关于VCO的调谐范围

lazdex

1.谐振腔振荡器的使用 为什么调谐范围会相对于 环形振荡器小？
2 文中指出
Consequently, the implemented PLL
incorporating the resulting linear transconductance VCO (LiT
VCO) achieves both an excellent measured phase noise of
130 dBc/Hz at 22 GHz (10-MHzoffset),and,incontrastto
the 6.7% tuning range of the VCO-only result reported using
a somewhat similar technique in [1], a large frequency tuning
range (FTR) of 23% (21.8–27.5 GHz). This range covers operation over 22.8–26.4 GHz, with margin, meeting requirements
for a 60-GHz superheterodyne radio。
请问 为什么22.8-26.4GHz的调谐范围可以满足60GHz的超外差接收机  这几个频率对应的是什么频率？本振频率？中心频率？