit were estimated so that the adjusted electrical reactance characteristic is reproduced in simulation. A fabricated InGaP/GaAs HBT amplifier with the thermal memory effect compensation circuit exhibited a symmetrized and suppressed IMD characteristics.

Distortion characteristics caused by the thermal memory effect in power amplifiers were accurately predicted using a multi-stage thermal RC-ladder network derived by simplifying the heat diffusion equation. Assuming a steep gradient of heat diffusion near an intrinsic transistor region in a semiconductor substrate, the steady state temperature, as well as the transient thermal response at the transistor region, was estimated. The thermal resistances and thermal capacitances were adjusted to fit a temperature distribution characteristic and a step response characteristic of temperature in the substrate. These thermal characteristics were calculated by thermal FDTD simulation. For an InGaP/GaAs HBT, a step response characteristic for a square-wave voltage signal input was simulated using a large-signal model of the HBT connecting the multi-stage thermal RC-ladder network. The result was verified experimentally. Additionally, for an RF-amplifier using the HBT, the 3rd-order intermodulation distortion caused by the thermal memory effect was simulated and this result was also verified experimentally. From these verifications, a multi-stage thermal RC-ladder network can be used to accurately design super linear microwave power amplifiers and linearizers.

A 4.5-/4.9-GHz band-selective GaN HEMT high-efficiency power amplifier has been designed and evaluated for next-generation wireless communication systems. An optimum termination impedance for each high-efficiency operation band was changed by using PIN diodes inserted into a harmonic treatment circuit at the output side. In order to minimize the influence of the insertion loss of the PIN diodes, an additional line is arranged in parallel with the open-ended stub used for second harmonic treatment, and the line and stub are connected with the PIN diodes to change the effective characteristic impedance. The fabricated GaN HEMT amplifier achieved a maximum power-added efficiency of 57% and 66% and a maximum drain efficiency of 62% and 70% at 4.6 and 5.0GHz, respectively, with a saturated output power of 38dBm, for each switched condition.

Unique spatial eigenmodes for the spherical coordinate system are shown to be successfully synthesized by properly allocated combinations of current distributions along θ' and φ' on a spherical conformal array. The allocation ratios are analytically found in a closed form with a matrix that relates the expansion coefficients of the current to its radiated field. The coefficients are obtained by general Fourier expansion of the current and the mode expansion of the field, respectively. The validity of the obtained formulas is numerically confirmed, and important effects of the sphere radius and the degrees of the currents on the radiated fields are numerically explained. The formulas are used to design six current distributions that synthesize six unique eigenmodes. The accuracy of the synthesized fields is quantitatively investigated, and the accuracy is shown to be remarkably improved by more than 27dB with two additional kinds of current distributions.

To evaluate whether electromagnetic disturbances that leak from PC displays contain information or not, we need to reconstruct the information from the measured disturbance. This requires a special receiver, and not all test houses have a special receiver. In this paper, we propose performing the evaluation with the spectrum analyzers commonly used for EMI measurement. First, we select a spectrum that containing the frequency component of the vertical sync signal using a spectrum analyzer (SA1). Then, we measure the video output of SA1 using another spectrum analyzer (SA2) and evaluate the disturbance from the frequency component of the horizontal sync signal.

A broadband miniature GaAs p-HEMT MMIC Doherty power amplifier (DPA) with a series connected load operating at the C band has been developed. To minimize the circuit size, a lumped-element load modulation circuit without a quarter wavelength transmission line has been introduced to MMIC technology. For both an input and output power divider/combiner circuit, two baluns are used to reduce the length of the phase adjuster circuit without causing instability. An inherent DPA instability problem related with the degenerated sub-harmonic frequency has been analyzed with the S and T parameters of DPA circuit components, resulting in a novel stabilized circuit. The developed stabilized DPA delivered a maximum power added efficiency (PAE) of 49% and a maximum output power of 23.4dBm. Greater than 40% PAE below a 10-dB input back-off from a saturated output power is obtained for a frequency range of 6.1 to 6.8GHz.

The first realization of a class-F InGaP/GaAs HBT amplifier considering up to 7th-order higher harmonic frequencies, operating at 1.9-GHz band, is described. A total number of open-circuited stubs for higher harmonic frequency treatment is successfully reduced without changing a class-F load circuit condition, using a low-cost and low-loss resin (tan δ=0.0023) circuit board. In class-F amplifier design at microwave frequency ranges, not only increasing treated orders of higher harmonic frequencies for a class-F load circuit, but also decreasing parasitic capacitances of a transistor is important. Influence of a base-collector capacitance, Cbc, for power added efficiency, PAE, and collector efficiency, ηc, was investigated by using a two-dimensional device simulator and a harmonic balance simulator. Measured maximum PAE and ηc reached 74.2% and 76.6%, respectively, using a fabricated class-F InGaP/GaAs HBT amplifier with collector doping density of 21016 cm-3. In case circuit losses were de-embedded for the experimental results, PAE and ηc were estimated as 78.7% and 81.2%, respectively. These are very close to obtainable maximum PAE for the use of the InGaP/GaAs HBT.

A novel experimental design method based on a low-frequency active load-pull technique that includes harmonic tuning has been proposed for high-efficiency microwave power amplifiers. The intrinsic core component of a transistor with a maximum oscillation frequency of more than several tens of gigahertz can be approximately assumed as the nonlinear current source with no frequency dependence at an operation frequency of several gigahertz. In addition, the reactive parasitic elements in a transistor can be omitted at a frequency of much less than 1GHz. Therefore, the optimum impedance condition including harmonics for obtaining high efficiency in a nonlinear current source can be directly investigated based on a low-frequency active harmonic load-pull technique in the low-frequency region. The optimum load condition at the operation frequency for an external load circuit can be estimated by considering the properties of the reactive parasitic elements and the nonlinear current source. For an InGaAs/GaAs pHEMT, active harmonic load-pull considering up to the fifth-order harmonic frequency was experimentally carried out at the fundamental frequency of 20MHz. By using the estimated optimum impedance condition for an equivalent nonlinear current source, high-frequency amplifiers were designed and fabricated at the 1.9-GHz, 2.45-GHz, and 5.8-GHz bands. The fabricated amplifiers exhibited maximum drain efficiency values of 79%, 80%, and 74% at 1.9GHz, 2.47GHz, and 5.78GHz, respectively.

An exchange of energy between nonrelativistic electrons and evanescent waves in an optical near-filed has been investigated in an infrared region. A metal microslit has been adopted as an optical near-field generator which produces a number of evanescent waves by illumination of a laser beam. The theory has predicted that electrons interact selectively with the evanescent wave whose phase velocity is equal to the velocity of the electrons. In order to verify the theory, two types of precise microslits with different shapes, a slot and a V-shaped groove, have been fabricated. Experiments performed using these slits at the wavelength of 10.6 µm have shown that the energy change of the electrons has varied from 2 eV to 13 eV with their initial energy between 25-95 keV for a 3.2 kW CO2 laser pulse. The measured results have given experimental verifications to the theory.

A practical Doherty amplifier design method has been developed based on an asymmetric configuration scheme. By embedding a load modulation function into matching circuits of a carrier amplifier (CA) and a peaking amplifier (PA) in the Doherty amplifier, an issue of the Doherty amplifier design is boiled down to the CA and PA matching circuit design. The method can be applied to transistors with unknown parasitic elements if optimum termination impedance conditions for the transistor are obtained from a source-/load-pull technique in simulation or measurement. The design method was applied to GaN HEMT Doherty amplifier MMICs. The fabricated 4.5-GHz-band GaN HEMT Doherty amplifier MMIC exhibited a maximum drain efficiency of 66% and a maximum power-added efficiency (PAE) of 62% at 4.1GHz, with a saturation output power of 36dBm. In addition, PAE of 50% was achieved at 4.1GHz on a 7.2-dB output back-off (OBO) condition. The fabricated 8.5-GHz-band GaN HEMT Doherty amplifier MMIC exhibited a maximum drain efficiency of 53% and a maximum PAE of 44% at 8.6GHz, with a saturation output power of 36dBm. In addition, PAE of 35% was achieved at 8.6GHz on a 6.7-dB (OBO). And, the fabricated 12-GHz-band GaN HEMT Doherty amplifier MMIC exhibited a maximum drain efficiency of 57% and a maximum PAE of 52% at 12.4GHz, with a saturation output power of 34dBm. In addition, PAE of 32% was achieved at 12.4GHz on a 9.5-dB (OBO) condition.

This paper describes the characteristic of negative group delay (NGD) circuits for various configurations including first-order, distributed, and second-order RC circuit configurations. This study includes locus, magnitude, and phase characteristics of the NGD circuits. The simplest NGD circuit is available using first-order RC or RL configuration. As an example of distributed circuit configuration, it is verified that losses in a distributed line causes NGD characteristic at higher cut-off band of a coupled four-line bandpass filter. Also, novel wideband NGD circuits using second-order RC configuration, instead of conventional RLC configuration, are proposed. Adding a parallel resistor to a parallel-T filter enables NGD characteristic to it. Also, a Wien-Robinson bridge is modified to have NGD characteristic by controlling the voltage division ratio. They are fabricated on MMIC substrate, and their NGD characteristics are verified with measured results. They have larger insertion loss than multi-stage RLC NGD circuits, however they can realize second-order NGD characteristic without practical implementation of inductors.

A novel spatially modulated communication method, appropriate for wireless power transmission applications at 5.8GHz, is proposed using dual scatterers embedded with lumped elements. Analytical expression for the received wave in the spatial modulation is derived, and the characteristics are verified with simulation and measurement by varying the embedded capacitor. The maximum measured variation of the received voltage is more than 15dB and that of the phase is more than 270 degrees at 5.8GHz. The estimated amplitude modulation factor is more than 70%. Using the data obtained, we estimate the practical received waveforms modulated by the applied voltage to a varactor for the amplitude modulation scheme.

A wideband InGaP/GaAs HBT MMIC amplifier with a low noise characteristic has been developed as a full-band UWB receiver. The amplifier was designed by applying a scaling law to a driver amplifier in order to decrease power consumption, including a modification for decreasing a noise figure. A triple base structure for a double-emitter HBT was employed to decrease a base resistance and to decrease a noise figure of the amplifier. A fabricated amplifier provided a 3-dB gain roll-off bandwidth from 1.1 GHz to 10.6 GHz with a 14.1 dB peak power gain. The amplifier exhibited a low power consumption of 15.9 mW and a low noise figure of less than 3.7 dB in the full-band of the UWB.

A novel predistortion technique using an automatic average-power bias controlled diode is proposed to compensate the complicated nonlinear characteristics of a microwave class-F power amplifier using an AlGaN/GaN HEMT. The optimum value for diode bias voltage is automatically set according to detected input average RF power level. A high-efficiency 1.9 GHz class-F GaN HEMT power amplifier with the automatic average-power bias control (ABC) diode linearizer achieves an improved third order inter-modulation distortion (IMD3) of better than -45 dBc at a smaller than 6 dB output power back-off from a saturated output power of 27 dBm, without changing drain efficiency. The adjacent channel leakage power ratio (ACPR) for 1.9 GHz W-CDMA signals is below -40 dBc at output power levels of smaller than 20 dBm for the class-F power amplifier.

This paper proposes Code-Modulated Synchronized (CMS) -OOK modulation scheme for normally-off wireless sensor networks, and demonstrates the operation of the transmitter for the CMS-OOK using 65nm SOTB (Silicon-On Thin Buried Oxide) CMOS technology. Based on investigating RF characteristics of SOTB CMOS, analog part of a CMS-OOK transmitter was designed, fabricated and evaluated in combination with based-FPGA digital part. With code modulation and controlling the carrier frequency by body bias of the SOTB devices, the spectrum of a CMS-OOK transmitter output is widen to achieve -62dBm/MHz peak power spectrum density at 15 MHz bandwidth. Chip of analog part on-board is supplied by 1V for power amplifier and 0.75V for the rest. It consumes average 83µW according to 83nJ/bit at 1kbps data transmission.