Stub-loaded square loop bandpass filter with equiripple response in both delay and magnitude

Abstract

It is shown that a stub loaded square loop filter, composed of six sections of commensurate transmission line, can achieve equiripple response in both magnitude and group delay simultaneously, when the admittances of the lines are properly chosen. Design formulas are given to calculate the admittances by given specifications such as fractional bandwidth and in‐band magnitude ripple. An interesting property of this filter is that the group delay can be adjusted while the in‐band magnitude response keeps almost unchanged. For verification, a filter sample is designed, fabricated and measured. In experiment, it exhibits a delay variation of 0.22 ns and minimal insertion loss of 0.21 dB within its passband (|S11| < −13.8 dB) from 0.48 to 1.52 GHz, which agree well with the theoretical predictions.

Response Diversity of Stub-Loaded Ring Bandpass Filter Based on Commensurate Line Element: Single- and Dual-Band Applications

“…According to [18], the overall transfer function F cir can be expressed by the admittances (y i ) of the filter, as follows,…”

“…Besides, the circuit area can be reduced by folding the connecting line into a coupled line section, with an improved equiripple delay response [14]. The signal interference is another new concept in filter design [15]- [18]. The reduction in circuit area and the steep rejection in stopband can be achieved simultaneously, by introducing one or more interferences from the multiple signal passages between the input/output ports [15].…”

“…In most of the reported wideband BPF designs, the group delay characteristic is ignored or fixed, because the design methodologies are derived entirely from magnitude response. In our recent works, two new wideband BPFs are given to show the co-existence of equiripple responses in both delay and magnitude, one of which is utilized by coupled lines section [14] while the other one is achieved by commensurate line ring [18]. The common part of the two BPFs in structure is a pair of short-ended stubs.…”

“…In this work, we will give a full demonstration on the responses based on the filter topology reported originally in [18], in the consideration of the passband number, delay, transmission zero, and circuit realization. The objective of this study is to reveal the response diversity/complexity of the stub-loaded ring structure, and the unity/simplicity in mathematical representation.…”

“…The objective of this study is to reveal the response diversity/complexity of the stub-loaded ring structure, and the unity/simplicity in mathematical representation. It will be shown that four filters of different types [9], [12], [13], [15], [16], [18] and different operation mechanisms have a common prototype in topology and can be analyzed through a generalized algorithm. Besides, all of the following discussions are based on equiripple magnitude response in passband, which is guaranteed by using an improved synthesis approach based on [18].…”