Abstract
A four-port dual-band dual circularly polarized (CP) stack-up patch antenna is introduced for multiple-input-multiple-output (MIMO) RFID application. The proposed antenna adopts two FR 4 substrates and one Rogers Ro4350b substrates. Two pairs of isolated ports work at FCC UHF/MW-RFID bands (0.902–0.928 and 2.4–2.485 GHz) with port isolations of 20 dB and 25 dB, respectively. Four inverted-F radiating elements fed with a 90° phase-delay feeding network realize the CP radiation at the FCC UHF-RFID band (0.902–0.928 GHz). The corner-truncated square slot and patch are implemented to obtain CP modes at the MW-RFID band. The relative impedance bandwidths in the FCC UHF and MW band are 10.9% and 9.4%, respectively, with peak gains of 4.1 and 7.2 dBic. The antenna’s MIMO performance of envelope correlation coefficient (ECC) is lower than 0.01, and diversity gain (DG) is close to 10 dB. Thanks to the stack-up configuration, the dual-band RFID antenna realizes good antenna performance with a compact size of 0.6 × 0.6 × 0.07 λ3.
Highlights
The radio-frequency identification (RFID) technique is a widespread research tendency for some fields, such as biomedicine, traffic, and logistics, because of its practical and low-cost labeling advantage. e RFID operating band includes 125/135 kHz, 13.56 MHz, 433/ 860–960 MHz, and 2.45/ 5.8 GHz. e MW-band RFID system has unique technical superiorities of excellent transmitting rate and distance in a compact configuration for the active RFID technique.operating at multiple frequencies in compact RFID system has become a critical need to enhance efficiency
Two feed lines and the radiating patch for the 2.45 GHz MW-RFID band are printed on the bottom side of Layers 2 and 1, respectively
Only one required band) are always necessary for the MIMO system [23]. e solution in this paper achieves dual-band circularly polarized (CP) simultaneous operation with two pairs of single-band ports and occupies a more compact dimension. us, the proposed solution is better for the dual-band RFID 2 × 2 MIMO system compared with other solutions
Summary
The radio-frequency identification (RFID) technique is a widespread research tendency for some fields, such as biomedicine, traffic, and logistics, because of its practical and low-cost labeling advantage. e RFID operating band includes 125/135 kHz (low-frequency band, LF), 13.56 MHz (high-frequency band, HF), 433/ 860–960 MHz (ultrahigh-frequency band, UHF), and 2.45/ 5.8 GHz (microwave band, MW). e MW-band RFID system has unique technical superiorities of excellent transmitting rate and distance in a compact configuration for the active RFID technique. Reference [23] duplicates its dual-feed dual-band CP RFID antenna elements for the 2 × 2 MIMO system and implements decoupling structures to enhance its port isolation This solution significantly enlarged the overall dimensions and design complexity. All of them are designed for linear polarization (LP) with a single feed and cannot work at the second FCC UHF-RFID band Since these two standards (0.915/2.45 GHz) need to operate simultaneously in one system, the four-feed dual-band antenna in this paper is necessary. A novel dual-port shared phase-delay feeding network, which consists of only two 90° hybrid couplers, has been proposed for the FCC UHF band It can simultaneously achieve orthogonal-CP radiation fields to enhance port isolation in a more compact dimension.
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