Jong-Ig Lee

Resonant Transmission of an Electrically Small Aperture with a Ridge

A resonant transmission of an electrically small aperture with a ridge in a conducting plane is analyzed. It is an example of resonant transmission and the ridge inserted at the center line of the electrically small aperture resonates it by increasing an equivalent capacitance of the aperture. At resonance condition, the transmitted power through the aperture can be significantly enhanced compared to that at off-resonance. It is found that the transmitted power at the resonance condition converges to the transmission cross section of the aperture regardless of its size or shape. In addition, the electric and the magnetic fields distributions on the aperture with and without the ridge are compared to facilitate the understanding of the resonant behavior.

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.

Modified Series-Fed Two-Dipole-Array Antenna With Reduced Size

In this letter, a modified series-fed two-dipole-array (STDA) antenna with reduced size is proposed for mobile communication applications. The proposed antenna consists of two modified dipole elements with different lengths and a modified ground plane, and these are serially connected through a coplanar strip (CPS) line. To reduce the lateral size of a conventional STDA antenna, rectangular patch-shaped top loading is employed for the two dipole elements, and a grooved ground plane is used by adding a patch at both ends of the ground plane. Tapered transitions are also used between the top-loading patches and CPS lines to improve the impedance matching of the antenna and, therefore, to increase the gain. A proposed antenna covering a frequency band of 1.7–2.7 GHz with a gain

Transmission Through a Narrow Slot in a Thick Conducting Screen

>

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

5 dBi is designed and fabricated on an FR4 substrate. The total width of the fabricated prototype of the proposed antenna is reduced by approximately 14.3% compared to the conventional STDA, and it presents a 49.7% bandwidth in the range of 1.68–2.79 GHz and a stable gain of 5.86–6.13 dBi, which is similar to that of the conventional STDA antenna. Moreover, a front-to-back ratio is improved by 2.07–5.66 dB.

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

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.

Bandwidth Enhancement of Double-Dipole Quasi-Yagi Antenna Using Stepped Slotline Structure

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.

Series-fed two dipole array antenna using bow-tie elements with enhanced gain and front-to-back ratio

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.

Design of a simple three-element quasi-Yagi antenna with a broad impedance bandwidth up to 2.4 : 1

In this letter, a method to enhance the bandwidth of a double-dipole quasi-Yagi antenna using a stepped slotline structure is presented. A stepped slotline with different widths is employed in the coplanar stripline connecting the two dipoles in order to improve impedance matching over a wide frequency band. In addition, two parasitic strip directors are appended to the antenna to enhance the gain in the high-frequency region. A detailed design procedure for the proposed antenna is explained, along with a performance comparison of the input impedance, voltage standing-wave ratio (VSWR), and realized gain. To demonstrate the effectiveness of the proposed design method, a prototype antenna operating in the 1.60-3.60 GHz frequency range with a gain is designed and fabricated on an FR4 substrate. Experiment results show that the proposed antenna has the desired impedance characteristics with a frequency band of 1.59-3.64 GHz (78.4%) for a , and a stable gain of 6.4-7.4 dBi in the 1.60-3.60-GHz frequency range. Moreover, a measured front-to-back ratio is obtained.

Design of series-fed dipole pair antenna with split-ring resonator directors for dual-band operation

In this paper, a miniaturized series-fed two dipole array antenna with bow-tie elements (STBDA) for mobile communication applications is presented. In the proposed antenna, two bow-tie-shaped dipole elements of different lengths, which are serially connected through a coplanar strip line, are used instead of conventional straight strip dipole elements in a series-fed two dipole array (STDA) antenna. In addition, a planar ground reflector is replaced by a V-shaped one. A modified integrated balun consisting of a microstrip line and slot line is used to match the input impedance of the antenna to the 50  feed line. As the flare angle of the bow-tie dipole elements increases, the lowest operating frequency of the antenna is shifted toward the low frequency and the average gain is lowered. To validate the proposed approach, an STBDA antenna with a flare angle of 10° covering a frequency band ranging from 1.7 to 2.7 GHz and with a gain >5 dBi is designed and fabricated on an FR4 substrate. Its performance is compared with that of the STDA antenna. Experimental results show that the proposed antenna presents a 48.8% bandwidth in the range of 1.69–2.78 GHz, a stable gain of 5.8 to 6.3 dBi, and a front-to-back ratio (FBR) of 14–17 dB with a 10% size reduction in total width of the antenna. In fact, the characteristics of the half-power beam width and FBR of the STBDA are improved compared to those of the STDA.