Roll-off

Abstract: A novel microstrip lowpass filter is proposed to achieve an ultra wide stopband with 12th harmonic suppression and extremely sharp skirt characteristics. The transition band is from 1.26 to 1.37 GHz with -3 and -20 dB, respectively. The operating mechanism of the filter is investigated based on proposed equivalent-circuit model, and the role of each section in creating null points is theoretically discussed. An overall good agreement between measured and simulated results is observed.

Abstract: A high roll-off, third-order frequency selective surface (FSS) with quasi-elliptic bandpass response is presented. It is based on substrate integrated waveguide technology. Its unit cell includes three cavities that support at the TE101 mode. Interactions of resonators are dominated by magnetic couplings. The coupling matrix is analyzed and used to design FSS. Guidelines for a coupling-matrix-based FSS design are given. Transmission zeros realized close to the lower and upper narrow passband lead to high roll-off characteristics. In addition, a cross-polarization feature is easily achieved. Finally, a prototype is designed and fabricated to validate the proposed structure. A stable frequency response in passband has been obtained with an oblique incidence of 40° for TE polarization. Good agreement between the simulated and measured results verifies the design concept of bandpass FSS.

Abstract: Transmission zeros are used to improve the roll-off factors of filters but as a consequence, the out-of-band rejection decreases. In this work, an LTCC filter design is presented which employs a series inductor (implemented as a via hole) to improve the out-of-band rejection by introducing a third transmission zero. The filter, designed for GPS band (1.57 GHz), has one of the smallest reported foot prints ( (0.063×0.048×0.005)λg) and demonstrates the highest roll off factor (16.7 dB/100 MHz) for this band. With only four LTCC layers, the design is cost effective and thus highly suitable for miniaturized, ultra-thin system-on-package applications.

Abstract: In this brief, a compact lowpass filter (LPF) with wide stopband, very sharp roll-off response and wide tuning range is presented for microwave diode detector applications. It employs two hexagonal-shaped resonators and multiple open-end stubs as suppression cells. The results of the proposed hexagonal-shaped resonator and LC circuits are in good agreement. The 3 dB cut-off frequency for the proposed LPF is 2.2 GHz and the roll-off-rate (ROR) parameter for the proposed LPF is very sharp and equal to 308.6 dB/GHz. Furthermore, insertion loss (IL) and return loss (RL) in the passband region are better than 0.3 dB and 18 dB, respectively. Moreover, the stopband is wide, ranging from 2.34 to 18 GHz, with a 22 dB rejection level. The tuning range of 3 dB cut-off frequency is also wide, equal 0.48 to 1.7 GHz (71%). As an application demonstrator, an envelope detector was designed and fabricated. The proposed detector (with LPF) highly suppresses any harmonics of the fundamental frequency. The proposed LPF and microwave detector is designed, simulated, fabricated and measured. The results of simulation and measurement are in good agreement.