Ji Hwan Yoon

Broadband Microstrip Reflectarray With Five Parallel Dipole Elements

A broadband microstrip reflectarray with five parallel dipole elements is proposed. Based on the operating mechanisms and the reflection phase characteristics of the five-dipole elements, the elements for the broadband reflectarray are designed. The radiation patterns of the five-dipole element reflectarray with the design frequency of f0 = 15 GHz are measured, and 1-dB gain bandwidth of 33.52% is achieved. The measured peak gain at f0 = 15 GHz is 31.4 dBi, which corresponds to the high aperture efficiency of 64.1%.

Low profile dual-band reflector antenna with dual resonant AMC

Dual-band reflector antenna with dual resonant artificial magnetic conductor (AMC) operating in WLAN band (2.4 GHz – 2.48 GHz, 5.15 GHz – 5.35 GHz) is proposed. Generally, a flat metal sheet is used with an antenna as a reflector to increase antenna gain. Since the reflection phase of a metal sheet is 180°, the antenna should be placed λ/4 away from the reflector to avoid destructive interference of the reflected wave from the metal sheet and the radiated wave from the antenna. If AMC with 0° reflection phase is used as reflector, the antenna can be closely placed to the AMC without destructive interference. There have been researches on low profile antennas using single layer AMC having 0° reflection phase in single band. In this paper, dual resonant AMC having 0° reflection phase in dual-band is designed as a reflector of dual-band reflector antenna. The dual resonant AMC is designed by adding another metallic patch-substrate layer on the conventional single layer AMC. Dual-band dipole is also designed with parasitic elements as a radiator. The height of the dual-band reflector antenna is 0.08λ which is one-third of 0.25λ, the height of reflector antenna using PEC. In addition, improvements of both gain and front lobe to back lobe ratio are achieved as a result of using dual resonant AMC which has surface wave suppression characteristic. To demonstrate improvement of gain and front lobe to back lobe ratio, comparison between the antenna using dual resonant AMC as reflector and the antenna using PEC as reflector for dual-band dipole is presented. Measured average peak gains of fabricated dual-band reflector antenna are 5.45 dB and 7.9 dB in 2.4 GHz – 2.48 GHz and 5.15 GHz – 5.35 GHz, respectively

Internal mobile antenna for LTE / GSM850 / GSM900 / PCS1900 / WiMAX / WLAN

An internal mobile antenna covering multiband for LTE (746 – 806 MHz), GSM850 (824 – 894 MHz), GSM900 (880 – 960 MHz), PCS1900 (1850 – 1990 MHz), WiMAX (3.4 – 3.6 GHz) and WLAN (5.15 – 5.85 GHz) frequency bands is proposed. In order to satisfy the operation at WLAN frequency band, a metal branch is placed near the feeding point. It is shown that the operation at low frequency bands (LTE / GSM850 / GSM900) can be achieved by increasing the length of the ground. Considering the size of the commercial mobile phones, more practical design which exhibits the similar effect that can be attained by increasing the length of the ground is proposed. The antenna was fabricated and its measured results of return loss and radiation patterns at each frequency bands are presented. FR4 substrate with relative permittivity of 4.4 was used. The overall size of the proposed antenna is 40 × 100 × 5 mm3.

Beam tilted base station antenna with electromagnetic gradient surface

A base station antenna for WCDMA band (1.920–2.170 GHz) application utilizing an electromagnetic gradient surface (EGS) is proposed. The EGS is applied as a reflector of 4 × 2 dipole array to tilt the beam with electrically without phase shifters on low-profile structure. Therefore the beam can be tilted with lower complexity, smaller size, and cheaper cost compared to conventional mechanical or electrical beam tilting methods. The EGS reflector is designed to provide 6° downward tilt angle of the main beam. The fabricated antenna exhibits 5.6 tilt angle with gain of 16.9 dBi at 2.045 GHz.

W-band microstrip reflectarray with double-cross element for bandwidth improvement

A broadband microstrip reflectarray is designed with the proposed element at W-band. The element consists of two cross-shaped resonators. Based on the analysis on the resonance mechanism of the double-cross element, the reflection phase of the element is controlled to achieve broadband characteristics by adjusting the dimensions of the element. Using the proposed element, a reflectarray with diameter of 50 mm is designed at f0 = 95 GHz. At f = f0, the peak gain of 31.73 dBi is achieved with aperture efficiency of 66.1%. Also, 1-dB gain bandwidth of 15.9% is achieved at W-band.

Reflection phase error analysis of microstrip reflectarrays

The radiation characteristics of a reflectarray antenna with element type combination is analyzed using reflection phase errors. The reflectarray is designed with the combination of three element types: square patch (SP), square ring (SR), and ring-loaded patch (RLP). The reflection phase error of the reflectarray is compared with those of two reflectarrays using single element types (SP and RLP, respectively). Compared to the reflectarrays with only SP elements or RLP elements, it is shown that the reflection phase errors are reduced with the combination of the element types at the target frequency, and thus improved radiation performances are achieved.

A breakdown study on the split horn antenna radiating high power pulses

Breakdown phenomena were studied when high power microwave pulses radiated to the atmosphere through the split horn antenna. The electrical characteristics of radiated signal such as power and pulse width strongly influence on the breakdown phenomena. This paper provides the information about threshold limitations of the antenna to radiate without breakdown phenomena.

Researches on radiation performance improvement of microstrip reflectarray antennas

The performances of reflectarrays are mainly determined by the characteristics of the elements. In this communication, various microstrip reflectarray elements to improve reflectarray performances are reviewed. Based on the figures of merits of the element (reflection phase range, sensitivity, and bandwidth) multi-layer elements, concentric multi-ring / patch element, and subwavelength elements are reviewed. Also, reflectarrays with elements having bandgap characteristic to reduce mutual coupling between the elements are reviewed.

Circular Dual Mode Horn Antenna(CDMHA) with Modified Aperture to Improve E/H-Plane Radiation Pattern Symmetry

In this paper, a circular dual mode horn with modified aperture is proposed to improve a E/H-plane radiation pattern symmetry of a conventional oversized circular dual mode horn. The proposed antenna consists of a feeding section, a mode generation section and a phase matching section which has aperture shape transition from circle to ellipse or rectangle to improve a E/H-plane radiation pattern symmetry. To compare the performances between the proposed antenna and the convenional circular dual mode horn, the conventional circular dual mode horn and the proposed circular dual mode horn with rectangular aperture are fabricated and researched at 15 GHz. The measured results show that the conventional circular dual mode horn has 3.394 dB difference while the proposed antenna has only 0.539 dB difference between E and H-plane radiation patterns within the -11 dB beamwidth() which is required beamwidth of the feed horn for the maximum aperture efficiency where f/d ratio of reflector antenna is 1.

A dual zeroth-order resonance antenna

In this paper, a dual ZOR antenna is demonstrated. The equivalent circuit model of general CRLH-TL is modified and the shunt inductances and capacitances that determine each of the ZOR frequencies are analyzed. The simulation result and the measured result of the fabricated antenna are presented, and the results are in good agreement. In addition, the ZOR frequencies with various lengths of the spiral-shaped slot of the patches are observed through simulation. From the result, it is verified that each of the ZOR frequencies can be controlled separately.