Young-Ki Cho

A New Ultra-wideband Microstrip-to-CPS Transition

A novel ultra-wideband microstrip-to-CPS (coplanar stripline) transition has been developed. The transition is designed to provide the field and impedance matching between adjacent transmission lines. The proposed design is applicable to substrates with any dielectric constant. The transition provides the balun role as well as the impedance transformation. The fabricated transition in back-to-back configuration provides the insertion loss less than 1 dB per transition and the return loss better than 10 dB for frequencies from 5.39 GHz to over 40 GHz. In addition, a simulation study indicates that this transition can possess a 3 dB bandwidth of ~ 100 GHz.

Tapered Slot Antenna With Band-Notched Function for Ultrawideband Radios

A novel tapered slot antenna (TSA) with a band-notched function for ultrawideband (UWB) radios is proposed in this letter. By inserting an Archimedean spiral-shaped slot into a microstrip open-circuit circular stub of microstrip-slotline transition, a UWB operation with a notched frequency band can be obtained. Measured data for the optimized case show the bandwidth for the VSWR <; 2 to be 8.8 GHz (from 2.4 to 11.2 GHz) with a notched band frequency from 4.6 to 6.2 GHz. By inserting the resonance slot on the nonradiating part of the antenna, the proposed antenna is capable of avoiding the spatial-dependent bandstop characteristics. Also, the designed antenna has a small size of 50 × 50 mm2, which is a size reduction of 40% with respect to previous similar antennas.

Analysis for a dielectrically filled parallel-plate waveguide with finite number of periodic slots in its upper wall as a leaky-wave antenna

A dielectrically filled parallel-plate waveguide (PPW) with finite number of periodic slots in its upper plate is analyzed as a leaky-wave antenna structure for E-polarization case. The characteristics of the finite periodic structure such as input impedance matching, antenna efficiency, gain, and radiation pattern are investigated. In particular, phenomena such as total reflection and transmission occurring in the practical finite periodic structure, associated with the coupling point and the real solution (propagation constant), respectively, in the fast wave region observed for the infinite open periodic structure case, are described in detail.

An ultra-wideband microstrip-to-CPW transition

A new design for an ultra-wideband microstrip-to-CPW (coplanar waveguide) transition is presented. The proposed transition provides the field and impedance matching between adjacent transmission lines by ground shaping. Clear design guidelines are provided to determine the ground shape and the transition length. As design examples, two transition designs for substrates with low (2.2) and high (10.2) dielectric constants are presented. The fabricated transitions in back-to-back configuration provide insertion loss less than 0.7 dB per transition and return loss better than 10 dB for frequencies from 7 GHz to over 40 GHz and from DC to over 20 GHz, respectively.

Transmission Through a Narrow Slot in a Thick Conducting Screen

In this communication, the electromagnetic transmission problem through a narrow slot in a thick conducting screen is dealt with by using the modal expansion Galerkins method in the space domain. The main concern centers on the condition for maximum power transmission through the slot in the thick conducting screen. Transmission cavity resonance phenomena, which are observed only when the resonance cavity is formed along the longitudinal direction inside the slot region in the thick conducting screen, are investigated. These transmission resonance peaks occur at particular values of the screen thickness, that is, when the thickness of the conducting screen is a little less than an integer number of half guide wavelength of the fundamental guided mode inside the slot region. It is also found that there is another type of transmission resonance phenomenon occurring regardless of the screen thickness. The latter type of transmission resonance is observed only when transverse resonance condition holds and can be taken as a generalization of the slot resonance in a thin conducting screen to that in an arbitrarily thick conducting screen.

A simplified design of quasi-Yagi antennas using the new microstrip-to-CPS transitions

A new, systematic, simplified design procedure for quasi-Yagi antennas is presented. The design is based on the simple impedance matching among antenna components: i.e., transition, feed, and antenna. This new antenna design is possible due to the newly developed ultra-wideband transition. As design examples, wideband quasi- Yagi antennas are successfully designed and implemented in Ku- and Ka-bands with frequency bandwidths of 53.2% and 29.1%, and antenna gains of 4-5 dBi and 5.2-5.8 dBi, respectively. The design method can be applied to other balanced antennas and their arrays.

Design of bow-tie-type UWB antennas using an ultra-wideband balun

A new UWB antenna in bow-tie-type has been designed and implemented by utilizing the new ultra-wideband balun. In order to reduce antenna size, the balun is bended without sacrificing the balun performance. The fabricated antenna provides the operating frequency ranges from 3.2 to 11.2 GHz covering for the whole UWB frequency. The antenna maintains gains from 2.5 - 4.9 dBi for the operating frequencies with quasi- omni directional radiation patterns.

A Novel Epsilon Near Zero Tunneling Circuit Using Double-Ridge Rectangular Waveguide

In this paper, an epsilon near zero (ENZ) tunneling circuit using a double-ridge rectangular waveguide (RWG) is proposed for the miniaturization of a waveguide component. The proposed ENZ channel and is located in the middle of the input-output RWG (IORWG). The ratio of the height to the width of the channel waveguide is very small compared to the IORWG. By properly adjusting the ridge dimensions, the tunneling frequency of the proposed ENZ channel can be lowered to near the cut-off frequency of the IORWG. For the proposed ENZ tunneling circuit, the approach adopted for extracting the effective permittivity, effective permeability, normalized effective wave impedance, and propagation constant from the simulated scattering parameters was explained. The extracted parameters verified that the proposed channel is an ENZ channel and electromagnetic energy is tunneling through the channel. Simulation and measurement results of the fabricated ENZ channel structure agreed.

Electromagnetic coupling mechanism to a conducting strip through a narrow slit in a parallel-plate waveguide

The problem of electromagnetic coupling to a conducting strip through a narrow slit in a parallel-plate waveguide (PPW) is reconsidered with an emphasis on the radiative coupling mechanism. Two different types of coupling are discussed: cavity and parasitic. The maximum coupled power in both cases is observed to be almost the maximum available power from the slit (half of the incident power in the PPW), even though the two types of coupling are quite different from each other in their equivalent circuit representation or coupling mechanism. The similarity between the problem of cavity-type coupling and the previously reported transmission resonance problem through a narrow slit in thick screens is also described in connection with the aperture-body resonance phenomenon.

A Study on the Coupling of a Flanged Parallel-Plate Waveguide to a Slit In a Nearby Conducting Screen for Near-Field Scanning Microscopy

The problem of electromagnetic coupling between a slit fed by a flanged parallel-plate waveguide(PPW) and a slit in an infinite nearby conducting screen parallel to the flanged ground conductor is studied as a simplified problem for a near-field scanning microscopy(NSM). The method of moments isused to solve the coupled integral equations for the electric field distributions over the slits. The performance of the proposed apparatus as an NSM is tested by examining the effects of some geometrical parameters on the equivalent slit admittance and coupled powers through the slits.