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Novel broadband monopole antenna designs with dual-band circular polarization (CP) are presented. The proposed antenna comprised of a ground plane embedded with an inverted-L slit, which is capable of generating a resonant mode for broadband impedance-bandwidth, and excites two orthogonal E vectors with equal amplitude and 90[degrees] phase difference (PD) for radiating left-hand circular polarization (LHCP) at 2.5 GHz and right-hand circular polarization (RHCP) at 3.4 GHz. A bevel is cut in the rectangular radiator to increase the impedance-band-width. The measured result of the impedance-bandwidth is about 4.46 GHz from 2.12 to 6.58 GHz; the 3-dB axial ratio (AR) bandwidths are about 150 MHz at the lower band (2.5 GHz) and 230 MHz at the upper band (3.4 GHz). Furthermore, embedding an I-shaped slit in the rectangular radiator and adding an I-shaped stub in the ground plane, the impedance-bandwidth can be further increased to 6.30 GHz (2.17-8.47 GHz), and the 3-dB AR-bandwidth at the upper band is greatly enhanced from 230 to 900 MHz. Index Terms--Axial ratio (AR), broadband antennas, circular polarization (CP), monopole antennas.

This paper presents a novel small differentially-fed open-slot antenna for diversity of the operated frequency and circular polarization. The proposed antenna structure, which consists of an L-shaped open slot and two bent feeding lines, provides two separate effective bandwidths. The proposed antenna achieves the operation bandwidths of a global positioning system (GPS) and satellite digital audio radio (SDAR) service system. To excite the even and odd modes for bandwidth enhancement, a rectangular patch was embedded in the vertical segment of the L-shaped open slot, thereby forming a coplanar-waveguide topology. An additional rectangular patch was placed above the open slot to increase the interport isolation performance between the two feeding ports. After optimization, the measurement results indicated that the final open-slot antenna provided −10-dB reflection coefficient (S11) bands from 1.29 to 1.70 GHz for the GPS operation and from 2.09 to 2.56 GHz for the SDAR application. Measured 3 dB axial-ratio bandwidths of the proposed structure were 410 MHz (28.5%) from 1.23 to 1.64 GHz and 430 MHz (18.4%) from 2.12 to 2.55 GHz for right- and left-hand circular polarization, respectively. [ABSTRACT FROM AUTHOR]

A new technique is proposed to increase the bandwidth (BW) of a Z-like slot antenna for operation at 2.4 GHz and 5 GHz, over the industrial-scientific-medical (ISM) bands and the Hiperlan2 bands. By splitting two side slots of the Z-like slot antenna into two or three fingers, several additional resonances can be created. After careful optimization of the geometrical parameters of the antenna, the resonances are merged and thus a wide impedance bandwidth is obtained. Index Terms--Double-slot, symmetrically tuning stub, triple-slot, Z-like slot.

This paper describes a two-directional linear scanned design by integrating a short leaky-wave antenna (LWA) with aperture-coupled patch antenna arrays. This architecture proposes a technique not only having the advantage of suppressing the backlobe due to the reflected wave in the short LWA but also producing two separate linearly scanned beams, each of them radiating in a different region of space (in both the front side and backside of the LWA). In this design, most of the reflected wave of the short LWA is coupled to the patch antenna arrays on the backside of the substrate. The phase of this coupled signal to each antenna element is adjusted by tuning the individual phase shifter in order to control electronically the patch antenna main beam in the cross plane (x < 0). Meanwhile, on the front side, the main beam of the short LWA can be simultaneously scanned in the elevation plane (x > 0) by changing the operating frequency. Hence, the two linear beam-scanning radiation patterns of individual direction can be created independently, including a narrow beam in the elevation plane (xy plane at x > 0) at the front side and a broadside beam in the cross plane (xz plane at x < 0) on the backside. The measured results show that the reflected wave of the short LWA in the proposed design is suppressed 8 dB as compared with a traditional short LWA without the aperture-coupled antenna arrays at 10.5 GHz. As a result, this novel architecture provides more flexibility both in the upward elevation plane (H plane) and the downward cross plane (backside-E plane) for possible beam-scanning applications in microwave communications and remote identification. Index Terms--Aperture-coupled patch antenna arrays, phase shifter, reflected wave, varactor diode.

A novel two-beam scanning active leaky-wave antenna (LWA) has been developed. This LWA with a two-terminal feeding microstrip line structure is integrated with a varactor-tuned X-band high-electron mobility transistor (HEMT) voltage-controlled oscillator (VCO). The signal of the VCO is injected via a T-divider into the radiating element. To excite the first higher order mode, the designed antenna is fed asymmetrically at both ends of the microstrip line. Compared with single-terminal feeding leaky-wave antennas, this configuration offers the advantages of dual-direction and suppression of the reflected wave caused by the open end of the radiating element. The scanning angle is steered over a range of 24-46 degrees for the right beam and 128-150 degrees for the left beam. The Effective isotropic radiated power (EIRP) is calculated to be 17.5 and 16.67 dBm at 10.4 GHz, respectively. The measured return loss S(sub 11) is less than -10 dB in the range of 9-11.5 GHz. The transmission coefficient S(sub 21) indicated that the power radiates into the space. Index Terms: Leaky-wave antennas, microstrip transmission lines, printed antennas, scanning antennas.