Design of compact microstrip lowpass filter with ultra-wide stopband using modified T-shaped resonator

Abstract

A new microstrip lowpass filter with compact size and ultra-wide stopband using T-shaped resonator is proposed. To make smaller the circuit size of the filter, cursive transmission line is also suggested. Moreover, exact equation of most important transmission zero is calculated based on LC equivalent circuit and transformation function. A demonstration filter with 3 dB cut-off frequency at 1.02 has been designed, fabricated, and measured. Results show that a relative stopband band width of 166.3% (referred to suppression degree of 20 dB) is achieved while obtaining high figure of merit of 46 274.

A novel compact lowpass filter with sharp roll-off and wide stopband

“…The significance of lowpass filters (LPFs) in increasing the quality of communicating signals cannot be ignored as these blocks eliminate undesired frequencies. Hence, various geometries have been introduced [1–18] to attain desired frequency response properties such as steep transition band, acceptable stopband, and passband characteristics. Addressing these challenging features, in [1], radial-shape resonators have been employed to obtain an LPF; however, the designed filter failed in attaining a steep skirt performance.…”

“…By employing radial stub resonator and folded microstrip lines, another LPF has been proposed in [17]. In [18], an LPF adopting modified T-shaped and cursive transmission lines has been reported. In spite of introducing new configurations in [15–18], each of them suffers from a weak frequency response performance in the transition band.…”

“…In [18], an LPF adopting modified T-shaped and cursive transmission lines has been reported. In spite of introducing new configurations in [15–18], each of them suffers from a weak frequency response performance in the transition band. In [19], to expand the stopband band width, an LPF capable of creating three transmission zeros (TZs) has been proposed, but the sharpness of the design is not satisfactory.…”

Ultra Sharp Transition-Band LPF with Miniaturized Size for GSM Applications

“…This structure has a weak sharpness and large dimensions. In [8], an LPF with sharp cut-off and compact size using T-shaped resonator was introduced. The presented LPF in [9] was composed of several open-circuited stubs, which a fractal defected ground plane was embedded to decrease the circuit size.…”

Compact low‐pass filters with deep and ultra‐wide stopband using tri‐ and quad‐mode resonators

“…Due to the etched resonators on the ground plane, the side effects are that electromagnetic leakages are increasing and the substrate must be suspended. LPFs can also be constructed by using patch resonators [9][10][11][12][13]. In [11], a LPF has been designed using the windmill resonators.…”