A thermodynamic formalism is developed to calculate the pyroelectric coefficients of epitaxial ͑001͒ Ba 0.6 Sr 0.4 TiO 3 ͑BST 60/40͒ and Pb 0.5 Zr 0.5 O 3 ͑PZT 50/50͒ thin films on ͑001͒ LaAlO 3 , 0.29 LaAlO 3 :0.35(Sr 2 TaAlO 6) ͑LSAT͒, MgO, Si, and SrTiO 3 substrates as a function of film thickness by taking into account the formation of misfit dislocations at the growth temperature. The role of internal stress is discussed in detail with respect to epitaxy-induced misfit and thermal stresses arising from the difference between the thermal expansion coefficients of the film and the substrates. It is shown that the pyroelectric coefficients steadily increase with increasing film thickness for BST 60/40 and PZT 50/50 on LSAT and SrTiO 3 substrates due to stress relaxation by misfit dislocations. Large pyroelectric responses ͑ϳ1.1 C/cm 2 K for BST 60/40 and ϳ0.3 C/cm 2 K for PZT 50/50͒ are theoretically predicted for films on MgO substrates at critical film thicknesses ͑ϳ52 nm for BST 60/40 and ϳ36 nm for PZT 50/50͒ corresponding to the ferroelectric to paraelectric phase transformation. Analysis shows that the pyroelectric coefficients of both BST 60/60 and PZT 50/50 epitaxial films on Si substrates are an order of magnitude smaller than corresponding films on LaAlO 3 , LSAT, MgO, and SrTiO 3 substrates.

A two-element multiple-input-multiple-output (MIMO) dielectric resonator antenna having wideband characteristics is presented. The wideband operation is achieved by using a mushroom shaped dielectric resonator excited by a conformal trapezoidal patch. In order to realise two-element MIMO configuration, two wideband radiators are arranged orthogonally which offers polarisation diversity. The measured bandwidth (VSWR ≤ 2) for Port1 is 61% (5.08-9.50 GHz), whereas for Port2 it is 65% (4.89-9.61 GHz). The isolation between the two ports is better than 20 dB for the desired frequency band. The antenna exhibits broadside radiation with cross polar level below 15 dB. The peak gain of antenna varies from 3.34 to 7.40 dBi at Port1 and from 2.34 to 7.9 dBi at Port2. Moreover, the various MIMO performance metrics including envelope correlation coefficient (ECC), diversity gain, channel capacity loss and total active reflection coefficient are investigated. The ECC is less than 0.01 and capacity loss is under 0.5 bps/Hz throughout the operating bandwidth. The results confirm that the antenna offers effective MIMO/diversity performance. The proposed antenna can be suitable for WLAN and upper ultra wideband frequency band applications.

Structural characteristics of phase transformations in epitaxial ferroelectric films are analyzed via a Landau-Devonshire thermodynamic formalism. It is shown that the phase transformation temperature, the lattice parameters, and the order of the phase transformation are a strong function of the misfit strain and are considerably different compared to unconstrained, unstressed single crystals of the same composition. Depending on the internal stress state, it is possible that the structural aspects of the paraelectric-ferroelectric phase transformation may be completely obscured in the presence of epitaxial strains. The thickness dependence of epitaxial stresses due to relaxation by misfit dislocations during film deposition is incorporated into the model using an ''effective'' substrate lattice parameter. There is a good quantitative agreement between the theoretical analysis and experimental observations reported in the literature on the variations in the lattice parameters and the phase transformation temperature with film thickness in epitaxial BaTiO 3 films.

The tunability of highly textured thin films of barium strontium titanate (Ba0.5Sr0.5TiO3, BST) is analyzed theoretically using a Landau–Devonshire thermodynamic model. The relative dielectric constant of BST films is determined as functions of the applied external electric field, deposition temperature, and the thermal expansion coefficient of the substrate. Our analysis shows that tunability is highly dependent upon thermally induced strains within the material. Both tension and compression produce deleterious tuning response. However, this effect can be minimized through judicious choices of deposition temperature and appropriate substrate material.

Abstract:In this communication, a novel compact high gain composite right/left-handed (CRLH) based leaky-wave antenna (LWA) is presented at Ku band. Half-mode substrate integrated waveguide (HMSIW) incorporating with suitably oriented Complementary Quad Spiral Resonator (CQSR) is used to achieve a CRLH LWA. The uni cell is realized by a CQSR in such a way that orientation of spirals exhibit higher leakage loss having minimum cross coupling between them. The antenna is capable to scan backward to forward along with broadside direction in visible space. The proposed configuration is just length of 4.85λ 0 which can scan within the frequency range of 13.5-17.8 GHz having beam scanning range of 86• (-66• to 20 • ) and maximum gain of 16 dBi. The simulated reflection coefficient of the proposed antenna is below -10 dB throughout the working frequency range with a side-lobe level of below -10 dB. The designed prototype is much compact in nature having high gain, fair scanning range, good cross-polarization level along with simpler design methodology and tuning capability to enhance the gain as well as radiation efficiency maintaining fixed size. The proposed antenna could be a promising candidate in Ku-band applications like Fixed Satellite Services (FSS) and Broadcast Satellite Services (BSS) etc.

In this article, a new A‐shaped dielectric resonator antenna (DRA) excited by a conformal strip is proposed for wideband applications. The wide bandwidth is achieved by combining two adjacent modes that is, TM101 and TM103. The experimental results demonstrate that the proposed DRA offers an impedance bandwidth (for S11≤−10 dB) of 59.7% (3.24‐6.0 GHz), covering IEEE 802.11 and U‐NII bands. The antenna provides a fairly stable radiation pattern with the gain ranging from 5.29 to 7 dBi across the operating bandwidth. A dual‐element multiple‐input multiple‐output (MIMO) system is also realized using the proposed wideband DRA. The impedance bandwidth of the dual‐element MIMO antenna is 59.2% and 60.9% for Port1 and Port2, respectively and the isolation between the ports is better than 20 dB across the bandwidth. For Port1, the gain of the MIMO antenna ranging from 6.03 to 7.45 dBi is obtained across the bandwidth. Furthermore, the diversity performance of the MIMO antenna is found to be good with envelope correlation coefficient below 0.003 over the operating band. The proposed antenna could be the potential candidate for worldwide interoperability for microwave access (WiMAX), wireless local area network (WLAN) and lower European UWB frequency band (3.4‐5.0 GHz) applications.

A novel single‐feed circularly polarized microstrip antenna with compact size is proposed for indoor wireless local area network (WLAN) applications. The antenna structure consists of eight slits which are introduced at the boundary and the corners in the radiating square patch with a cross‐slot at the center. The proposed antenna shows a compactness of 42% compared with the conventional circularly polarized antenna design at indoor WLAN frequency band. It is found that the resonance frequency of the proposed structure is highly depending on length and width of cross‐slot and corner slit for entire band of circular polarization. The 3 dB axial ratio bandwidth of the proposed antenna is 1.9%. Proposed structure is fabricated on the FR‐4 epoxy substrate and fed by a single coaxial probe. Measured results show a good agreement with the simulated results. Antenna shows stable radiation characteristics for the entire operating band. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1313–1317, 2014

A compact bi-directional leaky-wave antenna (LWA) based on TE 20 mode substrate integrated waveguide (SIW) is proposed at X-band. The microstrip power divider-slotline transitions are utilised to excite TE 20 mode SIW array in order to enhance the overall radiation capability of the designed structure. The rectangular slots are etched out on the top and bottom plane of SIW such a way that the orientation of the slots can perturb the distribution of electric field at TE 20 mode and provide bi-directional radiation. The proposed antenna is working within the frequency range of 9.6-11.2 GHz (S 11 < −10 dB) having the beam scanning range of 66°from both top and bottom side of the structure with maximum gain of 14 dBi. All experimental results show a fair agreement with the simulated data.