Shuji Urasaki

An ultra-broad-band reflection-type phase-shifter MMIC with series and parallel LC circuits

An ultra-broad-band reflection-type phase shifter is proposed. Theoretically, the proposed phase shifter has frequency-independent characteristics in the case of 180/spl deg/ phase shift. The phase shifter is composed of a 3-dB hybrid coupler and a pair of novel reflective terminating circuits. The reflective terminating circuit switches two states of series and parallel LC circuits. Using an ideal circuit model without parasitic circuit elements, we have derived the determining condition of frequency independence of circuit elements. Extending the concept, we can also obtain a broad-band phase shifter for other phase difference as well. In this case, for a given phase difference and an operating frequency, we also derive a condition to obtain minimum variation of phase difference around the operating frequency. This enables the broad-band characteristics for arbitrary phase difference. The fabricated 180/spl deg/ reflective terminating circuit monolithic microwave integrated circuit (MMIC) has achieved a phase difference of 183/spl deg/ /spl plusmn/ 3 over 0.5-30 GHz. The 180/spl deg/ phase-shifter MMIC has demonstrated a phase shift of 187/spl deg/ /spl plusmn/ 7/spl deg/ over 0.5-20 GHz. The 90/spl deg/ reflective terminating circuit MMIC has performed a phase difference of 93/spl deg/ /spl plusmn/ 7/spl deg/ over 4-12 GHz.

Electromagnetically coupled coaxial dipole array antenna

A new type of collinear antenna called electromagnetically coupled coaxial dipole array antenna is proposed. The antenna has an advantage of structural simplicity due to a novel use of an electromagnetically coupled feed structure for the radiating element. An analysis of the radiating element is presented and compared with experimental results. Fabrication and measurement of a prototype array antenna are also presented.

High-isolation series-shunt FET SPDT switch with a capacitor canceling FET parasitic inductance

A novel series-shunt FET narrow-band high-isolation single-pole double-throw switch, which employs series capacitors to cancel the parasitic inductances has been developed. The proposed switch can have significantly high isolation characteristics at higher frequency. The fabricated two switches have demonstrated high isolation characteristics of 28.9 dB in the 28- and 18-GHz band, respectively.

X-band MMIC power amplifier with an on-chip temperature-compensation circuit

An X-band MMIC power amplifier with an on-chip temperature compensation circuit has been presented. The temperature compensation circuit is composed of a diode and a resistor. The compensation circuit is applied to a 4 stage X-band MMIC power amplifier. The gain variation is improved from 5.5 dB to 1.3 dB in the temperature range between -10 degC and +80 degC.

Design of iris‐coupled broadband waveguide filter using modified reflection‐zero frequencies

In spite of its low loss and superior power handling capability, the waveguide filter cannot have broad bandwidth due to the strong frequency dependence of the reactance values for coupling of the cavity resonators and the guide wavelength. To achieve a broadband design of the iris-coupled waveguide bandpass filter with the Chebyshev function as the transfer function, the susceptance value of the inductive iris is optimized by specifying the ideal zero frequency of the reflection. Based on this method, a diplexer is trial fabricated and a broadband diplexing characteristic is realized. In addition, agreement with numerical results is demonstrated, confirming the effectiveness and validity of the method. The tested diplexer has a VSWR of less than 1.24 and an isolation of more than 53 dB at passband bandwidths of 32 and 7% relative to the wavelength.

Reduction of near field interference by beam controlling in a transmit phased array antenna

A method of reducing the electromagnetic interference over a broad frequency range by controlling the excitation phase of the element antennas for beam shaping in a phase array used in such systems as wireless LAN is discussed. In this method, an optimum excitation phase of each element antenna is determined by means of the output power minimization algorithm [1] with a directional constraint based on the amplitude and phase data of each element antenna in the far and near fields in the array configuration. The method presented here not only reduces the interference in the near field but also can maintain the radiation level in the desired direction in the far field. In regard to the reduction of interference in the near field by controlling the phase of the transmitting phased array, a method based on the output power minimization with a directional constraint is discussed. Also, in an experiment with an eight-element patch array antenna, the confirmed reduction of the interference is 13.2 dB with a bandwidth of 500 MHz at the frequency of 9.55 GHz and 31.7 dB at the center frequency only. Further, a method is presented for eliminating the effect of quantization error when a digital phase shifter is used for phase control, and its effectiveness is confirmed.

A design method of an offset trireflector antenna whose main reflector is of an offset parabola type with high efficiency and low cross polarization characteristics

A design method is developed for a high efficiency and low cross polarization offset tri-reflector antenna made of an offset parabolic main reflector and two shaped reflectors. In this method, the main reflector is an offset parabola while the #2 reflector corresponding to a subreflector and the #1 reflector as the focussing reflector are shaped by a method using reflector shaping functions. Further, the reflector system is selected as an initial value such that a low cross polarization characteristic is obtained after reflector shaping. As a method for determination of such initial values, a new reflector configuration transformation method is developed. Those design methods are applied to an offset tri-reflector antenna with an aperture diameter of 250 wavelengths. Validity of the design is confirmed by a numerical calculation.