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In this paper, a robust analysis of SO 2 concentration measurements taken at the Belisario air quality monitoring station, Quito, Ecuador is carried out. The analyzed data contain 12 years of measurements, from January 2008 to December 2019. In addition, this set of measurements was decomposed into variables that represent each year, month, day of the week, and hour of the day in groups of two hours. For the analysis, classic, nonparametric and robust statistical methods were used, and the data were classified based on criteria established by the Quiteno Air Quality Index, taking confidence intervals into account. The results showed that the level of air pollution at the Belisario station due to the SO 2 concentration is acceptable. In addition, the trend in the level of SO 2 concentration decreased over the years studied, with a sharp drop from 2008 to 2012, then a small rise in 2013 and another fall until 2019, presenting decreasing oscillations that tend toward a desirable level of pollution. In this paper, it was shown that the air pollution at the Belisario station due to the concentration of SO 2 in the last 12 years is not harmful to humans, with the measurement precision provided by robust statistical methods. Therefore, it can be concluded that the measures that have been taken by the Quito city council over the last few years are yielding good results.

This paper analyzes 12 years of tropospheric ozone (O3) concentration measurements using robust techniques. The measurements were taken at an air quality monitoring station called Belisario, which is in Quito, Ecuador, the data collection time period was 1 January 2008 to 31 December 2019, and the measurements were carried out using photometric O3 analyzers. Here, the measurement results were used to build variables that represented hours, days, months, and years, and were then classified and categorized. The index of air quality (IAQ) of the city was used to make the classifications, and robust and nonrobust confidence intervals were used to make the categorizations. Furthermore, robust analysis methods were compared with classical methods, nonparametric methods, and bootstrap-based methods. The results showed that the analysis using robust methods is better than the analysis using nonrobust methods, which are not immune to the influence of extreme observations. Using all of the aforementioned methods, confidence intervals were used to both establish and quantify differences between categories of the groups of variables under study. In addition, the central tendency and variability of the O3 concentration at Belisario station were exhaustively analyzed, concluding that said concentration was stable for years, highly variable for months and hours, and slightly changing between the days of the week. Additionally, according to the criteria established by the IAQ, it was shown that in Quito, the O3 concentration levels during the study period were not harmful to human health.

Negative impedance converters (NICs) have been proposed as structures to improve the performance of RF circuits and electrically small antennas. However, NICs suffer from stability problems. This paper presents a compact procedure to analyze the stability of NICs. Then, the required and sufficient conditions to predict the stability of a negative impedance converter are given. These conditions can be evaluated using standard computer-aided-design software. Finally, a NIC prototype is given to validate and illustrate the presented design procedure, it is also integrated with a printed, blade-type, electrically small monopole in the VHF band.

A low-cost, multiple-purpose, and high-precision timing test setup for the measurements of secondary Mode S radar transmission signal was proposed. The goal was to fully guarantee compliance of the proposed transmitter under test with the really hard International Civil Aircraft Organization requirements using traditional measurement equipment, which was difficult or even impossible to ensure up to now. The low-cost structure proposed in this paper allows the user to perform measurements independently of the measurements performed by the pieces of test equipment shelled by the manufacturer of radar, which is a very important aspect since the independence of the verifications is a mandatory requirement established by the safety standards of civil aviation. The proposed setup has been used to verify several transmitters with some defects that are not detected by monopulse secondary surveillance radar specific pieces of test equipment that are focused on more high-level functionalities. It also is valid and it has been used, as a general-purpose setup, for testing other radio navigation aids.

In this paper, the classic oscillator design methods are reviewed, and their strengths and weaknesses are shown. Provisos for avoiding the misuse of classic methods are also proposed. If the required provisos are satisfied, the solutions provided by the classic methods (oscillator start-up linear approximation) will be correct. The provisos verification needs to use the NDF (Network Determinant Function). The use of the NDF or the most suitable RRT (Return Relation Transponse), which is directly related to the NDF, as a tool to analyze oscillators leads to a new oscillator design method. The RRT is the "true" loop-gain of oscillators. The use of the new method is demonstrated with examples. Finally, a comparison of NDF/RRT results with the HB (Harmonic Balance) simulation and practical implementation measurements prove the universal use of the new methods.

In this paper, differential low-noise amplifiers are presented as a very powerful solution for radio astronomy applications. A fully differential amplifier topology has been analyzed and implemented in microstrip technology with discrete surface mount components. The amplifier design is made for an active receiving dense antenna array. Thus, the differential amplifier source impedance is no longer 50 Ω, but 150 Ω from the proposed bunny-ear antennas. A full characterization in terms of gain and noise has been undertaken. Source-pull measurements have been included in order to evaluate the performance of the amplifiers operating with variable source impedances. Noise temperatures below 55 K have been obtained for the differential design in the 300-1000-MHz band for the 150-Ω impedance. In addition, the results for different scanning angles are also presented.

In this paper, the most adequate architecture to implement dual frequency ampliflers is shown. Composite Right/Left Hand (CRLH) and Extended Composite Right/Left Hand (ECRLH) transmission lines are studied and evaluated to flnd the most suitable structure for dual band power ampliflers. As an example, the performance of a class CE amplifler, working in TETRA and GSM frequency bands, is compared with simulations and measurement, showing good agreement.

Composite transmission lines are one of the main developments in the increasingly popular field of electromagnetic metamaterials, artificial electromagnetic structures with both negative electric permittivity and magnetic permeability (Caloz & Itoh, 2005). These structures present a backward wave or left-handed (LH) propagation instead of the conventional right-handed one. The first experimental microwave structures that presented this behavior were the result of combining thin wires and split-ring resonators (Shelby et al, 2001). Soon it was evident that narrow bandwidth operation and high losses were inherent to the resonant nature of this kind of metamaterials. In order to overcome the previous problems, some authors proposed the so-called metamaterial transmission lines or lefthanded transmission lines LH TL (Sanada et al, 2004). The LH TL concept has been extended and generalized to the concept of composite right/left handed (CRLH) structures where mixed contributions of LH and RH cells occur in practice. More specifically, the CRLH transmission lines have become a very commonly used solution to obtain metamaterial properties with low losses and broader bandwidth. Then, below a certain frequency, a CRLH transmission line behaves as a left-handed transmission line while over higher frequencies it is basically a conventional right handed line. As a consequence of this combined behaviour, the phase response is not linear with respect to the frequency. From the circuit application point of view, the two main characteristics of the CRLH transmission lines consist on obtaining miniaturized and/or dual band circuits. Then, it can be mentioned that dual band hybrid couplers (Lin et al, 2004), branch-line couplers (Keung & Cheng, 2004), dual-performance rat-race couplers (Castro-Galan et al, 2009) and enhanced rat-race couplers (Okabe, Caloz & Itoh 2004). The most critical aspect in the design of combiners, filters or diplexers with conventional CRLH transmission lines is the losses associated to them. For the case of diplexers, using of the so called dual composite right left handed (D-CRLH) cells may overcome some of the previously stated problems. The D-CRLH transmission lines are the dual part of the CRLH transmission lines and were first proposed in (Caloz, 21

A semi-lumped balun transformer for UHF and ultrawideband (UWB) dipole antennas is presented in this paper. The proposed structure is based on two asymmetric filters that also transform the variable antenna impedance into the desired source impedance. These asymmetric filters make use of a binomial impedance transformer in each filter section. The asymmetric filters (one low pass filter, LPF, and other high pass filter, HPF) allow the balun bandwidth to be increased while the binomial transformer matches the variable balanced dipole impedance. In this way the ripple in the balun response due to the variation of the UWB dipole impedance is reduced. A balun for a UHF and UWB dipole antenna working from 220 to 820 MHz (bandwidth of 4:1) has been achieved with losses lower than 1 dB. These types of baluns are particularly useful in the low microwave frequency band.

In this study, the use of dual-composite right-left-handed (D-CRLH) transmission lines is proposed for the design of diplexers. The D-CRLH diplexers present advantages over conventional diplexers such as smaller size (especially in the ultra high frequency band). The design procedure and the design equations are presented in this paper. The non-linear phase response of a D-CRLH transmission line has been used to design diplexers at any arbitrary frequencies. Finally, two diplexers have been designed and manufactured: one for quite near frequencies and the other for further ones. The simulation results show good agreement with the measurements. A sensitivity analysis has been provided to show the robustness of this kind of circuits.

This paper is a deep analysis of oscillator plane reference design methods. It deflnes applicable conditions and the expected accuracy that can be archived with these methods. Some examples will be shown to illustrate wrong solutions that the use of linear reference plane methods can produce. The wrong solutions will be justifled by necessary conditions for proper use of these methods. The strengths and weaknesses of the, widely used, plane reference methods are described in this paper. Several classic topologies of microwave oscillators, as Grounded Collector Tuned Bases(GCTB) and Grounded Bases Tuned Oscillator (GBTO), are used to illustrate these results and the additional required conditions.

In this paper, a new linear method for optimizing compact low noise oscillators for RF/MW applications will be presented. The first part of this paper makes an overview of Leeson's model. It is pointed out, and it is demonstrates that the phase noise is always the same inside the oscillator loop. It is presented a general phase noise optimization method for reference plane oscillators. The new method uses Transpose Return Relations (RRT) as true loop gain functions for obtaining the optimum values of the elements of the oscillator, whatever scheme it has. With this method, oscillator topologies that have been designed and optimized using negative resistance, negative conductance or reflection coefficient methods, until now, can be studied like a loop gain method. Subsequently, the main disadvantage of Leeson's model is overcome, and now it is not only valid for loop gain methods, but it is valid for any oscillator topology. The last section of this paper lists the steps to be performed to use this method for proper phase noise optimization during the linear design process and before the final non-linear optimization. The power of the proposed RRT method is shown with its use for optimizing a common oscillator, which is later simulated using Harmonic Balance (HB) and manufactured. Then, the comparison of the linear, HB and measurements of the phase noise are compared.