Bert Woestenburg

Minimizing the Noise Penalty Due to Mutual Coupling for a Receiving Array

For phased array receivers, mutual coupling leads to beam-dependent active impedances which must be taken into account when matching the array ports to front end amplifiers for optimal noise performance. We study the noise penalty for several noise matching conditions and develop a matching condition that minimizes the average beam equivalent receiver noise temperature over multiple beams. For non-beamforming applications such as multiple input multiple output communications, we show that noise performance for coupled arrays can be quantified using the spectrum of an equivalent receiver noise temperature correlation matrix.

Equivalent System Representation to Model the Beam Sensitivity of Receiving Antenna Arrays

In this letter, it is demonstrated that the beam sensitivity of an antenna array receiving system can be analyzed by using an equivalent single-channel receiver model. In this model, the antenna array is represented by an equivalent single-port antenna and the multiport active beamforming network is replaced by an equivalent two-port amplifier. Herein, the beam sensitivity is defined at the input of the receiving system and is a function of the equivalent antenna model parameters. Such a simplified representation helps us to identify the predominant factors that affect the receiver sensitivity of complex antenna array systems, without having to consider the entire system in full detail. The receiver noise is computed with the proposed model and compared to the one computed by a direct numerical method to validate its consistency. For this purpose, we consider a four-element actively beamformed dipole array with strongly coupled antenna elements causing significant noise coupling effects.

Unified Definitions of Efficiencies and System Noise Temperature for Receiving Antenna Arrays

Two methods for defining the efficiencies and system noise temperature of a receiving antenna array have recently been developed, one based on the isotropic noise response of the array and the other on an equivalent system representation. This letter demonstrates the equivalence of the two formulations and proposes a new set of standard definitions of antenna figures of merit for beamforming arrays that accounts for the effect of interactions between antenna element mutual coupling and receiver noise on system performance.

Achieving Wideband sub-1dB Noise Figure and High Gain with MOSFETs if Input Power Matching is not Required

A 0.18 mum CMOS low noise amplifier (LNA) achieves sub-1 dB noise figure over more than an octave of bandwidth without external noise matching components. It is designed for a future radio telescope, requiring millions of cheap LNAs mounted directly on phased array antenna elements. The short distance between antenna and LNA and low frequency below 2 GHz allows for using an LNA with reflective input impedance, increasing the gain with 6 dB. Without any matching network, very low noise figure is achieved over a wide bandwidth. At 90 mW power, sub-1 dB Noise is achieved for 50 Omega source impedance over a 0.8-1.8 GHz band without external coils, and S21>20 dB, OIP2>25 dBm and OIP3>15 dBm. Preliminary results with 150 Omega source impedance show noise temperatures as low as 25 K around 900 MHz.

Noise-based antenna terms for active receiving arrays

For active receiving arrays with complex receiver chains, nonreciprocal components in the beamforming network, or digitally sampled and processed output signals, existing transmit-based antenna terms such as gain and radiation efficiency cannot be directly applied. Using the reciprocity principle to obtain an equivalence between the total power radiated by a transmitting antenna and the noise power at the output of a receiving antenna, a new set of more general, receiver-specific antenna terms have been obtained. For passive, reciprocal antennas, the new definitions are rigorously equivalent to existing definitions. The terms have received the IEEE Antenna Definitions Working Groups support for inclusion pending final approval by the Antenna Standards Committee in the next update of the IEEE standard for antenna terms.