Jaime Esteban

A dual frequency OMT in the Ku band for TT&C applications

A mixed characterisation by means of the generalized admittance matrix and the generalized scattering matrices, obtained with mode matching is proposed to design dual-band orthomode transducer (OMT) components. Accurate and efficient fullwave analysis software based on this procedure has been developed. A dual frequency OMT in the Ku band with high performance has been fully designed with the developed software. The good agreement between the numerical and experimental results validates the design process.

A Novel Planar Log-Periodic Array Based on the Wideband Complementary Strip-Slot Element

A novel microstrip log-periodic array based on the broadly-matched complementary strip-slot radiating element is proposed. The array consists of microstrip-fed log-periodically-scaled slots on the ground plane and their complementary stubs on the microstrip layer. Since the radiating element is not resonant, the analysis differs from the previously reported log-periodic arrays. Low scale factor (τ) with high radiation efficiency is possible, since the element radiation efficiency is not resonant and the relative spacing (σ) does not have to be selected for good matching, because the element is intrinsically matched. A design example with τ = 0.909, σ = 0.17 and 15 elements has been analyzed. The achieved bandwidth goes from 2.7 to 8.7 GHz, with a radiation efficiency and a gain of better than 85% and 5 dB, respectively. Moreover, the antenna can be terminated in an open circuit without affecting its performance. Simulated and experimental results show that the radiation pattern is stable over frequency. A method for computing the radiation pattern using equivalent circuits as well as results with a reflector plane for cancelling the beam in one half-space are also included. Due to the good performance, simplicity and low cost, this antenna can be suitable for broadband applications.

Design, implementation, and dosimetry analysis of an S‐band waveguide in vitro system for the exposure of cell culture samples to pulsed fields

The interaction between electromagnetic fields and biological media, particularly regarding very high power, short pulses as in radar signals, is not a fully understood phenomenon. In the past few years, many in vitro, cellular communications-oriented exposure studies have been carried out. This article presents a high-power waveguide exposure system capable of dealing with monochromatic, multicarrier or pulsed signals between 1.8 and 3.2 GHz (L- and S-band) with a pulse duration as low as 90 ns, minimum pulse repetition of 100 Hz, and maximum instantaneous power of 100 W. The setup is currently being used with a 2.2 GHz carrier modulated by 5 micros pulses with a 100 Hz repetition period and approximately 30 W of instantaneous power. After a worst-case temperature analysis, which does not account for conduction and convection thermal effects, the experiments exposure is considered sub-thermal. Evaluation of the results through the specific absorption rate distribution is not considered sufficient enough in these cases. An electromagnetic field distribution analysis is needed. For monochromatic signals, the representation of the modulus of the electric and magnetic field components is proposed as a suitable method of assessment.

Computer Aided Design of Non-Symmetric Six-Port Branch-Waveguide Directional Couplers

The Generalized Scattering Matrix of the Generalized 2-port discontinuity concept has been employed to develope a CAD package of non-symmetric six-port branch-waveguide couplers. The developed CAD has been succesfully applied to the design of HISPASATs Power Divider Networks. The proposed couplers yields a more compact design.

Planar multiband sequentially rotated array with polarisation agility based on the complementary strip-slot element

A novel planar travelling-wave ring array with polarisation agility is introduced. The array is built by applying the sequential rotation technique with the complementary strip-slot element. This element is a conventional microstrip series-fed slot with the special feature of very broad impedance bandwidth thanks to the strip superimposed into it on the microstrip layer. The feeding of the array elements and the required phase shift between them are provided by a ring-shaped microstrip line, which is terminated in two ports. Vertical linear polarisation, horizontal linear polarisation, right-handed circular polarisation and left-handed circular polarisation can be generated with this very simple planar structure, just by controlling the phase and amplitude of the excitation at the two ports. Moreover, thanks to the wide impedance bandwidth of the element, multiband behaviour is achievable. A design example that operates at three different bands (centred around 6, 9 and 12 GHz) is analysed, which presents very good matching ( dB), polarisation purity and broadside radiation pattern.

A self-diplexing dual-band planar array for GNSS applications

A planar dual-band sequentially-rotated array is proposed to cover the radionavigation bands at 1.19 and 1.57 GHz. The antenna consists of a two-port ring microstrip line that series feeds four radiating elements. The basic radiator is the so-called complementary strip-slot, a microstrip-fed slot that has its complementary stub superimposed to it on the microstrip layer, in order to cancel the slot resonant behaviour and provide ultra broad impedance matching. Thanks to this element feature, the antenna can cover the two bands and diplex them into the two ports without the need of additional passive or active components. The detailed design and results of the reflection coefficient, axial ratio and radiation patterns are provided, which confirm the good performance of this simple antenna.

Computation of the wire medium TEM mode by means of a Transverse Resonance Technique

In this contribution the TEM mode of wire media is obtained by means of a generalized Transverse Resonance Technique (TRT). The complete process is detailed since the TRT has not been previously applied to the characterization of bi-periodic TEM modes. The electrostatic potential distribution of a couple of examples is shown and some results for the characteristic impedance are presented.

Analysis of periodic structures by means of a generalized transverse resonance approach

The characterization of discontinuities in periodic structures with the generalized scattering matrix (GSM) is proposed. These GSMs are obtained by means of a field-matching method and used in combination with the generalized transverse resonance technique (TRT) to analyze periodic waveguides. The partitioning of the structure, the field expansions for TMz Bloch modes in each partition, and a new GSM cascading procedure are detailed. Three particular structures have been analyzed, two of which have been built and measured, to demonstrate the capabilities of the proposed approach. The measurements confirm the accuracy of this method. More complex cross-sections and even bi-periodic structures can be easily analyzed since the use of the generalized TRT in combination with the GSM concept gives rise to a great versatility.

Some considerations on lattice network-based lossless balanced Composite Right/Left-Handed transmission lines

Lattice network-based unit cells have been recently proposed for periodically loading conventional transmission lines as an alternative way to implement Composite Right/Left-Handed artificial transmission lines. In this contribution, some aspects of this new artificial transmission line are discussed. The availability of an equivalent simple lattice unit cell is discussed, and the capability to approximate by means of this simpler network, when the equivalence does not hold, is also presented.

Compact Orthomode Transducer Polarizer Based on a Tilted-Waveguide T-Junction

An alternative device to the well-known septum polarizer is proposed, which also provides the double function of an orthomode and a polarizer. It is based on a waveguide T-junction between a common dual-polarization waveguide and a tilted rectangular single-mode waveguide, and offers an intrinsically shorter geometry in the axial dimension, an advisable property when searching for compact antenna assemblies. The analysis of this new device is presented, along with the derivation and introduction of the S-parameters referred to the circularly polarized modes in the common waveguide. The working principle of the proposed T-junction is also explained in detail. A breadboard is designed, and its simulation and measurement results are presented. As a conclusion, the proposed device seems worthy of comparison in its electrical performances to the septum polarizer, showing some advantages in terms of geometrical dimensions and manufacturability.