High-frequency tunable filter

Claim 1

A high frequency tunable filter comprising: a first oscillating circuit and a second oscillating circuit, said first oscillating circuit and said second oscillating circuit comprising voltage-controlled varicap diodes and being tunable thereby; wherein said first oscillating circuit and said second oscillating circuit are coupled together via pairs of coupling varicap diodes connected in series each pair of said coupling varicap diodes directly coupled to one another in a cathode-to-cathode arrangement such that voltage potentials measured at each of the cathodes of said pairs of coupling varicap diodes are identical, wherein said voltage-controlled varicap diodes by which said first oscillating circuit and said second oscillating circuit are tunable and said coupling varicap diodes are controlled by an identical control voltage to achieve the tuning of said filter to its working frequency and to achieve the critical coupling between said first oscillating circuit and said second oscillating circuit, and wherein a resultant coupling capacitance formed between said first oscillating circuit and said second oscillating circuit is approximately Q c times lower than a necessary resultant capacitance for the tuning of each of said first oscillating circuit and said second oscillating circuit, Q c being the coefficient of loaded Q of said filter.