Hong-Goo Cho

A novel defected ground structure and its application to a microwave oscillator

This paper presents a new defected ground structure (DGS) and its application to a microwave oscillator. The presented oscillator is designed so as to use the suggested defected ground structure as a feedback loop inducing a negative resistance as well as a frequency-selective circuit. Applying the feedback loop between the drain and the gate of a FET device produces a high gain and precise phase conversion in the feedback loop. The equivalent circuit parameters of the DGS are extracted by using a three-dimensional EM calculations and simple circuit analysis method. The implemented 9 GHz oscillator provides +8.5 dBm output with high power efficiency over 40%.

A novel variable-impedance microstrip circuit and its application to direct antenna modulation

In this paper, we proposed a variable-impedance microstrip circuit using varactor diode as a control device. The proposed variable-impedance transmission line with a simple planar antenna can change the resonant frequency and the input impedance of antenna to achieve the DAM (Direct Antenna Modulation). As an application of the variable-impedance microstrip circuit, we have implemented the ASK modulation of RF signal for the low-power consumption RFID applications. The experimental results show that a patch antenna with a resonant frequency of 2.45GHz and a 30MHz bandwidth can transmit a 1Mbps digital modulated signal with the ultra low-power consumption.

A novel CAD algorithm for corrugated harmonic rejection filters based on the synthesis procedures combined with the cutoff frequency correction method

A novel CAD algorithm using a modified synthesis procedure combined with the cutoff frequency correction method is presented for a fast and accurate design of corrugated harmonic rejection filters. The filter structures are analyzed by mode-matching formulation. Without an iteration or an optimization procedure, the proposed method resolves the proximity effect problem and gives a solution that is accurate enough for design of practical filters. The cutoff frequency correction factor is derived from the actual insertion loss for a pre-designed filter at the cutoff frequency only. Validity of the new method was confirmed by computer simulations and experimental measurements of the filter designed by this method.