Abstract: A waveguide filter is provided which comprises a plurality of waveguide resonators arranged in series in the longitudinal direction of the filter with each contacting tightly with adjacent ones, each of the waveguide resonators being composed of a rectangular dielectric having a length and a permittivity complying with the center frequency of a bandpass filter, on the periphery of which a metal film is provided except on the portions of induction windows of its two sides mutually opposed in the longitudinal direction.

Abstract: A waveguide-microstrip line converter for mode conversion in transmitting signals from a waveguide to a microstrip line or in the reverse, which comprises a dielectric body, a probe formed integrally with and within the dielectric body, and a conductive layer formed over the surface of the dielectric body excluding a surface to be brought into contact with a waveguide and an area surrounding the connecting part of the probe. The conductive layer is formed over the entire surface of the dielectric body, and then part of the conductive layer is removed by etching to provide the uncoated surface to be brought into contact with the waveguide and the probe. Thus the probe is continuous with the conductive layer and is an integral part of the dielectric body, so that the performance of the probe is unaffected by vibration and the high frequency resistance across the short-circuit waveguide is reduced to reduce signal transmission loss.

Abstract: A waveguide filter comprises waveguides with length corresponding to the center frequency of a band pass filter, and shunt plates. Each shunt inductor plate has sufficient size to cover an opening of the wave guide and includes an induction window smaller than the opening, and each opening is opposed to each induction window. The waveguides and the shunt inductor plates are alternately arranged in close contact state, and the center frequency of the filter scarcely deviates.

Abstract: A waveguide-microstrip line coverter to be used in combination with a waveguide, for mode conversion in transmitting a signal from the waveguide to a microstrip line. A probe for receiving a signal transmitted through the waveguide is formed by forming a conductive layer over the inner surface of a hole formed in a cuboidal dielectric body and is connected directly to the microstrip line to avoid needless induction of inductance. Since the hole can be formed accurately in size and position in the cuboidal dielectric body and the probe is formed in the hole, the probe is formed accurately in size and position and is highly resistant to vibration.

Abstract: A waveguide filter for use in a communication system that treats microwaves or millimetric waves comprises waveguides of a U-shaped cross section and a support on which the waveguides are longitudinally connected in series. Two inductor plates bear on each of the waveguides to form a waveguide resonator. Each inductor plate has first and second planes meeting at right angles. Thus, each inductor plate assumes an L-shaped form. Each first plane covers the corresponding longitudinal U-shaped end of the waveguides. Each second plane covers half of the corresponding open bottom of the waveguides, and has a tongue formed by two notches. This tongue can be bent and inserted into the corresponding waveguide to adjust the center frequency of the passband of the bandpass filter formed by the waveguide filter.

Abstract: A microwave circuit apparatus is disclosed which includes at least one first microstrip line; at least one second microstrip line; at least one capacitor interposed between the first and second microstrip lines; and a functional element having a first electrode thereof connected high frequency-wise to the first microstrip line, and in which the second microstrip line is grounded with respect to a power source.

Abstract: A phase-locked loop oscillator circuit having a reference signal generator, a voltage-controlled oscillator and a phase comparator comprises a second phase comparator. The first phase comparator is supplied with an output of the reference signal generator whose frequency has been lowered and also an output of the voltage-controlled oscillator whose frequency has been lowered. The second phase comparator is supplied with a signal which has been derived from an intermediate position of a higher-frequency path extending from the reference signal generator to the first phase comparator and also a higher-frequency signal which has been derived from an intermediate position of a path extending from the voltage-controlled oscillator to the first phase comparator. Outputs of the first and second phase comparators are added and applied to the voltage-controlled oscillator to reduce residual FM noise.

Abstract: A high-frequency input circuit for two inputs has a pair of first and second pi variable attenuation circuits each composed of three P-I-N diodes, some of which are shared by both of the circuits. The P-I-N diodes serve as attenuator elements in the attenuation circuits and also as switching elements for switching between the first and second attenuation circuits.

Abstract: A double-balanced mixer circuit includes a diode ring, wherein each side of the diode ring is provided with a stripline to bypass high frequency signals.

Abstract: Disclosed is a phase locked loop (PLL) circuit adapted for use, for example, in TV tuners. The PLL circuit has a voltage-controlled type oscillator, program divider, a phase detector and a low-pass filter, as is the case of conventional PLL circuits, and in addition, includes means for making the phase of the variable signal input to the phase detector lag behind the phase of the reference signal when a program switch for determining the divisor number of the program divider and a power source switch are operated, or means are provided at the output side of the low-pass filter for preventing the oscillator from oscillating at a frequency higher than one octave above a preselected frequency. These means are each effective to avoid the locking of the PLL circuit at a frequency which is a multiple of the desired frequency, thereby to ensure a safe and stable operation of the circuit in which the PLL circuit is incorporated.