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Multiband bandpass filter is a key component in multistandard wireless communication system. This paper proposes a novel tri‐band bandpass filter (TB‐BPF) which consists of two mesh‐type multimode resonators (MT‐MMR) and two stub‐loaded U‐type feedlines. The MT‐MMR is formed by parallel connecting two open‐end stubs and one mesh‐type structure. Such specific configuration is featured by four inherent transmission zeros. The in‐depth analysis on the generation mechanism of the transmission zeros is made, and then a fast hybrid approach is developed for design procedure. Some explicit design equations are presented for fast determining initial values of some key parameters, and then further optimized by using a constraint condition, which effectively accelerate design process. For verification, an example of the TB‐BPF was designed fabricated and measured. Its center frequencies are at 3.16, 4.27, and 5.70 GHz, respectively. Six transmission zeros are generated for sharp frequency selectivity, and are at 1.46, 3.58, 3.86, 4.73, 5.51, and 7.18 GHz, respectively. Its size is about 0.59 × 0.19 λg2. [ABSTRACT FROM AUTHOR]

Nowadays, there is a trend to simultaneously integrate various applications in one communication system, in which multiband digital filter will play an important role in frequency selection. For digital signal processing, this paper proposes an advanced design method for the design of multiband IIR filter. This method is based on the concept of direct synthesis technique (DST) we proposed for analogue general Chebvshev filter, which is called the DST-O method here. According to specification requirement of the multiband IIR filter to be designed, main information such as transmission zeros and reflection zeros are determined by using the DST. Then, optimization is applied to achieve equal ripple in all passbands. Finally, the transfer function of the multiband IIR filter is obtained by applying the bilinear transformation on that of the analogue one. Such hybrid method fully combines the advantages of both analytical and optimal approaches, and is featured by flexibly controlling centre frequencies, bandwidths and passband ripples. Some multiband IIR filter examples are provided for demonstration. [ABSTRACT FROM AUTHOR]

In this letter, a four‐pole balanced frequency‐agile bandpass filter (BAL‐FA‐BPF) with constant absolute bandwidth (CABW) and four transmission zeros (TZs) is reported. This design is based on the advanced coupling matrix technique which ensures the realization of CABW for the filter. The fully‐canonical coupling topology with cross‐coupling and source‐load coupling is adopted, which introduces four TZs for the differential‐mode passband. The tunable half‐wavelength resonators are used and loaded by resistors, which effectively enhances the common‐mode (CM) suppression. The demonstrative BAL‐FA‐BPF has a frequency tuning range of 1.92‐2.97 GHz (42.9%) and keeps the absolute bandwidth within 167 ± 3.7 MHz (2.2%) over entire the FTR. CM suppression is better than 40 dB. [ABSTRACT FROM AUTHOR]

This paper proposes a 3‐pole wide‐tuning‐range, balanced frequency‐agile bandpass filter (BAL‐FA‐BPF) with constant absolute bandwidth (CABW) and 3 transmission zeros (TZs). Under the differential‐mode (DM) operation, the cascaded trisection coupling topology with source‐load coupling is constructed. Thus, 3 adaptive TZs are generated for the DM responses, which improves the passband selectivity and stopband suppression. Under the common‐mode (CM) operation, the short stubs and lumped elements are added at the symmetric plane which effectively improves the CM suppression. Using the advanced matrix synthesis, a demonstrative BAL‐FA‐BPF is designed with stable CABW and controlled by single‐DC‐bias. The measured frequency tuning range of the DM passband is 2.0 to 3.0 GHz (40%) and 3 dB‐bandwidth is kept at 174 ± 3 MHz (±1.7%). The CM suppression is better than 25 dB. [ABSTRACT FROM AUTHOR]

In this article, a pair of stub‐loaded interdigital hairpin resonators‐based filter with high group delay and improved stopband suppression is used to design an S‐band ultra‐low phase noise single‐ended oscillator. A transmission zero closed to the edge of passband in the filter is generated by introducing strong electric and magnetic coupling, which can improve the phase noise performance of the proposed oscillator. A low phase noise figure‐of‐merit (FOM) that considers both insertion loss and group delay of the feedback loop is used to evaluate the overall phase noise performance of the proposed oscillator. In order to verify the concept, the proposed oscillator is designed and fabricated. The measured results show that the oscillation frequency is 2.037 GHz with the output power of 8.92 dBm while the second harmonic suppression level is about 35.66 dB. The phase noise and the FOM of the proposed oscillator at 100 kHz frequency offset are −127.95 and −199.31 dBc/Hz, respectively. According to the open literature, this is one of the best phase noise performances of the single‐ended hybrid integrated oscillators oscillating at the similar frequency range. [ABSTRACT FROM AUTHOR]

Summary: In reality, it is not easy to design microstrip filters for the sake of distributed‐element effect. It is an effective approach to approximate distributed‐element structures through appropriate lumped‐element circuits. In this paper, some basic microstrip structures are discussed, whose equivalent lumped‐element circuits are derived. Then, a novel microstrip filter is obtained by connecting these microstrip structures, according to the similar topology of the third‐order lumped‐element bandpass filter. The equivalent lumped‐element counterpart of the proposed microstrip filter clearly reveals its physical mechanism, ie, how the resonances are created and coupled and how the transmission zeros are created. Furthermore, a set of the design formulas are presented, which can be used to calculate initial structure parameters and then facilitate design process. The proposed microstrip bandpass filter can realize a third‐order elliptic bandpass response with one transmission zero at each side of the passband. In addition, two short‐circuited stubs are added to input/output ports to create the third transmission zero. The filter is featured by good frequency selectivity and out‐of‐band suppression. For demonstration, an actual example was designed, fabricated, and measured. In reality, it is not easy to design microstrip filters for the sake of distributed‐element effect. It is an effective approach to approximate distributed‐element structures through appropriate lumped‐element circuits. In this paper, a novel microstrip filter is obtained by applying the distributed‐ to lumped‐element equivalence. The equivalent lumped‐element counterpart of the proposed microstrip filter clearly reveals its physical mechanism, ie, how the resonances are created and coupled and how the transmission zeros are created. The filter is featured by good frequency selectivity and out‐of‐band suppression. [ABSTRACT FROM AUTHOR]

A compact ultra‐wideband (UWB) bandpass filter based on a novel multi‐mode resonator (MMR) is proposed. The MMR consists of a pair of open‐circuited stubs and three pairs of coupled‐line sections, which can generate four main resonant modes in the desired band, i.e. two odd modes and two even modes. The measured results of a fabricated one show that its bandwidth can cover the UWB frequency range and it has a sharp skirt due to two transmission zeros near its passband. Return loss in the passband is better than −10 dB. Meanwhile, at least −40 dB suppression can be achieved from 11.86 to 15.13 GHz and −30 dB suppression from 12 to 16 GHz. [ABSTRACT FROM AUTHOR]