Amr M. E. Safwat

Tunable Bandstop Defected Ground Structure Resonator Using Reconfigurable Dumbbell-Shaped Coplanar Waveguide

A modification of the conventional dumbbell-shaped coplanar waveguide defected ground structure (DGS) is proposed. This modification permits the continuous tuning of the rejected frequencies by using reconfiguration technique and it allows the control of the DGS equivalent-circuit model. The modified DGS possesses two-dimensional symmetry, hence, it has been studied under different symmetry conditions and the corresponding equivalent-circuit model in each case has been developed. Based upon this study, a tunable bandstop DGS resonator is proposed. 19% tuning range centered at 3.7 and 7.4 GHz, respectively, is achieved. The equivalent-circuit model of the resonator is also developed. All proposed structures have been fabricated. Measurements as well as three-dimensional simulations are found to be in a very good agreement with theoretical predictions

Triple-Band Microstrip-Fed Monopole Antenna Loaded With CRLH Unit Cell

This letter presents a novel metamaterial-inspired planar monopole antenna. The proposed structure consists of a monopole loaded with a composite right/left-handed (CRLH) unit cell. It operates at two narrow bands, 0.925 and 1.227 GHz, and one wide band, 1.56-2.7 GHz, i.e., it covers several communication standards. The CRLH-loaded monopole occupies the same Chus sphere as a conventional monopole that operates at 2.4 GHz. The radiation patterns at the different operating frequencies are still quasi-omnidirectional. Measurements and EM simulations are in a good agreement with the theoretical predictions.

Novel transition between different configurations of planar transmission lines

New designs of coplanar waveguide (CPW)-microstrip, CPW-stripline, conductor backed CPW (CBCPW)-microstrip, and CBCPW-stripline transitions are presented. Simulation using the high frequency structures simulator (HFSS) shows that the return loss of the CPW-microstrip transition is less than -25 dB up to 11 GHz. Similarly is the CPW-stripline transition. In the case of two back to back CBCPW-stripline transitions, the return loss is less than -22 dB up to 9 GHz. Experimentally, the S/sub 11/ of two back to back CBCPW-microstrip transitions on an alumina substrate is less than -15 dB up to 25 GHz.

Microstrip-Fed Monopole Antennas Loaded With CRLH Unit Cells

The theory and implementation of a new family of monopole antennas loaded with composite right/left handed (CRLH) unit cells are presented. The proposed antennas have a number of narrow bands that is twice the number of unit cells and one wide band that is centered around the monopole original frequency. The new operating frequencies are below the original one and they are controlled by the unit cell dispersion relation. The proposed antennas occupy the same Chu sphere as the original monopole, all the operating frequencies have omni-directional radiation patterns, and matching is better than -10 dB. Three antennas are realized; the first is loaded with one distributed CRLH unit cell, the second is loaded with lumped components CRLH unit cell, and the third is loaded with two CRLH unit cells. All proposed antennas are fabricated and measured. Measurements and EM simulations confirm the proposed theory.

Microstrip Coupled Line Composite Right/Left-Handed Unit Cell

This letter presents a new composite right/left-handed (CRLH) unit cell, which takes advantage of the microstrip coupled line even and odd modes. The new cell does not require vias, it is patterned on a single metal layer, and it has a geometrical circuit model that simplifies the design flow. A novel CRLH transmission line is also proposed. It does not have a cutoff frequency, the operating bandwidth extends from dc to 4 GHz, and it is balanced at the first and second transition frequencies between right- and left-handed bands. The theoretical expectations have been confirmed by EM simulations and measurements.

On the Applications of the Coupled-Line Composite Right/Left-Handed Unit Cell

This paper presents two applications of the coupled-line composite right/left-handed (CL-CRLH) unit cell, compact-size rat-race hybrid, and arbitrary coupling directional coupler. Benefiting from the slow-wave effect present in both the right- and left-handed regions of the CL-CRLH unit cell, two compact-size rat-race hybrids were realized. 60% area reduction was achieved while preserving the conventional rat-race performance. The arbitrary coupling directional coupler, which operates in the stopband around the balance frequency, showed excellent in-band and out-of-band performance. To reduce its size, a slow-wave CL-CRLH unit cell was proposed. The proposed unit cell achieves a 38% size reduction. The rat-race hybrids were fabricated on microstrip technology, whereas the directional couplers were fabricated on stripline technology. Simplified circuit models for the unit cells were developed. Theoretical expectations were confirmed by electromagnetic simulations and measurements.

Sensitivity Analysis of Calibration Standards for SOLT and LRRM

We investigate the sensitivity of SOLT and LRRM on wafer calibrations to probe positioning. Calibration comparison derived error-bounds were calculated for data sets differing only by a single change in probe/standard overlap. The SOLT calibration was found to be significantly more sensitive to probe placement variations, consistent with theoretical predictions.

Resonant-Type Antennas Loaded With CRLH Unit Cell

The concept of loading monopole antennas with composite right/left-handed (CRLH) unit cell is extended to cover other types of resonant antennas, namely loop antennas and printed inverted-F antennas (printed IFAs). By adding one unit cell, these antennas achieve three operating bands while having their sizes unmodified. The new frequencies are lower than the unloaded antennas nominal frequency. The printed IFA is fabricated, and measurements are consistent with theoretical predictions.

High-Impedance Wire

This letter introduces the concept of high-impedance wire (HIW), proposes an implementation for it, and provides new insight to conventional slotted planar transmission lines. Theoretical expectations have been confirmed with simulations and measurements.

On the improvement of the performance of the optically controlled microwave switch

In this paper, a new design for the gap used as an optically controlled microwave switch is proposed. This new design is based on the use of a rib structure in the gap region. The proposed structure is studied using the finite-difference method (PDM). Obtained results show that for small gaplengths, the structure figure of merit, defined as the product of the ON/OFF ratio and the bandwidth, can be improved by about 38 dB*GHz.