Standing-Wave Dielectric Array Antennas

Due to the evolutions in wireless communication systems, antenna engineers have been confronting a number of challenges regarding improving the performance of antennas, miniaturizing the size as well as considering the fabrication simplicity. Although dielectric resonator antennas typically suffer from exhibiting low gain, they have been thoroughly under investigating as they are being excellent candidates to be utilized to fulfill contemporary communication systems requirements and specifications, especially at high-frequency ranges. The reason behind this solicitude is because they have several advantageous features, including but not limited to the simplicity of the used excitation mechanism and fabrication easiness. One of the well-known methods to improve the gain is by arraying additional individual DRAs. However, one major obstacle evokes when designing the array to operate at a higher frequency. Spurious radiations from the feeding network are considerable and unfavorably influence the overall array performance. Moreover, it is mandatory to have several quarter-wavelength transmission lines and power dividers which, in turns, lead to high configuration complexity. The substantial intention of this dissertation is to explore dielectric resonator array antenna designs where the concept of standing waves is utilized. In contradictory to corporate-fed traveling-wave array antennas designs, the need to utilize microstrip discontinuities such as quarter-wave transformers or power dividers is eliminated while having a single feeding port to excite the entire array structure. Consequently, undesired spurious coupling and radiations can be exceedingly minimized especially when operating at very high-frequency bands. The dissertation proposes two novel dielectric array configurations based on the concept of standing-wave. In the first configuration, vertical and horizontal low-profile dielectric bridges have been employed to connect 3x3 dielectric array elements. The top surface of each bridge is covered by a metallic patch to prevent unfavorable radiations coming out of the bridges. The array structure is fed using a single coupling aperture resides symmetrically underneath the center element only. When exciting waves are coupled to the center element, these waves can be transferred to other array elements via the introduced dielectric bridges. Therefore, the entire structure resonates at the resonant frequency as a whole. The proposed design provides a realized gain of about 15 dBi at the boresight. The return loss is about -20 dB possessing about 35.7% useful impedance bandwidth. The experimental results show excellent agreement with those obtained by simulation. The second proposed configuration consists of four dielectric resonator antennas forming a linear array. On the top surface of the substrate and between the array elements, there are three metallic patches which are employed to excite the array elements. These patches are slightly extended under the slabs to allow sufficient coupling. Under each dielectric slab, there is one metallic patch reside symmetrically at the center to enhance the wave coupling in both directions toward the array elements. The single feeding coaxial probe is attached to the center patch, and its location was optimized to provide excellent impedance matching. The maximum observed gain is 15 dBi at the boresight. The array structure is well matched and the return loss is measured to be -45 dB. The validity and versatility of both designs are realized and illustrated. One powerful advantageous feature is that the feeding network was extremely simplified to a single port to excite the entire array structure. Another advantage is that both designs were partially fabricated using 3D printing technology. Therefore, it can be said that the proposed configurations are easy to fabricate since the complexity of designing feeding networks was obviated

Interaction suppression technique for high-density antenna arrays for mm-wave 5G MIMO systems

This paper presents the feasibility study of applying a combination of suppression techniques to improve isolation between the radiation elements in high-density antenna arrays and thereby improve the arrays impedance bandwidth and radiation performance. High isolation between adjacent radiation elements was achieved by embedding a crisscrossed decoupling structure comprising slotted microstrip-lines and locating in the ground-plane under each slot a dielectric ring. The proposed periodic array behaves as artificial magnetic conductor (AMC) surfaces as incident waves in the substrate are fully reflected with a near zero degrees reflection phase. The proposed technique suppresses surface-wave propagation. Proof of concept was verified by applying the technique to a 2×4 linear array of triangular radiation patches designed to operate between 30-35 GHz. The array was implemented on a standard the Rogers RT 5880 substrate. Dimensions of the array are 40×20×0.8 mm3. Measurement confirm improvement is the array’s impedance bandwidth, fractional bandwidth, average isolation, radiation gain, and efficiency by 2 GHz, 6.15%, >10 dB, 6.6 dBi, and 29%. The array operates across 30–35GHz with average isolation between its radiation elements better than 23 dB, average gain and efficiency of 12 dBi and 85%, respectively. The technique can be applied to mm-Wave 5G MIMO systems

An innovative and simpleiImpedance matching network using stacks of metasurface sheets to suppress the mismatch between antennas and RF front-end transceivers circuits

A innovative and simple impedance matching network is presented that is implemented by stacking together metasurface (MTS) sheets. The technique is shown to reduce the mismatch between free-space and RF front-end antenna of a receiver. The MTS based impedance matching network is modeled as a transmission-line loaded with shunt and series capacitances and inductances, respectively. The proposed MTS impedance matching network can be employed to effectively interface the free-space to the antenna of an RF receiver and thereby optimize power absorption. Each MTS impedance matching sheet comprises two-dimensional periodic array of subwavelength microstrip resonator unit-cells that are spaced at a wavelength that is smaller than the frequency of operation. The unit-cells are square shaped patches and embedded with cross-shaped slots that are grounded through a via-hole. The MTS impedance matching network was fabricated using FR-4 substrate. 3D full-wave EM tool by Ansys HFSS™ was used to verify its effectiveness. The proposed MTS impedance matching sheet is relatively easy to implement in practice

Compact and low-profile on-chip antenna using underside electromagnetic coupling mechanism for terahertz front-end transceivers

The results presented in this paper show that by employing a combination of metasurface and substrate integrated waveguide (SIW) technologies, we can realize a compact and low-profile antenna that overcomes the drawbacks of narrow-bandwidth and low-radiation properties encountered by terahertz antennas on-chip (AoC). In addition, an effective RF cross-shaped feed structure is used to excite the antenna from its underside by coupling, electromagnetically, RF energy through the multi-layered antenna structure. The feed mechanism facilitates integration with the integrated circuits. The proposed antenna is constructed from five stacked layers, comprising metal–silicon–metal–silicon–metal. The dimensions of the AoC are 1×1×0.265 mm3. The AoC is shown to have an impedance match, radiation gain and efficiency of ≤ −15 dB, 8.5 dBi and 67.5%, respectively, over a frequency range of 0.20–0.22 THz. The results show that the proposed AoC design is viable for terahertz front-end applications

Overcoming inherent narrow bandwidth and low radiation properties of electrically small antennas by using an active interior-matching circuit

A technique is described to extend the working frequency-band and increase the radiation gain and efficiency of an electrically small antenna (ESA). The geometry of the proposed ESA is in the shape of an “H” structure. A small gap is included at the symmetry of the H-shape structure to embed an inductive load that is used to connect the two halves of the H-shaped antenna. With the lumped element inductor, the bandwidth of the H-shaped antenna is restricted by Chu-lower bound. However, it is demonstrated by analytical analysis and through 3D full-wave electromagnetic simulations that when the inductive load is replaced with negative reactance from a negative impedance converter (NIC) the antenna’s bandwidth, radiation gain and efficiency performance can be significantly improved by ~40%, 3.6 dBi and 55%, respectively. This is because NIC acts as an effective interior matching circuit. The resonant frequency of the antenna structure with the inductive element was used to determine the required inductance variation in the NIC to realize the required bandwidth and radiation characteristics from the H-shaped antenna

Realizing UWB antenna array with dual and wide rejection bands using metamaterial and electromagnetic bandgaps techniques

This research article describes a technique for realizing wideband dual notched functionality in an ultra-wideband (UWB) antenna array based on metamaterial and electromagnetic bandgap (EBG) techniques. For comparison purposes, a reference antenna array was initially designed comprising hexagonal patches that are interconnected to each other. The array was fabricated on standard FR-4 substrate with thickness of 0.8 mm. The reference antenna exhibited an average gain of 1.5 dBi across 5.25–10.1 GHz. To improve the array’s impedance bandwidth for application in UWB systems metamaterial (MTM) characteristics were applied it. This involved embedding hexagonal slots in patch and shorting the patch to the ground-plane with metallic via. This essentially transformed the antenna to a composite right/left-handed structure that behaved like series left-handed capacitance and shunt left-handed inductance. The proposed MTM antenna array now operated over a much wider frequency range (2–12 GHz) with average gain of 5 dBi. Notched band functionality was incorporated in the proposed array to eliminate unwanted interference signals from other wireless communications systems that coexist inside the UWB spectrum. This was achieved by introducing electromagnetic bandgap in the array by etching circular slots on the ground-plane that are aligned underneath each patch and interconnecting microstrip-line in the array. The proposed techniques had no effect on the dimensions of the antenna array (20 mm × 20 mm × 0.87 mm). The results presented confirm dual-band rejection at the wireless local area network (WLAN) band (5.15–5.825 GHz) and X-band satellite downlink communication band (7.10–7.76 GHz). Compared to other dual notched band designs previously published the footprint of the proposed technique is smaller and its rejection notches completely cover the bandwidth of interfering signals

A Miniaturized and Highly Sensitive Microwave Sensor Based on CSRR for Characterization of Liquid Materials

In this work, a miniaturized and highly sensitive microwave sensor based on a complementary split-ring resonator (CSRR) is proposed for the detection of liquid materials. The modeled sensor was designed based on the CSRR structure with triple rings (TRs) and a curve feed for improved measurement sensitivity. The designed sensor oscillates at a single frequency of 2.5 GHz, which is simulated using an Ansys HFSS simulator. The electromagnetic simulation explains the basis of the mode resonance of all two-port resonators. Five variations of the liquid media under tests (MUTs) are simulated and measured. These liquid MUTs are as follows: without a sample (without a tube), air (empty tube), ethanol, methanol, and distilled water (DI). A detailed sensitivity calculation is performed for the resonance band at 2.5 GHz. The MUTs mechanism is performed with a polypropylene tube (PP). The samples of dielectric material are filled into PP tube channels and loaded into the CSRR center hole; the E-fields around the sensor affect the relationship with the liquid MUTs, resulting in a high Q-factor value. The final sensor has a Q-factor value and sensitivity of 520 and 7.032 (MHz)/Er) at 2.5 GHz, respectively. Due to the high sensitivity of the presented sensor for characterizing various liquid penetrations, the sensor is also of interest for accurate estimations of solute concentrations in liquid media. Finally, the relationship between the permittivity and Q-factor value at the resonant frequency is derived and investigated. These given results make the presented resonator ideal for the characterization of liquid materials.Publicad

3-D-Printed dielectric resonator antenna arrays based on standing-wave feeding approach

A novel feeding method for a dielectric resonator array antenna is introduced. Unlike in a corporate feed network, power dividers or quarter-wave transformers are not needed in the new feeding scheme as the design is based on the standing-wave concept. Consequently, the feed network is greatly simplified, and undesired spurious radiation in the feeding network is minimized. The simulated and measured results are in good agreement. A 3-D printer is utilized where the entire array structure is fabricated as a single piece with a dielectric material of polylactic acid. The 3-D printer provides a cost-efficient, simple, and rapid manufacturing process.This work was supported by Comunidad de Madrid under Projects S2018/NMT-4333 MARTINLARA-CM and TEC2016-80386-P.Publicad

Dual band and dual diversity four-element MIMO dipole for 5G handsets

The increasing popularity of using wireless devices to handle routine tasks has increased the demand for incorporating multiple-input-multiple-output (MIMO) technology to utilize limited bandwidth efficiently. The presence of comparatively large space at the base station (BS) makes it straightforward to exploit the MIMO technology’s useful properties. From a mobile handset point of view, and limited space at the mobile handset, complex procedures are required to increase the number of active antenna elements. In this paper, to address such type of issues, a four-element MIMO dual band, dual diversity, dipole antenna has been proposed for 5G-enabled handsets. The proposed antenna design relies on space diversity as well as pattern diversity to provide an acceptable MIMO performance. The proposed dipole antenna simultaneously operates at 3.6 and 4.7 sub-6 GHz bands. The usefulness of the proposed 4×4 MIMO dipole antenna has been verified by comparing the simulated and measured results using a fabricated version of the proposed antenna. A specific absorption rate (SAR) analysis has been carried out using CST Voxel (a heterogeneous biological human head) model, which shows maximum SAR value for 10 g of head tissue is well below the permitted value of 2.0 W/kg. The total efficiency of each antenna element in this structure is −2.88, −3.12, −1.92 and −2.45 dB at 3.6 GHz, while at 4.7 GHz are −1.61, −2.19, −1.72 and −1.18 dB respectively. The isolation, envelope correlation coefficient (ECC) between the adjacent ports and the loss in capacity is below the standard margin, making the structure appropriate for MIMO applications. The effect of handgrip and the housing box on the total antenna efficiency is analyzed, and only 5% variation is observed, which results from careful placement of antenna elements