This paper presents a high selectivity frequency selective rasorber (FSR) with an adjustable out-band absorptivity property. This rasorber is composed of a dynamic absorptive-frequency-selective-surface (AFSS) on the top, with PIN diodes employed to achieve tunable absorptivity, and a high-quality (Q)-factor bandpass frequency-selective-surface (FSS) in the bottom, with aperture-coupled resonators (ACRs) structure to obtain a high-selectivity transparent window. To begin with, theoretical analyses and extensive simulations are performed to evaluate the performance. Subsequently, a prototype is fabricated and measured, showing a 1 dB transmission window with high selectivity at 8.43-8.51 GHz and electrical tuning on the absorption rate response with a wide tunable span of 0.9 at out bands of 4.43-7.76 GHz and 9.21-13.45 GHz, respectively. The proposed rasorber with dynamic tunability of absorptivity can provide radar cross section (RCS) consistent with the environment, which is potential for radar stealth, deception, and anti-identification.

This paper presents an ultra-wideband antipodal Vivaldi antenna from 1-40 GHz for photonic-assisted reconnaissance. The antenna's performance is enhanced through a systematic optimization progress. By embedding a director into the tapered slot, the gain and the directivity at the high frequency are significantly improved without increasing the size. By emploing periodic slots and double split ring resonators around the radiators, the impedance bandwidth is effectively extended at low frequency. The optimized antenna demonstrates excellent impedance matching across L to Ka band with a gain ranging from 4-17 dBi. The measured results of the fabricated prototype align well with the simulated results. Furthermore, a pair of proposed antennas are implemented in a photonic-assisted system to validate the transceiving performance.

Analog photonic channelized receivers based on dual optical frequency combs (DOFC) are widely used in microwave photonic wideband signal processing. It uses photonic means to perform narrowband segmentation of the wideband signal spectrum, thus avoiding the tradeoff between speed, bandwidth, and accuracy of ADC. However, many factors such as link noise and device nonlinearity restrict the dynamic range of the system, thus affecting the signal detection and processing performance. In this paper, a Long-Short-Term-Memory-Residual network (LSTM-Resnet) is designated to realize the linearization of the DOFC parallel channelized receiver. Benefiting from efficient feature extraction and adaptive processing capabilities, the third-order spur-free dynamic range (SFDR _2/3 ) of the system is improved from 84.12 dBm· $\mathrm{H}{{\mathrm{z}}^{{\rm{2/3}}}}$ to 107.19 dBm· $\mathrm{H}{{\mathrm{z}}^{{\rm{2/3}}}}$ .The spurious suppression ratio (SSR) of the single-tone signal and linear frequency modulation (LFM) signal have been improved by 37.54 dB and 33.39 dB. In addition, the mutual interferences between muti-channels caused by distortion are also significantly suppressed. Experimental results on signals of different format types validate the generalization of LSTM-Resnet and demonstrate its advantages in improving the linearity of DOFC channelized receivers.

Switchable frequency selective rasorbers (FSRs) have been extensively studied recently due to their out-of-band stealth and in-band electromagnetic wave manipulation abilities. Nevertheless, the vast majority of the reported FSRs are incapable of in-band waves control, including simultaneous transmission, reflection, and absorption. Herein, this article proposes a multifunctional switchable FSR that is capable of switching among all three transmission modes at the operation band. This FSR consists of two periodic layers embedded with p-i-n diodes that are separately controlled by bias voltages. By changing the states of the p-i-n diodes in each layer, the incident wave within the operation band can be manipulated continuously (transmission mode in the on–on state, reflection mode in the on–off state, absorption mode in the off–off state). Furthermore, the broad region below the operation band retains high absorptivity throughout all states. The physical properties of the multifunctional switchable FSR are investigated with an equivalent circuit model. The measured results show that a switchable operation frequency is located at 10.15 GHz, and an effective absorption band ranges from 3.8 GHz to 8.6 GHz. The proposed design has promising potential for multiple applications, such as communication for the transmission mode, protection of high-power microwaves for the reflection mode, and stealth and electromagnetic compatibility for the absorption mode.

A reconfigurable bandwidth antenna for an impulse radio-UWB (IR/UWB) system design is illustrated in this paper. By adopting a continuously tunable low-pass filter by varactor at the feed of the antenna, the proposed antenna obtains a continuous tunable bandwidth from 1.02 GHz to 2.42 GHz. To ensure the identifiability of transmitted pulses in (IR-UWB) system, the antenna is analyzed in both frequency domain and time domain. The proposed antenna is valid with a system fidelity factor (SFF) above 0.8 while the bandwidth is tuning. The compact size, low cost, and tunable bandwidth with the identifiability of the transmitted pulse makes it suitable for UWB impulse radars to improve the utility ratio of frequency, and dynamic adjustment avoids interference of the IR-UWB in other communication frequency bands.

A novel reconfigurable filter antenna with three ports for three dependent switchable states for impulse radio-ultrawideband (IR-UWB)/wireless local area network (WLAN)/worldwide interoperability for microwave access (WiMAX) applications is presented in this paper. Three positive-intrinsic-negative diodes, controlled by direct current, are employed to realize frequency reconfiguration of one ultra-wideband state and two narrowband states (2.4 GHz and 3.5 GHz). The time domain characteristic of the proposed antenna in the ultra-wideband state is studied, because of the features of the IR-UWB system. The time domain analysis shows that the reconfigurable filtering antenna in the wideband state performs similarly to the original UWB antenna. The compact size, low cost, and expanded reconfigurable filtering features make it suitable for IR-UWB systems that are integrated with WLAN/WiMAX communications.