A contribution to linearity improvement of a highly efficient pa for WIMAX applications

This paper describes the design of a highly efficient and linear GaN HEMT power amplifier which may be used in WiMAX application. To improve linearity of highly efficient power amplifiers, a technique using diodes in the gate DC path was applied to TL and 2HT amplifier. This solution using diodes offers a good manner to improve linearity near saturation zone compared to the approach using only a DC gate resistor for TL (tuned load) case as well as for 2HT (second harmonic tuning approach). A 2.5 GHz 2HT power amplifier circuit was built, and measured data confirm the linearity improvement, particularly near saturation zone, as predicted by simulation, maintaining higher power performances. An output power of 36.8 dBm has been measured with an associated power added efficiency of 46.5% and carrier to third order intermodulation (C/I3) of 53.4 dBc. A 2HT PA also exhibits good performances across the full (2.3-2.7) GHz band. An output power ranging from (35-36.9) dBm with an associated gain of $12.9±0.9 and a power added efficiency ranging from (40-46)% are measured across the full (2.3-2.7) GHz band.Our acknowledgment to the financial support provided by the Spanish Ministry of Science and Innovation (MICINN) through projects TEC2008-06684-C03-01 and CONSOLIDER-INGENIO 2010 CSD2008-00068

Arbitrary-angle single-step waveguide twist for quasi-octave bandwidth performance

A quasi-octave bandwidth arbitrary-angle compact waveguide twist using a single matching step is presented. The proposed twist, based on a single intermediate ridge waveguide section that broadens its mono-mode operation, exhibits a similar wave impedance to the rectangular waveguide connected to its ports thus facilitating the reflections minimization in an extended frequency range. An exemplary 45° twist has been manufactured in the 10 GHz to 19.3 GHz frequency range (~64%) for demonstration purposes. The measured data are in concordance with those predicted by the simulation. This result represents, to the authors' knowledge, today's state-of-the-art in terms of compactness and bandwidth performance.This work was supported by the Spanish Ministry of Economy and Competitiveness (reference ESP2015-70646-C2-2-R) and FEDER funding from the EU

An enhanced algorithm for complex permittivity extraction at microwave frequencies

An efficient technique of complex permittivity extraction is employed to characterize low-loss conventional dielectric materials at microwave Ku-band. The computational approach eliminates mathematically the systematic errors of the experimental setup. This method needs two uncalibrated S-parameter measurements. The first is performed with a sample under test and the second is done with an empty rectangular waveguide. Three low-loss dielectric materials (Celotex, Plexiglas and Teflon) are characterized to validate experimentally the extraction method over the Ku-band frequencies [12-18] GHz. The average relative errors between the calibrated and uncalibrated results are then calculated and compared. The proposed method has been improved using the mobile average to the experimental results obtained from the uncalibrated measurements, therefore, the stability is then enhanced

Ultra-broadband high efficiency mode converter

In this paper we develop a small-sized mode converter with high performance, high conversion efficiency and instantaneous bandwidth as high as 55%. This mode converter transforms energy from the TM01 first high-order mode towards the fundamental TE11 circular waveguide mode. The proposed structure increases the free spurious operating bandwidth in comparison with the existing results in literature. An X/Ku-bands experiment prototype unit was designed, ensuring practical return losses better than 28 dB and insertion losses less than 0.1 dB (conversion efficiency > 98.8%) within the entire frequency bandwidth ranging from 9.25 GHz to 16.25 GHz. The presented architecture offers useful features such as very wide bandwidth, small size, easy achievement as well as excellent performance, which makes it very suitable for High-power microwave (HPM) sources that generate the TM01 circular waveguide mode. In these cases the TE11 mode is needed since it has a convergent radiation pattern able to drive conventional antennas. Moreover, this compact concept is fully scalable to any millimeter frequency band

Characterization of magneto-dielectric materials by a rectangular waveguide using the 2D-FDTD method

In this paper, a new measurement method is proposed to estimate simultaneously the complex permittivity and the complex permeability for a magneto-dielectric sample using a X-band rectangular waveguide WR90. The Sij-parameters at the reference planes in the rectangular waveguide loaded by a material sample are measured as a function of frequency using the E8634A Vector Network Analyzer. Also, by applying the two-dimensional finite difference in time domain (2D-FDTD), the expressions for these parameters as a function of complex permittivity and complex permeability are calculated. The Nelder-Mead algorithm is then used to estimate the complex permittivity and complex permeability by matching the measured and calculated Sij-parameters. This method has been validated by estimating, at the X-band, the complex permittivity and complex permeability of two materials such as FR4 Epoxy and Titanium Carbide powder (TiC)

An accurate method to estimate complex permittivity of dielectric materials at X-band frequencies

In this paper, a measurement method is presented to estimate the complex permittivity of a dielectric material even if its length is higher than the half wavelength in the waveguide. The Sij-parameters at reference planes in the rectangular waveguide loaded by material sample are measured by Network Analyzer. First of all, the expression of the complex permittivity as a function of Sij-parameters are calculated by applying the transmission lines theory. Further, a comparison of the estimated values of the complex permittivity obtained from the presented method and the Nicholson-Ross method is presented. Finally, the results for complex permittivity of Teflon, Nylon and Verde measured at the X-band frequencies are presented

Complex permittivity estimation for each layer in a bi-layer dielectric material at Ku-band frequencies

In this paper, a new measurement method is proposed to estimate the complex permittivity for each layer in a bi-layer dielectric material using a Ku-band rectangular waveguide WR62. The Sij-parameters at the reference planes in the rectangular waveguide loaded by a bi-layer material sample are measured as a function of frequency using the E8634A Network Analyzer. Also, by applying the transmission lines theory, the expressions for these parameters as a function of complex permittivity of each layer are calculated. The Nelder-Mead algorithm is then used to estimate the complex permittivity of each layer by matching the measured and calculated the Sij-parameters. This method has been validated by estimating, at the Ku-band, the complex permittivity of each layer of three bi-layer dielectric materials. A comparison of estimated values of the complex permittivity obtained from bi-layer measurements and mono-layer measurements is presented

2D-FDTD method to estimate the complex permittivity of a multilayer dielectric materials at Ku-band frequencies

In this paper, a new measurement method is proposed to estimate the complex permittivity for each layer in a multi-layer dielectric material using a Ku-band rectangular waveguide WR62. The Sij-parameters at the reference planes in the rectangular waveguide loaded by a multi-layer material sample are measured as a function of frequency using the E8634A Network Analyzer. Also, by applying the two dimensional finite difference in time domain (2D-FDTD), the expressions for these parameters as a function of complex permittivity of each layer are calculated. The Nelder-Mead algorithm is then used to estimate the complex permittivity of each layer by matching the measured and calculated Sij-parameters. This method has been validated by estimating, at the Ku-band, the complex permittivity of each layer of three bi-layer and one tri-layer dielectric materials. A comparison of estimated values of the complex permittivity obtained from multi-layer measurements and mono-layer measurements is presented

A dual band orthomode transducer in K/Ka bands for satellite communications applications

This article presents the design, simulation and machining of a dual Orthomode Transducer for feeding antenna using waveguide technology. Linear orthogonal polarizations in common port are separated to single linear polarizations in other ports. This device is developed to work in K and Ka bands and could be exploited in satellite communications applications. Also, it is designed to provide good scattering parameters results experienced with simulation tools and real load laboratory measurement. The designed circuit exhibits important results with return losses less than 25 dB, insertion losses in theory of about 0.05 dB as well as a good isolation of 40 dB in both frequency bands of interest (19.4 GHz-21.8 GHz) and (27 GHz-32 GHz)

Characteristic planes of microstrip and unilateral finline tee-junctions

A unique set of reference planes which enters into the description of a three port E or H-plane tee-junction are its characteristics planes. These planes correspond to the positions of a short circuit at one typical port that will decouple a second port from one input port. The purpose of this paper is to establish these planes in the cases of microstrip and unilateral finline circuits. This is done in each case for a number of different geometries. The spacing between the first two characteristic planes across the junction is 360 deg. In the case of the H-plane tee junction, it is 180 deg in the case of the E-plane geometry.The authors would like to thank the Spanish Ministry of Science and Innovation (MICINN) by the financial support provided through project TEC2011-29126-C03-01 and CONSOLIDER-INGENIO 2010 CSD2008-00068