Tommaso Turillo

A broadband microstrip to waveguide transition for FR4 multilayer PCBs up to 50 GHz.

A broadband microstrip-to-waveguide transition has been studied and tested for low-cost microwave circuits on FR4 multilayer boards having an internal thick metal plate (1). It is obtained, at first, milling a slot in a thick metal plate. Subsequently the PCB is built up, using standard PCB process, inserting the thick metal plate as the second layer. In this way the slot results filled with FR4 prepreg. A further simple milling process removes the lower layers up to the thick metal plate and creates a part of the waveguide transformer and an area for plate to metal housing connection. The transition integration in the multilayer is obtained just fixing the board on the metal housing which includes the rest of the transformer and the waveguide. Moreover, as the transition shows low sensitivity to manufacturing tolerances, the above process is characterised by high reliability and reproducibility.

Microstrip to waveguide 3dB power splitter/combiner on FR4 PCB up to 50 GHz

A two microstrips-to-waveguide transition has been studied and tested for low-cost microwave circuit applications on FR4 multilayer boards, which have an internal thick metal plate. In order to improve the transmitted power, its traditionally necessary to use a 3dB coupler and combine two MMIC devices. The implementation of the combiner on the substrate presents low performance due to the high loss factor of the material (i.e. tg/spl delta/FR4=0.025). To avoid this negative effect a novel circuit has been studied without any added insertion loss; the novelty of this approach is to sum the signal power inside the waveguide, in which two microstrip patch feeders, coming from the same side of the waveguide, are coupled through a slot. The slot works as transformer and it is implemented in the thick metal plate. The transition integration in the multilayer is obtained just screwing the board on the metal housing which includes the waveguide. Connecting properly the MMIC devices its possible to improve the waveguide-side return loss or to obtain a push-pull configuration. Moreover, as the transition shows low sensitivity to manufacturing tolerances, the above process is characterized by high reliability and reproducibility.

Microwave Dielectric Resonator Discriminator Oscillator

A new method (**) to improve the phase noise near the carrier of microwave frequency sources, particularly suitable for Low Capacity Digital Radio (LCDR) systems, is here presented. This is obtained including in a DRO a frequency discriminator, realized by means of the same oscillator cavity. The transmitted and reflected waves of the cavity are measured, combined and detected by a couple of diodes with low 1/f noise. These signals are compared in a differential amplifier that drives a varactor phase-shifter set between the active device and the cavity. In this way the reflection coefficient phase of the active device can be changed in order to correct its phase transients. As a result, lower the 1/f noise of the diodes with respect to the 1/f noise of the active device, greater the reduction of the oscillator phase noise. This technique applied to a microwave DRO may replace the synthesizer architecture achieving the same performance with lower circuit complexity, greater hardware compactness and lower cost.