EXPERIMENTAL RESULTS

Simulation was performed with IE3D electromagnetic (EM) simulation software, a simulator based on the method of moments. The filter was designed on a RT/duroid® RO4350B substrate, with a dielectric constant of 3.38, thickness of 0.508 mm and loss tangent of 0.003. The dimensions of the filter (see Figure 1) were: l1 = 8.0 mm, l2 = 7.2 mm, w0 = 1.1 mm, w1 = 0.2 mm, w2 = 0.4 mm, w3 = 0.4 mm, w4 = 0.3 mm, w5 = 0.8 mm, w6 = 0.6 mm, d1 = 0.5 mm, d2 = 0.2 mm, d3 = 0.3 mm, d4 = 0.2 mm and d5 = 0.2 mm.

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The fabricated UWB filter was measured with a Keysight Technologies N5238A vector network analyzer. The measured |S21| and |S11| are compared with the simulations in Figure 5, showing good agreement. The differences between the measurements and simulation are attributed to fabrication tolerances and the SMA connectors. Figure 6 shows the fabricated UWB bandpass filter, which is only 22 × 10 mm.

Figure 5

Figure 5 Measured vs. simulated |S21| and |S11|.

Figure 6

Figure 6 Fabricated UWB bandpass filter.

The passband of the fabricated filter covers 3.2 to 10.4 GHz, with a 100 percent fractional bandwidth at 6.80 GHz. The mid-band insertion loss was 0.25 dB, with return loss higher than 15 dB over the entire passband. The upper stopband stretches to 29 GHz, with insertion loss greater than 15 dB. For the two notched bands, the measured results show better than 15 dB insertion loss at 5.8 and 8.0 GHz with 3 dB FBWs of 5.9 and 4.2 percent, respectively. Comparisons with the performance of other published UWB bandpass filters are presented in Table 1.

Table 1

CONCLUSION

A miniaturized UWB bandpass filter achieved a wide upper stopband, good selectivity, low passband insertion loss and small size using four high-low impedance resonant cells periodically placed in the inner area of a conventional square ring MMR. An E-shaped resonator coupled to the MSRMMR provides dual notch bands. The filter is designed for UWB wireless communication systems, offering a simple topology, compact size and excellent performance.

ACKNOWLEDGMENT

This work was supported by the Shaanxi Provincial International Cooperation Project (2018KW-068), Shaanxi Provincial Department of Education Research Project (17JK0265) and Weinan City Science and Technology Project (2017 JCYJ-2-1).

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