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

An up-to-date literature overview on relevant approaches for controlling circuital characteristics and radiation properties of dielectric resonator antennas (DRAs) is presented The main advantages of DRAs are discussed in detail, while reviewing the most effective techniques for antenna feeding as well as for size reduction Furthermore, advanced design solutions for enhancing the realized gain of individual DRAs are investigated In this way, guidance is provided to radio frequency (RF) front-end designers in the selection of different antenna topologies useful to achieve the required antenna performance in terms of frequency response, gain, and polarization Particular attention is put in the analysis of the progress which is being made in the application of DRA technology at millimeter-wave frequencies

/pdf/dielectric-resonator-antennas-basic-concepts-design-3dxtctyxib.pdf

Dielectric Resonator Antennas: Basic Concepts, Design Guidelines, and Recent Developments at Millimeter-Wave Frequencies

A novel design for a beam-switching antenna using active cylindrical slot frequency selective surface (ACSFSS) is presented. The antenna system is composed of an omnidirectional monopole antenna and the ACSFSS, which employs a new technique of switching slot arrays. The ACSFSS is made up of 12 columns with 8 slots each, dividing the cylinder by 30 $^{\circ}$ . To steer the beam of the antenna the diodes are set off and on, so that the radiation pattern of the antenna is determined by the number of off state columns. To estimate the general dimension of the cylindrical FSS, an equivalent metallic reflector is introduced and optimized, and then parametric studies for the unit cell dimensions are discussed. The fabricated prototype works within the WLAN band, centered around 2.45 GHz, and can agilely select either a narrow-beam or wide-beam operating mode. Simulation and measurements confirm the operation of the ACSFSS antenna, with good matching and gain observed. In particular, the narrow-beam mode $-$ 3 dB beamwidth is 47 $^{\circ}$ which offers enhanced angular resolution compared with other reported beam-sweeping work.

Cylindrical Slot FSS Configuration for Beam-Switching Applications

Progress in frequency selective surface-based smart electromagnetic structures: A critical review

This letter describes an asymmetrical coplanar strip (ACPS) wall to suppress the mutual coupling between two closely spaced 5.8-GHz microstrip antennas. The ACPS wall, which is inserted vertically between the two antennas, introduces an additional coupling path to reduce the antenna coupling, occupying just a small area between the two antennas. The decoupling effect of the proposed structure is verified by the simulation and measurement. The experimental results show that the achieved isolation is better than 35 dB and reaches a maximum of 54.3 dB at 5.8 GHz, with an extremely close antenna distance of 0.03λ0 (edge-to-edge distance). The measured patterns indicate that the proposed structure also improves the radiation of the microstrip antenna.

Mutual Coupling Suppression Between Two Closely Spaced Microstrip Antennas With an Asymmetrical Coplanar Strip Wall

The design, simulation, and measurement results of a high-gain broadband gradient refractive index (GRIN) planar lens fed by an antipodal exponential taper slot antenna (ATSA) are presented. As a constituent part of this lens, a novel nonresonant metamaterial unit cell, composed of bilayer triple rectangular rings, is proposed and its equivalent circuit model is developed and described. It is shown that, by utilizing this element, stronger capacitive couplings between adjacent metallic layers are realized resulting in a large refractive index variation of about 2.5, and hence, a thin lens with a thickness of $0.38\lambda_{0}$ , where $\lambda_{0}$ is the wavelength at 9.5 GHz. In addition, since the unit cell is designed to resonate at higher frequencies, its refractive index response is smoothly increased over a broad frequency range and this considerably enhances the operating bandwidth of the lens. The achieved measured results demonstrate a broad matching and $-3\;{\rm dB}$ gain bandwidths of 52% (7–12 GHz) and 65% (7–13.2 GHz), respectively. Furthermore, this lens offers a high aperture efficiency of 50% (21.2 dB gain) at the center frequency, and its sidelobe and cross-polarization levels are less than $-20\;{\rm dB}$ and $-26\;{\rm dB}$ across the entire matched band, respectively.

A High-Gain Broadband Gradient Refractive Index Metasurface Lens Antenna

A new incorporated planar ultrawideband (UWB)/reconfigurable-slot antenna is proposed for cognitive radio applications. A slot resonator is precisely embedded in the disc monopole radiator to achieve an individual narrowband antenna. A varactor diode is also deliberately inserted across the slot, providing a reconfigurable frequency function in the range of 5-6 GHz. The slot is fed by an off-centered microstrip line that creates the desired matching across the tunable frequency band. The measured antenna parameters are presented and discussed, confirming the simulation results.

Design and Implementation of an Integrated UWB/Reconfigurable-Slot Antenna for Cognitive Radio Applications

An electronically sweeping radiation-pattern antenna using a new active cylindrical frequency-selective surface (ACFSS) is presented for 2.45-GHz operating frequency. The ACFSS screen is constructed by a new reconfigurable hybrid unit cell, providing more freedom to control the antenna radiation characteristics. A design guideline based on the reflector antenna principles is also introduced to estimate the overall dimensions of the antenna geometry, and then the required number of unit cells for the ACFSS surface is calculated. Furthermore, to confirm the proposed design guideline, the performance of the designed antenna is compared to three conventional reflector antennas constructed with solid perfect electric conductors. The achieved simulation results for these antennas are carefully examined and the impact of the FSS surface on enhancing the ACFSS antenna gain is discussed. Moreover, parametric studies for the crucial dimensions of the unit cell are also presented to demonstrate the effect of each parameter on the antenna radiation characteristics. To completely examine the achieved results, the transmission coefficient response of the applied FSS sheet is experimentally assessed, and the antenna measured parameters are accordingly interpreted.

Electronically Sweeping-Beam Antenna Using a New Cylindrical Frequency-Selective Surface

A new dielectric resonator antenna (DRA) is introduced for ultrawideband applications. Three methods of a Z-shaped dielectric resonator, a bevel feeding patch, and an air gap between the DR and the ground plane are used to obtain an ultrawideband impedance bandwidth. The effective dielectric constant and the -factor can be reduced by introducing the air gap. The bevel-shaped feeding mechanism provides a smooth impedance transition from one resonant mode to another. Furthermore, the results show that by applying a Z-shaped DRA, the electric field inside the dielectric is reformed over the desired bandwidth leading to improve the matching. A comprehensive parametric study is carried out using CST to optimize the bandwidth of the proposed antenna. The measurement results demonstrate that the proposed DRA provides an ultra bandwidth of about 120%, ranging from 2.5 GHz to 10.3 GHz for the reflection coefficient less than .

Z-Shaped Dielectric Resonator Antenna for Ultrawideband Applications

A hybrid compact isolator with a cross section of 17 × 11 mm2 is proposed to reduce the electromagnetic coupling between two vertically polarized Tx/Rx microstrip antennas, both operating at 9.4 GHz. This isolator is built by embedding a piece of artificial material between two metallic walls. The obtained results using this hybrid isolator demonstrate that the coupling between the two antennas is significantly reduced across at least 55% of the matching band. To substantiate the proposed configuration, a prototype is fabricated and tested, and the corresponding measured results are presented. Furthermore, the discrepancies between the simulations and measurements are interpreted with the aid of the electromagnetic (EM) simulator.

Mahmoud Niroo-Jazi

Papers

A High-Gain Broadband Gradient Refractive Index Metasurface Lens Antenna

Design and Implementation of an Integrated UWB/Reconfigurable-Slot Antenna for Cognitive Radio Applications

Electronically Sweeping-Beam Antenna Using a New Cylindrical Frequency-Selective Surface

Z-Shaped Dielectric Resonator Antenna for Ultrawideband Applications

A Hybrid Isolator to Reduce Electromagnetic Interactions Between Tx/Rx Antennas