ANN Synthesis Model of Single-Feed Corner-Truncated Circularly Polarized Microstrip Antenna with an Air Gap for Wideband Applications

A computer-aided design model based on the artificial neural network (ANN) is proposed to directly obtain patch physical dimensions of the single-feed corner-truncated circularly polarized microstrip antenna (CPMA) with an air gap for wideband applications. To take account of the effect of the air gap, an equivalent relative permittivity is introduced and adopted to calculate the resonant frequency and Q-factor of square microstrip antennas for obtaining the training data sets. ANN architectures using multilayered perceptrons (MLPs) and radial basis function networks (RBFNs) are compared. Also, six learning algorithms are used to train the MLPs for comparison. It is found that MLPs trained with the Levenberg-Marquardt (LM) algorithm are better than RBFNs for the synthesis of the CPMA. An accurate model is achieved by using an MLP with three hidden layers. The model is validated by the electromagnetic simulation and measurements. It is enormously useful to antenna engineers for facilitating the design of the single-feed CPMA with an air gap

Reconfigurable Wideband Circularly Polarized Microstrip Patch Antenna for Wireless Applications

In this thesis, developments of rectangular microstrip patch antenna to have circular polarization agility with wideband performance, for wireless applications are presented. First, a new technique to achieve circularly polarized (CP) probe feed single-layer microstrip patch antenna with wideband characteristics is proposed. The antenna is a modified form of the popular E-shaped patch, used to broaden the impedance bandwidth of a basic rectangular patch antenna. This is established by letting the two parallel slots of the E-patch unequal. Thus, by introducing asymmetry two orthogonal currents on the patch are excited and circularly polarized fields are realized. The proposed technique exhibits the advantage of the simplicity inherent in the E-shaped patch design. It requires only slot lengths, widths, and position parameters to be determined. Also, it is suitable for later adding the reconfigurable capability. With the aid of full-wave simulator Ansoft HFSS, investigations on the effect of various dimensions of the antenna have been carried out via parametric analysis. Based on these investigations, a design procedure for a CP E-shaped patch is summarized. Various design examples with different substrate thicknesses and material types are presented and compared, with CP U-slot patch antennas, recently proposed in the literature. A prototype has been constructed following the suggested design procedure to cover the IEEE 802.11b/g WLAN band. The performance of the fabricated antenna was measured and compared with the simulation results for the reflection coefficient, axial ratio, radiation pattern, and antenna gain. Good agreement is achieved between simulation and measured results demonstrating a high gain and wideband performance. Second, a polarization reconfigurable single feed E-shaped patch antenna with wideband performance is proposed. The antenna is capable of switching from right-hand circular polarization (RHCP) to left-hand circular polarization (LHCP) and vice versa, with the aid of two RF PIN diodes that act as RF switches. The proposed structure which is simple; consists of a single-layer single fed radiating E-shaped patch and RF switch placed on each of its slots at an appropriate location. The design targets WLAN IEEE 802.11b/g frequency band (2.4- 2.5 GHz) as one example of the wireless applications. The idea is based on the first proposed design. In other words, if one of the switches is ON and the other is OFF, the two slot lengths will become effectively unequal and circular polarization will be obtained. If the states of the two switches are reversed, circular polarization with opposite orientation will be obtained at the same frequency band. Full-wave simulator Ansoft HFSS is again used for the analysis. Complete detailed DC biasing circuit of the switches for integration with the antenna is presented. Also, characterizations of the microwave components used in the biasing circuit are discussed. Antenna prototype has been fabricated and tested. Simulation results along with the measured one, for the reflection coefficient, axial ratio, radiation pattern, and antenna gain agree well, showing wide bandwidth and high gain for the two circularly polarized modes

Monolithic superconducting emitter of tunable circularly polarized terahertz radiation

We propose an approach to control the polarization of terahertz (THz) radiation from intrinsic Josephson-junction stacks in single crystalline high-temperature superconductor $Bi_2Sr_2CaCu_2O_{8+\delta}$. By monolithically controlling the surface current distributions in the truncated square mesa structure, we can modulate the polarization of the emitted THz wave as a result of two orthogonal fundamental modes excited inside the mesa. Highly polarized circular terahertz waves with a degree of circular polarization of more than 99% can be generated using an electrically controlled method. The emitted radiation has a high intensity and a low axial ratio (AR<1 dB). The intuitive results obtained from the numerical simulation based on the conventional antenna theory are consistent with the observed emission characteristics.Comment: Submitted to PRApplie

Doctor of Philosophy

dissertationAntenna design and reduction of losses in antenna systems are critical for modern communications systems. Two categories of antennas suffer from limited power supply and difficult operating environments: implantable antennas and antennas for spacecraft applications. Minimizing and controlling losses in these two antenna types is critical for developing next-generation implantable devices, spacecraft, and satellites. Research suggests that future tattoo antennas will be made from low-conductivity ink utilizing the natural insulating property of the body's fat and lossy ground plane of muscle. This paper supports tattoo antenna work by: (1) demonstrating the insulating properties of fat and conductivity of muscle with various antenna systems, (2) showing the effect of biological materials on the current distribution of subdermal antennas, and (3) validating the use of lower-conductivity materials in subdermal antenna design including a novel gold nanoparticle material. Simulations and measurements are used to evaluate current distributions shared between solid, segmented, and meshed strip dipole antennas and surrounding body tissues. Fat insulates the antenna similar to a thin layer of plastic wrap. Muscle acts as a conductive ground plane. Dipole antennas with mesh or gap structures are more strongly coupled to body tissues than solid antennas. A minimum acceptable conductivity benchmark of 105 S/m is established for dipole antennas and Radio-Frequency Identification (RFID) antennas. This work also provides novel information on the design of low-cost, circularly polarized (CP), Ka-band (26 GHz), millimeter-wave, 50 Ω edge-fed, corners truncated patch antennas on RT/duroid 5880 (εr = 2.2, ½ oz. copper cladding). Microstrip feed width, axial ratio (AR) bandwidth, and best AR at 26 GHz are optimized by the use of 10 mil substrate. The effects of corner truncation are further investigated, showing that increasing corner truncation increases AR bandwidth, increases percent offset between best S11 and AR frequencies, and worsens the best AR. A truncation of 0.57 mm is a good compromise between these effects with AR bandwidth of 6.17 % (measured) and 1.37 % (simulated). Increasing ratio of substrate thickness to design frequency, t / λd, improves AR bandwidth. For t / λd below a certain threshold a corners truncated patch antenna will not produce CP. A new nearly-square, corners truncated patch antenna is measured and simulated as a method of increasing circular polarization bandwidth (CPBW)

DESIGN AND IMPLEMENTATION OF RECONFIGURABLE PATCH ANTENNAS FOR WIRELESS COMMUNICATIONS

Reconfigurable patch antennas have drawn a lot of research interest for future wireless communication systems due to their ability to adapt to changes of environmental conditions or system requirements. The features of reconfigurable patch antennas, such as enhanced bandwidths, operating frequencies, polarizations, radiation patterns, etc., enables accommodation of multiple wireless services. The major objective of this study was to design, fabricate and test two kinds of novel reconfigurable antennas: a dual-frequency antenna array with multiple pattern reconfigurabilities, and a pattern and frequency reconfigurable Yagi-Uda patch antenna. Comprehensive parametric studies were carried out to determine how to design these proposed patch antennas based on their materials dimensions and their geometry. Simulations have been conducted using Advanced Design Systems (ADS) software. As a result of this study, two kinds of novel reconfigurable patch antennas have been designed and validated at the expected frequency bands. For the new reconfigurable antenna array, the beam pattern selectivity can be obtained by utilizing a switchable feeding network and the structure of the truncated corners. Opposite corners have been slotted on each patch, and a diode on each slot is used for switchable patterns. By controlling the states of the four PIN diodes through the corresponding DC voltage source, the radiation pattern can be reconfigured. The simulation and measurement results agree well with each other. For the novel frequency and pattern reconfigurable Yagi-Uda patch antenna detailed in Chapter 4, two slots have been used on driven element to achieve frequency and pattern reconfigurability, and two open-end stubs have been used to adjust working frequency and increase bandwidth. In this design, an ideal model was used to imitate a PIN diode. The absence and presence of a small metal piece has been used to imitate the off-state and on-state of the PIN-diode. Pattern reconfigurability and directivities with an overall 8.1dBi has been achieved on both operating frequencies. The simulation and measurement results agree closely with each other. Advisor: Yaoqing Yan

Omnidirectional GPS antenna for Vorsat

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores. Universidade do Porto. Faculdade de Engenharia. 201

Planar EBG Loaded UWB Monopole Antenna with Triple Notch Characteristics

A triple band-notched ultra-wideband (UWB) monopole antenna using a planar electromagnetic bandgap (EBG) design is proposed. The EBG unit cell composed by an Archimedean spiral and inter-digital capacitance demonstrates the notch frequencies. The antenna with EBG cells near the feed line occupies only 30 × 36 mm2 with triple band-rejection characteristics. The three notched bands at 4.2 GHz, 5.2 GHz, and 9.1 GHz can be used in C-band satellite downlink, wireless local area network (WLAN), and X-band radio location for naval radar or military required applications. In addition, the proposed design is flexible to tune different notched bands by altering the EBG dimensions. The parametric analysis is studied in details after placing the EBG unit cells near the feed line to show the coupling effect. The input impedance and surface current distribution analysis are also analyzed to understand the effect of EBG at notch frequencies. The proposed design prototype is fabricated and characterized. A fairly considerable agreement is observed between simulated and measured results

Bandwidth Optimization of Microstrip Patch Antenna- A Basic Overview

An antenna is a very important device in wireless applications. It converts the electrical energy into RF signal at the transmitter and RF signal into electrical energy at the receiver side. A micro strip antenna consists of a rectangular patch on a ground plane separated by dielectric substrate. The patch in the antenna is made of a conducting material Cu (Copper) or Au (Gold) and this can be in any shape of rectangular, circular, triangular, elliptical or some other common shape. Researches of past few year shows that, various work on Microstrip Patch Antenna is attentive on designing compact sized Microstrip Antenna with efficiency and bandwidth optimized. But inherently Microstrip Patch Antenna have narrow bandwidth so to enhance bandwidth various techniques are engaged. Today’s Communication devices need several applications which require higher bandwidth; such as mobile phones these days are getting thinner and smarter but many applications supported by them require higher bandwidth, so microstrip antenna used for performing this operation should provide wider bandwidth as well as their shape should be more efficient and size should be compact so that it should occupy less space while keeping the size of device as small as possible. In this review paper, a review of different techniques used for bandwidth optimization & various shapes of compact and broadband microstrip patch antenna is given