C-band Frequency Research Articles

Geophysical Model Function for the AMSR2 C-Band Wind Excess Emissivity at High Winds

Measurements of the Advanced Microwave Scanning Radiometer 2 (AMSR2) onboard the Global Change Observation Mission–Water 1 (GCOM-W1) satellite at 6.925 and 7.3 GHz and both linear polarizations over tropical cyclones (TCs) during 2012–2014 are used to derive a new geophysical function relating the brightness temperature to the sea surface wind speed (SWS) in extreme conditions. Similar sensitivity to the SWS at close C-band frequencies allowed correcting for the atmospheric contributions to the microwave radiance and estimating the brightness temperature $(T_{B})$ at the surface under TCs, combining theoretical modeling and measured $T_{B}$ analyses. Estimated oceanic $T_{B}$ 's were regressed against the wind speeds from the Best Track Archive to derive a new geophysical model function for the wind speed excess emissivity at AMSR2 C-band microwave frequencies.

Ku대역 전파고도계 체계점검장비 개발

For performance improving of C-band radar altimeter used in a missile system, Ku-band radar altimeter is developed. To utilize the time delay devices which are used in testing C-band radar altimeter, we proposed C-band and Ku-band frequency conversion method and implemented it as a part of missile system test equipment. In this paper we present design contents, development results and test application results of radar altimeter test equipments.

Wideband four-element two-segment triangular dielectric resonator antenna with monopole-like radiation

In this paper, a wideband two-segmented four-element triangular dielectric resonator antenna (TDRA) with coaxial probe feed has been proposed. The proposed antenna has been analyzed, optimized, and studied through Ansoft HFSS simulation software. The prototype of the proposed antenna has been fabricated and its input characteristics are measured with the help of R&S Vector Network Analyzer. Good agreement has been obtained between simulated and measured results. The proposed design has been compared with two segments TDRA and found wider bandwidth with lower resonant frequency. The proposed antenna provides monopole-like radiation pattern over the entire bandwidth with nearly 33% bandwidth (return loss ≥10 dB) at a resonant frequency 6.9 GHz and 4.93 dBi peak gain. The proposed antenna is suitable for application of C-band microwave frequencies.

A Methodology to Determine Radio-Frequency Interference in AMSR2 Observations

A study to determine radio-frequency interference (RFI) in low-frequency passive microwave observations of the Advanced Microwave Scanning Radiometer-2 (AMSR2) is performed. RFI detection methods, such as the spectral difference method, have already been applied on microwave satellite sensors. However, these methods may result in false RFI detection, particularly in zones with extreme environmental conditions. To overcome this problem, this paper proposes an approach that uses the additional 7.3-GHz channel of the AMSR2 sensor in a new RFI detection method. This method uses calculated standard errors of estimate to detect RFI contamination in 6.9- and 7.3-GHz observations. It was found that 6.9-GHz observations are mainly contaminated in the USA, India, Japan, and parts of Europe. The 7.3-GHz observations are contaminated in South America, Ukraine, the Middle East, Southeast Asia, and Russia. The fact that these channels are not affected by RFI in exactly the same regions is useful for studies that prefer C-band brightness temperature observations (e.g., soil moisture retrieval algorithms). Therefore, a decision tree approach was set up to determine RFI and to select reliable brightness temperature observations in the lowest frequency free of any man-made contamination. The result is a reduction of the total contaminated pixels in the 6.9-GHz observations of 66% for horizontal observations and even 85% for vertical observations when 7.3 and 10.7 GHz are used. By linking RFI maps with civilization maps, this paper further shows that RFI sources at the C-band frequency are mainly located in urbanized areas.

Intercalibration of Advanced Microwave Scanning Radiometer-2 (AMSR2) Brightness Temperature

Here, we describe the characteristics of brightness temperature (Tb) measured by the Advanced Microwave Scanning Radiometer-2 (AMSR2) onboard the Global Change Observation Mission 1st-Water (GCOM-W1). This mission aims to achieve long-term global monitoring of Earth using two polar-orbiting satellite observation systems with three consecutive generations. GCOM-W1, the first satellite of the GCOM-W (Water) series, was launched successfully on May 18, 2012. AMSR2 is a single-mission instrument onboard the GCOM-W1 satellite. The basic characteristics of AMSR2 are similar to those of its predecessor, AMSR-E; this allows the continuation of AMSR-E observations but with several improvements, including a larger main reflector (2.0-m diameter), additional channels at C-band frequency, an improved calibration system, and increased reliability imparted by the addition of a redundant momentum wheel. Since July 3, 2012, the instrument has functioned properly and has accumulated a data set of Tb measurements. During the initial calibration and validation period, Tb values are being evaluated and characterized according to various methodologies, including intercalibration between similar microwave radiometers [e.g., the Tropical Rainfall Measuring Mission Microwave Imager (TMI)] based on radiative transfer computations. The intercalibration results for the ocean area as the cold end and the rainforest area the as warm end demonstrate that Tb measured by AMSR2 exhibits no apparent seasonal variation, with a maximum calibration difference of approximately 5 K compared to TMI and AMSR-E. This calibration difference appears to depend on the Tb of the observed object.

一种新颖的双陷波UWB天线

在一款新型平面超宽带天线的基础上，通过在辐射贴片上开一个环形槽、在接地板上开一对对称的弯槽，实现了3.7~3.9 GHz和5~5.9 GHz的双陷波特性，有效地抑制了卫星C波段和无线局域网频段的信号对超宽带系统的干扰。对天线的陷波特性及原理进行了分析，并对所设计的天线进行了实物加工和测试，最后研究了天线的方向图和增益特性。结果显示，该天线性能优良，结构简单，易于集成，具有较高的应用价值。 The proposed antenna achieved 3.7 - 3.9 GHz and 5 - 5.9 GHz dual band-notched characteristics with opening an annular slot on the radiating patch and etching a pair of symmetrical curved slot on the ground on the basis of a new planar ultra-wideband antenna, which effectively suppressed the interference of the satellite C-band and wireless LAN frequency band signal on UWB system. The notch characteristics and principle of the antenna were analyzed. The designed antenna were given physical processing and tested. Finally, the antenna radiation pattern and gain characteristics were studied. The results show that the antenna has high application value with excellent perfor- mance, simple structure and easy integration.

English

This study presents experimental measurements of complex dielectric constant at C-band microwave frequency of dry and moist saline soils collected from Dandi (Dist. Navsari) site of Gujarat state (India). An automated microwave set-up tuned at 5.3 GHz frequency is used for this purpose. Measured values of dielectric constant are then used to estimate the scattering coefficient by using perturbation model. Our results indicate relatively lower rate of increase in e' and order of magnitude higher values of e'' for these saline soils when their gravimetric MC is changed from 10 to 30% than that reported for non-saline soils by earlier researchers. Further, at constant value of MC, scattering coefficient of soil sample also increases with increase in the incident angle for vertical polarization, and this increase continues up to angles between 60o to 70o, at which it reaches maximum value and beyond this, it decreases sharply. Further, for vertical and horizontal polarizations, at constant value of incident angle, our results indicate relatively lower rate of increase in scattering coefficient values for saline soils than reported earlier for non-saline soils when gravimetric MC is changed from 10 to 20%. This data is very useful in understanding dielectric behaviour of saline soils and also for designing the active sensors for these soils.

The scattering simulation of DSDs and the polarimetric radar rainfall algorithms at C-band frequency

This study explores polarimetric radar rainfall algorithms at C-band frequency using a total of 162,415 1-min raindrop spectra from an extensive disdrometer dataset. Five different raindrop shape models have been tested to simulate polarimetric radar variables—the reflectivity factor (Z), differential reflectivity (Zdr) and specific differential phase (Kdp), through the T-matrix microwave scattering approach. The polarimetric radar rainfall algorithms are developed in the form of R(Z), R(Kdp), R(Z, Zdr) and R(Zdr, Kdp) combinations. Based on the best fitted raindrop spectra models rain rate retrieval information using disdrometer derived rain rate as a reference, the algorithms are further explored in view of stratiform and convective rain regimes. Finally, an “artificial” algorithm is proposed which considers the developed algorithms for stratiform and convective regimes and uses R(Z), R(Kdp) and R(Z, Zdr) in different scenarios. The artificial algorithm is applied to and evaluated by the Thurnham C-band dual polarized radar data in 6 storm cases perceiving the rationalization in terms of rainfall retrieval accuracy as compared to the operational Marshall–Palmer algorithm (Z=200R1.6). A dense network of 73 tipping bucket rain gauges is employed for the evaluation, and the result demonstrates that the artificial algorithm outperforms the Marshall–Palmer algorithm showing R2=0.84 and MAE=0.82mm as opposed to R2=0.79 and MAE=0.86mm respectively.

A New Double Negative Metamaterial for C-Band Microwave Applications

Metamaterials are artificial materials that show extra ordinary electromagnetic properties which are not available in nature. It has opened a new era in the field of material science. It can be defined as an exotic electromagnetic structure that may show both negative permittivity and negative permeability simultaneously within a frequency range. Metamaterials with simultaneous negative permeability and permittivity are called Double Negative Metamaterials (DNG). In this paper, a new metamaterial unit cell structure has been proposed that exhibits resonance within frequency of C-band and shows a negative permeability and permittivity at that resonant frequency. In the proposed structure, two separate split ring resonators and a metallic bar has been used. A commercially available simulation software CST Microwave Studio has been used to get the reflection and transmission parameters for the unit cell.

Design of compact reconfigurable ultra‐wideband slot antenna with switchable single/dual band notch functions

A compact reconfigurable microstrip slot antenna with switchable single and dual band notch functions for ultra-wideband (UWB) applications is presented in this study. In the proposed structure, an additional resonance is excited by etching two symmetrical notches on the feed-line and thereby a UWB characteristic is obtained. Then, by cutting two slots on the radiating patch and embedding two positive-intrinsic-negative (PIN) diodes along these slots, switchable single and dual band notch performances are added to the antenna performance. By changing the bias states of the PIN diodes, the antenna is capable of exhibiting four different performances of UWB spectrum coverage, UWB coverage with single rejection of the wireless local area network (WLAN) band, UWB coverage with single rejection of the WiMAX and C-band spectrum, and UWB coverage with dual band notch function at the WLAN, the WiMAX and the C-band frequencies. Good agreement between the simulated and the measured results is achieved at different performances of the antenna. The designed antenna has a small size of 20 × 20 mm 2 and the measured results reveal that the fabricated antenna has good radiation behaviour in the UWB frequency spectrum with switchable band notch functions at 3.15-3.85 and 5.43-6.1 GHz which can eliminate the UWB frequency band interference with the WiMAX, the C-band and the WLAN systems.

Design of Multilayer Polarization Beam Splitters Using Multiobjective Evolutionary and Genetic Algorithms

Multilayer polarization beam splitters (MPBSs) are important optical components in optical communication systems and optical devices. The components of transverse electric (TE) and transverse magnetic (TM) light plane wave in MPBSs are separated in different ways. In this paper, the Pareto optimization (multiobjective evolutionary and genetic algorithms) is used to design MPBSs on C-band frequency. The reflectances of TM light plane wave for Pareto optimization are the lowest and zero at the wavelength of 1.535 μm. The degree of polarization for Pareto optimization is the highest at wavelength from 1.528 - 1.54 μm and reaches 100% at wavelength of 1.535 μm.

Characterization of High Power Microwave Radiation by an Axially Extracted Vircator

Characterization results of high-power microwave radiation, from an axial vircator driven by pulsed electron beam accelerator AMBICA-600 are reported in this paper. We present a study on variation in pulsed microwave power output and dominant frequency by discretely varying anode-cathode (A-C) gap. While keeping the cathode diameter fixed at 40 mm, for the A-C gap distance in the range 5-9 mm, dominant frequencies have been measured to be lying in the range 4.7-9.8 GHz. The trend of a subsequent increase in the dominant frequency at lower A-C gap distances (and vice versa) revealed that center frequency is mainly governed by the longitudinal size of the potential well. The highest microwave power of ~ 14 MW for ~ 75-ns pulse duration was obtained at A-C gap of 7 mm having the dominant frequency in C-band at ~ 6.9 GHz. The beam-to-microwave power conversion efficiency of ~ 1.2% has been demonstrated in our experiments. On the basis of power distribution pattern obtained by the gas breakdown technique, the dominant mode of emission is believed to be transverse magnetic mode. Relative analysis of frequency spectrums obtained for various A-C gap distances evidenced experimental recognition of optimum A-C spacing as a generation of narrowband distinct frequency peak of large magnitude with minimal mode hopping.

A compact broadband microstrip patch antenna with defective ground structure for C-Band applications

AbstractA novel design of a circular patch antenna having defected ground structure is presented in this communication. The antenna is designed for C-band applications. A wide bandwidth of 60.3% (4.04–7.28) GHz is obtained in the C-band frequency range 4–8 GHz. It is also found through parametric analysis that shape and dimensions of the finite ground plane and slots in the patch are the key factors in improving the bandwidth of the proposed geometry. The antenna is fabricated using FR-4 substrate and parameters like return loss, VSWR and input impedance are measured experimentally.

Demonstration of Helical Antenna Stability Beyond C-Band Frequency

The paper demonstrates design of helical antenna to achieve stable frequency response and impedance matching beyond C-band microwave frequency. An impedance matching cavity is developed for excitation of higher order modes along with the fundamental mode in the helical antenna. Triple frequency bands are resonated by loading the designed helical antenna inside the cavity and a dual band response is realized by introducing variation in feed pin height with an incremental offset of 0.1λ to the initial height which is taken as 0.2λ. The broadband gain for all the designs and a detail analysis of modes along the helical antenna loaded in rectangular cavity is reported. A highest measured bandwidth of 5.4 GHz and a peak gain of 10.65 dB is obtained. The antenna being compact and conformal in design may find its application for terrestrial, aerospace communication and personal wireless communication. DOI: http://dx.doi.org/10.11591/ij-ict.v2i3.4861

Slant-Path Rain Attenuation Statistics over Nigeria

Slant path attenuation of microwaves due to rainfall intensities exceeding 0.01 and 0.001per cent of average year have been computed for five different geographical zones in Nigeria, using relevant ITU-R recommendations and global rain rate data. The resulting charts can be used for preliminary estimates of maximum rain-induced attenuation of microwaves expected on earth-satellite paths of elevation angles 20-90degrees in Nigeria, for the L, C, ka and ku frequency bands, which are presently used by the Nigerian communication satellites. The study shows that attenuation is higher for western, southern, or lower altitude stations. Also attenuation of horizontally polarized waves exceed that of vertical polarization by increasing margins at higher frequencies, which makes vertical polarization more preferable at higher microwave frequencies. Thus, the emerging LEO and MEO satellite systems that will operate on frequencies as high as 40 GHz may be practically restricted to vertical polarization due to rain attenuation. Based on the curves, rainfall attenuation in Nigeria may be negligible on slant microwave links at L-band and lower frequencies, no matter the elevation angle; but may cause significant propagation problems at C-band and higher frequencies,especially at low elevation angles.Key words: Microwave attenuation, polarization, radio propagation, frequency band, rainfall rate .

Polarimetric Radar Observations in the Ice Region of Precipitating Clouds at C-Band and X-Band Radar Frequencies

AbstractData collected by C-band and X-band radars in northwestern Italy are analyzed to study the behavior of the polarimetric variables in the ice region of precipitating clouds, with special emphasis on the specific differential phase Kdp. It is found that stratiform precipitation, irrespective of the precipitation type at the ground and as opposed to convective systems, is characterized by well-pronounced positive differential reflectivity Zdr and Kdp values near the model-predicted −15°C isotherm. The regions of enhanced Zdr and Kdp are likely related to the growth of dendrite crystals in the region where the difference between the saturation vapor pressure over water and the saturation vapor pressure over ice is greatest. Coincident C-band and X-band measurements, in conjunction with electromagnetic scattering simulations, demonstrate that Kdp scales with frequency, indicating that the ice particles in the vapor deposition preferential growth zone are Rayleigh scatterers. Peak values around 2.0° and 3.5° km−1 are observed at C band and X band, respectively. Most noteworthy is that an extended analysis of hourly and daily vertical profiles of C-band data over 1 year has shown that Kdp observations around the −15°C temperature level in stratiform precipitation are well correlated (0.8) with the reflectivity in the underlying rain layer.

Core/Shell Metal/Heterogeneous Oxide Nanocapsules: The Empirical Formation Law and Tunable Electromagnetic Losses

We report an empirical thermodynamic law for the synthesis of core/shell metal/heterogeneous oxide nanocapsules, such as Fe/SiO2, Ni/SiO2, Fe/B2O3, Ni/B2O3, Fe/Al2O3, Fe/MnO2, Fe/Y2O3, Fe/CeO2, and Fe/La2O3, by arc-discharge evaporating a compressed mixture of Fe (or Ni) powders and the oxide powders of shell components. By integrating such dielectric oxide shells and magnetic metal cores in each particle, the electromagnetic losses can be artificially manipulated at the whole S-band, C-band, X-band, and Ku frequency ranges. The microscopic origins of the controllability of electromagnetic losses are ascribed to the specific matching and interfacial coupling between the magnetic cores and dielectric shells.

Note: Tunable notch filter based on liquid crystal technology for microwave applications

In this work, a compact design of an electrically tunable notch filter, based on liquid crystal (LC) technology, has been designed, manufactured, and characterized. The proposal has been achieved through particular configuration schemes with low cost inverted-microstrip structures and conventional spurlines structures due to its ease of integration. Central frequency tunability has been induced by applying low ac voltages, thus involving low power consumption. For these devices, filter responses have been approached specifically at microwave C-band frequency allocated for many satellite communications applications. Also, it has taken advantage of new highly anisotropic nematic LC mixtures at those frequency ranges.

A Novel Miniature Band-Notched Wing-Shaped Monopole Ultrawideband Antenna

A small band-notched monopole ultrawideband (UWB) antenna is proposed in this letter. In this antenna, the band-reject is achieved by attaching a strip to the hollow center of a wing-shaped monopole. The height and width of the strip are dependent on the center frequency of the notch band. The proposed antenna is printed on a very small (11 × 15 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) substrate. The measured results reveal that the proposed antenna offers a wide bandwidth covering 5-15 GHz with a notched band covering a 6.7-7.1-GHz IEEE INSAT/super-extended C-band frequency. The proposed antenna shows very narrow and accurate band rejection.

An 8-W 250-MHz to 3-GHz Decade-Bandwidth Low-Noise GaN MMIC Feedback Amplifier With &gt; +51-dBm OIP3

This paper describes a GaN monolithic microwave integrated circuit (MMIC) cascode feedback amplifier design which achieves up to 8 W of output power and greater than +51 dBm OIP3 across a 250-3000-MHz decade bandwidth. The LNA also achieves 20 dB of flat-gain across the band. The design was fabricated with a 0.25-μm GaN HEMT technology with an fT ~ 50 GHz and a BVgd >; 60 V. A 40-V 750-mA high-bias LNA design achieves an OIP3 of 51.9 dBm, P1dB of 38.5 dBm, and NF ~ 3 dB at 2 GHz . A 40-V 500-mA medium-bias LNA design achieves a lower NF ~ 2.5 dB , an OIP3 of 48.4 dBm, and a P1dB of 36.8 dBm at the same frequency. At an optimum low-noise bias of 20 V and 300 mA, a NF ~ 0.96 dB, an OIP3 of 43.4 dBm, and a linear P1dB of ~32.2 dBm was also obtained. The combination of high OIP3 and low NF from these GaN MMIC LNA designs exceed that achieved by many state-of-the-art PHEMT, HBT, and HFET technologies for decade-BW MMIC amplifiers operating in the popular wireless and wire-line S- and C-band frequency ranges. The linear GaN LNA performance demonstrated here can enable new generations of software-defined and reconfigurable radios which require ultra-linearity over multiple octaves of bandwidth.