Abstract-This paper presents the novel design of a wideband circularly polarized (CP) Radio Frequency Identification (RFID) reader microstrip patch antenna for worldwide Ultra High Frequency (UHF) band which covers 840-960 MHz. The proposed antenna, which consists of a microstrip patch with truncated corners and a cross slot, is placed on a foam substrate (ε r = 1.06) above a ground plane and is fed through vias through ground plane holes that extend from the quadrature 3 dB branch line hybrid coupler placed below the ground plane. This helps to separate feed network radiation, from the patch antenna and keeping the CP purity. The prototype antenna was fabricated with a total size of 225 × 250 × 12.8 mm 3 which shows a measured impedance matching band of 840-1150 MHz (31.2%) as well as measured rotating linear based circularly polarized radiation patterns. The simulated and measured 3 dB Axial Ratio (AR) bandwidth is better than 23% from 840-1050 MHz meeting and exceeding the target worldwide RFID UHF band.
the equivalent T-shaped line. Here, the equivalent T-shaped line works like a bandstop filter at the second harmonic frequency. Therefore, the proposed BPF has better characteristic with the second harmonic rejection than the earlier one. These BPFs show insertion losses of 1.2 and 0.75 dB and return losses of 17.8 and 18.2 dB at the central frequency of 10 GHz and bandwidth of 18%, respectively. The characteristic of the second harmonic rejection for the compact BPF with T-shaped line is 21.5 dB at 17.3 GHz. The new BPFs can be fabricated with microelectro mechanical systems, nanoelectro mechanical systems, and hybrid microwave integrated circuits or the MMIC technique due to its entirely planar structure.
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