Jungje Ha

Application of Stepped-Impedance Technique for Bandwidth Control of Dual-Band Filters

This paper demonstrates application of the popular stepped-impedance technique to control the bandwidths of dual-band filters independently. Unlike previous dual-band stepped-impedance filters, the role of the stepped-impedance technique is to control the bandwidths of the two bands rather than to provide dual-band performance. The exact relationship between stepped-impedance ratios and the ratio of the two absolute bandwidths is obtained through rigorous analysis. Moreover, since the proposed filters can be synthesized with popular transmission lines and coupled lines that are very-well characterized, time-consuming full-wave simulation can be minimized. Along with the complete set of design equations, experimental results for transmission-line and coupled-line dual-band filters are provided that verify the proposed approach.

Miniaturized quasi-asymmetric forward-wave coupled-line coupler with arbitrary coupling level

A design method is demonstrated for quasi-asymmetric forward-wave coupled-line couplers. By loading a symmetric coupled line asymmetrically with shunt capacitors, a miniaturized forward-wave coupler is constructed with an arbitrary maximum coupling level. Most importantly, elimination of lengthy impedance transformers makes the method the most effective miniaturization method. Experimental results are provided for a 3-dB coupler with a miniaturization rate of 92.9% at 5 GHz.

Monostatic RCS Measurement for Dielectric Barrier Discharge Plasma

In this paper, reduction of monostatic RCS by DBD plasma is measured. For the calibration of monostatic RCS, S-parameters of two metallic plate in different sizes are used and the result is within 0.4 dB error. Metallic plate is put behind DBD plasma generator for measuring reduction of monostatic RCS by DBD plasma. To prevent arc discharge between metallic plate and DBD plasma generator, measurement is progressed spacing the interval between metallic plate and DBD plasma generator. As a result, maximum reduction of monostatic RCS is about 3 dB at 7.4 GHz.

Retrodirective Antenna Array Based on Double Conversion Mixer System and Its Application to Cancellation of Electromagnetic Reflections

In this paper, a retrodirective anatenna array system is proposed and the possibility of actively cancelling electro- magnetic waves based on this system is investigated. When a rectrodirective array system receives an electromagnetic wave, it can send waves in the direction of the incoming signal without prior knowledge of the direction. In applications to cancellation of radar signals, the system can generate and send signals to the radar so that it cancels the radar signals that are reflected back to the radar. In such a system, isolation between the input and output ports is a key factor that determines the effectiveness of cancellation. In this work, a dual-conversion mixer system is proposed to maximize the isolation. Since this minimizes the difference between the direction of reflection of radar signals and the trans- mission of cancellation signals, the effectiveness of cancellation is maximized. Experimental results for a metallic plate and metallic cylinder shows as much as 29-dB reduction in reflection for a 2×2 retrodirective array based on proposed dual-conversion mixer system, which verifies the proposed method of active cancellation.

An Inductive-Loading Method for Directivity Enhancement of Microstrip Coupled-Line Couplers

This letter demonstrates a series-inductive loading method for the directivity enhancement of microstrip coupled-line couplers. The method has an extreme structural simplicity that is based on two pairs of mutually coupled inductors. Furthermore, it shows little, if any, compromise in the performance, as verified with a 20-dB coupler at 2 GHz. Experimental results show a ±0.5-dB bandwidth of 42%, which is the widest reported for reactively loaded coupler. The demonstrated 20-dB directivity bandwidth of 147% is the highest reported for a 20-dB coupler. Most importantly, the peak directivity of 59.9 dB is the highest reported thus far, which is a clear indication of the effectiveness of the proposed method.

A Retro-Directive Array System for Reduction of Electromagnetic Wave Reflection

In this paper, a cancellation technique for electromagnetic waves is realized based on a retrodirective antenna array system. The system re-transmits a signal to the direction of the incoming signal, with the same frequency and opposite phase. For the experimental verification, a 2×2 retrodirective array system is designed and fabricated. Experimental results for a metallic cylinder show as much as 26-dB reduction in reflection.

Wideband suppression of spurious response for microstrip filters based on coupled lines of incommensurate lengths

This work demonstrates design methods that can achieve remarkable enhancement in the stopband response of microstrip coupled-line filters. The frequencies of resonance and/or the transmission zeros of a coupled-line section can be controlled by its length. Therefore, by constructing a filter with coupled lines of incommensurate lengths such that these frequencies do not overlap, substantial improvement in the stopband response can be obtained. Besides its compact structure and simple design procedure, an unprecedented performance is demonstrated experimentally in which the transmission level is maintained below −20 dB up to as high as 11.9 f 0 for a third-order filter, where f 0 is the center frequency.

A Filter Synthesis Method without Bandwidth Reduction for Dual-Band Filters Based on Coupled Lines

This paper proposes an improved filter synthesis method for dual-band filters based on coupled lines loaded with shunt stubs. The conventional design method relies on equality of the response of the conventional single-band filter and its dual-band counterpart at two frequencies. On the other hand, the proposed method is based on equivalence of the propagation constants and the image impedances of the two filters. Therefore, the proposed method does not suffer from bandwidth reduction phenomena, which requires complex compensating process in the conventional method. Also, the alternative design parameters provided by the demonstrated method enable to construct dual-band filters with more flexibility. For experimental verification, a Chebyshev type dual-band filter with center frequencies at 1 GHz and 3.5 GHz is designed and fabricated. The measured results are in excellent agreement with the full-wave simulated results.