I thought I'd provide a look inside of the Mini-Circuits unit that I am using. Specs are available on their website and I looked for something that covers to 2GHz in order to ensure reasonable performance to 1.5GHz. I might add that the basic concept here was taken from application notes that were available on the HP website (and probably also on the Agilent web site).
I've been in the RF business for some time working variously at SBE, KLM Electronics, Identronics/IDX, Inc (one of two pioneer RFID companies), Allen-Bradley (again, RFID), RF Technologies, and Savi Technologies (purchased by Lockheed-Martin a few years ago). This included HF through 2.4 GHz stuff but mostly low powered devices in the VHF and UHF region up to 915 MHz.
I am semi-retired but still working at Telewave part time since their plant is only a few miles (7 minutes) from my home in San Jose, CA.
Overall I would place the DSA815-TG in the Two-Way Radio Service Monitor level of capabilities though not quite as portable but with display, print out and screen shot saving features superior to many of them.
Noise wise, the unit is on a par with many of the lower end ($5K) Service Monitors available today but not as good as some of the $15-30K models and not specifically set up with all site management features found on the higher end products. Several of those that I have used over the years were more expensive than the DSA815-TG but not as good in terms of their display, screen shot resolution, and even sensitivity.
This is clearly not a unit designed with aerospace measurements in mind but it is far superior in many ways to some of the Spectrum Analyzers I've used in my 40 year career as a Technician/Engineer.
If you've got the room (I don't), spend $1-2K more for a good used HP analyzer then you can do exotic PLL work, broadband matching, etc. Or if you really need a Network Analyzer, you will need to spend a bit more than that. However, be prepared for a large, heavy, and mostly non-portable unit with poor, if any, modern flash drive or usb-based control capability. Most will require IEEE 488 bus I/O which is almost always extra. The DSA815-TG has this option available as well.
Jim