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This article tries to address the unstable radiation pattern issue of the planar‐coupled patch antennas with two different methods. First, characteristic mode analysis (CMA) reveals that the coupled patch antennas generate three characteristic modes with distinctive radiation patterns. A slot‐loading scheme is proposed to reshape the current distribution of the higher mode and reduce its sidelobe level significantly. Then a 13.4% bandwidth with consistent radiation patterns and high gain is achieved by exciting modes 1 and 3 while suppressing unwanted modes with an aperture‐coupled feeding. Second, the radiation pattern stability of the coupled patch antennas is further improved by employing shorted parasitic patches. The presented antenna can be equivalent as the same magnetic current array model under the in‐phase and out‐of‐phase modes, and thus the radiation patterns hardly get changed. Moreover, the non‐radioative nature and high radiation quality factor of the higher mode improve the radiation performance in a new principle. It not only enhances the bandwidth up to 18.5% but also results in a sharp filtering edge of gain response. [ABSTRACT FROM AUTHOR]

Programmable metasurface, or reconfigurable intelligent surface is one of the most promising strategies to enhance communication and sensing capacities via arrays of reconfigurable meta‐atoms. The functionalities of conventional programmable metasurfaces are usually limited, and active meta‐atoms are connected with steering‐logic board through cables, which makes the whole system inconvenient for installation and stable use. Here an all‐in‐one integrated multifunctional metasurface for various application purpose is proposed. The integration of metasurface and steering‐logic board produces an all‐in‐one system, which makes it compact, low profile, and stable. The novel meta‐atom structure provides all‐in‐one functionalities, including 1) dispersion‐reconfigurable spatial phaser for analogue signal processing, 2) polarization conversion, 3) beam steering and orbital angular momentum generation for high‐speed communication and, 4) near‐field scanning for sensing. The proposed metasurface also has a broadband property, which is operating from 9.5 to 10.5 GHz with 10% relative bandwidth. Such a design integrates functionalities of signal processing, communication, and sensing in a single programmable metasurface, which makes it especially useful for integrated sensing and communication toward next‐generation wireless networks. [ABSTRACT FROM AUTHOR]

This communication presents the design of 1 bit coding engineered reflector for wideband monostatic/bistatic radar cross section (RCS) reduction under a wide angle of incidence by redirecting the backscattered electromagnetic (EM) energies into wide and countless angles. The proposed surface can achieve an excellent monostatic/bistatic RCS reduction performance of more than 10 dB over a wide frequency range from 60 to 120 GHz under wide angles of incidence up to 75°. This is achieved by designing a wideband anisotropic polarization rotator unit cell with a relative polarization conversion bandwidth of 66.7% and polarization conversion efficiency of more than 99%. The unit cell and its mirrored version are used to represent the “0” and “1” coding states of an optimized 1 bit coding sequence. The distribution of the “0” and “1” coding states and the dimensions of the anisotropic unit cell are optimized carefully, such that the unit cell will have 180° ± 30° reflection phase difference between the $x$ - and $y$ -axes over the whole three frequency bands (V-, E-, and W-bands) and obtains ultrawideband and wide-angle diffusion scattering patterns under oblique incidence up to 75°. The simulation and experimental results show that the proposed coding engineered reflector has nearly uniform diffusive scattering characteristics under normal and wide-angle off-normal incidences of EM waves up to 75° over the three frequency bands. [ABSTRACT FROM AUTHOR]

The independent control of two orthogonal polarizations that possess dual functionalities is highly desirable in antenna and wireless communication technologies. Spin-decoupled metasurfaces with integrated dynamic and geometric phases have been proposed to generate two independent right-handed and left-handed circularly polarized (RCP and LCP, respectively) waves. However, the RCP and LCP phases are correlated by a linear equation of the dynamic and geometric phases. In this article, we propose a meta-atom in which the 1 b phase of two orthogonal polarizations can be controlled independently. Moreover, a high-gain broadband millimeter-wave multidimensional metasurface to generate an $x$ -polarized $l=0$ beam with a 10° beam deflection and a $y$ -polarized $l=+1$ beam independently is simulated, fabricated, and tested. The proposed metasurface operating over the frequency range of 16–28 GHz has the maximum gains of 28.7 and 23.8 dBi for the $l=0\,\,x$ -polarized waves and $l=+1\,\,y$ -polarized waves, respectively. Compared with spin-decoupled metasurfaces, the proposed metasurface provides a simpler design process to generate two independent vortex beams for the two orthogonal polarizations. The proposed vortex metasurface also has the advantages of dual polarization, high gain, wide relative bandwidth, and is broadband. The proposed metasurface has potential application in high-capacity communication systems. [ABSTRACT FROM AUTHOR]

This paper proposes a triple-mode dielectric-loaded cylindrical cavity diplexer by using a novel packaging technique for long term evolution (LTE) base station applications. Four metal cavities, loaded by a triple-mode dielectric resonator (DR), are designed to resonate at two different frequencies for the diplexer operation. In this context, three resonant modes of a single cavity are classified as a TM mode and a pair of hybrid degenerate modes (HE modes). The two degenerate modes in the same cavity are properly excited by employing an off-centered DR instead of a traditional corner-cut structure as a perturbation element. Finally, such a diplexer is designed and fabricated, and good agreement between measurement and simulation is achieved. [ABSTRACT FROM AUTHOR]

A substrate integrated waveguide (SIW) H-plane horn antenna loaded with tapered multistrip transition and dielectric slab is proposed for broadband high-gain operation. The broadband characteristic of the proposed antenna is obtained by loading a tapered multistrip transition. The theory of coupled resonator is introduced to reveal the mechanism of bandwidth enhancement. On the other hand, a dielectric slab is used to enhance the gain of the proposed antenna. The optimal length of this dielectric slab is determined based on the design principles of a dielectric rod with maximum gain. Besides, the tapered multistrip transition also contributes to the gain improvement by suppressing the feed radiation and prompting the transverse expansion of the surface wave. To verify the design theory and concept, a prototype operating at the K- and Ka-bands is fabricated and measured. The measurement results show that the impedance bandwidth of the proposed antenna is from 20.6 to 38.4 GHz (60%). Within the operating band, a peak realized gain of 19.1 dBi and excellent endfire radiation patterns with low cross polarization (<−30 dB) and high front-to-back ratio (FBR >20 dB) are achieved simultaneously. With its broad bandwidth, high gain, low cross polarization, and high FBR, the proposed antenna is promising for various millimeter-wave applications. [ABSTRACT FROM AUTHOR]

A novel ultra-wideband (UWB) reflectarray antenna for the Internet of Vehicles (IoV) is introduced in this paper. By simply connecting the neighboring reflectarray elements, the proposed reflectarray antenna achieves a remarkable radiation pattern bandwidth of 20 GHz, ranging from 10 GHz to 30 GHz. To explain the operating principles of the proposed reflectarray antenna, the equivalent circuit (EQC) model of the unit cell is built, which also provides an efficient and rapid way to analyze the performance of the proposed reflectarray element. It is found from the EQC analysis that the connected elements can achieve better reflection phase responses than conventional separated elements, thereby improving the array bandwidth. As a proof of concept, a 503-element reflectarray antenna simultaneously covering the vehicle-to-satellite bands (12.25–12.75 GHz/14.0–14.5 GHz/19.6–21.2 GHz/29.4–31.0 GHz), the 24-GHz short-range vehicle radar band (24.25–26.65 GHz) and the 5G millimeter-wave band (27.5–28.35 GHz) is designed, fabricated, and characterized. The experimental results demonstrate that the presented reflectarray antenna can maintain undistorted beams, high antenna gain, low cross-pol level, and moderate aperture efficiency over a bandwidth of 100%, i.e., from 10 to 30 GHz. With its simple and planar aperture as well as excellent performance, the proposed reflectarray antenna can be a promising candidate for vehicles that require reliable high data-rate satellite links and 5G millimeter-wave connections simultaneously. [ABSTRACT FROM AUTHOR]

High-isolation in-band full-duplex (IBFD) cavity-backed slot antennas (CBSAs) in a single resonant cavity are presented in this article. The TE101 and TE011 cavity modes combined with a modified orthogonal feeding structure are first used to design the duplex antenna. The proposed feeding structure can reduce the port-to-port coupling strength and produce a very high isolation. By replacing the crossed radiation slots with two pairs of parallel radiation slots, enhanced radiation gain is achieved. To tackle the narrow bandwidth for the single-mode operation, two orthogonal resonant-iris modes produced by the two feeding slots are introduced to design a dual-mode wideband IBFD antenna. The simulated bandwidth is increased from 0.8% to 5.7%. All the presented antennas with improved performances are designed and realized in a single full-metal resonant cavity. Compared with the conventional design method, high isolation, enhanced gain, and enhanced bandwidth are simultaneously achieved without enlarging the antenna size. Finally, the prototype of the wideband IBFD slot antenna is measured and presented to validate the design concept, which has a 5.8% bandwidth, higher than 95% total efficiency, especially an isolation higher than 72 dB. [ABSTRACT FROM AUTHOR]

A dual-band planar crossover with simple structure is proposed. This crossover is derived from the conventional single-band two-section branch-line crossover by doubly extending the length of its vertical transmission lines, which realizes the dual-band operation. Closed-form equations for design parameters are derived, which simplifies design procedure of the proposed crossover and shows that the available bandwidth of the passband increases with the increasing frequency ratio. By adding one short-circuited stub and one open-circuited stub to the originally proposed dual-band crossover, two types of modified dual-band crossovers and their closed-form design equations are proposed for smaller and larger frequency ratios applications. For verification, four different dual-band crossovers are designed and simulated, of which two microstrip crossovers operating at 1/1.8 and 1/2.3 GHz are fabricated and measured. The measured results are in good agreement with the simulated ones. [ABSTRACT FROM PUBLISHER]

With the arrival of the 5G era, the working frequencies of wireless devices are being transferred to a higher spectrum with a wider available bandwidth. However, conventional metal wire antennas used in 5G communication systems are often limited by their resonant structure, which inevitably leads to narrow operating bands and fixed sizes at integral multiples of λ/2 or λ/4. In this Letter, a ceramic inverted-L antenna with a non-resonant architecture is proposed to achieve a wide bandwidth and flexible size. Its leaky-wave radiation is based on the cutoff region of dielectric waveguides, which verifies that the working frequencies of the proposed antenna are related to the cross section rather than the length. Ceramic 3D printing technology is adopted for precise manufacturing of the proposed antenna, which covers the frequency range of 3.28–5.28 GHz, including the bands n77/n78/n79 of the sub-6 GHz spectrum. [ABSTRACT FROM AUTHOR]

This article presents a fully integrated design of probe‐fed open‐ended waveguide filtering antenna by adopting 3‐D printing technology. As for the conventional processing technologies such as computer numerical control machining, they usually suffer from mutually separated parts and inquire post‐processing assembly in the fabrication of complex waveguide structure. Compared with them, the 3‐D printing technology can provide possibility to directly form an all‐in‐one architecture after reasonable design to avoid unexpected concave, thus eliminating the error caused by assembly as can as possible. In this article, the aforementioned manufacture strategy has been successfully applied to waveguide filtering antenna. By adopting a tilted setting in selective laser melting process that is a kind of 3‐D printing technologies, the proposed waveguide antenna with internal structure can be fabricated without flaw and extra supporter. The probe‐fed waveguide antenna is designed herein by reforming the first‐ and last‐order cavities of a waveguide‐fed metal‐insert filter to achieve similar filtering characteristics. This design offers a feasible example of all‐in‐one waveguide filtering antenna and can be extended to other waveguide components. [ABSTRACT FROM AUTHOR]

A balanced dual‐band bandpass filter (BPF) with enhanced common‐mode (CM) suppression is proposed. The dual‐band differential‐mode (DM) bandpass response is obtained using a double‐layer substrate. The stub‐loaded stepped‐impedance resonators are used both in the top and the bottom layers to constitute a dual‐band BPF with two controllable passbands. The slotline portion in the middle layer is excited under DM operation. Moreover, the even‐symmetrical field along the slotline is highly attenuated under CM excitation, thus achieving excellent CM suppression over the desired DM passbands. To verify the proposed concept, a balanced dual‐band BPF, operating at 1.9 and 2.8 GHz, is designed and fabricated, and the simulated and measured results are in good agreement. [ABSTRACT FROM AUTHOR]

An ultrawideband stacked single-turn spiral antenna with an integrated feeding structure is presented in this communication. The proposed antenna consists of two stacked planar single-turn Archimedean spirals which are wound in orthogonal directions. By connecting these two stacked spirals through two vertical posts, the traveling-wave current path is lengthened and, hence, the operating frequency of Mode 1 is decreased. To reduce the feeding complexity, an integrated tapered microstrip line is used to feed the spiral, which also acts an impedance transformer. It is demonstrated that the proposed antenna can operate across 0.29–5 GHz with |S11| < −10 dB and 0.75–3.64 GHz with axial ratio (AR) < 3 dB. Compared with the single-turn Archimedean spiral with the same radius, the impedance and AR bandwidth of the proposed antenna are enhanced from 5:1 to 17:1 and from 1.6:1 to 4.9:1, respectively, showing that the proposed antenna can be a good candidate for ultrawideband applications. [ABSTRACT FROM AUTHOR]

Based on characteristic mode theory (CMT), a quad-polarization reconfigurable antenna with suppressed cross polarization is proposed in this article. The proposed antenna is composed of the radiator, excitation units, and feeding network. A square conductive slab (SCS) is used as the main radiator, which is designed elaborately by characteristic mode analysis (CMA). Different modes of the radiator are stimulated selectively by four groups of balanced inductive exciters (BIEs) to realize horizontal polarization (HP), vertical polarization (VP), left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP). Two p-i-n diodes are embedded into the feeding network to switch the excitation states of the four groups of BIEs, thereby achieving quad-polarization reconfiguration. More importantly, a novel method exploiting the CMA is adopted for achieving low cross polarization. By means of introducing the orthogonal mode, the cross-polarization component of the fundamental mode can be canceled out by the co-polarization component of the orthogonal mode, which greatly reduces the cross polarization from −10 to −40 dB in the two principal planes. The measurement results demonstrate that the quad-polarization agility and a cross-polarization level around −30 dB under all polarization states are achieved simultaneously, verifying the functionality and reliability of the proposed method. [ABSTRACT FROM AUTHOR]

A compact substrate integrated waveguide (SIW) cavity slot antenna with enhanced bandwidth and quasi‐elliptic filtering response is proposed. Served as radiating elements, two slots are etched on the top plane of a square SIW cavity. Quality factors of two original modes are greatly reduced and a new resonant mode is introduced by etching an additional slot on the bottom plane. By merging these three modes within a single passband, the bandwidth can be enhanced. In addition, a radiation null is generated in the lower and upper stopband, respectively. Therefore, a quasi‐elliptic filtering response is achieved with three resonant modes in the passband and two radiation nulls in the stopband. A fabricated prototype with the size of 0.48λ0 × 0.48λ0 × 0.02λ0 has been measured. The measured 10 dB bandwidth is 11.5% (3.28–3.68 GHz). The measured efficiency is about 77% in the passband but it sharply drops to 5.6% at 3.26 GHz and 10.5% at 3.76 GHz. [ABSTRACT FROM AUTHOR]

Filtering baluns are proposed based on the hybrid cavity-microstrip structures in this article. The cavity acts as the resonator to obtain the filtering response. In the meanwhile, the microstrip feeding networks are used to excite multiple modes and achieve the balun characteristics simultaneously. The coupling mechanism between the slots and the cavities is utilized to analyze the single- and dual-band filtering baluns. Therefore, by combining the benefits of the cavities and the microstrip lines, multifunctional filtering baluns are realized. Besides, to reduce the volume and insertion loss further, a filtering balun based on the dielectric cavity-microstrip structure is presented and designed. It possesses high selectivity passband response, magnitude imbalance of 0.075 dB, and phase difference of 180° ± 0.2°. It is much smaller than that fed by the waveguide. On the other hand, it is easy to integrate with other components and robust in structure compared to that fed by the probe. Thus, the proposed hybrid structure not only maintains the high performance of the cavity but also has the flexibility of the planar circuit. [ABSTRACT FROM AUTHOR]

A printed dual‐band dipole filtenna with flexible frequency ratio and improved band‐notched performance is proposed. It consists of a driven dipole and three parasitic elements. For the driven dipole with short and long arms, a radiation null is found between two passbands, which achieves a band‐notched filtering characteristic. Two parasitic elements are introduced to enhance the passband bandwidth and an additional parasitic element is utilized to improve the band‐notched performance. In addition, the characteristics of the proposed design including flexible frequency ratio, independent controllable operating frequency, and controllable band‐notched bandwidth have also been demonstrated. A filtenna prototype is fabricated and tested. Measured results show that a fractional bandwidth of 21.1% and 18.1% is obtained in the lower and upper passbands, respectively. The measured efficiency is 84% in the lower band and 74% in the upper band but the efficiency sharply decreases to about 13% within the notched band. [ABSTRACT FROM AUTHOR]

In this paper, a novel on-chip circuit design approach is proposed using hybrid coupling technique. Taking advantage of this technique, a microwave bandpass filter (BPF) is proposed as a design example for proof of concept. Based on stub-loaded stepped-impedance transmission lines and folded stepped-impedance meander line from different metal layers, the proposed BPF can generate three transmission zeros (TZs) and two transmission poles (TPs), which are excited through the hybrid mutual couplings between the inductive and capacitive metals. To understand the principle of this configuration, an equivalent LC-circuit model is presented and simplified, of which the TZs and TPs of the proposed BPF are estimated by the extracted transfer function. The calculated results exhibit good agreements with the simulated and measured ones. In addition, the bandwidth and center frequency of the proposed BPF can be tuned flexibly. Finally, to further demonstrate the feasibility of this approach in practice, the structure is implemented and fabricated in a commercial 0.13- $\mu \text{m}$ SiGe (Bi)-CMOS technology. The measurement results show that the proposed BPF, whose chip size is 0.39 mm $\times0.45$ mm (excluding the test pads), can realize a wide bandwidth from 19.7 to 33.2 GHz with a return loss of 15.8 dB and insertion loss of 3.8 dB at the center frequency of 26.5 GHz. [ABSTRACT FROM AUTHOR]

A response from the authors of the article "Compact broadband Gysel power divider with arbitrary power-dividing ratio using microstrip/slotline phase inverter" in the May 2012 issue is presented.