A New Class of Dual-Band Waveguide Filters Based on Chebyshev Polynomials of the Second Kind

Abstract

This paper presents for the first time a method of mathematical synthesis involving chaining of Chebyshev polynomials of the second kind for the application of a dual-band waveguide filter. This method takes advantage of second kind Chebyshev polynomials that have high out-of-band rejection, and overcomes unequal-ripple properties. It is applicable to high filter orders greater than five, and will always possess symmetrical dual-band filter properties. This proposed approach is able to achieve an optimum and constant ripple, the flexibility of return loss, and high adjacent band's rejection. The design method is based on suitably defined transmission zeros at the centred frequency to the chained Chebyshev of the second kind. A sixth-order waveguide filter based on a prescribed return loss of 15 dB centred at a frequency of 28 GHz, with a fractional bandwidth of 1% in each passband, has been implemented and fabricated. The measured results show that the return loss, total bandwidth, and the frequency shift are 12 dB, 860 MHz, and 0.24%, respectively. The measured and ideal responses of the waveguide model are in a good agreement. INDEX TERMS Narrowband, second kind Chebyshev, symmetrical dual-bandpass filters, transmission zeros, waveguide.

Design and Implementation of Microwave Dual-Band Pass Interdigital Filter Using an Analytical Approach

“…Comparing with some of the works that were mentioned in some recent scientific references, we can note that the required specifications of the designed filters are approximately achieved in [2], [7], while 11 in [2] doesn't meet the required value, although the value of 11 adopted in [2] was -15dB compared to -20dB in the case of the designed filter presented in this paper. While the required specifications of the filter in [7] are met in terms of the required pass-bands, however, the filter obtained in [7] showed poor selectivity compared to the filter presented in this paper, especially in the stop band between the two pass bands.…”

“…Therefore, in order to incorporate two or more desired communication bands in a single hardware unit, or to reject unwanted interfering frequencies, multi band filters are needed. Multi-band filters are attracting more and more interest in modern microwave filters design [2]- [8].…”

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“…For example, Kim et al in [1] established some sums of finite products of the second, third, and fourth kinds. From a practical point of view, a new class of dual-band waveguide filters is introduced based on Chebyshev polynomials of the second kind in [2]. Oloniiju et al in [3] utilized Chebyshev polynomials of the first kind to obtain a pseudo-spectral solution to a certain multi-dimensional fractional problem.…”