Abstract-A new design has been proposed for a single layer polarization-insensitive dual-band metamaterial absorber at C and X bands. The proposed structure consists of a periodic arrangement of a circular resonator embedded in a square resonator. A commercially available FR4 dielectric has been used as a substrate with metallic grounded bottom and imprints on the other side. This structure resonates at 5.5 GHz and 8.9 GHz with absorptivity of 99.8% and 99.97%, respectively. It exhibits polarization-insensitive behaviour for Transverse Electric and Transverse Magnetic polarization under oblique and normal angles of incidence. The field distributions have been studied for better understanding of the absorption mechanism. The fabricated structure has been tested, and the experimental results are similar to the simulated ones. This polarization-insensitive metamaterial absorber with its ease of design and nearly unity absorption can be used for radar applications.

A multifrequency phased-array Doppler sodar system has been installed recently at the National Atmospheric Research Laboratory (NARL) for the continuous observation of the lower atmosphere from near ground to the atmospheric boundary layer (ABL). The NARL sodar, developed in technical collaboration with the Society for Applied Microwave Electronics Engineering and Research (SAMEER), was built using piezoceramic tweeters, which are capable of generating 100-W acoustic power. In favorable atmospheric conditions, the sodar gives wind profiles up to 1 km. The performance evaluation is one of the most important aspects for quality assurance of sodar operations. This paper presents the first results of experimental observations of the NARL sodar system and its scientific validation. The NARL sodar has been validated using the simultaneous observation of another sodar system (Scintec model MFAS64). Various physical parameters of the atmosphere are derived using the results obtained from both of the systems. Comparison of simultaneous measurements by both of the sodars, located about 100 m apart, shows good agreement on wind speed, wind direction, and vertical wind variance. The correlation coefficient of more than 0.80 in wind speed and direction between the sodars shows the usefulness of the system for observing the atmosphere and deriving physical parameters below the ABL.

This study presents a new, ultra‐thin compact microwave metamaterial absorber for wideband applications. The proposed metamaterial absorber comprises an outer ring and inner split ring patches on the upper surface and metallic ground in the bottom surface. A dielectric FR4 substrate of thickness 1.6 mm was placed between the top patch and the bottom ground. The designed structure was ultra‐thin of λ0/13.9 thickness with respect to the centre frequency of the bandwidth. The simulation results showed ultra‐wideband absorption of 6.31 GHz from 10.36 to 16.67 GHz above 85% absorptivity, and peaks at 11.1, 13.2, 14.4 ,and 16.2 GHz and full width half maximum of 9.6 GHz. The mechanism of absorption for the proposed ultra‐wideband metamaterial absorber was studied. Also, the polarization behavior was tested under oblique and normal angles of incidence for transverse electric polarization. Due to its asymmetrical design, the proposed structure is polarization sensitive. The designed structure was fabricated and measured, and the practical results were in good agreement with the simulation results.

In this article, a compact dual-mode dual-band bandpass filter with adjustable second passband using a star shaped resonator is proposed. It is loaded with two T-shaped stepped impedance stubs inside the resonator and these stubs introduce a transmission zero on the upper side of the first passband. A small triangular perturbation element attached to the star loop resonator excites dual degenerate modes and is responsible for the first passband with two transmission poles. Two U-shaped slots etched on the ground plane control second passband frequency which is derived from the first harmonic. It also helps in attaining two transmission poles in the second passband. Unlike, the conventional orthogonal feed used for dual mode filters, the proposed filter is fed by two arrow shaped feed lines oriented along the straight line and are parallel coupled to the resonator. Finally, a dual-mode

Abstract. This article reports an ultra-thin

Atmospheric winds in the troposphere have been observed routinely for many years with wind profiling (VHF and UHF) radars using the Doppler beam swinging (DBS) technique. Accuracy of wind estimates using wind profiling radars with different beam configurations has its limitations due to both the system of observation and atmospheric conditions. This paper presents a quantitative analysis and evaluation of horizontal wind estimation in different beam configurations up to an altitude of 18 km using the mesosphere-stratosphere-troposphere (MST) radar located in Gadanki, India. Horizontal wind velocities are derived in three different ways using two-, three-, and four-beam configurations. To know the performance of each configuration, radar-derived winds have been compared with the winds obtained by simultaneous GPS sonde balloon measurements, which are considered to be a standard reference by default. Results show that horizontal winds measured using three different beam configurations are comparable in general but discrepancy varies from one beam configuration to the other. It is observed that horizontal winds measured using four-beam configuration (east, west, north, and south) have better estimates than the other two-beam configurations. The standard deviation was found to be varying from 1.4 to 2.5 m s Ϫ1 and percentage error is about 9.68%-12.73% in four-beam configuration, whereas in other beam configurations the standard deviation is about 1.65-3.9 m s Ϫ1 and the percentage error is about 11.29%-15.16% with reference to GPS sonde balloon-measured winds.

A graphite calorimeter similar in size and shape to a Farmer type 0.6-cm3 ionization chamber was developed for direct measurement of absorbed dose at a specified depth in a water phantom irradiated by a beam of 60Co gamma radiation. The accuracy of the absorbed dose determined was estimated to be +/- 1.1% at a dose level of 4 rad/s (4 X 10(-2)Gys-1). The absorbed dose to water at the calibration depth of 5 cm was standardized for our 60Co gamma bean, for a 60-cm SSD and 10 X 10 cm2 field. Farmer type ionization chambers were calibrated against the standardized absorbed dose. The overall accuracy in calibrating the ionization chambers was +/- 1.2%.

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