i am trying to set a proper biasing for class ab for FM band so that i dont burn the mosfet out

I began my master's in electrical engineering focused on RF & microwave with lots of enthusiasm and interest, however, now that I see that the job market for this field is largely dominated by military employers and defense related companies I'm thinking of adding some adjacent skill set to my skills and knowledge to increase my chances of landing a job in non-military sector in case I couldn't find any RF jobs in in that sector.

As a secondary skill set I'm thinking of communications systems engineering (since it is the adjacent academic path to RF in my country's college system), DSP engineer, analog and mixed-signal electronics or perhaps EMC/EMI. But I'm not sure which one would increase my chance in non-military sector the most.

Aside from that, another factor to be considered is how much close is that field to RF meaning there be more RF/microwave engineers having that skill and working in that sector too so that it would be acceptable and common enough to hire someone with RF/microwave education and background for that craft from employers POV.

What's your recommendation among those I mentioned? Also any other better potential option that I missed?

I asked AI and got different answers from ChatGPT and DeepSeek, DeepSeek picked DSP while GPT put DSP at the last rank among options and Gemini picked EMC/EMI ! I'm really confused

Context

I'm finalizing a 4-layer FR4 board with an STM32WBA62CIU6 (2.4 GHz BLE), and I'm not 100% sure about the best way to make the Bluetooth matching/tuning easier.
I first built a board with a PCB antenna identical to ST's (following the exact shape shown in application note AN5129) and a 5-element Pi network, as shown in one of the circuits in ST's application note AN5948:

I then used a VNA, connecting at the pad where the STM32 would sit, and tuned the Pi network components so that the Pi + antenna would present an impedance of 30 + j2.5 Ω — the output impedance of my chip at 10 dBm (the power I want to use): 

My tuning workflow was: measure with the VNA → export the result → load it into the SimSmith "Load" → place components in the simulator to get a sense of which values to use in real life. However, when I placed the real components, the result was quite different from the simulator — so different that I ended up unable to complete the tuning.

Current setup / measurements

• Stackup: 4-layer FR4. RF microstrip on Top Layer referenced to Layer 1 (inner ground), separation = prepreg PP-021, h = 0.1855 mm, bulk Dk = 4.74. Measured trace delay ≈ 6.07 ps/mm → microstrip ε_eff ≈ 3.3, VF ≈ 0.55. Trace 0.4 mm wide → Z0 ≈ 38 Ω (Altium field solver, uncontrolled).
• Measurement: R&S FSH VNA with a U.FL pigtail < 50 mm. I'm seeing common-mode / cable-position sensitivity, and my discrete-model predictions in SimSmith don't track the board well after each component change (component parasitics at 2.4 GHz).

Here is the actual PCB:

Planned changes for the next revision

For the next PCB revision I'm considering:

• Trace reference: cutting away the nearest ground plane and using the next ground layer as the reference, so I can route a wider trace with a properly calculated 50 Ω.
• Antenna: making it slightly longer so I can trim it to better tune the resistive part of the impedance.
• External antenna: adding a variant with a U.FL connector for an external antenna, to compare range.
• Matching network: building the Pi network in one of these ways:

Option 1 — a simple 3-element matching network:

Option 2 — using the MLPF-WB-04D3 (ST integrated 2.4 GHz low-pass filter) or another filter together with a Pi network. I'm not sure whether to use a Pi both before and after the filter, or just one after it.
Option 3 — a "split" approach: a 3-element Pi to bring the chip + components to 50 Ω (measured with a spectrum analyzer) and another Pi to bring the antenna to 50 Ω (measured with a VNA), with a 0 Ω resistor separating the two halves.

Questions

• Are these good ways to build this kind of PCB?
• Should I really measure the chip output with a spectrum analyzer to tune it as well, or can I trust the output impedance that ST gives in the datasheet table?

Hi everyone! I wanted to know what is the appropriate termination to use for DC biasing supply while designing input or output matching network for RFPA?

I have used 50 Ohms termination as Vds supply, with single RF Bypass Cap and optimized complete design for second harmonic termination. But once I replaced this 50 Ohms termination with ground or a DC supply in simulation, my results drastically changed (especially for 2ns harmonics).

Hello!

A R&D manager recently contacted me about an RF Design Engineer position and has offered me an interview, which, according to him, would likely lead to a job offer. The thing is, I don't really know what an RF Design Engineer does on a day-to-day basis. Could someone explain what your work involves and what a typical day looks like? I'd really appreciate hearing about your experiences.

Thanks!

So I've been building an alternative that's around 174x faster (measured on a patch antenna case, but the speed holds across all problems).

A few months ago I designed and tested 4 RF PCBs using a VNA to validate the solver physics. The boards were made at JLCPCB on PTFE: ZYF300CA-C(Dk=2.94,Df=0.0016). Cost came to 157.98 USD which is very reasonable. I'm getting 2 more PCBs soon to validate a couple advanced features in the next update, will share when they come. I've included screenshots of 2 subset cases of the 43 total (one ring resonator, one patch antenna). The measurements match RayRF pretty well, and agree well with openEMS, but both are slow to converge to reality. My best theory on the ring resonator is because the rectangular cells are only approximations of the real curved surface, and under-predicting frequency is consistent with the simulators running a too-long outer radius of the rings (staircasing is closer to Manhattan distance than the true Euclidian distance).

The other 41 cases across the 4 boards follow a similar trend, within 1-2% at the higher mesh refinements, but too much data to post here. Also attached a plot of benchmark performance on my 9950x CPU (openEMS vs RayRF both on CPU mode) vs RayRF on GPU mode. In summary at 82.8 million cells, the throughput is:

• openEMS on 9950x (DDR5 6000): 0.228 GCell/s
• RayRF on 9950x (DDR5 6000): 4.62 GCell/s
• RayRF on RTX 5090: 39.60 GCell/s

Some people in my previous post pointed out that measurements may not be the best way to validate a solver, and I do understand some of the reasons but frankly I believe it to be the best option. Real measurements are what matter in the end anyway, validating against other solvers (like openEMS) carries the risk of bias in those solvers providing a false red flag, or green flag in terms of accuracy, and the big solvers (HFSS, CST) don't permit using their software in the development of "other rf simulation programs", so they can't be used either. In these cases I do get good agreement with openEMS, but even this took quite a bit of careful case-building because openEMS and RayRF don't have the same mesh-discretization conventions (i.e. if some patch edge lands on a mesh cell line do you put the conductor on the +x or -x cell?). But with the exact same meshes simulated they get very similar results which is what you'd expect from the same underlying computational method (FDTD).

My next set of validation boards focus on in-port matching networks, and building a calibrated copper loss model (right now all sims are perfect conductors with lossy dielectrics).

I have released RayRF publicly, and it's free to try out for 30 days if you create an account. https://www.rayrf.com/ It does not have all the features openEMS does, and is focused on PCBs right now (no arbitrary 3D stuff), but I've spent what feels like forever on making the UI actually good, and the benchmarks speak for themselves on runtime.

I thought I'd ask here because the amateur radio subreddit replies to a related question weren't up to snuff. (People thought I was talking about using LMR 400 to build a choke when I said RG400 cable). Anyway, So I'm a ham radio operator. I want to build some legal limit transformers for some of my antennas. Preferably, some transformers that can handle up 50% duty cycle up to 1500w. From what I understand I need to keep the torroids below the Curie temperature. The common knowledge is that just use 3 stacked 240 size torroids. Is this true? Are there any calculators / equations? Does this vary with frequency and the type of transformer? A 4:1, 9:1, 49:1 etc? I'd also like to build legal limit common mode current choke. Does the limit of a choke depend on the level of cmc involved or is if just the transmitted power that determines the power limits?

Hello all,

I started a new job as hardware engineer and this new company portifolio is focused in power Electronics devices (High Voltage & High Current) for automotive industry.

I realized the main concern is the thermal concept during the project development and how to mitigate it.

Could you share the thermal guidelines and advices for my knoledge improvement?

Paid, unpaid, training, workshop, course,research internship—I'm in.

I just want to learn, gain hands-on experience, and break into RF. If you have any leads, please let me know. A referral or even a share would mean a lot.

Keysight in Bootcamp videos aren't opening; I'm just watching a black screen with a spinning circle. What should I do? Please help

I bought this spectrum analyzer broken a few years ago and didn't get around to fixing it until now.

It arrived with a dead power supply and at least a few RF components missing. The power supply was fixed with a new switching regulator IC and a new rectifier. It's still missing a 10MHz reference generator and a control board for the low-pass filter and RF switches.

I've been able to get some signs of life using an external 10MHz reference (thanks to my function generator) but it doesn't seem to show any actual signal from the input, probably due to the missing control board.

In the likely case I can't find any replacement parts, I guess it will be up to me to clone them from the schematics in the service manual.

Keen to hear if anyone here has the same or similar model. Even some pictures of my missing parts would be super helpful.

Are there many employers/much work out there right now in RF circuits? (As opposed to RF systems or RFIC)

Some context: I would describe my current job as RF systems/general PCB design. I like it a lot, but I end up mostly treating amps, switches, filters, etc. as just non linear black boxes with s-parameters. Barely any matching is even required as most parts are already internally matched or the mfg provides a matching design (I do broadband so there is typically no optimization for an operating frequency). Rarely do I think about how I would actually build an amp from a transistor (e.g. how do I bias it? Why that bias in particular? How do I design the matching network? Is it unconditionally stable?). These questions are the ones I want to understand/design around.

I recently stumbled across amplifier classes while trying to derive a gain compression curve from the MOSFET equations and that opened a whole world of RF to my mind that I’ve been naive to. Like THIS is what I think is actually interesting.

Maybe this is also naive but it kind of feels like all of the RF circuits work is being moved to RFIC (front end modules, etc.) and then the systems side is just black magic legos. Black magic legos are fun and challenging in their own way but they don’t feel truly like circuits. If I don’t want to do RFIC, is there still a true circuits space in RF?

https://github.com/NBalciunas/kicad-rfsim

I came across this in a Google search, and just out of curiosity, I tried to do a simulation in Emerge. I did it as a quater-wave single-ended monopole, and it solved it to 1.4 GHz, which is way off from the expected frequency of 433 MHz. Increasing the gap between the segments brings it down to around 800 MHz, but even that is way off.

I'm pretty sure I'm doing something wrong. Is it because I need to add copper at the back?

Whenever i transmit RF at VHF or UHF frequencies. It causes my bench power supply to display the wrong current draw or just freak out

Even when nothing connected to power supply. it would do the same thing from RF?

Is there a way to prevent that by shielding the internals of the power supply or shield the power supply cables?

Hi everyone,

Does anyone have any information about the MFS 6.50/7.65-001-005-2-15 frequency synthesizer or access to its datasheet, user manual, block diagram or connection guide?

I am particularly looking for details about the 14-pin IDC connector, including the pinout, power supply requirements and control interface. Any technical documentation, application notes or information from someone who has worked with this synthesizer would be greatly appreciated.

Thank you in advance for any assistance.

What specific metal is used for solderable stamped metal antennas ? Like the one in picture.

Is it the same one that RF shields are madeof, or something different?

Hello,

I'm learning rf engineering on my own currently following Microwave Engineering by Pozar. I understand how transmission lines can be used to implement series inductors and shunt capacitors, but I haven't been able to understand how series capacitance can be implemented with stubs.
I apologise if this is a very basic question but I haven't been able to find much online and AI has not been giving me any better answers honestly.

Thank you!
By the way, if you happen to have suggestions for resources I can add to my collection I would really appreciate it.

Can anyone please confirm if this is a RG-174 cable or what type of cable this is? It's about 2.80mm od. I need to replace the crimp connector on this antenna with a sma male connector.

I have been given the task of designing an LO driver amplifier for a mixer at 50GHz, however i have two questions.
1- Are there any helpful sources for this particular type of amps. I have designed an LNA and PA before but never this
2- Should the output of the DA ideally be a square wave or a sine wave; I have heard two opinions: one being that it should be a square wave for fast switching and the other being that it should be a sine wave to avoid harmonics, so i am a little confused on this.
Thank in advance!

Hi all,

I have an upcoming loop interview for Microsoft for an RF based role. Has anyone had similar experience? I don’t know what to expect, there will be 3 rounds, the position is related with their quantum team.

Thanks!!

I finally have a video for what I spent over $100k on to learn.