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A dual-band bandstop filter (DBBSF) with a dual-mode loop resonator is presented. In order to allow the DBBSF to exhibit high skirt selectivity and to generate a wide rejection bandwidth a capacitive coupled-line section is introduced. By properly controlling the length of the coupled-line section and the cross-coupled capacitor, more than two finite transmission zeros were inserted at the stopband and enhanced the rejection bandwidth.Introduction: A high performance bandstop filter (BSF) is one of the most important components of microwave circuits. To meet the size requirements of modern microwave communications systems, BSFs with low insertion loss, sharp rejection and wide rejection bandwidth are in high demand. A microstrip dual-mode loop resonator BSF has been developed for the aforementioned requirements [1,2]. In recent years, various topologies for microstrip dual-mode loop-resonators (DMLRs) have been reported to elucidate the mechanism of coupling between the two degenerated modes, which is mainly determined by the feed-line structure or different types of perturbation [1][2][3][4][5]. In [3][4][5], dual-mode BSFs have been illustrated to obtain high selectivity, low insertion loss and good stopband attenuation. However, the loopresonator coupled to a thru-line is suitable for the design of narrowband BSFs. In this Letter, in order to achieve size reduction and a wide rejection bandwidth, a dual-mode BSF with a cross-coupled capacitor is proposed and a frequency-selecting coupling structure (FSCS) is implemented [6,7]. The basic FSCS is realised by using a capacitive coupled-line section between microstrip feeding lines. The rejection bandwidth is extended by the FSCS and the design of the DBBSF. Moreover, adjusting the length of the capacitive coupledlines can determine the centre frequency of the first stopband and produce three transmission zeros (TZs) which effectively enhance the rejection bandwidth. The proposed DBBSF achieves the stopband frequency at 2.1 GHz with over 100% fractional bandwidth. More than 20 dB rejection is measured from 1.1 to 3.4 GHz.

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A novel balun based on an asymmetric coplanar waveguide with finite ground plane (ASYCPWFGP) to coplanar strip (CPS) transition is presented. A return loss better than 16dB is obtained up to 50GHz. The baluns are combined with four silicon Schottky barrier crossover diodes to yield a planar doublebalanced mixer (DBM) which demonstrates an ultra-broadband performance up to 40GHz.

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A complementary metal oxide semiconductor (CMOS) power amplifier (PA) using a wafer-level bondwire spiral inductor with high-quality factor (Q) is presented. The inductor is made by three top metal traces connected with bondwire loops above the CMOS chip. The proposed inductor with 2.75-nH inductance achieves a Q of 18, which is three times as much as that of a conventional CMOS standard spiral inductor at 2.4 GHz. The Q of the inductor is over 15 from 2 to 14 GHz, which can cover the frequency band of wireless sensor network and worldwide interoperability for microwave access applications. The output power and power-added efficiency of the PA with the inductor are improved by 1.5 dBm and 7% as compared with those of the fully integrated CMOS PA, respectively. Index Terms-Bondwire loop, complementary metal oxide semiconductor (CMOS), power added efficiency (PAE), power amplifier (PA), quality factor (Q), spiral inductor.

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