Herein, a novel self-oscillating active integrated array antenna (AIAA) is proposed for beam switching X-band applications. The proposed AIAA comprises four linearly polarized microstrip antenna elements, a Gunn oscillator, two planar magic-Ts, and two single-pole single-throw (SPST) switches. The in/anti-phase signal combination approach employing planar magic-Ts is adopted to attain bidirectional radiation patterns in the φ =90° plane with a simple structure. The proposed antenna can switch its beam using the SPST switches. The antenna is analyzed through simulations, and a prototype of the antenna is fabricated and tested to validate the concept. The proposed concept is found to be feasible; the prototype has an effective isotropic radiated power of +15.98dBm, radiated power level of +4.28dBm, and cross-polarization suppression of better than 15dB. The measured radiation patterns are in good agreement with the simulation results.

This paper represents a low noise second harmonic oscillator using mutually synchronized Gunn diodes. A multi-layer MIC technology is adopted to reduce the circuit size of the oscillator. The oscillator consists of Gunn diodes, slot line resonators and strip lines. By embedding Gunn diodes in the slot line resonators, a harmonic RF signal can be generated very easily. The strip lines are used for the power combining output circuit. The shape of slot line resonator is square in order to achieve the low phase noise and the suppression of undesired harmonics. The second harmonic oscillator is designed and fabricated in K band. The output power is +8.89 dBm at the design frequency of 18.75 GHz (2f0) with the phase noise of -116.2 dBc/Hz at the offset frequency of 1 MHz. Excellent suppression of the undesired fundamental frequency signal (f0) of -33 dBc is achieved. Also, the circuit size is reduced by three-tenths relative to that of the previously proposed circuit.

We fabricated and examined current limiting effect for InP Gunn diodes with stable depletion layer mode operation of diodes for high efficiency Gunn oscillators. Current limiting at the cathode was achieved by a shallow Schottky barrier at the interface. We discussed fabrication procedure, the results for negative differential resistance and rf tests for InP Gunn diodes. It was shown that the fabricated Gunn diodes have the output power of 10.22 dBm at a frequency of 90.13 GHz. Its input voltage and corresponding current were 8.55 V and 252 mA, respectively.

An improved nonlinear circuit model for a GaAs Gunn diode in an oscillator is proposed based on the physical mechanism of the diode. This model interprets the nonlinear harmonic character on the Gunn diode. Its equivalent nonlinear circuit of which can assist in the design of the Gunn oscillator and help in the analysis of the fundamental and harmonic characteristics of the GaAs Gunn diode. The simulation prediction and the experiment of the Gunn oscillator show the feasibility of the nonlinear circuit model for the GaAs Gunn oscillator.

This paper represents a novel second harmonic power combining oscillator using mutually synchronized Gunn diodes embedded on slot line resonators. A both-sided MIC technology is adopted in the oscillator. The oscillator consists of Gunn diodes, slot line resonators and microstrip lines. By embedding Gunn diodes on the slot line resonators, the harmonic RF signal can be generated very easily. The microstrip lines are used for the power combining output circuit. This oscillator has advantages such as easy circuit design, simple circuit configuration and miniaturization of the circuit size. The second harmonic oscillator is designed and fabricated in K-Band. The output power is +5.75 dBm at the design frequency of 19.0 GHz (2f0) with the phase noise of -111.7 dBc/Hz at the offset frequency of 1 MHz. Excellent suppression of the undesired fundamental frequency signal (f0) of -39 dBc is achieved.

A 76-GHz Gunn voltage-controlled oscillator (VCO) with a high output power and a wide tuning-frequency range was fabricated by optimizing VCO circuits and using laser micromachining. The tuning-frequency range of the fabricated Gunn VCO was more than two times higher than that attained in our previous experiments by optimizing VCO circuits. The VCO attained a tuning-frequency range of 493 MHz, output power variation of 1.0 dB, and tuning-frequency linearity of 6.1% over a tuning-voltage range from 0 to 10 V. Its power consumption was 2.0 W at operation voltage of 3.6 V. And it measured output power was 13.3 dBm with DC-RF conversion efficiency of 1.0% at 76.5 GHz. Moreover, under fundamental-mode operation, it achieved low phase noise of -107.8 dBc/Hz at an offset frequency of 1 MHz. Since laser micromachining was used in fabricating the Gunn VCO, the reproducibility of its RF performance was improved.

We studied planar graded-gap injector GaAs Gunn diodes designed for operation at 94 GHz. Two types of planar Gunn diodes were designed and fabricated. In the first diode, a cathode was situated inside a circular anode with a diameter of 190 µm. The distance between the anode and cathode varied from 60 µm to 68 µm depending on the cathode size. Also, we designed a structure with a constant distance between the anode and cathode of 10 µm. In the second diode, the anode was situated inside the cathode for the flip-chip mounting on the oscillator circuits. The fabrication of the Gunn diode was based on ohmic contact metallization, mesa etching, and air-bridge and overlay metallization. DC measurements were carried out, and the nature of the negative differential resistance, the operating voltage, and the peak current in the graded-gap injector GaAs Gunn diodes are discussed for different device structures. It is shown that the structure with the shorter distance between the cathode and anode has a higher peak current, higher breakdown voltage, and lower threshold voltage than those of the structure with the larger distance between the cathode and anode.

The size of the microscopic electron spot is an important parameter for the white-uniformity of a CRT. It changes as a function of the focus voltage and beam repulsion. This paper explains the mechanism behind this phenomenon. The model is supported by means of measurements.

We've been developing new electron guns for a high brightness CRT. The electron guns were modified to increase the emission current without the increase of the driving voltage. We achieved the high brightness CRT with "low cut-off electron gun" and the gun was successfully introduced into our multimedia CRT. Now we are developing next generation gun or "double drive electron gun" for larger screen CRT. The gun can emit about double current in comparison with the "low cut-off electron gun."

We developed the new electron gun, which can emit about twice electron in comparison with the conventional gun and could achieve the screen brightness of over 300 cd/m2 even if the ordinal driving circuit is applied. We tried two methods to improve the drive characteristics, and we chose to lower the cathode cut-off voltage. To maintain the resolution, we optimized the triode. And we used the tungsten-coated oxide cathode to guarantee the long life.

A 5.3-GHz klystron has been recently designed and fabricated. In many countries, the transmitting frequency of 5.6 GHz (5,600 to 5,650 MHz) is commonly used for C-band meteorological radars. However, 5.3 GHz is generally used in Japan. To detect low-level wind shears by a Doppler radar, it is essential to use a MOPA (Master Oscillator and Power Amplifier) that generates stable coherent microwaves. The klystron is most suitable for this purpose. However, there are no commercially available klystrons in C-band that operate at 5.3 GHz. We developed a klystron for this band, making use of a simulation technique originally devised for S- and X-bands. The klystron operates at frequencies between 5,250 and 5,350 MHz. The typical operating parameters are a peak output power of 200 kW, a pulse width of 1 µs, and an RF duty cycle of 0.002. The klystron, including the electromagnet for focusing the magnetic field, is approximately 67 cm long with a diameter of 40 cm and a weight of 162 kg. Phase modulation is suppressed below 20% of the phase change required for the minimum resolution of Doppler velocity measurement by the radar for which this klystron is employed. The klystron shows favorable performance for Doppler radars operated in major airports in Japan.

The design of an electron gun was examined from the viewpoints of pre-focus lens, main lens, corner focus and cathode current. Accordingly, multi-beam electron gun has been developed to catch up with the remarkable progress of resolution in computer peripheral devices such as digital still cameras and video boards. Multi-beam electron gun has two slot beam apertures of G1 for one cathode, and a key point of its design is to realize two-beam simultaneous convergence and focusing. To satisfy this condition, the divergence angles of electron beam bundles were designed. With this multi-beam electron gun that is superior in both of beam spot size and drive voltage, the 5 million pixels CRT could be realized.

Spatiotemporal chaos in a multidomain regime in a Gunn-effect device is numerically investigated as an example of collective domain oscillations under global constraints. The dynamics of carrier densities are computed using a set of model partial differential equations. Numerical results reveal some distinctive and chaotic clustering features caused by the global coupling and boundary effects. The chaotic regime is then characterized in terms of a Lyapunov spectrum and Lyapunov dimension, the latter increasing with the size of the system.

Theoretical and experimental aspects of GaN-based Gunn diodes are reviewed. Since the threshold field for Gunn effect in GaN (FTH>150 kV/cm) is reported to be much higher than in GaAs (FTH=3.5 kV/cm), the active layer of GaN-based devices can be made thinner (<3 µm) and doped higher (>1017 cm-3) than in conventional Gunn diodes. Consequently, GaN-based devices are expected to offer increased frequency and power capabilities. The advantages of GaN are demonstrated with the help of large-signal simulations of GaN and GaAs Gunn diodes. The simulations revealed that GaN diodes can be operated at a higher frequency (up to 760 GHz vs. 100 GHz) and with larger output power density (105 W/cm2 vs. 103 W/cm2) than GaAs diodes. Epitaxial layers of n+/n-/n+ GaN (1019 cm-3/1017 cm-3/1019 cm-3) designed for millimeter-wave operation were grown using MOCVD on SiC substrates. GaN Gunn diodes with 4 µm-thick active layers were fabricated using specially developed dry etching techniques. The RIE was optimized to allow deep low-damage etching and allowed reduction of contact resistivity of etched layers (RC10-6 Ωcm2). GaN diodes fabricated on SiC substrates with high thermal conductivity were tested on-wafer and demonstrated high voltage and current capability (60 V and 2.5 A). High frequency testing of these devices requires proper dicing, mounting on efficient heatsinks, and connection to appropriate oscillator cavities.

To improve the resolution of the color CRTs, we propose a new electrostatic lens system which has two additional electrodes between the focus electrode and the anode electrode. The anode voltage and focus voltage are supplied on these additional electrodes. The numerical simulation shows that the system can reduce the third order aberration coefficients almost up to 31% of the conventional system. And the experiments show that the typical beam spot diameter is improved by nearly 20% of the conventional system.