I am looking at AP placement on my ceiling and trying to determine if it can reach a IoT device in my attic. I am looking at Ubiquiti U7 Pro XGS and found the AP spectrum pattern for this device.
From what I can gather, I should have pretty good coverage I place my wireless plug 9' horizontal and 3' vertical from the AP. The device uses the 2.4GHz band.

[](blob:https://www.reddit.com/f5c025c6-d241-4984-955f-3091d4f4a8f1)

Anyone good at reading spectrum maps? From what I can gather through google, I should have pretty good coverage if my IoT device is 9' horizontal and 3' vertical from the AP. At 9' out and 3' up, the device sits at a diagonal angle of approx 72 degrees off the center vertical axis. Near the 60° to 75° mark, the color is a solid, vibrant orange/red.

Just trying to confirm I am reading this correctly, as I am not an RF engineer and not really sure what the charts describe.

I have a 1:1 50-ohm balun, a 50-ohm source, and a complex load on the differential side of the balun. I’m trying to understand whether it makes a difference to perform the impedance matching on the source side before the balun or on the differential side after it.

If matching on the differential side is the better approach, how should I set up and test the matching network in Ansys Circuit?

I’m also confused about defining the differential port correctly. Should I set the differential reference impedance to 100 ohms and the common-mode reference impedance to 25 ohms, and why exactly are these values used? Are these the correct settings for my case, or does it depend on how the balun and differential load are modeled? I’d appreciate any practical guidance on how to set this up and verify the results.

Hello! I’m new to RF design and struggling with differential impedance matching for example for impedances attached in the picture. I’m unsure what impedance to use on the Smith chart and how to implement the resulting component values in my circuit. Any help or explanation would be greatly appreciated. Thanks!

I’ve been building this interactive simulator as a side project aimed to help students understand and visualize electromagnetic phenomena such as radiation, near field effects, polarization and wave interference.

You can:

• place many radiation sources and set their parameters (amplitude, phase and more)
• place perefect wire conductors
• observe the electric field, magnetic field or energy flow field
• zoom in and out and translate the canvas
• change the simulation resolution, frequency and propogation speed

and more!

I hope someone might find it useful and I’d love to hear what people think :)

Live:
https://www.antennasim.com/

GitHub:

https://github.com/rotemTsafrir/antenna_sim

Hi everyone,

I recently completed my Master's degree in Information and Communication Engineering at Huazhong University of Science and Technology, China.

My background is mainly in antenna design, electromagnetic simulation, and optimization.

My technical experience includes:

• EM Simulation: CST Studio Suite, Altair FEKO
• Optimization: Altair HyperStudy
• RF & Microwave: ADS, S-parameters, impedance matching, antenna radiation patterns, and VNA measurements
• Research Projects: Dual-layer metamaterial magnetic-induction antenna, 3.5 GHz dual-polarized antenna, and omnidirectional slot antenna

I also published a first-author paper in IEEE Antennas and Wireless Propagation Letters (AWPL) in 2026.

I'm currently looking for RA or engineering opportunities, especially in antenna design, RF/microwave engineering, electromagnetic simulation, or magnetic coupling.

I'm based in China and open to remote opportunities worldwide, as well as on-site opportunities where work authorization is possible.

If you know of any relevant research groups, companies, startups, or projects, I'd really appreciate your suggestions.

I'm happy to share my CV and publication details by DM.

Thanks!

Hi so for my academics, me and my team are doing a microstrip patch antenna for our project. we simulate it in CST using the student edition. There are few things im worried about before getting it fabricated as this is our first time, and we have only started using the software three months ago.

We were supposed to get a proper resonant impedance value for the S paramater dip at 3.45Ghz but the simulation is only showing us a dip around near 3.4Ghz, that would be a problem right? also we are worried about how and what to expect from a fabrication of the said antenna, would it work as expected in the expected frequency? what are the other nitty gritty details we r over looking? any sort of help i would appreciate. i feel like this post is really inadequate in terms of technicality so any questions about that also ill try my best to answer it properly in the comments. Thank you

Whats the best free alternative to CST, my uni doesnt have many licenses and the learning edition isnt enough for phased arrays which i want to simulate for a project

What’s new:

- New solver: EMerge (FEM) alongside openEMS (FDTD)
- RLC components: R, L and C parts are simulated as lumped elements
- Multiple RLC states, so you can simulate phase shifters and switches
- Plus coax feed ports, current animation, GIF export and many bug fixes

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

Hi,

I've messed about with directional antennas a little bit in the past, but never really got right down into the maths and physics of it before. I have a quad input wifi repeater, so I wanted to build a directional 2.4ghz antenna with 4 elements. Initially I was just going to have four separate ones side by side, but wondered if there was a way to incorporate them all into one. I started iterating on a design using AI, and quickly fell down a rabbit hole of changes and improvements. I ended up with three designs, and I'd love to get some human feedback on them. They seem viable to me, but I really don't know what I'm talking about or if I've been led astray.

The three designs I came up with are below:

#1: 4-port 2.4 GHz patch panel cut from one FR4 board, air-gap patches on feed barrels

Goal. Four independent 2.400–2.4835 GHz ports for 4×4 MIMO from one 300 × 300 mm single-sided FR4 board (Jaycar HP9510, 1.575 mm, 35 µm Cu). The backplate, lip strips and four patches are all cut from that board. The patches sit on an air gap, with polarisations rotated 90° each in a pinwheel and cavity-backed by a copper lip.

Build. Each patch is an FR4 plate cut to the patch size, copper side up. It rests on its feed barrel and two small PLA posts that sit on the field-null line. The feed is an RP-SMA crimp plug (Jaycar PP0590) mounted under the base board, its face recessed 1 mm into the board. Its rear barrel (4.0 OD / 2.0 ID × 6 mm) passes up through a drilled hole and is soldered to the backplate copper. A solid Cat5 core (0.51 mm) runs from the plug contact up the barrel and through the plate to the top copper.

Dimensions (mm)

Simulated performance (openEMS, build model incl. the plug, barrel, recess and base board; 1.5 mm max cell)

S-parameters patterns ECC

How it was simulated

• Solver: openEMS v0.37.0-rc2 (FDTD), CPU only. PML on all sides, 70 mm of clearance.
• Feed: the plug body is a 50 Ω PTFE coax driven by a coaxial port below the board. The model includes the rear-face annulus, the barrel bonded to the copper, the 0.51 mm core and the base-board FR4. |S| = √(P_ref/P_inc).
• Materials: FR4 εr 4.4, tanδ 0.02; PLA εr 2.7, tanδ 0.01.
• Far field: a frequency-domain NF2FF box, with its bottom face excluded because the feed coax crosses it. The coax's internal field had been counted as radiation, making the gain about 3 dB too low.

Caveats

• Front-to-back is not determined by this run, because of the excluded bottom face. The ideal-feed model gives the same directivity (9.5 dBi), so the forward pattern is trustworthy.
• Plate orientation is critical: the same plates mounted copper-down resonate at 2.6 GHz.
• RP-SMA needs an adapter for standard SMA test gear.

Questions

1. Feeding an air-gap patch with the connector barrel standing almost to the plate (a capacitive top gap through 1.575 mm of FR4): good practice, or asking for trouble?
2. Is soldering a crimp-plug barrel to the backplate copper a reasonable ground bond at 2.4 GHz?
3. Do −28 dB between opposite patches and −31 dB between adjacent patches look plausible for this cavity size?

#2: 4-port 2.4 GHz horn for MIMO: 3D-printed PLA, tape outside, SMA probes

Goal. A compact receive antenna for 2.400–2.4835 GHz Wi-Fi with four independent ports (4×4 MIMO in one enclosure). A square waveguide with a short stepped flare has one probe on each wall. Opposite probes share a polarisation axis and adjacent probes are orthogonal; a grounded centre post decouples them. The objective was the worst in-band |S| over self-match, adjacent coupling and opposite coupling.

Build. The horn is printed in PLA (2 mm walls) with aluminium tape on the outside of the shell, so the tape is the conductor and the PLA lines the inside. Each port is a 4-hole-flange SMA panel jack with its flange directly on the tape, carrying a 3 mm brass rod that starts 1 mm inside the wall.

Dimensions (mm, conductor = tape surface)

Simulated performance (openEMS, build model incl. PLA and SMA, div 40 ≈ λ/40)

S-parameters patterns ECC

How it was simulated

• Solver: openEMS v0.37.0-rc2 (FDTD), Python interface, CPU only.
• Domain: a free-standing horn with PML on all six sides and 40 mm of clearance. The far field comes from a frequency-domain NF2FF box.
• Feed: SMA as a 50 Ω PTFE coax (1.27 mm pin, 4.1 mm bore) through the wall, flange on the tape. A coaxial port 10–20 mm outside the flange runs into the PML. |S| = √(P_ref/P_inc).
• Mesh: λ/40 maximum cell, with fixed lines on every wall plane and step, and z lines through the probe rods. Zero-thickness tape skins sit on the mesh lines to the last bit, which proved essential: an unrounded coordinate silently removed the skins.
• Convergence: the ranking holds from div 28 to 64, but opposite coupling gets 0.5–1 dB worse from div 40 to 64. Treat the absolute isolation as roughly 0.5–1 dB optimistic.

Caveats

• The two efficiency estimates (NF2FF and 1 − Σ|S|²) differ by a few percent either way, so efficiency is quoted as ±0.05.
• The short flare (22 mm) was chosen by the optimiser: about 1 dB less gain than a 45 mm flare, in exchange for about 1 dB better worst-case coupling.
• The PLA's εr is assumed. The tape-outside build puts little field in the PLA, so the sensitivity is low.

Questions

1. Is ~−15 dB worst-case port-to-port isolation realistic for four probes in one square guide, and are there better decoupling tricks than a centre post (fins gave less than 0.5 dB in my runs)?
2. Do you see any problem with aluminium tape on the outside of a printed shell (seams, overlap bonding at the steps, oxide)?
3. Any experience with how far openEMS isolation numbers drift against measurement for this kind of structure?

#3: 2.4 GHz slotted-cavity antenna, 4 modules bonded in a pinwheel for MIMO

Goal. A high-gain 2.400–2.4835 GHz element with four modules (two along x, two along y) for 4×4 MIMO, loosely after Sun et al. (MOTL 2025, a 79 GHz slotted cavity). Each module is an all-metal rectangular cavity running a TE10 standing wave. Four longitudinal slots in the top wall sit at the field antinodes, with alternating offsets so they radiate in phase. A coax probe feeds each module from below.

Dimensions (mm)

Simulated performance (openEMS; module at λ/64, array at λ/48)

S11 module patterns array S-parameters

How it was simulated

• Solver: openEMS v0.37.0-rc2 (FDTD), CPU only. PEC walls, PML on all sides. Lumped 50 Ω port in a 1 mm gap at the probe base.
• Gain: directivity × (1 − |S11|²). The metal is treated as lossless, so ohmic loss isn't included.
• Mesh: the design was first optimised at div 24–40. That turned out to be a mesh artefact: at div ≤ 40 the 3 mm slotted top wall is about one cell thick, and the model shows a resonance at 2.44 GHz that converged meshes put at 2.28 GHz. The design was then re-optimised at div 48 and polished at div 64, and checks at div 80 agree.

Caveats

• The array S-parameters are at div 48, with the cavity length re-centred to 359.2 mm for that mesh. The simulated array is therefore 445 mm square; the build, at L = 355.2, is 439 mm.
• The bonded layout assumes a solid electrical bond between modules (screws every few cm, or soldered or welded seams), as modelled. Merely touching surfaces would make the coupling unpredictable.
• Efficiency excludes metal loss.

Questions

1. Layout trade-off: with the modules centred on the four sides of a 524 mm square, opposite-module coupling is −30.3 dB. The bonded pinwheel (439 mm) gives −26.3 dB, and opening the pinwheel to a 10 or 20 mm gap only recovers −28.2 / −28.8 dB. Adjacent modules stay at −39 dB or better throughout. For 4×4 MIMO Wi-Fi, is −26 dB between parallel modules comfortably enough, or would you take the bigger square?
2. Is a 4-slot, 355 mm cavity a sensible way to get about 12 dBi at 2.4 GHz, or is a short slotted waveguide array simply better?

Something worth paying attention to when measuring antennas on compact PCBs is how much the measurement setup itself can affect the result.

With an unbalanced feed or insufficient common-mode suppression, the coax shield can end up carrying current and effectively become part of the radiating structure. Move the cable, and the S11 trace may change even though nothing on the PCB has changed.

That makes it difficult to separate actual antenna detuning from changes introduced by the measurement setup.

calibrating the VNA properly is important, but it doesn't automatically eliminate this kind of coupling. The cable routing, feed arrangement and common-mode behavior still matter.

сurious how others approach this on small embedded devices. Do you usually check for cable sensitivity before adjusting the matching network?

Disclosure: I work in defense electronics.

Hey guys, I am an undergrad doing research on PLLs. It's an IC design project. The problem is that while it's not the most novel architecture like SSPLLs or full ADPLLs, I still want to take every block of it seriously since I understand how important foundational knowledge is. It's closer to a Fractional-N-PLL.

I've been trying to look for good resources to learn how to derive models in the s and possibly z domain but I can't find any good resources that show this. The problem with the textbooks I've seen like Gardner and Razavi is that they either overfit you on a specific block derivation, don't show the full process of how they went from start to finish or just don't go deep enough into modelling.

I've also heard control systems books can be too vague when it comes to connections to circuits. I honestly don't know what to do because I want to develop the toolset needed to model blocks at least at a foundational level without having to always rely on pre-defined models for blocks(like in Matlab/simulink) especially if I'm designing a block that isn't conventional.

I would love to hear from engineers who learnt how to do this. How did you learn how to do this? What resources would you recommend for learning such modelling? I don't mean deep stochastic math or any of that stuff, just the basics like learning what you need equations first in linear or nonlinear systems, how to analyze non-linear systems and how to linearize them when they can be linearized and any other thing like that.

It’s starting to clog up the feed between people advertising their AI applet miracle solution or whatever and bots sourcing text explaining why RF isn’t easy, maybe put up a catch-all mega thread for mitigation instead but something should happen.

This is a capture from a Keysight E5071C, sweeping 300 kHz to 8.5 GHz with a 30 kHz IFBW. Five traces: S11/S22 in SWR format, S21 log-mag at two different scales per division, and S21 group delay (Tr4). You can see clear passband tilt plus in-band ripple, and the group delay peaking near the band edges — a very typical picture for a wideband cavity/dielectric filter.

A question we get a lot: how do you do "reverse-slope equalization" (amplitude slope equalization) on the passband? Here's a breakdown of the approaches that are actually used in production, organized by where in the design flow they get applied.

I've started using AI to cut the grind in my RF work. I am designing an RF T/R module using COTS. I am finding parts that meet a spec using distributers online search or web search. This requires digging out the datasheet page behind each figure, re-running the same numbers after a change.

Some of it saves real time. Most LLMs currently not capable of excluding obsolete parts even with web search ON. I still have to check by hand in the datasheet, because it will confidently quote a figure I can't find in any datasheet. I have actually started developing my own MCPs to do a lot of the manual work. Hopefully open source it some day.

Curious how others here use it day to day:

- Which tasks do you hand to AI now?

- Which ones did you try and give up on?

- What's still fully manual that you wish wasn't? I can add to my MCPs.

I recently wanted some good project experience for my resume and really wanted to design a custom circuit board for RF signals. It seems to be a lot more complicated than PCB Design with a lot more factors to consider. Just wondering where to start and what are some good resources to follow. I'm also relatively new to PCB Design and just looking for some tips.