Bijumon, P V; Sreedevi, Menon K; Suma,M N; Sebastian,M T; Mohanan, P(IEE Electronics letters,UK, March 31, 2005)
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Abstract:
The impedance bandwidth of a high permittivity cylindrical dielectric
resonator antenna excited by a micro strip line was significantly
improved by modifying the feed geometry. The 10 dB return loss
bandwidth is enhanced from 12 to 26% without much affecting the
gain and other radiation properties of the antenna. Good agreement
has been observed between the predicted and measured results
Jacob,George; Aanandan,C K; Mohanan, P; K G Nair; Sreemoolanathan,H; Sebastian,M T(Microwave and Optical Technology Letters, February 20, 1998)
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Abstract:
A new method for enhancing the 2.1 VSWR impedance
bandwidth of microstrip antennas is presented. Bandwidth enhancement
is achieved by loading the microstrip antenna by a ceramic microwave
dielectric resonator (DR). The validity of this technique has been established
using rectangular and circular radiating geometries. This method
improves the bandwidth of a rectangular microstrip antenna to more
than 10% (= 5 times that of a conventional rectangular microstrip
antenna) with an enhanced gain of I dB
Bijumon, P V; Sreedevi, Menon K; Sebastian,M T; Mohanan, P(Microwave and Optical Technology Letters, November 20, 2002)
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Abstract:
A novel technique fitr the bat dividth enhancement of conventional
rectangular microstrip antenna is proposed in this paper. When a
high permittivity dielectric resonator of suitable resonant frequency was
loaded over the patch. the % bandwidth of the antenna was increased by
more than five tunes without much affecting its gain and radiation performance.
A much more improved bandwidth was obtained when the dielectric
resonator was placed on the feedline. Experimental study shows a 2:1
VSWR bandwidth of more than 10% and excellent cross polarization performance
with increased pass band and radiation coverage abnost the same
as that of rectangular microstrip antenna
Hamsakutty, V; Dr.Mathew, K T(Cochin University of Science and Technology, March , 2007)
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Abstract:
In this thesis, the author proposes a new geometry DR antenna-the Hexagonal Dielectric Resonator Antenna(HDRA)-capable of multiple frequency operation on a single feed of excitation.This avoids the conventional use of miniaturizes the structure.The properties of the HDRA on microstrip as well as coaxial feeding have been studied.The analysis of radiation characteristics indicates a gain comparable with other shapes.The antenna is capable of providing efficiency around 98%.The simulation using HFSS also yields results in conformity with the experimental results.Mode analysis is carried out and the modes are identified.The determination of the reflection characteristics through theoretical analysis using FDTD validates the multifrequency operation of the antenna,The antenna finds application in DCT,PCS and WLAN bands.
Description:
Department of
Electronics, Cochin University of Science and Technology
A new group of compounds with composition (Ba5-xSrx) Nb4015, having high
permittivity and low loss have been prepared and characterized 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
and c f showed smooth variation with x , while the unloaded quality factor (Qu)
showed remarkable improvement with x
A microwave dielectric ceramic resonator based on BaCe2Ti5O15 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 X 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 (Tr) of BaCe2Ti5O15 and Ba5Nb4O15 have been measured accurately using different
resonant modes and are + 41 and + 78 ppm/K, respectively
Microwave dielectric ceramics based on RETiTaO6 (RE = La, Cc, Pr, Nd, Sm, Eu,
Gd, Tb, Dy, Ho, Y, Er, Yb, Al, and In) were prepared using a conventional solid-state
ceramic route. The structure and microstructure of the samples were analyzed using
x-ray diffraction and scanning electron microscopy techniques. The sintered samples
were characterized in the microwave frequency region. The ceramics based on Ce, Pr,
Nd, Sm, Eu, Gd, Tb, and Dy, which crystallize in orthorhombic aeschynite structure,
had a relatively high dielectric constant and positive T f while those based on Ho, Er,
and Yb, with orthorhombic euxenite structure, had a low dielectric constant and
negative Tf. The RETiTaO6 ceramics had a high-quality factor. The dielectric constant
and unit cell volume of the ceramics increased with an increase in ionic radius of the
rare-earth ions, but density decreased with it. The value of Tf increased with an
increase in RE ionic radii, and a change in the sign of Tf occurred when the ionic
radius was between 0.90 and 0.92 A. The results indicated that the boundary of the
aeschynite to euxenite morphotropic phase change lay between DyTiTaO6 and
HoTiTaO6. Low-loss ceramics like ErTiTaO6 (Er = 20.6, Qxf = 85,500), EuTiTaO6
(Er = 41.3, Qxf = 59,500), and YTiTaO6 (Er = 22.1, Q„xf = 51,400) are potential
candidates for dielectric resonator applications
Ceramics of composition BaO-Ln2O3-STiO2 have been prepared with four elements (Ln=La,Pr,Nd.Sm) by a conventional solid state ceramic preparation route and the dielectric properties measured in the microwave frequency range
The dielectric ceramics BaNd2Ti3Oto, BaNd2Ti4O12 and BaNd2Ti5O14 have been prepared by
Conventional solid state ceramic route. The sintered ceramic samples have been characterized by
X-ray diffraction and Scanning Electron Microscopy (SEM). The dielectric properties in the
microwave frequency range have been measured using conventional microwave dielectric
resonator methods. The BaNd2Ti1O10, BaN2Ti4O12 and BaNd2Ti5O14 have dielectric constants
(Er) ~ 60, 84 and 77 respectively. They have relatively high quality factors
Abdul Khalam,L; Sreemoolanadhan,H; Ratheesh, R; Mohanan, P; Sebastian,M T(ELSEVIER, 2003)
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Abstract:
Microwave dielectric resonators (DRs) based on Ba(B1,2Nbi/2)03 [B' = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Yb, and In] complex
perovskites have been prepared by conventional solid state ceramic route. The dielectric properties (relative permittivity, Er; quality factor, Q;
and resonant frequency, rr) of the ceramics have been measured in the frequency range 4-6 GHz using resonance methods. The resonators
have relatively high dielectric constant in the range 36-45, high quality factor and small temperature variation of resonant frequency. The
dielectric properties are found to depend on the tolerance factor (t), ionic radius (r), and lattice parameter (ap)
The (Ba1-x Srx) (Nd1/2, Nb1/2) O3 ceramics have been prepared by the conventional
ceramic route for different values of x. Addition of a small amount of
CeO2(1 wt%) as a sintering aid increased the density of the samples. The structure
and microstructure of the sintered samples are studied by X-ray diffraction
and SEM methods. The dielectric properties of the samples are measured in the
microwave frequency region as a function of composition. The dielectric constant
decreases as x increases. The coefficient of thermal variation of resonant
frequency decreases as the Sr content increases and goes to the negative side.
The dielectric properties of (Ba1-x Srx) (Nd1/2, Nb1/2) O3 are in the range suitable
for application as dielectric resonators in microwave circuits
Microwave dielectric ceramics based on GdTiNb,-,.Ta,O6 and Sml _.,Y,TiTa06 have been prepared by conventional solid state
method . The GdTiTaO6 and SmTiTaO6 have aeschenite structure with positive rr and GdTiNbO6 and YTiTaO6 have euxenite
structure with negative rr. The rr of the ceramics has been tuned by preparing solid solution phases between the aeschynites and
euxenites for a possible zero rr material . It is observed that GdTiNbt_YTa.,O6 undergoes a phase transition from aeschynite to
euxenite when x=0.75 and in Sml-,YxTiTa06 for x= 0.73. The microwave dielectric properties change abruptly near the transition
region . The rr value approaches zero near the phase transition region while the samples have poor sinterability and poor quality
factor . The unloaded quality factor, dielectric constant and the sign of rr of the solid solution phases are found to depend on the
average ionic radius of the rare earth ion in RE ,-5RE',TiTaO6. The boundary of the euxenite-aeschynite phase transition occurs at
an average ( RE) ionic radius of 0.915 A in Sm,_, Y,.TiTaO6 solid solution phases