Jihwan Ahn

High-impedance Surface with Nonidentical Lattices

An HIS with nonidentical lattices and its reflection properties are investigated and discussed. Using a linear reflection phase gradient from pi/2 to pi/2 with pi10 step with unit cell index across face, the surface can steer a reflected beam to 20.2deg in thetas. The pattern of the electromagnetic field reflected with the normally incident y-polarized wave is analyzed and experimented.

Mode Conversion of High-Power Electromagnetic Microwave Using Coaxial-Beam Rotating Antenna in Relativistic Backward-Wave Oscillator

Mode conversion of high-power electromagnetic microwave (HPEM) was successfully accomplished using a coaxial-beam rotating antenna (COBRA) in an X-band relativistic backward-wave oscillator (RBWO). The mode conversion from the TM01 mode to the circularly polarized TE11-likeness mode was identified by both cold test and hot test. To observe whether mode conversion is effective or not, the radiation pattern of TE11-likeness mode by COBRA lens was compared with the case of the radiation pattern of TM01 mode using simple horn antenna. Their radiation patterns could be described by fluorescent lamps. The experimental results of radiation pattern measurements are shown to be in a reasonable agreement with the simulated one. The maximum value of RF output power appeared at the center of COBRA lens from the experimental results.

Artificial surface with asymmetric reflection properties

An artificial surface with asymmetric reflection properties is presented. By covering a metal ground plane with periodic metal-dielectric composite textures, the electromagnetic reflection properties can be altered. By tuning the individual lattice of a periodic mushroom-type texture to vary the surface impedance, a surface with graded reflection phases as a function of position can be designed. Applying a linear gradient in the reflection coefficient phase along the face, the proposed surface is electromagnetically inclined, even though physically flat. For the whole ranges of the incident angle, this metasurface reveals asymmetric reflection properties contrary to the law of reflection. The reflection patterns from the surface, the boundary condition, and the relation between the incident angle and the reflection angle are presented.

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.

Gain enhancement technique for an antipodal vivaldi antenna

A gain enhanced antipodal vivaldi antenna using parasitic elements for the frequency range of 2.0 to 10.6 GHz is proposed. Adding metals to flared slot between radiators and a substrate of the antenna, gain is increased while return loss is maintained. The dimension of parasitic elements is optimized to realize proper gain increment and radiation pattern improvement at the operating frequency bandwidth. The simulated results acceptably agree with measured ones that prove the validity of design procedure and ensure the profits of the modification.

The miniaturization and electrical performance improvement of base station array antenna with artificial magnetic conductor

In this paper, a base station array antenna with AMC in PCS frequency band is proposed. Due to the 0° reflection phase on AMC, the thickness (43.2 mm) of the base station array antenna can be reduced into 10.3 mm without the destructive interaction of forward/backward waves. In addition, due to the surface wave suppression by the high surface impedance on AMC, the FBR (24.8 dB) of the base station array antenna is improved into 35.9 dB. Therefore, it is demonstrated that the base station array antenna can be made as low profile and the electrical performance is highly improved by AMC.

A simple method for miniaturization of self-complementary Archimedean spiral antenna

This paper suggests a very simple method to miniaturize self-complementary Archimedean spiral antenna (SCASA). Just extending the ends of spiral arms within the outer radius of conventional spiral antenna can bring the lowest operating frequency down about 9%. Compared with the conventional design method, the proposed method leads to size reduction more than 17% despite the same operating frequency range.

Planar inverted F-antenna with suppressed harmonic

In this paper, a novel method to suppress harmonic component of PIFA is proposed. The spur-line is inserted between the feed and short line of PIFA and obstructs the feed line to suppress harmonic without induction of dual-band resonance. Additionally, partial ground is inserted the bottom side of radiator to improve the performance of suppression. The simulated and measured results show that the proposed method can suppress the harmonic component of PIFA without any distortion of operating band and can be used widely in many applications using PIFA.

Enhanced technique for miniaturization of wideband spiral antenna

This paper introduces miniaturization techniques of wideband spiral antenna. The lowest operating frequency of spiral antenna can be dropped approximately 9 ~ 21% by extended arms and outer ring without size expansion. Compared with the conventional spiral antenna, the size reduction of antenna area up to 37% can be achieved by the proposed technique.

Pattern reconfigurable antenna for Wireless LAN dual-band

A novel type of compact and printed pattern reconfigurable antenna for dual Wireless LAN application is presented. Dual band is realized by dipole and bow-tie antenna which is connected by a chip inductor. Also, each parasitic element as a reflector changes the direction of main beam. Results show good pattern reconfigurablity for WLAN dual band.