Nihad Dib

Theoretical and experimental characterization of coplanar waveguide discontinuities for filter applications

A full-wave analysis of shielded coplanar waveguide (CPW) two-port discontinuities based on the solution of an appropriate surface integral equation in the space domain is presented. Frequency-dependent scattering parameters for open-end and short-end CPW stubs are computed using this method. The numerically derived results are compared with measurements performed in the frequency range 5-25 GHz and show very good agreement. From the scattering parameters, lumped-element equivalent circuits have been derived to model the discontinuities. The inductors and capacitors of these models have been represented by closed-form equations, as functions of the stub length, to compute the circuit element values for these discontinuities. >

Study of a novel planar transmission line

A new type of monolithic planar transmission line, the microshield line, is proposed. This line can operate without the need for via-holes or the use of air-bridges for ground equalization. Furthermore, it has shown the tendency to radiate less than the conventional microstrip or coplanar waveguide (CPW) and can provide a wide range of impedances due to the many available parameters for design. The space domain integral equation method is used to analyze four different discontinuities of the proposed type. A comparison to conventional CPW with respect to radiation shows very good performance.<<ETX>>

Characterization of high frequency interconnects using finite difference time domain and finite element methods

MIC and MMIC packages capable of good performance at frequencies as high as 60 GHz need to have small volume, low weight, microstrip and/or coplanar waveguide (CPW) compatibility and exhibit negligible electrical interference with the rest of the circuit. In order to acquire some of these characteristics, special provisions need to be made during circuit layout and design, resulting in high-density packages. The designed circuits have a large number of interconnects which are printed on electrically small surface areas and communicate through the substrate in a direct through-via fashion or electromagnetically through appropriately etched apertures. In a circuit environment of this complexity, parasitic effects such as radiation and cross talk are intensified, thus, making the vertical interconnection problem very critical. In this paper, transitions using through-substrate vias are considered and analyzed both in the time and frequency domains using the Finite Difference Time Domain (FDTD) technique and the Finite Element Method (FEM), respectively. The merits of each method in conjunction with accuracy, computational efficiency and versatility are discussed and results are compared showing excellent agreement. Specifically, a microstrip short-circuit, a microstrip ground pad, a CPW-to-microstrip through-via transition and a channelized CPW-to-microstrip transition are analyzed and their electrical performance is studied. >

A class of novel uniplanar series resonators and their implementation in original applications

A class of novel millimetric uniplanar series resonators are presented, which can be used in monolithic and hybrid uniplanar microwave integrated circuits (MICs). The proposed structures are able to demonstrate low radiation and compactness characteristics, which are attractive for passive and active monolithic and hybrid integrated circuits. A principle of achieving these high-quality circuits is described and also confirmed by experimental and theoretical results, which are in good agreement up to 50 GHz. To illustrate the features of the proposed series resonators and demonstrate their effectiveness, two classes of miniature coplanar waveguide (CPW) filters (namely, low-pass and bandpass) are designed using these resonators. The developed low-pass filter has some important advantages such as low insertion loss in passband, very wide stopband, high cutoff rates, small size, low number of elements, and an effective control of spurious signals. On the other hand, the newly developed bandpass filter provides an alternative, yet compact, structure to classical filters. Obviously, many other classes of filters or passive components can also be designed.

Application of Taguchi's Optimization Method and Self-Adaptive Differential Evolution to the Synthesis of Linear Antenna Arrays

In this paper, the problem of designing linear antenna arrays for speciflc radiation properties is dealt with. The design problem is modeled as a single optimization problem. The objectives of this work are to minimize the maximum side lobe level (SLL) and perform null steering for isotropic linear antenna arrays by controlling difierent parameters of the array elements (position, amplitude, and phase). The optimization is performed using two techniques: Taguchis optimization method and the self-adaptive difierential evolution (SADE) technique. The advantage of Taguchis optimization technique is the ability of solving problems with a high degree of complexity using a small number of experiments in the optimization process Taguchis method is easy to implement and converges to the desired goal quickly in comparison with gradient-based methods and particle swarm optimization (PSO) Results obtained using Taguchis method are in very good agreement with those obtained using the SADE technique.

New uniplanar transitions for circuit and antenna applications

New uniplanar microstrip-to-slotline, microstrip-to-coplanar strips (PS) and microstrip-to-coplanar waveguide (CPW) transitions for MIC/MMIC and slotline antennas for phased array applications are described. Such transitions are compact and suitable to be used in an open environment inside a package or a multichip module. The transitions share the concept of using a balun which consists of two microstrip lines connected to a slotline through a pair of coupled microstrips. In this paper, the transitions are studied theoretically using the Finite Difference Time Domain (FDTD) technique and measured experimentally using an HP8510C Network Analyzer. For a back-to-back microstrip-to-slotline transition, an insertion loss of less than 1.3 dB per transition is achieved over a 49% bandwidth with a minimum of 0.6 dB around the design frequency.

Theoretical modeling of cavity-backed patch antennas using a hybrid technique

A hybrid technique that combines the method of moments (MoM) and the finite element method (FEM) to analyze cavity-backed patch antennas is presented. This technique features the use of FEM in solving the electromagnetic field distribution in the cavity and the use of MoM in solving integral equations outside the cavity. The results of MoM and FEM are combined through the continuity conditions on the boundary of the cavity. Due to the flexibility of FEM, complex cavities filled with inhomogeneous media can be analyzed by this technique. The results obtained by this hybrid technique are compared to the finite difference time domain (FDTD) results and good agreement is found. >

Impedance calculation for the microshield line

The microshield line, a new type of monolithic planar transmission line, is investigated analytically, highlighting its features with respect to conventional planar lines. The characteristic impedance of the new line is obtained using two different techniques: the computationally intensive point matching method (PMM) and the analytical conformal mapping method (CMM). In the latter method, a CAD-oriented analytical expression, in terms of all finite line dimensions, is obtained using conformal mapping techniques. It is shown that the results of both methods agree very well, verifying both analyses. In addition, the effect of finite-extent ground planes on the characteristic impedance is demonstrated.<<ETX>>

Characterization of asymmetric coplanar waveguide discontinuities

A general technique to characterize asymmetric coplanar waveguide (CPW) discontinuities with airbridges where both the fundamental coplanar and slotline modes may be excited together is presented. First, the CPW discontinuity without airbridges is analyzed using the space-domain integral equation (SDIE) approach. Second, the parameters (phase, amplitude, and wavelength) of the coplanar and slotline modes are extracted from an amplitude modulated-like standing wave existing in the CPW feeding lines. Then a 2n*2n generalized scattering matrix of the n-port discontinuity without airbridges is derived which includes the occurring mode conversion. Finally, this generalized scattering matrix is reduced to an n*n matrix by enforcing suitable conditions at the ports which correspond to the excited slotline mode. For the purpose of illustration, the method is applied to a shielded asymmetric short-end CPW shunt stub, the scattering parameters of which are compared with those of a symmetric one. Experiments are performed on both discontinuities and the results are in good agreement with theoretical data. The advantages of using airbridges in CPW circuits as opposed to bond wires are also discussed. >

Modeling of coplanar stripline discontinuities

The paper presents a technique to obtain lumped equivalent circuit models for typical coplanar stripline (CPS) discontinuities such as an open circuit, a short circuit, and a series gap in one of the strip conductors and gives their element values as a function of the discontinuity physical dimensions for a specific substrate. The model element values are determined from the discontinuity scattering parameters which are de-embedded from the measured scattering parameters using a thru-reflect-line (TRL) algorithm. In addition, the resonant frequency of a spur-slot is presented as a function of the spur length. The experimental results are validated by data obtained using the finite-difference time-domain (FDTD) technique.