Lk Products Oy

Remec Oy

Kimmo A Ervasti

Seppo Ojantakanen

Jorma Ohtonen

Jarmo Pyykko

Pertti Nissinen

The invention relates to a high-frequency filter comprising a block-like housing ( ) made of a dielectric material, the housing comprising ends ( ) and side surfaces ( ), the section between the ends being provided with a conductive plating ( ) acting as the filter's outer conductor ( ). In addition, the filter comprises at least two holes ( ) extending on the section between the ends of the block-like housing, the holes being plated with a conductive plating to provide two inner conductors ( ). The filter further comprises a connection base ( ) provided with a conductive pattern ( ), the block-like housing being arranged onto the base, and the conductive pattern ( ) of the filter comprising connecting areas ( ) for connecting the inner conductors ( ) onto the connection base ( ). According to the idea of the invention, the filter, which is connected to the conductive pattern ( ) of the connection base ( ), the connection base ( ) being outside the conductive plating ( ) acting as the filter's outer conductor ( ) and arranged on the surface of its block-like housing ( ), comprises one or more coupling members ( ) for setting capacitive couplings between the inner conductors.

Filter

A stepwise regulated filter includes a resonator structure and a coupling connected to the resonator structure. The resonating frequency of a transmission line (HX1) acting as a resonator may be switched between at least three values. The switching is implemented using coupling elements (SL1, SL4) which are in an electromagnetic coupling (M2, M3) with the resonator (HX1). The potentials of the coupling elements (SL1, SL4) are affected by PIN diodes (D1, D2) acting as switches. A RF power signal, which is coupled from the resonator (HX1) to the coupling elements (SL1, SL4), is applied to both terminals of at least one diode (D1) with the same phase and power. Then the voltage across the diode (D1) cannot, in the blocking state, rise to a level that would cause undesirable mixing results or would damage the diode (D1).

Stepwise regulated filter having a multiple-step switch

The invention relates to a resonator coupling and a radio frequency filter, which comprise a transmission line resonator (106), preferably a helix resonator, having an upper and lower end, a transmission line (108, SL3) for coupling to the resonator, and a tap point (121), at which the transmission line (108, SL3) and the transmission line resonator (106) are in direct contact with each other, whereby the transmission line (106) is divided at the tap point (121) into a lower and upper part, the lower part comprising a first part (SL1) and the upper part comprising a second part (SL2). A coupling element (SL4) is placed at the tap point (121) in parallel with the transmission line resonator (106), coupled (M1) electromagnetically to the transmission line resonator (106), thus improving the stop/pass ratio of the filter. In addition, a second transmission line (SL5) can be arranged in parallel with the coupling element, coupled (M2) to said coupling element (SL4), whereby said coupling (M2) compensates for the resonating frequency change of the helix resonator with respect to the temperature.

Filter with improved stop/pass ratio

The invention relates to a resonator structure and radio frequency filter in which the resonating frequency of a transmission line resonator can be switched in a stepwise manner between at least three values. The switching is implemented as follows: a regulating element including a switch that has at least three states is arranged in connection with the resonator. The three states of the switch correspond to different values of the specific impedance and, hence, the resonating frequency of the transmission line resonator. The regulating element is in accordance with a known arrangement: it may be e.g. a coupling element formed of a strip line on the surface of a low-loss substrate or ceramic, or a side circuit including a capacitive and inductive element, coupled to the resonator. In the former example the switch is open in its first state, in its second state it grounds one end of the coupling element directly and in its other states it grounds the end of the coupling element through differently dimensioned transmission lines. In the latter implementation the switch is open in its first state, in its second state it forms at the side circuit a capacitive-inductive coupling in series and in its third state it bypasses the inductive element.

Stepwise switched filter

An advantageous embodiment of the invention is the filter of the receiver branch of the duplex filter in a multi-channel radio transmitter/receiver having reception and transmission bands composed of plural radio-frequency channels. In the first state of the filter, when the radio transmitter/receiver is only receiving radio signals, the width of the pass band of the filter corresponds to said reception band. In the second state, in which the radio transmitter/receiver additionally transmits radio signals, the pass band of the filter is switched by current control to cover only part of the reception band. By constructing the filter in the manner proposed it is possible to use current control in the first resonator in the filter of the receiver branch. Because of its power consumption current control is otherwise unsuitable for use in e.g. the duplex filter of a portable radio-telephone.

Resonator filter with variable tuning

The present invention relates to a radio frequency filter the resonators (6,7) of which are made up of a wire wound into a cylindrical coil comprising a number of turns and of a surrounding casing (41). Finger-like projections (3) of an insulating plate (1) support the conical coils from the inside, and the coupling to the resonator is from a microstrip line (8), at a tap point (21), on the insulating plate. Each cylindrical coil has, adjoining the first turn, a straight portion (2) which is parallel to the axis of the cylindrical coil and extends towards the bottom plate (44) of the filter. On the inside surface of the bottom plate (44) there is a lead (51) one end (E) of which is short-circuited and the other end open, and the tip (12) of the straight portion (2) adjoining the cylindrical coil (6) is in contact with this lead (51). In this case, in spite of any rotation of the cylindrical coil relative to its own axis at the assembling stage of the filter, the distance of the tap point from the short-circuited end (E) of the lead (51) will remain unchanged, in which case the tap impedance will not change. The lead (51) is preferably a microstrip line on the surface of the insulating plate.

Helical resonator filter including short circuit stub tuning

In the mechanical supporting of the resonator coil it is known to use around the resonator coil an injection moulded plastic U-shaped binder ring, with the loops of the coil running through the arms in the binder ring. The resonator wire can also be wound around a plastic body. The methods of the prior art considerably weaken the Q value of the resonator. According to the invention it is possible to achieve good supporting, without a weakening of the Q value, in such a way that the resonator coil (1) is supported from at least one point by a supporting leg (6) of metal, which one end is fastened to the wire of the resonator coil (1) and the other end is fastened to an insulation piece (8) having low losses, which in turn is fastened to the installation plate.

Supporting of a helix resonator

The present invention relates specifically to the temperature compensation of a resonator in which a rod or a conductor wound in the form of a cylindrical coil serving as an inner conductor is enclosed within a metal cover and in which the open end of the rod or the coil is spaced a given distance from the cover, thus forming a loading capacitance. A change in the resonant frequency caused by thermal expansion can be compensated for in that at the open end of the inner conductor within the housing there is provided a compensation plate (5), the center part (12) of which is spaced at a distance (a) from the top surface (4) of the housing and preferably in parallel therewith and which has at least at two opposite edge parts (8, 9) been attached to the top surface (4). The thermal coefficient of expansion of the compensation plate (5) is less than the coefficient of thermal expansion of the top surface (4), whereby the center part of the compensation plate (5) together, in response to a rise in temperature of the resonator, is urged towards the top surface (4), thus reducing the loading capacitance.

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Oulunsalo, Finland

Kimmo A Ervasti