A compact Ka-band monopulse Cassegrain antenna based on the reflectarray elements is presented in this letter. The proposed antenna consists of a main-reflectarray, a sub-reflectarray, a SIW comparator and a monopulse feed to achieve good sum-difference characteristics. Compared with traditional monopulse Cassegrain antenna, the total length of the proposed antenna is shrinked to 67.85%. The results of measurement agree with that of simulation very well. The measured SUM beam gain of the proposed antenna is 29.4 dBi by eliminating the loss of Ka-band comparator, the 3-dB beamwidth is 3.85°, the first sidelobe level is under -12 dB, the cross-polarization level is better than -20 dB, and the gain ratios between the SUM and DIFF are about 3 dB and 5 dB in azimuth and elevation plane, respectively. The measured results show that the proposed antenna is a good candidate for the low-cost multi-mode tracking system with limited space, especially for that working at high frequency.

Based on the linear responses and nonlinear (NL) loss effects of ferrite, a filtering–limiting (FT) integrated device applicable to the high-power microwave (HPM) electromagnetic environment is proposed. The small-signal bandpass filtering characteristics of the FT device with polycrystalline yttrium iron garnet (YIG) as a substrate are achieved using the conventional parallel-coupled microstrip structure. When HPM pulses within the operating frequency band are injected, the NL loss effects are excited in this device, achieving power-limiting characteristics. However, the spatial distribution of the RF magnetic fields in such a device is extremely inhomogeneous. There is currently no commercially available simulation tool that can effectively calculate the power loss performance of ferrite materials in the HPM electromagnetic environment. Therefore, combined with the transient-state NL threshold theory, an equivalent iterative simulation method for structure partition is proposed. This method is utilized to quantitatively evaluate the power loss of such resonant structures. The simulated results align well with the measured trends and can successfully indicate the limiting threshold, limiting isolation, and dynamic range of the FT device under HPM conditions.

With a low guiding magnetic field, a highly efficient X-band coaxial superradiant relativistic backward wave oscillator (SR-RBWO) with a front-extraction cavity and a built-in mode converter is proposed in this paper. The coaxial structure is used to reduce the guiding magnetic field of the intense relativistic electron beam. To decrease the transmission loss of microwave power in the slow wave structure (SWS), a front-extraction cavity is introduced. The inner conductor of the coaxial SWS is hollowed out as the output waveguide, and then, the microwave is extracted by the front-extraction cavity and enters the hollow waveguide rather than re-enter the SWS to output. With this improvement, the power conversion factor K can be increased by 0.44 even more. Making use of the feature of longer SWSs of SR-RBWOs, a built-in mode converter is designed, which can convert the circular TM01 mode propagating in the output waveguide into the circular TE11 radiation mode that can be radiated into free space directly. Therefore, the length of the radiation system can be reduced significantly, which is beneficial to the miniaturization of the entire high-power microwave system. Particle-in-cell simulation demonstrates that with a diode voltage of 180 kV and a guiding magnetic field of 0.37 T, the output SR pulse with an average power of 1.00 GW corresponding to power conversion factor K = 1.8 can be obtained.

In this letter, a novel high-power microwave (HPM) phase shifter (PS) is proposed. The PS is based on the principle of tunable electrical length and can shift phase by turning a rotary choke piston in a toroidal-shaped phase-shifting segment. The simulation results show that the PS can shift phase linearly over 360 $^{\circ}$ in the frequency range of 2.7–2.9 GHz, the power handling capacity of this PS exceeds 450 MW, and the phase-shifting precision reaches 3.29 $^{\circ}$ / $^{\circ}$ at the central frequency. The cold test showed that the measured phase-shifting performance of the PS is in good agreement with the simulation results, furthermore, the PS can shift phase within 360 $^{\circ}$ in 30 ms, the return loss is higher than 12 dB, and the insertion loss is less than 0.4 dB.

A novel polarization rotation element (PRE) is employed to design a wideband transmitarray antenna (TA). The PRE comprises three metallic layers. The middle layer features double C-shaped patches, while the upper and bottom layers consist of two grating polarizers. By adjusting the opening sizes and directions of the double C-shaped patches, full phase coverage within -1 dB transmission magnitude can be achieved. Moreover, the polarization conversion ratio (PCR) is more than 97% from 9.2 to 15.2 GHz. Based on the proposed PREs, a horn-fed TA with a 256×256 mm2 aperture area have been designed, fabricated and measured. The measured results of the TA show that the peak gain of 27.3 dBi and the aperture efficiency of 61.9% are achieved at 9.7 GHz. The maximum sidelobe level (SLL) and cross-polarization level at this frequency are -18.14 dB, and -37.36 dB, respectively. Furthermore, the 1-dB and 3-dB gain bandwidth of the TA is 33.9% and 46.9%, respectively. The measured results are in reasonable agreement with the simulated ones.

A novel S-band lightweight relativistic magnetron, packaged with permanent magnets and equipped with a compact axial extraction structure, is proposed. In this design, five alternately arranged anode vanes in a 10-cavity rising-sun magnetron are connected via a ring-like structure to enhance the $\pi $ -mode coupling capability. This innovative ring extractor significantly reduces the overall radial dimension of the magnetron, making it consistent with the radius of the resonant cavity structure. Namely, the output structure introduces no additional radial size. Consequently, the proposed design effectively balances structural compactness and high conversion efficiency simultaneously. The reduced output aperture enables the use of a lightweight permanent magnet, bringing the total weight—including both magnetron and magnets—to only 20 kg. Finally, experiments have been conducted to validate the device’s performance, which demonstrates that, under a diode voltage of 172 kV, the proposed relativistic magnetron with permanent magnet achieves an average output power of 175 MW with a conversion efficiency of 30.8%. The combination of compact size and relatively high conversion efficiency makes this device particularly suitable for portable high-power microwave applications.