Photonic generation of tunable microwave signal has gained the attention of many research communities. Various active components such as vertical-cavity surface-emitting laser diode, semiconductor optical amplifier, and Fabry-Perot laser diode have been used for generating microwave signals using different techniques including side mode injection, feedback injection, and frequency combs. In this paper, we propose and demonstrate a novel approach to generate millimeter wave, simultaneous microwave and millimeter wave, and microwave together with hopping of RF frequency using a single external beam. Furthermore, we demonstrate injecting multiple external beams in a spatial-mode Fabry-Perot laser diode (SMFP-LD) to generate simultaneous multiband signals with negative wavelength detuning. The generated signal ranges from microwave to terahertz. We inject four external beams in SMFP-LD to generate RF frequencies that lie in Ku-, K-, Ka-, V-bands and higher millimeter wave. The frequency of generated signals can be tuned from a few gigahertz to several terahertz. The effects of changing the dominant mode, injecting external beams to different side modes, wavelength and power stability of beating wavelengths, and harmonic generations are analyzed. The maximum linewidth of the generated RF signals with multiple input beams (up to 42.5 GHz) is found to be about 300 kHz.