Recently, wireless data, entertainment and mobile communications technologies have become increasingly prevalent, particularly in the household and computing environment. The convergence of these wireless data, entertainment and mobile communications within the home and elsewhere has created the need for merging many disparate devices into wireless network architectures capable of seamlessly supporting and integrating the requirements of all of these devices. Seamless connectivity and rapid transfer of data, without confusing cables and wires for various interfaces that will not and cannot talk to each other, is a compelling proposition for a broad market.
To that end, communication industry consortia such as the MultiBand OFDM Alliance (MBOA), Digital Living Network Alliance (DLNA) and the WiMedia Alliance are establishing design guidelines and standards to ensure interoperability of these wireless devices. For example, Wireless 1394, Wireless USB, and native IP-based applications are currently under development based on ultra wideband (UWB) radio or WiMedia Convergence Platform.
Although it began as a military application dating from the 1960s, UWB has recently been utilized as a high data rate (480+Mbps), short-range (up to 20 meters) technology that is well suited to emerging applications in the consumer electronics, personal computing and mobile markets. When compared to other existing and nascent technologies capable wireless connectivity, the performance benefits of UWB are compelling. For example, transferring a 1 Gbyte file full of vacation pictures from a digital camera to a computer take merely seconds with UWB compared to hours using other currently available, technologies (i.e. Bluetooth) and consume far less battery power in doing so.
Typically, devices which employ UWB utilize a fixed channel bandwidth that is static in frequency, or a fixed channel bandwidth that can be frequency agile. In either case, the bandwidth utilized by a device must remain substantially fixed. Thus, the range and data rate of the device is, for the most part, determined by the modulation/coding of the signal, and the power with which the signal is transmitted.
In most cases as UWB, by definition, is spread over a broad spectral range, the power spectral density of a signal utilized by a UWB device is usually very low, and hence, usually results in low incidence of interference with other systems which may be utilizing the same bandwidth as the UWB device or system. However, to transmit signals of this type effectively an antenna must usually be utilized.
In fact, no matter the UWB system implemented, almost any transceiver implemented for a UWB system of the type discussed will require an antenna to transmit and receive information exchanged between the UWB systems. The antenna implemented in a UWB system is usually implemented in conjunction with the analog front end of the UWB transceiver and, as such, is responsible for radiating and receiving wideband (analog) electromagnetic signals.
In most cases, as the devices utilized to implement the UWB radio itself have shrunk in size, not only have portions of the radio itself shrunk, but additionally, the distances between the elements of the radio have decreased. In fact, in many cases UWB radios are implemented on a single printed circuit board (PCB), or one or more coupled PCBs, for use as a daughtercard, as a CardBus card, a PMCIA card, or with another type of interface.
Traditionally, monopole antennas were employed in these types of applications. However, monopole antennas present certain problems. Namely, these monopole antennas tend to be rather large, they often require large ground planes and their functionality and efficacy may vary widely if other elements of the UWB radio are placed in proximity to the ground plane. More specifically, monopole antennas, when placed over finite sized groundplanes may result in non-localized currents in these groundplanes which, in turn, could result in interference to other components of the radio with which these monopole antennas are being utilized.
Additionally, there may be frequency bands within a UWB channel where it is important to suppress interference. For example, some existing UWB spectrum allocation encompasses the C-Band satellite downlinks. Thus, there is a potential for UWB systems to interfere with television reception of those types of system. Currently, coexistence with 802.11a/b/g systems is regarded as important. Operation of a UWB radio in presence of these systems can be significantly improved if signal levels at the characteristic frequencies (802.11a in the US: 5.15-5.35 GHz and 802.11b/g in the US: 2.4 GHz) are suppressed before they reach an analog front end of a receiver. In these types of environments, it may be desired to create to reduce the power of a transmission in one or more areas of the transmission spectrum.
Thus, as can be seen, there is a need for antennas which may have reduced size, utilize smaller ground planes, exhibit a lesser degree of sensitivity to other elements of the radio in proximity to the antenna or which may be utilized to reduce the power of a signal within a certain frequency band.