Harmonic-frequency communication system with improved diversity scheme

A harmonic-frequency communication system, comprising:

• a transmitting section including:
• modulation means for modulating a carrier serving as a fundamental frequency wave with data to be transmitted, to generate a modulated output, including at least the fundamental frequency wave and a double frequency wave included in harmonic frequency waves of the fundamental frequency;
• and
• transmitting antenna means for radiating electromagnetic waves into the air, the electromagnetic waves including the fundamental frequency wave and the double frequency wave included in the modulated output generated by the modulations means;
• and
• a receiving section including:
• receiving antenna means for receiving the electromagnetic waves including the fundamental frequency wave and the double frequency wave radiated from said transmitting antenna means;
• diversity means for processing the fundamental frequency wave and the double frequency wave included in the electromagnetic waves received by said receiving antenna means,
• said diversity means including:
• a first band-pass filter for filtering the fundamental frequency wave;
• a second band-pass filter for filtering the double frequency wave;
• first and second frequency converters for converting outputs from said first and second band-pass filters into outputs having the same frequency which is an intermediate frequency of the fundamental and double frequency waves;
• a level detector for detecting and comparing signal levels from the outputs or inputs of said first and second frequency converters to generate a control signal;
• and
• switching means for selecting any one output of outputs from said first and second frequency converters in accordance with the control signal from said level detector, and
• demodulation means for demodulating the output selected by said diversity means, thereby outputting data which is the same as the data to be transmitted.

A harmonic-frequency communication system, comprising:

• a transmitting section including:
• modulation means for modulating a carrier serving as a fundamental frequency wave with data to be transmitted, thereby to generate a modulated output including at least the fundamental frequency wave and a double frequency wave included in harmonic frequency waves of the fundamental frequency;
• and
• frequency converting means for converting the fundamental frequency wave and the double frequency wave included in the modulated output generated by said modulation means into first and second signals each having a predetermined frequency higher than that of the fundamental and double frequency waves;
• and
• transmitting antenna means for radiating electromagnetic waves into the air, the electromagnetic waves including the first and second signals converted by said frequency converting means;
• and
• a receiving section including:
• receiving antenna means for receiving the electromagnetic waves including the first and second signals radiated from said transmitting antenna means;
• diversity means for processing the first and second signals included in the electromagnetic waves received by said receiving antenna means,
• said diversity means including:
• a first band-pass filter for filtering the first signal;
• a second band-pass filter for filtering the second signal;
• first and second frequency converters for respectively converting outputs from said first and second band-pass filters into outputs having the same frequency, which is lower than that of the fundamental frequency wave;
• a level detector for detecting and comparing signal levels from the outputs or inputs of said first and second frequency converters to generate a control signal;
• and
• switching means for selecting any one output of outputs from said first and second frequency converters in accordance with the control signal from said level detector, and
• demodulation means for demodulating the output selected by said diversity means, thereby outputting data which is the same as the data to be transmitted.