Earth observation missions rely on microwave and sub-terahertz radiometry for retrieving atmospheric parameters such as temperature, humidity, and cloud properties, with the 183- and 229-GHz spectral regions being particularly relevant. Local-oscillator (LO) generation at these frequencies requires low phase noise and high frequency stability while meeting stringent size, weight, and power (SWaP) constraints. Conventional architectures employ dielectric resonator oscillators followed by cascaded frequency-multiplication stages, requiring dedicated generation chains for different frequency bands and increasing hardware complexity. Furthermore, frequency multiplication degrades the phase noise of the generated signal. This work proposes and numerically investigates a reconfigurable self-oscillating microwave photonic architecture for LO generation in Earth observation receivers. Cascaded Mach-Zehnder and phase modulation within an optoelectronic feedback loop generate an optical frequency comb with enhanced higher-order components. A combination of optical filters is used to select the required comb line. First, a conventional bandpass filter with a bandwidth of approximately 10 GHz isolates the spectral region containing the desired component, after which a narrowband dual cavity Bragg grating ring resonator (BGRR) with a bandwidth of approximately 3 MHz provides the final line selection. The selected comb line is then combined with an optical reference derived from the same laser and photodetected to generate the desired millimeter-wave or sub-terahertz signal through optical heterodyning. Numerical simulations are presented for 183- and 229-GHz generation, demonstrating the ability of the same underlying architecture to address multiple LO frequencies by tuning the OEO electrical filter to the appropriate oscillation frequency and selecting the corresponding comb order.