Compact filtering monopole patch antenna with dual-band rejection
© The Author(s) 2016
Received: 19 April 2016
Accepted: 16 June 2016
Published: 24 June 2016
In this paper, a compact ultra-wideband patch antenna with dual-band rejection is proposed. The proposed antenna filters 3.3–3.8 GHz WiMAX and 5.15–5.85 GHz WLAN by respectively rejecting these bands through a C-shaped slit and a λg/4 resonator. The λg/4 resonator is positioned as a pair, centered around the microstrip line, and a C-type slit is inserted into an elliptical patch. The impedance bandwidth of the proposed antenna is 2.9–9.3 GHz, which satisfies the bandwidth for ultra-wideband communication systems. Further, the proposed antenna provides dual-band rejection at two bands: 3.2–3.85 and 4.7–6.03 GHz. The radiation pattern of the antenna is omnidirectional, and antenna gain is maintained constantly while showing −8.4 and −1.5 dBi at the two rejected bands, respectively.
The unlicensed use of ultra-wideband (UWB) set by the United States Federal Communications Commission requires the satisfaction of −41.3 dBm/MHz noise strength at a frequency band ranging between 3.1 and 10.6 GHz, along with 25 % fractional bandwidth and at least 500 MHz frequency bandwidth (Dullaert and Rogier 2010).
For UWB antennas, proposals have been developed to reduce interference from other UWB bands and for realizing a wide bandwidth with a stable radiation pattern (Kim and Min 2009; Kim and Kim 2010). To satisfy these requirements, a variety of structures for UWB antennas have been proposed, such as bow-tie antennas (Kiminami and Hirata 2004; Dadgarpour et al. 2009) that are easy to mount inside systems, elliptical antennas (Jang and Hwang 2008), Vivaldi antennas (Hood et al. 2008), and fractal antennas (Oraizi and Hedayati 2011).
Two bands coexist in the unlicensed use of UWB: IEEE 802.16 WiMAX (3.3–3.8 GHz) and IEEE 802.1a WLAN (5.15–5.85 GHz). However, these two bands are known to degrade the performance as a result of their interference with UWB communication systems.
Thus, this paper proposes the insertion of a λg/4 resonator and a C-shaped slit into an antenna in order to reject both WiMAX and WLAN bands. To reject WiMAX, a pair of λg/4 resonators is centered on the microstrip line, and a C-shaped slit is inserted into an elliptical patch. The proposed antenna satisfied the required bandwidth for UWB communication systems specified by the Federal Communications Commission, while maintaining dual-band rejection to prevent interference between bands.
The remainder of the paper is organized as follows: the “Background” section briefly introduces the proposal and design of the tapered slot antenna. The section, “Methodology and analyses of experimental data,” deals with the characteristics of the antenna, which were analyzed through a simulation and measurement process. The “Result and discussion” section presents the comprehensive results for the proposed antenna. Finally, in the “Conclusion”, we draw conclusions regarding the proposed antenna.
For the structure of the proposed antenna, a λg/4 resonator and a C-shaped slit were inserted into an antenna. The antenna was designed with an elliptical patch structure, in order to reject both WiMAX and WLAN. It was fabricated using the Taconic TRF-45 substrate, which is 1.62 mm in thickness and offers a relative permittivity of 4.5 and a loss tangent of 0.0035. The structure of the antenna is compact, with a total size is 40 × 35 mm2.
Parameters of the proposed antenna (mm)
Two bands coexist for unlicensed use in the UWB:WiMAX (3.3–3.8 GHz) and WLAN (5.15–5.85 GHz). The proposed antenna rejects both of these bands using a λg/4 resonator and a C-shaped slit (Sarkar et al. 2014; Wu et al. 2013).
Methodology and analyses of proposed antenna
The antenna is expressed by the reflection coefficient Γ, which is the amount of reflected signal due to the impedance mismatch between the source and the antenna.
As shown in Fig. 6, Structure-1 converged with a VSWR ≤ 2 over the 3.27–10.48 GHz band, thereby satisfying the impedance bandwidth for standard UWB communication systems. Structure-2 successfully rejected the 3.27–3.87 GHz band, and its impedance bandwidth converged with a VSWR ≤ 2 at the 2.99–9.50 GHz band. Structure-3 successfully rejected both the 3.28–3.85 GHz band and the 4.7–6.03 GHz band, and its impedance bandwidth converged with a VSWR ≤ 2 at the 2.94–9.63 GHz band. Therefore, we demonstrated that dual-band rejection is feasible, and we verified that the proposed structure offers suitably high bandwidth for UWB communications.
Figure 7 shows that, as the length of the λg/4 resonator increased from 9.6 to 13.6 mm, the rejected band shifted to a higher frequency. At 11.6 mm, the WiMAX band was exclusively rejected.
Figure 8 shows that, as the length of the C-shaped slit increased from 6.4 to 7.4 mm, the rejected band shifted to a lower frequency. At 6.8 mm, the WLAN band was exclusively rejected.
As shown in Fig. 9, as the gap narrowed between the antenna and the λg/4 resonator, the VSWR increased and antenna gain reduced to below −10 dBi.
As shown in Fig. 10, as the gap narrowed between the antenna and the C-shaped slit, the VSWR increased and antenna gain reduced to below −8 dBi.
Analysis of the antenna’s band rejection
Gap 1: 0.6 mm
Gap 1: 1.8 mm
Gap 1: 3.0 mm
Gap 1: 4.2 mm
Gap 2: 0.75 mm
Gap 2: 1.75 mm
Gap 2: 2.75 mm
Gap 2: 3.75 mm
Table 2 shows that, for WiMAX, the antenna gain was −10.7 dB when Gap 1 was 0.6 mm. For WLAN, the antenna gain was −8.7 dB when Gap 2 was 0.75 mm. These results confirm the feasibility of the proposed antenna with dual-band rejection.
As shown in Fig. 11, the impedance bandwidth of the proposed antenna satisfied dual-band rejection at two bands: 3.3–3.85 and 4.8–6.1 GHz. Its impedance bandwidth converged with a VSWR ≤ 2 over the 2.9–9.3 GHz band. Therefore, the simulation results are consistent with the measurement results.
As shown in Fig. 12, the analysis of the radiation pattern of the proposed antenna demonstrated its omnidirectional characteristics at the 4 and 7 GHz bands.
As shown in Fig. 13, the analysis of the proposed antenna’s gain revealed that the simulation and measurement results were similar. However, the simulation analysis results and measurement results at 5.5 GHz were different by approximately 6 dBi. This was because of the loss in the physical size of the C-shaped slot during the production process. However, the band-rejection proceeded downward below 0 dBi, which is a suitable value.
Results and discussion
Overall analysis of the proposed antenna
Dual-band notched bandwidth
Antenna gain [dBi]
Dual-band notched bandwidth
A mismatch was observed between the simulation results and the measured results for the proposed antenna. This occurred in two forms: the first pertained to errors during the manufacturing process, and the second to loss between the antenna and the connector. However, this mismatch is not a major problem with the proposed performance. On this basis, the impedance bandwidth was achieved with a VSWR ≤ 2, and the rejected band proceeded downward below 0 dBi.
In this paper, we proposed a UWB monopole patch antenna with dual-band rejection. The impedance bandwidth of the proposed antenna satisfied VSWR ≤ 2 at the 2.9–9.3 GHz band and dual-band rejection from an impedance mismatch at the 3.3–3.85 and 4.8–6.1 GHz bands. Furthermore, we demonstrated that the antenna’s radiation pattern is omnidirectional, and that the antenna gain proceeded downward to below 0 dBi for dual-band rejection. Furthermore, the proposed antenna offers the advantage of dual-band rejection and a compact design, compared with different antennas.
The design of the proposed antenna was optimized through HFSS, a commercial electromagnetic simulator provided by Ansys. The antenna was designed using the Taconic TRF-45 substrate, which is 1.62 mm thick with a relative permittivity of 4.5 and a loss tangent of 0.0035.
SWK involves in design and interpretation of statistical analysis of collected data along with drafting of the manuscript. DYC have been involved for supervision, guidance and critically reviewing manuscript for important intellectual content. Both authors read and approved the final manuscript.
The authors declare that there is no competing interests.
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