Meander antenna question when using nRF51822

Question

Hi, I just bought the PCA10031 nRF51422 based USB dongle and PCA10028 nRF51422 based development board. 
 The difference between nRF51822 and nRF51422 was the ANT protocol stack. 
 My client wants to choose the nRF51822-QFAA for his personal reasons 
 and he wants to use the meander antenna which is drawn at the PCA10031. 
 My questions are; 
 
 
 Although the nRF51822-QFAA and the nRF51422 are similar, 
 
 I want to know whether it is fine to use the same values for the RF and the antenna components, the RLC values. 
 I'm planning to use the FR-4, 1.6mm thick, 2-layered PCB. 
 Can I use the same components, which is described in the PCA10031's schematic, when I work with nRF51822-QFAA? 
 // Edited 2017.05.09 - Summary & Compare referring Jørn's answer 
 nRF51822 Product Spec 3.3 
 nRF51422 Product Spec 3.1 
 
 
 
 I just want to double check. 
 
 Compared to the Inverted F antenna, the meander antenna, which is drawn on PCA10031, doesn't connect the antenna trace to the ground plane, right? 
 
 By looking at the Digi-key number, the PCA10028 (Rev 1.2.0) used FC-135 32.7680KA-AC-ND , a product that uses 9pF as the load capacitance . 
 
 In this blog , 
 C1 = C2 = 2Cl - C_pcb - C_pin // C_pcb + C_pin is approximately 4 pF
 
 I expected the capacitor values to be 14pF. However, the schematic tells that 12pF capacitors are populated. 
 Is there a reason for choosing the 12pF, such as 
 reducing the type of items for the pick and place machine or that Rev 1.2.0 board's C_pcb + C_pin value is approximately 6pF? 
 -Best Regards, MANGO

Jørn · Accepted Answer

Hello MANGO 
 
 
 
 The chip on the nRF51 dongle is the nRF51422-QFAC. This package is a little larger than the QFAA and QFAB packages and the matching network is therefore a little bit different to compensate. For the correct output network, please see the reference schematics for nRF51822-QFAA QFN48 on pages 82-87 of the nRF51822 product specification. Specifically you will see that the inductor L2, and capacitor C5 have different values. 
 
 
 
 Correct, the meander antenna will not have the arm shorted to the ground plane as the IFA has. Please keep in mind that any changes to the PCA10031 antenna design will require changes to the antenna matching network encircled in green in your figure. 
 
 
 
 At this time I'm afraid I don't have the specifics as to why 12 pF was chosen in this particular instance. I will need to look further into it and get back to you on that. 
 Best regards 
 Jørn Frøysa