Impedance bandwidth improvement for microstrip-fed slot antennas using short-circuited termination

Abstract

as inductors. C L represents the loading capacitance resulting from the gap between the two microstrip open-ends. C p represents the capacitance between the microstrip and the ground. The equivalent circuit exhibits an elliptic lowpass characteristic. We simulate the proposed lowpass filter using Ensemble by ANSOFT. Low insertion loss in the passband, sharp and wide rejection in the stopband, and compact size are realized. MEASURED RESULTSAn experimental lowpass filter was designed, fabricated, and tested. The filter was fabricated on substrate with relative dielectric constant r ϭ 9.6 and thickness of 0.8 mm. The dimensions of the proposed lowpass filter are shown as follows: a ϭ 1 mm, w 1 ϭ w 3 ϭ 0.2 mm, w 2 ϭ 2 mm, s ϭ 0.2 mm, and w ϭ 0.76 mm and l ϭ 3 mm are the width and length of feed line with 50⍀, respectively. Figure 3 shows the simulated and measured results. The filter has a 3-dB passband from DC to 1.65 GHz. The insertion loss is better than 0.68 dB from DC to 1.35 GHz. The stopband rejection levels are larger than 20 dB from 2.25 to 3.45 GHz. Two attenuation poles are realized at 2.5 and 3.25 GHz. The 2 nd harmonic resonant frequency is at 3.98 GHz. The size of the proposed lowpass filter is 8.6 ϫ 4.96 mm. As can be seen from Figure 3, the simulated results nearly agree with the measured results. However, some discrepancy between them can still be observed, which can be attributed to the unexpected tolerance of fabrication. CONCLUSIONA novel compact microstrip lowpass filter using a meander openloop resonator has been proposed. The advantages of compact size, low insertion loss in the passband, wide stopband, and sharp rejection in the stopband have been verified by simulation and experiment. Without any lumped element, the lowpass filter can be easily fabricated with good repeatability. The lowpass filter is desirable in many microwave-system applications due to its compact size and high performance.

Bandwidth Enhancement and Size Reduction of Microstrip‐Fed Folded‐Slot Antenna

“…Figure shows the E ‐plane ( x‐y plane) and H ‐plane ( x‐z plane) radiation patterns at 3, 5, and 7 GHz, respectively. The radiation patterns are similar to those of the conventional folded‐slot antennas , except that the proposed antenna has a maximum radiation power in the vicinity of φ = 180° (i.e., toward the negative x ‐axis) in the E ‐plane. These radiation patterns are formed because of the aperture electric fields distributed in the two open‐terminations of the slot caused by the cut.…”

“…In this article, a half‐wavelength folded‐slot antenna, which is cut at the finite ground plane edge as in , is proposed to achieve bandwidth enhancement as well as the size reduction of conventional folded‐slot antenna. The validity of the proposed antenna is confirmed by presenting its simulation and experimental results in comparison with those of the previous slot antennas .…”

“…The measured bandwidth and maximum antenna gain are approximately 92.5% (2.67–7.27 GHz) and 4.69 dBi, respectively. When compared with the measured bandwidth of 29% (2.1–2.8 GHz) of a double folded‐slot antenna in and 82% (2.42–5.78 GHz) of a monopole L‐slot antenna in , it is notable that the current value of 92.5% (2.67–7.27 GHz) is a significantly improved one, even though the slot width of the prototype antenna ( S w = 0.9 mm) is the narrowest in comparison with 1.89 mm in and 5 mm in . For understanding the effect of this wide‐impedance bandwidth performance, we have investigated the simulated equivalent magnetic current distributions on the slot at resonant frequencies.…”

“…The geometry of a conventional folded‐slot antenna fed by a short‐circuited microstrip line is shown in Figure . In this case, a conducting via is specifically used to connect the end of the microstrip feed line and the ground plane surrounded by the etched slot for bandwidth improvement.…”

“…Some of these research studies have dealt with the techniques for bandwidth enhancement and size reduction of resonant half‐wavelength slot antennas, which are achieved by using a quarter‐wavelength monopole slot cut at the finite ground plane edge . Others have proposed methods for bandwidth improvement of folded‐slot antennas which is achieved by short‐circuited termination of the microstrip feed line instead of open‐circuited termination . Among these microstrip‐fed slot antennas, folded‐slot antennas have attracted attention because of their input impedance being close to 50 Ω, whereas the resonant half‐wavelength slot antennas exhibit a relatively large input impedance (typically > 300 Ω).…”