Pevand Bahramzy

Compact Agile Antenna Concept Utilizing Reconfigurable Front End for Wireless Communications

The conventional full-duplex radio communication systems require that the radio transmitter (Tx) is active at the same time as the radio receiver (Rx). The Tx and the Rx are using separate dedicated frequency bands and the Tx-Rx isolation is ensured by duplex filters. However, increasing number of frequency bands crave for multiband and multimode operation, which either require agile duplexers or a bank of narrow-band filters with a switch. While practical agile duplexers are not available, a bank of narrow-band filters with a switch is bulky and incurs switching loss. This paper proposes an approach that separates the Tx and Rx chain throughout the front end (FE). The complexity of the FE is reduced dramatically by replacing the duplex filters with tunable filters and closely integrating the tunable antennas in the FE, providing filtering which can be used to lower requirements for the tunable filters. For this purpose, very small narrow-band antennas are designed, which can cover 1710-2170 MHz by using tunable capacitors. Simulations and measurements of the antenna concept are carried out in the proposed FE architecture, serving as a proof of concept.

Dual-feed ultra-compact reconfigurable handset antenna for penta-band operation

In the past two decades, antenna engineers have achieved impressive reductions in the size of mobile phone antennas, although physical constraints have essentially limited such reductions [1]. The design challenge posed by handset antennas is becoming more critical as networks evolve to offer a wider range of services, such as video telephony, web browsing, navigation services, entertainment etc. The increasing number of different functionalities in the mobile terminal puts great pressure on the available space for antennas, while handset designers expect that antennas can be operated successfully in close proximity to components such as cameras, flash units, loudspeakers, batteries and other hardware.

Isolation of high-Q antennas for mobile handsets

Isolation, beween the antennas at low frequencies (700 MHz), is one of the major issues in 4th Generation Long Term Evolution. This paper presents a practical method to improve the isolation between the ports of Tx an Rx antennas through narrow-band antennas used in separate transmit and receive mode. Furthermore, a patented feeding technique is applied to feed the antenna, which helps improving the isolation between the antenna ports. An isolation of better than -22dB at 700 MHz, is shown to be possible to achieve, by utilizing this method.

A Tunable RF Front-End With Narrowband Antennas for Mobile Devices

In conventional full-duplex radio communication systems, the transmitter (Tx) is active at the same time as the receiver (Rx). The isolation between the Tx and the Rx is ensured by duplex filters. However, an increasing number of long-term evolution (LTE) bands crave multiband operation. Therefore, a new front-end architecture, addressing the increasing number of LTE bands, as well as multiple standards, is presented. In such an architecture, the Tx and Rx chains are separated throughout the front-end. Addition of bands is solved by making the antennas and filters tunable. Banks of duplex filters are replaced by tunable filters and antennas, providing a duplexer function over the air between the Tx and the Rx. A hardware system has been designed and fabricated to demonstrate the performance of this front-end architecture. Measurements demonstrate how the architecture addresses inter-modulation and Rx desensitization due to the Tx signal. The filters and antennas demonstrate tunability across multiple bands. System validation is detailed for LTE band I. Frequency response, as well as linearity measurements of the complete Tx and Rx front-end chains, show that the system requirements are fulfilled.

Group Delay of high Q antennas

Group Delay variations versus frequency is an essential factor which can cause distortion and degradation in the signals. Usually this is an issue in wideband communication systems, such as satellite communication systems, which are used for transmitting wideband data. However, group delay can also become an issue, when working with high Q antennas, because of the steep phase shift over the frequency. In this paper, it is measured how large group delay variations can become, when going from a low Q antenna to a high Q antenna. The group delay of a low Q antenna is shown to be around 1.3 ns, whereas a high Q antenna has group delay of around 22 ns. It is due to this huge group delay variation characteristics of high Q antennas, that signal distortion might occur in the radio system with high Q antennas.

Near-field reduction techniques in the speaker area of slide mobile phones for improved HAC performance

This paper presents a method to improve the HAC of slide mobile phones. Although, the technique is demonstrated with a given commercial phone and for PCS band only, it could be adapted to other phones and bands as well. Simple antenna design and matching techniques can allow multi-band operation as well as high dimension flexibility. In the investigated cases, the two ILPE that are connected to the DPWB results in a reduction in excess of 45:9% for passive NF and of 40:3% for active NF at the resonant frequency of the ILPEs.

SAR Study of Mobile Phones as a function of Antenna Q

High-Q tunable antennas are good alternatives to low-Q passive antennas because the antenna size can be smaller while covering the required long-term evolution (LTE) frequency bands. However, among other things, specific absorption rate (SAR) can become a challenge due to the relative high current density associated with high-Q antennas. The higher energy stored in the electric and magnetic near-field components can result in higher SAR. Hence, SAR study of high-Q antennas is necessary which, if not addressed, might not comply with the SAR safety guidelines. In this paper, SAR as a function of antenna Q is investigated numerically as well as experimentally at two distinct frequencies (720 and 1700 MHz). It is found that SAR increases as a function of antenna Q when no losses are considered. But when losses are included, there is no more a clear trend between SAR and antenna Q. Thus, the final SAR values depend on total losses of the mock-up (MU).

Tunable Design for LTE Mobile-Phones

Antenna volume has become a critical parameter in mobile phone antenna design, as broader bandwidths are required for high connectivity between users. Shrinking the antenna size affects its efficiency, if one does not sacrifice bandwidth. This paper proposes an architecture to address the need for small and wide-band antennas. The study focuses on the low-frequencies (700 MHz - 960 MHz) in order to address a tough scenario for small platforms. A tunable design of the front-end and the antennas of the mobile phone is proposed and investigated. Operation is achieved on all low-bands with an efficiency of -3 dB at 700 MHz.

Thermal loss of high-Q antennas in Time Domain vs. Frequency Domain Solver

High-Q structures pose great challenges to their loss simulations in Time Domain Solvers (TDS). Therefore, in this work the thermal loss of high-Q antennas is calculated both in TDS and Frequency Domain Solver (FDS), which are then compared with each other and with the actual measurements. The thermal loss calculation in FDS is shown to be more accurate for high-Q antennas.

High-Q Antennas with built-in coils: for Mobile Devices

Efficiency and isolation, at low frequencies (700 MHz), are two of the most important metrics for successful multi-communication implementation. This paper presents an antenna concept, that exhibits a very high isolation between high-Q Tx and Rx antennas at 700 MHz. Furthermore, it is shown how coils can be integrating into the antenna structure for obtaining better efficiency. It is shown that by integrated coils into the antenna structure, the efficiency can be improved by 2dB for each antenna.