P. Mohanan

High permittivity and low loss ceramics in the BaO-SrO-Nb2O5 system

Abstract A new group of compounds with composition (Ba5 5 − x Sr x )Nb 4 O 15 , having high permittivity and low loss have been prepared and characterised in the microwave frequency region. X-ray diffraction studies showed that monophase compound existed for all values of x from 0 to 5. Microwave dielectric properties such as e r and τ f showed smooth variation with x, while the unloaded quality factor (Q u ) showed remarkable improvement with x. A range of ceramic dielectric resonators(DR) with 40 e r τ f 10,000 can be obtained in this system.

Microwave dielectric properties of MO–La2O3–TiO2 (M = Ca, Sr, Ba) ceramics

Single-phase polycrystalline ceramics in the MO-La 2 O 3 -TiO 2 (M = Ca, Sr, Ba) system, such as cation-deficient hexagonal perovskites CaLa 4 Ti 4 O 1 5 , SrLa 4 Ti 4 O 1 5 , BaLa 4 Ti 4 O 1 5 , and Ca 2 La 4 Ti 5 O 1 8 and the orthorhombic phases CaLa 4 Ti 5 O 1 7 and CaLa 8 Ti 9 O 3 1 , were prepared through the solid-state ceramic route. The phases and structure of the ceramics were analyzed through x-ray diffraction and scanning electron microscopy. The microwave dielectric properties of the ceramics were studied using a network analyzer. The investigated ceramics show high ∈ r in the range 42 to 54, high quality factors with Q xf in the range 16,222 to 50,215 GHz, and low τ f in the range -25 to +6 ppm/°C. These high dielectric constant materials with high Q xf up to 50,215 GHz are suitable for applications where narrow bandwidth and extremely low insertion loss is necessary, especially at frequencies around 1.9 GHz.

A New Compact Microstrip-Fed Dual-Band Coplanar Antenna for WLAN Applications

A novel compact microstrip fed dual-band coplanar antenna for wireless local area network is presented. The antenna comprises of a rectangular center strip and two lateral strips printed on a dielectric substrate and excited using a 50 Omega microstrip transmission line. The antenna generates two separate resonant modes to cover 2.4/5.2/5.8 GHz WLAN bands. Lower resonant mode of the antenna has an impedance bandwidth (2:1 VSWR) of 330 MHz (2190-2520 MHz), which easily covers the required bandwidth of the 2.4 GHz WLAN, and the upper resonant mode has a bandwidth of 1.23 GHz (4849-6070 MHz), covering 5.2/5.8 GHz WLAN bands. The proposed antenna occupy an area of 217 mm2 when printed on FR4 substrate (epsivr=4.7). A rigorous experimental study has been conducted to confirm the characteristics of the antenna. Design equations for the proposed antenna are also developed

Compact Asymmetric Coplanar Strip Fed Monopole Antenna for Multiband Applications

A compact asymmetric coplanar strip fed monopole antenna for multiband applications is presented. The antenna exhibits three resonances around 1.8, 2.4, and 5.6 GHz covering the DCS/PCS/UMTS/IEEE 802.11b/g/IEEE802.11a/HIPERLAN2 bands. The multiband characteristic of the antenna is due to the various meandered current paths excited in the radiating structure. The antenna has an overall dimension of only 2830 when printed on a substrate of dielectric constant 4.4. The uniplanar design, simple feeding technique and compactness make it easy for the integration of the antenna into circuit boards. Details of the antenna design, experimental and simulated results are presented and discussed.

DESIGN OF COMPACT RECONFIGURABLE DUAL FREQUENCY MICROSTRIP ANTENNAS USING VARACTOR DIODES

The design of a compact, single feed, dual frequency dual polarized and electronically reconfigurable microstrip antenna is presented in this paper. A square patch loaded with a hexagonal slot having extended slot arms constitutes the fundamental structure of the antenna. The tuning of the two resonant frequencies is realized by varying the effective electrical length of the slot arms by embedding varactor diodes across the slots. A high tuning range of 34.43% (1.037–1.394 GHz) and 9.27% (1.359–1.485 GHz) is achieved for the two operating frequencies respectively, when the bias voltage is varied from 0 to −30 V. The salient feature of this design is that it uses no matching networks even though the resonant frequencies are tuned in a wide range with good matching below −10 dB. The antenna has an added advantage of size reduction up to 80.11% and 65.69% for the two operating frequencies compared to conventional rectangular patches.

A5B4O15 (A=Ba, Sr, Mg, Ca, Zn; B=Nb, Ta) microwave dielectric ceramics

Abstract The microwave dielectric properties of A5B4O15 (A=Ba, Sr, Mg, Ca, Zn; B=Nb, Ta) ceramics are investigated. The ceramics are prepared through the solid-state ceramic route. The dielectric properties are studied at microwave frequencies and structure and microstructure by XRD and scanning electron micrograph (SEM) methods. The ceramics show er in the range 11–51, Q×f is in the range 2400–88,000 GHz and τf in the range −73–232 ppm/°C.

High frequency dielectric properties of A5B4O15 microwave ceramics

High-frequency dielectric properties of A5B4O15 (A=Ba, Sr, Mg, Zn, Ca; B=Nb, Ta) dielectric ceramics are studied by means of the microwave cavity technique, a combination of far-infrared reflection and transmission spectroscopy and time-resolved terahertz transmission spectroscopy. Microwave permittivity e′ and Q×f factor vary, depending on the chemical composition, between 11 and 51, and 2.4 and 88 THz, respectively. The temperature coefficient τf varies between −73 and 232 ppm/°C, and in two samples |τf| is less than 15 ppm/°C. It is shown that the microwave permittivity e′ of the ceramics studied is determined by the polar phonon contributions and that linear extrapolation of the submillimeter dielectric loss e″ down to the microwave region is in agreement with the microwave data of single phase samples. The relationship among phonon spectra, the crystal structure, and the unit cell volume is discussed.

Design of a Compact Semi-Elliptic Monopole Slot Antenna for UWB Systems

A printed semi-elliptic monopole slot antenna for use in ultrawideband (UWB) communication systems is presented. The antenna features a coplanar waveguide signal strip terminated with a semi-elliptic stub and a modified ground plane to achieve wide bandwidth from 2.85-20 GHz. An exhaustive study of the radiation characteristics of this antenna in the frequency and time domains are presented. Design equations are derived and experimentally validated. Transient analysis indicates linear phase response and minimum dispersion to the transmitted pulse. The proposed radiator is omnidirectional with appreciable gain throughout the band.

Dielectric response of high permittivity polymer ceramic composite with low loss tangent

The present communication investigates the dielectric response of the Sr9Ce2Ti12O36 ceramics loaded high density polyethylene and epoxy resin. Sr9Ce2Ti12O36 ceramic filled polyethylene and epoxy composites were prepared using hot blending and mechanical mixing, respectively. 40 vol % ceramic loaded polyethylene has relative permittivity of 12.1 and loss tangent of 0.004 at 8 GHz, whereas the corresponding composite using epoxy as matrix has permittivity and loss tangent of 14.1 and 0.022, respectively. The effective medium theory fits relatively well for the observed permittivity of these composites.

Microwave characterisation of BaCe2Ti5O15 and Ba5Nb4O15 ceramic dielectric resonators using whispering gallery mode method

A microwave dielectric ceramic resonators based on BaCe2Ti5015 and Ba5Nb4O15 have been prepared by conventional solid state ceramic route. The dielectric resonators (DRs) have high dielectric constant 32 and 40 for BaCe2Ti5O15 and Ba5Nb4O15, respectively. The whispering gallery mode (WGM) technique was employed for the accurate determination of the dielectric properties in the microwave frequency range. The BaCe2Ti5O15 and Ba5Nb4O15 have quality factors (Q×F) of 30,600 and 53,000 respectively. The quality factor is found to depend on the azimuthal mode numbers. The temperature coefficient of resonant frequency (τf) of BaCe2Ti5O15 and Ba5Nb4O15 have been measured accurately using different resonant modes and are +41 and +78 ppm/K, respectively.