A balanced microstrip bandpass filter (BPF) with quasi-reflectionless (QR) characteristics on both input and output ports and good common-mode (CM) rejection is proposed in this brief. The presented QR BPF consists of a Pi-shaped BPF and two absorptive bandstop filters (ABSFs). Good QR performance is achieved by the complementary duplexer architecture formed with these two parts. The balanced microstrip-to-slotline (MSTS) transition structures are used to achieve exceptional CM rejection without deteriorating differential-mode (DM) transmission. The in-band energy is transmitted by the BPF section, where the ABSFs appear as open circuits. The out-of-band energy is absorbed by a pair of loaded resistors in the bandstop section. Through detailed analysis, it shows that by loading the ABSF structures at both ends of the BPF section, the DM passband selectivity is improved and six quasi-transmission poles (Quasi-TPs) are generated on both sides of the DM passband to eliminate out-of-band reflections. To verify the feasibility of the proposed model, a prototype was designed and fabricated, whose simulations and measurements are in good agreement.

In this brief, a balanced dual-band bandpass filter (BPF) using quad-mode ring loaded resonator (RLR) is presented. The resonance characteristics of the proposed quad-mode RLR are analyzed and the design graphs of the electrical lengths and the four resonant modes are given. Based on the above analysis, four resonant modes are applied to achieve two differential-mode (DM) passbands. U-shaped microstrip lines and stepped impedance microstrip/slotline (MS) transition structures are employed to achieve good common-mode (CM) rejection without affecting DM ones. In addition, an additional transmission pole is realized in the lower passband due to the stepped impedance slotlines. Meanwhile, six transmission zeros (TZs) are generated due to the horizontal transmission interference of the resonator and new coupling path, which improves the selectivities of the passbands. Furthermore, based on the proposed filter, a balanced dual-band filtering power divider (FPD) is designed for miniaturization. By loading isolation resistors on the slotline, the output ports isolation is improved. To verify the theoretical design, two proposed designs have been manufactured and measured. The measured and simulated results are presented with a good agreement.

An accelerated shooting and bouncing ray (SBR) method is presented in this letter to improve the efficiency of radar cross section (RCS) prediction for electrically large and complex objects. The SBR method is inefficient because it needs to trace a large number of ray tubes. Therefore, its efficiency can be improved by reducing the amount of ray tubes and increasing the speed of ray tracing. In this paper, we use rays instead of ray tubes to reduce the amount of rays that need to be traced, and construct a virtual ray tube (VRT) at the ray exit position for field integration. Moreover, ray tracing and integration operations are executed on the graphics processing unit (GPU) to further improve the efficiency of SBR method. Several examples are designed to prove the effectiveness of the proposed method.

A 3D printed conformal polarization converter, based on a novel dielectric unit cell, is proposed for linear-to-circular polarization conversion. The designed dielectric unit cell comprises a cuboid-shaped dielectric block and a thin square dielectric substrate layer for ease of fabrication with 3D printing technology. Meanwhile, the unit cell can achieve linear-to-circular polarization conversion performance from 14.2 GHz to 20.1 GHz with 3-dB axial ratios (ARs) of 34% and good angular stability within 40°. Then, the unit cell is applied to design the conformal dielectric linear-to-circular polarization converters (LCPCs) for cylindrical and spherical surfaces, respectively. To verify the feasibility, three kinds of dielectric converters including planar, cylindrical, and spherical shapes are fabricated and measured. The measured results demonstrate that the proposed dielectric polarization converters with different shapes can produce almost similar linear-to-circular polarization performances with low loss, high conversion efficiency, and angular stability within 40°.

A balanced filtering directional coupler (BFDC) based on slotline is designed in this paper. The proposed coupler is composed of balanced microstrip/slot (MS) transition feed structures, three-line cross-finger-coupled resonant structures and asymmetric parallel loaded branch. The MS transition feed structure is adopted at the input and output ports to make the differential mode (DM) response independent of the common mode (CM) one and achieve a good CM suppression. Two transmission zeros (TZs) are generated and controlled by the coupling of three-line cross-finger-coupled resonant structure, thereby the out-of-band selectivity can be enhanced. Asymmetrical parallel loaded branch can effectively improve the flatness of the coupler. In order to verify the design strategy, the coupler was designed, fabricated and measured, and the measurement results are in good agreement with the simulation ones. The DM operating band of the designed coupler covers 4.2 GHz to 5.3 GHz (FBW=24%) with 15 dB return loss. Isolation is better than 15 dB and CM suppression is better than 40 dB.

In this paper, we firstly reveal the performance degradation and physical failure mechanism of a lab-designed GaN power amplifier (PA) module based on a commercial GaN High-Electron-Mobility-Transistor (HEMT) with high power electromagnetic pulse injected. We carried out a systematic step pulse injection experiment to hunt out the degradation and failure threshold of PA module by monitoring its S-parameter and the gate-source resister ( R _GS ) of GaN HEMT. Moreover, the performance indexes of GaN PA, including Gain, power-added efficiency (PAE), output power, and signal-to-noise ratio, have been measured before/after degradation for comparative analysis. The intact surface circuit microscope of PA module and the degradation electrical characteristics of GaN HEMT demonstrated that the GaN HEMT is the vulnerable component of GaN PA. Furthermore, the numerical simulations and de-capsulation experiments are carried out for GaN HEMT to gain insight into the failure process and physical failure mechanism. The results reveal that the failure mode is thermal induced gate metal melting of the GaN HEMT. The failure mechanism is mainly attributable to the impact ionization which induced by the high pulse voltage under the gate near the source. This is followed by the thermal-electrical feedback state in the device internal until the temperature finally reaching the melting point of the gate metal.