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This paper presents a universal design approach of multiport filtering power divider with the arbitrary power-division ratio, which is applicable for the designs of the single-ended/balanced circuit or hybrid of them. The power allocation in a specified passband is fulfilled by relying on two key factors in building a filter, i.e., coupling coefficient and external Q -factor (Qe). After synthesis for the bandpass response, the total input/output Qe and the total coupling coefficient at each power dividing level can be determined. Subsequently, according to the desired power-dividing ratio, the coupling coefficient between the two coupled resonators and Qe of each output can be easily determined. Once the parameters for filtering response are fixed, the power allocation can be determined by Qe without effect on the filtering response. Thus, the two functions of bandpass and power dividing can be designed independently, which provides tremendous freedom for the overall design with the arbitrary order of filtering and number of output ports. The proposed topology has several advantages, such as flexibility, cost efficiency, and simple design procedure, which would be a good candidate for multiple-path operation in the current and future MIMO systems.

A fully-integrated 24/77 GHz dual-band receiver is presented for automotive radar applications. The proposed receiver consists of a dual-band LNA, a dual-band sub-sampling PLL, and a wideband mixer, operating at 24 and 77 GHz alternatively. Implemented in 65 nm CMOS technology, the receiver achieves 760 and 1800 MHz bandwidth with 52 and 60 mW power consumption in 24 and 77 GHz operation modes, respectively. To the best of authors' knowledge, this is the first fully-integrated CMOS 24/77 GHz dual-band receiver for automotive radar applications.

A compact rectifier with high efficiency at wide input power dynamic range is proposed in this paper. The circuit consists of a matching network, two shunt connected diodes with an integrated impedance compression network (IICN) and a dc-pass filter. The IICN significantly reduces the diode impedance variation when input power changes, hence improves matching as well as efficiency of the rectifier at wide input power dynamic range. Different from the conventional resistance/impedance compression networks, which can only work under certain impedance condition with dual-branch topology, the IICN can directly operate two diodes in parallel in a single-branch with no impedance limitation. Thus, less components and branch are needed, resulting in size reduction and lower circuit complexity. The design flexibility is also enhanced. Mechanism of the IICN is analyzed. A prototype operating at 2.45 GHz is optimized, fabricated and measured. The total size of the prototype is 0.18λ2. The efficiency higher than 70% of the peak value is realized at input power ranging from 0.8 dBm to 18.0 dBm.

A polarization-reconfigurable and frequency-tunable mechanism based on an active artificial magnetic conductor (AMC) structure is proposed. The active AMC unit cell consists of a four-corner-cut inner patch and four triangles loaded with four varactors, and it can realize polarization-reconfigurable and frequency-tunable reflection characteristics by adjusting the capacitance of the varactors. By employing it as a ground plane of a pair of linearly-polarized dipole antennas, a multi-functional antenna can be well designed with polarization reconfigurability and frequency-tuning capability. By controlling the DC bias of the varactors accordingly, the three polarization states of right-/left-handed circular polarization (R/LHCP) and linear polarization (LP) can be switched, respectively, while the operating frequency of each polarization can be flexibly tuned. The measured tuning frequency ratio for the LP state (|S11|

A novel class of low-temperature cofired ceramic (LTCC) bandpass filters (BPFs) is proposed in this paper, featuring of compact size and good filtering responses in both microwave and millimeter-wave (mm-wave) bands. By effectively merging the lumped elements and distributed effects, a modified LTCC-based hybrid lumped and distributed resonator (HLDR) is introduced. In detail, the lumped part of a LTCC interdigital capacitor and a high-impedance line is used to reduce circuit size, loss, and cross-talks. The distributed part, saying, the mutual couplings between adjacent HLDRs and to the ground, is used to improve the design flexibility and filtering performance for HLDR filters. With mutual couplings, the coupling matrix method can be applied. Furthermore, the frequency-variant mixed couplings between HLDRs are investigated, and coupling matrix method is improved by introducing a new coupling mechanism. Multiple transmission zeroes (TZs) are firstly realized with second-order in-line topology, but without adding cross-couplings or bandstop structures. To validate above design strategies, one S-band and one Ka-band second-order HLDR BPFs are simulated and measured, respectively. Very compact size, low loss, high-selectivity, and wide upper stopband are observed, especially in mm-wave range.

This paper presents a novel four ports double Y-shaped photonic crystals circulator with ultra-wide bandwidth in 5G millimeter wave band. Its insertion loss can be designed as low as 0.38 dB at 26.10 GHz while its optimal isolation is up to 74.86 dB at 25.00 GHz. The circulator keeps its isolation above 20 dB from 21.80 to 29.04 GHz. Our simulations also show the relative bandwidth can be effectively broadened to be 28.48% through adding an impedance matching transformer composed of four triangular metal pedestals. We confirmed our theoretical results with a circulator sample made of a triangular-lattice Al2O3 ceramic rod array and ferrite posts. The minimal measured isolation and insertion loss have reach 47.61 dB and 0.80 dB at 25.55 GHz and 26.10 GHz, respectively. The operating spectral region of our sample covers from 24.08 to 28.23 GHz (the relative bandwidth is 15.87%), which is about seven times higher than the best simulated result of 2.5% and fifteen times higher than 1.07%, the published experimental value. Our experimental results are well matched with the numerical simulations. The low loss, high isolation and ultra-wideband characteristics demonstrate that our photonic crystal circulator has potential applications in 5G communication systems.

This paper presents a wideband circularly polarized (CP) antenna based on two Vivaldi antenna elements. The two elements are orthogonally placed for compact consideration, and are driven by a specially designed wideband feeding network that splits the input signal into two-way signals with equal magnitude and orthogonal phase. In order to avoid crossing of the feeding lines of two Vivaldi elements, a small shift between them is introduced. This, however, will result in the undesired phase difference of two Vivaldi elements inevitably. To compensate the phase difference and ensure a wide axial ratio bandwidth, the feeding network is specially designed. Besides, to make full use of the antenna space, the feeding network is placed on the surface of two Vivaldi elements. For demonstration purpose, a prototype is fabricated. The measured results show a -10 dB impedance bandwidth of 101.3% (2.35 to 7.18 GHz) and 3 dB axial-ratio bandwidth of 118.4% (2.05 to 8 GHz), and the maximum realized gain is 7.5 dBic. Meanwhile, stable radiation patterns are achieved with the cross-polarization lower than -20 dB across the wide operating bandwidth at boresight direction.

This paper presents a V-band Doherty power amplifier (PA) which is implemented in a standard 65-nm CMOS technology. The voltage combination technique is used to realize the millimeter-wave Doherty PA without the λ/4 transmission lines. A Marchand balun with balance compensation is designed to combine the output power with reduced power loss. Moreover, a nonlinear driver is used to drive the peaking amplifier to enhance the output power and the turn-on speed of it. The power-added efficiency (PAE) of this PA at the 6-dB power back-off point is 8.7% and the peak PAE reaches 16.8%. The small signal power gain is 18 dB, and the maximum output power is 14.9 dBm. The core circuit only costs 0.195 mm2 chip area as no λ/4 transmission lines.

A dual-layer patch antenna using multiple parasitic patches for the bandwidth enhancement is presented. Two additional resonances can be obtained with the help of the parasitic patches of the antenna. Consequently, a wide impedance bandwidth of 17% (|S11|

Patch antennas with multiple feeds are proposed in this paper. The antennas consist of a traditional square patch and feeding probes that are set in a line orthogonal to the polarization direction. In addition to radiating EM energy just like the conventional antennas, the proposed multi-port antennas can also realize on-antenna power combining without power combiner. Thanks to this, high-line losses and large system size caused by extra power combiner can be avoided. Moreover, since the location and the number of ports have a limited effect on the antenna performances, flexible feeding strategies can be chosen in different applications. For demonstration, four patch antennas with a different number of ports (one port, two ports, three ports, and four ports) are designed at the center frequency of 1.5 GHz. Compared with the traditional one-port patch antenna, the proposed three multi-port patch antennas can achieve nearly the same antenna performance, including bandwidth, polarization, efficiency, and radiation pattern. Besides, one-port antenna and two-port antenna integrated with a two-way power amplifier are designed and measured, respectively. Then, they are compared to further prove the proposed power combining method in multi-port antennas.

Based on the concept of conventional Gysel power divider, a novel concept of half-mode substrate integrated waveguide (HMSIW) Gysel power divider was reviewed and developed, by simply combining a traditional HMSIW power divider and a microstrip isolation network. The proposed concept was reviewed, investigated, and analyzed thoroughly, after that, Y-type, T-type, and Parallel-type HMSIW Gysel power divider were designed and analyzed, respectively. Furthermore, based on Parallel-type design, a developed version using two isolation networks was proposed for frequency bandwidth enhancement. All the four prototypes were fabricated and measured for verification and comparison. The good electrical performances and compact configuration indicate the advantages of the proposed concept and an excellent candidate for high power-handling HMSIW/SIW circuits or systems.