Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles.

Gain enhancement methods for printed circuit antennas

In this paper, a new dense dielectric (DD) patch array antenna prototype operating at 28 GHz for future fifth generation (5G) cellular networks is presented. This array antenna is proposed and designed with a standard printed circuit board process to be suitable for integration with radio frequency/microwave circuitry. The proposed structure employs four circular-shaped DD patch radiator antenna elements fed by a 1-to-4 Wilkinson power divider. To improve the array radiation characteristics, a ground structure based on a compact uniplanar electromagnetic bandgap unit cell has been used. The DD patch shows better radiation and total efficiencies compared with the metallic patch radiator. For further gain improvement, a dielectric layer of a superstrate is applied above the array antenna. The measured impedance bandwidth of the proposed array antenna ranges from 27 to beyond 32 GHz for a reflection coefficient (S11) of less than -10 dB. The proposed design exhibits stable radiation patterns over the whole frequency band of interest, with a total realized gain more than 16 dBi. Due to the remarkable performance of the proposed array, it can be considered as a good candidate for 5G communication applications.

Dense Dielectric Patch Array Antenna With Improved Radiation Characteristics Using EBG Ground Structure and Dielectric Superstrate for Future 5G Cellular Networks

A novel method is presented to design single-feed high-gain EBG resonator antennas (ERAs) with significantly wider bandwidths. Dielectric contrast is introduced to 1-D EBG superstructures composed of unprinted dielectric slabs, and the thicknesses of each of these slabs is optimized to achieve a wideband defect mode in a unit-cell model. Next, antennas are designed and their superstructure areas are truncated to increase the antenna bandwidth and aperture efficiency while decreasing antenna footprint. We demonstrate that a small superstructure area increases the 3-dB bandwidth of ERAs significantly. A prototype ERA designed with a single feed and superstructure area as small as ${\hbox {1.5}} \lambda_0 \times {\hbox {1.5}} \lambda_0$ has a measured 3-dB directivity bandwidth of 22% at a peak gain of 18.2 dBi. This prototype antenna was made out of three slabs of different dielectric constants, two of them touching each other. This prototype demonstrates more than 85% reduction in the ERA footprint alongside a drastic improvement in bandwidth over the 3%–4% measured bandwidth of the classical single-feed ERAs with unprinted slabs.

Wideband High-Gain EBG Resonator Antennas With Small Footprints and All-Dielectric Superstructures

We propose a novel approach to enhance the bandwidth of the high directivity of the resonant cavity antenna (RCA) by applying two dielectric layers as superstrates. The approach is based on creating two cavities corresponding to two operating frequency bands that combine to form a single wide band of operation. The RCA design is discussed in a methodological manner to determine the thicknesses of the superstrates, the separation distance between them, and the separation distance to the ground plane. We show that the proposed technique is capable of enhancing the bandwidth from 9% of the single superstrate RCA to 17.9% of the two superstrate RCA, with only 0.1-dB reduction of the maximum directivity (17.5 dBi). The presented design method can be replicated for any RCA with any directivity level and type of primary feeding. The performance of the analytically designed antenna is validated by simulation using commercial numerical electromagnetics software.

Bandwidth Enhancement of the Resonant Cavity Antenna by Using Two Dielectric Superstrates

This letter presents a new design of a Fabry–Perot resonator antenna (FPRA) with a wide gain bandwidth. A double-layered dielectric superstrate, which produces a reflection phase curve versus frequency with a positive slope, is used as a partially reflective surface (PRS) to enhance the bandwidth of the FPRA. For a physical insight, the PRS is analyzed by using the transmission line theory and Smith Chart. Experimental results demonstrate that the antenna has a 3-dB gain bandwidth over 13.5–17.5 GHz, relatively 25.8%, with a peak gain of 15 dBi. Furthermore, the gain band is overlapped well by the impedance band for the reflection coefficient ( ${ S}_{11}$ ) less than $-$ 10 dB.

Wideband Fabry–Perot Resonator Antenna With Two Layers of Dielectric Superstrates

We develop a high-gain antenna with wideband operation and compact size by placing a small dielectric superstrate (puck) in front of the feeding antenna. The antenna performance is a combination of the leaky-wave effect, naturally existing in this type of antennas, and the edge diffraction effect occurring at the puck perimeter. Compared to the typical resonant cavity antenna utilizing a large superstrate, the proposed puck antenna has nearly four times enhanced performance (gain-bandwidth combination) while using a square puck of side slightly smaller than two wavelengths (at the design frequency). Further enhancement is achieved by making the puck circular in shape in order to add the diffracted fields in phase. The study is conducted through full-wave simulations and validated through measurements in the $Ku$ band. The effect of puck misalignment is then discussed as a potential practical issue. Last, the ground plane is optimized for maximum antenna performance and relatively acceptable values of aperture efficiency (up to 51%).

The Puck Antenna: A Compact Design With Wideband, High-Gain Operation

A compact four-step 90-degree waveguide twist is designed for operation over the full W- band. The waveguide cross section is modified from the conventional sharp-corners rectangle to comply with the fabrication constraints. The designed twist is fabricated by two processes; CNC machining of the four steps then assembling, and 3D printing through direct metal laser sintering (DMLS). Both of the realized twists measure better performance than that of the commercially-available longer and more expensive twists. Moreover, they are better suited for integrated systems and delicate machining restrictions in W band.

Design and Fabrication of a Full W-Band Multi-Step Waveguide 90° Twist

A quad-ridge horn antenna with stabilized gain and minimum difference between E- and H-plane half-power beamwidths (HPBWs) is demonstrated for operation over 45–110 GHz bandwidth. Multistep flaring and corrugations on a finite ground plane are applied to obtain stable radiation patterns with 16-dBi minimum gain over the entire range. The computational studies are validated through measurements of a 3-D printed prototype using the direct metal laser sintering (DMLS) process. Accurate fabrication with achieved surface roughness of $ of the fabricated antenna is verified with digital microscope. The obtained gain variation, VSWR, and HPBW variation with rotation and over 45–110 GHz bandwidth are below 1.7 dB, 1.7:1, and 9°, respectively. This work demonstrates that the DMLS is a viable fabrication process for wideband horn antennas at millimeter-wave frequencies.

45–110 GHz Quad-Ridge Horn With Stable Gain and Symmetric Beam

A square horn antenna with rotationally-stable radiation patterns that are also nearly invariant with frequency across the entire W band (75–110 GHz) is demonstrated. The flaring is designed such that the horn can support two perpendicular linear polarisations with very similar radiation patterns. The antenna is fabricated in two ways; by assembling two computer numerical control (CNC) machined split blocks, and by metallic 3D printing using direct metal laser sintering (DMLS). All fabricated antennas (one CNC aluminium, one DMLS aluminium, and one DMLS stainless steel) have similar performances that agree well with theory. Effect of surface roughness with the DMLS antennas is found to be electrically insignificant which is desired for fast prototyping and many current and emerging applications.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2017.0167

Muhannad A. Al-Tarifi

Papers

Bandwidth Enhancement of the Resonant Cavity Antenna by Using Two Dielectric Superstrates

The Puck Antenna: A Compact Design With Wideband, High-Gain Operation

Design and Fabrication of a Full W-Band Multi-Step Waveguide 90° Twist

45–110 GHz Quad-Ridge Horn With Stable Gain and Symmetric Beam

On the design and fabrication of W‐band stabilised‐pattern dual‐polarised horn antennas with DMLS and CNC