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This paper presents the study of special nonlinear transmission lines (NLTLs) designed for the generation of millimeter waves with high efficiencies. In particular, so called bi-modal NLTLs are described which are characterized by a prescribed dispersion in order to establish phase matching condition for the frequencies under investigation. The underlying concept is demonstrated by second and third harmonic generation on NLTLs consisting of a periodic arrangement of suitable varactor diodes loading a coplanar waveguide.

In this paper a novel nonlinear MMIC structure based upon monostable resonant tunneling (RTDs) is studied. For the first time, it is shown that an input signal can be converted diodes into a se:t of output spikes to be used for GHz A/D conversion. 1 INTRODlJCTlON A huge amount of work has recently been dedicated to the study of resonant tunneling diodes (RTDs)i which can provide gain and can directly be used as the key components for oscillator circuits approaching the THz frequency range [I]. The underlying characteristic is a nonlinear N-shaped current voltage relationship even at millimetenvaves. The lack of these very interesting devices, however, is the low power conversion efficiency and the small output power levels [2]. Up to now the only solution to the latter problem which has become known is the use of a series i.e. (distributed connection of several RTDs using R4MIC technology [3,4]. Such a RTD nonlinear transmission line (NLTL) can further provide the basis of very interesting microwave signal processing devices as has been predicted by Crane already in 1962 [ 5 ] . In this paper, we discuss first the fundamental concept of nonlinear active wave propagation effects along monostable RTDNLTLs utilized to generate a set of spikes from anelectrical input. The idea of such a transmission line, where losses are exactly compensated by distributed amplification, dates back to the so called 'neuristor' [5] as a line-analog of axons in the nervous system, where the information of an input signal is converted into a number of output spikes, travelling in a stationary way for arbitrarily long distances. In a second step, we describe an electrical circuit, where the monostable 497