Microwave cavity perturbation technique: Part III: Applications

The resonant cavity perturbation method as described in the preceding two parts of this series is applied to study the electrodynamical properties of different materials in the microwave and millimeter wave spectral range. We briefly discuss the relevant uncertainties which are asociated with the different measurement techniques and we find that employing the amplitude technique it is possible to measure both the width and frequency to nearly the same precision. We then demonstrate the broad range of applicability of this technique by showing results obtained on several different materials, ranging from an insulator to a superconductor. The performance limitations of this technique are discussed in detail.     

Microwave cavity perturbation technique: Part II: Experimental scheme

In this paper, the second in a three part series, we describe an experimental scheme used to measure the electrodynamical response of a material in the millimeter wave range of frequency. In particular, with this technique we can directly evaluate the complex conductivity from a measurement ofboth the bandwidth and characteristic frequency of a resonator containing the specimen. We will describe in detail all the technical improvements achieved which provide the required accuracy.     

Microwave measurements Part I: Linear Measurements

By convention, radio frequency (RF) and microwave frequencies range between 30 MHz and 300 GHz. Conversely, this means their wavelengths range between 10 m and 1 mm. Intense research in radar development during World War II extended the RF spectrum beyond the usual applications in radio communications. The use of shorter wavelengths resulted in laboratory equipment with proportionally smaller dimensions to generate, convey, transmit, and detect higher-frequency signals. Wavelengths shorter than 1 mm require equipment too small to be realized. Voltage, current, and impedance concepts lose their conventional meanings when the operating wavelength is approximately equal to the dimensions of the structures under test. The behavior of propagating electromagnetic waves must then be analyzed in terms of electric and magnetic field. Unfortunately, no simple and direct way exists to measure these quantities, so we must resort to indirect methods. In the following sections, we briefly review the concept and need for measurements of scattering parameters. We also describe the two key instruments for microwave measurements: VNAs and spectrum analyzers.     

Extended cavity perturbation technique to determine the complexpermittivity of dielectric materials

An improved measurement technique to determine the complex dielectric properties of materials has been developed that extends the validity of the conventional cavity perturbation technique for circular cylindrical rod-shaped samples in circular cylindrical cavities resonating in TM_0n0 modes. The method is particularly useful for the dielectric characterization of fragile, low-loss materials that are difficult to machine to typically required thin dimensions. The method further allows for multi-frequency measurements using higher-order radial modes and somewhat alleviates the very small cavity dimensions typically required by the conventional perturbation technique at higher microwave frequencies. A validity criterion for the extended method is given. Measurements of the complex permittivity of NaCl single crystals are presented, showing excellent agreement with theory     

Microwave attenuation by realistically distorted raindrops: Part I.Theory

By using a new raindrop model developed earlier and applying the first-order perturbation-expansion technique, the effects of realistic and nonaxisymmetric distortion of varying raindrop shapes on microwave attenuation are re-investigated in this paper. Under the assumption of nonaxisymmetric raindrop scatterers, a system of general equations satisfied by the scattering and transmission coefficients of the electromagnetic (EM) fields are derived under the zeroth-order and the first order approximations. Both the horizontal and the vertical polarizations are discussed. The scattered and transmitted EM fields are obtained by means of expansion of spherical vector wave functions. Under the first-order perturbation approximation, the total cross section is calculated and discussed. Compared with the previous formulas presented for the axisymmetric raindrop scattering, the new results of total cross section obtained here consist of two additional terms resulting from the nonaxisymmetric distortion. These additional terms due to the raindrop's nonaxisymmetry are represented analytically and discussed numerically. Part II of this paper will present an application of the analysis to the specific microwave attenuation due to rain in the moderate climatic region and in Singapore's tropical region     

Radio-Over-MMF Techniques—Part I: RF to Microwave Frequency Systems

Recent work on radio-over-multimode-fiber (MMF) transmission, for the support of wireless LANs and current cellular systems operating at below 6 GHz, has shown that excellent performance (e.g., spur-free dynamic range well in excess of 100 dB.Hz$^{2/3}$) can be achieved. However, it is shown here that for multisystem operation, spurious emissions may be more of a restriction than meeting good signal quality requirements (such as low error vector magnitude). Initial results are reported for error vector magnitude and adjacent channel leakage for UMTS transmission over a radio-over-MMF link with a multisystem remote antenna unit with conformance to standards being demonstrated.      

Accuracy of microwave cavity perturbation measurements

Techniques based on the perturbation of cavity resonators are commonly used to measure the permittivity and permeability of samples of dielectric and ferrite materials at microwave frequencies. They are also used to measure the local electric- and magnetic-field strengths in microwave structures including the shunt impedances of cavity resonators and the coupling impedances of slow-wave structures. This paper reexamines the assumptions made in the theory of these techniques and provides estimates of the errors of measurement arising from them     

The GSMaP Precipitation Retrieval Algorithm for Microwave Sounders—Part I: Over-Ocean Algorithm

We develop an over-ocean rainfall retrieval algorithm for the Advanced Microwave Sounding Unit (AMSU) based on the Global Satellite Mapping of Precipitation (GSMaP) microwave radiometer algorithm. This algorithm combines an emission-based estimate from brightness temperature (Tb) at 23 GHz and a scattering-based estimate from Tb at 89 GHz, depending on a scattering index (SI) computed from Tb at both 89 and 150 GHz. Precipitation inhomogeneities are also taken into account. The GSMaP-retrieved rainfall from the AMSU (GSMaP_AMSU) is compared with the National Oceanic and Atmospheric Administration (NOAA) standard algorithm (NOAA_AMSU)-retrieved data using Tropical Rainfall Measuring Mission (TRMM) data as a reference. Rain rates retrieved by GSMaP_AMSU have better agreement with TRMM estimates over midlatitudes during winter. Better estimates over multitudes over winter are given by the use of Tb at 23 GHz in the GSMaP_AMSU algorithm. It was also shown that GSMaP_AMSU has higher rain detection than NOAA_AMSU.      

Observations on resonant cavity perturbation by dielectric objects

Microwave resonators can be used as sensors for sorting dielectric objects. Differences in volume or mass can be distinguished among objects of irregular shape but of uniform dielectric properties. Moisture content, or other permittivity-dependent qualities can also be distinguished independent of mass or volume when objects are of uniform shape. Fundamental principles of the shape-independent and size-independent measurements are discussed, and experimental results are presented     

Absolute photoconductivity value determined by the cavity perturbation method

A method of measuring the absolute value of the photoconductivity based on the envity perturbation principle is proposed. Another bolometer circuit is used which modulates the Q of the sample cavity with the same frequency as the light-induced signal. Knowing the magnitude of the modulation and the corresponding output signal we can calibrate the whole measuring system. This allows the absolute value of the light-induced dielectric losses to be determined without the use of ‘standard sample’.     

Microwave cavity made from high temperature superconductor

The authors report surface impedance measurements made on a cylindrical cavity resonator constructed entirely from the sintered high temperature superconductor YBa₂Cu₃O₇, and have measured the temperature dependence of the surface impedance for five different modes in the frequency range 10-18 GHz, in the temperature range form 4-300 K     

微波硫灯的工作机理

对微波琉灯的工作机理进行了探讨,设计了微波硫灯的原理装置,并对其工作特性进行了初步的研究。     

Microwave measurements - Part III: Advanced non-linear measurements

This work completes the sequence started with articles [1] and [2], previously published in this journal, which presented the most important aspects of RF and microwave linear and non-linear measurements. In [1], some off-the-shelf linear measurement approaches at microwaves were described, whereas [2] showed the conventional characterization of non-linear devices under large-signal conditions, such as active and passive load-pull at fundamental and harmonic frequencies. In basic load-pull systems, the device under test (DUT) is driven by a single tone microwave source while the DUT performance metrics, typically output power and power added effi ciency (PAE), are monitored as a function of the load and/or source terminations. This strategy enables the straight-forward identifi cation of the optimum input and output loads. In this article, we describe two of the most advanced measurement techniques that can provide the required information for power amplifi er design and transistor modeling. The first technique is the multi-tone/complex modulation load-pull. It is useful especially for wireless applications, where conventional single tone excitations do not give suffi cient information for model and design development. The measurement conditions would be too far from the typical working ones. The second measurement technique is the timedomain waveform load-pull. Its applications span from highly accurate and reliable device model extraction to monitoring of actual operating conditions and "waveform engineering" for high-performance design.     

Quasi-three-dimensional perturbation technique, includingdielectrics for TWT's

A perturbation technique is described for finding phase velocities and coupling impedances in a traveling wave tube for an arbitrary distribution of dielectric material. A model of the sheath helix is presented. Tape helix results will be presented in a separate paper. In all cases presented, without adjusting the dielectric constant, the calculated perturbed phase velocity provided a better answer than the homogeneous dielectric solution, or Naval Research Laboratories' Small Signal Gain Program. Deviation from theory versus experiment is reported by stating the average sum of the squares difference between theoretical calculations and a second order least squares fit of the measured data. Phase velocities can be calculated for uniform dielectric support rods where the average sum of the squares ⩽1.19×10^-5. For cases with notched dielectric support rods phase velocities can be calculated where the average sum of the squares ⩽1.94×10^-5. For NRL's SSG program the average sum of the squares was ⩽1.01×10^-4 by comparison. For uniform dielectric support rods the perturbation does not significantly alter the basic shape of the predicted dispersion curve. For notched dielectric support rods applying the perturbation does alter and flatten the shape of the predicted dispersion curve in agreement with experiment     

A vector-perturbation technique for near-capacity multiantenna multiuser communication-part II: perturbation

Recent theoretical results describing the sum-capacity when using multiple antennas to communicate with multiple users in a known rich scattering environment have not yet been followed with practical transmission schemes that achieve this capacity. We introduce a simple encoding algorithm that achieves near-capacity at sum-rates of tens of bits/channel use. The algorithm is a variation on channel inversion that regularizes the inverse and uses a "sphere encoder" to perturb the data to reduce the energy of the transmitted signal. The paper is comprised of two parts. In this second part, we show that, after the regularization of the channel inverse introduced in the first part, a certain perturbation of the data using a "sphere encoder" can be chosen to further reduce the energy of the transmitted signal. The performance difference with and without this perturbation is shown to be dramatic. With the perturbation, we achieve excellent performance at all signal-to-noise ratios. The results of both uncoded and turbo-coded simulations are presented.     

Microwave Allpass Networks--Part I

In this paper it is shown that any arbitrary delay characteristic of a commensurate microwave network, which supports a TEM mode of propagation, may be realized by means of a transformerless, coupled-line network within an arbitrary additive constant. The realization procedure presented is based upon the synthesis of microwave C-type and D-type allpass sections.     

LTE Part I: Core network

Current cellular networks based on Third Generation Partnership Project (3GPP) and 3GPP2 technologies provide evolution from circuit-switched technologies, originally developed for voice communications, to packetswitched technologies. Next-generation networks need to deliver IP-based services (voice, video, multimedia, data, etc.) for all kinds of user terminals while moving between fixed (fiber, DSL, cable) and wireless (3GPP-based, 3GPP2-based, IEEE-based) access technologies, and roaming between various operator networks. Users expect the network to originate, terminate, and maintain a session while the user is moving and roaming. Services have to be delivered to users based on serving network functionality (quality of service [QoS], bandwidth, etc.), availability, and user preferences. The network and users must be protected through various authentication, encryption, and other security mechanisms at the access, network, and application layers. Mobility has to be provided through coordinated link, network, and application layer mobility mechanisms that ensure user expectations of service performance are met. Requirements on the radio technology include improved performance as well as reduced system and device complexity. 3GPP Release 8 specifies the architecture to meet the above requirements.     

Microwave Measurements Part II Non-linear Measurements

This paper addresses the problems in microwave non-linear measurements. It discusses techniques to synthesize loads, the most used non-linear measurement techniques, and harmonic load-pulling. An experimental setup for characterizing power amplifiers must be able to measure the complex spectrum of the waves at the amplifier ports as a function of frequency, input power, and source and load termination at the fundamental and harmonic frequencies. The vector network analyzer (VNA) is the core instrument used in the non-linear characterization scenario. The basic idea is to keep the operations of VNA/mixers linear, diverting to them only a small portion of the signal present at the device under test (DUT) ports, therefore keeping unaltered the VNA capabilities already exhibited for small signal measurements.     

A quasi-optics perturbation technique for measuring dielectric constants

A method of measuring dielectric constants of materials in sheet form by insertion in a Fabry-Perot resonator is described. By tilting the dielectric sheet at a slight angle with respect to the system axis, the reflected wave can be eliminated. The working formula for determing the dielectric constant then reduces to a simple linear relation involving the ratio of the mirror motion required to restore resonance to the thickness of the dielectric. The method is applicable at all frequencies where Fabry-Perot resonators can be used and for materials with loss tangents less than one. A table of measured values of common dielectrics is presented for 143 Gc/s and 343 Gc/s.