I have PCB strip from router antenna section. It has a varying width trace laid on thick FR4 green masked PCB. Why varying width trace doesn't cause any reflection issues?

Another relates observation is ESP01 (8266) PCB module which has 1mm wide meander PCB trace.

Query -1) Whether there can be GND plane on other side of PCB beneath inverted F trace. II) Can we use PCB mounted SMA connector at right angle to supply RF to inverted F antenna

 

Varying width in a trace like that is probably transforming, or matching, from one impedance to another.