A novel multiband frequency-reconfigurable antenna is presented. The designed antenna can realize L-band single-frequency operation and S-band dual-frequency operation through electronic tuning. Annular ring and sawtooth patches are used as radiators for L/S-band operation and are excited by a broadband reconfigurable orthogonal network through the coupling of a T-shaped slot and a ring slot in the ground plane, respectively. By changing the bias of the p-i-n diodes loaded on the feed network, the operating frequency can be switched between the navigation state and the satellite link receiving state. A high tuning frequency ratio (1.64:1) is obtained. The simulated and measured results show good agreement. Good impedance matching (VSWR < 1.3) and circular polarization characteristics (AR < 3) are obtained in all three operating bands. Achievement of a highly reconfigurable frequency ratio of a circularly polarized antenna provides solutions for multifunction CP antenna aperture sharing.

Variable numerous types of equipment/subsystems may exist in complex systems, which makes it difficult to analyze and identify electromagnetic emission sources. A theory named “basic emission waveform theory” is presented in this paper to solve this problem. This innovation theory characterizes emission with four basic waveforms, including square wave, sine wave, damped oscillation, and spike wave. Then, the effectiveness of the theory is discussed in both theoretical and engineering ways. In particular, the basic waveforms reflect the physical characteristics of the equipment. Furthermore, the basic waveforms generally do not vary with the locations or loading conditions. Therefore, the identification and analysis of an emission source can be realized by analyzing the basic waveforms from the emission of a complex system. Finally, the applications of damped oscillation and square wave in emission source identification field are used as validations of the proposed theory. Moreover, an example of emission source identification for an electric vehicle is also presented. The examples show that the proposed theory can be used to simply and accurately identify and analyze the emission sources of complex systems.

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.

We present a novel printed dual-layer three-way directional coupler, which can be utilized as 3 × 3 beamforming network (BFN) to provide orthogonal three-beam switching capability. The three-way directional coupler is a passive component with six input/output ports. The signal injected into the input port is equally distributed into the three output ports, with a constant phase difference of -120 ^° , 0 ^° , or +120 ^° . Simulation and measurement results show that within 7% relative bandwidth, good matching, high isolation, equal power division, and constant phase difference have been achieved simultaneously. Utilizing the three-way directional coupler as a 3 × 3 BFN, an orthogonal three-beam antenna array for 5.8-GHz application has been designed, fabricated, and tested to verify its capability experimentally.