A pulse-Doppler (PD) radar has the advantage of strong anti-interference ability, and it is often used as a solution for maneuvering target tracking. In the application of target monitoring and tracking in PD radars, the interacting multiple model algorithm (IMM) has become the main and preferred choice due to its flexibility and high accuracy. However, the probability transfer matrix in classical IMM algorithms generally depends on constant prior knowledge, and if a PD radar is tracking a strong maneuvering target, it is inevitable to encounter some limitations, such as the possibility of target tracking trajectory deviation, and even a loss of the target. The Markov probability transfer matrix is proposed with an adaptive modification ability in real time to overcome the above problems in this paper. Additionally, for improving the speed of switching between the models, the fuzzy control system for secondary updating of model probability is adopted. By this means, the tracking accuracy of maneuvering targets is enhanced. Compared with the classical IMM algorithm, the corresponding simulation results for the PD radar indicate that the overall tracking accuracy of the proposed adaptive IMM algorithm is improved by 19.6%. In conclusion, the continuity and accuracy of the target trajectory can be effectively improved with the proposed adaptive IMM algorithm in PD radar cases.

A polarization reconfigurable metasurface wideband antenna with dual polarized and a low radar cross section (RCS) is presented. The antenna employs a diode positioned between two transmission lines to control the current direction and a resistor on a defected-ground branch to manage phase shifts, enabling seamless transitions between circular polarization (CP) and linear polarization (LP). The elliptical metasurface design contributes to a reduced RCS. The design results are verified through measurement, showing an impedance bandwidth (IBW) of 49.1%, an axial ratio bandwidth (ARBW) of 23.2% for the diode is OFF, an IBW of 36.4% for the diode is ON, the IBW of the connected resistor is 40.7%, and the peak gains for the three states are 6.4 dBi, 4.4 dBi, and 4.2 dBi, respectively. The metasurface achieves a low RCS bandwidth ranging from 2 GHz to 24 GHz, showing a 6 dBsm reduction in RCS from 4.9 GHz to 19.7 GHz, which corresponds to a 120.3% decrease compared to a PEC plate.

A millimeter-wave (mmW) dual-band dual-circularly polarized high-efficiency radial line slot array (RLSA) antenna fed by gap waveguide technology is presented in this paper. By introducing the periodic bed of metallic pins, an air-filled slow-wave parallel-plate waveguide (PPW) is constructed without high precision electrical connection. The slow-wave characteristic is realized since the height of pins are controlled, and the modes of electromagnetic wave is changed. Meanwhile, the rotation mode of traveling wave field inside the PPW is controlled by different phase excitations from feeding ports. The characteristics of concentric slots are analyzed based on equivalent models as well. Based on this foundation, the dual-circularly polarized performance is realized, including the left-hand circular polarization (LHCP) radiation at 30 GHz based on concentric slots, and the right-hand circular polarization (RHCP) radiation at 25 GHz based on continuous rotation theory. The feedings for the proposed RLSA are improved with a mid-section feeding method to increase the compactness and bandwidth of the antenna. In addition, a butler matrix based on gap waveguide technology is designed for the array excitation with low loss advantages. Finally, the dual band dual-circularly polarized antenna array is designed and fabricated to validate the performance. The measured results show that the impedance bandwidths are 24.3-26.8 and 29.1-31.1 GHz, and the axial ratio is lower than 1.5 dB over the bandwidth. Besides, the aperture efficiency reaches up to 54.6% and 68.2% respectively.

A low‐profile wideband circularly polarized (CP), single‐layer antenna with low radar cross section (RCS) reduction based on staggered elliptical metasurface using characteristic mode analysis (CMA) is presented. The staggered arrangement of the elliptical metasurface has a 90° relationship, ensuring the generation of circular polarization, and their modes of fusion can achieve RCS reduction by CMA. The defective ground shows that the difference in characteristic angle (CA) between the two pairs of modes is about 90°. The measured results show that the antenna has a 40.6% (5.5 GHz–8.3 GHz) impedance bandwidth (IBW), a 26.2% (6.3 GHz–8.2 GHz) 3‐dB axial ratio bandwidth (ARBW), and a peak gain of 5.1 dBic is achieved at 6.3 GHz, and with a large RCS reduces across the frequency range from 2.0 GHz to 22.0 GHz (166.7%). Monostatic RCS reduction of more than 5 dBsm is achieved within the frequency range from 4.6 GHz to 22.0 GHz (130.8%).

In this paper, a wideband circular polarized (CP) antenna based on double ridge gap waveguide (GWG) with end-fire radiation is proposed. The symmetric tapered slots are etched for CP condition. The periodic ridge structures are introduced between the transition ridge and periodic pins to increase the current path. By this means, the appropriate phase differences of orthogonal electric fields are achieved within compact radiation aperture. The bent dipoles are added at the end of the tapered slot to improve the amplitude and phase condition in lower frequency. Additionally, the gradient transitions from the ridge to radiation aperture are adjusted for wide impedance matching performance. To validate the proposed antenna, a 1×4 CP array fed from the double ridge GWG power divider was fabricated and measured. A measured bandwidth of 32.6% (28.2-39.2 GHz) for both S₁₁<-10 dB and AR<3 dB is achieved. Taking advantage of the double ridge GWG, the radiation performances of this antenna are measured with symmetric patterns and peak gain of 15 dBi. Besides, the efficiency of this antenna is more than 74.5% over the frequency band.