Geum-Chul Hwang

The design of a broadband waveguide magic-T was accomplished using a genetical swarm optimization (GSO) technique. A multi-stepped, off-centered conducting cone was used to enhance the bandwidth performance of the conventional magic-Ts. The geometrical parameters of the stepped cone were optimized by GSO, and the optimized magic-T for X-band application was fabricated and tested. Measured scattering parameters are shown to be in good agreement with the computed results. The optimized design exhi

A broadband circularly-polarised fractal antenna is proposed, designed, and tested. The concept of a novel Spidron fractal system is employed to achieve both broadband and circular-polarisation characteristics. Presented is the first known application of a Spidron fractal to antenna design. A simple 50 Ω microstrip line is used to excite the Spidron-shaped slot. The total dimensions of the fabricated antenna are 40×40×1.52 mm3. The measured −10 dB return loss bandwidth and the 3 dB axial ratio b

The design of a wideband circularly polarized pixelated dielectric resonator antenna using a real-coded genetic algorithm (GA) is presented for far-field wireless power transfer applications. The antenna consists of a dielectric resonator (DR) which is discretized into 8 × 8 grid DR bars. The real-coded GA is utilized to estimate the optimal heights of the 64 DR bars to realize circular polarization. The proposed antenna is excited by a narrow rectangular slot etched on the ground plane. A proto

In this article, a high gain and compact 4 × 4 circularly polarized microstrip patch antenna array is reported for the data transmission of the next-generation small satellite. The radiating element of the circularly polarized antenna array is realized by the conventional model of the patch with truncated corners. A compact two-stage sequential rotational phase feeding is adopted that broadens the operating bandwidth of the 4 × 4 array. A small stub is embedded in the sequential rotational feed,

Radiation from a ferrite-filled waveguide with multiple thick slits is investigated. The Fourier transform and mode matching are utilized to obtain a rigorous solution. The effect of the ferrite linewidth is included to account for the magnetic loss of ferrite. The maximum beam steering ratio 4.33/spl deg//100 oe is achieved with the magnetic bias field ranging from 1000 to 1400 oe. The ferrite-filled rectangular waveguide with nine slits is fabricated and its radiation patterns are measured at

A novel broadband polarization twist reflector using a meander-grooved conducting plane is proposed in this study. A genetical swarm optimization (GSO) technique was utilized to achieve the broadband design of the meander-grooved polarization twist reflector for Ku-band applications. Measured reflection coefficients are shown to be in good agreement with the simulated results. The optimized design exhibits a 17 dB suppression bandwidth over 12.5% (15.48-17.55 GHz). The measured polarization twis

Abstract A planar meander‐line monopole antenna was designed for wireless Universal Serial Bus (USB) dongle devices. The proposed antenna shows dual‐wideband resonant characteristics and supports the WiBro, Bluetooth, WLAN, WiMAX, and S‐DMB (Satellite Digital Multimedia Broadcast) services. The designed antenna measures 19 × 50 × 1 mm 3 , which is suitable for compact USB dongles. The measured 2:1 bandwidths of the voltage standing wave ratio are 18.1% (2.26–2.71 GHz) and 16.4% (5.09–6.0 GHz). T

A dual-wideband fractal monopole antenna for handheld terminals is proposed. A modified half-Sierpinski gasket patch is used to cover GPS, DCS1800, PCS1800, UMTS, IMT-2000, WiBro (Wireless Broadband Internet Service), Bluetooth, S-DMB (Satellite Digital Multimedia Broadcast) and WLAN bands. The proposed antenna exhibits two wideband frequency resonances. The measured −10 dB reflection bandwidths for two resonant frequencies are 55% (1517–2670 MHz) and 12.6% (5135–5828 MHz). The radiation charact

In this communication, a wideband circularly polarized (CP) Spidron fractal microstrip antenna is proposed based on the concept of embedded structures. The proposed antenna is excited by a tapered microstrip feedline. A wide 3 dB axial ratio (AR) bandwidth of 28.81% (3.09–4.13 GHz) is obtained by merging the CP bands of the Spidron fractal slot and patch antennas. In addition, a measured −10 dB reflection bandwidth of 47.25% (2.57–4.16 GHz) is reported. The measured results are in reasonable con

The design of a 112-element millimeter-wave waveguide slot array antenna to reduce the grating lobe level is presented. A hybrid-phase feeding technique combining a cophase feed and an alternating-phase feed is applied to facilitate the suppression of grating lobes. In addition, a stepped feed waveguide and offset coupling slots aligned in a line are employed to realize a tapered aperture distribution. As a result, grating lobe suppression of 8.1 dB was achieved on the diagonal planes compared t

A planar super‐wideband (SWB) antenna fed by an asymmetric coplanar strip is proposed, fabricated, and tested. The antenna consists of a hexagonal loop strip in which a signal strip is prolonged, curved, and shorted to a ground plane to facilitate SWB characteristics. In addition, by adding a boomerang‐shaped strip to the ground plane, the effective electrical length is increased, thereby decreasing the lowest operating frequency. The simulated results show that the proposed antenna exhibits a −

A shared-aperture dual circularly-polarized Spidron fractal slot antenna is presented. The proposed antenna, which includes a Spidron fractal slot with an L-shaped slit and a cutting corner, is fed by two individual excitation ports. The left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP) at the same operating frequency band are simultaneously achieved using the even and odd modes in a coplanar waveguide transmission line. The measured –10 dB reflection and 3 d

This paper presents the performance improvement of a circularly polarized (CP) retrodirective array (RDA) through the suppression of mutual coupling effects. The RDA is designed based on CP Koch-shaped patch antenna elements with an inter-element spacing as small as 0.4 λ for a compact size ( λ is the wavelength in free space at the designed frequency of 5.2 GHz). Electromagnetic band gap (EBG) structures are applied to reduce the mutual coupling between the antenna elements, thus improving the

This paper presents a low-profile log-periodic meandered dipole array (LPMDA) antenna with wideband and high gain characteristics. The antenna consists of 14 dipole elements. For compactness, a meander line structure is applied to each dipole element to reduce its physical length. As a result, a compact and wideband LPMDA antenna is realized, exhibiting a wide impedance bandwidth of 1.04-5.22 GHz (ratio bandwidth of 5.02:1) for | S 11| < -10 dB. To enhance the antenna gain performance while main

In this paper, a microstrip-fed broadband circularly polarized (CP) slot antenna is presented. CP operation can be attained simply by embedding an S-shaped strip. By loading with a multiple-circular-sector patch, which consists of 12 circular-sector patches with identical central angles of 30° and different radii, the 3 dB axial ratio (AR) bandwidth is significantly broadened. To validate the performance of the proposed antenna, an antenna prototype is fabricated and tested. The fabricated anten