Compact multifunctional antennas for wireless systems

Chapter 4

Receiving Amplifying Antennas

4.1 Introduction

As early as the 1960s, dipoles were integrated with low-noise amplifiers (LNAs) to enhance the signal-to-noise ratio (SNR) at receivers (1–3). The new integrated antenna was called an antennafier because it combined the functions of radiation and amplification. Such integration was used to reduce the number of matching and tuning elements for a lower RF loss. When integrated with a transmitter (3), the power amplifying antenna was also called an antennamitter. In 1997, Radisic et al. (4) used a patch antenna as the harmonic tuning load of a power amplifier. By terminating the second harmonic of the power amplifier, the power-added efficiency (PAE) was found to be better. This method was later extended for suppressing the higher harmonics of a push–pull power amplifier (5). Again, significant enhancement (with PAE > 55%) in the output power was observed. In the past two decades, antennas have been combined with both transmitters and receivers for designs of multifunctional transceivers (6, 7). Also, a lot of research has been reported on the integration of antenna and transceiver for quasi-optical spatial power combining during the millimeter-wave technology boom (8–11).

Obviously, the main advantage of integrating an antenna with an amplifier is the significant reduction in the length of signal transmission path that leads to improvement of signal quality and reduction of circuit size. Although fewer circuit elements are ...