Bierng-Chearl Ahn

A Small and Lightweight Antenna for Handheld RFID Reader Applications

This letter presents a circularly polarized antenna suitable for handheld radio frequency identification (RFID) reader applications. The proposed antenna consists of four meandered monopole elements fed by a series feed network, each segment having an equal magnitude and a successive 90° phase difference. The monopole elements and the feed network are created on two separate printed circuit boards. Four coaxial lines are used to connect the feed network to the monopoles. Short-circuited tuning stubs are employed for impedance matching. A prototype antenna measuring 45 × 45 × 9 mm3 and weighing 13 g is designed, fabricated, and tested. Measurements show that the fabricated antenna has at 919 MHz a gain of 2.2 dBic, a 3-dB gain beamwidth of 150°, and a 3-dB axial-ratio beamwidth of 146°.

A New Dual-Polarized Gap-Fed Patch Antenna

In this paper, a new compact dual-polarized microstrip patch antenna is proposed. The patch is of rectangular shape and fed by a gap between the patch edge and a microstrip open end. Gap feeding at the edge of a rectangular patch antenna is proposed for the first time in this paper. This method of feeding occupies a negligible space compared to other feeding methods such as a quarter-wave transformer feeder, an inset feeder, a proximity coupler, and an aperture-coupled feeder. Dual-polarized radiation is realized by feeding a rectangular patch with two orthogonal gaps. First, a single-polarized patch is designed. The impedance matching property of the gap is analyzed using an equivalent circuit. Next, starting from dimensions of the single-polarized patch, a dual-polarized patch antenna is designed by optimizing the patch length and gap width. The designed antenna is fabricated and tested. The fabricated antenna has reflection coefficient less than −10 dB, port isolation greater than 30 dB, over 14.5–15.2 GHz, and a gain of 6.2 dBi at 14.9GHz.

A Conical-Cylindrical Monopole Antenna

In this paper, a monopole antenna of conical-cylindrical compound shape is presented. The conventional circular conical monopole antenna is modified by placing a cylinder at the top of the inverted cone. The cylindrical portion is useful in the wideband impedance matching, in adjusting the antenna gain in the horizontal direction, and in reducing the cone diameter. The dependence of the antenna performance on various geometric parameters is investigated using a commercial electromagnetic simulation software, from which an optimum design of the antenna is derived. The diameter of the circular ground plane is minimized to 1/5 wavelength at the lowest operating frequency. The antenna proposed in this study shows a reflection coefficient less than ?10 ㏈ and a 1～6 ㏈i gain over 3～20 ㎓ frequencies. The antenna shows a circular-symmetric radiation pattern in the horizontal plane and a null-free pattern in the vertical direction over the whole operating frequency range.

A Compact GPS Antenna for Artillery Projectile Applications

This letter presents a compact antenna suitable for the reception of GPS signals on artillery projectiles over 1.57-1.60 GHz. Four inverted-F-type elements are excited by a series feed network in equal magnitude and successive 90° phase difference. The shape and form factor of the antenna is tailored so that the antenna can be easily installed inside an artillery fuze. Measurements show that the proposed antenna has a gain of 2.90-3.77 dBic, an axial ratio of 1.9-2.86 dB, and a reflection coefficient of less than -10 dB over 1.57-1.62 GHz.

A NEW DUAL-POLARIZED HORN ANTENNA EXCITED BY A GAP-FED SQUARE PATCH

A new dual-polarized horn antenna fed by a microstrip patch is proposed. The patch is excited in two orthogonal polarizations by small gaps between the patch edge and the microstrip open end. A horn antenna operating at 14.9GHz is designed, fabricated and tested. Measurements show that the horn has a re∞ection coe-cient of less than i10dB, and a port isolation greater than 30dB, over 14.6{ 15.2GHz, and a gain of 12.34dBi and 10-dB beamwidths of 87 - and 88 - at 14.9GHz.

New Design Method for a Dual band Waveguide Iris Polarizer

In this paper, we present new design method for a square iris polarizer to be used in dual-band (Ka-band; 20.8 ~ 21.2 GHz, 30.6 ~31 GHz) antenna feeds. To act principles for a square iris polarizer, design concept, design method are proposed and Ka-band polarizer is designed using the commercial software HFSSreg The designed polarizer has less than 30 dB return loss and less than 0.3 dB axial ratio in all operation band.

Two-Element Conformal Antenna for Multi-GNSS Reception

This letter presents a two-element conformal antenna for receiving the global positioning system L1, L2, and GLONASS L1 signals for precision artillery applications. The antenna consists of two stub-loaded shorted conformal patches fed by coaxial cables and a stripline power combiner. The patch is realized on a cylindrical polymer substrate wrapped around an artillery fuze body. Two patches are placed 180° apart and combined to realize an omnidirectional pattern. The fabricated antenna shows good Global Navigation Satellite System signal receiving performance.

Design of a w-band monopulse comparator based on E- and H-plane waveguide couplers

In this paper, we present the design of a W-band waveguide monopulse comparator based on E- and H-plane couplers. E- and H-plane couplers are of 180-degree 3-dB type and consisted of a coupling section and dielectric-slab phase delayer. A monopulse comparator is realized using two E- and two H-plane couplers in tandem. The designed comparator shows amplitude balance within ±0.5 dB and phase balance within +4/−8 degrees, reflection coefficient less than −15 dB and isolation greater than 20 dB at 90–98 GHz.

Evaluation of Safety for the 900MHz RFID Reader of Defense Ammunition Management System

The received power level in the bridgewire of the military ammunition in the close proximity of a mobile RFID reader is analyzed. The electric detonator is modelled as a receiving antenna and its gain, directivity and input impedance are evaluated using a commercial electromagnetic simulation software. The near-field coupling between a half-wave dipole antenna and the 105/120-mm tank ammunition detonator is measured and compared with the theoretical prediction at 900 MHz. Based on the measurement and theory, the safety of the 900 MHz passive RFID system for defense ammunition management is discussed.

A New Dual Circularly Polarized Feed Employing a Dielectric Cylinder-Loaded Circular Waveguide Open End Fed by Crossed Dipoles

This paper presents a new dual circularly polarized feed that provides good axial ratio over wide angles and low cross-polarized radiation in backward direction. A circular waveguide open end is fed with two orthogonally polarized waves in phase quadrature by a pair of printed crossed dipoles and a compact connectorized quadrature hybrid coupler. The waveguide aperture is loaded with a dielectric cylinder to reduce the cross-polarization beyond 90 degrees off the boresight. The fabricated feed has, at 5.5 GHz, 6.33-dBic copolarized gain, 3-dB beamwidth of 106°, 10-dB beamwidth of 195°, 3-dB axial ratio beamwidth of 215°, maximum cross-polarized gain of −21.4 dBic, and 27-dB port isolation. The reflection coefficient of the feed is less than −10 dB at 4.99–6.09 GHz.