Balanced BPF with wide upper stopband and wide common‐mode suppression response for WiMax applications

Abstract

patch will be kept unchanged as long as the cutting plane can be viewed magnetic wall. Under such situation, HCSRR, sharing the same magnetic wall with the half patch antenna, can be suitably sandwiched between the radiating patch and the ground plane, thus, a further miniaturization can be realized. Given that the electric field of the dominant mode within a patch cavity is kept unchanged, it is possible to excite properly designed HCSRR sandwiched between the ground plane and radiating patch and, thus, lower the resonant frequency of the half patch.Comparison of the return losses among four different types antennas are made in Figure 5. To make the explanation concise, circular patch antenna, circular patch antenna loaded with CSRR, half circular patch antenna, and half circular patch antenna loaded with HCSRR are renamed as Type-A, Type-B, Type-C, and Type-D antenna, respectively. As depicted in Figure 5, in terms of the fundamental mode, it can be observed that Type A and Type C antennas almost resonate at the same frequency (near 4 GHz), while Type A and Type C antennas almost resonate at another same frequency (near 2.2 GHz). It can be concluded that the half beveled technology shows little impact on the impedance matching of the antenna. Moreover, when the HCSRR (CSRR) is loaded, the resonant frequency decreases to 2.2 GHz, which is much lower than the original 4 GHz. Through the above analysis, conclusion can be drawn that HCSRR can reduce the antenna size to half while the impedance characteristic is kept almost unchanged. By the way, weaker resonances occurring at around 3.3 and 3.75 GHz mainly result from the higher order resonance of the HCSRR.To validate the above design, a prototype of the proposed antenna is fabricated on the two 1 mm-thickness Rogers RT/ duroid 5880 substrates (e r 5 2.2) with the parameters optimized by the simulation software HFSS. The photograph of the proposed antenna is depicted in Figure 6 and the parameters of the antenna structure are listed in Table 1. As shown in Figure 7, the fabricated antenna operates at 2.26 GHz, which is about 0.05 GHz higher than the simulated result. Figure 8 depicts the radiation patterns for the proposed antenna operating at 2.26 GHz. Good accordance between the simulated and measured results is obtained. The measured copolarization is at least 10 dB higher than the cross polarization in terms of the broadside radiation. As stated above, these results can effectively validate the characteristic of the proposed HCSRR structure. Moreover, a further size reduction for the HCSRR can be realized through introducing more slots, which owns the similar working principle as the one-slot HCSRR structure. CONCLUSIONA novel miniaturized HCSRR structure is investigated and its employment for designing miniaturized patch antenna is researched in this letter. The HCSRR shows almost the same resonant characteristic as the original CSRR, which can be explained in terms of the equivalent circuit model. Then the circular patch antenna can be beveled into a half an...