Mehmet Abbak

MODIFIED DIRECTIONAL WIDE BAND PRINTED MONOPOLE ANTENNA FOR USE IN RADAR AND MICROWAVE IMAGING APPLICATIONS

This paper presents a modifled design of directional monopole antenna with parabolic-shaped ground plane. To increase the directivity, axis of parabola in the ground plane is rotated 45 degrees (in comparison with the previous antenna) to extend throughout the direction of the substrates diagonal. Consequently, vertex of the parabola is placed at the optimum point in the corner of the substrate. The aim of this attempt is to design an extended and symmetrical ground plane around the patch, with more clarity, to maximize its capability as a re∞ector. Directivity is further improved by inserting parabolic-shaped slots at the corners of the ground plane. Simulation and measurements show that the proposed antenna has stable directional radiation pattern and higher gain compared to the previous directional monopole antennas. Impedance bandwidth of the antenna covers the frequency range of 4{9GHz. Measured HPBW is among the degrees 54{22 between 4 and 9GHz. Gain and HPBW of the antenna are improved 1.3{3.1dB and 5{15 degrees, respectively among the bandwidth in comparison with previous antenna. Results conflrm the good characteristics of the antenna for use in microwave imaging, where high resolution is required.

Qualitative Microwave Imaging With Scattering Parameters Measurements

Microwave imaging (MWI) systems extensively employ vector network analyzers for microwave measurements due to their high availability and accuracy. This is in contrast to theoretical models, which are naturally formulated in terms of scattered electric field vectors. Accordingly, experimental verification of MWI methods requires an intermediate step where measured scattering parameters are converted to scattered electric fields. In parallel to recent research, which formulates the Born iterative method in terms of scattering parameters, we develop formulations of two closely related qualitative inverse scattering methods-the linear sampling method and the factorization method-directly in terms of scattering parameters to avoid the intermediate conversion step. To this aim, we introduce vector S-parameters and we extend the vector Greens function for S-parameters to the dyadic case. There are certain advantages of these formulations over their electric field counterparts. First of all, the resulting formulations inherently incorporate the antenna radiation characteristics. Moreover, they reduce the measurement time since they do not require any pre- or post-measurement process. We experimentally verified the presented novel formulations against multi-frequency measurements performed inside an anechoic chamber. Obtained results show that the proposed methodologies can accurately reconstruct the shape of the targets by directly exploiting multifrequency measurements in the imaging process.

Experimental Assessment of Linear Sampling and Factorization Methods for Microwave Imaging of Concealed Targets

Shape reconstruction methods are particularly well suited for imaging of concealed targets. Yet, these methods are rarely employed in real nondestructive testing applications, since they generally require the electrical parameters of outer object as a priori knowledge. In this regard, we propose an approach to relieve two well known shape reconstruction algorithms, which are the linear sampling and the factorization methods, from the requirement of the a priori knowledge on electrical parameters of the surrounding medium. The idea behind this paper is that if a measurement of the reference medium (a medium which can approximate the material, except the inclusion) can be supplied to these methods, reconstructions with very high qualities can be obtained even when there is no information about the electrical parameters of the surrounding medium. Taking the advantage of this idea, we consider that it is possible to use shape reconstruction methods in buried object detection. To this end, we perform several experiments inside an anechoic chamber to verify the approach against real measurements. Accuracy and stability of the obtained results show that both the linear sampling and the factorization methods can be quite useful for various buried obstacle imaging problems.

Compact slot type CPW-Fed ultra-wideband (UWB) antenna

A compact coplanar waveguide (CPW)-fed Ultra-wideband antenna is presented. The proposed antenna embody wide-slot with a fork feed with a modified CPW ground. By modifying the ground plane, lower cut-off frequency of the bandwidth is decreased and thus bandwidth of the antenna is increased. By decreasing the lower cut-off frequency, and keeping antenna size same, antenna becomes also more suitable to the microwave imaging applications due to better penetration depth. The antenna has a simple one-layer planar structure and occupies a compact size of 28×21 mm2, including the finite ground CPW feeding mechanism. Proposed antenna, which is printed on Taconic RF-35 substrate with a relative permittivity of 3.5, has a bandwidth from 2.54 GHz to 9.75 GHz, and has a stable omni directional pattern at y-z plane over the frequency band.

Experimental Microwave Imaging With a Novel Corrugated Vivaldi Antenna

In this communication, a novel corrugated Vivaldi antenna (CVA) is developed for microwave imaging (MWI) applications. In particular, different from the previous works, the lengths of the corrugations are independently optimized to reach the final design. It is shown that by letting more parameters to be optimized in the design process, we can obtain a more effective CVA, which has more suitable characteristics for MWI applications (i.e., higher gain, broader bandwidth) compared with the previous designs. Apart from that, the imaging performance of the proposed design is compared with a generic VA having the same size of the proposed antenna. As imaging algorithm, a recently introduced qualitative MWI technique, the scattering parameter-based linear sampling method (S-LSM), is employed. The similarity between exact shapes of the targets and the obtained qualitative results are compared with the help of the well-known Jaccard index. Experimental results show that the proposed CVA performs better than a generic VA in such real-world MWI problems.

A planar ultra-wideband monopole antenna with half-circular parasitic patches

A simple planar ultra-wideband (UWB) microstrip-fed antenna with defected ground structure and two parasitic patches is presented. Two symmetrical quarter-circle shaped segments are cut both on the each of lower edges of the radiating patch and on the each of upper edges of the ground plane. These segments provide a wider bandwidth than the ordinary rectangular antenna especially in the middle frequencies. By means of removing U-shaped slot in the radiating patch the radiation characteristics of the 7-10 GHz frequency range are improved. Two half-circle shaped parasitic patches are connected via a hole to the ground plane. These patches are added on both sides of the 50-Ω microstrip-fed line to achieve good radiation performance for frequencies higher than 10 GHz. The proposed antenna is simulated by ANSYSs HFSS program using finite element method (FEM). The simulation results show that 127% of the impedance bandwidth is between 3.1 and 13.8 GHz for 20log|S11|<;-10 dB. The simulated antenna is fabricated on FR4 substrate and measured.

A novel compact wideband directional monopole antenna for use in radar applications

A novel compact directional monopole antenna in microstrip technology is presented. Basic aim of this paper is to maintain a tradeoff between the size and directivity of the antenna for use in radar and microwave imaging systems. Dimensions of the antenna are considerably miniaturized in comparison with conventional directional antennas. The main effort is to convert an Omni-directional radiation pattern of a compact monopole antenna to the desired directional radiation pattern, by using a novel ground plane, and a parasitic element. The ground plane and parasitic element are accurately designed in a way that make the surface currents of radiating elements to move toward the desired direction, which increase the radiation density in the preferred direction and also decrease the radiation intensity in the opposite sides. Simulations confirm a good directional characteristic of the antenna at the frequencies between 5 and 9 GHz. Gain of the antenna is increased over 5 dBi at the desired frequencies. Also Half Power Beam Width (HPBW) of the antenna is significantly decreased. Return-loss bandwidth of the antenna covers the frequencies among 5-9 GHz. Measurements confirm the simulations and desired directional characteristic and return-loss bandwidth of the antenna. Miniaturized size and a good directional characteristic of the antenna make it possible to use it in the microwave imaging systems and radar applications.

Broad-band three layer suspended plate antenna

In this paper the results of a broadband three layer suspended plate patch antenna covering a frequency band from 1.575 GHz to 4.76 GHz is presented. Proposed suspended plate antenna consists of three layers. Three radiators connected by folded and tapered feeding strips. Antenna achieved a −10 dB impedance bandwidth in excess of 100.5% with an antenna size of 0.341λo × 0.341λo × 0.47λo at its centre frequency of 3.1675 GHz. Average gain of 5.77dB is obtained across this bandwidth.

Broadband antenna for GSM, UMTS and LTE Wi-Max applications

This paper la y outs the proposed novel broadb and suspended plat e antenna folded patch feed. It is appr opriate for distinctive applications which include GSM, U MTS, WLAN and LTE Wi-Max technologies. Simula tions are performed using a EM softw are package HF SS. Fr om the simulations of t he proposed ante nna, impe dance bandw idth of 65. 6 % obtaine d between the frequencies of 1.71GHz and 3.38GHz

An improved stopband and sharp roll off microstrip low pass filter with defected ground structures

In this paper a novel low pass filter (LPF) design procedure is proposed for electromagnetic bandgap based microstrip filters without using classical filter design approach. LPF is designed for ultra-wide stopband and sharp roll-off rate via proposed design procedure. It has been shown that finite periodic fan-shaped defected ground structures (FSDGSs) and double radial stubs (DRSs) yield broad stopband and very sharp transition band. The proposed LPF has −3 dB passband from dc to 1.49 GHz, and −20 dB broad stopband from 1.65 GHz up to 7.41 GHz. Full wave electromagnetic (EM) simulation of the proposed filter is achieved with ANSYSs High Frequency Structure Simulator (HFSS) and equivalent circuit (EC) model of the filter is proposed and verified via Applied Wave Research (AWR) software. To verify the simulations, filter is realized on ARLON AD1000 substrate, and measured with Agilent 5245A PNA-X Vector Network Analyzer. Measurement results of fabricated filter are in good agreement with EM and EC simulations.