Slot-coupled Microstrip Research Articles

A Series of Ultra-low Permittivity ALaP4O12 (A = Li, Na, K) Metaphosphate Microwave Dielectric Ceramics for Ultra-wideband Dielectric Resonant Antenna Application.

The employment of ultra-low permittivity materials in the configuration of antennas has been demonstrated to augment the antenna bandwidth and diminish signal delay effectively. This study presents three ultra-low permittivity metaphosphate microwave dielectric ceramics (MWDCs). The ALaP4O12 (A = Li, Na, K) metaphosphate ceramics, which all belong to the monoclinic crystal system, exhibit extremely low permittivity (εr ≈ 5) and excellent quality factor (Q·f > 10,000 GHz) at a low sintering temperature (T < 950 °C). Terahertz time-domain spectroscopy indicates that the εr of ALaP4O12 at terahertz frequencies is comparable to that observed in the microwave band and its value remains stable over an extensive frequency range. Furthermore, the relationship between the crystal structure and the dielectric properties of ALaP4O12 has been analyzed through the lens of chemical bond theory. The highest Q·f value observed for LiLaP4O12 can be attributed to the high chemical bond strength and stability of its crystal structure. The lowest ionic polarizability per unit volume is exhibited by NaLaP4O12, which results in the lowest pore-corrected permittivity. The thermal expansion of the chemical bonds within KLaP4O12 is considerable, resulting in the highest coefficient of thermal expansion. Finally, the performance of a LiLaP4O12-based dielectric resonator antenna (DRA) excited by slot-coupled microstrip lines was designed and optimized by using different ceramic radius-to-height (RH) ratios. It was found that when the RH ratio of DRA reached 1.85, both the fundamental mode (HEM11δ) and the higher-order mode (HEM12δ) of DRA were simultaneously excited. The two modes overlap significantly, resulting in an ultra-wideband (UWB) of 46.8% (bandwidth = 7.93 GHz). Concurrently, the maximum radiation efficiency and gain of the DRA, obtained from the simulation, are 97.9% and 7.92 dBi, respectively. The findings of this study may inform the investigation of ultra-low permittivity phosphorus-based MWDCs and UWB DRAs.

Dual-Polarized, Dual-Band, and Aperture-Shared Synthesis Method for Phased Array Applications

A dual-band and dual-polarized shared-aperture synthesis method for phased array applications is proposed. Dual-polarized slot-coupled microstrip patch elements operating in the Ku <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</i> band are arranged in a regular array configuration. Two orthogonal probes share a common radiating patch structure and are fed by two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -shaped coupling slots. Sidewall metalized cavity waveguide elements operating in the W-band are fed by a substrate-integrated waveguide and arranged in a sparse array configuration, which is based on an optimization algorithm proposed in this work. Furthermore, the feeding locations are regularly determined, which is beneficial to transceiver/receiver design, thus reducing the cost of a phased array system. By exploiting this compact array topology and optimization algorithm, two-phased arrays with a large frequency ratio employing a shared aperture simultaneously exhibit wide-angle scanning properties. A 64-element array is designed, fabricated, and measured. The measurement results show that the Ku-band dual-polarized antenna exhibits a wide impedance bandwidth of 20% in the 14.3–17.6 GHz frequency range for two orthogonal polarizations and high isolation (>20 dB) between the feeding ports. The W-band antenna exhibits a 5.4% fractional impedance bandwidth covering 90–95 GHz frequency range with a ±45° scanning angle in the E <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</i> and H-planes.

5G SIW-Based Phased Antenna Array With Cosecant-Squared Shaped Pattern

In this article, a concept of a phased antenna array based on substrate integrated waveguide (SIW) technology for 5G base stations is proposed. The array has a cosecant radiation pattern in the vertical plane for uniform illumination in a sector area. The array itself consists of 16 SIW traveling wave subarrays of 12 slot-coupled microstrip patch antennas associated with a pair of reflection-canceling vias and phasing elements to get the tapered distribution both in amplitude and phase for the cosecant-shaped radiation pattern. The array is designed to be operational at 28 GHz with a bandwidth of more than 10%, a candidate mm-wave frequency band for 5G. The phased antenna array supports wide-angle scanning of +/−60° in azimuth and exhibits good active impedance properties. The array design is successfully verified experimentally.

Gain Stabilization Method for Wideband Slot-Coupled Microstrip Antenna

Wideband slot-coupled microstrip antenna (SCMSA) is a distinctive electromagnetic wave radiator in recent years with wide bandwidth and low profile. In such a wide frequency range, the electrical distance, i.e., normalized to operating wavelength, between dual equivalent magnetic currents increases obviously with upward frequency. Therefore, the realized gain is usually with a large variation, which limits the wideband performance of SCMSA. In this communication, a feasible method is proposed to stabilize the realized gain of an SCMSA over its entire impedance bandwidth by utilizing a properly designed reflector-plus-sidewall structure (RPSS), which includes a reflector with an optimized height and two vertical sidewalls. Each part has its own function in realized gain compensation and enhancement, performing a flatter and higher realized gain in a wide frequency range. To validate this method, an antenna prototype is fabricated and tested. Compared with the referenced SCMSA, the measured results indicate that the proposed one adding RPSS maintains a wide impedance bandwidth of 24.8% (3.75–4.81 GHz), but reduces gain variation from 4.1 to 0.5 dB (10.5–11 dBi) with an average realized gain increment of 2.1 dB.

A High-Gain Dielectric Resonator Antenna With Plastic-Based Conical Horn for Millimeter-Wave Applications

A novel high-gain dielectric resonator antenna, featuring a peak realized gain of 11.3 dBi over a fractional bandwidth of 16.6% around 30 GHz, is presented. The proposed antenna structure, excited by a slot-coupled microstrip line, is composed of a cylindrical dielectric resonator and of a truncated plastic-based conical horn useful to enhance the gain. An annular perturbation notch is realized in the dielectric horn to achieve a better focusing of the RF energy along the antenna boresight direction, while reducing the sidelobe levels (SSLs). The presented antenna design achieves SSLs below −10 dB for both the E - and H -plane so to meet the requirements of next-generation 5G wireless communication protocols and of low-cost satellite and mobile systems.

Design and Implementation of Slot-coupled Microstrip Components for Wideband Butler Matrix

Design and Implementation of Slot-coupled Microstrip Components for Wideband Butler Matrix

Omnidirectional Dual-Polarized Antenna With Sabre-Like Structure

In this communication, a sabre-like dual-polarized antenna with omnidirectional patterns in the azimuthal plane is presented for low wind drag airborne applications. The proposed antenna consists of a thin cavity for the horizontal polarization and a coplanar waveguide-fed monopole for the vertical polarization. The colocated thin cavity and the monopole construct a compact sabre-like structure with low wind drag, and it is suitable for airborne use. Especially, a hybrid-feeding structure, including a capacitive slot-coupled microstrip line and an inductive probe, is proposed for impedance matching of the thin cavity to provide omnidirectionally horizontal polarization. In order to verify the proposed design, a prototype is fabricated and tested with the dimensions of $42 \times 29 \times 9$ mm3. ( $0.42\lambda _{0} \times 0.24\lambda _{0} \times 0.07\lambda _{0}$ , $\lambda _{0}$ is the free-space wavelength at 2.44 GHz.) The measured −10 dB reflection coefficient bandwidths of the two ports are 2.38–2.51 and 2.28–2.53 GHz. The measured gain variation in the azimuth plane is less than 3.60 and 3.45 dB for horizontal polarization and vertical polarization.

Design of Multilayered K-Band and Ka-Band Slot-Coupled Microstrip 90° Hybrid Couplers Employing Circular Ring Patch Shapes

Numerical analysis and design of millimeter-wave (mmWave) slot-coupled microstrip 90° hybrid couplers employing circular ring patches, which is operating between 18 and 40 GHz frequency range for K...

A Frequency Reconfigurable Directive Antenna With Wideband Low-RCS Property

In this communication, a frequency reconfigurable directive antenna with low-radar cross section (RCS) property is presented. This antenna is composed of a slot-coupled microstrip patch and a two-layer metastructure. The top-layer metastructure integrates a partially reflection surface (PRS) with an absorbing surface, and the bottom-layer one consists of tunable reflection phase cells, which are loaded around the antenna source. The absorbing surface can absorb most of the incoming wave, and thus reduce the antenna RCS. The PRS and tunable reflection phase cells form a Fabry–Perot resonance cavity, making the antenna produce a highly directive beam. In addition, the operation frequency can be dynamically tuned by controlling the varactor diodes in the reflection phase cells. Both simulated and measured results have verified that employing the two-layer metastructure makes the antenna RCS largely reduced at a wide band ranging from 8 to 14 GHz. Compared with the traditional microstrip antenna, this antenna radiates a highly directive beam with gain enhancement of about 7 dB, and its operation frequency can be actively tuned from 9.05 to 10 GHz.

Dual-Polarized Slot-Coupled Microstrip Antenna Array With Stable Active Element Pattern

A dual-polarized slot-coupled microstrip antenna array with stable active element pattern is investigated. The antenna element of the array is a slot-coupled microstrip antenna with a reflector. The effect of the ground size on the radiation pattern of the antenna element is analyzed based on the electric field and current distributions. The method of adding copper pillars around the antenna element is proposed to mitigate the influence of the ground plane. A prototype of ${1} \times {3}$ microstrip antenna array is fabricated and measured. Its measured impedance bandwidth for $\mathrm{VSWR} is 520 MHz (1.69–2.21 GHz). Within the operating band, the performances of low mutual coupling, low cross polarization, and stable active element pattern are achieved.

Design of ultrawideband multilayer slot-coupled vertical microstrip transitions employing novel patch shapes

Design of two different slot-coupled vertical microstrip–microstrip transitions for ultrawideband (UWB) multilayer microwave circuits are introduced. Transitions consist of two stacked substrates with common ground in the middle and two microstrip-feed-lines connected to microstrip patches on the top and bottom. The proposed transitions use broadside coupling between microstrip patches at the top and the bottom layers via a rectangular-shaped slot in the common ground plane (midlayer). The proposed patch shapes are trapezoidal and butterfly shapes, which are capable of achieving broadband characteristics for UWB operation. Extensive parametric studies are performed to address the effect of varying the transition parameters on the coupling value and the operational frequency bandwidth. The simulated results using two simulation programs with two different numerical techniques show that the proposed transitions have low transmission coefficient (less than 1.2 dB) and a high reflection coefficient (better than 16 dB) over the 3.1–10.6 GHz frequency range. Two transition prototypes are fabricated and then tested experimentally using Agilent E8364B PNA Network Analyzer. Experimental results agree well with the simulated ones. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:747–756, 2015

HEXA-BAND HIGH-ISOLATED DUAL-POLARIZED LOOP ANTENNA FOR MOBILE COMMUNICATIONS

This paper presents a broadband hexa-band dual-polarized loop antenna for mobile communications. Two orthogonal one-wavelength-perimeter modes of a rectangular loop are excited by two orthogonal feedings. One mode for vertical polarization is excited by a circular monopole, and the other mode for horizontal polarization is excited by a slot-coupled microstrip line. By optimizing the antenna structure and the orthogonal feedings, the orthogonal polarizations can be achieved in a wide bandwidth with high ports isolation. The overall size of the proposed antenna is only 58 × 53 mm 2 (0.43λ0 × 0.39λ0, λ0 is the free-space wavelength at 2.2 GHz). A prototype of the proposed antenna is built and tested. The measured bandwidth with reflection coefficient less than −10 dB is 61.4% (1.65-3 GHz) for both orthogonal polarizations, covering the DCS, PCS, UMTS, WLAN, LTE2300, and LTE 2500 operation. The measured ports isolation is better than 28 dB over the entire band. In addition, the radiation patterns, gains and diversity performance are also discussed.

Compact Integrated Feeding Network for Excitation of Dual-Circular Polarization in Series-Fed Antenna Lattice

A novel approach for realization of a feeding network allowing for achieving dual-circular polarization in the slot-coupled microstrip antenna lattice has been proposed. The presented feeding network is an eight-port composed of four 3\mathchar"702DdB/90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> directional couplers, and when appropriately integrated with the four-port series-fed antenna lattice ensures a full symmetry of the antenna layout and produces simultaneously right-handed and left-handed circular polarization. The proposed low-profile, low-cost solution can be easily integrated with the antenna lattice, and it allows for reduction of the introduced dissipation losses comparing to the known solutions, i.e., external feeding networks such as Butler matrices or power combiner/divider networks connected via coaxial cables. The proposed concept has been examined by measurements of the manufactured feeding network integrated with the previously developed antenna lattice operating at 5.4 GHz.

An Ultra-Thin, High-Power, and Multilayer Organic Antenna Array With T/R Functionality in the $X$-Band

The transmit-receive (T/R) operation of an ultra-thin organic antenna array is presented at a center frequency of 9.5 GHz. High transmit power is achieved while maintaining an ultra-low profile in a novel system-on-a-package scheme whereby 32 silicon-germanium (SiGe), transmit/receive integrated-circuit (TRIC) modules have been flip-chip bonded to the array board. Each SiGe TRIC drives a pair of slot-coupled microstrip patch antennas that form an 8 × 8 rectangular array, which is all packaged in an organic substrate stack of liquid crystal polymer and RT/Duroid 5880LZ. The organic package occupies an area of 30.5 cm × 25.4 cm and has a total thickness of only 1.80 mm. The small-signal characterization of the array showed a G/T=-6.64 dB , and a measured receive gain of 20.1 dB with a variation of 0.7 dB over a 1-GHz bandwidth (BW). Finally, far-field large-signal experiments showed a measured effective isotropically radiated power of 47.1 dBm with a variation of 2.36 dB over the same BW, and without the aid of additional thermal management components.

Series-Fed Microstrip Antenna Arrays and Their Application to Omni-Directional Antennas

The analysis of a series feed approach for N-element slot-coupled microstrip antenna arrays is presented. A cylindrical arrangement of six four-element arrays using this feeding mechanism is shown to achieve optimum omni-directional beam characteristics and exhibit pattern stability over frequency in the C-band. The cylindrical arrangement is measured to have a gain of 6 dB over 750 MHz of bandwidth. A closed-form omni-directional pattern analysis is also developed.

A New Broadband Marchand Balun Using Slot-Coupled Microstrip Lines

In this letter, a new broadband Marchand balun is proposed using slot-coupled microstrip lines. The developed balun is connected by two sections of diamond-shape slot-coupled microstrips with short- and open-circuited terminations at specified ports. To achieve the broadband operation, the simple formulas have been derived to convert the conventional rectangular-shape slot-coupled microstrip to the diamond-shape counterpart. The measured results of the developed balun not only agree with the full-wave simulation results very well, but also resemble the calculated results by ideal coupled lines. The new Marchand balun developed in this letter has a 10 dB return loss bandwidth of 90%, while in this frequency range the amplitude imbalance varies from -0.37 dB to 0.32 dB, and the phase difference in the range of -180.4° ~ -181.8°.

Low-Profile Planar Tripolarization Antenna for WLAN Communications

A tripolarization and low-profile planar antenna is designed, prototyped, and tested for WLAN application. The developed three-port antenna provides three orthogonal polarization radiations. Two slot-coupled microstrip antennas and a disk-loaded monopole are integrated into one structure. The total height of the antenna is 5.8 mm. Obtained gain for the two slot-coupled directive elements at 2.42 GHz is 7 dBi, while the gain for the monopole omnidirectional element is 2.5 dBi. The bandwidths of the three elements are 2.352.52, 2.32.54, and 2.382.49 GHz, respectively. Simulation results of the radiation patterns are presented and validated by experimental measurements.

A NEW ULTRA-WIDEBAND BEAMFORMING FOR WIRELESS COMMUNICATIONS IN UNDERGROUND MINES

In this paper, a novel ultra-wideband switched-beam antenna system based on 4×4 two-layer Butler matrix is presented and implemented to be used in hostile environment, such as underground mines. This matrix is based on the combination of a broadband two- layer slot-coupled directional coupler and a multilayer slot-coupled microstrip transition. With this configuration, the proposed matrix was designed without using any crossovers as used in conventional Butler matrices. Moreover, this new structure is compact and offers an ultra-wide bandwidth of 6 GHz. To examine the performance of the proposed matrix, experimental prototypes of the multilayer microstrip transition and the Butler matrix were fabricated and measured. Furthermore, a three 4-antenna arrays were also designed, fabricated and then connected to the matrix to form a beamforming antenna system at 3, 5.8 and 6 GHz. As a result, four orthogonal beams are produced in the band 3-9 GHz. This matrix is suitable for ultra- wideband communication systems in confined areas.

Wideband dual-polarized slot-coupled microstrip array for synthetic aperture radar application

An 8 × 1-element wideband dual-polarized slot-coupled microstrip antenna array with high isolation and low cross-polarization in X-band is presented. The array antenna offers an impedance bandwidth (VSWR≤2) of 23% and 21% for dual polarization ports, respectively. The measured isolation between two polarization ports is better than 35 dB and the measured cross-polarization level below −25 dB in the main beam over the operation frequency band of 9.35 GHz to 9.75 Ghz. This array is well suitable for X-band SAR (synthetic aperture radar) antenna application.

Compact Reflectometers for a Wideband Microwave Breast Cancer Detection System

The design of compact wideband microwave reflectometers for the purpose of inclusion in a breast cancer detection system is presented. In this system, a wideband frequency source is used to synthesize a narrow pulse via the step-frequency synthesis method. The reflectometer undertakes measurements in the frequency domain and the collected data is transformed into the time/space domain using IFFT. In order to accomplish reflection coefficient measurements over a large frequency band, compact wideband couplers and power dividers are used to form the reflectometer. Two compact six-port reflectometer configurations are investigated. One uses the Lange coupler and the Gysel power divider and the other one employs a 3dB slot-coupled microstrip coupler and a 2-stage Wilkinson power divider. The reflectometer employing the slot-coupled coupler and the Wilkinson divider provides a wider operational bandwidth, as shown by simulation results performed with Agilent ADS.