Compact Microstrip Lowpass Filter With an Ultra-Wide Stopband and Sharp Transition Band Using T-Shaped and Polygon Resonators

Abstract

In this paper, a lowpass filter with −3 dB cutoff frequency of 5.3 GHz using T-shaped and polygon resonators is presented. The applied resonators create a sharp transition band of 0.2 GHz from −3 dB to −40 dB. To obtain an ultra-wide stopband about 54 GHz (10.18f c) with a suppressing level of −21 dB, two different suppressing cells are employed. The overall circuit size is 59.16 mm 2 , which indicates a small occupied area. To clarify the performance of each resonator and describe the location of the transition zeros, exact equations based on the equivalent LC circuits have been calculated.

A Compact Microstrip Lowpass Filter with Ultra-Wide Rejection Band and Sharp Transition Band Utilizing Combined Resonators with Triangular Patches

“…7(a), an acceptable relative stopband bandwidth RSB equal to 1.78 has been achieved. The closest figures to this have been reported in [11] and [14] (1.72 and 1.666, respectively). The suppressing cells reject spurious frequencies with a suppressing level of 21 dB, which is to some extent similar to the other works, except for the reported suppressing factors in [1], [3], [9], [10] as their rejecting levels are less than the others, considerably.…”

“…Two other methods to present a LPF with sharp transition band are employing asymmetric high-low impedance patches and LC tank resonators, which has been introduced in [12] and [13], respectively. In [14], a lowpass filter using polygon patch resonant cells, T-shaped resonators and two different suppressing cells has been designed, however, this filter does not have a sharp transition band. In [15], a LPF composing of two main resonators with polygon patches and six suppressing cells to omit spurious frequencies in the stopband has been proposed, but this filter occupies a large area.…”

A Design of Microstrip Lowpass Filter with Wide Rejection Band and Sharp Transition Band Utilizing Semi-Circle Resonators

“…7a, leads to obtaining an acceptable relative stopband bandwidth RSB, which is 1.78. The closest RSB to this have been cited in [9], [11] and [14] (1.65, 1.72 and 1.666, respectively). The suppressors suppress spurious frequencies with a suppressing factor of 32 dB, which is better than the other works.…”

“…Two other techniques to design LPFs with steep transition band are employing asymmetric high-low impedance patches and LC tank resonators, which have been reported in [12] and [13], respectively. In [14], a lowpass filter employing polygon patch resonant cells, T-shaped resonators and two different suppressing cells has been designed, although, this filter does not have a steep skirt performance. One more method to present a LPF with acceptable frequency response is cascading resonators with polygon patches [15], but it occupies a large area.…”

Compact Microstrip Lowpass Filter With High and Wide Rejection in the Stopband Utilizing Flabelliform Resonators

“…However, the occupied area of circuits, [11][12][13], are relatively large. In [14], a lowpass filter using polygon patch resonant cells, T-shaped resonators and two different suppressing cells is designed; however, this filter does not have a sharp transition band. Another method to design an LPF with acceptable frequency response is cascading resonators with polygon patches [15], but it has a large circuit size.…”