A bandpass filter (BPF) design using a dual-mode microstrip triangular loop resonator is presented for the first time. The circuit produces frequency responses with one real finite frequency transmission zero and one imaginary finite frequency zero on either side of the passband. Depending on the perturbation arrangement, the nature of the coupling between degenerate modes causes the zeros to exchange their axis locations from real to imaginary and from imaginary to real while keeping their magnitude. This behavior results in frequency responses that are suitable for applications with asymmetrical requirements. Results show 8% bandwidth filters with insertion loss ranging from 0.82 dB to 1.4 dB at 10 GHz. Advantages in size reduction and design flexibility are demonstrated when the triangular loop is compared to other dualmode resonators.
This paper demonstrates a six-state reconfigurable band-pass filter intended to add frequency tunability to antenna systems. The present topology produces filter responses with center frequencies of 0 = 9, 10, and 11 GHz and achieves independent bandwidth control with an average tunable passband ratio of 1.73:1 between the wideband configurations ranging from 13.4% and 14.7% and the narrowband configurations ranging from 7.7% and 8.5%. PIN diodes are implemented as switching elements and the distinct states are discretely accomplished by the connection and isolation of strategically placed transmission line sections. The insertion loss of the filter ranges between 1.74 and 1.92 dB. The circuit produces no significant signal distortion resulting in third-order intermodulation intercept points (IIP3) greater than 48 dBm for tones separated by 1 MHz around the center frequencies.
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