This communication presents a design of a new compact circularly polarized (CP) slot antenna fed by a microstrip feedline. The 3-dB axial ratio band can be achieved by simply protruding a horizontal stub from the ground plane toward the center of the wide slot (WS) and then feeding the WS with a microstrip feedline positioned to the side of the WS, underneath the protruded stub. The feedline and metallic stub are perpendicular to each other, and they resemble a T shape when viewed from the top. The proposed antenna is fabricated with an area of $25 \times 25\;{\rm mm}^{2}$ . Measurement results show that the antenna attains an ${\rm S}_{11}\le-10\;{\rm dB}$ impedance matching bandwidth of 90.2%, from 3.5 to 9.25 GHz, and a broadband 3 dB-AR bandwidth of 40%, ranging from 4.6 to 6.9 GHz. A peak gain of 0.8–4.5 dBi is achieved within the AR band. The proposed antenna is suitable for circular polarization applications in C band.

A Novel Simple and Compact Microstrip-Fed Circularly Polarized Wide Slot Antenna With Wide Axial Ratio Bandwidth for C-Band Applications

A novel broadband CPW-fed circularly-polarized slot antenna with an open slot is presented. The broadband circular polarization can be achieved simply by opening the radiation slot at the lower left of slot. From the experimental results, the 3-dB axial-ratio bandwidth can reach as large as 1000 MHz (27% relative to the center frequency of 3700 MHz) which can cover the 3.3-3.8 GHz WiMAX band. In addition, the proposed design has the VSWR ≤ 2 impedance bandwidth of 5330 MHz (111% relative to the center frequency of 4795 MHz) which can cover the 2-6 GHz WiMAX band. The proposed antenna also has a peak antenna gain of about 5.3 dBic and gain variations can be less than 1 dBic for frequencies within the CP bandwidth.

Broadband CPW-Fed Circularly-Polarized Slot Antenna With an Open Slot

A novel compact ring monopole antenna with double meander lines is proposed for wireless local area networks (WLAN) applications in IEEE 802.11b/g/a systems. The designed antenna, fed by a 50 Ω microstrip transmission line, is only 32 mm in height and 16 mm in width. By introducing a horizontal and a vertical branched strips to a closed rectangular strip ring, the proposed antenna can generate two separate impedance bandwidths. Prototypes of the proposed antenna have been constructed and tested. The obtained impedance bandwidths reach about 12% for the 2.4 GHz band and 45.3% for the 5 GHz band, which meet the required bandwidth specification of 2.4/5 GHz WLAN standard. Also, good radiation performance and antenna gain over the two frequency ranges have been obtained.

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Compact ring monopole antenna with double meander lines for 2.4/5 ghz dual-band operation

A novel dual-band coplanar waveguide (CPW)-fed slot antenna with a C-shaped grounded strip is proposed for dual-sense circularly polarized radiation. The circular polarization in the lower band is achieved by the slots loaded in two opposite corners, and the C-shape grounded strip can offer a current path for the upper band. A rectangular tuning stub protruded into the slot from the signal strip of the CPW is used to obtain good impedance matching over the whole frequency band. Axial-ratio (AR) bandwidth can be significantly enhanced through tuning the horizontal length of the C-shaped grounded strip. The antenna has been investigated numerically and experimentally. Experimental results show that the antenna possesses the measured 10-dB return loss impedance bandwidth of 106.9% (1.01-3.33 GHz). The measured 3-dB AR bandwidths for the lower and upper bands can be up to 32.35% (1.41-1.96 GHz) and 5.6% (2.45-2.59 GHz), respectively.

Dual-Band Dual-Sense Circularly Polarized Slot Antenna With a C-Shaped Grounded Strip

A single-feed, cavity-backed, circularly polarized (CP) antenna is designed for wideband wireless applications. The antenna is made up of asymmetric crossed bowtie dipoles and achieves broadband characteristics in terms of impedance and 3-dB axial-ratio (AR) bandwidths. A double vacant-quarter printed ring with orthogonal asymmetric bowties is employed for CP radiation and then combined with slot-mode radiation to significantly enhance the CP operation bandwidth. Measurements of an optimized antenna prototype with an overall size of 0.88λ
 o
 × 0.88λ
 o
 × 0.23λ
 o
 at 2.4 GHz show that it can yield an impedance bandwidth of approximately 57% and a 3-dB AR bandwidth of approximately 51%. In addition, a unidirectional CP radiation pattern with a high broadside average gain of 9.6 dBic was achieved across the operating bandwidth.

Wideband Circularly Polarized Cavity-Backed Asymmetric Crossed Bowtie Dipole Antenna

A novel broadband circularly-polarised (CP) square slot antenna fed by an asymmetric coplanar waveguide (CPW) from a corner of the slot is proposed. A CP bandwidth larger than 10% can be attained simply by using an inverted-L tuning stub protruded from the signal line of the CPW. With an additional pair of grounded strips implanted in the slot, the 3 dB axial-ratio bandwidth and the VSWR les 2 impedance bandwidth can be greatly raised to be as high as 30 and 35%, respectively.

Axial-ratio bandwidth enhancement of asymmetric-CPW-fed circularly-polarised square slot antenna

A circular slot antenna fed by a coplanar waveguide (CPW) is proposed for dual-band operations. Dual frequency bands that cover the 2.4 GHz (2400-2484 MHz) and 5 GHz (5150-5825 MHz) bands were obtained by embedding a pair of slits in the circular back-patch that is printed on the backside of the substrate and concentric with the circular slot. This design resulted in broadside far-field patterns with low cross-polarisation levels in both frequency bands and a small antenna size of 40/spl times/40 mm with the ground plane regarded as part of the antenna structure.

J.-Y. Sze

Papers

Axial-ratio bandwidth enhancement of asymmetric-CPW-fed circularly-polarised square slot antenna

CPW-fed circular slot antenna with slit back-patch for 2.4/5 GHz dual-band operation