A diversity combiner is provided for combining two received radio signals having the same frequency and modulation. For each of the radio signals (s, s') there is included a mixer (1, 1') with an associated voltage controlled local oscillator (2, 2') and a following intermediate frequency filter (3, 3') for generating an intermediate frequency signal (m,m') and a phase comparator (5, 5') for comparing the intermediate frequency signal with a reference signal (a) originating from a weighted aggregate (e) of the intermediate frequency signals (m, m). Each phase comparator (5, 5') sends a signal responsive to the phase difference and which controls the frequency of the local oscillator (2, 2'). The weights of the sub signals can be varied such that the quotient of the contribution of the sub-signals to the aggregate can be caused to correspond to an arbitrary power, which is greater than or equal to one, of a corresponding quotient before the addition. This is achieved by the aggregate being formed by a signal weighting and adding circuit (8), which includes four bipolar transistors, and which is controlled by two voltages (N, N') which are responsive to the logarithm of the amplitude of the intermediate frequency signals (m, m').
In the diversity receiver which switches between receiver branches to receive phase modulated signals, this invention can achieve a diversity effect with a circuit of simple construction which by switching between receiver branches based on relative modulation phase error, and can attain diversity effect not only against fading but also against any factor which might affect the transmission lines.
Two or more signal paths are provided for receiving a radio frequency signal. One or more signal paths include conventional bandpass filters for eliminating interference and noise signals. One or more remaining signal paths include reduced filtering devices for increasing the sensitivity of a radio frequency receiver to the desired signal. Each of the receiving paths is coupled to a respective radio frequency amplifier. Provided that each radio frequency amplifier has equivalent current-source output impedances, the output signals from each amplifier are added constructively if they are in-phase. If the output signals are out-of-phase, a phase inverter inverts the phase of one signal so that the signals may be added constructively. The combined signals of the two or more radio frequency amplifiers pass through various signal processing components associated with conventional superheterodyne receivers. A control unit produces gain variation signals for controlling the gain of each radio frequency amplifier. Accordingly, the control unit controls whether the desired signal is received from a first signal path, a second signal path, or as a weighted combination of two or more signal paths.
A radio receiver antenna system including an antenna arrangement (1) which provides two signals (v.sub.a, v.sub.b) respectively as are provided by two antennas having different reception characteristics, and circuitry (T1, T2, 35 to 47) for combining the signals so that the output (V.sub.0) is significant for all values of the relative phase of the two signals. A particular application is in vehicle radio receiver systems using the rear window heater as an antenna.
A radio module for a radio base station of a mobile radio system which transmits and receives radio signals from stationary or moving mobile radio stations over given frequencies. A module comprises an antenna part and a transceiver part of given mechanical construction. Each module of a base station transmits and receives over a given specific frequency which may be different when transmitting and receiving but which is not the same frequency as that used by any other module in the station. A radio base structure is comprised of a plurality of modules, each having its own specific or individual transmitting and receiving frequency and being provided with suppression means which prevent a module from disturbing neighboring modules. A radio base structure having diversity reception is also provided.
