Jan Machac

Quasi-Elliptic Microstrip Low-Pass Filters Using an Interdigital DGS Slot

This letter introduces a DGS slot with an interdigital shape. The resonant frequency of the slot can be easily controlled by changing the length of the metal fingers, without changing the area taken by the structure. Using this slot, two quasi-elliptic low-pass filters were designed, fabricated and tested. The filters have a cut-off frequency of about 3 GHz.

Estimation of Wall Parameters From Time-Delay-Only Through-Wall Radar Measurements

Knowledge of the basic characteristics of the wall is especially important for the proper function of through-wall radars (TWR). In this paper, we introduce an estimation method that can provide the unknown wall parameters in real time. Our algorithm is based on a modified version of common midpoint processing, a technique adopted from geophysics. Using this method, it is possible to estimate the thickness and the permittivity of the wall from time-delay-only measurements performed at several different transceiver-receiver separations. Time-delay estimation (TDE) of echoes backscattered from the wall at each antenna separation is performed entirely in the frequency domain by a subspace super-resolution method. Our TDE approach is capable of resolving overlapping echoes reflected from the wall even in the case of only one snapshot of the measured data, suboptimal calibration possibilities, imperfect deconvolution of the measurement system, and limited radar bandwidth. The performance of our estimation algorithm is verified by simulations, and we also present the results for two real brick walls measured by using the time-domain technique. The estimated wall parameters can be utilized for improving the accuracy of real-time locating and tracking of moving humans by TWR.

A Simple Ultra-Wideband Suspended Stripline Bandpass Filter With Very Wide Stop-Band

This letter introduces a simple ultra-wideband suspended stripline filter with a pass-band from 3.1 to 10.6 GHz and a very wide stop-band up to more than 25 GHz. The filter is realized by capacitive coupling of a quasi-lumped low-pass filter to the I/O ports. Insertion loss in the pass-band is better than 0.5 dB. The filter has a length of 13.8 mm. Excellent agreement is achieved between measured and simulated results.

Realization of a microstrip triple-mode bandpass filter using a square-loop resonator

This paper introduces a microstrip triple-mode resonator that is realized by adding an additional path to an already reported microstrip square-loop dual-mode resonator. The additional path is realized by a meander half wavelength strip that is connected to two opposite corners of the square-loop resonator. A third order pseudo-elliptic bandpass filter utilizing this resonator is presented. Good agreement is achieved between the theoretical, simulated and measured results.

A Dual Band Leaky Wave Antenna on a CRLH Substrate Integrated Waveguide

This communication presents the results of an investigation of a new version of a leaky wave antenna designed on a CRLH substrate integrated waveguide. The antenna operates in two frequency bands and its main beam can be steered from backward to forward direction by changing the frequency. The antenna structure is planar and can be fabricated by a standard PCB technology, so it is suitable for mass production. An efficient method for determining the complex dispersion characteristic of periodic 1D structure is proposed.

A Magnetic Metamaterial Composed of Randomly Oriented SRRs

The concept, manufacture and testing of a volumetric isotropic magnetic metama- terial composed of randomly distributed broadside coupled split ring resonators is presented in this paper. An estimate of the isotropy based on the measured transmissions is made in terms of the arithmetic mean value and the standard deviation of the sample. We ofier conclusions and recommendations for the development of a genuine bulk isotropic medium of various densities and distributions of the particles, based on the 64 measured frequency responses of each sample.

MICROWAVE NOISE FIELD BEHAVES LIKE WHITE LIGHT

This paper presents various applications where wide-band signals are the dominant factor. The approaches applied here are based on the present knowledge in the fleld of white light theory (the THz band), the particle theory of light, and the wave theory of light. White light theory is used to investigate wide-band applications of non-coherent electromagnetic waves in the GHz range represented by noise. In addition, the theoretical approaches to the fleld of white light are conflrmed by various experiments with noise flelds applied in the GHz range. These experiments show clear advantages of measurements performed by means of noise flelds. The most important feature of these flelds is the absence of interference efiects.

Isotropic Epsilon-Negative Particles

This paper presents two particles with negative permittivity in some frequency band. The response of a single dipole loaded by an inductance is strongly anisotropic. The response of a spider dipole does not depend on the orientation of the electric field of a wave being incident perpendicular to the particle substrate. These two particles are used in designing an isotropic epsilon-negative metamaterial. A unit cell of the metamaterial consists of a cube bearing the proposed particles on its faces, located with specific orientations. The experiments showed that only the single inductively loaded dipole is suitable for manufacturing of an isotropic epsilon-negative metamaterial. The isotropy of the new particles was checked by measurements.

Upper cutoff frequency of the bound wave and new leaky wave on the slotline

This paper contributes to a more profound understanding of uniplanar circuit behaviour. A simple closed-form formula providing the upper cut-off frequency of the bound wave propagating over the slotline is presented. A new leaky wave which brings down this limit due to the overlapping of the bound- and leaky-mode regions is identified and reported. This wave can deteriorate circuit performance, especially in the mm-wave band. Conclusions made for the slotline hold generally for open printed-circuit lines.

On the design of waveguide-to-microstrip and waveguide-to-coplanar line transitions

New versions of the waveguide-to-microstrip and waveguide-to-coplanar line transitions are described and analyzed. The transitions differ from the standard ones by a probe in the shape of a rectangular patch. The structure is very simple, easily adjustable, it has a broad bandwidth, and there is no need to use an impedance transformer. These transitions have been analyzed by the method of minimal autonomous blocks and the integral equation method. The results obtained were compared with experimental data. An optimized structure has been designed by a simple optimization process using the integral equation method. Its transition band is flat with return losses better than ¿15dB nearly in the whole X-band.