el or dB) indicates the degradation of the signal as compared to an "ideal" receiver with the same gain/bandwidth characteristics. A lower number is better. The NF of a combined system can be calculated from the NF of each component through the Friis formula: where G represents the gain from each component in the system. Friis shows that the domi- nating factor is the NF of the first component in the system (NF1) associated with the first LNA in the receiver chain. 168 Open Radio Access Network (O-RAN) Systems Architecture and Design mmWave radio frequency module The high frequencies of the mmWave RF bands allow for more bandwidth to be assigned to communication and promises to achieve the throughput and latency targets of 5G standards. mmWave RF solutions require in-depth RF knowledge to design and build. For this reason, mmWave RF components are not only sold standalone, but (even more SO than in the <6 GHz band) integrated in complete RF subsystems by specialized companies targeting a specific band, output power and beamforming characteristics. The mmWave RF module integrates filters, modulator/de-modulator, PA, LNA, TDD switch, PLL, and other compo- nents into a single optimized Printed Circuit Board or even a single chip (Fig. 4-25). Note that in the low- to mid-end market, beamforming for mmWave is implemented in the analog and not the digital domain. This means that rather than having a single analog interface for each antenna element, there are two interfaces (horizontal and vertical polarization) that are shared across all antenna elements. Key specifications of the mmWave RF subsystem include: Effective Isotropic Radiated Power (EIRP) depicts the equivalent power if the RF subsystem would be radiating in all directions accounting for beamforming gains. High EIRP numbers are enabled by increasing the amount of PAs (and thus LNAs) in the system because an increased amount of PAs not only increases the absolute number of transmitted power, but also improves the beamforming gain-the Antenna Element (AE) cou