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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]

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]

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]

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 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]

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]

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]