Soon Young Eom

Switchable Quad-Band Antennas for Cognitive Radio Base Station Applications

A novel antenna configuration for quad-band operation is presented. The quad-band antenna has a directional radiation pattern in four frequency bands, i.e., B1 (800-900 MHz), B2 (1.7-2.5 GHz), B3 (3.3-3.6 GHz), and B4 (5.1-5.9 GHz), covering all spectrums for existing wireless applications, such as GSM, PCS, WCDMA, WiFi, and WiMax. The operating frequency of the quad-band antenna can be adjusted by the use of a MEMS switch, making it suitable for cognitive radio applications. First a switchable quad-band antenna element is introduced. Then a two-element antenna array is developed to increase the antenna gain for base station applications featuring a gain value of about 9-11 dBi over all four frequency bands.

Design and Test of a Mobile Antenna System With Tri-Band Operation for Broadband Satellite Communications and DBS Reception

The tri-band mobile antenna system for broadband multimedia services in the Ka/K-band and a simultaneous direct broadcast service in the Ku-band has been developed. The radiating part of the antenna consists of a shaped dual reflector system and a tri-band feed of circular polarization. The low-profile offset main reflector has an aperture size of 60 cm 20 cm; therefore, a fan beam is formed which is sharp in azimuth and wide in elevation. The feed system contains a protruding dielectric rod for Ka/K-band and 2 2 active phased array. The latter provides the beam for Ku-band along with four fast electrical beams for stable satellite tracking. The new tracking algorithm based on a fusion technique involving various sensors and fast electrical beams has also been introduced. The antenna system was mounted on a large ship and a test car, and successfully operated via Koreasat-3.

Shaping of flat-topped element patterns in a planar array of circular waveguides using a multilayered disk structure. I. Theory and numerical modeling

An infinite planar array of stepped circular waveguides radiating through a multilayered disk structure, which is arranged above the waveguide apertures in order to shape the flat-topped element patterns, is analyzed. The analysis is based on modal representations for the fields in the partial regions and for the currents on the disks with subsequent application of the mode-matching method and Galerkins method for determining the modal coefficients used in the calculation of the array characteristics. The application of the algorithm is demonstrated by an array design that provides flat-topped element patterns of /spl plusmn/20/spl deg/ width in the main planes within a 5.6% frequency band. Outside the indicated band, the disk structure can cause sharp dips in the element patterns at the broadside, and some features of this effect are discussed.

Shaping of flat-topped element patterns in a planar array of circular waveguides using a multilayered disk structure. II. Experimental study and comparison

For pt.I see ibid., vol.51, no.5, p.1040-47 (2003). A symmetrical 19-element K/sub a/ band breadboard corresponding to the array considered in part I, as well as a similar X band breadboard with dipole exciters arranged in waveguides, are studied experimentally. In both breadboards the central ports are connected to microwave sources, while all the other ports are terminated with matching loads. The multilayered periodic structures placed above the waveguide apertures are composed of thin polymer films with conducting disks deposited by ion-beam. It is shown that the calculated and measured element patterns of the K/sub a/ band breadboard are in good agreement within the flat-topped main lobe. The edge effects and design elements explain some of the disagreement in the side lobe area. The measurement of the X band breadboard gives similar results, and confirms the desirable properties of the disk structures for application in limited-scan arrays.

Compact Broadband Microstrip Crossover With Isolation Improvement and Phase Compensation

In this letter, we present a broadband microstrip crossover structure in two different configurations. Both structures have compact size, i.e., less than 10 mm × 10 mm. Across the measured band from dc to 10 GHz, the structure 1 has less than 1 dB insertion loss, more than 20 dB return loss and at least 23.3 dB isolation. Within the same band, the structure 2 has less than 1 dB insertion loss, more than 22 dB return loss and at least 18.9 dB isolation. Phase difference between two paths in both structures is kept in less than 5 °.

High gain bidirectional microstrip dipole antenna

In this paper, we propose a new bidirectional stacked microstrip dipole antenna with a multilayered disk array structure (MDAS) for a high gain WLAN application. In the proposed structure, two identical MDAS are attached on the both sides of a dipole exciter which is composed of two linearly polarized stacked microstrip patches placed back to back and fed with balanced input power using unbalanced-to-balanced (balun) transformer. The proposed antenna structure where MDAS has overall height of 1λ0 was designed and fabricated to operate at 2.44GHz. The maximum gain of the antenna was found to be 10.29dBi with highly symmetric bidirectional beam pattern in both E- and H-plane.

A RECONFIGURABLE ACTIVE ARRAY ANTENNA SYSTEM WITH THE FREQUENCY RECONFIGURABLE AMPLIFIERS BASED ON RF MEMS SWITCHES

In this paper, a frequency reconflgurable active array antenna (RAA) system, which can be reconflgurable at three difierent frequency bands, is proposed. The proposed RAA system is designed with a novel frequency reconflgurable front-end ampliflers (RFA) with the simple reconflgurable impedance matching circuits (RMC) with the MEMS switches. With the MEMS switch, the RFA is realized without any performance sacriflce especially linear characteristic. The proposed RAA antenna system is composed of the RMC, RFA with the RMC, 2 £ 2 array of reconflgurable antenna elements (RAE), as well as a reconflguration control board (RCB) for MEMS switch control, and the validity of the proposed RMC, RFA, as well as RAA system which is presented with the experimental results.

A novel tracking control realization of phased array antenna for mobile satellite communications

This paper describes a realization of a tracking phased array antenna system for the shipboard station in X-band satellite communication. This antenna system is necessary to accurately track a target satellite due to the narrow beamwidth. This developed antenna has Tx and Rx antenna beams as well as tracking beam. These beams are independently steered electronically in elevation and mechanically in azimuth. However, a Korean target satellite will be launched into geostationary orbit after a few years. We verified the real-time tracking performance by means of transmission and reception of television broadcasting signal between the developed antenna system and satellite transponder simulator under operation of ship motion simulator. In addition, the measured results of antenna system are presented and discussed.

TRx stacked microstrip patch antenna with high isolation

This paper presents the use of a double spur-line band rejection filter (DSL-BRF) to improve port-to-port isolation of a TRx stacked microstrip patch antenna. The simple DSL-BRF has two different sideband suppression characteristics by tuning the separation between the end points of two spur-lines. A simple TRx stacked microstrip patch antenna designed to operate at Ku-band with downlink frequency band of 12.25 ~ 12.75 GHz and uplink frequency band of 14.0 ~ 14.5 GHz had inherent isolation of 17 dB within TRx-band. Isolation performance of the antenna was improved by more than 13 dB for Rx-band and 16 dB for Tx-band after introducing DSL-BRFs into Tx- and Rx-feed networks, respectively. Because the DSL-BRFs are compatible to be embedded in 50-Ohm transmission lines, the TRx antenna with filters are remained as in same size as the antenna without filters.

A Horn Antenna Design with Novel Waveguide Polarizer for Mobile Satellite Communications Applications

Conventional polarizers usually include complicated corrugations and lossy insertions such as an iris, septa and dielectric slab, causing performance degradation and fabrication difficulties. At high frequencies, such fabrication difficulties and lossy components are limiting factors to achieving low costs and high performance. In this paper, a novel waveguide-type polarizer with an oval shaped cross-section that is inclined at a ± 45° angle for right-handed and left-handed circular polarization is presented. Due to the oval cross-section, the polarizer can be easily fabricated by mechanical processing with considerable performance. The proposed polarizer structure is fabricated using a pyramidal horn with a square aperture. From measured results, it is confirmed that the horn antenna has a gain of 9.4 dBi at 30.5 GHz with 20 dB cross-polarization level. The return loss is below -15 dB from 28 GHz to 34 GHz, and the axial ratio bandwidth is about 18% at a 3-dB level. This horn antenna will be applied to a feeder design with electrical beam scanning for a reflector-based mobile satellite antenna terminal.