A computational scheme is proposed that can be applied to the analysis of cascaded waveguide discontinuities of alternating boundary-enlargement and boundary-reduction type. Based on the mode-matching technique, the proposed procedure makes use of the admittance matrix characterization of waveguide stubs. With respect to the conventional S-matrix formulation, it leads to a notable reduction of the computational effort, particularly for lossless structures. At the same time, the criterion for avoiding relative convergence problems can be satisfied. The procedure has been used to set up a very accurate and efficiency computer-aided design tool of branch guide couplers (BGCs). These are key elements of beam-forming networks for multicontoured beam satellite antennas and have to be designed with very high accuracy so as to eliminate the necessity for tuning the components realized. Design accuracies better than 0.1 dB in Ka-band are demonstrated by experimental result

A microwave oscillator topology based on CRLH (Composite Right-/Left-Handed) unit cells is\ud analyzed theoretically and experimentally tested. The oscillator consists of a CRLH based\ud distributed amplifier and a positive feedback realized by a simple transmission line. The oscillator\ud has two output ports, where the power levels are practically the same. For this topology, we have\ud found the oscillation condition and we demonstrate that each transistor gives the same contribution\ud to the power delivered at the two output ports, in this way, the output power is maximized. The\ud oscillator has been designed for a frequency of oscillation of 2.8 GHz and fabricated in hybrid\ud technology, by using InGaAs HEMTs and microstrip lines. The measured powers at the two output\ud ports are equal to 12.6 dBm and 10.4 dBm, the small difference between these values being given\ud by the insertion loss of the gate line. The experimental frequency of oscillation is 2.77 GHz, with a\ud difference of less than 1% in comparison with the expected value. Due to the frequency selectivity\ud of the CRLH unit cells, numerical simulations predict low phase noise for this configuration of\ud oscillator.

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This paper presents the fabrication processes for micromachined millimetre-wave devices, on two different types of semiconductor substrates. The first process uses micromachining on high-resistivity 100 oriented silicon. A three-layer dielectric membrane, with a total thickness of 1.5 µm is used as support for the millimetre-wave structures. This process was used for the manufacturing of two coupled line filters, with central operating frequencies of 38 and 77 GHz, respectively. The second process is based on GaAs micromachining. For the first time, a 2.2 µm thin GaAs/AlGaAs membrane, obtained by molecular beam epitaxy growth and micromachining of semi-insulating 100 GaAs, is used as a support for millimetre-wave filter structures. Cascaded coplanar waveguide open-end series stubs filter type structures, with central frequencies of 38 and 77 GHz, respectively, were designed and manufactured on a GaAs micromachined substrate. 'On wafer' measurements for the filter structures were performed. Losses of less than 1.5 dB at 38 GHz and less than 2 dB at 77 GHz have been obtained for both the silicon as well as for the GaAs-based micromachined filters.

In this paper, a circuit model to predict the microwave response of a shunt-connected capacitive microelectromechanical coplanar switch is proposed. The numerical values of the lumped elements composing the equivalent circuit are computed by means of a fully analytic approach. In particular, the contribution of resistive and inductive parasitic elements has been evaluated by using closed-form expressions. Configurations characterized by different technological solutions have been obtained and modeled. Simulations performed with the proposed approach correlate very well with actual measurements.