My use case is a hobby greenhouse which I am trying to automate with a battery powered ESP32 microcontroller. Running a power or ethernet cable is not an option, so I am communicating via wi-fi. I have placed a Wi-Fi Access Point in the laundry which is 15m with line-of-sight to the greenhouse. Most of the time the Wi-Fi reception is OK.
To prolong battery life I am trying to reduce the power usage, and of the wi-fi connection in particular. Since the greenhouse ESP32 only has to communicate with the WAP, I assume that using a directional antenna at the greenhouse end should be more efficient than broadcasting an omni-directional signal from the greenhouse, and therefore take less electrical energy to achieve the same signal strength in the target direction.
Given the increasing number of ESP32 development boards (I canât speak for other brands) with LiPo and solar ports - making them ideal for remote IoT applications - I think that a relatively small, fairly directional antenna with u.FL connector would have a good market.
Core sell 3 PCB antennas with u.FL connectors plus several rod antennas (which require a SMA to u.FL adaptor which i am told can eliminate any benefit) - but very inconsistent specifications, and only a couple have a radiation pattern available. Only Directional Patch 2.4Ghz SMA Articulated Antenna (Seeed Studio) claims to be directional - but may be overkill for our purpose.
Does anyone else see a market for a relatively cheap, fairly directional antenna with u.FL connector and low electricity consumption ? I do understand there are trade-offs, so no one perfect product.
I think the reason that there are so few directional wifi antennas on the market these days is that most people are moving towards LoRa for these sorts of applications since itâs already designed for long range and low power.
But if WiFi is essential, no other unidirectional antenna is ever going to beat the pringles can antenna for price. Now that doesnât make the antenna use less power, but itâs a good way to drastically improve the efficiency of low power antennas.
The directional antenna will not affect the transmitted power at all. It will only utilise the same power more effectively. It has no control over the power supplied to it.
BUT, if you are able to do so you could reduce the power supplied accordingly so achieving your aim in extending battery life. Just how much would be debatable depending on other introduced losses, connector, cable etc.
Cheers Bob
This is a classic Efficiency vs. Convenience debate. interesting
A directional antenna doesnât âconsumeâ less power (itâs a passive component), but its High Gain allows the transmitter to lower its output power while still hitting the target. This is a game-changer for battery-powered IoT sensors in remote areas.
We donât see this in every home is simply because of multiple reaosns and one of those is the Alignment. Most users want a âset it and forget itâ experience, and directional beams require precise pointing. if a sensor or the gateway shifts an inch (depending on beamwidth), the connection drops. However, for fixed industrial setups or agricultural monitoring where devices never move, there is definitely a solid niche market for low-profile, high-gain directional patch antennas that can extend battery life from months to years (in ideal cases).
A directional antenna wonât significantly reduce the ESP32âs power draw, but it can improve link reliability, reducing the time the device spends retrying. For battery life, focus on TX power, duty cycle, and deep sleep. A small 2â5 dBi u.FL directional antenna is useful for a stable, fixed link.
Yes, there are a few key additions regarding efficiency and hardware:
1. Receive Side Efficiency
While a directional antenna focuses transmission power, it also amplifies incoming signals. If the ESP32 can âhearâ the Access Point better, it reduces packet errors and retransmissions. Spending less time actively listening for retries saves significant battery life.
2. The âSleepâ Factor
On an ESP32, the radio consumes power just by listening (Rx). A stronger link means the device can sleep more reliably and wake up less often to handle retries. The battery savings often come from increased sleep efficiency rather than just lower transmission wattage.
3. Cable Loss Reality
The hesitation regarding SMA-to-u.FL adapters is valid. At 2.4 GHz, cheap pigtails introduce high signal loss (attenuation). If the cable loss is greater than the antennaâs gain, the setup is useless. A viable market product needs a native u.FL connector or an exceptionally low-loss pigtail.
4. Why LoRa Wins
As noted, LoRa is superior for this because it handles low-power long-range natively. Wi-Fi has high protocol overhead; if the signal is weak, the Wi-Fi radio drains power rapidly shouting and retrying. However, if you need Wi-Fi bandwidth, a directional antenna is the best workaround.
The antenna canât actually âAmplifyâ anything. It is a passive thing. It just makes better use of what is available by âgathering inâ more of of what is around. It is said to have âGainâ over an isotropic dipole and this itself is a bit ambiguous as this canât exist in practice. I personally believe it is far more use th express this Gain in relation to an actual physical (ie; something tangible you can make) dipole. The difference is I think 2 point something db. Could look it up but am not going to. Just knowing about will do. Thus an antenna quoted as having a gain of say 12dbi will have a gain (compared to a ârealâ dipole of 9 to 10db (note NO âiâ). I have believed for a long time that is a marketing ploy as it makes a device look that couple of db better.
So in a way I suppose it could be regarded as âAmplifyingâ a signal.
An antenna will behave EXACTLY the same transmitting or receiving. Fact of life.
Cheers Bob
Here is a link explaining the difference in fairly simple terms without mentioning the actual difference. https://moonrakeronline.com/us/blog/what-is-antenna-gain-dbi-db
The couple of db difference is because the isotropic antenna is assumed to radiate in a spherical manner while a ârealâ dipole does not radiate off the ends and concentrates this energy in a carded pattern at right angles to its length. Thus the apparent couple of db over dbi
After reading this article myself I could be wrong about the marketing ploy.
But I still think that calculating using âdbdâ will produce closer âmeasuredâ results.
Found it
Conversion:
A dipole antenna (dBd) has about 2.15 dB more gain than an isotropic antenna, so 10 dBi = ~7.85 dBd.
Thanks for the technical correction, Bob. You are absolutely right.
Antennas are passive devices; they do not create or amplify energy. They only redirect itâconcentrating the radio frequency (RF) energy into a specific pattern rather than broadcasting it spherically. The âgainâ comes entirely from this efficiency of focusing the signal.
You are also correct about the distinction between dBi and dBd:
dBi (decibel-isotropic) compares the antenna to a theoretical spherical point source that doesnât exist in reality.
dBd (decibel-dipole) compares the antenna to a real dipole antenna.
Since a real dipole is already slightly directional compared to the theoretical isotropic sphere (concentrating energy at right angles to its length), it has a natural advantage of 2.15 dBi. Therefore, a marketing spec claiming â10 dBiâ is effectively â7.85 dBd.â While this might be technically accurate, using dBi often inflates the numbers for marketing purposes, making the performance seem higher than it would when compared against a tangible reference like a dipole.
So, in the context of the greenhouse project, the directional antenna isnât âamplifyingâ the signal in the sense of adding power, but it is effectively âgatheringâ more of the signal from the target direction, resulting in the same performance benefit.
In the real (practical) world this is the only way to actually âmeasureâ antenna gain. Unless of course you gan replicate this imaginary isotropic source. I canât think of a way to do that but I am reluctant to say it is not possible these days.
Cheers Bob
interesting
