A novel frequency reconfigurable antenna based on substrate integrated waveguide (SIW) for S-band and C-band applications is proposed. The antenna employs a SIW resonant cavity structure with a rectangular-ring slot and a long slit etched on the top surface. An extra via post is introduced to adjust the resonance frequency of the low-frequency mode independently without affecting the impedance matching of the high-frequency mode or decreasing the gain. Several PIN diodes are symmetrically placed along the rectangular-ring slot to attach the patch to the top surface. The working state of PIN diodes is controlled by a simplified bias structure. A prototype was fabricated and measurements show the proposed antenna has a bandwidth of 18 MHz in S-band low-frequency mode and 322 MHz in C-band high-frequency mode. Good agreements between the simulated and measured return losses, as well as radiation patterns, are observed.

A new technique for designing a dynamically controllable transparent window in the metamaterial absorber is investigated. Active lossy layer and lossless layer are proposed to establish the rasorber. First, the impedance-controllable embedded resonator is presented as a choke to limit the current flowing through the lossy elements. The interdigital and meander lines are applied to independently equivalent the large lumped capacitor and inductor required for low-frequency (L/S-band) resonance. It is demonstrated that the impedance loading of the inductive embedded resonator makes for a miniaturized unit size of 0.086 $\lambda_{L}$ . Then, the cascaded embedded resonator on the lossless layer realizes a switchable high-selectivity passband in the reflection band. The transition from transmission band to absorption band is reduced due to the sharp roll-off edges of the passband. Finally, the rasorber prototype is fabricated and validated by the free-space measurement. By switching the bias of the p-i-n diodes, a high-selectivity window at 2.2 GHz can be triggered while it keeps absorbing in the whole band (1.2–3.7 GHz, 102%) at window-off state. Principles of operation and synthesis procedure are presented in this article.

This brief presents a dual-band (DB) high-efficiency power amplifier (PA) with extended bandwidth. A novel output matching network (OMN) that integrates harmonic control into DB fundamental matching design is proposed. Bandwidth of the DB PA can be efficiently extended by the OMN presented since it can offer DB broadband harmonic control while maintaining the input impedance at DB fundamentals. By precise control of the characteristic impedance on the part dual transmission line (part-DTL) and the double shunt stub (DSS), these two structures are made equivalent to the series and parallel transmission line (TL) performance at DB fundamentals. Additionally, the part-DTL modulates the input impedance in broadband near DB harmonics to pure reactive, and the DSS optimizes the imaginary part of the input impedance at DB harmonics. For validation, a DB PA is designed and fabricated with a Cree CGH40010F GaN transistor. The fabricated DB PA features the saturated output power of 42.4 dBm and 41.7 dBm with the power-added efficiency of 73.5% and 68.4% at 2.6 GHz and 3.5 GHz, respectively. Specially, the bandwidth of the DB PA is extended to over 300 MHz and 200 MHz.

A wideband quad-polarization-agility antenna is proposed. The antenna consists of four folded dipoles each integrating with a 1 b phase-reconfigurable balun (PRB). The PRB achieves (0 ^° , 90 ^° ) or (0 ^° , 180 ^° ) phase shifting while matching the microstrip feeding networks and the printed dipoles. By switching the p-i-n diodes on the baluns, proper combinations of the signal phases on the four dipoles can be obtained, which generate two orthogonal linear polarizations (LPs) and two orthogonal circular polarizations (CPs). Folding the dipoles broaden the overlapped $-$10 dB impedance bandwidth (BW). Measurement results show that the overlapped impedance BW of the four polarizations is more than 40% (1.4-2.12 GHz). In this band, the antenna radiates a stable pattern, the cross-polarization level of the LP modes is below $-$15 dB and the axial ratios of the CP modes are smaller than 3 dB. Experimental results show good agreement with the simulated results.

A novel technique for constructing multiple passbands in an active absorber is proposed. Unlike conventional fragmented designs, the lossless reflective layer is produced by eliminating loss from the lossy layer, leading to the additional benefit of a more adaptable multiband match. The series embedded resonator integrated with p-i-n diodes is presented to switch the open-circuit frequencies, allowing multiple windows to switch between transmission and absorption modes over a flexible frequency range. Consistent metallic-strip-based configuration ensures consistent transmission characteristics for both layers under the same control scheme, facilitating coordinated design for transmission/absorption in multiple bands. A prototype of the active rasorber is fabricated for demonstration. The single-polarized response of the structure has been validated in the polarization direction parallel to the metallic strips. The transparent windows can be toggled between dual-pass-band mode (A-T-A-T-A) at 3.5 and 8 GHz, and single-pass-band (A-T-A) mode at 6 GHz. Flexible frequency ratios of 2.3:1 and 1.33:1 are achieved. The reflection is effectively suppressed when the window is closed, and it consistently exhibits such behavior outside the window. The operation principles and design procedure are presented.

To achieve multifunctional communication and safe driving of a vehicle, a half-mode substrate-integrated waveguide (HMSIW) leaky-wave frequency-scanning antenna with flexible polarization is proposed in this article. It includes two linearly polarized interdigital slot antennas, a compact directional coupler, and microstrip transition lines. It can generate either linear polarization (LP) for base station communication or circular polarization (CP) for satellite navigation by configuring the means of excitation. Its radiation beam can be continuously steered with varying frequency in either the LP or the CP state, which is of benefit to safe vehicular driving. In addition, the use of the HMSIW structure reduces the size of the antenna by almost one-half in comparison with the full SIW structure. Measurements were performed on antenna scattering parameters, radiation patterns, gain, and axial ratio (for CP states); the results show good agreement with the simulated results. With its low profile, low weight, low cost, and capability for continuous frequency scanning and variable polarization states, the multifunctional antenna could be extensively used for adapting to changes in environmental conditions or system requirements.