A Low-Profile Frequency Reconfigurable Grid-Slotted Patch Antenna

This paper presents a novel low-profile high gain frequency reconfigurable patch antenna with unidirectional radiation pattern by using a grid-slotted patch with tunable varactors loading. The antenna consists of two stacked substrates and three metal layers. A grid-slotted patch with two tunable varactors is placed on the top layer, a microstrip line is placed in the middle of two substrates, and the ground plane is on the bottom layer. A single dc voltage applied on two varactors is used to control the working frequencies of the proposed antenna. By altering the bias voltage, the working frequency of the proposed antenna can be continuously changed within a wide range from 2.45 to 3.55 GHz. The antenna maintains broadside radiation and stable radiation pattern in all the operating modes. The measured antenna gain of the proposed antenna rises from 4.25 to 8.49 dBi with the working frequency increases from 2.45 to 3.55 GHz. Compared to other frequency-reconfigurable antennas available in the literature, the proposed antenna has advantages of a wide frequency tuning range over a bandwidth of 1.45:1, high frequency selectivity, low profile (0.016 free-space wavelength at 2.45 GHz), high gain, stable unidirectional pattern, simple structure, and low cost. These advantages make it a promising candidate for cognitive radio and future wireless communication system

Frequency reconfigurable antennas for cognitive radio applications: a review

Wireless communication systems undergo tremendous growth these days and devices able to operate in a number of frequencybandsarehighlydemanded. Reconfiguration in antenna characteristic striggered the evolution of antennas that can workin multiple frequency, pattern or polarization environment.The frequency reconfigurable antennas thuse mergedarewell suited in Cognitive Radios which take part in the effective utilization of unused bands of frequencies by continuously interacting with the RF environment. Thus, Cognitive Radios enhancetheutilization of frequency spectrum and establish reliable communication. The most recent research works carried out in the arena of Frequency Reconfigurable Antennas for Cognitive Radio applications are reviewed and summed up in this paper to present the attributes and categorization. Four techniques adopted to attain frequency reconfiguration are extensively compared in this paper to find the advantages and constraints of each methodology. The applications of the works reviewed here are not only limited to Cognitive radios, but extended to a number of wireless communication services like, WLAN, WiMAX, et

Frequency reconfigurable rectangular patch antenna for cognitive radio applications

A frequency reconfigurable microstrip transformed rectangular patch antenna consisting of two slots able to radiate in S-band and C-band is proposed. Spectrum occupancy is first analyzed using the data from literature and internet sources and hence spectrum holes are identified. A rectangular radiating patch is then designed for 5.8 GHz resonant frequency. A coaxial feed is used in the bottom by a suitable feed point. Two slots at an angle of +45 degree are made at the two corners. The electrical length of the patch is changed by using two varactor diodes in the slots. The varactors enable frequency reconfiguration in the band of frequencies that are unused or the spectral occupancy is very less. The return loss, voltage standing wave ratio (VSWR), and 2D-radiation patterns are analyzed for various values of the capacitances. high-frequency structure simulator (HFSS) is used for simulation. FR4 substrate which is economical, is used with height, h=1.6 mm, width W=25.33 mm, and length L=21.34 mm. On the substrate the rectangular patch is of width 15.73 mm and length 11.74 mm. The return loss and radiation patterns for different values of capacitances is presented. The tunability ratio obtained is 1.93. The results obtained agree with the standards

Design and realization of a frequency reconfigurable multimode antenna for ism, 5g-ub-6-ghz, and s-band applications

This paper presents the design and realization of a compact size multimode frequency reconfigurable antenna. The antenna consists of a triangular-shaped monopole radiator, originally inspired from a rectangular monopole antenna. Slots were utilized to notch the desired frequency while the PIN diodes were utilized to achieve frequency reconfigurability. The antenna can operate in wideband, dual-band, or tri-band mode depending upon the state of the diodes. To validate the simulation results, a prototype was fabricated, and various performance parameters were measured and compared with simulated results. The strong agreement between simulated and measured results along with superior performance as compared to existing works in the literature makes the proposed antenna a strong candidate for ISM, 5G-sub-6 GHz, and S-band applications

WIRELESS ANTENNA MULTIPLEXING USING TUNABLE ANTENNA FOR SPACE APPLICATIONS

Recent development in communication technologies shifts the communication paradigm from point to point to multi-user wireless systems. These developments eased the use of mobile telephone, satellite services, 5G cellular, smart application, and the Internet of Things. The proliferation of mobile devices has necessitated an elaborate mechanism to serve multiple users over a shared communication medium, and a multiplexing approach is introduced to serve this purpose. Multiplexing refers to a method that aims at combining multiple signals into one signal such that each user would be able to extract its desired data upon receiving the multiplexed signal. This spectrum sharing allows wireless operators to maximize the use of their spectrum to accommodate a large number of users over fewer channels. In Space applications, where sensors like temperature, attitude, IR, Magnetic, etc. send information using antennas operate at a different frequency, there is a need to collect all or some of these data using a single device. A wideband antenna requires a filtering process in order to remove unwanted signals that lead to a complex circuit design. Furthermore, the use of multiple antennas ends up with a larger size and additional complexity. Therefore, the tunable antenna is an excellent candidate which provides a perfect solution for such scenarios. A tunable antenna whose frequency characteristics shifted by applying tuning action can be used to operate as a multiplexing device that can collect signals from different surrounding antennas; each operates at a fixed frequency. A system architecture for wireless multiplexing using a tunable antenna is proposed in this project. An electronically tunable antenna using varactor diode as a tuning element is used as the multiplexing device that can collect signals from different surrounding antennas. The system consists of an RF front end and a control circuit/system for wireless multiplexing. The RF front end consists of a tunable antenna, tunable phase shifter, tunable bandpass filter, low noise amplifier, mixer, voltage-controlled oscillator, and an intermediate frequency filter. The control unit comprises a microcontroller, DAC, CMOS oscillator, power module, and a USB interface for communication with custom-built software installed on a PC. The device has functions for control, digital signal processing, and de-multiplexing. The device is fed with an input multiplexed signal, and the de-multiplexed output signals are extracted and displayed on the graphical user interface of the software. Due to the reconfigurability and programmability of the device, it presents a flexible, cost-effective solution for a variety of real-world applications

Frequency-Reconfigurable Low-Profile Omnidirectional Antennas

The high demand of today’s wireless technologies has resulted in increasing research efforts dedicated to modern antenna designs. A ”smart” antenna with abilities to tune its performance properties into a new environment can significantly increase communications reliability and decrease systems costs. Therefore, reconfigurable features have become a new standard of antenna designs, particularly when stringent performance indicators are required to keep up with increasing system demands. Owing to the radiation characteristics of antennas, an omnidirectional pattern is one that is widely sought after by antenna designers. Due to their uniform coverage, omnidirectional antennas are an ideal choice for numerous indoor or outdoor implementations. In this context, this thesis investigates substrate-integrated, low-profile, and reconfigurable design solutions for omnidirectional antennas. Firstly, the thesis discusses the development of low-profile monopoles made of shorted patches, where the main objective of this work is to find via-less alternatives for the antenna shortings. Two alternative strategies, namely quarter-wave stubs and complementary split ring resonators, are deployed in substrate-integrated monopoles and are compared with the classical shorting pins in terms of performances. Secondly, the thesis focuses on the investigation of frequency-tunable antennas. The stub-loaded monopole from the first part of the thesis is further developed to create reconfigurable antennas. This work aims to provide multi-band reconfigurable devices with independent tunability between the operating frequencies. In this part, a novel method of designing reconfigurable lowprofile monopoles is proposed based on independent magnetic current loops sharing the same thin aperture. Lastly, a circularly-polarized frequency-reconfigurable omnidirectional antenna is demonstrated as the final contribution of the thesis. The antenna operation principle is based on a combination of magnetic current sources, electric current sources, and phase compensation lines between them. Varactor-loaded slots are added to the structure to enable frequency reconfigurability. Moreover, a description of the antenna feeding aspects to maintain the circular polarization in real conditions is presented. Overall, this thesis provides different designs of high performance low-profile omnidirectional antennas. The results suggest that all the antenna designs are promising for numerous wireless applications. The benefits include simple antenna geometry, ease of fabrication, and low-profile. Importantly, the proposed design principles can be extended to other types of reconfigurable antennas.Thesis (M.Phil.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201

Programmable Microwave Devices (PMDs) based on Liquid Metal

This thesis presents microwaves device which we term a programmable microwave device (PMD). This thesis presents building block elements (BBEs)/PMDs which can realize functional and parametric reconfiguration. This thesis also discusses how to implement Gallium-based liquid metal in a reconfigurable circuit/antenna. Two works were finished and presented in this thesis. The first work presented a BBE and a PMD that can realize the functional reconfiguration. The proposed BBE/PMD can alter its function between non radiating (resonator/filter) mode and radiating (antenna) mode. The proposed BBE/ PMD realizes functional reconfiguration with the aid of liquid metal (LM). The proposed single BBE operates in resonator mode when the fluidic channels are filled with liquid metal. Whereas it operates in antenna mode when the fluidic channels are emptied of liquid metal. When several BBEs are cascaded, they form a PMD. A PMD can realize filter mode operation when the fluidic channels are filled with liquid metal or antenna mode operation when liquid metal is withdrawn. In this work, an easy approach of 2D-shaping LM was also introduced. This approach allows 2D-shaped LM for being used in realizing reconfiguration. When operating in the antenna mode the proposed PMDs provides a measured peak realized gain of 7.23 dBi and a simulated total efficiency of 84%. When operating in the filter mode the proposed PMDs provides a band pass response and exhibits a maximum insertion loss of 1.9 dB, within the passband. The filters have a 10 dB return loss bandwidth of 340 MHz ranges from 2.28 GHz to 2.62 GHz. The second work presents an operating frequency reconfigurable antenna mode BBE, which realizes a wide operating frequency reconfiguring range with the aid of liquid metal. The capability of LM could have a significant impact on reconfigure capability of the proposed PMD. We firstly designed and manufactured a hardwired version of operating frequency reconfigurable antenna mode BBE. After we verified the measurement results of hardwired antenna mode BBE, we 3D-printed the fluidic channels using Polylactic acid (PLA). LM can be filled into the 3D-printed fluidic channels with a changeable length which tunes the operating frequency of the antenna mode BBE. The measurement results of the operating frequency reconfigurable antenna mode BBE agree with the simulation results, verifying the capability of this antenna mode BBE

Ultrawideband and Multi-state Reconfigurable Antennas with Sum and Difference Radiation Patterns

Pattern diversity is a term used to describe the operation of several antenna elements working together to produce multiple different radiation patterns with the aim of improving the quality and reliability of a communications system. One useful implementation of pattern diversity considers sum and difference radiation patterns which can be exploited to extend high-gain space coverage and tackle multipath fading. The conventional forms of such pattern diversity antennas are generally working at a single or multiple narrowband frequencies and are designed for specific applications. Hence, generating sum and difference pattern diversity in wide range of frequencies requires the development of new pattern diversity antenna designs. Ultrawideband and frequency reconfigurable designs of pattern diversity antennas are desirable to help reduce the cost and increase the flexibility in applications of pattern diversity antennas. These two types of performances constitute the principal parts of this thesis. The first part of this thesis deals with the challenges of designing ultrawideband Vivaldi antennas with sum and difference radiation patterns. When two Vivaldi antennas are placed next to each other, two mutually exclusive phenomena of grating lobe generation at the highest end of frequency and mutual coupling at the lowest end of frequency will define the bandwidth. Hence, to enhance the bandwidth, the separation between the antenna elements is reduced, which delays the grating lobes generation, and the coupling at lower frequencies is mitigated by introducing an asymmetry in the design of each Vivaldi antenna element. It is shown that this method can be extended to multi-element Vivaldi antennas for higher gain. Next, the bandwidth is further enhanced by adding two vertical metal slabs between the antenna elements improving the isolation at lower frequencies. The proposed antennas use commercially available couplers as feeding networks. As a potential replacement for couplers, an out-of-phase power divider with unequal power division is also proposed. In the second part of this thesis, the pattern diversity function is combined with multistate frequency-reconfigurable filtering functions in a series of novel designs. In the first proposed design, two quasi-Yagi-Uda antennas are used for pattern diversity, while two switchable and reconfigurable bandpass-to-bandstop filters are used to excite the antenna elements. The whole system is excited by an external commercially available rat-race coupler. In a next step, this design is modified to attain wideband, tunable bandpass, and tunable bandstop operations while obviating the need for an external coupler by using three antenna elements excited by a switchable power divider. In another implementation, the filtering functions is extended to dual-band independently tunable bandpass and bandstop to excite wideband antennas. While all the former designs featured E-plane pattern diversity, in another design aiming at increasing space coverage, a switchable patch antennas with sum and difference radiation patterns in both E- and H-plane of the antenna is designed.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 202