Forward and backward leaky wave radiation in split-ring-resonator-based metamaterials

The ability of planar left-handed metamaterials (LHMs) based on split-ring resonators (SRRs) to radiate backwards in a certain frequency range, as predicted by theory, is demonstrated. A comparison between an LHM and a negative permeability metamaterial in terms of the experimental backward and forward radiation cones (which are related to their dispersion diagrams) is carried out. The results of this work open the possibility to use SRRs as miniaturised and flexible radiating elements for antennas and arrays in wireless communication applications     

Ku-band high-power lowpass filter with spurious rejection

A Ku-band high-power lowpass filter with spurious passband suppression up to 40 GHz is proposed in rectangular waveguide technology. The new design consists of a conventional E-plane corrugated lowpass filter cascaded with a quasi-periodic structure tuned to reject the undesired spurious passbands. This new design technique allows the minimum gap of the original corrugated filter to be kept wide enough to permit high-power operation     

An Electronic UWB Continuously Tunable Time-Delay System With Nanosecond Delays

We propose and demonstrate an electronic system achieving continuously tunable time-delays with nanosecond-scale delay excursions for ultra-wideband signals. Our demonstration system yields an adjustable delay of up to 1.6 ns for input signals spanning 3 to 7 GHz. The key component is a dispersive length of microstrip line created by etching a chirped electromagnetic bandgap structure in the conducting strip.     

Bragg Reflectors and Resonators in Microstrip Technology Based on Electromagnetic Crystal Structures

Recently, new promising two-dimensional (2-D) Photonic Bandgap Structures (PBG), or more properly Electromagnetic Crystal Structures, for microstrip lines have been proposed. In this paper, we analyze these structures in a manner like a Bragg reflector in optical wavelengths. Joining two of such Bragg like reflectors by means of a conventional microstrip transmission line allows one to design Bragg Resonators. The 2-D periodic pattern of the electromagnetic crystal structure is implemented with circles etched in the ground plane of the microstrip line by means of a numerical milling machine. Simulations have been performed by using HP ^TM Momentum and MDS software, and in accordance with the measurements give, for the Electromagnetic Crystal Structures, new promising potential applications both in microwave and millimeter wave integrated circuits, and also in the experimentation of expensive short wavelength (including photonic) devices by using simpler and cheaper microwave down scaling.     

Design of Microwave Filters With Arbitrary Frequency Response Based on Digital Methods

This letter presents a novel general technique for the design of microwave filters with arbitrary frequency response. It is based on the translation of the microwave specifications to the digital domain, where the well known and readily available digital filter design techniques are applied. By means of these digital techniques, the method provides a straightforward procedure to calculate the poles and zeros corresponding to the analog frequency response that satisfies the target specifications. From the poles and zeros, the microwave filter can be readily obtained using conventional techniques. As an example to demonstrate the proposed technique, a filter with user-defined specifications over two independent passbands has been implemented and successfully tested in microstrip technology.     

A Series Solution for the Single-Mode Synthesis Problem Based on the Coupled-Mode Theory

In this paper, we present an exact analytical solution for the inverse scattering problem formulated by using the coupled-mode theory in the microwave range, assuming single-mode operation. The solution is a series that gives the required coupling coefficient for the microwave device as a function of the target frequency response. A clear physical meaning for the terms of the series is discussed, and several useful properties for the synthesis are given, thus providing a deep understanding of the synthesis mechanics. The method allows for the design of microwave devices with arbitrary frequency response only constrained by principles of causality, passivity, and stability. The resulting device is, in general, a nonuniform waveguide that features a continuously varying profile, e.g., a nonuniform microstrip line with continuously varying strip width. As an example of the potential of the synthesis method, a matched filter for ultra-wideband applications is finally designed in microstrip technology and successfully tested.     

Real-time spectrum analysis in microstrip technology

We report on a time-domain analog in microwave lines to the spatial Fraunhofer (far-field) diffraction in paraxial conditions. Microstrip lines are used to design filtering configurations acting as spectrum analyzers. They are based on linearly chirped distributed Bragg coupling between the fundamental microstrip mode and the same but counterpropagating mode. Linearly chirped continuous impedance modulation in a microstrip line with varying upper plane strip-width is shown to yield a mode-coupling location and group delay linearly distributed in frequency. Under the condition of a temporal equivalent to the spatial Fraunhofer inequality, the energy spectral density of the input signal is directly recoverable from the average output (reflected) power. It is only necessary to take into account a linear axis-change, given by the dispersion coefficient (group-delay slope) of the structure, from time to Fourier frequency. Both pulsed and nonpulsed RF signals are studied. Sequential time-gated segments of the input have to be processed in the nonpulsed case. The maximum frequency resolution achievable in this situation is discussed. The devices developed here could have important potential applications in the field of temporal signal processing, such as filtering using time-division techniques.     

Effective negative-/spl epsiv/ stopband microstrip lines based on complementary split ring resonators

In this letter a super-compact stopband microstrip structure is proposed. The frequency gap is produced by an array of complementary split ring resonators (CSRRs)-a concept proposed here for the first time-etched on the ground plane. This behavior is interpreted as due to the presence of a negative effective dielectric permittivity in the vicinity of resonance. The resulting device produces a deep rejection frequency band with sharp cutoff, and a pass band that exhibits very low losses and good matching. Due to the sub-lambda operation of CSRRs, the electrical size of the device is very small.     

Passive Microwave Planar Circuitsfor Arbitrary UWB Pulse Shaping

We propose and demonstrate a new technique for generating customized pulse-shapes intended for use in ultrawideband (UWB) applications. The technique employs tailored microstrip lines that have been designed using an exact analytical series solution of the synthesis problem derived from the coupled mode theory. This solution permits the synthesis of waveguides and transmission lines with arbitrary impulse responses limited only by the principles of causality, passivity and stability. Time-domain measurements are performed demonstrating the generation of two pulse-shapes using microstrip circuits and satisfying pre-established UWB mask requirements.     

New microstrip “Wiggly-Line” filters with spuriouspassband suppression

In this paper, we present a new parallel-coupled-line microstrip bandpass filter with suppressed spurious passband. Using a continuous perturbation of the width of the coupled lines following a sinusoidal law, the wave impedance is modulated so that the harmonic passband of the filter is rejected while the desired passband response is maintained virtually unaltered. This strip-width perturbation does not require the filter parameters to be recalculated and, this way, the classical design methodology for coupled-line microstrip filters can still be used. At the same time, the fabrication of the resulting filter layout does not involve more difficulties than those for typical coupled-line microstrip filters. To test this novel technique, 3rd-order Butterworth bandpass filters have been designed at 2.5 GHz, with a 10% fractional bandwidth and different values of the perturbation amplitude. It is shown that for a 47.5 % sinusoidal variation of the nominal strip width, a harmonic rejection of more than 40 dB is achieved in measurement while the passband at 2.5 GHz is almost unaltered