MAX2235EUP RF Amplifier Input/Output Impedance for 50 Ohm Antenna Matching

Hi there. First time using this forum. I was working on a project that requires impedance matching and I'm going to match a 50ohms antenna to a RF amplifier MAX2235EUP. However, I'm not sure how can I get the impedance of the amplifier from the datasheet in order for me to design the matching circuit. Or I will need to measure it? It might be a stupid question but I'm not familiar with these so I'm here to learn. Thanks!

This device is designed for frequencies in the range of 800 MHz to 1 GHz. The data sheet (which I assume you have) is pretty typical for RF power amps.  The device is designed as is to have 50-ohm input and output impedance; this is explicit on the data sheet only insofar as the VSWR is specified as less than 1.5 in a 50-ohm system.  Your circuit should look very much like the one in the data sheet if you are expecting to use 50-ohm impedance for both input and output.  My assumption is that since you are using a power amp, then you will be transmitting to the antenna in question. Most commercial antennas (and also simple dipole or monopole designs) will have impedance close enough that no matching network should be needed.  I suggest a god source for ways to actually design matching networks when required would be the Radio Amateur's Handboook published by the ARRL. It includes lots of other useful information including many proven designs for anything radio. It's become a bit pricey but may be available at a local library.I've bought these about every 12-15 years; my oldest is 1962   I am a Life member of ARRL, current license W4LGN.   Mark Rackin

There are a lot of gaps in the data sheet for the device.Are you using the evaluation module, or putting the chip down on your own PCB. If either case you need to read the app note. If you are doing your own PCB, this will not be an easy chip to put down by hand, it has a thermal slug on the underside, and it is needed, with the output stage less than %50 efficient there is a lot of heat to remove, see this  hand soldering note for a possible solution. An antenna does not represent a broadband match, which may lead to problems. Additionally, you need to put a suitable harmonic trap in the output collector, or you may end up radiating a lot of harmonic content, probably in or near the 2.4Ghz band. The notes make it clear that there is a lot of work needed to optimize the chip, good luck.Just for interest sake, see the CC1190,Cheers,
Richard

An amplifier designed to have 50-ohm input impedance will measure 50 ohms resistive to an RF impedance meter (operating at the intended frequency) connected to input, so little or none of the incoming signal is reflected back into the transmission line. Note that the MAX2235 datasheet specifies the input VSWR.A power amplifier designed to drive a 50-ohm load efficiently, will measure far from 50 ohms to an RF impedance meter (operating at the intended frequency) connected to the output. An efficient amplifier's output will look like an open or short circuit (compared to 50 ohms) to the impedance meter looking into the output.Linear circuit theory teaches that maximum power transfer occurs when the load resistance equals the series resistance of the amplifier's output. The price, is that half of the power is wasted as heat in the series resistance of the amplifier's output, so the efficiency must be less than 50%.Doing this is called reverse-termination in the RF world, and is not done in power amplifiers.I agree with Richard Gabric that you need to read the app note. None of the documentation states what load impedance the MAX2235 output pins want to drive. See the RF Power Amplifiers and Transmission Lines chapters of the ARRL Handbook for discussion of matching networks.The MAX2235 datasheet states that the output stage operates in Class E. Class E is similar to CRT-television horizontal-output stage operating with 50% retrace time.I agree with Mark Rackin that the ARRL Handbook (formerly called the Radio Amateur's Handbook) published by the ARRL, is a good text for learning the building, care, and feeding of RF power amplifiers, antennas, matching networks, and the instruments used to measure what's going on. The Handbook is particularly good due to its emphasis on practical understanding of real apparatus. Academic texts have a tendency to abstract away the physical reality to enjoy purely mathematical analysis.I still have the 1963 Handbook I learned radio electronics from as a boy, when I started building radios beyond crystal sets. I took two decades to learn to receive Morse code, so I earned my first amateur-radio license in 1980. My current call is KC1HR, though I haven't operated in years.Peter Traneus Anderson

I would say that the output of the MAX2235 will be close to
50 ohms, as the data sheets says the “last stage delivers 30dBm to a 50Ω load.”
Have you tried contacting Maxim to get a more definitive answer?

If you really want to be sure, Alan Wolke, W2AEW, has
produced an excellent video on how to measure output impedance. In general,
what you must do is to measure the
change in output level as you change the load resistance. From those
measurements, you can then calculate the output impedance. Alan has nearly 300
videos on all manner of electronics and test and measurement topics on his
YouTube channel. He does a really great job with them.