Dongya Shen

Impact of Optical Transmission on Multiband OFDM Ultra-Wideband Wireless System With Fiber Distribution

Multiband (MB) orthogonal frequency-division multiplexing (OFDM) ultra-wideband (UWB) wireless, which provides high data rate access, is required to be distributed by using optical fiber. The performance of MB-OFDM UWB over fiber transmission system is investigated considering optical modulation and demodulation impact. Theoretical analysis of the effect of fiber dispersion, optical transmitter, and optical receiver response on system performance is carried out considering amplitude and phase distortion. Experiments are conducted and verified by our theoretical analysis and good agreement is obtained. It is found that RF modulation index of ~4% is optimum for optical transmitter with Mach-Zehnder modulator, and optical receiver with Chebyshev-II response is the best for MB-OFDM UWB over fiber. Compared to back-to-back UWB over fiber, optical transmission is mainly limited by laser phase noise converted relative intensity noise and phase distortion induced by fiber dispersion when optimum modulation index is used. Higher modulation index is limited by amplitude and phase distortion to OFDM signal induced by optical transmitter and receiver response nonlinearities and fiber dispersion and the spectral mask. It is also found that highly received optical power is required for transmission of MB-OFDM UWB signal over fiber.

A Small UWB Antenna with Dual Band-Notched Characteristics

A small novel ultrawideband (UWB) antenna with dual band-notched functions is proposed. The dual band rejection is achieved by etching two C-shaped slots on the radiation patch with limited area. A single band-notched antenna is firstly presented, and then an optimized dual band-notched antenna is presented and analyzed. The measured VSWR shows that the proposed antenna could operate from 3.05 to 10.7 GHz with VSWR less than 2, except two stopbands at 3.38 to 3.82 GHz and 5.3 to 5.8 GHz for filtering the WiMAX and WLAN signals. Radiation patterns are simulated by HFSS and verified by CST, and quasiomnidirectional radiation patterns in the H-plane could be observed. Moreover, the proposed antenna has a very compact size and could be easily integrated into portable UWB devices.

A Compact Disc UltrawideBand (UWB) Antenna With Quintuple Band Rejections

A compact disc ultrawideband (UWB) antenna with quintuple band rejections is proposed and demonstrated, which has a portrait shape and is therefore “portrait antenna.” The quintuple band-notched functions are achieved by utilizing C-shaped slots, nested C-shaped slots, U-shaped slots, and open-circuit stubs. It is demonstrated that the portrait antenna operating from 2.45 to 12 GHz (VSWR <; 2) has omnidirectional radiation patterns with a gain greater than 2 dBi, and also five stopbands (VSWR >; 2) of 3.27-3.57, 5.01-5.45, 5.55-6.05, 7.05-7.45 and 7.83-8.19 GHz are implemented simultaneously for rejecting WiMAX, WLAN, downlink of X-band satellite communication, and ITU 8-GHz band signals. Moreover, the antenna has a simple structure and a compact size.

Broadband Predistortion Circuit Using Zero Bias Diodes for Radio Over Fiber Systems

A low-cost broadband analog predistortion circuit (PDC) is designed and experimentally verified in a radio over fiber (RoF) system. A miniature hybrid microwave integrated circuit technique is used to reduce the size and parasitics of PDC. Only two zero bias GaAs beam lead detector diodes and capacitors are used in the PDC. The diodes can be biased at due to zero bias characteristic so that power consumption is reduced. No broadband matching network is required because of high series resistance of the zero bias diodes. The linearization performance is evaluated using an RoF system without and with the PDC. It is shown that the PDC improves the input 1-dB compression power by 0.4-2.2 dB from 7 to 18 GHz; and spurious free dynamic ranges are improved by ~ 10 dB from 7 to 14 GHz and ~ 6 dB from 15 to 18 GHz, limited by fifth order nonlinear distortion.

Gap Waveguide PMC Packaging for a SIW-GCPW-Based Filter

In addition to microstrip line and basic grounded coplanar waveguide (GCPW) line circuits with perfect magnetic conductor (PMC) package, we further study the PMC package for a real component-a fifth order bandpass filter designed based on substrate integrated waveguide (SIW) with transitions to GCPWs. In particular, a simplified design of the PMC package is proposed for such a hybrid circuit. A fabricated SIW-GCPW filter was characterized without a lid, and with a traditional smooth lid, a modified smooth lid, a complete PMC lid and a simplified PMC lid. Both simulated and measured S-parameters show that the filter outband rejection using the proposed simplified PMC lid is better than the traditional and existing lids.

Mach-Zehnder: A Review of Bias Control Techniques for Mach-Zehnder Modulators in Photonic Analog Links

The Mach-Zehnder modulator (MZM) has been widely used for broadband photonic analog links and high-speed digital optical fiber communication systems because it possesses large modulation bandwidth, low driving voltage, and low chirp. The MZM is a very important optical modulator for photonic applications. In an MZM, the input light is split into two paths, each of which is modulated by an electrical signal. Then the two arms are combined to generate an intensity-modulated light or a phase-modulated light at the output of the MZM. An MZM can be made of lithium niobate (LiNbO3), gallium arsenide (GaAs), or indium phosphide (InP), materials that exhibit some anisotropy in their dielectric properties. Theoretically, the relation of output optical field and driving voltage is a cosine function, i.e., nonlinear transfer function. For RF photonics, the MZM has typically two applications: optical harmonic generation for optical frequency multiplication and optical subcarrier modulation for optical signal modulation. For optical frequency multiplication, high transfer-function nonlinearity is preferred. In contrast, high transfer-function linearity is preferred for optical subcarrier modulation. It is well known that a cosine transfer function can present high or low nonlinearity dependent on operation voltage. Specifically, bias voltages determine the degree of nonlinearity or linearity of the MZM transfer function. For optical frequency multiplication such as millimeter-wave generation, the MZM should be biased at some specific bias points, such as minimum transmission, maximum transmission, and quadrature bias points, to enhance nonlinearity [1]?[2]. For optical subcarrier modulation, biasing an MZM in its linear region such as quadrature bias points allows transmitting broadband RF signals with multioctave bandwidth and improves spurious free dynamic range (SFDR). Therefore, care must be taken to maintain and control the MZM bias point for a specific application.

A Novel Wideband Printed Diversity Antenna for Mobile Handsets

A novel printed compact wide-band diversity antenna for mobile handsets is proposed in this paper. The antenna comprises two back-to-back G-shaped monopoles placed symmetrically with respect to a T-shaped and dual inverted-L-shaped ground plane. The measured results show that the proposed diversity antenna operates in a very wide bandwidth of 1200 MHz starting from 1700 MHz to 2900 MHz. In the above bands, the isolations of the prototype are better than -15 dB. The antenna can provide pattern diversity to combat multipath fading.

Novel broadband analog predistortion circuit for radio-over-fiber systems

A novel broadband analog predistortion circuit (PDC) is designed to linearize radio-over-fiber (RoF) systems. Dual Schottky diode is used as predistorter. The PDC with high bandwidth and small dimension is achieved by removing quarter-wavelength transformers and power dividers. Measured S-parameters show that the PDC can work from 10 MHz to up to 40 GHz. The PDC is verified using two-tone and WiFi signals in an RoF system. The spur-free dynamic range with respect to third order intermodulation distortion is improved by more than 10 dB from 1 to 5 GHz and more than 5 dB from 1 to 30 GHz, and it is found that the RoF system is limited by fifth order nonlinearity. Error vector magnitude is improved by 1 dB for WiFi signals at 2.4 and 5 GHz by using the PDC.

Gap Waveguide-Based PMC Packaging for via Holes-Caused Nonsmooth PEC Surface

We investigate the application of perfect magnetic conductor (PMC) packaging for a nonsmooth perfect electric conductor surface, caused by metalized via holes. The PMC shielding is artificially built by a metal lid of pins, based on the gap waveguide (GW) technology. As a foundation, the effects of via hole in a unit cell are studied first considering its diameter, substrate thickness, pin size, pin height, as well as relative position between the via hole and the pin. The via adjacent space and pin rows are also considered for a general grounded coplanar waveguide along with ground vias. The effectiveness of package for such a transmission line containing metalized via holes is then verified experimentally. It is shown that the measured performance agrees well with the simulation. This paper presents a guideline for the GW-based PMC packaging technology.

A novel miniaturized UWB antenna with 5.7 GHz band rejection function

A novel miniaturized ultra wide band (UWB) antenna with 5.7 GHz band rejection function is presented. By utilizing asymmetric structure, the antenna has been miniaturized and has a very compact size of 22×12.7×1.5 mm3. Band rejection function is achieved by etching a C-shaped slot on the patch. Simulated and measured results show that the proposed antenna could operate from 3.1 to 11.4 GHz for S11 ≤ -10 dB with stable radiation patterns. A miniaturized UWB antenna is also provided for reference.