1. Field of the Invention
The present invention relates to an microwave band or millimeter wave band oscillator having an oscillation circuit using a Gunn diode and other components, and to an output transmission line for outputting oscillation signals, and to radio equipment using this oscillator.
2. Description of the Related Art
Oscillators for use in the microwave band or millimeter wave band generally employ a negative resistance element such as a Gunn diode. Oscillators of this type intended for multiple oscillation (generation of harmonics) are disclosed in Japanese Examined Patent Application Publications 6-105851 and 6-22289.
Such an oscillation circuit intended for multiple oscillation can operate in, e.g., a millimetric band over 60 GHz, in which a Gunn diode cannot directly oscillate.
The oscillator disclosed in the above-mentioned Japanese Examined Patent Application Publication 6-105851 is characterized in that oscillation is obtained by cavity resonance using a waveguide, and in that the resonance frequency thereof is determined by a spatial volume. This raises problems, however. Since this oscillator has difficulty in adjusting frequency, it is unsuitable for mass production so as to incur a high cost, and it inevitably has a large size.
The oscillator disclosed in the above-mentioned Japanese Examined Patent Application Publication 6-22289, has a feature such that the occurrence of a fundamental wave is inhibited only by microstrip patterns. This creates a problem, however, that it is difficult to sufficiently suppress the occurrence of a fundamental wave, and that the microstrip patterns for inhibiting the fundamental waves attenuate even the signals of the higher harmonic to be used, resulting in an increased loss.
However, the present invention is able to solve the above-described problems and to provide an small-sized oscillator facilitating the adjustment of a resonance frequency, suitable for mass production and permitting a cost reduction, and to provide radio equipment using it.
The present invention is also able to provide an oscillator sufficiently suppressing the occurrence of a fundamental wave, and permitting a low loss, and to provide radio equipment using it.
In order to accomplish the above, the oscillator in accordance with the present invention may comprise an oscillation circuit formed on a dielectric substrate, and an output transmission line for transmitting the oscillation output signals of the oscillation circuit. In this oscillator, the output transmission line is a transmission line having cut-off characteristics, the output transmission line including a dielectric portion between two conductor plates substantially parallel to each other; and the cut-off frequency of the transmission line is determined so as to cut off the fundamental wave component, or the fundamental wave component and lower order harmonic components of an oscillation signal generated by the oscillation circuit, so that the higher harmonic components having higher frequencies than them are propagated. Thereby, a fundamental component and/or lower order harmonics are cut off, and only higher harmonics are outputted to the output transmission line.
Also, by forming the oscillation circuit on the dielectric substrate, the formation of a circuit pattern is facilitated, and a reduction in the size is achieved.
In the oscillator in accordance with the present invention, the output transmission line may be a dielectric line formed by disposing a dielectric strip between two, conductor plates substantially parallel to each other. Also, the output transmission line may be a planar dielectric line formed by providing conductor patterns constituting slots opposed to each other on the top and bottom surfaces of a dielectric plate.
In the oscillator in accordance with the present invention, the oscillation circuit may be formed by mounting a negative resistance element in the vicinity of the short circuit position of the line of which at least one end is opened, the line having a length of integral multiples of a half wavelength; and the line and the output transmission line are coupled.
In the oscillator in accordance with the present invention, stubs may be provided on a bias line supplying the bias voltage with respect to the negative resistance element so that the impedance when viewing the bias power source from the connection point of the negative resistance element is high at the frequency of the fundamental wave and the frequencies of the higher harmonics.
In the oscillator in accordance with the present invention, a variable reactance element may be connected to the line of the oscillator, and the line for supplying the control voltage to the variable reactance element is provided, which permits an adjustment or modulation of an oscillation frequency.
In the oscillator in accordance with the present invention, a weak-coupled terminal may be provided to the oscillating circuit, so that this terminal can monitor an oscillation signal.
In the oscillator in accordance with the present invention, the output transmission line may be a dielectric line formed by disposing a dielectric strip between two conductor plates substantially parallel to each other; a slot is formed in one of the conductor plates; the dielectric substrate is disposed on the outside of the one of the conductor plates; and the line of the oscillator and the dielectric line are coupled.
Also, in the oscillator in accordance with the present invention, the dielectric substrate may be accommodated in a case; the bias line comprises portions each having wider widths and portions each having narrower widths; and a spring for fixing the dielectric substrate at the inner surface of the case is provided in the vicinity of the narrower portion of the bias line.
The radio equipment in accordance with the present invention may be a transmitter/receiver such as millimeter wave radar, using an oscillator having any one of these structures.
The above and other features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings in which like references denote like elements and parts.