Application of Nonuniform Transmission Lines to Ultra Wideband Pulse Shaping

Abstract

The work presented in this letter demonstrates that nonuniform transmission lines (NUTLs) can be used for pulse shaping applications in ultra wideband pulsed systems and presents an approach to their design for this application. The pulsed waveforms generated are modified Hermite polynomials and encoded pulse trains thereof and are characterised by a broad bandwidth ranging from near DC to over 10 GHz and relatively long temporal duration in the region of nanoseconds. These pulses are more mathematically complex and at least three times higher bandwidth than previously has been reported in the literature. It is also believed to be the first time that modified Hermite polynomial pulses have been generated in practice. The NUTL design approach is verified by test structures fabricated on FR4 circuit board. The results demonstrate that NUTLs, which are completely passive structures, allow generation of complex pulse shapes in applications requiring fast, transient waveforms.

A Two-Step Perturbation Technique for Nonuniform Single and Differential Lines

“…NUTLs have been widely used in several microwave applications, such as filters [1], impedance transformers [2], directional couplers [3], and very large scale integration (VLSI) interconnections [4]. Also, they are applied for impedance matching [5] and ultra wideband pulse shaping [6]. Since skin, proximity, edge and roughness effects can lead to signal integrity problems at high frequencies [7], transmission lines with (undesirable) nonuniformities must be accurately modeled at the early stage of the design process.…”

Miniaturization of nonuniform transmission lines for ultra-wideband pulse shaping

“…The sampling time of the pulse is 8.3 ps. According to the new design methodology the velocity of propagation in each section of the line will be calculated where as the velocity assumes as constant for all sections of NUTL in the state of art literature [3]. The one directional propagation delay of each section of the line will be half of the sampling time and in this case which is 4.15 ps.…”

“…Apart from the NUTLs traditional applications their use was recently proposed for an ultra-wide band (UWB) pulse shaping [3]. Ultra-wide band (UWB) systems use pulses with broad bandwidth and complex shapes that are difficult to generate with other, more traditional methods.…”

“…Although, NUTLs are very flexible devices for UWB pulse shaping, they tend to be big in size; therefore not suitable for compact systems. Spiral shaped NUTLs for size reduction were reported in [3].…”

“…However, he used it for to generate low bandwidth chirped waveforms and which is not suitable for UWB communication applications. Additionally, to the use of the different substrates a section dependent step size is used to design NUTL, where the state of art literature [3] uses a fixed step size.…”