AF4NB David Baker's Chicken Foot Antenna
This antenna is both broad banded and efficient. If you study the design, the three wires tied to the center conductor form one half of a biconical dipole. the other half of the biconacal diplole is formed by the fourth wire connectd to the coax braid.
A good reference is Tierman's Radio Engineering "Third Edition" Section 14-9 including Figure 14-52-b.