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In this article, H-plane cross-polarization (X-pol) radiation of probe-fed air-filled patch antennas is substantially suppressed by introducing two or more floating metal cylinders underneath the patch, respectively. The X-pol is canceled by the radiation of induced currents on metal cylinders. The working principle of the new X-pol suppressed patch (XSP) antenna is revealed by an approximate model. The X-pol level of a typical XSP antenna can be suppressed to lower than −49 and −37 dB theoretically and experimentally for $| \theta |\le 60^{\circ }$. Two $1\times $ 8-element arrays constructed by XSP antennas and conventional patch antennas are prototyped and measured at scanning beam angles of $\theta = 0^{\circ }$ , −40°, and −65°. The measured co-polarization (co-pol) gain of the XSP antenna array is 0.7 and 0.9 dB larger than that of the conventional patch array at $\theta = -40^{\circ }$ and −65°, respectively. Besides, the beam scanning angle with −30 dB X-pol level of the XSP antenna array can be as wide as $| \theta |\le 40^{\circ }$ , while that of the conventional patch array is about $| \theta |\le 12^{\circ }$. A wide-band dual-polarized XSP antenna is also presented. The measured maximum H-plane X-pol level can be lower than −29 dB within 8.7% fractional bandwidth. [ABSTRACT FROM AUTHOR]

In this work, we propose and demonstrate an integrated dual linearly polarized cavity-backed patch antenna, which is excited by a concurrent dual-mode substrate integrated waveguide (SIW) structure. For the first time, we have exploited the TE10 and TE20 modes of a traveling wave in a dual-mode SIW configuration to excite the horizontal and vertical polarizations of the patch antenna. The proposed methodology yields a low-profile structure with a high interport isolation thanks to the inherent symmetry of the structure. Measurement results indicate an isolation performing better than 42 dB over a 600 MHz impedance bandwidth of the antenna. Moreover, a methodology is developed to implement transitions from the dual-mode SIW to the two different TEM transmission lines for separate but concurrent excitations of the device. Detailed field and impedance analyses are presented to explain the operation principle of the proposed antenna, which are supported by an excellent agreement between the obtained measurement and simulation results. [ABSTRACT FROM AUTHOR]

This article proposes and presents a fully planar endfire circularly polarized (CP) antenna with mingled three-layer substrates. It consists of a unidirectional dielectric radiator (UDR) and an antipodal linearly tapered slot antenna (ALTSA) surrounded by a UDR. The ALTSA is fed by a substrate integrated waveguide (SIW) on a thin substrate of $0.05\lambda _{0}$ , which can easily be integrated with RF subsystems. The UDR is fed by the ALTSA, which enables the UDR to enhance the original vertically polarized radiation rather than the horizontally polarized radiation from the ALTSA. Due to the polarization selectivity enhancement, an endfire CP antenna with a very thin substrate is created. An experimental prototype of the proposed antenna has been studied, designed, and measured. The measured impedance bandwidth of −10 dB covers a broadband of 29.7 GHz from 26.1 to 55.8 GHz, and the 3 dB AR bandwidth is 19.7 GHz ranging from 25.3 to 45 GHz. The measured gain is over 9 dBic from 27.8 GHz to over 32 GHz. A good performance with a small size of only $2.57\lambda _{0} \times 0.78\lambda _{0} \times 0.33\lambda _{0}$ , including the CPW-SIW transition, makes it an attractive option in the development of high gain planar endfire CP antennas and arrays for 5G and B5G applications. [ABSTRACT FROM AUTHOR]

This work devises and investigates a Fabry–Perot-styled planar unidirectional dielectric radiator (UDR) antenna fed by a thin embedded slotted substrate integrated waveguide (SIW). The proposed UDR-SIW antenna consists of two identical dielectric substrates and an embedded feeding SIW between the two dielectric substrates. This diligently mingled multilayer structure makes it possible to not only use the thick dielectric substrates to narrow down the E-plane pattern for symmetrical radiation but also facilitate its integration with RF subsystems through the thin embedded feeding SIW, thereby achieving a compact size and an effective excitation. An experimental prototype of the URD-SIW antenna is simulated, fabricated, and measured. It features a size of $2.96\lambda _{0}\,^\ast \,0.65\lambda _{0}\,^\ast \,0.33\lambda _{0}$ and a nearly symmetrical endfire radiation pattern. The antenna presents a measured impedance bandwidth of 9.4% from 26.3 to 28.9 GHz, a gain varied from 8.2 to 10.3 dBi, which is over 10 dBi from 27.7 to 28.4 GHz, and a front to back ratio over 20 dB from 27.5 to 29 GHz. The proposed UDR-SIW antenna has vertically polarized radiation pattern that is different from a conventional UDR antenna; thus, it is an appropriate candidate to replace the SIW H-plane horn in certain applications. [ABSTRACT FROM AUTHOR]

In this work, we present a comprehensive analysis of port impedance effects on a signal coupled across two-port networks, derive an equation to evaluate the impedances for a specified coupling, and demonstrate two beam-shaping active array antenna prototypes to validate the theory. In this context, the generalized S-parameters are theoretically studied and verified through an example. Subsequently, a closed-form equation is derived to accurately evaluate the port impedances that enable the achievement of a desired magnitude and phase of the signal coupling across the two-port network. The meaningfulness of all the potential results and the additional capabilities of derived equations are then discussed. With this understanding, a general modeling procedure is formulated to achieve the simultaneous amplification and phase shifting only through the active devices, without resorting to any additional passive circuitry. As a proof of concept, two 1 × 5 active array antenna prototypes are developed and fabricated at 5 GHz: one for broadside radiation with a sidelobe level of less than −20 dB requirement, and the other for flat-top radiation beam between −10° and 30°. They are integrated with a 1 × 5 Wilkinson power divider that is designed for radiation pattern measurements, and the corresponding results agree reasonably well with the simulated counterparts and theory, thereby proving the developed concept. Such solutions demonstrate the inherent advantages of being low-loss, compact, and efficient, which are essential for the next generation of wireless systems. [ABSTRACT FROM AUTHOR]

This paper presents an LC low-pass $\pi $ network to decouple a pair of coupled antennas working at low frequencies. Comparing with existing decoupling techniques, the proposed decoupling network provides a wideband but compact decoupling solution. Moreover, a generalized one-fit-all scheme is justified to implement the decoupling network with an antenna independent core network. By adjusting a few external components, the same core network can be applied to a collection of antenna pairs with different coupling levels and antenna form factors. Four design examples are given to demonstrate the unique features of the proposed network for low-frequency applications. In all cases, the decoupling network significantly improves the isolation between two antennas over a wide frequency band while the intrinsic matching bandwidth of the antennas is maintained. [ABSTRACT FROM PUBLISHER]

A new decoupling scheme called dual-band coupled resonator decoupling network (CRDN) is presented. By properly designing the coupling coefficients between two pairs of coupled resonators, the network can effectively reduce the mutual couplings between two coupled dual-band antennas in two bands simultaneously. The new scheme is proved by a practical microstrip version of the device for two dual-band antennas working at 2.4 and 5.2 GHz frequency bands. A compact planar dual-band CRDN consisting of a pair of dual-band open-loop square ring resonators is proposed. The measured scattering parameters of two coupled antennas with and without the dual-band CRDN in free space (FS) and with hand phantom demonstrate that the isolation between the two antennas in both the low and high bands can be improved from 8 to 10 dB, respectively, to below 20 dB while maintaining a good matching performance. The total efficiency and envelop correlation coefficient for the decoupled antennas show a significant improvement as compared to the coupled antenna case. The proposed dual-band CRDN scheme is easy to be implemented in an integrated device, and is very attractive for practical multiple input and multiple output (MIMO) applications. [ABSTRACT FROM PUBLISHER]

In this work, an accurate radiation model for the partial element equivalent circuit (PEEC) technique is introduced for modeling of microstrip structures. By making use of the concept of generalized complex inductance proposed recently for the free-space case, an accurate decomposition of the radiation resistance for a small dipole on microstrip substrate is derived for the first time using PEEC. Using the semi-analytical Green's functions for microstrip substrates, the imaginary part of this complex inductance can be shown to represent a frequency-dependent resistance containing contributions from spatial radiations (spherical and lateral) and surface waves (cylindrical). Hence, depending on how the structure of interest is divided into meshes, an equivalent circuit network of “distributed” radiation resistances can be obtained. Two numerical examples have been carried out to validate the model. Results obtained are in good agreement with those from commercial full-wave electromagnetic (EM) solvers, showing the potential of the proposed model for representing high-speed/high-frequency microstrip structures and antennas in the network realm. [ABSTRACT FROM PUBLISHER]

This communication presents a leaky-wave antenna (LWA) in substrate integrated nonradiative dielectric (SINRD) waveguide. An SINRD waveguide being a periodic structure, the bandwidth of the fast-wave frequency band can be controlled by changing the periodicity of the hole array. As a result, a fast or a slow scanning is possible by appropriate choice of the periodicity without changing the substrate parameters. Leakage characteristics of an SINRD waveguide for different parametric variations are discussed. Measurement results are provided. [ABSTRACT FROM AUTHOR]

A cylindrical open-ended substrate-integrated waveguide (SIW) cavity is studied and analyzed in this work. Two orthogonally oriented gaps are used to shrink the dimension of the cylindrical open-ended SIW cavity. Then, the miniaturized cylindrical open-ended SIW cavity is used to construct dual-band antennas. One dual-band antenna is realized by a composite structure that supports two independent modes: they are the half-circular loop mode for the lower band and the half quasi TE11(1/2) mode for the upper band. The other dual-band antenna is an aperture-shared structure: the lower band is related to the miniaturized cylindrical open-ended SIW cavity which works at the quasi TE11(1/2) mode; the upper band is characterized by suspending a concentric slot-loaded circular patch which works at the TM11 patch mode over the empty space of the miniaturized cylindrical open-ended SIW cavity. All modes involved in the two dual-band antennas, the half-circular loop mode, the half quasi TE11(1/2) mode, the quasi TE11(1/2) mode, and TM11 mode, are featured by broadside radiation. The structures of the two dual-band antennas are easy to fabricate by using conventional printed circuit board (PCB) techniques and can be integrated with other planar circuits. Compared to other open-ended cavity antennas, the proposed cylindrical counterpart shows a more compact size and lower profile. [ABSTRACT FROM AUTHOR]

The concept and feasibility of deploying higher-order space harmonics (HSHs) in 1-D periodic leaky-wave antennas (1-D periodic LWAs) is proposed, studied, analyzed, and demonstrated in this article. This can lead to the creation of multiband multibeam antennas (MBMBAs) with the capability of wide scanning ranges. To show the proposed concept, the excitation and flexibility of odd (n ε [−1, −3]) and even (n ε [−2, −4]) HSHs based on the analysis of a Brillouin diagram along with the effect of unit-cell geometrical structures of substrate integrated waveguide (SIW) for different propagating media are investigated. The proposed analysis is experimentally validated by prototyping and measuring a 1-D periodic LWA in SIW technology in which two HSHs (n ε [−1, −2]) are utilized for achieving a dual-band multibeam LWA with wide scanning range capability. In addition, a triple-band multibeam LWA design based on this concept is also analyzed and demonstrated where we take advantage of the characteristics of four HSHs (n ε [−1, −2, −3, −4]). Furthermore, the band edge issue of different stop-bands of HSH is also examined, and a method is proposed and used to address this issue where we use a quarter wavelength technique to overcome the matching problem at different frequencies related to different stop-bands of various HSHs (n ε [−1, −2, −3, −4]). Another design of a SIW-based 1-D periodic LWA is also discussed to extend and generalize the proposed concept in solving the mismatch issues of HSHs focusing on broadside radiation of the n = −2 space harmonic. The measured results are found to agree very well with their simulation and analysis counterparts. [ABSTRACT FROM AUTHOR]

A scalable planar 2-D active array antenna configuration that can realize amplified radiation through co-existing active devices is proposed, studied, and demonstrated in this work. The input and output of these amplifying active devices are directly integrated with the feed network and array elements, respectively, thereby eliminating the matching networks typically required in an amplifier circuit. A comprehensive analysis of the rectangular patch antenna (RPA) performance with different feeding techniques is initially analyzed and the choice of nonradiating edge feed RPA as array elements is justified for not only realizing the maximum radiation efficiency but also facilitating the direct active device integration. Subsequently, a physical arrangement of these array elements is devised to reduce cross-polarization. The design of $4\times {2}$ active array antenna unit cell operating at 5.8 GHz is then discussed through extensive analysis of active devices, optimization procedure, potential excitation signal control, and influence of faulty transistors. From simulations, this active array scheme has realized a higher matching bandwidth and exhibited an amplifier gain of around 13.6 dB, compared with its passive counterpart. Eventually, these unit cells are integrated through an equal power hybrid feed network for realizing an $8\times {8}$ active array antenna configuration that is fabricated and measured. The measured results of the experimental prototype match reasonably well with the simulation results, thereby confirming the proposed integration technique. The resulting paralleled configuration promises efficient handling of greater powers, making them suitable for high-power applications. [ABSTRACT FROM AUTHOR]

This paper proposes and presents a cost-effective fundamental-and-harmonic dual-frequency (FHDF) Doppler radar system for vital signs detection from a mobile radar platform. The proposed FHDF radar architecture concurrently transmits the fundamental signal component (FSC) and its inherent second harmonic signal component (SHSC) of the voltage-controlled oscillator toward opposite directions. The FSC is transmitted toward a target in motion, while the SHSC is transmitted toward a stationary low-cost reflector. For the receiver, a coherent dual-band dual-low-IF architecture is derived and proposed for the first time. This architecture can concurrently receive the reflected FSC that is phase modulated by both motions of the target and the radar platform, and the reflected SHSC that is phase modulated only by the motion of the radar platform, without aliasing, thus enabling the reduction of the overall radar size, power consumption, and system cost. Through the subtraction of a pertinent information contained in the received SHSC from the information embedded in the received FSC using an adaptive noise cancellation technique, the resulting signal contains the desired information that is free of motion artifacts from a moving radar platform. Experimental results show that the proposed radar system is capable of extracting human vital signs, including respiration and heartbeat, even in the presence of a large radar platform movement. By using the proposed FHDF radar system, a see-through-wall vital signs detection from a mobile radar platform can also be successfully conducted without using any additional sensors. [ABSTRACT FROM AUTHOR]

We investigate and present a very low-profile, high-efficiency, and high-gain 2-D leaky-wave antenna (2DLWA) implemented on a high permittivity substrate operating in the millimeter-wave range, paving the way for the seamless integration of a high-gain and high-efficiency antenna with a frontend. In contrast to the typical air-filled 2DLWA, where a perturbation of the first higher-order mode (TE1/TM1) results in highly directed broadside radiation, in the proposed antenna, the propagation and leakage of a quasi-TEM (Q-TEM) mode results in an extremely low-profile ($0.065\lambda _{0}$), high-gain (~15 dBi) antenna. In this scenario, the transverse resonance condition for a Q-TEM mode is established by employing a capacitive partially reflective surface (PRS) in a thin ($0.065\lambda _{0}$) substrate with a relative permittivity of 10.2. The proposed periodic 2DLWA, unlike the conventional uniform/quasi-uniform air-filled counterparts, radiates based on the $\mathbf {n}=-\mathbf {1}$ space harmonic operation. Due to a strong mutual interaction between the PRS and ground plane, conventional design and analysis approaches are no longer relevant in this low-profile architecture. Instead, we employ the Floquet modal expansion theory to create an equivalent circuit model (ECM) for the PRS that takes into account the contributions and mutual interactions of the Floquet harmonics as well as the ground plane effect. By employing reflecting boundaries realized with edge truncation (air trenches) in a high permittivity substrate, we show that the aperture efficiency is enhanced by 15% compared to conventional counterpart. [ABSTRACT FROM AUTHOR]

The gain bandwidth constraint of sequential-rotation arrays (SRAs) has been an open issue since it was first pointed out in 1989. This paper reveals the reason, provides some useful conclusions and proposes an optimum design. Firstly, a first-order analytical formula is derived for the array factor (AF) of the 4-element sub-SRA. The formula embraces the polarization properties of the antenna elements. The AF is found to be dependent on the elements' polarization properties and frequency, which is not found in conventional regular arrays. Based on the theoretical results and full-wave simulations, these dependencies are analyzed in detail. Secondly, an optimum design is proposed to enhance the gain bandwidth: to constitute SRA with elliptically polarized elements (this type of SRA is denoted as EP-SRA) rather than the conventional circularly polarized elements (this type of SRA is denoted as CP-SRA). Detailed design guidance is presented for this new method. Finally, as an example, a CP-SRA and an EP-SRA are designed and tested for comparison. According to the example, by employing EP-SRA, the 1 dB AF bandwidth is improved by 80%, the measured 1 dB/3 dB gain bandwidth is enhanced by 114%/76%. In fact, the conventional CP-SRA and LP-SRA (SRA with linearly polarized elements) are two special cases of the proposed EP-SRA. [ABSTRACT FROM PUBLISHER]

A new microwave device called the cascaded type of coupled resonator decoupling network (C-CRDN) is proposed in this paper. The four-port device can be used to reduce the interference between two radio systems that work in adjacent or even contiguous frequency bands. A C-CRDN is cascaded between the two antennas to be decoupled and the I/O ports of their radio systems, respectively. The coupling matrix of a C-CRDN can be designed to meet the required isolation and return-loss specifications. To prove the concept, a fourth- and sixth-order C-CRDN using coaxial combline cavities are designed, fabricated, and measured according to the characteristics of a testing array that consists of two high-gain sleeve dipoles working in the adjacent time-division long-term evolution and wireless fidelity bands. The measured results have demonstrated that the proposed C-CRDN can effectively mitigate the coexistence interference between the two collocated systems by providing at least 20-dB isolation improvement and enhanced matching performance. The proposed technique is general and can find many applications in heterogeneous wireless systems. [ABSTRACT FROM AUTHOR]

We present a multifilament current method (MFCM) incorporated with generalized sheet transition condition (GSTC) to simulate 2-D cylindrical metasurfaces with arbitrary cross sections. The GSTC casts in the form of an impedance-type boundary condition to relate the tangential fields on two sides of a cylindrical metasurface. The MFCM is subsequently introduced and formulated by employing the GSTC. The doublet-current unit, including both electric and magnetic filamentary sources, is introduced in order to capture both co- and cross-polarized scattered and transmitted fields from the GSTC characterized cylindrical metasurfaces. Three illustrative examples are presented to validate the proposed simulation technique. The behaviors of filamentary sources in terms of scattered field singularities and the ill-conditioning issue of the constructed matrix are also discussed in detail. In comparison to existing numerical methods, the proposed technique has its merits on simplicity and conciseness. [ABSTRACT FROM AUTHOR]

A low pulling effect self-isolated harmonic active radiator operating around 28 GHz is proposed, investigated, and demonstrated in this article. Thanks to the inherent self-isolation property of a feedback loop of the proposed active radiator, a superiority of pulling effect mitigation, harmonic output, and simple structure is achieved. As part of the loop, a partially air-filled dual-mode substrate integrated waveguide cavity with a dielectric-loaded broadside slot is designed to realize the functions of resonators, harmonic diplexers, and antennas concurrently. The radiator oscillates at a fundamental frequency which is set by the first mode of the cavity resonator, and the generated second harmonic signal is extracted and radiated by the diplexer and antenna functions, respectively. Self-isolation is achieved because a pulling signal is attenuated by the synergetic effect of the reverse isolation and harmonic separation of the loop amplifier and diplexer, respectively. Measured results of a fabricated prototype show a maximum equivalent isotropic radiated power of 15 dBm at 28.15 GHz and a phase noise of −108 dBc/Hz at 1 MHz offset. Load pulling and injection pulling are reduced by a factor of 10 and 17, respectively, compared with an active radiator transmitting a fundamental signal around 28 GHz. Such a robust and compactly integrated structure is a good candidate for low-cost millimeter-wave Internet-of-Things applications in connection with identification, sensing, tracking, and communication. [ABSTRACT FROM AUTHOR]

A novel diplexer-based fully passive transponder is presented in this paper, which targets sub-6-GHz 5G-compatible internet-of-things applications. To alleviate the antenna design restrictions of traditional transponder with two separate antennas, a new architecture has been proposed with the introduction of a diplexer, which allows transponder to simply employ a dual-band antenna. In this paper, a dual-band circularly polarized omnidirectional spiral slot antenna, with enhanced bandwidth and gain performance, is designed as the transponder Tx/Rx antenna. Besides the new architecture, a diode selection criterion is proposed as well. Analytical models are derived, showing relationships between the diode’s SPICE parameters and the conversion efficiency or conversion loss (CL) of such diode-based transponders. With help of the analysis, transponder designers can easily identify diodes to implement transponders with better performance. Under the guidance of the criterion, low-barrier diode SMS7630 is chosen for verification. Measured CL results of the transponder circuitry part show a noticeable improvement over the state-of-the-art works. The complete prototype was tested with radar’s transmitting power of 25 dBm, and it presents a maximum read-out distance up to 7 m when the operating fundamental frequency is 3.5 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a class of high-data-rate battery-free yet active miniature radio-frequency identification tag without any external components (except antenna) operating at millimeter (mm)-wave frequencies is proposed and demonstrated. This fully embedded tag consists of a recently proposed CMOS-based zero-intermediate-frequency self-oscillating mixer, a high power conversion efficiency mm-wave-to-dc rectifier, and an ultralow-power voltage regulator on a single chip, integrated with ceramic-based antennas. Interconnection between the CMOS die and the antenna is realized using a wire-bonding technique, which is compensated and optimized to match the antenna input impedance and also to minimize the wire-bond associated losses at mm frequencies. The $10 \times 10$ mm2 tag wirelessly harvests its energy from an incoming signal at 24 GHz, receives, and recovers the data sent by reader on an amplitude modulation (AM)-modulated 40-GHz carrier, and transmits its data back to the reader on a 40-GHz carrier, using AM modulation as well. The tag exhibits a bit rate of about 500 kb/s during the reader-to-tag communication and 10 Mb/s during the tag-to-reader communication, solely relying on the rectified energy for powering its operation. To the best of our knowledge, such an mm-wave identification tag at mm-wave frequencies has never been reported in the literature. [ABSTRACT FROM PUBLISHER]