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This article presents a Ka-band switchable filtering power combiner monolithic microwave integrated circuit (MMIC), which unifies the functionalities of the switch, bandpass filter, and power combiner. For effective integration, a codesign approach is proposed by sharing the switchable resonant units and coupling matrix based impedance matching technique. Moreover, this approach offers great design freedom to realize arbitrary bandwidth and power ratios. For good return loss, the input external quality factor (Qe) is ensured as half of output Qe based on even-mode analysis. By analyzing the odd-mode circuit, the complex isolation element is introduced to improve the isolation between input ports. For demonstration, one prototype is implemented using a 100-nm GaN-on-Si process. Over 18-dB return loss, 1.7-dB minimum insertion loss (excluding 3-dB power ratio), >22 dB input–input isolation, and over 47-dB off-state isolation can be observed throughout 24–32 GHz. Besides, the proposed MMIC shows good linearity with a measured IP1dB of over 30 dBm within the passband, while the die size is 0.81 mm2. [ABSTRACT FROM AUTHOR]

This article presents a novel broadband dual-polarized filtering patch antenna array using low-temperature cofired ceramic (LTCC) process for 5G millimeter-wave (mmW) applications. The filtering antenna element is implemented using a ± 45° polarized patch antenna fed by two pairs of differential L-type probes. An additional square ring and open strips are connected to each probe, resulting in radiation nulls and realizing the lower/upper stopband rejection level over 24 dB with skirt selectivity. The cross coupling among these structures not only introduces filtering responses, but also contributes to broadening the passband of 24.25–29.5 GHz covering 5G n257/n258/n261 bands. The antenna performance is validated by equivalent circuits based on transmission line models, which reveals clearly the principles of filtering antenna step by step and provides guidelines for further designs. The proposed filtering antenna element is expanded to a $4\times 4$ filtering antenna array with shunt-fed feeding networks. The spacing between elements is $0.48~\lambda _{0}$. The measured results demonstrate that the array performs good filtering characters including high stopband rejection, high selectivity, and wide upper stopband up to 40 GHz, where the antenna efficiency (considering radiations from all the directions) is less than 5%. In addition, the differential feeds provide symmetric radiation patterns with low cross-polarized counterparts. Compared with other reported works, the proposed filtering antenna/array has excellent performances of wideband, high stopband rejection and wide upper stopband for potential 5G mmW applications. [ABSTRACT FROM AUTHOR]

This article presents an analytical design for millimeter-wave monolithic microwave integrated circuit (MMIC) switches. First, the field-effect-transistor-based (FET-based) resonator is proposed, whose resonant frequency and bandwidth can be controlled flexibly. As a result, the design flexibility of MMIC switches can be highly improved by using FET-based resonators. Second, a fast and flexible impedance matching technique is presented for MMIC switches based on the coupling matrix method. By selecting appropriate coupling parameters, the MMIC switches can be easily designed without designing multistage impedance matching circuits. In this way, low insertion loss (IL) and compact chip size can be accordingly obtained. For design validation, two single-pole single-throw (SPST) switch prototypes are designed and fabricated by using two or four FET-based resonators, respectively. Implemented in 100-nm GaN-on-Silicon HEMT process, high input 1-dB compression point (IP1 dB) of over 30 dBm is realized. The return losses are better than 15 dB, the minimum IL is only 1.1 dB at 30 GHz, and the isolations are higher than 45 dB. The above features indicate the validation of the proposed design method for MMIC switches. [ABSTRACT FROM AUTHOR]

In this article, a highly miniaturized absorptive bandpass filter based on a novel topology is presented. The filter topology utilizes a resistor-loaded network to achieve absorptive characteristics while additional capacitive coupling between series resonators is introduced to enhance selectivity. The proposed filter with a center frequency of 2.5 GHz and a 3-dB bandwidth of 2800 MHz is implemented using a GaAs integrated passive device (IPD) technology, exhibiting a small die size (0.7 mm × 1.13 mm), low loss in-band insertion loss (0.9 dB), high out-of-band rejection (8.8 f 0 ¿25 dB), and a wide low-reflection frequency range. The measurement results show good agreement with the simulations. These features show promising applications in highly integrated RF systems. [ABSTRACT FROM AUTHOR]