Mathew,K T; Stephen,D S; Aanandan,C K; Mohanan,P; K G Nair(Department of Electronics, May 12, 1994)
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Abstract:
A trapezoidal strip grating surface that eliminates specular
reflections almost over the entire X -band frequency range for TM
polarization is reported This new grating structure overcomes the
bandwidth limitation of conventional rectangular strip grating surfaces
Supriyo,Dey; Aanandan,C K; Mohanan,P; K G Nair(Microwave and Optical Technology Letters, September , 1994)
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Abstract:
A simple technique to improve the impedance bandwidth of a circular
microstrip patch antenna using two sectorial slots is proposed. Using this
design more than 5% impedance bandwidth is obtained. The added
advantage of this new antenna is that it can be fed by a 50- microstrip line
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
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 (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
Dielectric resonator ceramics with composition formula Ba[(D3+0.3 Bi0.2)Nb0.5]O3,where D3+=Y,Pr,Sm,Gd,Dy and Er,were prepared by the conventional ceramic preparation route
George,J; Deepukumar,M; Aanandan,C K; Mohanan,P; K G Nair(Department of Electronics, March , 1996)
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Abstract:
A new microstrip antenna geometry with considerable reduction
in size, with similar radiation characteristics to those of an
equivalent rectangular patch antenna is proposed. A relationship
has been suggested for fmding out the resonant frequency of the
new geometry, and its validity has been established by the
experimental results. Without increasing the aperture area, this
geometry also offers a facility for considerably reducing the
resonant frequency compared to conventional patches.
Haskins, P M; Dahele, J S(Department of Electronics, March 14, 1996)
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Abstract:
Two three-clement polarisation-agile active microstrip patch
arrays have been developed . The radiating elements are square
patches each with two transistors mounted on adjacent edges. The
patches radiate orthogonal modes , the relative phase of which can
be varied. Radiation patterns show good agreement with
predictions from theory, in both linear and circular polarization,
and no grating lobes were observed
Deepukumar,M; George,J; Aanandan,C K; Mohanan,P; K G Nair(IEE Electronics letters,UK, June 19, 1996)
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Abstract:
A new dual port microstrip antenna geometry for dual frequency
operation is presented. The structure consists of the intersection
of two circles of the same radius with their centres displaced by a
small fraction of the wavelength . This antenna provides wide
impedance bandwidth and excellent isolation between its ports.
The gain of the antenna is comparable to that of a standard
circular microstrip antenna operating at the same resonant
frequency. A theoretical analysis for calculating the resonant
frequencies of the two ports is also presented
A new microwave dielectric resonator Ba(Tb1/2Nb1/2)03 has been prepared and characterized in the microwave frequency region. 1 wt% CeO2 is used as additive to reduce the sintering temperature. The sintered samples were characterized by XRD, SEM and Raman spectroscopic methods. Microwave DR properties such as er, Q factor and temperature-coefficient of resonant frequency (Ti) have been measured using a HP 8510 B Network Analyzer. Cylindrical DRs of Ba(Tb1/2Nbi/2)03 showed high Er (~ 37), high Q (~3,200) and low Tf (~10 ppm /°C) at 4 GHz and hence are useful for practical applications
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
Jacob,George; Aanandan,C K; Mohanan,P; K G Nair(IEEE Journals/ Transactions (USA), 1998)
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Abstract:
A new compact micro strip antenna element is analyzed.
The analysis can accurately predict the resonant frequency,
input impedance, and radiation patterns. The predicted results
are compared with experimental results and excellent agreement
is observed . These antenna elements are more suitable in applications
where limited antenna real estate is available
New dielectric ceramics with formula BaTi3Nb4, O„ and Ba6Til4Nbz039 have been prepared and characterized. BaTi3Nba017 was densified to 92% of TD after firing at 1310 oC for 4 h. However, Ba6Ti 1 4Nb2O39 fired under optimized conditions (1260 ` C for 4 h) showed only 85% TD together with secondary phase. The crystal system of both of the compositions is orthorhombic
Botha, E C; Odendaal, J W; Geggus, K M(Microwave and Optical Technology Letters, February 20, 1998)
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Abstract:
Compact-range radar backscatter measurements are taken
of aircraft scale models. In addition, computer software is used to predict
the RCS of the aircraft. Synthetic down-range profiles formed from the
two sources of backscatter data are compared and visualized in an
innovative manner. Similar discrimination rates between the two aircraft
are obtained on data from both source
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
Mailadil,Sebastian T; Sam,Solomon; Ravindran,Ratheesh(Regional Research Laboratory, April , 1999)
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Abstract:
Microwave ceramic dielectric resonators (DRs) based on RETiNbO6
(RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, and Yb)
have been prepared using the conventional solid -state ceramic
route. The DR samples are characterized using XRD and SEM
methods. The microwave dielectric properties are measured
using resonant methods and a net work analyzer . The ceramics
based on Ce, Pr, Nd, and Sin have dielectric constants in the
range 32-54 and positive coefficient of thermal variation of
resonant frequency (r,). The ceramics based on Gd, Tb, Dy, Y.
and Yb have dielectric constants in the range 19-22 and
negative Tf
Jianlang,Li; Liren,Liu; Yingchun,Guo; Huaisheng,Wang; Changhe,Zhou(Microwave and Optical Technology Letters, December 20, 1999)
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Abstract:
The transient interaction between a refraction index grating
and light beams during simultaneous writing and thermal fixing of
a photorefractive hologram is investigated. With a diffusion- and
photovoltaic-dominated carrier transport mechanism and carrier thermal
activation (temperature dependent) considered in Fe:LiNbO3 crystal, from
the standpoint of field-material coupling, the theoretical thermal fixing
time and the space-charge field buildup, spatial distribution, and temperature
dependence are given numerically by combining the band transport
model with mobile ions with the coupled-wave equation
Mridula,S; Jacob,George; Mohanan,P(Microwave and Optical Technology Letters, December 20, 1999)
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Abstract:
A novel antenna configuration comprised of two circular
micro strip antennas (CMAs) resonating in the TMtt and TM2, modes,
producing radiation characteristics suitable for a mobile telephone handset,
is presented. The antennas operating at the same frequency are
placed back to back with a separation comparable to the thickness of a
typical handset. The radiation pattern consists of a region of reduced
radiation intensity, which minimizes the radiation hazards to the user
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