Image Frequency Rejection Research Articles

Demonstration of continuous multiple access with homodyne and image-rejection heterodyne coherent receivers using directly modulated laser transmitters

This work presents a comprehensive set of experiments for the multipoint-to-point coherent passive optical network (PON), where the wavelength locking between the optical network unit (ONU) and optical line termination lasers is critical, especially if operating in burst mode. Here, we test the performance of continuous multiple access in a splitter-based PON with both an ultra-dense wavelength division multiplexing and RF-subcarrier multiplexing configuration, with simple distributed feedback (DFB) lasers along non-return to zero and pulse amplitude modulation of four levels. Most interestingly, we test a spectrally efficient heterodyne receiver with image-frequency rejection and polarization independence based on the 3×3 optical front-end. Two users at the same intermediate frequency are detected simultaneously avoiding image frequency interference while minimizing complexity, with transmissions of 2.5 Gb/s. We provide comparison with an asynchronous homodyne receiver. The achieved results demonstrate the feasibility of continuous multiple access using thermally controlled ONUs with conventional DFBs as an enhanced alternative to commercial time division multiplexing access.

Tunable OEO-based photonic RF receiver with image frequency rejection.

A tunable optoelectronic oscillator (OEO)-based photonic radio frequency (RF) heterodyne receiver with the capability of image frequency rejection is proposed and experimentally demonstrated. The OEO incorporating a dual-electrode Mach-Zehnder modulator (DEMZM) operates as a high quality local oscillator (LO) and a broadband mixer simultaneously, with one electrode port of the DEMZM used for the feedback of the generated LO signal and the other port for receiving external RF signals. Two channels of immediate frequency (IF) signals can be achieved in optical domain by beating the +1-order sideband of LO with the +1-order sideband of input RFs and beating the -1-order sideband of LO with the -1-order sideband of input RFs correspondingly. Through setting the bias angle of the DEMZM at π/4 or 5π/4 and quadrature combining of the two channels of the IF signal, the combined IF signal down-converted from the target RF signal gets enhanced due to the in-phase sum of two channels, while the combined IF signal down-converted from the image frequency can be rejected due to out-of-phase sum of two channels. In the experiment, the input RF signals with operating frequency range from 8.85 to 14.85GHz are successfully received with the image rejection ratio reaching 42.6dB, and the spurious free dynamic range of the system is better than 94.8 dB Hz2/3.

On Optimal Resource Allocation in Multi-RAT Wireless Networks With Receiver Characteristic Awareness

Next-generation wireless systems are expected to use multiple coexisting radio access technologies with different receive and transmit characteristics. This will make the radio frequency front-ends susceptible to unprecedented adjacent-channel interference (ACI), which can jeopardize communication performance. In this paper, we propose a novel ACI-aware joint channel and power allocation framework that takes into account the receiver imperfections arising due to: 1) imperfect image frequency rejection and 2) analog-to-digital converter aliasing. The objective is to minimize the number of allocated channels and the aggregate power transmitted while satisfying the rate demands of different links in a multi-radio access technology environment. As the overall problem is NP-hard, we develop an efficient algorithm to solve it through decomposing the problem into two subproblems: channel allocation and power assignment. Then, it solves the decomposed problem by iteration using a two-phase structure. In Phase I, a particle swarm optimization-based algorithm is tailored to obtain good solutions for the channel allocation subproblem. Phase II solves the power allocation subproblem optimally given the channel allocation solution obtained in Phase I. The results demonstrate: 1) the criticality of receiver-characteristic awareness when designing resource allocation schemes and 2) the superiority of the proposed algorithm in solving the overall problem efficiently.

An Image Frequency Rejection Filter for SAW-Less GPS Receivers

We have developed an on-chip RF filter in 130 nm BiCMOS for SAW-less GPS receivers. The filter is implemented as a cascode amplifier stage with reactive resonant tanks. The filter employs two Q-enhanced LC tanks to create a transfer function with steep roll-off characteristic and narrow passband. The image rejection filter achieves a 3 dB bandwidth of less than 12 MHz at the GPS L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> center frequency of 1575.42 MHz. The resulting magnitude response exhibits a notch at 1540 MHz and at 1610 MHz, attenuating noise and interference 30 MHz away from the center frequency by more than 30 dB. The NF of the RF filter is 4.0 dB. A competitive power consumption of only 5.7 mW is achieved.

Design of Active Integrated Antenna for Dual Frequency Image Rejection

This paper is discusses a new configuration of integrated antenna for dual frequency operations and image frequency rejection. Microstrip patch antenna is design in such away to operate in dual frequencies band. The RF 90° hybrid, LNA's, mixers, LO and IF coupler are integrated to a dual frequency microstrip patch antenna to produce a single module of integrated antenna system that can perform for in dual-band frequencies. The design technique and simulation result for active integrated antenna (AIA) with image rejection is presented.

A High Performance C-Band Subharmonic Modulator Exploiting Branch-line Couplers as Input/Output Ports

Digital direct modulation at microwave frequencies represents the best way to develop a component requiring a simple system design, low cost and compact size. In this paper, a novel architecture of a C-band modulator, which exploits a branch line hybrid to provide an equal amplitude division of Local Oscillator signal (LO), is proposed and experimental results are reported. Using of subharmonic mixer offers the following advantages: inherent Local Oscillator/Radio Frequency (LO/RF) isolation, no bias network is required, low power of LO, rejection of LO's even harmonics. Measured conversion loss is around 10 dBc with LO rejection approximately 29 dBc and image frequency rejection around 26 dBc. At last, the modulator exhibits Radio Frequency/Intermediate Frequency (RF/IF) and RF/LO isolation levels better than 30 dBc. A comparison is also reported to evaluate the performances of three different topologies of the same direct vector modulator.

Even-harmonic C-band modulator

Direct modulation at microwave frequencies promises the advantages of compact size, low cost, and relatively simple system design. In this paper, a novel architecture of a direct-vector C-band modulator is described. In particular, a subharmonic mixer is used to overcome the high carrier leakage that is associated with conventional fundamental modulators at microwave frequencies. The topology exhibits relative low conversion loss (11 dBc) and good image frequency rejection (23.5 dBc) and local oscillator (LO) rejection (23.9 dBc). The LO power level used by the mixer is approximately 6 dBm for optimal performance in the operating band.

Image Frequency Rejection in a Radio Direction Finder

An analysis is given of the bearing error in a radio direction finder due to simultaneous reception of two signals, referred to as target and spurious signals. The carrier frequency of the spurious signal is assumed to be the image of the target-signal frequency around the local-oscillator frequency, so that both signals are passed by the IF amplifier of the direction-finder receiver. The analysis applies to any DF receiver having a carrier-suppressed double-sideband input, such as is obtained using a mechanical or electronic goniometer. The results can serve as a basis for specifying the image rejection requirements on the RF amplifier of the receiver. In particular, it is shown that in order to have less than one degree of error, the spurious signal must be attenuated to at least 35 db below the target signal amplitude at the RF output of the receiver.