Hongjoon Kim

Linear tunable phase shifter using a left-handed transmission line

We demonstrate a compact, linear, and low loss variation hybrid phase shifter using a left-handed (LH) transmission line. For frequencies from 4.3 to 5.6 GHz, this phase shifter gives a nearly linear phase variation with voltage, with a maximum deviation of /spl plusmn/7.5/spl deg/. Within this frequency range, the maximum insertion loss is 3.6 dB, and the minimum insertion loss is 1.8 dB over a continuously adjustable phase range of more than 125/spl deg/, while minimum return loss is only 10.2 dB. Furthermore, this phase shifter requires only one control line, and it consumes almost no power.

Wave propagation in nonlinear left-handed transmission line media

Using a one-dimensional system, we demonstrate a wide variety of wave propagation phenomena possible in nonlinear left-handed media. These include effective second-harmonic generation where the fundamental wave and the second-harmonic wave are badly mismatched. We also observe parametric instabilities accompanying intensive harmonic generation.

Parametric amplification in left-handed transmission line media

We introduce active negative-index metamaterials based on left-handed nonlinear transmission line media and measure a greater than 10dB amplification of a weak signal wave at the output of the transmission line due to its parametric interaction with an intensive pump wave, by which energy in a pump wave at one frequency is transferred to the energy in a weak signal wave at another frequency.

Combined Left- and Right-Handed Tunable Transmission Lines With Tunable Passband and 0

We combine a right-handed (RH) and a left-handed (LH) nonlinear transmission line (NLTL) to realize a new frequency and phase-tunable bandpass filter (BPF). An RH NLTL is a voltage-controlled low-pass filter and an LH NLTL is a voltage-controlled high-pass filter, so combining both allows for simultaneous and independent control over the low and high cutoff frequencies of the passband. Also, by using the positive phase propagation of a RH NLTL and the negative phase propagation of an LH NLTL, control over the phase propagation in the passband can be achieved. In the fabricated circuit, the controllable low cutoff frequency is from 480 to 721 MHz and the high cutoff frequency is from 625 to 1005 MHz. Also, we note that whatever the passband is, the phase propagation close to the center frequency is 0deg

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We construct a synthetic left-handed transmission line with cascaded varactors and shunt inductors. By modulating dc bias, the capacitance of the varactors can be changed and modulation of the output phase state is possible. For frequencies from 4.7 to 6.4 GHz, a very linear phase variation versus voltages of over 200deg phase variation with low insertion-loss variation (plusmn0.5dB) is demonstrated. This circuit can also act as an efficient harmonic generator when a large signal is applied. Since the left-handed transmission line shows high-pass filter response, harmonics generated are not seriously attenuated. However, because this synthetic transmission line is a very dispersive medium, strong dispersions and instabilities may arise. The circuit size is determined by the diode size and lumped-element inductor, allowing it to be compact

Phase Shift

This study presents three different magnetization models for identifying unknown magnetization of the ferromagnetic thin plate of a ship. First, the forward problem should be solved to accurately predict outboard magnetic fields due to the magnetization distribution estimated at a certain time. To achieve this, three different modeling methods for representing remanent magnetization (i.e., magnetic charge method, magnetic dipole array method, and magnetic moment method) were utilized. Material sensitivity formulas containing the first-order gradient information of an objective function were then adopted for an efficient search of an optimum magnetization distribution on the hull. The validity of the proposed methods was tested with a scale model ship, and field signals predicted from the three different models were thoroughly investigated with reference to the experimental data.

Compact Left-Handed Transmission Line as a Linear Phase–Voltage Modulator and Efficient Harmonic Generator

We describe a reflection type phase shifter which exhibits a large phase shift range. We characterized its response between 1.95 GHz and 2.15 GHz and achieved over 400/spl deg/ phase shift with less than 4dB insertion loss. The transition time from 0/spl deg/ to 180/spl deg/ is <20 nS. Our design is scalable to mm-wave operation because it uses no inductors.

Comparison of Three Modeling Methods for Identifying Unknown Magnetization of Ferromagnetic Thin Plate

The current paper presents an effective methodology for assessing the reliability of electromagnetic designs when considering uncertainties of design variables. To achieve this goal, the reliability index approach based on the first-order reliability method is adopted to deal with probabilistic constraint functions, which are expressed in terms of random design variables. The proposed method is applied to three different designs of a superconducting magnetic energy storage system that corresponds to initial, deterministic, and roust designs. The validity and efficiency of the method is investigated with reference values obtained from Monte Carlo simulation.

A scalable reflection type phase shifter with large phase variation

In this letter, we present a compact, tunable delay line based on left-handed nonlinear transmission line (LH NLTL). The widely tunable range of the large group delay is achieved by controlling a reverse bias voltage of series varactors in the LH NLTL. The proposed tunable delay line can be made in a very compact form since its size is dominated by the cascaded varactors. Our experiment shows that the fabricated prototype exhibits tunable group delay between 1.2 ns and 2.2 ns at a frequency of 1.42 GHz with good return loss. The circuit size is merely 1.6 cm in length.

Reliability Assessment on Different Designs of a SMES System Based on the Reliability Index Approach

We present a balanced distributed-element phase shifter based on a nonlinear transmission line (NLTL) structure. Results show the second harmonic is more than 13dB lower at 0-V bias than a conventional single-ended NLTL phase shifter. We fabricated both balanced and conventional NLTL phase shifters with the same coplanar waveguide (CPW) design and diodes, and observed that phase shifting and insertion loss for both structures were quite similar, yet harmonic distortion was greatly improved in the balanced structure.