Compact Circularly Polarized Microstrip Ring Antenna Using Capacitive Coupling Structure for RFID Readers

Abstract

This paper presents a compact circularly polarized microstrip antenna for radio frequency identification (RFID) readers. The dimensions of the proposed antenna are reduced by etching a cross slot in the radiation patch and loading four grounded coupling patches on the four corners of the radiation patch. An inverted Z-shaped coupling feedline is used to realize circularly polarized operation. The measured −10 dB |S 11 | bandwidth, 3-dB axial ratio bandwidth and maximum gain are 872−1095 MHz, 888−933 MHz, and 5.52 dBi, respectively, at 922 MHz frequency. The overall dimension of the proposed antenna is 0.36 λ g × 0.36 λ g × 0.05 λ g (λ g is the guide wavelength at the center frequency of 915 MHz). The proposed antenna has small size with good overall performance and is suitable for compact RFID devices. INDEX TERMS Circular polarization (CP), coupling patch, coupling feedline, microstrip antenna, radio frequency identification.

A Compact Broadband Circularly-Polarized Patch Antenna With Wide Axial-Ratio Beamwidth for Universal Uhf Rfid Applications

“…The cost of these advantages is the antenna height larger than 0.05λ 0 and a moderate antenna gain. [4] 0.27λ 0 × 0.27λ 0 × 0.014λ 0 1.9% 0.7% 100 • / 3.8 [5] 0.60λ 0 × 0.60λ 0 × 0.171λ 0 56.5% 6.1% / / 7.0 [6] 0.60λ 0 × 0.60λ 0 × 0.18λ 0 48.6% 16.5% / 73 • 8.6 [7] 0.45λ × 0.45λ 0 × 0.074λ 0 14.2% 9.0% / 77 • 7.3 [9] 0.60λ 0 × 0.60λ 0 × 0.089λ 0 21.4% 13.4% 90 • / 7.0 [10] 0.67λ 0 × 0.67λ 0 × 0.043λ 0 10.6% 6.0% / 65 • 8.9 [11] 0.75λ 0 × 0.75λ 0 × 0.074λ 0 20.2% 17.7% 90 • / 6.5 [12] 0.75λ 0 × 0.75λ 0 × 0.075λ 0 13.1% 25.1% / / 7.0 [13] 0.75λ 0 × 0.75λ 0 × 0.11λ 0 25.6% 16.4% 75 • / 8.3 [14] 0.36λ 0 × 0.36λ 0 × 0.05λ 0 22.7% 4.9% / / 5.5 [15] 0.463λ 0 × 0.463λ 0 × 0.032λ 0 3.5% 0.65% / 72 • 7.2 This work 0.408λ 0 × 0.408λ 0 × 0.053λ 0 18.4% > 32.8% 177 • 118 • 5.1 * 3-dB AR beamwidth at the center frequency. # Half-power beamwidth at the center frequency.…”

“…Many works have been done to design compact CP patch antennas for UHF RFID readers. By etching a cross-slot in the radiation patch and loading four grounded coupling patches on the four corners of the radiation patch, the antenna size was reduced to 0.36λ 0 × 0.36λ 0 × 0.05λ 0 [14]. The realized gain at 922 MHz was 5.5 dBic with an AR bandwidth of 4.9%.…”

“…However, this method is complicated. The bandwidth and 3-dB AR beamwidth of these CP antennas [14][15][16] are narrow.…”

Broadband Circularly Polarized Antenna With Non-Planar Reflector

“…On the contrary, single-feed has a distinct advantage in simple structure [9][10]. To achieve broadband, many other derived feeding structures have been proposed, such as the single L-shaped probe [11], the Z-shaped coupling feedline [12], and the coplanar waveguide (CPW) [13].…”

Modeling and analysis of microstrip annular ring antenna with capacitive coupling matching network

“…A hybrid‐embedded ring antenna is proposed in References 13‐16 the antenna size can be reduced to λ /4 × λ /4 without influence the other performances especially radiation efficiency. With capacitive coupling structure and inverted Z‐shaped coupling feedline, 17 a circularly polarized ring antenna with compact size and wide impedance bandwidth is designed.…”