Antenna module breaks new (balanced) ground
By Bill Schweber -- EDN, March 17, 2005
Significant innovation has occurred in the past few years in antennas for handheld devices, and an entry from Antenova Ltd offers further proof. The company’s Radionova radio-antenna module combines radio and RF components with a balanced dielectric antenna that yields, according to company analysis, lower cost; pc-board-design flexibility and noninteraction; improved radiation efficiency; and reduced chassis currents, which adversely affect pc-board design (Picture). The product also offers reduced front-end losses, user-induced detuning, and SAR (specific absorption ratio). Notes Professor Simon Kingsley, chief scientist of Antenova, “In all phones, the RF groups fight for every millimeter, while the antenna guys are given a comparative ‘football field’ of space to play in.”
By using balanced, self-complementary antennas resting atop an active-circuitry module and integral balun, this approach minimizes the need for designers to customize antennas for each radio and reduces the pain of redesign when their underlying pc-board-design layout or ground plane changes. Although engineers have for about 100 years understood the advantages of balanced, dipole antennas over unbalanced, monopole antennas, the balanced devices have practical implementations challenges, such as the inability to work well near ground planes. The balanced Radionova design, in contrast, works with a full ground plane. Designers can reflow the lower module with the electronics onto the pc board and test it, and then snap on the upper antenna module, which uses a plastic substrate. “Everyone has looked at integration of the baseband, transceiver, and RF sections, but nobody has looked at integration for the other end—the antenna and RF section,” says Kingsley.
OEMs can optimize Antenova designs for bands in the 800-MHz to 6-GHz range, and, because the devices require no ground plane, designers can build a diversity antenna into the handset for improved performance. Tests on actual units confirm the simulation results that show directivity of the design is strongly in the z-axis (normal to the antenna plane). In a representative design, low-band (900-MHz) return loss was –21 dB, and high-band return loss (1750 to 2000 MHz) was –9 to –11 dB. Low- and high-band efficiency exceeded 50 and 55%, respectively, including balun loss. The Antenova module costs approximately $5 (OEM quantities).
Antenova Ltd, www.antenova.com.
