Marc Sans

Design of Planar Wideband Bandpass Filters From Specifications Using a Two-Step Aggressive Space Mapping (ASM) Optimization Algorithm

This paper is focused on the automated and unattended optimization of a type of planar wideband bandpass filters by means of aggressive space mapping (ASM). The considered filters are microstrip filters implemented through a combination of shunt connected stepped impedance resonators (SIRs) and grounded stubs coupled through admittance inverters. The most relevant and novel aspect of this paper is the fact that the filter layout is automatically generated from filter specifications, i.e., central frequency, fractional bandwidth, in-band ripple and order, without the need of any external aid to the design process. To achieve this layout generation, filter optimization has been divided into two independent ASM processes. The first one generates the filter schematic (circuit element values) providing the required specifications. This first iterative process is necessary since, due to the narrow band operation of the admittance inverters, the target specifications are achieved by compensating the effects of such narrow band operation. The purpose of the second ASM algorithm is to automatically generate the layout from the filter schematic resulting from the first ASM process. To validate the new two-step ASM optimization tool, two sets of filter specifications (inputs of the developed tool), are considered. The generated filter layouts exhibit frequency responses that satisfy the specifications, and are in excellent agreement with the responses of the schematics.

Automated Design of Common-Mode Suppressed Balanced Wideband Bandpass Filters by Means of Aggressive Space Mapping

The automated and unattended design of balanced microstrip wideband bandpass filters by means of aggressive space mapping (ASM) optimization is reported in this paper. The proposed filters are based on multisection mirrored stepped impedance resonators (SIRs) coupled through quarter-wavelength transmission lines, acting as admittance inverters. Such resonant elements provide transmission zeros useful for the suppression of the common mode in the region of interest (differential filter pass band) and for the improvement of the differential-mode stopband (rejection level and selectivity). Due to the limited functionality of the inverters, related to the wide fractional bandwidths, the automated filter design requires a two-step process. With the first ASM, the filter schematic satisfying the required specifications (optimum filter schematic) is determined. Then, the layout is synthesized by means of a second ASM algorithm. Both algorithms are explained in detail and are applied to the synthesis of two filters, as illustrative (and representative) examples. With this paper, it is demonstrated that the two-step ASM optimization scheme (first providing the optimum schematic and then the layout), previously applied by the authors to wideband single-ended filters, can be extended (conveniently modified) to common-mode suppressed differential-mode bandpass filters. Thus, the value of this two-step ASM approach is enhanced by demonstrating its potential for the unattended design of complex filters, as those considered in this paper.

Size reduction and spurious suppression in microstrip coupled line bandpass filters by means of capacitive electromagnetic bandgaps

This paper is focused on the application of electromagnetic bandgaps based on capacitive loading to the implementation of microstrip coupled line bandpass filters with reduced size and spurious suppression. Size reduction is due to the slow-wave effect caused by the loading capacitances of the different coupled lines, whereas spurious suppression is related to periodicity. By properly designing the capacitively-loaded coupled line sections of the filter, implemented by means of square patches in practice, it is possible to significantly reduce filter size and simultaneously achieve spurious cancellation. As an example, an order-3 Chebyshev bandpass filter with 30% length reduction (as compared to the conventional counterpart) and spurious rejection up to the third harmonic is reported.

Design of differential-mode wideband bandpass filters with wide stop band and common-mode suppression by means of multisection mirrored stepped impedance resonators (SIRs)

We present balanced microstrip wideband bandpass filters that simultaneously suppress the common-mode within the differential filter pass band and reject the differential-mode over a wide band above the pass band of interest. These filter characteristics are achieved by using multisection mirrored stepped impedance resonators (SIRs) transversally oriented to the filter axis and coupled through admittance inverters. Each mirrored SIR acts as a pair of independent shunt-connected series resonators for the common-mode. One of such resonators (the central one) is tuned through the patch capacitance in order to suppress the common-mode by providing a transmission zero for that mode within the differential filter pass band. For the differential-mode, the capacitances of the central resonators are virtually grounded, and the resulting inductances are determined according to the required differential-mode response. For the external resonators, the patch capacitances contribute to the differential-mode response and, combined with the inductors, provide transmission zeros useful to enhance the differential-mode stop band. The design of an order-5 quasi-Chebyshev prototype balanced filter with central frequency 2.4 GHz, 40% fractional bandwidth and 0.2 dB ripple is reported.

Automated synthesis of planar wideband bandpass filters based on stepped impedance resonators (SIRs) and shunt stubs through aggressive space mapping (ASM)

This paper is focused on the automated synthesis of wideband bandpass filters by means of aggressive space mapping (ASM). The considered filters are microstrip filters implemented through a combination of shunt connected stepped impedance resonators (SIRs) and grounded stubs coupled through impedance inverters. By virtue of the transmission zeros introduced by the shunt connected SIRs, the filters exhibit a wide rejection band with strong attenuation. The main contribution and originality of the paper is the fact that the layout of the whole filter is automatically generated from the circuit schematic without human intervention in the process. In a first step, the ASM algorithm is applied to the SIR/stub resonators and inverters. After that, each filter cell is automatically generated, and no further optimization is required. As an example, the synthesis of an order-7 bandpass filter is reported. The agreement between the electromagnetic response of the synthesized filter and the target response is very good, pointing out the validity of the proposed synthesis approach.

Automated design of balanced wideband bandpass filters based on mirrored stepped impedance resonators (SIRs) and interdigital capacitors

This paper presents small balanced bandpass filters exhibiting wide differential-mode pass bands and high common-mode suppression. The filters are implemented in microstrip technology and their topology consists of multisection mirrored stepped impedance resonators (SIRs) alternating with mirrored interdigital capacitors. The mirrored SIRs provide the required common-mode transmission zeros to achieve effective rejection of that mode in the region of interest, i.e. the differential-mode pass band. An automated design method for such filters, based on aggressive space mapping, is reported. The method uses the equivalent circuit model of both the mirrored SIRs and the interdigital capacitors, and filter synthesis is based on a quasi-Newton iterative algorithm where parameter extraction is the key aspect. The automated design approach is illustrated through an order-3 filter, where it is demonstrated that the filter topology is generated from the specifications. As compared with previous balanced filters based on mirrored SIRs coupled through admittance inverters, the proposed filters of this work are smaller and the design method is simplified, since bandwidth compensation due to the narrowband functionality of the inverters is avoided.

Robust optimization and tuning of microwave filters and artificial transmission lines using aggressive space mapping techniques

Aggressive Space Mapping (ASM) techniques are widely used for the automated design of many passive microwave components. In this work, we will show their practical application to the robust design and post-manufacturing tuning of waveguide filters, as well as to the automated synthesis of planar filters and passive devices based on semi-lumped elements and artificial transmission lines. Efficiency and robustness, key issues in all these automated procedures, will be also deeply considered.

Optimized wideband differential-mode bandpass filters with broad stopband and common-mode suppression based on multi-section stepped impedance resonators and interdigital capacitors

This paper presents optimized balanced microstrip filters, in terms of size and design simplicity, by combining multi-section mirrored stepped impedance resonators (SIRs) and interdigital capacitors. The mirrored SIRs provide the necessary transmission zeros (for both the differential- and common-mode responses) to simultaneously achieve a broad stopband for the differential mode and efficient common mode suppression in the region of interest (differential-mode pass band) and beyond. The interdigital structures actually act as series resonators and allow for the design of filters with smaller size (as compared to other implementations based on quarter wavelength admittance inverters) and, most important, reduce the complexity of the automated (and unattended) design algorithm, based on aggressive space mapping (ASM). The design of an order-3 balanced quasi-Chebyshev filter with central frequency f0 = 1.5 GHz, fractional bandwidth FBW = 43% and 0.15 dB ripple, is reported as an illustrative example.

Unattended Design of Wideband Planar Filters Using a Two-Step Aggressive Space Mapping (ASM) Optimization Algorithm

This chapter deals with the automated and unattended design of planar wideband bandpass filters by means of aggressive space mapping (ASM) optimization. The approach can be applied to bandpass filters based on semi-lumped element resonators (e.g., stepped impedance resonators, ring resonators, etc.) coupled through admittance inverters (implemented with quarter-wavelength transmission lines). It will be explained how the filter layout is automatically generated from filter specifications, i.e., central frequency, fractional bandwidth, in-band ripple, and order, without the need of any external aid to the design process. For this purpose, a novel optimization algorithm based on two independent ASM processes will be fully described. The proposed automatic design procedure will be detailed and validated through its application to generate several filter layouts starting from different sets of practical specifications.