In some embodiments, a single local oscillator 932 (of any suitable type) may be used to generate signals for mixing with signals obtained via receive antenna 122. In other embodiments, multiple oscillators may be used to generate such signals. For example, in some embodiments, including the embodiment illustrated in FIG. 9C, increased stability in the signal generated by local oscillator 932 may be obtained by coupling local oscillator 932 to a controlled local oscillator 931. Controlled local oscillator 931 may be an oven-controlled oscillator, a temperature-controlled oscillator, and/or any other suitable type of controlled oscillator. In such embodiments, local oscillator 932 may comprise a phase-locked loop having output of the controlled oscillator 931 as the reference signal such that the phases of signals produced by local oscillator 932 are synchronized with the phases of signals produced by controlled local oscillator 931. The frequency of signals produced by local oscillator 932 may be a multiple of the frequency of signals produced by controlled local oscillator 931.
In the illustrated embodiment of FIG. 9C, each of amplifiers 936, 940, 944, 946 may be of any suitable type and may be used to induce any suitable amount of gain to the input signals. Frequency multiplier 934 may be of any suitable type including any of the types described with reference to frequency multiplier 908 with reference to FIG. 9A. Each of filters 942 and 948 may be of any suitable type (e.g., high-pass, low-pass, and band-pass). Frequency mixer 945 may be of any suitable type and may be implemented using one or more non-linear elements such as by using one or more diodes.
