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In this article, a capacity-oriented envelope correlation coefficient (ECC) that incorporates a preferred channel model for assessing a multiple antenna system of a multiple-input-multiple-output (MIMO) mobile device is proposed. Originated from the rudimentary law of ergodic channel capacity, the ECC for multiple antennas (ECC-M) is proven to holistically reflect the impact of radiation patterns and total efficiencies of multiple antennas on channel capacity. The closed-form ECC-M expressions for Rayleigh fading channel model and ray-based spatial channel model are studied, leading to an easy-to-use ECC-M expression that approximately incorporates a realistic channel model. The correlation of the proposed ECC-M to the channel capacity is demonstrated through the Monte Carlo (MC) simulation of three four-element MIMO antenna testbeds in two channel models, showing that the antenna total efficiency and a realistic channel model involved in the ECC-M play an important role in assessing the performance of multiple antennas. It is justified that the difference in channel capacities of two multiple antenna systems is highly relevant to their ECC-Ms at high signal-to-noise ratios (SNRs). The proposed ECC-M is also experimentally validated through over-the-air (OTA) throughput measurement, revealing that the ECC-M can effectively assess the OTA performance of multiple antenna systems for MIMO terminal devices. [ABSTRACT FROM AUTHOR]

A cost-effective and accurate method for predicting over-the-air (OTA) data throughput of multiple-input and multiple-output (MIMO) wireless devices in the antenna design stage is proposed. The method incorporates passive characteristics of MIMO antennas, realistic channel model, and conductive measurement results in a computer simulation framework. With extracted relation between received power and signal-to-noise ratio (SNR) of a wireless device at antenna ports by a conductive test and measured passive characteristics of MIMO antennas, OTA throughput versus received power in a realistic channel model is obtained by the Monte Carlo simulation of Shannon’s law. The unique features of this method include: no channel emulator equipment is required; a wide variety of precoding schemes can be applied; passive characteristics of antennas are fully incorporated; and frequency-selective fading channel can be adopted. The method has been intensively validated by comparing the calculated OTA throughputs with those measured by a multiprobe anechoic chamber method under spatial channel model extension (SCME) in three aspects: spatial correlation, radiation efficiency, and mutual coupling, showing as low as 0.2–0.3 dB discrepancy in power level in most cases. The method can be used to evaluate a MIMO array antenna design of a wireless device with respect to OTA performance. [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]

A low-profile single-layer endfire circularly-polarized (CP) antipodal linearly tapered slot antenna (ALTSA) is proposed and investigated through simulations and experiments. This antenna is a composite structure consisting of a novel width-tapered slotted substrate-integrated waveguide (SIW) and an ALTSA fed by the SIW. The former also serves as a radiator to produce vertically polarized radiation, which is crucial to achieve a fully planar endfire CP antenna when a thin substrate is deployed. Compared to the previous ALTSA fed by the SIW, this proposed antenna utilizes slots on the spare broad walls of the SIW to form an extra slotted width-tapered SIW radiator, which presents an extension of the conventional width-uniform slotted SIW. Moreover, there are no space harmonics in the slotted width-tapered SIW; it is a slow wave that produces the vertically polarized radiation. The proposed antenna is demonstrated at 28 GHz, which is one of the millimeter-wave bands specified for 5G. An experimental prototype of the antenna has an impedance bandwidth of about 9 GHz from 23.8 to 32.8 GHz and an axial ratio bandwidth of about 1.4 GHz from 27.35 to 28.75 GHz, which coincide well with simulated results. [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]

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]

Radiation efficiency of electrically small antennas largely depends on antenna geometry. However, the actual mechanism that governs the antenna radiation efficiency remains unclear, although various models have been developed since the 1940s. Extant circuit models are either intuition-based or mathematic representations of input impedance/far-field spherical mode functions for structurally simple antennas with limited uses and physical insight. In this article, a recently developed physical micromodeling circuit (MMC) model is utilized to explain the nature of radiation of an electrically small antenna of arbitrary configuration. It is theoretically discovered and experimentally validated for the first time that the radiation efficiency decisively depends on mutual radiated power associated with partial segments of the antenna. A circuital figure of merit for describing the total mutual radiated power is introduced to quantify the measure. The graphical representation of the figure of merit called the holographic radiation diagram is also proposed for illustrating the correspondence of the positive and negative radiated power and the antenna structure. The applications of the proposed theory to antenna design is demonstrated by designing a highly efficient loop antenna. The physical circuit model paves a new way of understanding electromagnetic (EM) radiation problems. [ABSTRACT FROM AUTHOR]

This letter presents a possibility of increasing the radiation efficiency of double-sided leaky-wave antennas (LWAs) by using the substrate integrated slab waveguide (SISW). The idea originates from the fact that double-sided LWAs usually operate on the second mode, and the attenuation constant of the second mode in the SISW is smaller than that in the standard substrate integrated waveguide (SIW). This inherently leads to an increase of antenna radiation efficiency, as less power is dissipated by the traveling wave. In order to prove this concept, two antennas have been designed with the same characteristics (central frequency of 28 GHz, pointing angle of 50°, and beamwidth of 10°), one based on SIW and the other based on SISW. Our experimental verification yields 64% radiation efficiency for the SIW LWA and 80% radiation efficiency for the SISW LWA, thus proving the theoretical and simulated predictions. [ABSTRACT FROM AUTHOR]

A cylindrical substrate-integrated waveguide cavity-backed slot antenna is presented in this paper, which is devised for wideband operation. The fundamental and critical approach to generate a wide antenna bandwidth performance, in this case, is to merge three basic resonant modes (TM010, TM110, and TE111 modes) of the cylindrical cavity. In this paper, a fractional impedance bandwidth of 60% with S11 < −10 dB from 8 to 14.8 GHz has been achieved through this scheme. This antenna has a compact size of $0.33\lambda $ ($\lambda $ denotes the space wavelength corresponding to the operating center frequency $f =11.25$ GHz in this demonstration), which is found suitable for many wireless applications. Its resulting simple structure is definitely of benefit to the fabrication and integration with other front-end parts. The proposed antenna exhibits a broadside radiation pattern, which is stable within the operating frequency band of interest. The simulated radiation efficiency is above 85%. The antenna has been fabricated and experimentally verified. Measured results show a good agreement with simulated counterparts. [ABSTRACT FROM AUTHOR]

Ambient electromagnetic and RF energy is an ubiquitous energy resource that is found everywhere but difficult to harvest because of the time-varying orientation of incoming radiations and the low efficiency of RF rectifiers resulting from a low input power density operation. In response to these two challenges that come with the design of rectennas for ambient energy harvesting, this paper discusses a figure of merit to evaluate the rectenna performance that combines the rectification efficiency, the radiation efficiency, and the spherical coverage of the antenna. To illustrate this proposed figure of merit, a rectenna with a strengthen RF-to-dc efficiency and also a full spatial coverage is designed using beam-forming networks. The resulting system is demonstrated for a wireless sensor mounted on a pole. To maintain a reasonable size of the prototype, a miniaturization technique of a $4 \times 4$ Butler matrix (BM) is investigated, which allows for the reduction of the footprint of the BM by 2 compared to its classical microstrip design counterpart at 2.4 GHz. The overall rectification efficiency and dc power patterns are reported for the elevation plane of one multidirectional rectenna at 2.4 GHz for an incident power density of $0.45\,\,\mu \text {W}\cdot \text {cm}^{-2}$. It is shown that the system can triple the dc output power compared to a three-dipole counterpart occupying the same area. Furthermore, while the maximum harvesting capability at $1 \,\,\mu \text {W}\cdot \text {cm}-^{2}$ does not exceed $28\pi $ %.steradian in the literature, it reaches $43.6\pi $ %.steradian with the proposed demonstrator. [ABSTRACT FROM AUTHOR]

This letter proposes a simple method to turn a single-band inverted-F antenna (IFA) or loop antenna into a dual-band antenna with a small frequency ratio and similar radiation patterns by simply adding a capacitor near the shorting end of a conventional single-band IFA or a loop antenna. Two demonstration examples imitating a mobile terminal application using IFA and loop antenna are present. The measured results show that the IFA and loop antenna with an added capacitor near the shorting end have comparable radiation patterns and total efficiencies in the two designed frequency bands compared with the antennas without the capacitor. The measured frequency ratio of the two resonances is 1.15 (2.23 and 2.56 GHz) for IFA and 1.19 (2.19 and 2.61 GHz) for loop antenna. And the two resonant frequencies can be easily controlled by tuning the added capacitor so that this method can be easily applied to frequency agility applications. To illustrate the physical mechanism, a transmission line model is presented and analyzed. [ABSTRACT FROM AUTHOR]

A new wideband ±45° dual-polarized metal loop dielectric resonator magnetoelectric antenna is proposed in this communication. The antenna consists of two orthogonal dielectric bars that support two orthogonal electric dipoles and two cross interlaced metal semi-loops that are equivalent to two orthogonal magnetic dipoles above the ground. With a legitimate combination of the electric and magnetic dipoles, a unidirectional radiation with low backward radiation and equal E-plane and H-plane radiation patterns can be achieved. The antenna can be made of a monolithic dielectric block with simple installation. To validate the new antenna configuration, a prototype is designed, manufactured, and measured. The prototype antenna using ceramic with the electrical size of $0.33\lambda _{o} \times 0.33\lambda _{o} \times 0.21\lambda _{o}$ demonstrates that an impedance bandwidth of 11.4% ($\vert S_{11}\vert < -15$ dB) in the 3.5 GHz frequency band can be achieved with the measured forward/backward ratio of better than 22 dB. The proposed antenna is suitable as antenna element for massive-MIMO array antennas, where a large number of antenna elements need to be installed in a compact space. [ABSTRACT FROM AUTHOR]

This communication presents a high-order-mode microstrip patch antenna driven by substrate integrated waveguide (SIW) for millimeter-wave polarization-adjustable applications. Different polarization status can be yielded from variable excited signals, including vertical and horizontal linear, right-handed and left-handed circular polarizations. In the patch antenna configuration, an enlarged aperture coming from high-order mode makes it easy to be fed by orthogonal SIWs for dual polarizations. Loaded slots on the patch significantly improve the radiation patterns. The impedance bandwidth with dual resonances is originated from the SIW slot and patch modes. A Ka-band $2\times 2$ antenna array integrated with single-layer SIW feeding network is designed and tested to illustrate this technique. The results manifest that the planar integrated $2 \times 2$ antenna array features adjustable polarization with considerable gain. Furthermore, a two-layer scheme of orthogonal SIW feeding is developed, which would provide a more flexible topology for the scale-expandable array antenna with adjustable polarizations. [ABSTRACT FROM AUTHOR]

To achieve broadband performances in the millimeter-wave range, antipodal linearly tapered slot antenna (ALTSA) designs with new combined substrate integrated waveguide (SIW) and regular coplanar waveguide (CPW) feeds are presented and studied. This feed structure eliminates the fabrication of air bridges in direct CPW-fed tapered slot antennas (TSAs). Two millimeter-wave design techniques are introduced for the selected 41–61 GHz and 90–120 GHz frequency ranges, demonstrating very good impedance match and nearly constant gain, beamwidth, and cross-polarization levels over bandwidths of 39% and 28%, respectively. The design procedure is validated by comparing simulated results with measurements performed on a 21–31 GHz (38% bandwidth) prototype. Very good agreement between measured and calculated performance characteristics is obtained with only cross-polarization levels slightly higher than predicted. The structural design parameters and dimensions of all three designs are given. [ABSTRACT FROM AUTHOR]

A wideband planar dielectric rod antenna with substrate integrated non-radiative dielectric (SINRD) waveguide feed, is presented in this communication for W-band and up-millimeter-wave applications. The antenna and its feeding structure are integrated into a single layer substrate, which decreases the fabrication cost and integration complexity. Simulated and measured results show that the antenna has a wide bandwidth. Due to the structure of the SINRD guide which is shielded on top and bottom of the substrate, the proposed antenna is suitable for multilayer structure techniques such as LTCC or on-chip antenna. This antenna presents numerous features such as broad bandwidth, relatively high and stable gain, use of high dielectric constant substrate, and substrate-oriented end-fire radiation. The proposed antenna is suitable for gigabyte chip-to-chip communications. Measured bandwidth of the antenna is 10 GHz (93–103 GHz) while a relatively flat gain of 9.5 \pm 1~dB is obtained over the bandwidth of interest. [ABSTRACT FROM PUBLISHER]

A class of three-dimensional planar arrays in substrate integrated waveguide (SIW) technology is proposed, designed and demonstrated with 8 \times 16 elements at 35 GHz for millimeter-wave imaging radar system applications. Endfire element is generally chosen to ensure initial high gain and broadband characteristics for the array. Fermi-TSA (tapered slot antenna) structure is used as element to reduce the beamwidth. Corrugation is introduced to reduce the resulting antenna physical width without degradation of performance. The achieved measured gain in our demonstration is about 18.4 dBi. A taper shaped air gap in the center is created to reduce the coupling between two adjacent elements. An SIW H-to-E-plane vertical interconnect is proposed in this three-dimensional architecture and optimized to connect eight 1 \times 16 planar array sheets to the 1 \times 8 final network. The overall architecture is exclusively fabricated by the conventional PCB process. Thus, the developed SIW feeder leads to a significant reduction in both weight and cost, compared to the metallic waveguide-based counterpart. A complete antenna structure is designed and fabricated. The planar array ensures a gain of 27 dBi with low SLL of 26 dB and beamwidth as narrow as 5.15 degrees in the E-plane and 6.20 degrees in the 45^\circ-plane. [ABSTRACT FROM PUBLISHER]

In this article, a multilayered substrate integrated waveguide (SIW) Butler matrix beam-forming network is proposed, designed, and demonstrated at 24 GHz for automotive radar system applications. The proposed low-cost SIW structure can be used to develop a highly integrated multibeam antenna platform in automotive radar systems and other applications. In this structure, an SIW H-plane coupler is optimized with an H-plane slit to provide the required phase shift. A class of SIW E-plane 3-dB couplers in doubled layer substrate are studied and designed as the fundamental building blocks to avoid crossovers usually required in the construction of a Butler matrix. A 4 × 4 matrix is investigated and designed, which shows excellent performance over 22-26 GHz frequency band. Two types of antenna are tested with the proposed matrix scheme. First, an antipodal linearly tapered slot antenna (ALTSA) is incorporated into the Butler matrix to verify the broadband performances. Second, a longitudinal slotted waveguide antenna array is examined to generate radiation patterns in the broadside direction. Measured results agree well with simulated counterparts, thus validating the proposed multilayer SIW design concepts. In the next sections, the use as feeding networks for providing the reconfigurability operation of an antenna will be illustrated. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2012. [ABSTRACT FROM AUTHOR]

A novel class of low-cost, small-footprint and high-gain antenna arrays is presented for W-band applications. A 4 \times 4 antenna array is proposed and demonstrated using substrate-integrated waveguide (SIW) technology for the design of its feed network and longitudinal slots in the SIW top metallic surface to drive the array antenna elements. Dielectric cubes of low-permittivity material are placed on top of each 1 \times 4 antenna array to increase the gain of the circular patch antenna elements. This new design is compared to a second 4 \times 4 antenna array which, instead of dielectric cubes, uses vertically stacked Yagi-like parasitic director elements to increase the gain. Measured impedance bandwidths of the two 4 \times 4 antenna arrays are about 7.5 GHz (94.2–101.8 GHz) at 18 \pm 1 dB gain level, with radiation patterns and gains of the two arrays remaining nearly constant over this bandwidth. While the fabrication effort of the new array involving dielectric cubes is significantly reduced, its measured radiation efficiency of 81 percent is slightly lower compared to 90 percent of the Yagi-like design. [ABSTRACT FROM PUBLISHER]

Millimeter wave applications such as short-range high-speed wireless links require modular, compact-size and high-directivity antennas. In this paper, high-gain compact stacked multilayered Yagi designs are proposed and demonstrated in the V-band. This novel design shows for the first time an antenna array of Yagi elements in millimeter wave stacked structure. To demonstrate the proposed concepts and design features, a 4\,\times\,4 antenna array is created having excellent gain performance as well as very small footprint. A single element stacked Yagi antenna fed with microstrip is studied in order to obtain the desired performance. An analysis is performed to define the structure limitations. Measured results of the fabricated antenna prototypes are in good agreement with simulated results The measured Yagi antenna attains 11 dBi gain over 4.2% bandwidth with a size of 6.5\,\times\,6.5\,\times\,3.4 mm^3. A 4\,\times\,4 array of Yagi antenna using an SIW (Substrate Integrated Waveguide) feeding technique is conceived. Both simulated and measured results match with each other very well. The 4\,\times\,4 array has a size of 28\,\times\,24\,\times\,2.4 mm^3, and reaches a measured gain of 18 dBi over 7% bandwidth. An alternate configuration of the array using angled Yagi antenna elements allows a significant improvement of the side lobe level (SLL) with a low impact on the gain performances. The proposed antennas are excellent candidates for integrated low-cost millimeter-wave and even terahertz systems. The small foot print, the antenna design flexibility as well as its easy adaptation to automatic fabrication processes are good assets for making short range portable imaging systems. [ABSTRACT FROM AUTHOR]

Two types of substrate integrated waveguide (SIW) long slot leaky-wave antennas with controllable sidelobe level are proposed and demonstrated in this paper. The first prototype is able to achieve an excellent sidelobe level of -27.7~dB by properly meandering a long slot etched on the broadside of a straight SIW section from the centerline toward the sidewall then back. But it is known that an asymmetrically curved slot would worsen the cross-polar level. To overcome this drawback, a modified leaky-wave antenna is proposed, which has a straight long slot etched on the broadside of a meandering SIW section. It yields an outstanding sidelobe level of -29.3~dB and also improves the cross-polar level by more than 11 dB at 35 GHz. Experimental results agree well with simulations, thus validating our design. Then, a two-dimensional (2-D) multibeam antenna is developed by combining such 14 leaky-wave antennas with an SIW beamforming network (BFN). It has features of scanning both in elevation orientation by varying frequency and in cross-plane direction by using the BFN. Excited at ports 1–10 of such a 2-D multibeam antenna at 35 GHz, angular region of 86.6^\circ in azimuth can effectively be covered by 3 dB beam-width of ten pencil beams. Varying frequency from 33 GHz to 37 GHz, the angular region of 37.5^\circ and 38.9^\circ in elevation can be covered by 3 dB beam-width of those continuous scanning beams excited at ports 6 and 8 respectively. [ABSTRACT FROM AUTHOR]