Simple models based on neural networks for suspended and inverted microstrip lines

Abstract

where ␦ is the fractional bandwidth given by ␦ ϭ ⌬/ 0 . In the above formula, ⌬ is the filter bandwidth defined with respect to the passband ripple level of attenuation, 0 is the filter center frequency, n is the order of the filter, and g 0 , g 1 , . . . g i , g iϩ1 are the low-pass prototype values corresponding to the designed filter response. k i,iϩ1 , which corresponds to a designed bandpass response, is calculated from Eq. (8). The physical dimensions of the filter are determined with the use of stripline and filter synthesis. A SIRs bandpass filter with a center frequency of 2.4 GHz and a fractional bandwidth of 10.4% was designed based on the previously discussed method. Substrates were made of CBLST dielectric material. Figures 5 and 6 show the computer simulation result using HFSS from Ansoft Co. Ltd. For illustration, measurement of the filter response was also plotted in Figures 5 and 6. In this case, the difference between designed and measured results, such as the measured center frequency's shift up to 2.39 GHz compared to the design's value of 2.4 GHz, is very small. The results of measured and simulated are in good agreement. The difference may be due to the pattern mismatch and the 90°bend between the resonators and input/output ports. By using a cofiring process, improvement of the filter response can be expected.The broadband frequency response of the filter is shown in Figure 7. The response has a stop-band attenuation pole at 1724 MHz. The insert loss is Ϫ48 dB at 3f 0 , thus demonstrating an improvement in stop-band performance when using SIRs. The first frequency of the harmonic passband is shifted up to 9004 MHz, far from that at 3f 0 , which is 7160 MHz.A comparison of [2,3] and the proposed filter's characteristic, given in Table 1, shows that the insertion loss of the proposed filter is very small. This is because four of six faces of the filter are metaled, which reduces the radiation loss. CONCLUSIONThe concept of SIRs was used to develop a compact stripline ceramic filter, using LTCC technology, with a controllable spurious harmonic-resonance frequency. Using a series-coupled SIR, a compact bandpass filter was designed with a center frequency at 2390 MHz and 3-dB bandwidth at 250 MHz. Tapped input/output ports were used to simplify the topology of filter. Simulated and measured results showed good agreement. Simulated insertion loss was Ϫ48 dB at 3f 0 and the frequency of the first harmonic passband center frequency was increased to 9004 MHz. The size of proposed filter is reduced dramatically and insertion loss in the passband is also smaller than ever. The results demonstrate that the proposed filter has good characteristics and its performance will be applicable to wireless communication systems, such as 2400-MHz wireless local area networks. ACKNOWLEDGMENTSThis project was supported by Shanghai leading academic discipline program and the establishment foundation of Ph.D. in Shanghai.