Below, you see the only schematic of a 6 pages-datasheet of an UHF RFID module (working frequency = 840...930 MHz):

Schematic of UHF RFID module

There are three questions:

  1. What is that ANT-MMCX? I search it in Google and I found two components named ANT-GPS-MMCX and ANT-GSMQB-MMCX-ND. Which one is appropriate for this module?
  2. The antenna is connected to the module with a 50Ω microstripe line. The question is "What is this microstripe line?". I must design and build it myself or there are created ones in the stores? What happens if I connect the antenna to the module with a simple wire?
  3. Will the above circuit works properly if I use a 5V mobile phone charger as the power supply (let assume it can provide the require current) and connect RXD and TXD to my computer's serial port and also put all the circuit on a simple bread board? or there are a lot of points in high frequency communication circuits that I must consider and apply to the board design that are not shown in the image? (If so, let me know the most important ones).
  • \$\begingroup\$ You can use any RF connector which suits you. I recommend using SMA, MMCX is microscopic, very hard to hand solder, and the mating cables can only be made by a machine. \$\endgroup\$
    – tomnexus
    Commented Jun 27, 2015 at 9:42

1 Answer 1


ANT-MMCX means Antenna MMCX connector. It depends on your antenna, but basically its just a matched connector.

A Microstrip line is a transmission lines structure which is easy to build on a pcb. It consists of a trace over a reference plane with a set width and distance to produce 50 ohm impedance. You can find plenty of calculators online to calculate the width and distance from the reference plane for you. If you connect the antenna with a simple wire you can expect an impedance mismatch and very bad performance to the point of being impossible to receive the signals. You cannot build this on a breadboard, you need a proper pcb.

I would suggest you buy a complete module, this way you could probably use it on a breadboard.


From looking at this datasheet it seems like this module is meant to be soldered on a pcb, how did you plan to use it on a breadboard ? you might be able to solder some sort of a 50ohm coax directly to the module and connect it to an antenna.

  • \$\begingroup\$ Thank you for your answer dear Mike. May I ask you to add "How I can design or simply select a proper antenna? should I build it myself or I can buy it?" \$\endgroup\$ Commented Jun 27, 2015 at 6:48
  • \$\begingroup\$ You cannot build this on a breadboard, you need a proper PCB. : Just because of the micro strip line? or there is another reason? \$\endgroup\$ Commented Jun 27, 2015 at 6:49
  • \$\begingroup\$ I am just checked two online tool [ here and here]. Based on the pictures that I see in those pages, I conclude that it is common that the designers of high frequency PCBs, make whole of one side of the PCB Grounded! Is my conclusion right? If so, am I must ground one side of my PCB grounded also? \$\endgroup\$ Commented Jun 27, 2015 at 6:59
  • \$\begingroup\$ And please correct me if I am wrong: I calculate an stripe-line based of my PCB characteristics using above online tools. The put that line on the PCB and connect one side of it to the RLM Module and connect the other side to the antenna. Can I use simple wires to make connection between the designed stripe line and the antenna? or the antenna must connect to the stripe line directly and without any further simple wire? \$\endgroup\$ Commented Jun 27, 2015 at 7:04
  • \$\begingroup\$ You should be able to find an UHF RFID antenna with a coax cable, you may be able to solder the cable directly to the module. You can use the module on a breadboard, but you will have to solder the decoupling capacitors directly on the module's pins. And you would have to solder a 50 ohm coax or some kind of a transmission line to connect the antenna. Yes, high speed pcb's will usually have a complete ground plane on one of the pcb rails. You can put a connector at the end of the transmission line to connect to the antenna (a 50ohm matched connector) \$\endgroup\$
    – Mike
    Commented Jun 27, 2015 at 8:04

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