Annular Slot Antenna Research Articles

Design and characterisation of a 200 GHz tunable lens‐coupled annular‐slot antenna with a 50 GHz tuning range

A frequency-tunable lens-coupled annular-slot antenna (ASA) with a nearly 50 GHz tuning range has been designed, fabricated and characterised at the G-band (140–220 GHz). Initial numerical electromagnetic simulation results show that the resonant frequency of the antenna can be tuned effectively, with a tunability of ∼2.5 GHz/fF associated with the capacitive loading from the varactor. In addition, simulated far-field antenna patterns have demonstrated that the addition of the varactor used to implement the capacitive loading does not strongly affect the antenna's radiation properties. This design has been demonstrated experimentally, using a Schottky varactor diode with a zero-bias junction capacitance of ∼16 fF mounted on a 200 GHz ASA fabricated on a semi-insulating silicon wafer. Measurement at G-band shows a frequency tuning range of nearly 50 GHz by varying the voltage bias of the Schottky varactor diode from −5 to 1 V. The measurement results agree well with simulations based on an equivalent circuit model for the Schottky diode and the antenna. Measured far-field radiation patterns of the lens-coupled tunable ASA at 203 GHz show good agreement with calculations based on the ray-tracing technique, verifying that the diode mounting does not affect the antenna radiation properties significantly. This type of tunable ASA is very promising for realising reconfigurable detectors and focal-plane arrays at terahertz (THz) frequencies, and may find applications in future adaptive submillimetre-wave/THz communication systems.

A Frequency Reconfigurable Half Annular Ring Slot Antenna Design

The design of a switchable microstrip-fed half annular ring slot antenna for multi-frequency operation is proposed. By incorporating three switches along the meandered tuning stub that is loaded on top of the half circular patch located within the circular slot, easy reconfigurability of four frequency bands over a frequency ratio of approximately 1.7:1 can be achieved. Furthermore, the proposed antenna structure does not require additional DC biasing circuit. Simulation and measurement results have demonstrated that the four frequency bands can exhibit good impedance matching, stable radiation patterns and desirable gains.

Independently Tunable Annular Slot Antenna Resonant Frequencies Using Fluids

An annular slot antenna with surface integrated fluidic channels is presented. The fluidic channels provide independent, tunable control of the first and second resonant frequencies. Simulation and measurement results for channels filled with air, acetone, or deionized (DI) water are investigated. A tunable range from 3.3 to 4.2 GHz for the first resonance and 5.2 to 8 GHz for the second resonance is demonstrated. The loss tangent effects are also assessed for the fluids in terms of peak realized gain degradation.

MINIATURIZED ANNULAR RING SLOT ANTENNA FOR SMALL/MINI UAV APPLICATIONS

A miniaturized annular ring slot antenna is presented. The antenna consists of an annular ring slot structure and a novel folded matching structure. The annular ring slot structure is printed on a substrate and shorted concentrically with a set of conductive vias. The additional matching structure is a ring cavity attached to the back of the annular ring slot structure. Firstly, the diameter of the proposed antenna is reduced by using the folded matching structure comparing with traditional annular ring slot antennas. Secondly, the impedance matching of the proposed antenna is achieved by optimizing the size of the matching structure. A prototype of the proposed antenna with a height of 3.048 mm (0.03λ) and a radius of 47.2 mm (0.4λ) is designed, fabricated and measured. The antenna resonates at 2.67 GHz and has a monopole-like radiation pattern, which shows that the antenna is suitable for the applications of taking off, landing, and long distance communications for a small or mini UAV.

Radially Polarized Annular-Slot Leaky-Wave Antenna for Three-Dimensional Near-Field Microwave Focusing

Microwave three-dimensional near-field focusing with radial polarization using a holographic annular-slot antenna is demonstrated in this letter. This radial polarization can generate axially polarized focused fields in the near-field regime, which complements the more conventional synthesis of transversally polarized near-field focusing patterns. Moreover, it is shown that more symmetrical focal region is obtained thanks to the radial polarization for similar Fresnel number N and operation frequency. The theory is demonstrated with experiments for a design operating at 10 GHz, with aperture diameter D=6λ and a Fresnel number N=4.

Tunable 200 GHz lens‐coupled annular‐slot antennas using Schottky varactor diodes for all‐electronic reconfigurable terahertz circuits

A tunable lens-coupled annular-slot antenna using a Schottky varactor diode has been designed, fabricated and characterised at 140 to 220 GHz. Simulation results show that the resonant frequency of the annular-slot antenna can be effectively tuned by varying the capacitance of the imbedded varactor diode, with an average tunability of ∼2.5 GHz/fF. Prototype demonstration using a varactor with zero-bias capacitance of 3.8 fF has shown a frequency tuning range from 197 to 202.7 GHz by varying the diode DC bias voltage from 1 to −5 V (corresponding to a diode capacitance change from 4.97 to 2.4 fF). The measured tunability is 2.22 GHz/fF, which agrees well with simulation. Projections indicate tuning ranges of ∼50 GHz in the G-band should be possible using varactor diodes with ∼20 fF zero-bias capacitance.

Circularly polarized annular slot antenna with switchable frequency

A design for frequency reconfigurable annular slot antennas with circular polarization (CP) is described.The slot antenna is excited with a shorted microstrip line through coupling, and one varactor diode placed on the slot is used to generate CP radiation. By controlling the dc bias of the varactor, the CP operating frequency of the slot antenna can be switched between two frequencies with a frequency ratio of about 1.6; moreover, the antenna operating at each CP frequency has a return loss of less than 10 dB and the broadside radiation with a peak gain of higher than 3 dB. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1115–1118, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27509

Design of an ultrawideband UHF embedded annular slot antenna

A novel ultrawideband annular slot antenna for ultrahigh-frequency airborne communication applications is presented. This antenna is composed of concave cylinder, four shorting inductive posts, a top plate, and backed cavity, and achieves a wide impedance bandwidth from 225 to 400 MHz. Measurements show that the proposed structure can get omnidirectional radiation pattern, and can be used in airborne applications as flush-mounted alternatives to monopole blade antenna. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:680–682, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27400

INTEGRATED COMPACT CIRCULAR POLARIZATION ANNULAR RING SLOT ANTENNA DESIGN FOR RFID READER

An integrated compact circular-polarized annular ring slot antenna is proposed in this paper. It consists of an annular ring slot radiator and a hybrid patch coupler. The hybrid patch coupler is integrated with the annular ring slot antenna to radiate the circular- polarized wave, while size of the antenna remains the same. Both the impedance bandwidth and axial ratio bandwidth of the proposed design almost cover the entire UHF band of RFID system and it has the features of easy fabrication and low cost. To verify the proposed design, a prototype is fabricated. Measured results agree well with the simulated results.

DESIGN AND INVESTIGATION OF A DUAL-BAND ANNULAR RING SLOT ANTENNA FOR AIRCRAFT APPLICATIONS

A novel dual-band annular ring slot antenna is investi- gated. The antenna consists of a center-fed circular microstrip patch antenna with a coupled annular ring. And it is shorted concentrically with a set of conductive vias. By adjusting the parameters of the an- tenna, the dual resonant frequencies for two modes (TM01 and TM02 modes) are achieved. The antenna is fabricated and tested. Results show that the proposed antenna with height of 0:0217‚0 can provide gains of 3.01dBi at 2.6GHz (the receiving frequency) and 5.74dBi at 2.95GHz (the transmitting frequency). Good agreement between the measurement and simulation for the return loss and radiation patterns is achieved. The proposed antenna has dual-band characteristics, sim- ple structure, low proflle, and omni-directional azimuth radiation pat- tern. It is suitable for aircraft both receiving and transmitting signals and frequency division duplex (FDD) applications.

A FUNCTIONAL MICROSTRIP CIRCUIT MODULE FOR ANNULAR SLOT ANTENNA

A functional microstrip circuit module for annular slot antenna is proposed. This module consists of an annular microstrip line component, two PIN diodes and a DC bias circuit. Reconflgurable circular polarizations can be simply controlled by this functional module. Axial ratio is adjustable by changing the clip angle of the notch made by the annular microstrip line component. Simulated and experimental results have shown good impedance bandwidth for return loss and antenna gains in circularly polarized states.

A frequency reconfigurable antenna based on digital microfluidics

We present a novel antenna reconfiguration mechanism relying on electrowetting based digital microfluidics to implement a frequency reconfigurable antenna operating in the X-band. The antenna built on a quartz substrate (εr = 3.9, tan δ = 0.0002) is a coplanar waveguide fed annular slot antenna, which is monolithically integrated with a microfluidic chip. This chip establishes an electrowetting on dielectric platform with a mercury droplet placed in it. The base contact area of the mercury droplet can be spread out by electrostatic actuation resulting in a change of loading capacitance. This in turn changes the resonant frequency of the antenna enabling a reversible reconfigurable impedance property. This reconfigurable antenna has been designed, fabricated and measured. The frequency of operation is tuned from around 11 GHz to 13 GHz as demonstrated by simulations and measurements. The design methodology, fabrication processes and the experimental results are given and discussed.

Circular Polarization and Polarization Reconfigurable Designs for Annular Slot Antennas

A simple design for circularly-polarized (CP) annular slot antennas is first described. The antenna is fed by a V-shaped coupling strip loaded with a small resistance, and it can generate CP radiation as long as the inclined angle of the V-shaped coupling strip is properly adjusted. Numerical analyses to the effects of varying the angle on CP axial ratio are performed. Several CP prototypes are fabricated. Both simulated and measured results demonstrate that the proposed feeding mechanism can give good CP performances for the case that the slot width is varied from 0.008 to 0.09 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Then, a design for polarization reconfigurable antennas is developed from the feeding mechanism. Only two PIN diodes are involved in the reconfigurable design that can offer the switching among three different polarizations, including one linear polarization and dual orthogonal circular polarizations. Details of the designs and experimental results are shown.

Tri-band circularly polarized annular slot antenna for GPS and CNSS applications

A novel single-feed tri-band circularly polarized (CP) annular slot antenna is presented. The antenna structure is composed of two nonconcentric annular slots that are fed by an L-shaped series step impedance microstrip line configuration. The proposed antenna is designed to operate at the L 1 and L 2 bands of the global positioning system and the operating band of the compass navigation satellite system. Compared to the most of the previously reported tri-band CP antenna structure, the proposed antenna has low profile, compact size, and easy fabrication on the single-layer PCB. The measured results show that the impedance bandwidths are good for all bands. The axial ratio bandwidth and radiation patterns are also measured at the three resonant frequencies. The proposed compact tri-band CP antenna design is suitable for mounting onto the mobile communication devices and portable positioning systems.

Dual-Band Circularly Polarized Cavity-Backed Annular Slot Antenna for GPS Receiver

A circularly polarized (CP) cavity-backed annular slot antenna for GPS receiver is designed to operate in both the L1 and L2 bands of the Global Positioning System (GPS). The measured impedance bandwidths with VSWR less than 2 are 3.7% (1.19-1.235 GHz) and 1.2% (1.565-1.585 GHz), respectively, the measured 3 dB axial-ratio (AR) bandwidth are 0.9% (1.220-1.231 GHz) and 0.6% (1.572-1.581 GHz), respectively. A cavity is designed to render a unidirectional radiation pattern.

A Broadband Pattern Diversity Annular Slot Antenna

An annular slot antenna suitable for pattern diversity in wideband applications is presented. Pattern diversity is obtained by feeding the antenna simultaneously with two microstrip lines printed on the back of the substrate, which generate orthogonal radiation patterns. Two shorts placed at 45 degrees between the microstrip lines and in the opposite direction ensure an isolation above 15 dB according to measurements. The antenna operates in the range of frequencies from 3 GHz to 12 GHz (1:4 bandwidth) and covers many different standards (Wireless-LAN, HIPERLAN2, WIMAX, UWB). Simulations and measurements for return loss, isolation and radiation patterns are presented. Furthermore, measurements have been carried out in a real multipath environment in order to evaluate pattern diversity performance. Results of measurements of the correlation coefficient and diversity gain over the entire operating bandwidth show that the antenna is suitable for antenna diversity systems.

DESIGN OF CPW-FED DUAL-BAND CIRCULARLY-POLARIZED ANNULAR SLOT ANTENNA WITH TWO PERTURBATION STRIPS

A new CPW-fed dual-band circularly-polarized(CP) annular slot antenna with two perturbation strips is proposed. The structure of the annular slot, along with two concentric annular- ring patches, can achieve dual-band input impedance matching. And circular polarization at the operation bands can be achieved by using the two perturbation strips placed on the backside of the antenna. To reduce the resonant frequencies, a third strip protruded from the ground plane is introduced. Both the simulated and measured results show that the impedance bandwidths determined by 10-dB return loss are about 29.1% for the lower band (1.92{2.61GHz) and 12.1% for the upper band (3.21{3.65GHz). And the AR bandwidths are about 7.5% and 11.0%, respectively.

Concentric Annular Ring Slot Antenna for Global Navigation Satellite Systems

In this letter, we present the design of a concentric annular ring slot antenna with right-hand circular polarization. Two concentric rings have been etched in the ground plane to generate a dual-band response. A broadband feeding network and a thicker substrate below the slots have been used to improve the axial-ratio bandwidth and gain. The proposed antenna covers the bands of the positioning systems GPS and Galileo. Experimental results show a 3-dB axial-ratio bandwidth for the lower and upper band of 19.2% and 18%, respectively. The measured gain is higher than 4 dB in both bands.

A PROXIMITY-FED ANNULAR SLOT ANTENNA WITH DIFFERENT A BAND-NOTCH MANIPULATIONS FOR ULTRA-WIDE BAND APPLICATIONS

A proximity-fed annular slot antenna for UWB applica- tions with a band rejection using difierent techniques is presented. The proposed antenna provides an UWB performance in the frequency range of … 2:84 to … 8:2GHz with relatively stable radiation parame- ters. Three difierent techniques to construct a resonant circuit for the proposed antenna are investigated to achieve the band-notch property in the band … 5:11 to … 5:69GHz band which include the WLAN and HIPERLAN/2 services without degrading the UWB performance of the antenna. Three resonators are considered; a single complementary split ring resonator (CSRR), a complementary spiral loop resonator (CSLR) and a spurline slot. Furthermore, the band-notched resonance frequency and the bandwidth can be easily controlled by adjusting the dimensions of the resonator. The proposed antenna is simulated, fab- ricated and measured. The measured data show very good agreements with the simulated results. The proposed antenna provides almost om- nidirectional patterns, relatively ∞at gain and high radiation e-ciency over the entire UWB frequency excluding the rejected band.

Wideband circularly polarised antenna using two linked annular slots

An annular-slot antenna composed of two linked annular slots is presented. The return loss and the axial-ratio bandwidths are enhanced by tuning the distance between the two centres of the two annular slots. Under the optimum condition, the two circular patches associated with the two annular slots are found to be separated from each other. The measured 3 dB axial-ratio bandwidth is 1.4 GHz (46.7%) centred at 3 GHz.