Microwave Part 1. Intro to Microwave Engineering | Transition from RF to mmWave & Applications.
The field of Radio Frequency (RF) and microwave engineering generally deals with the behavior of alternating current (AC) signals with frequencies ranging from 100 MHz to 1000 GHz.
RF frequencies typically span from Very High Frequency (VHF) (30–300 MHz) to Ultra-High Frequency (UHF) (300–3000 MHz), while the term microwave usually refers to frequencies between 3 GHz and 300 GHz, corresponding to electrical wavelengths from λ = c/f = 10 cm down to λ = 1 mm, respectively. Signals with wavelengths on the order of millimeters are often called millimeter waves.
Due to the high frequencies (short wavelengths), standard circuit theory often cannot be directly applied to solve microwave network problems. In a sense, standard circuit theory is an approximation—or a special case—of the broader theory of electromagnetics, as described by Maxwell’s equations. This is because the lumped circuit element approximations used in circuit theory may not hold true at high RF and microwave frequencies.
Microwave components often behave as distributed elements, where the phase of the voltage or current changes significantly over the physical extent of the device. This occurs because the device dimensions are on the order of the electrical wavelength. At much lower frequencies, the wavelength is large enough that phase variation across a component’s dimensions becomes negligible.
In RF and microwave engineering, one must often work with Maxwell’s equations and their solutions. The nature of these equations introduces mathematical complexity, as they involve vector differential or integral operations on vector field quantities—fields that are themselves functions of spatial coordinates.
Moving to microwave frequencies (typically 300 MHz to 300 GHz) offers several advantages in communication, radar and other applications. Here are the key reasons:
Higher Bandwidth & Data Rates
Microwave frequencies provide wider bandwidths than lower-frequency bands (such as HF, VHF,
or UHF).
This allows for faster data transmission, supporting high-speed internet, satellite communications, 5G and radar systems.
2. Less Interference & Congestion
Lower-frequency bands (e.g., radio waves) are crowded with AM/FM radio, TV broadcasts, and legacy systems.
Moving to microwaves reduces interference and allows more efficient spectrum utilization.
3. Smaller Antenna Size
Antenna size is inversely proportional to frequency. Microwaves enable compact antennas, making them useful for mobile devices, satellites, and radar systems.
4. Line-of-Sight Communication
Microwaves travel in straight lines because:
Diffraction Effects are Reduced at Higher Frequencies
Diffraction is the bending of waves around obstacles. Lower-frequency signals diffract more easily, allowing them to bend around.
Higher frequencies have much shorter wavelengths, making them less prone to diffraction. As a result, they travel in more straight-line paths (line-of-sight propagation) and are blocked by obstacles.
Lower Refraction in the Atmosphere
Lower-frequency signals can refract (bend) due to interactions with the ionosphere, allowing them to "bounce" back to Earth for long-distance communication.
Higher frequencies (above ~30 MHz) typically penetrate the ionosphere rather than refracting, making them suitable for satellite communication but limiting their ability to follow Earth's curvature.
5. Better Directional Control
Microwaves can be focused into narrow beams using parabolic antennas, enabling point-to-point communication (e.g., satellite links, microwave relay stations).
This reduces signal leakage and improves security.
6. Improved Resolution in Radar & Imaging
Higher frequencies provide finer resolution in radar systems (used in aviation, weather monitoring, and military applications).
Microwave imaging (e.g., in medical diagnostics and security scanners) benefits from shorter wavelengths.
7. Support for Modern Technologies
5G Networks: Rely on mmWave (a subset of microwaves) for ultra-fast, low-latency communication.
Satellite & Space Communication: Microwaves (e.g., Ku-band, Ka-band) are essential for high-speed data links.
Wireless Backhaul: Used in cellular networks to connect towers without fiber optics.
Challenges of Microwave Frequencies
Higher Attenuation: Microwaves are more easily absorbed by rain, fog, and obstacles (requiring line-of-sight transmission).
Shorter Range: Compared to lower frequencies, microwaves travel shorter distances, necessitating repeaters or satellites.