Multi-heterodyne stage for a receiver or spectrum analyzer

#1. Field of the Invention

#The present invention relates to a multi-heterodyne stage for a receiver or spectrum analyzer.

#2. Description of the Prior Art

#The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

#FIG. 1 is a schematic illustration of a double heterodyne stage according to a preferred embodiment of the present invention;

#FIG. 2 is a schematic illustration of a first mixer according to a preferred embodiment of the present invention;

#FIG. 1 shows a circuit diagram of a double heterodyne stage as it can be used with a high frequency receiver or spectrum analyzer. After preselection in a low pass 1, an input signal RF that is, for example, to be received in a frequency range between 0 and 3 GHz is fed to a first mixer 2 and there is converted, with a heterodyne frequency 1. LO of a first local oscillator 12, which is, for example, adjustable between 3.5 and 6.5 GHz, into two equal-value, oppositely-phased intermediate-frequency signals IF+ and IF−, which are respectively, separately, amplified in intermediate-frequency to amplifiers 3 and 4 and fed, via adjustable phase shifters 5 and 6 and adjustable attenuator elements 7 and 8, as well as an intermediate-frequency filter 9, to a symmetrical input of a second mixer 10, in which they are converted, with a fixed intermediate frequency 2.L0 of 3 GHz, for example, of a second local oscillator 13, to a lower output intermediate frequency of 500 MHz, for example.

#FIGS. 2 and 3 depict examples of structures for the two mixers 2 and 10 as diode ring mixers. The first heterodyne frequency 1.LO and the input frequency RF are fed via a symmetrical transformer 14 across one diagonal of the diode ring, and resulting intermediate frequencies IF+ and IF− are directly tapped across the other diode ring diagonal. Since the voltages at this other diode ring diagonal are oppositely-phased, intermediate-frequency signals IF+ and IF− which are equal-value and oppositely-phased are thus produced and fed directly to inputs of amplifiers 3 and 4. The second mixer 10 is similarly constructed, with the equal-value, oppositely-phased intermediate-frequency signals IF+ and IF− coming from an output of the IF filter 9 being fed to a diagonal of a diode ring thereof and with the other diode diagonal being again connected to a transformer 15 thereof to which the second heterodyne frequency 2.L0 is asymmetrically fed, and from which the resulting output intermediate frequency IF is tapped.

#In the depicted embodiment the intermediate-frequency filter 9 is constructed, in the manner of FIG. 4, as a filter with a symmetrical input E and a symmetrical output A, so that only a single filter is required for both intermediate-frequency signals. Instead of such a single, symmetrical filter, of course, separate respective asymmetrical filters could be provided in each respective branch. All known filter circuits of this type are suited for symmetrical filters, and any customary asymmetrical bandpass filter can be altered through a symmetrical construction to be a symmetrical bandpass filter as in FIG. 4. In the example of FIG. 4, a customary, asymmetrical bandpass filter constructed of three magnetically coupled resonators is modified to an overall symmetrical filter by symmetrical construction of the input and output.