Dual-Band Circularly Polarized Microstrip RFID Reader Antenna Using Metamaterial Branch-Line Coupler

Abstract

A dual-band circularly polarized aperture coupled microstrip RFID reader antenna using a metamaterial (MTM) branch-line coupler has been designed, fabricated, and measured. The proposed antenna is fabricated on a FR-4 substrate with relative permittivity of 4.6 and thickness of 1.6 mm. The MTM coupler is designed employing the provided explicit closed-form formulas. The dual-band (UHF and ISM) circularly-polarized RFID reader antenna with separate Tx and Rx ports is connected to the designed metamaterial (MTM) branch-line coupler. The maximum measured LHCP antenna gain is 6.6 dBic at 920 MHz (UHF) and RHCP gain is 7.9 dBic at 2.45 GHz (ISM). The cross-polar CP gains near broadside of the RFID reader antenna are approximately less than compared with the mentioned co-polar CP gains in both bands. The isolations between the two ports are about 25 dB and 38 dB, at 920 MHz and 2.45 GHz, respectively. The measured axial ratios are less than 0.7 dB in the UHF band (917-923 MHz) and 1.5 dB in the ISM band (2.4-2.48 GHz).

A Miniaturized Triple-Band Metamaterial Antenna With Radiation Pattern Selectivity and Polarization Diversity

“…This is especially true for the circularly polarized (CP) microstrip antenna which owns additional advantages of imposing less strict restrictions on orientation of the transmitter and receiver and mitigative multi path effects. A survey of recent literature indicates that a considerable amount of efforts have been devoted to the antennas with CP, for instance, CP antennas for bandwidth enhancement by using left handed (LH) metamaterial transmission line (TL) [8] and reactive impedance substrates [9], respectively, CP antennas with gain and directivity enhancement [10][11][12][13], omnidirectional radiations [14][15][16] and even dual-band or multifrequency operation with radiation pattern selectivity and polarization diversity [16][17][18][19][20][21][22][23][24][25].…”

“…Among them, the multiband antennas [16][17][18][19][20][21][22][23][24][25] with one or more CP bands have generated much attention because the multifunctional systems exhibit the benefits of high stability, reliability and integrity. Although these antennas present a miniaturized layout at the lowest resonant mode and decent CP radiation performances with good axial ratios (ARs), some of them are confined to mushroom structure which provides the shorted LH stub inductor through drilling via holes [16][17][18][19].…”

“…Accordingly, the antenna's gain and radiation efficiency may be degraded by a few percentages. Recently, a metamaterial branch-line coupler [20] and a power divider [21] were utilized for dual-band CP antennas with dual-fed technology. Although the excitation of the two orthogonal modes with 90 • phase difference for CP is convenient and straightforward, the complicated feeding network occupies a large area which conflicts with currently increasing demand on compactness.…”

Generalized Impedance-Transforming Dual-Band Branch-Line Couplers for Arbitrary Coupling Levels

“…With the rapid development of modern wireless communication systems, dual-band Doherty power amplifier [17] and dual-band-or dual-circularly polarized antenna and antenna array [18][19][20] featured lower cost and compact size have drawn much attention recently. Therefore, the branch-line couplers as the key components of it and several functions are required simultaneously, such as dualband operation, arbitrary coupling levels, and inherent impedance transforming.…”

Dual band microstrip antenna with non regular polygonal patch for satellite applications

“…They are used in lots of applications such as wireless local area network (WLAN), satellite communications and global system for mobile (GSM) [4]. In addition, different types of dual band microstrip patch antennas are presented in literatures such as dual band microstrip antenna with single patch [5] and stacked patches [6] and using two separate antennas which are connected to by a shorting pin [7] and using metamaterial branch-line coupler [8]. Chen et al [9] reported a modified inverted-L monopole with meandered wire and a conducting triangular.…”