This point cannot be emphasized enough as it is a common mistake. The mounting of dipoles and monopoles parallel to the local RF ground plane must be avoided.
One additional point with respect to external is that when selecting a commercially available external antenna, it is critical to verify that the antenna performance meets the manufacturer's specifications. Most electronic components available today have detailed and accurate specifications. However, this is generally not true of off-the-shelf antennas. Purchasing from a known or respected supplier and/or performing independent testing are the only ways to ensure that the antenna conforms to what the datasheet claims. In the world of commercial antennas for small devices, especially at the low end of the cost scale, incorrect and misleading datasheets are much more common than one might expect.
4.2.1 Embedded Antenna Type
Inverted-F Style Antenna (IFA)
The inverted-F antenna is the most common embedded antenna in use today in wireless devices in the 900 MHz to 6 GHz frequency range. It can be formed in a multitude of ways, has excellent multi-band capability, and can be made highly efficient. Originally designed in the early 1960s as a single-band conformal UHF antenna for use on aircraft, the inverted-F has evolved into a low-profile multi- band antenna than can be integrated into today’s small and complex product designs.
In its most basic form, the inverted-F is a quarter-wave long conductor parallel to and within a few mm of the RF ground plane, grounded at one end, and has a 50- ohm feedpoint close to the grounded end. The quarter-wave conductor can be a thin wire, a trace on a PCB, or a 3D surface and can be straight or folded into complex shapes. The 3D version is commonly called a PIFA, or Planar Inverted-F Antenna. An IFA can be referred to as a two-dimensional antenna while the PIFA would be a three-dimensional antenna. The following photos show sheet metal and
Antenna Fundamentals – Technical Brief