Matsushita Electric Industrial Co., Ltd.

Hiroshi Saka

Toshihide Tanaka

Tsuyoshi Mekata

Kazunao Urata

Yoshikazu Yoshimura

Shigeru Soga

Yasuhumi Shiomi

A QPSK modulation signal is processed with frequency conversion into an IF signal by a channel selection circuit, and then is converted into a baseband signal by a quadrature demodulator. The baseband signal has a wave thereof shaped by DTFs and then sent to a carrier recovery circuit. An offset frequency of the IF signal detected by an AFC circuit is compensated for by a baseband frequency converter including a complex multiplier and a DVCO. The frequency tracking circuit detects whether an operating frequency of another DVCO in the carrier recovery circuit goes beyond a range. By tracking an oscillation frequency of the DVCO in the baseband frequency converter so as not to go beyond the reference value, frequency deviation of the spectrum of signals which are input to the DTFs is controlled not to go beyond the reference value. By offsetting a frequency dividing ratio of a variable frequency divider of the channel selection circuit by an amount corresponding to the offset frequency of the IF signal detected by the frequency detector, the frequency deviation of the QPSK modulation signal can be compensated for whichever channel is selected.

Demodulation apparatus performing different frequency control functions

A channel selecting apparatus simultaneously selects both the modulation signals, which are simultaneously received at different channels where modulation signals having a continuous phase and digital modulation signals having a discontinuous phase are located. As both the modulation signals are propagated on the same transmission path or approximately the same inclination of transmission path, modulation signals existing on different channel frequencies suffer approximately similar frequency shift from the transmission path before being inputted to the channel selecting apparatus. Therefore, the frequency of the digitally modulated IF signal can be controlled in accordance with the frequency shift information related to an IF signal having a continuous phase and the frequency of the digitally modulated IF signal may be focused into the comparatively narrow frequency range around the synchronous pull-in frequency of the digital demodulating circuit and the modulation signal having a continuous phase may be focused into the comparatively narrow frequency range around the optimum input frequency of the demodulation circuit.

Channel selecting apparatus for simultaneous use with both

In a microwave band-pass filter provided with a main line having an input terminal and an output terminal on both ends thereof, first, second, third and fourth open-ended stubs having lengths L1, L2, L3 and L4 connected electrically in parallel to the main line at intervals L0, L0' L0', respectively. The lengths of two of the four open-ended stubs are selected to be substantially equal to a quarter of the wavelength of the first stop-band frequency signal on the band lower than the pass-band, and the lengths of the others thereof are selected to be substantially equal to a quarter of the wavelength of the second stop-band frequency signal on the band higher than the pass-band. In this case, the insertion loss thereof steeply increases on a boundary band from one stop-band to the pass-band. In particular, there can be obtained the microwave band-pass filter having a simpler structure, in which the insertion loss steeply increases on the band higher or lower than the pass-band, and the insertion loss on the band lower or higher than the pass-band is relatively large over a relatively wide band, respectively.

Microwave band-pass filter having frequency characteristic of insertion

In a directional coupler having four input/output terminals in a planar circuit using strip lines or microstrip lines, a quarter-wavelength line is connected between first and third terminals, and between second and fourth terminals, respectively, and furthermore between first and second terminals, and between third and fourth terminals, individually, a branch line is connected, having a length which is (2N+1)/4 wavelength, cascading (2N+1) pieces of quarter-wavelength lines (where N is a positive integer). These (2N+1) quarter-wavelength lines composing the branch lines are set so that lines of high characteristic impedance and lines of low characteristic impedance appear alternately. The (2N+1) quarter-wavelength lines in which the lines of high characteristic impedance and low characteristic impedance appear alternately function equivalently to (2N+1)/4 wavelength lines of a higher characteristic impedance, or equivalently to (2N+1)/4 wavelength lines of a lower characteristic impedance, thereby operating as a directional coupler having a small coupling coefficient or as a directional coupler of having a large coupling coefficient.

Directional coupler using a microstrip line

A microwave filter is disclosed in which open-ended lines are connected at three or four points of a main line having input and output terminals. The open-ended lines have a length about one fourth the wavelength of an image signal frequency thereby to produce a band-stop filter characteristic with an image frequency, all or parts of the open-ended lines constitute open-ended parallel-coupled lines arranged in parallel to the main line, and the intevals of connection of the open-ended lines with the main line are properly selected. The insertion loss of the filter within the pass band of a radio frequency signal is reduced and the filter attenuation within a stop band of an image signal is increased, thus providing a compact band-stop filter which has a steep rise characteristic.

Microwave filter

A feedback type microwave oscillator using a three-terminal active element employs both series feedback and parallel feedback and capacitance in its output circuit, thereby increasing the small signal negative resistance, and the output power and its resistance to impedance fluctuations of a load attached thereto.

Microwave oscillator having series and parallel feedback

A dielectric resonator microwave oscillator in which the gate of a FET is connected to a resonance circuit. An inductor is connected to the drain of the FET, and the output is taken from the source of the FET. This dielectric resonator microwave oscillator has enhanced negative resistance and positively starts the oscillation even when there is a low reflection coefficient of the resonance circuit. Using a circuit which consists of a capacitor and inductor between the source and the output terminal, a further increasing of negative resistance at the gate of the FET is obtained.

Dielectric resonator microwave oscillator having enhanced negative

In a waveguide-to-microstrip line coupling arrangement, a microstrip line is placed on an outer surface of a wall of a waveguide which is coupled with the microstrip line via a metallic post connected at its one end to a center strip conductor of the microstrip line and is inserted inside the waveguide via through-holes made in a ground plane of the microstrip line and in the wall of the waveguide where the diameter of the through-hole made in the ground plane is made smaller than that of the through-hole made in the wall of the waveguide. The waveguide has a short-circuited end and the metallic post is placed close to the short-circuited end. The coupling arrangement may be used in a microwave frequency converter having an microwave integrated circuit including a local oscillator and a mixer, where the MIC is located on an outer surface of a longitudinal wall extending from a short-circuited end to an open end.

Waveguide-to-microstrip line coupling arrangement and a frequency

A microwave integrated circuit comprises a shield case having a pair of opposed first and second end walls, a pair of side walls and top and bottom walls, and a dielectric substrate on the bottom wall. First and second interconnected integrated circuit portions are arranged on the substrate between the first and second end walls. An input strip line is arranged on the substrate, the strip line having one end coupled to the input of the first integrated circuit portion and the other end terminating at a position spaced from the first end wall by a distance approximately equal to an integral multiple of the half wavelength of a signal propagating in the shield case. An elongated coupling member is disposed in parallel with the first end wall, the coupling member extending from the other end of the input strip line to an external circuit.

Microwave integrated circuit immune to adverse shielding effects

An input matching circuit for a first stage amplifying element of a microwave preamplifier comprises at least one capacitive open-ended stub which is located in the vicinity of an input terminal of the first stage amplifying element so that the structure of the input matching circuit is simple. Input impedance of the first stage amplifying element is designed to assume a state of impedance matching for minimum noise, while the distance between the first stage amplifying element and a second stage amplifying element is appropriately determined with an input matching circuit of the second stage amplifying element being appropriately set. With this arrangement input VSWR of the preamplifier is set to a value smaller than an input VSWR of the first amplifying stage, and therefore it is possible to provide a microwave preamplifier which shows satisfactory input VSWR characteristic and noise figure such that the input VSWR of the preamplifier is improved when compared with the input VSWR exhibited on impedance matching for minimum noise while the noise figure is less deteriorated compared to the noise figure exhibited on impedance matching for minimum noise.

Microwave preamplifier

A mixer circuit in which resonance characteristics of a resonance circuit coupled to the RF input terminal are prevented from entering the mixer circuit, and in which negative resistance characteristics in the local oscillator circuit are prevented from causing spurious oscillations in the mixer circuit. The mixer circuit comprises a main strip line connecting an RF input terminal to an output terminal through a frequency mixing diode and a low pass filter. The IF signal is short circuited where the mixer diode is connected to the main strip line, by a high frequency short-circuiting technique. An IF interrupt circuit is provided in the main strip line near the RF input. A resistor ended low pass filter is connected between the RF terminal and the IF interruption circuit. The local oscillator includes a strip line having a length equal to one quarter of the wavelength of the spurious oscillation which is to be prevented.

Mixer circuit

In a mixer using a planar circuit such as a strip line or a microstrip line etc., an IF signal interruption circuit which passes an RF signal but exhibits an open-circuit impedance against an IF signal is provided in shunt with a main line on which the RF signal propagates toward a mixer diode, and a low-pass filter is connected in the vicinity of the IF signal interruption circuit in order to short-circuit a mount point of the diode for the IF signal by high frequency short-circuiting technique wherein an open-ended quarter-wavelength transmission line or a short-circuited half-wavelength transmission line is used, whereby low noise performance can be obtained over a wide frequency band even under such an operating condition that the IF signal is in the GHz band.

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Katano, Japan

Hiroshi Saka