Rong Liu

In 5G N78 front-ends, nonlinear harmonics from power amplifiers degrade receiver sensitivity and require compact suppression. This letter presents a miniaturized ferrite circulator integrated with a second-harmonic absorptive filtering (SHAF) branch. Utilizing a WYE resonator, a reflective central junction is constructed to effectively block second-harmonic leakage toward the receiver (RX) port. A filtering branch is shunted to absorb the harmonic component with limited impact on fundamental-band transmission. Measurements show a 21.5% fundamental bandwidth from 3.1 to 3.85 GHz with insertion loss below 1 dB and $\vert $ S $11\vert $ below −10 dB over 6.68–7.73 GHz. A continuous subband from 3.185 to 3.59 GHz further achieves IL 14.6 dB, and isolation > 20 dB. The proposed scheme provides a compact solution for integrating circulation and internal second-harmonic absorption.

Four-port single-junction circulators are widely employed in in-band full-duplex systems owing to their advantages in size and manufacturing cost. This article presents a broadband synthesis method for miniaturized four-port single-junction microstrip circulators. By applying multiple rotation mode (MRM) analysis to the design of the four-port single-junction configuration, the azimuthal characteristics of the internal modes within the cross resonator are effectively reconstructed. For the central junction with arbitrarily complex conductor geometries, a simple and effective method for extracting input impedance is proposed, and the reactance compensation principle of the central junction is analyzed in combination with the equivalent circuit. A folded transmission circuit is constructed via a compact impedance-matching network to achieve the miniaturization of broadband circulators. The proposed miniaturized four-port single-junction circulator prototype is fabricated and measured, with the measurement results demonstrating an excellent agreement with the expected performance. Measurement results indicate that the proposed circulator achieves a relative bandwidth of over 70% for 1-dB insertion loss, with return loss better than 17 dB. The isolation of S₃₁ and S₄₁ is better than 16 and 17.8 dB, respectively. The cross-sectional circuit dimensions of the miniaturized circulator are only $11\times 11$ mm ( $0.39\lambda _{0} \times 0.39\lambda _{0}$ ).

An ultrawideband (UWB) microstrip circulator loading spoof surface plasmon polaritons (SSPPs) based on multiple azimuthal-rotating modes is presented. To address the limitations of existing ferrite resonator theories in UWB circulators, a design methodology for enhancing the frequency bandwidth is realized through characteristic analysis and mapping mechanism discussions of multiple rotation modes (MRMs). By employing various resonator configurations, the frequency responses of multiple forward azimuthal-rotating modes are effectively regulated. The construction of composite ferrites (CFs) is leveraged to suppress radial radiation, significantly improving the isolation performance. The stable and compact topological circuit is achieved via utilizing a metal conductor loaded with multiple SSPP stubs. The experimental prototype demonstrates an excellent agreement with simulated and measured results. The proposed compact circulator boasts a cross-sectional dimension of merely 0.264λ₀ × 0.264λ₀. Within frequency band of 6.83–18 GHz, both return loss and isolation of the circulator are better than 15 dB, and the insertion loss of the circulator remains below 1.2 dB. The proposed circulator possesses potential for future applications in broadband communication and radar components.

An X-band active phased array horn antenna with high power capacity and high peak power is proposed in this paper. At the horn aperture, the baffles are loaded to suppress higher-order modes and eliminate blind spots during beam scanning. Straight walls are added to improve impedance matching. Considering that the peak power that T/R modules can provide is very limited, the proposal of a dual-port waveguide breaks through the bottleneck of the power capacity of a single-port input for the first time. The proposed curved dual-port waveguide is used to connect the horn antenna and the T/R module, which is verified to improve the power capacity of the overall internal structure. Simulated and measured results show that VSWR ≤ 2 in the frequency range of 7.5–8.5 GHz. There is no grating lobe in the ±10° scanning range and the maximum gain drop does not exceed 0.4 dB. The power capacity of the proposed HPM array is 56.34 MW. The phased array antenna has the characteristics of flexible scanning, small size, and high gain, and can be applied in high-power microwave systems.