Microwave bandstop filter for an output multiplexer

Description of the offer:

The innovation relates to a bandstop filter for operating in the microwave region of the spectrum, and more particularly in bands from X to V band enabling signals to be transmitted at high RF power, in the order of kilowatt. Such a filter is intended particularly, but not exclusively, for application to output multiplexers of transmitters in telecommunications satellites. This innovation also relates to a filter assembly including such a bandstop filter, and to an output multiplexer of a microwave multichannel transmitter including such a filter assembly. Such device makes it possible to achieve effective filtering over a broad band at high frequencies even in high power applications, and it presents a structure that avoids multipaction effects thanks to large inner gaps compared to the wavelength. This technological proposal makes it possible to obtain attenuation of at least 25 decibels (dB) over a wide stop bandwidth having a width of several gigahertz and can suppress higher harmonics thanks to the inner structure of the bandstop filter. The filter is based on a special waveguide structure not using any dielectric material. It relies on the principle of Bragg reflection, which is already used in the field of microwaves for producing mode converters and filters, but has never been used in high power and broadband multimode filters, as in the present circumstances. This innovation provides a microwave bandstop filter comprising a waveguide segment of cross-section that presents longitudinal variation of the sinusoidal type that is modulated by an amplitude function that is continuous, the period of the longitudinal variation of sinusoidal type being the Bragg period for the fundamental guided mode at a centre frequency of the band to be stopped.

Innovations and advantages:

Advantageous characteristics of the innovation are:

• The waveguide segment may be a metal waveguide segment of rectangular cross-section, the longitudinal variation in the cross-section being obtained by symmetrical deformation of two opposite faces thereof, and preferably of the two opposite faces of the greatest length;
• The maximum amplitude of the variation of the cross-section may be such that the minimum spacing or gap between two opposite walls lies in the range 30% to 70%, and preferably in the range 40% to 60% of the mean gap;
• The waveguide segment may extend over a length lying in the range ten periods to 30 periods of longitudinal variation of sinusoidal type of the cross-section;
• The amplitude function may present a rising front and a falling front of slope that is sufficiently small for the coefficient of reflection at the input of waveguide section is less than or equal to -20 dB for frequencies lower than those of band that is to be stopped;
• The amplitude function may be selected from: a cosine-squared function, a cosine even-power function, a Gaussian function, and a Hamming, Kaiser-Muller, or Black window;
• The longitudinal variation of sinusoidal type in the cross-section of the waveguide segment may also present continuous phase modulation (or frequency modulation, since that constitutes a special case of phase modulation).

Domain of Application:

This technological innovation was conceived as an application for telecommunication satellites, but it may be applied as an electronic device.

• Satellite Microwave Communications
• Microwave and satellite components (including antennae and amplifiers)
• Other satellite/microwave Other Communications Related Communications services