English (UK) 
简体中文 Hey, RF design partners, have you ever encountered such a situation - obviously the circuit board is beautifully drawn, but the signal is attenuated to dregs as soon as it is transmitted? Or the equipment does not move on the overheating strike? Hey, eighty percent of the transmission line is not selected! Today we are going to break up the RF industry, the three major bearers.Coaxial lines, waveguides, microstrip lines, make sure you read it and never step in the pit again!
🔍 I. First, understand the basics: what exactly is the transmission line working on?
To put it bluntly, transmission lines areSignal's delivery boy.The HF signal is delivered from point A to point B. But the "delivery method" varies a lot from one man to another. But the "delivery method" of the different guys can be very different:
- coaxLike a metal hose.The inner core signals, the outer layer acts as a shield.Suitable for small to medium power scenarios
- wave guide: Hollow metal tubes.Reflected signals from the pipe wallPowerful but bulky
- microstrip lineThe "copper strips" on the circuit boards.Running signals against the baseboards.The king of integration but afraid of heat
To give you a chestnut 🌰: the WiFi module in your mobile phone - themicrostrip lineworking in silence; and the radar station tower? That's got to bewave guideIt's only holding up!
🔧 Second, the top three players in the real world PK: Who's right for your field?
1. Coaxial lines: flexible and versatile
framework: Inner conductor + insulation + outer shielding, like a condom
vantage::
- Wide frequency coverage: DC to 110 GHz can be carried (high-end models)
- plug-and-play: SMA, N-type connectors are open at the first twist.
- high degree of shieldingThe outer skin is wrapped around it, and the interference goes away.
drawbacks:: - It gets hot when it's powerful.: skinning effect leading to high frequency loss spikes
- Too long and it fades.: 10 metres or more? The signal may drop by half!
Applicable Scenarios: Test instrument cables, car antennas, home TV signal cables (75Ω model)
📌Key parameters: Choose 50Ω or 75Ω?50ΩIt's an industry compromise (low loss + high power) and only 75Ω is used for TV lines!
2. Waveguide: high power muscle man
frameworkHollow metal rectangles/tubes in which signals "bounce".
vantage::
- power capacity crush: Carrying kilowatts with ease, coaxial cables that look like they're weeping
- Lowest wear and tear: Air as a medium, no waste of energy
- inherently anti-interference: Metal casing covers, zero signal leakage
drawbacks:: - Expensive and bulky.One pipe is worth ten wires. You need a crane to install it.
- frequency rigidity: Each size corresponds to a specific frequency band (e.g. BJ100 waveguide can only transmit from 8 to 12 GHz).
Applicable Scenarios: 5G base station millimetre wave, satellite communications, military radar
📌lesson learnt through blood and tears: A factory used coaxial cable to transmit radar signals, the result is that the power burned through the connector ... ... replaced with waveguide immediately stable as the old dog!
3. Microstrip lines: integration of the little ones
framework: Copper wires on PCB + dielectric substrate + ground plane
vantage::
- The cost is low.: engraved directly on the circuit board, saving material
- Ultra-thin volume: mobile phones, drones rely on it to save space
- Design Freedom: Serpentine alignment? Minute by minute!
drawbacks:: - Thermal pull crotch: When the substrate is hot, the signal shakes three times.
- Power bottoming outBeware of burnt copper!
Applicable Scenarios: Mobile phone antennas, Bluetooth modules, IoT sensors
📌Design Secrets: Substrate SelectionCeramic or RO4350BThe high-frequency loss is reduced by 30%!
📊 Third, a table to end choice difficulties!
| parameters | coax | wave guide | microstrip line |
|---|---|---|---|
| main attack frequency | DC~110GHz | 1GHz or more | <10GHz |
| power capacity | Medium (100 watt class) | High (kW) | Low (decawatt level) |
| dilapidation | Medium (high attenuation at high frequencies) | lower (one's head) | High (baseboard drag) |
| degree of integration | Difficult (to joint) | unlikely | Direct PCB |
| (manufacturing, production etc) costs | ￥￥ | ￥￥￥￥ | ￥ |
| Data sources: |
🛠️ IV. Selection mnemonics + guide to avoiding pitfalls
rhyme for remembering (arithmetic tables, character stroke order etc)::
📣"High-frequency high-power selection of waveguide, flexible wiring microstrip good, test wiring coaxial screw!"
Newbie must see to avoid the pitfalls::
- Don't let the signal get stuck in traffic.: Microstrip line too long? Add a relay amplifier!
- Impedance matching is the soul: Mixing 75Ω cables with a 50Ω system? Signal reflection until you cry
- Don't ignore the environment.: Outdoor Wire? Recognise it!PE sheath moisture resistantcoax
- Simulation first: Draw a model with HFSS/CST and see the loss impedance at a glance!
💡 And finally, the big truth.
Old bird who's been doing RF for ten years tells you.There is no such thing as the best transmission line, only the right application scenario.Think about it. Think about it. Stick a waveguide in a mobile phone? The board goes straight to bricks! A microstrip line for a radar? The signal will turn into a dud in a second...
Next time before you design, pat your head and ask three questions:
❓How far does it go?(Constant loss)
❓How much power?(Definition of materials)
❓How much money is there?(final programme)
Figure out these three things and pick a line? You can get it right with your eyes closed!
(Write up and call it a day! Feel useful? Collect and forward to ensure that you take three years less detours ~)
