capturing ethernet headers in winpcap

I sent an ethernet header from a computer to another and printed its length and timestamp in receiver side by following the Winpcap tutorial. However, beside that I also see other protocol's timestamp and length too.

I know that I need packet filtering but I couldn't find an example for ethernet filtering.

The example of the WinPcap is for "ip and udp" as in this link: https://www.winpcap.org/docs/docs_412/html/group__wpcap__tut6.html

I tried writing "ether", "ethernet" for

char packet_filter[] = "ip and udp";

definition in the link but didn't work. Any advice?