This paper presents a polarization switchable self-oscillating active integrated array antenna (AIAA) using a multi-layer approach. The antenna comprises two antenna elements, four PIN diodes, and a Gunn oscillator employing a microstrip line resonator. Reconfiguring the feed network of the array antenna realizes slant polarization (± 45°) switching. The multi-layer structure allows the patch spacing to be adjusted, thereby helping to minimize the antenna's sidelobe level. The Gunn oscillator, which employs a λ/2 microstrip–line resonator, is placed at the bottom layer. The proposed AIAA has an effective isotopic radiated power (EIRP) of + 18.25 dBm at the oscillation frequency of 9.47 GHz. EIRP is improved by better than 8.45 dB compared to the single-layer structure. The proposed AIAA features a transmitted power of + 8.45 dBm, DC-to-RF efficiency of 1.0%, and a low phase noise of −101.8 dBc/Hz at 1-MHz offset frequency with better than 12-dB cross-polarization suppression.

Narrowband microwave generation with tuneable frequency is demonstrated by illuminating a photoconductive semiconductor switch (PCSS) with a burst-mode fibre laser. The whole system is composed of a high-power linearly polarized burst-mode pulsed fibre laser and a linear-state PCSS. To obtain a high-performance microwave signal, a desired envelope of burst is necessary and a pulse pre-compensation technique is adopted to avoid envelope distortion induced by the gain-saturation effect. Resulting from the technique, homogenous peak power distribution in each burst is ensured. The maximum energy of the laser burst pulse reaches 200 μJ with a burst duration of 100 ns at the average power of 10 W, corresponding to a peak power of 4 kW. When the PCSS is illuminated by the burst-mode fibre laser, narrowband microwave generation with tuneable frequency (0.80–1.12 GHz) is obtained with a power up to 300 W. To the best of the authors’ knowledge, it is the first demonstration of frequency-tuneable narrowband microwave generation based on a fibre laser. The high-power burst-mode fibre laser reported here has great potential for generating high-power arbitrary microwave signals for a great deal of applicable demands such as smart adaptive radar and intelligent high-power microwave systems.

A polarization and band reconfigurable cross-slot antenna for multiband applications is presented in this paper. The antenna consists of four p–i–n diodes embedded in the cross-shaped slot in a ground plane and excited by a microstrip feed line. The p–i–n diodes are placed in such a way that they produce multiple bands, with linearly and circularly polarized (CP) radiation. By switching the states of the p–i–n diodes, the sense of rotation of the electric field in CP radiation can be reconfigured. The proposed structure can be configured to produce two bands that radiate linearly polarized waves or three bands, where, two are linearly polarized and one is CP. The proposed design concepts are validated bythe CST studio suite as well as measurementsare carried out on fabricated prototypes.

We demonstrate an all-fiber high-power linearly polarized supercontinuum source with polarization-maintaining photonic crystal fibers (PM-PCFs) as the nonlinear medium. The source exhibits an average output power of 3.8 W with a flat spectrum from 480 nm to 2100 nm at the $-$10 dB level, except for the residual pump peak. The polarization extinction ratio (PER) is measured to be greater than 20 dB at selected sample wavelength points (532 nm, 1064 nm and 1550 nm) at the highest pump power level and greater than 20 dB at all wavelengths from 800 nm to 1500 nm at the low pump power level. We also experimentally study the spectral properties when the pump light propagates along different axes of the PM-PCF. The results show that propagating parallel to the slow axis enables a broader spectrum in the PM-PCF in this case, probably due to matching of the dispersion properties with the pump light, which is qualitatively in accordance with the numerical simulation. To our best knowledge, this is the first demonstration of a watt-level linearly polarized supercontinuum source generated from PM-PCFs in an all-fiber structure.

An all-fiberized high-average-power narrow linewidth ns pulsed laser with linear polarization is demonstrated. The laser system utilizes a typical master oscillator power amplifier (MOPA) configuration. The stimulated Brillouin scattering (SBS) is effectively suppressed due to the short fiber length and large mode area in the main amplifier, combined with the narrow pulse duration smaller than the phonon lifetime of SBS effect. A maximal output power of 466 W is obtained with a narrow linewidth of ${\sim}$203.6 MHz, and the corresponding slope efficiency is ${\sim}$80.3%. The pulse duration is condensed to be ${\sim}$4 ns after the amplification, corresponding to the peak power of 8.8 kW and the pulse energy of $46.6~\unicode[STIX]{x03BC}\text{J}$. Near-diffraction-limited beam quality with an $M^{2}$ factor of 1.32 is obtained at the output power of 442 W and the mode instability (MI) is observed at the maximal output power. To the best of our knowledge, this is the highest average output power of the all-fiberized narrow linewidth ns pulsed fiber laser with linear polarization and high beam quality, which is a promising source for the nonlinear frequency conversion, laser lidar, and so on.

Patch antennas with a meandering slot and different distributions of grounded metallic vias are presented in this paper. The meandering slot is adopted to stimulate dual-band operation, while the number and position of the grounded metallic vias are suggested to achieve different radiation performances. The characteristics are analyzed in detail where we find that the existence of the vias also improves the impedance matching. Four samples are designed, where dual-band with both linear polarization, dual-band with circular- and linear-polarization, and single band with linear polarization are obtained, respectively. The samples are finally fabricated and the measurement results agree well with the simulation results.

This paper proposes planar antennas with quadri-polarization diversity using a pair of orthogonal linear polarizations and a pair of orthogonal circular polarizations (CP). A novel feeding network with four input ports and four output ports is presented, allowing antenna polarization diversity by selecting different input ports, which can generate right-handed CP, left-handed CP, horizontal linear polarization, and vertical linear polarization. The first design uses two square patch resonators to synthesize the four polarizations; the second design comprises four circularly polarized patches to synthesize the four polarizations with an improved axial-ratio (the ratio of orthogonal components of an E-field) bandwidth. The proposed designs do not require for embedding PIN diodes and DC-biasing circuits, making them suitable for use in higher-frequency applications where using lump elements would be difficult. The novel antennas provide potential polarization diversity features which can be used for many applications. Details of the antenna design are shown, and the measurement and simulation results are also provided to validate the proposed concept.