HARMONIC PERFORMANCE OF SINGLE AND DUAL DEVICE GUNN OSCILLATOR MICROSTRIP ANTENNAS Christos Kalialakis, Peter Gardner, Peter S. Hall University of Birmingham School of Electronic and Electrical Engineering, Edgbaston, Birmingham, B15 2TT, United Kingdom Email: p.gardner@bham.ac.uk INTRODUCTION Integrated active antennas offer compact and multifunctional configurations. Arrays of compact antenna-circuit modules utilising quasi-optical power combining techniques avoid interconnect losses, offering an attractive solution for power generation[1]. Nonlinearities of active devices cause harmonic generation. The compact arrangement does not accommodate the use of filters. Consequently harmonics can become a problem when addressing system specifications. This paper focuses on the harmonic performance of single and dual device Gunn oscillator microstrip antennas. A great number of configurations have been shown in the literature [2]. The engineering process demands CAD (Computer Aided Design) and CAE (Computer Aided Engineering) tools, which are necessary to avoid costly trial and error approaches. The issues that need to be addressed for the successful analysis and design of integrated active antennas are nonlinearities from active devices, broadband operation and parasitic coupling. Here the lumped element FDTD (or extended) method is used. FDTD is a structure and geometry flexible method with the capability of including circuit elements [3]. The wealth of information produced by FDTD simulations can be very useful especially when novel combinations are sought [4]. GUNN DIODE MODELLING One port active elements like Gunn and IMPATT diodes exhibit negative resistance. The most common way of representing them is through equivalent circuits. There are different equivalent circuits even for the same device. A current source F(V) in parallel with a capacitor was used in [5]. More recently, a large signal equivalent circuit was implemented allowing for loss (Fig. 1a) in an attempt to model a single device waveguide oscillator [6] The nonlinear current source is represented as a function of the voltage involving cubic nonlinearities: 3 S 2 S 1 S V G V G ) V ( F ⋅ + ⋅ - = (1) In order to produce an FDTD expression, the discrete solution of the circuit of Fig. 1(a) is required. The numerical solution is given by ) E E ( z A ) V ( F A V A V n Z 1 n Z 3 n S 2 n S 1 1 n S + - - = + + ∆ β β β (2) where: ) F R 1 ( t RC 2 & + + = ∆ β (3) ) F R 1 ( t RC 2 A 1 & - - = ∆ (4) t R 2 A 2 ∆ = (5) t A 3 ∆ = (6) The corresponding FDTD solution at the Gunn diode cell reads