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A dipole antenna with a bent dumbbell shape was positioned above and horizontal to a metal reflector to improve peak gain and steering of the radiation pattern. A parasitic square patch etched on the bottom side of the dumbbell arms provided a feeding delay line for producing dipole radiation in the 3600 MHz band. For gain enhancement and beam reconfiguration, the height of the horizontal dipole and the metal reflector could be adjusted to generate constructive reflections in phase with the radiated waves. When a dipole antenna with a height equal to half a wavelength was installed above the metal reflector, it exhibited a tilted main beam of 48° and maximum gain reached 9.2 dBi. A multiple-input–multiple-output antenna with a pair of strip stubs was also investigated. Simulation and measurement results indicated that the proposed structure achieved good isolation. The antenna had an impedance bandwidth (VSWR ≤ 2) of approximately 19.0% (3146–3818 MHz) and a low coupling (S21) of less than −25 dB. In this band, the average gain enhancement approximated 5.1 dBi. [ABSTRACT FROM AUTHOR]

A novel design for a radio-frequency identification (RFID) tag antenna mounted on a metallic plane is presented. The tag antenna has a rectangular radiating plate with a Z-shaped slot, which enables it to function like a half-wavelength slot resonator and a dipole-type ground radiator. A conjugate match to an Alien Higgs-3 chip with an impedance of 8 – j142 $\Omega$ at 925 MHz is obtained by etching a half-wavelength slot resonator in the center of the rectangular radiating plate (120 \text{ mm}\times60\text{ mm}). The tag antenna resistance and inductive reactance can be matched to the desired chip impedance by simply tuning the length and width of the Z-slot resonator. The space between the half-wavelength resonant radiating plate (dipole-type ground radiator) and the metallic plane enhances the antenna gain by increasing the reflection from the metallic plane. A horizontal electric dipole placed above the perfectly flat electric metallic plane enables a maximum gain of 8.7 dBi over a short distance, which is fourfold higher than that of an isolated half-wavelength dipole. Tests of an RFID reader with an effective isotropic radiated power of 4.0 W showed that the maximum read coverage of the proposed tag antenna mounted on a metallic plane exceeded 10 m. Measurement data were in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

A novel miniature folded square patch antenna is proposed and developed for Global Positioning System (GPS) receivers. Four different lengths of meander strips connected to the four edges of the square patch of a single coaxial-feed square patch antenna are folded to obtain a circularly polarized antenna. Properly positioning the coaxial feed on the square patch excites two orthogonal resonant modes with a 90^\circ phase difference and achieves a pure circular polarization. Conventional antennas for roof-mounted vehicle communication devices use commercially available ceramic corner-truncated patches whereas the proposed GPS antenna is designed to use a less expensive and more compact FR4 patch. Experiments also showed that mounting the proposed GPS antenna in different locations on the roof of a vehicle had little effect on circular polarization radiation. The fabricated prototype revealed an impedance bandwidth of 2.1% and a 3-dB axial-ratio bandwidth approximating 0.76% at a GPS frequency of 1575 MHz. Experiments confirmed that the characteristics of the proposed antenna were consistent with the simulation results. [ABSTRACT FROM PUBLISHER]

A novel, compact X-shaped slotted square-patch antenna is proposed for circularly polarized (CP) radiation. A cross-strip is embedded along the X-shaped slot for a novel proximity-fed technique to produce CP radiation in the UHF band. In the proposed design, two pairs of T-shaped slots are etched orthogonally on the square patch, connected to the center of the X-shaped slot for CP radiation and antenna size reduction. Proper adjustment of the length and coupling gap of the cross-strip will excite two orthogonal modes with 90^\circ phase difference for good CP radiation. Simulated and measured results indicate that the proposed structure can achieve circular polarization. A measured impedance bandwidth (VSWR\leq 2) of about 3.0% (909–937 MHz) and a 3-dB axial-ratio (AR) bandwidth of about 1.3% (917–929 MHz) were obtained. [ABSTRACT FROM AUTHOR]

An UHF RFID tag antenna which is comprised of a trapezoidal loop and a dual-dipole radiator with an L-slit for omnidirectional polarized reading patterns is designed, fabricated and measured. For a conjugate match to the Monza 3 microchip impedance of 44-j231 at 915 MHz, an orthogonal dual-dipole tag antenna (91 mm \times 91 mm) with L-slit on each dipole arm was designed. Simple size adjustments of the L-slit and dipole radiator of the antenna allow for easy control of the antenna resistance and inductive reactance, from which the microchip impedance requirement may be readily satisfied. The read range of the prototype attached on a different glass can reach more than 9 m, which has been tested for an RFID reader with 4.0 W of EIRP. Good tag sensitivity and near omnidirectional radiation patterns were obtained in the desired frequency band. [ABSTRACT FROM PUBLISHER]

To produce circularly polarized (CP) radiation, a small, double-sided, crossed dipole antenna with two metal strips loaded for phase delay is proposed. The proposed antenna uses two orthogonal, unequal length dipoles, connected in parallel to a coaxial probe feed. It requires no matching network. The required power and phase relationships are obtained by proper choice of dipole lengths and the metal strips attached to them. The antenna also operates at its half wavelength orthogonal modes, for the UHF band. The phase delay metal strip generates the two resonant modes for CP radiation. Simulated and measured results indicate that the crossed dipole structure can produce CP radiation. An impedance bandwidth (VSWR \leq 2) of about 11.8% and a 3-dB axial-ratio (AR) bandwidth of about 3.3% around the center frequency of 925 MHz were measured. [ABSTRACT FROM PUBLISHER]