Electrically Small Antennas
Department of Electronics of this laboratory has developed different types of miniature Zeroth order antenna for various applications. A novel extremely compact Zeroth Order Resonator (ZOR) antenna with a chip inductor, for Digital Video Broadcasting-Handheld (DVB-H) application an overall dimension of 0: 0186λ x0: 020λx0: 003λ mm² operating at 503 MHz is developed. The zeroth resonance property makes the resonant frequency to be independent of the antenna dimension. The 3: 1 VSWR bandwidth of the antenna is 39MHz and offers an Omnidirectional pattern. A 99% reduction in the overall area of the structure is achieved compared to a conventional patch antenna operating at the same frequency. A novel via free, asymmetrical coplanar strip fed zeroth-order directional antenna suitable for 2.4 GHz WLAN applications is also developed. The zeroth-order resonance is achieved by realizing a composite right/left-handed transmission line-based inter digital capacitor inserted into the shorted asymmetric coplanar strip. The structural asymmetry provides an improved directivity for the antenna. The prototype made on a low cost substrate of relative permittivity 3.7 and height 1.6 mm with an overall dimension 29x16.5x1.6 mm³. An electrically small, broadband-modified, truncated ground metamaterial EZ antenna is also developed. This, a modified EZ antenna system, achieves a larger bandwidth of the order of 650 MHz by adjusting the metamaterial-inspired meandered ground element fed by a top loaded monopole. The design is devoid of the large ground planes and the external parasitic elements used in conventional designs for achieving proper impedance matching characteristics. The antenna requires a small foot print of λg/5 x λg/10. In another attempt a compact coplanar waveguide (CPW) fed electrically small antenna suitable for 2.4 GHz WLAN applications is presented. The resonance of the structure is achieved by implanting a chip inductor in between the centre conductor of an open-ended CPW transmission line and a short metal strip. The total electrical size of the fabricated antenna is 0.08λ 0 x 0.0479λ.
A novel composite right/left-handed (CRLH) coplanar waveguide (CPW)-fed zeroth-order resonator antenna is proposed. The shorted CRLH transmission line exhibits zeroth-order resonance at 2 GHz and operates with narrow bandwidth. The dispersion analysis is also carried out and presented in this article. The proposed antenna has been fabricated and tested. Omnidirectional radiation pattern with a gain 3.5 dBi has been obtained. We had also developed different types of miniature PIFA antenna for different applications.
Substrate Integrated Waveguide
Department of Electronics of this University has started work onthe discovery of a new method to implement substrate integrated waveguides (SIW). The constructions of via holes are the difficult and necessary requirement for conventional SIW operation. By feeding the waveguide structure differentially, it is possible to effectively eliminates the need of via from the structure altogether. The differential feed provides a forced Dirichlet electric boundary of the first order at the centre of the structure and hence creates a pair of half SIW modes that propagate with similar characteristics. The size of the waveguide structure remains the same as a conventional SIW. The bandwidth and the propagation properties of the fundamental modeare similar to that of SIW. The newly discovered waveguide can be thought of two separate Half Mode Substrate Integrated Waveguides (HMSIW) sharing the common electric boundary otherwise would have provided with metallised via holes. Small fringing field from the both side of the waveguide can be used for exciting planar dipoles to generate radiation. This technique was implemented using normal HMSIW as well as with newly proposed waveguide. Leaky wave characteristics are observed. The major application of the new waveguide is in millimetre wave application. These designs are simulated and measured at 24GHz and 60 GHz and observed similar results.
Miniature Antenna for Medical Applications
Another major area on which the department is concentrating is the antennas for medical applications. Research activities are going on two areas like cathedral antenna and Implantable antenna. A floating sleeve antenna for a cardiac ablation procedure is already developed. The antenna can produce localized heating of the myocardium in a controllable and effective manner. In vitro experiments were performed on phantom models and on an isolated perfuse goat's heart to identify how much power would be required to effectively ablate myocardial tissue during microwave ablation. The results highlight the ability of the floating sleeve catheter antenna to produce high specific absorption rate (SAR) values. Department has already developed extremely small antenna suitable for implantable applications. Using this antenna it is planned to real time monitor of glucose level in Blood.
We have also developed different types of RFID tags. Radio Frequency Identification (RFID) is employed conveniently to replace barcodes in contactless data capturing. The RFID tag can be embedded within the object and it ensures enhanced security and flexibility. Our present works are based on frequency domain with Multiple scattered based tag using Stepped Impedance Resonators (SIR), open stub resonator, lumped element resonators etc. with high data encoding capacity. Monostatic or Bistaic RCS measurement method with some modifications can be used for detecting backscattered encoded signal from the RFID tags. RFID tag with Frequency Shift Coding technique is used to enhance the surface encoding density of the tag up to 7.9bits/cm2. Research works are mainly concentrated on designing appropriate resonators with good polarisation independency, compactness, data encoding capacity and readable range. Works is also concentrated in the signal processing side of backscattered signal, which contains noise, reflection from metallic & non-metallic objects and signal from the RFID tags. Readable range of the SIR based RFID tag is found to be 50cm with 1mW reader output power. Post processing of backscattered signal will increase the readable range more than 1 meter.
Ultra Wide Band Antennas
Department is also actively engaged in the development oflow profile Ultra Wide band Antennas. The overall size of the antenna is nearly 30 mm x 27 mm x 1.6 mm. Different methods are employed to reduce the size of the antenna. All the developed antennas are characterised in Time domain and frequency domain. The pulse distortion is insignificant and is verified by the measured antenna performance with high signal fidelity and virtually steady group delay. The simulation and experiment reveal that the proposed antennas exhibits good impedance match, stable radiation patterns and constant gain and group delay over the entire operating band.
Low Radiation Hazard Antennas for Mobile Applications
Another main area where Department of Electronics is concentrated is low radiation hazards antennas for mobile applications. Different types of planar antennas are developed using SRR, strip loading and dielectric loading. Using this technique a deep null of radiation is produced along the direction of the head. From the experimental analysis a reduction of nearly 20dB radiated power is observed towards the head. This can effectively reduce the SAR (Specific Absorption Ratio) below 0.8 W/Kg in 1g of tissue.
Multiple-input-multiple-output (MIMO) antenna technology is used to increase wireless throughput without increase in additional bandwidth and power requirements. In typical MIMO systems multiple antennas are used at both transmitter and receiver ends to improve wireless performance. Research involving multiple antennas employing spatial diversity and polarization diversity plays a crucial role in future wireless communication system. MIMO systems are characterized by their maximum available capacity, which is reduced if there is correlation between the signals on different channels. Research is done in developing new MIMO systems for ISM band frequencies which can provide increased channel capacity with least correlation between elements. New structures for 4X4 MIMO antenna systems employing polarization diversity and ultra wideband MIMO antennas are developed with novel isolation techniques keeping in mind the compactness, ease of fabrication and low cost. Correlation values as low as 0.08 and isolation below -25dB is achieved with the developed antennas which can replace current single-input-single-output systems for wireless communication.
Microwave properties of conducting polymers
The department is also actively concentrated on synthesis of nano composite materials consisting of conducting nanoparticles dispersed in a nonmagnetic matrix and their microwave characterization like electromagnetic shielding, dielectric properties, conductivity etc. This work mainly concentrated on the preparation of Polyanilne (PANI) nano composite with different doping acids. One way to improve the current electromagnetic absorbers is to exploit the polymer composites reinforced with conducting nanoparticles (NPs).Nanoparticles could offer novel physicochemical properties arising from the core/shell structure and the particle interactions. Another side benefit of using NPs as fillers that cannot be ignored is the nano-size scale in diameter. This work reports on the electromagnetic wave absorption properties of a highly particle-loaded conducting nano composite fabricated by the surface-initiated-polymerization (SIP) method. This can be used for Stealth Radar applications, Reduction of RCS etc.
High Impedance Surfaces
The department has also started works to exploit different applications of High Impedance Surfaces (HIS).High Impedance Surfaces are planar artificial structures made up of many identical cells forming a periodic lattice of cells to provide high electromagnetic surface impedance characteristics.. Unlike normal conductors it does not support propagating surface current and it reflects external plane wave with no phase reversal .Due to the suppression of surface current it can be used in antenna field to provide isolation of radiating element from nearby electromagnetic surroundings, to improve the antenna gain and to minimise backward radiation. Also the high surface impedance allows the antenna to lie directly adjacent to the ground plane without being shorted out. This allows compact antenna designs where radiating elements are confined to limited space. These can also be used in ultra-thin electromagnetic absorbers (RCS reduction), Fabry-Perot or Leaky wave antennas and to mitigate the simultaneous switching noise (SSN) in PCB circuit.
Integrated Antenna For Future Millimeter Wave Wireless Communications
Another major area on which the department concentrating is integrated antenna for future millimeter wave wireless communications. Gigabit wireless communications require a considerable amount of bandwidth, which can be supported by millimeter waves. The technology has attracted new commercial wireless applications and new markets, such as the capacity for high-speed downloading and wireless high-definition TVs. The current Wi-Fi standards operate at 2.4 and 5 GHz and allow a maximum data transfer of 54 Mbps. The current Wi-Fi standards are creating a data 'bottle-neck' which means large amount of data cannot be transmitted wirelessly. This has resulted in a new standard being proposed (IEEE 802.11ad).The new standard specifies an operating frequency of 60 GHz and allow at least a 50 fold increase in the available bandwidth with a maximum data transfer of 7Gbps.
In this research work, the feasibility of the system-on-substrate concept using standard printed circuit board fabrication to produce smart antenna arrays at 60GHz will be investigated. The use of PCB fabrication will allow complete systems to be fabricated on a single multilayer printed circuit board, combining the low frequency signal processing and control elements with high frequency microwave and antenna arrays which will greatly reduce the cost of a complete communications system. The rotated Half-Mode SIW is a new variant of a Half-Mode Substrate Integrated Waveguide which enables direct interaction with the wave energy. Rotated Half Mode Substrate Integrated Waveguide (HMSIW) antenna array is introduced to reduce the size and complexity without compromising the performance.