Input Impedance Mismatch Research Articles

Effect of input impedance mismatch on the large-signal noise figure of microwave photonic links

In this paper the effect of mismatch and loss of the input lossy impedance matching network on the noise figure (NF) of microwave photonic links (MWPLs) operating under large radio frequency (RF) signal modulation is theoretically investigated. An intensity-modulation with direct-detection (IMDD) MWPL in which the external modulator is a Mach-Zehnder modulator (MZM) is studied here. The nonlinear input-output relationship of the MZM under large RF signal modulation can lead this link to operate in the nonlinear large-signal regime. The main goal of this paper is to investigate and find the input impedance mismatch conditions for minimizing large-signal NF of MWPLs. To the best of our knowledge, this is the first study on this subject. It is found that large-signal NF of an IMDD MWPL depends on the input impedance mismatch factor and input applied RF power. It is shown that for M≃0.39 the NF can be minimized that is approximately 0.95dB lower compared to the NF at the perfect match (M=1). Regarding a generic optoelectronic oscillator (OEO) containing a MWPL at saturation, the value of this analytical approach is to study the effect of such large-signal NF on the OEO phase noise performance.

CSRR based folded monopole tri-band antenna array and its system level evaluation

In this article, a folded monopole antenna loaded with complementary split ring resonators (CSRRs) is proposed for tri-band applications. The two bands of the antenna are generated by the folding of the monopole (first band is caused due to fundamental mode and another due to higher order mode) and CSRRs have been responsible for the third band. By using four such antennas in form of an array, the gain and bandwidth have been improved. The prototype of the antenna array is developed on FR4 substrate and simulated results are experimentally validated. A simplified equivalent circuit model of the antenna has been developed and analyzed to quantify the power loss due to input impedance mismatch at each resonance frequency. By using the EM model of the proposed antenna in the Keysight ADS verification test bench its suitability to operate in the system environment has been confirmed.

A high FoM monopole antenna with asymmetrical L‐slots for WiMAX and WLAN applications

AbstractA triband monopole patch antenna with high figure‐of‐merit (FoM) for WiMAX and WLAN applications has been proposed. It consists of a rectangular patch with two asymmetrical L‐shaped slots, where L‐slots generate two lower resonance frequencies and patch the higher. A parametric study to optimize the slot length is carried out to achieve the desired frequency bands. An equivalent circuit model of the antenna is developed and analyzed for loss due to input impedance mismatch at each resonance frequency. The simulated results of return loss of antenna and radiation patterns are validated with experimental results.

Analysis of an Enhanced-Q N-Path Filter with Improved Even-Order Harmonic Rejection

Based on a feedback system, an N-path bandpass filter robust to even-order harmonic mixing (BPF-REHM) is presented. BPF-REHM consists of a conventional differential N-path filter around a gain stage. Despite assuming a single-ended antenna, this work aims at partial rejection of even-order harmonics before the signal travels through the baseband circuitry. Linear periodically time-varying analysis of the new filter is presented. Mathematical derivations verify an enhanced-Q filtering behavior in addition to even-order harmonic rejection at RF nodes. Drawback of BPF-REHM, i.e., input impedance mismatch, is addressed by proposing a two-stage LNA. The second stage of the new LNA, which is the BPF-REHM, suppresses even-order harmonic blockers while the first stage matches the input to the source and provides enough gain to accomplish an acceptable overall noise performance. The design example is a 500?MHz four-path filter simulated with the 90?nm CMOS. It achieves >22?dB even harmonic rejection with an enhanced-Q filtering characteristic thanks to the new technique. Besides, this design achieves 21?dB gain, 2?dB NF, and $$+$$+2.5?dBm out-of-band IIP3 at 50?MHz offset while consuming 8.3?mW of power.

Miniaturization of Ultrawideband Monocone Antennas Using Dielectric Loading

A so-called intelligent approach for miniaturization of monocone antennas using dielectric loading is presented. Two impedance mismatches causing the degradation in impedance bandwidth due to high permittivity dielectric loading are identified. The input impedance mismatch is addressed by modifying the structure of the antenna feed. Adding a spatial quarter-wave transformer matches the wave impedance of the loading region to that of free space. The feasibility of such a loading scheme is validated by effectively miniaturizing a monocone antenna with a material of ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 9.0. Simulations show the diameter of the ground plane is reduced by 55.2%, while the miniaturized monocone has a relative impedance bandwidth of 106.3%. The proposed dielectric loading concept is further applied to miniaturize three other monocone antennas to show its generality. In addition, the feasibility is further validated through miniaturization of monocone antennas using dielectric materials of various permittivity values. Finally, a miniaturized monocone antenna using a dielectric material of ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 9.0 is fabricated and measured to experimentally verify and validate the concept.

Development of Fixed Frequency Beam Steering Wide Band Leaky Wave Cavity Antenna

A complete design of substrate integrated leaky wave cavity antenna for fixed frequency beam steering is presented. The antenna consists of a small rectangular metallic tapered cavity fed by hook-shaped element and covered by the substrate. The steering of the beam in the desired direction is achieved by controlling the taper of the cavity. The beam is scanned at fixed frequency by changing position of the microstrip lines on the substrate. The substrate placed on the cavity resolves the problem of input impedance mismatch. The pertinent features of the antenna are compactness, broadband, and fixed-frequency beam steering capability.

Input impedance conditions for minimizing the noise figure of an analog optical link

We use an equivalent-circuit model to derive the minimum noise figure (NF) for an amplifierless optical analog link with a perfect lossless input impedance-matching circuit. This minimum, which is 3 dB, is called the lossless passive match limit. We contrast the link model with an analogous equivalent-circuit model for a transistor amplifier, which does not have the same limiting NF under this impedance-matching condition. It turns out that the link's 3-dB limit arises from the ohmic nature of the impedance of the device that modulates the light, and not from the electro-optic conversion processes in the link. In a prior experimental link, with near-perfect impedance matching, dissipative loss in our input circuit precluded achieving a measured NF of less than 4 dB. Investigation of the effects of input impedance mismatch indicates that mismatch can actually lower the NP to below 3 dB even when dissipative loss is present in the input circuit. We have used this mismatch effect to reduce the measured NF of our link to 2.5 dB at 130 MHz. We believe this is the first demonstration of amplifierless-link NF of less than 3 dB.

Circularly polarized microstrip antenna with a single feed

A novel circularly polarized (CP) microstrip antenna with a single coaxial feed is introduced. The antenna consists of two layers, each radiating fields which at the zenith are perpendicular to each other with 90/spl deg/ phase difference. The CP bandwidth is substantially higher than that of the previously reported CP microstrip antennas with two nearly degenerate modes. In principle, a perfect CP radiation is feasible without the input impedance mismatch. The CP design procedure is independent of the feed location.