In 2002, since FCC has permitted the use of 3.1-10.6 GHz band for commercial use to meet the demands in communication for short range distance with high capacity, the UWB technology has become a promising next generation technology in wireless communication and vast research and development has been made.
Massive research has been made in this area to realize the ultra wideband communication with co-existing communication systems which mostly are WiMAX (3.4–3.69 GHz), C-band (3.7–4.2 GHz), the WLAN (5.15–5.875 GHz) band, and X-band (7.25–8.4 GHz). This work has been accomplished by rejecting these bands in UWB system to avoid interference. For this particular purpose, UWB antenna has been designed with band rejection characteristics in multiple spectrum instead of employing multiple band rejection filters.
In this paper, an UWB antenna with band suppression characteristic is designed, fabricated, and characterized. The wide band performance is inherited by the conical monopole and band rejection characteristic is realized through Split Ring Resonators. The input impedance of the proposed antenna is based on the length of the conical monopole and band rejection frequency can be tuned by changing the diameters of SRRs.
The conventional band rejection antennas have issues in adjustment of their band rejection frequencies. Most of the elements for the band rejection purpose were patterned on the antenna body with broad band characteristic. Thus, any changes in antenna elements for band rejection eventually alter the broadband characteristic which requires a significant redesign procedure. But the rejection band for the proposed antenna can be easily adjusted only by adjusting the diameter of the SRR instead of changing the whole antenna structure. Since the SRR is located on the empty space of the substrate instead of patterning on the other antenna element, the band rejection characteristic can be determined separately to the broadband characteristic.
The principle of the band rejection phenomena for the proposed antenna is based on the impedance mismatch. When the SRR resonates, the resonant energy is stored inside the ring. This reactive energy causes the impedance mismatch between the antenna body and the feeding part. Thus the antenna has band suppressed characteristic at the resonance frequency of SRR.
The proposed antenna satisfies the 3.1~10.6GHz UWB band with capability of adjusting band rejection frequency for WiMAX (3.4-3.69 GHz), C-band (3.7-4.2 GHz), WLAN (5.15-5.875 GHz) bands, and X band (7.25–8.4 GHz). The surface current of conical monopole with two SRRs operating at 3.5 GHz and 5.8 GHz are simulated and the current distribution proves that the two SRRs operate in separate mode.
Based on the simulation and measurement results, the presented paper finds its design methodology to tune the rejection resonances in UWB band without altering the other performances.
This study presents a systematic design method for a conical-type monopole antenna exclusively for use in an ultrawide band (UWB). The suggested antenna adopts a structure called the split ring resonator (SSR), in which one resonant element can be easily attached and detached. It is possible to adjust the size of the SSR and the gaps; this SSR, operating at the relevant frequency, can be attached to and removed from the antenna, making it easier to adjust the rejection band. The suggested antenna covers a UWB ranging from 3.1 to 10.6 GHz. Through a simulation, we found that the rejection characteristics of the suggested antenna can be changed among WLAN (5.75 GHz), C-band (4 GHz), WiMAX (3.5 GHz), and X-band (7.8 GHz), and that the measurements in the WLAN and WiMAX bands show rejection characteristics. Additionally, the suggested antenna has a peak gain of over 3 dBi in the operation band and shows omnidirectional radiation patterns.
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