Miniaturized dielectric radio frequency filter for 850 MHz band mobile radio

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Abstract
A newly designed 806 ∼ 947 MHz band RF filter has been developed for the vehicular communication radio. This newly developed filter features a simple structure of miniaturized size and light weight. The new waveguide which makes the basis of the resonator is constructed with a dielectric rod having a thin central conductor, inserted between two parallel plates. The principal modes of the electromagnetic field propagating along the waveguide are the quasi-TEM mode on the lower frequency side and the quasi-TM01mode on the higher frequency side of the mode coupling frequency. Two new coupling design methods are employed: spacing control and wire control. In the spacing control method, the required amount of coupling is obtained by slightly changing the spacing between adjacent resonators. The wire control method obtains the expected amount of coupling by changing the number of equi-distantly inserted thin wires and their positions. The lowest spurious spectrum is about 2.3 GHz. The unloaded Q (Qu) of the resonator is about 1600, and of the resonator having loop excitation, Qu is about 1000. The relative permittivity of the dielectric is 20.0 and tan δ is 1.1 × 10-4at 6 GHz.

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