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In this article, two types of substrate-integrated defected ground structure (SIDGS) resonant cells with wide upper stopband and low radiation loss are presented for filter implementation. Such SIDGS resonant cells are composed of two dissimilar DGSs surrounded by the bottom ground and metal-vias, which cannot only introduce wide stopband with low radiation loss but also be flexible for integration. Based on the aforementioned SIDGS resonant cells, single-and dual-band bandpass filters (BPFs) are designed and fabricated. The singleband BPF centered at 2.40 GHz exhibits an ultrawide upper stopband up to 19.7 GHz with a rejection level of 31 dB, whereas the measured stopband total loss (i.e., including radiation, metal, and substrate loss) remains about 30% up to 19.3 GHz. The dualband BPF operated at 2.10 and 3.78 GHz exhibits an ultrawide upper stopband up to 17.8 GHz with a rejection level of 23 dB, whereas the measured stopband total loss is less than 16% up to 11.4 GHz.

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In this paper, two types (i.e., type-A and type-B) of hybrid microstrip/defected ground structure (DGS) cells are proposed for passive circuit implementation with ultra-wide stopband. Both cells consist of the stepped-impedance DGS and embedded folded slotline on the ground, which could obtain the dual-resonances. In type-A cell, a microstrip T-stub on the top side is introduced, which can not only allocate a strong coupling to the DGS with slotline on the bottom side, but also act as the input/output port. To finely adjust the dual-resonances of the type-B cell, a grounded microstrip patch is used. Meanwhile, such compact cells could feature an ultra-wide upper stopband, due to their own slow-wave effect. Based on the aforementioned hybrid microstrip/DGS cells, two dual-band bandpass filters (BPFs) and a dual-band filtering power divider (FPD) are proposed and fabricated. Measured and simulated results are in a fairlyclose agreement. Both dual-band BPFs exhibit the ultra-wide upper stopband, which extends up to 40 GHz with a high rejection level about 30 dB. Besides, the dual-band FPD has merits of more than 18.7 dB of in-band isolation and 28 dB stopband rejection levels up to 40 GHz. INDEX TERMS Bandpass filter (BPF), defected ground structure (DGS), dual-band filter, filtering power divider (FPD), slow-wave, ultra-wide stopband.

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A quadrature digital power amplifier (PA) with hybrid Doherty and impedance boosting (HDIB) technique is presented for deep power back-off (PBO) efficiency enhancement in the complex domain. Less power-combining ways and dc power supplies are required for proposed PA comparing to previously reported works with deep PBO efficiency enhancement. A reconfigurable matching network (RMN) based on a novel reconfigurable transformer is proposed with more freedom to achieve a flexible load impedance tuning range of the sub-PAs. The characteristics of the reconfigurable transformer based on tunable inductors are analyzed. Efficiency enhancement is achieved at 3-/6-/9-/12-/15-dB PBOs without any supply switching or PA short-switches. The PA is fabricated in 40-nm CMOS technology with a core size of 0.83 mm 2 . Operating at 2.3-3.4 GHz, it introduces 24.2-dBm peak P out with 38.5% peak drain efficiency (DE) at 2.8 GHz. It achieves 38.5%/29.6%/18.4% at 2.8 GHz and 34.7%/26.6%/17.8% DE at 3.3 GHz for 0-/6-/12-dB PBO, 39.3%/29.5%/14.9% at 2.8 GHz, and 35.3%/27.9%/15.9% DE at 3.3 GHz for 3-/9-/15-dB PBO, respectively. For 10-MHz 256-QAM modulation signal, it delivers 16.22-/15.50-dBm average P out with EVM of −32.3/−33.0 dB, average DE of 24.6%/22.7%, and ACLR of −33.20/−31.54 dBc at 2.8/3.3 GHz, respectively. For 20-MHz 64 QAM modulation signal, it exhibits 16.42-/15.52-dBm average P out with EVM of −29.1/−29.3 dB, average DE of 24.9%/22.78%, and ACLR of −30.78/−30.74 dBc at 2.8/3.3 GHz, respectively.

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