Pt is a variable, basically it says will depend in the radar, σ = radar cross-section [m²] is another variable, it is not fixed thus the illustration you use will depend on the radar nothing is fixed
In theory, the RCS of some simple objects, such as a perfect sphere, can be
well defined. In practice, most targets are rather complex objects and their RCS
usually fluctuates considerably, as they move with respect to a radar. In fact, the
monostatic or backscatter RCS depends on the following
Position of radar antenna relative to target
Angular orientation of target relative to radar antenna
Frequency of the electromagnetic energy
Radar antenna polarization.
For the F-35, the approach was the construction of a l.o. aircraft, taking seriously
into account the cost parameter. Therefore, in the frame of cost reduction, some
capabilities were “sacrificed”: RCS is really low in the X-band (8 – 12 GHz) and in
the Ku-band (12 – 18 GHz), while it is not so low at lower frequency bands. The
scope is the break of the killing chain: even if the F-35 is detected by surveillance
radar, it will not be easy to be engaged by a fire control radar, which usually operate
in the X or Ku bands. On the other hand, the F-22 presents a lower RCS from all
aspects and at more frequency bands, of course at a considerably higher cost
The production F-35 is expected to present a higher RCS than the prototype
X-35, since more volume was required for the internal equipment and armament bays.
The curves of the redesigned fuselage will incur an RCS increase, from some certain
directions. It was calculated that the RCS will remain very low from the frontal sector
and more precisely from a sector of 29ο in front of the aircraft. However, the RCS will
not be so low from the lateral aspect and also from the rear aspect. The whole
behavior deteriorates at lower frequency bands
Very low frequency band radars, for medium to high altitude
surveillance: as the frequency decreases, the wavelength increases and becomes
comparable with major parts of the aircraft. Thus, scattering enters the resonance
region, exhibiting a higher Radar Cross Section (RCS), at least momentarily. Also, the
Radar-Absorbent Materials (RAM) are not very effective at lower frequencies. For
these reasons, radars operating, e.g., in the VHF band, are expected to see a l.o. target
at a longer distance with respect to “conventional”, higher frequency radars,
transmitting in the L or S-band.
https://www.researchgate.net/publication/259503614_Low_Observable_Principles_Stealth_Aircraft_and_Anti-Stealth_Technologies
