How much of an improvement is the SPY6 and SPY3 compared to the SPY1?
I just realised basically all the Korean, Japanese, Australian aegis destroyers and earlier Arleigh Burkes use the AN/SPY-1D(V), which is a PESA dating back to the 1990s. Does that limit their effectiveness in any way? How does it compare to the 346A?
SPY-4 is more comparable to the SPY-1 as these are both longer ranged S-band radars that is optimized for search. SPY-3 is an X-band AESA, its a different category of radar that is more comparable to a dedicated fire control radar. The SPY-3's can be more directly compared to the Thalas APAR, and its Chinese equivalent is not the Type 346A itself but the smaller secondary X-band radars you see on the mast of the Type 055, whose proper Type number remains unknown to this day.
SPY-4 is considered troublesome and its techs outdated so its already considered discontinued, with all efforts going to the SPY-6. Other than the Gerald Ford, there are no other users of the SPY-4, making it a loner. The SPY-3 is active only on the two Zumwalts and the Gerald Ford, the last Zumwalt will use SPY-6 instead.
Zumwalt program canceled the SPY-4, leaving it with the SPY-3 only. Originally the ship planned to go dual band, with the typical S and X-band approach, with the S-band for broad air volume search, and the X-band for tighter tracking, fire control and surface search. Each band has their advantages and disadvantages so naval sensor architecture leans towards being multiband. Left with the X-band only, they added search modes on the SPY-3, however, X-band is far from optimal for search compared to S-band, so its range and ability to detect low RCS objects is not as good as you would expect with an S-band radar.
For different reasons, PESA as an architecture can match AESA in range and power but that's not really about what AESA is anyway. Your range and power depends on other factors that's not about the architecture anyway. PESA however, is limited to only one beam are emitted from the array at one time whereas on AESA you can emit several off from the same array. Since the receiver low noise amps are directly below the elements in the AESA instead of behind the array on PESA, its sensitivity is far greater with little loss or internal interference to the signal. This lets you use a weaker signal and still detect a target using a weaker echo. There are other advantages but discussing them are TLDR. Let's just say overall, AESA is more ECM resistant than PESA.
The SPY-X radar family can be listed as such.
SPY-1 --- You know what that is.
SPY-2 --- AESA version of SPY-1. Experimental purposes only, and not approved for production.
SPY-3 --- X-band AESA instead as part of a dual band approach with SPY-4.
SPY-4 --- S-band AESA
SPY-5 --- reserved for second generation X-band AESA. Originally planned as a dual band counterpart to the SPY-6/7. Progress unknown. Might be cancelled.
SPY-6 --- Second generation S-band AESA with GaN by Raytheon.
SPY-7 --- Lockheed's second generation S-band AESA with GaN. Export only for Canada and Spain and used with AEGIS ASHORE in Japan. With AEGIS ASHORE cancelled in Japan, Japan looks to use the SPY-7s on two new destroyers instead.
AEGIS is actually a Lockheed Martin trademark and SPY-1 is an LM product. However, SPY-6 is a Raytheon radar, so legally, the system isn't 'AEGIS' by copyright definition, so from the Lockheed Martin perspective, SPY-7 is the true successor to the SPY-1.