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We present novel PIN photodiode (PD) continuous wave (cw) terahertz (THz) emitters with an increased responsivity and reduced substrate thickness compared to the state-of-the-art. Our improved devices feature up to 4 dB higher output power below 500 GHz with maximum power of -0.53 dBm at 115 GHz and strongly reduced THz absorption of the substrate for frequencies above 3 THz. The latter enables us to measure coherent cw THz spectra with a record bandwidth of 5.5 THz, for the first time, which is 1 THz (22%) more than the state-of-the-art. [ABSTRACT FROM AUTHOR]

A novel broadband antenna designed for the terahertz (THz) frequency range is proposed and developed for the THz emitter on a photomixer chip. This THz emitter comprises an ultra-high-speed indium phosphide photodetector integrated with a planar THz antenna. This paper presents a novel broadband antenna configuration comprising a combination of bowtie and circular patch elements designed for the frequency range of 150 GHz to 500 GHz. Detailed parametric analysis of the antenna's design parameters is also provided. The simulation results demonstrate that the optimized antenna achieves an impedance bandwidth of 350 GHz, satisfying the |S11| ≤ −10 dB condition, and exhibits a relative bandwidth of 107% within the 150 GHz to 500 GHz frequency range. This novel broadband terahertz antenna showcases an exceptional wideband performance and is highly suitable for high-speed transmission systems. [ABSTRACT FROM AUTHOR]

A novel broadband antenna designed for the terahertz (THz) frequency range is proposed and developed for the THz emitter on a photomixer chip. This THz emitter comprises an ultra-high-speed indium phosphide photodetector integrated with a planar THz antenna. This paper presents a novel broadband antenna configuration comprising a combination of bowtie and circular patch elements designed for the frequency range of 150 GHz to 500 GHz. Detailed parametric analysis of the antenna’s design parameters is also provided. The simulation results demonstrate that the optimized antenna achieves an impedance bandwidth of 350 GHz, satisfying the |S11| ≤ −10 dB condition, and exhibits a relative bandwidth of 107% within the 150 GHz to 500 GHz frequency range. This novel broadband terahertz antenna showcases an exceptional wideband performance and is highly suitable for high-speed transmission systems.

We present an ultra-broadband and inexpensive photonic spectrum analyzer (PSA) for wireless signals with a frequency coverage from the microwave range till deep into the terahertz range. The difference frequency of two continuous-wave laser diodes works as the local oscillator frequency and a photoconductive antenna downconverts a signal under test with the aid of the optical local oscillator. With this approach we achieve a frequency coverage from less than 25 GHz to more than 1.25 THz, mostly limited by the tuning range of the lasers. No component of our spectrum analyzer needs to be interchanged in order to achieve the full tuning range, which makes our spectrum analyzer a fraction of the cost of an electronic spectrum analyzer that requires several extension modules for covering a similar frequency range. The system offers a minimum resolution bandwidth of 1.2 MHz at a displayed average noise level (DANL) as low as −113.8 dBm/Hz at 100 GHz or as low as −88.2 dBm/Hz at 1050 GHz.

A configuration and test samples of photoconductive dipole antennas based on SI-GaAs:Cr and LT-GaAs for generation and detection of terahertz radiation are developed. Their operating characteristics in the pulsed mode and in the mode of operation as photomixers are experimentally investigated. [ABSTRACT FROM AUTHOR]

We developed a thermo-optic effect based silica optical phased array (OPA) chip and evaluated its tunability of phases of lightwaves. The THz waves, whose phases are controlled by the OPA chip, are generated from four arrayed uni-travelling-carrier photodiodes (UTC-PDs) based on heterodyne photomixng. Meanwhile, the UTC-PDs, which integrated with $4\times 4$ slot antennas, are fabricated on a monolithic InP substrate chip for 300-GHz wave beam combining and steering. Through the optoelectronic THz-wave phase control, the feasibility of 300-GHz beam continuous steering is successfully demonstrated in a range of 50°. [ABSTRACT FROM AUTHOR]

This manuscript reports the first leaky-wave antenna (LWA) array excited by a photomixer as well as its potential application for alignment in wireless links. The designed array is manufactured in printed circuit board (PCB) technology, works at the E-band (from 75 to 85 GHz), and provides a directive beam of about 18 dBi with a frequency scanning span of 22°. The antenna element consists of a microstrip line periodically loaded with stubs, and it has been designed employing a hybrid approach combining full-wave simulations and transmission line theory. This approach enables the optimization of the periods when the open-stopband of the LWA is mitigated or removed at the frequency of broadside emission. The proposed antenna was first tested using a ground signal ground (GSG) probe; the measured return loss and radiation patterns of the fabricated prototype were in good agreement with full-wave simulations. Then, the LWA array was integrated with the photomixer chip using conductive epoxy threads. Measurements of the radiated power yielded a maximum of 120 µW at 80.5 GHz for a 9.8 mA photocurrent. Finally, the antenna was used in a 25 cm wireless link, obtaining a 2.15 Gbps error-free data rate. [ABSTRACT FROM AUTHOR]

In this manuscript, the use of dielectric rod waveguide antenna (DRW) with an embedded planar lens is proposed as a highly directional alternative to an electrically large hyper-hemispheric silicon lens for emission at millimeter and sub-millimeter wave frequencies. DRW antennas radiate properly if only the fundamental mode is excited to the structure. Since photomixer-based terahertz sources excite many modes, single-lobe radiation patterns are obtained only for lower frequencies of their potential working band. The use of embedded planar lenses is proposed for rectifying the wavefront phase and suppressing such higher-order modes in DRW, allowing an ultra-wideband operation. [ABSTRACT FROM AUTHOR]

A slot fed terahertz dielectric resonator antenna driven by an optimized photomixer is proposed, and the interaction of the laser and photomixer is studied. It is demonstrated that in a continuous wave terahertz photomixing scheme, the generated THz power is proportional to the 4th power of the surface electric field of photocondutive layer. Consequently, the optical to THz conversion efficiency of the proposed photomixer has an enhancement factor of 487. This is due to the fact that the surface electric field of the proposed photomixer with a 2D-Photonic Crystal (PhC) superstrate has been improved from 2.1 to 9.9 V/m, which represents a substantial improvement. Moreover, the electrically thick Gallium-Arsenide (GaAs) supporting substrate of the device has been truncated to create a dielectric resonator antenna (DRA) that offers a typical radiation efficiency of more than 90%. By employing a traditional coplanar strip (CPS) biasing network, the matching efficiency has been improved to 24.4%. Therefore, the total efficiency has been considerably improved due to the enhancements in the laser-to-THz conversion, as well as radiation and matching efficiencies. Further, the antenna gain has been improved to 9dBi at the presence of GaAs superstrate. Numerical comparisons show that the proposed antenna can achieve a high gain with relatively smaller dimensions compared with traditional THz antenna with Si lens.

This manuscript reports the first leaky-wave antenna (LWA) array excited by a photomixer as well as its potential application for alignment in wireless links. The designed array is manufactured in printed circuit board (PCB) technology, works at the E-band (from 75 to 85 GHz), and provides a directive beam of about 18 dBi with a frequency scanning span of 22°. The antenna element consists of a microstrip line periodically loaded with stubs, and it has been designed employing a hybrid approach combining full-wave simulations and transmission line theory. This approach enables the optimization of the periods when the open-stopband of the LWA is mitigated or removed at the frequency of broadside emission. The proposed antenna was first tested using a ground signal ground (GSG) probe; the measured return loss and radiation patterns of the fabricated prototype were in good agreement with full-wave simulations. Then, the LWA array was integrated with the photomixer chip using conductive epoxy threads. Measurements of the radiated power yielded a maximum of 120 µW at 80.5 GHz for a 9.8 mA photocurrent. Finally, the antenna was used in a 25 cm wireless link, obtaining a 2.15 Gbps error-free data rate.

We have fiber-coupled an array of n-i-pn-i-p superlattice photomixers using a fiber array of same pitch of 145 \mu \textm . We experimentally investigate the effect of the finite size of the implemented silicon lens on the interference between the array elements in the far field. We compare the results from a geometry optimized for a collimated terahertz (THz) beam to theory and simulations. Further, beam steering is demonstrated by controlling the optical phase of the individual photomixers. Due to broadband antennas attached to each array element, the array is frequency tunable. It is exemplarily characterized at 165 and 310 GHz. Such arrays can overcome power limitations of individual photomixers. In contrast to bulky individually packaged free space solutions, this array can be packaged to a compact terahertz source, limited in size only by the size of the silicon lens. The investigated $2 \times 2$ array features a spot diameter (full-width at half-maximum) of 12.1 mm at a distance of 19 cm at 310 GHz with a silicon lens of only 20-mm diameter. [ABSTRACT FROM AUTHOR]

A photoconductive fractal antenna significantly improves the performance of photomixing-based continuous wave (CW) terahertz (THz) systems. An analysis has been carried out for the generation of CW-THz radiation by photomixer photoconductive antenna technique. To increase the active area for generation and hence the THz radiation power we used interdigitated electrodes that are coupled with a fractal tree antenna. In this paper, both semiconductor and electromagnetic problems are considered. Here, photomixer devices with Thue-Morse fractal tree antennas in two configurations (narrow and wide) are discussed. This new approach gives better performance, especially in the increasing of THz output power of photomixer devices, when compared with the conventional structures. In addition, applying the interdigitated electrodes improved THz photocurrent, considerably. It produces THz radiation power several times higher than the photomixers with simple gap. [ABSTRACT FROM AUTHOR]

Photoconductive antennas are promising sources of terahertz radiation that is widely used for spectroscopy, characterization, and imaging of biological objects, deep space studies, scanning of surfaces, and detection of potentially hazardous substances. These antennas are compact and allow for generation of both ultrabroadband pulses and tunable continuous wave terahertz signals at room temperatures, with no need for high-power optical sources. However, such antennas have relatively low energy conversion efficiency of femtosecond laser pulses or two close pump wavelengths (photomixers) into the pulsed and continuous terahertz radiation, correspondingly. Recently, an approach to solving this problem that involves known methods of nanophotonics applied to terahertz photoconductive antennas and photomixers has been proposed. This approach comprises the use of optical nanoantennas for enhancing the absorption of pump laser radiation in the antenna gap, reducing the lifetime of photoexcited carriers, and improving the antenna thermal efficiency. This Review is intended to systematize the main results obtained by researchers in this promising field of hybrid optical-to-terahertz photoconductive antennas and photomixers. We summarize the main results on hybrid THz antennas, compare the approaches to their implementation, and offer further perspectives of their development including an application of all-dielectric nanoantennas instead of plasmonic ones. [ABSTRACT FROM AUTHOR]

In this manuscript, the use of dielectric rod waveguide (DRW) antennas in the millimeter and sub-millimeter wave range is presented as a solution for covering two issues: getting more radiated power and filling a technological gap problem in the terahertz band, namely a fully electronic beam steering. A 4x4 element array working at 100 GHz fed by a rectangular waveguide is manufactured and measured for showing its capabilities. This topology can be used as a cost-affordable alternative to dielectric lenses in photomixer-based terahertz sources. [ABSTRACT FROM AUTHOR]

Compact and tunable semiconductor terahertz sources providing direct electrical control, efficient operation at room temperatures and device integration opportunities are of great interest at the present time. One of the most well-established techniques for terahertz generation utilises photoconductive antennas driven by ultrafast pulsed or dual-wavelength continuous wave laser systems, though some limitations, such as confined optical wavelength pumping range and thermal breakdown, still exist. The use of quantum dot-based semiconductor materials, having unique carrier dynamics and material properties, can help to overcome limitations and enable efficient optical-to-terahertz signal conversion at room temperatures. Here we discuss the construction of novel and versatile terahertz transceiver systems based on quantum dot semiconductor devices. Configurable, energy-dependent optical and electronic characteristics of quantum-dot-based semiconductors are described, and the resonant response to optical pump wavelength is revealed. Terahertz signal generation and detection at energies that resonantly excite only the implanted quantum dots opens the potential for using compact quantum dot-based semiconductor lasers as pump sources. Proof-of-concept experiments are demonstrated here that show quantum dot-based samples to have higher optical pump damage thresholds and reduced carrier lifetime with increasing pump power. [ABSTRACT FROM AUTHOR]

We designed and fabricated a semiconductor optical amplifier-integrated dual-mode laser (SOA-DML) as a compact and widely tunable continuous-wave terahertz (CW THz) beat source, and a pin-photodiode (pin-PD) integrated with a log-periodic planar antenna as a CW THz emitter. The SOA-DML chip consists of two distributed feedback lasers, a phase section for a tunable beat source, an amplifier, and a tapered spot-size converter for high output power and fiber-coupling efficiency. The SOA-DML module exhibits an output power of more than 15 dBm and clear four-wave mixing throughout the entire tuning range. Using integrated micro-heaters, we were able to tune the optical beat frequency from 380 GHz to 1,120 GHz. In addition, the effect of benzocyclobutene polymer in the antenna design of a pin-PD was considered. Furthermore, a dual active photodiode (PD) for high output power was designed, resulting in a 1.7-fold increase in efficiency compared with a single active PD at 220 GHz. Finally, herein we successfully show the feasibility of the CW THz system by demonstrating THz frequency-domain spectroscopy of an a-lactose pellet using the modularized SOA-DML and a PD emitter. [ABSTRACT FROM AUTHOR]

We propose a dielectric rod waveguide antenna (DRW) integrated with a photomixer as a THz emitter. This represents a different approach as opposed to the classical solution of a substrate lens. Main goals are an inexpensive alternative to substrate lenses, reduction of both reflections on the semiconductor-air interface and scattering of terahertz-generated power into the substrate. A radiation pattern measured at 137 GHz is shown as a proof-of-concept. In order to increase radiated power, the improvement of the rod antenna is discussed. Finally, as an application example, evanescent coupling of the DRW into a high index whispering gallery mode resonator is shown. [ABSTRACT FROM PUBLISHER]

We propose a new generation of unbiased (biasfree) antenna-less CW THz photomixer emitters array made of asymmetric MSM gratings with subwavelength pitch, operating in optical nearfield regime. We take advantage of the size effects in near-field optics and electrostatics to demonstrate the possibility of enhancing the THz power by four orders of magnitude, as compared with a similar array of the same size that operates in the far-field regime. We show that with an appropriate choice of grating parameters in such THz sources the first plasmonic resonant cavity mode in nano-slit between two adjacent MSM can enhance the optical near-field absorption and hence the photo carriers' generation under the slit in the active medium. These photo carriers, on the other hand, are accelerated by the large built-in electric field sustained under the nano-slits by two dissimilar Schottky barriers to create the desired large THz power that is mainly radiated downward. A hybrid numerical simulation method is used to model and analyze these phenomena. [ABSTRACT FROM AUTHOR]

By a convolution approach for the spectra generated by photoconductive and photomixing THz emitters, the intrinsic response of the material can be separated from the spectrum of the optical pulse and that of any attached antenna. The spectrum turns out to be simply a product of the spectra of the individual components and can be calculated analytically. This result has impact on materials design and derivation of the optimum excitation conditions for photoconductors and photodiodes. Spectra of three technologically important devices, namely low-lifetime materials, semi-insulating materials and devices supporting ballistic transport, are calculated. The derived pulse shape is compared to experimental data. [ABSTRACT FROM AUTHOR]

In this letter, we present low-temperature grown GaAs (LTGGaAs)- based photoconductive antennas for the generation and detection of terahertz (THz) waves. The growth of LTG-GaAs and the annealing temperatures are systematically discussed based on the material characteristics and the properties of THz emission and detection. The optimum annealing temperature depends on the growth temperature, which turns out to be 540°C to 580°C for the initial excess arsenic density of 2×1019/cm³ to 8×1019/cm³. [ABSTRACT FROM AUTHOR]

We report on a study of terahertz (THz) generation using implanted InGaAs photomixers and multi-wavelength quantum dot lasers. We carry out InGaAs materials growth, optical characterization, device design and fabrication, and photomixing experiments. This approach is capable of generating a comb of electromagnetic radiation from microwave to terahertz. For shortening photomixer carrier lifetime, we employ proton implantation into an epitaxial layer of lattice matched InGaAs grown on InP. Under a 1.55 µm multi-mode InGaAs/InGaAsP quantum dot laser excitation, a frequency comb with a constant frequency spacing of 50 GHz generated on the photomixer is measured, which corresponds to the beats of the laser longitudinal modes. The measurement is performed with a Fourier transform infrared spectrometer. This approach affords a convenient method to achieve a broadband multi-peak coherent THz source. [ABSTRACT FROM AUTHOR]

A full-wavelength dipole antenna on a GaAs membrane, covered with a silicon lens to improve the output power of a terahertz (THz) photomixer, is proposed. A full-wavelength dipole antenna supported by a GaAs membrane structure has been proven to achieve both high input resistance and high radiation efficiency for improved overall efficiency. However, the antenna has insufficient directivity. An extended hemispherical lens was introduced in front of the antenna in a non-contact configuration and coupled to the antenna radiation to achieve high directivity by beam collimation. This approach greatly enhances the antenna directivity while avoiding an inherent obstacle of the input resistance reduction caused by the high permittivity lens substrate. The resulting antenna after optimization had a 3818-Ω input resistance and a 71.2% radiation efficiency, corresponding to approximately 57% total efficiency at the 1.07-THz resonance frequency. The total efficiency of this structure is approximately 6.8 times that of a full-wavelength dipole antenna with the same hemisphere lens size while exhibiting slightly lower directivity. [ABSTRACT FROM AUTHOR]

In this paper, a full-wavelength dipole antenna, supported by a GaAs membrane structure, is examined. The antenna was designed with both high input resistance and high radiation efficiency to improve the overall efficiency of a terahertz photomixer design. The geometrical effects of the GaAs membrane structure on the overall antenna performance were investigated through an optimization process. To supply DC bias to the antenna, a bias line with a photonic bandgap (PBG) structure was designed and optimized. The resulting antenna had a 2742-Ω input resistance and a 65% radiation efficiency, corresponding to an approximately 44% total efficiency at the 1.05-THz resonance frequency. The proposed antenna is expected to efficiently generate THz waves and be applicable to many practical applications where large coverage (detection area), easy alignment, and high scanning speed, rather than high-resolution, are preferred. [ABSTRACT FROM AUTHOR]

We present design and experimental results on novel antenna-integrated edge-coupled photodiodes, examining particularly their suitability as photomixers for broadband terahertz sources. We show that a simple “stub” detector positioned at the edge of the chip can yield promising overall performance when integrated with a number of different planar antennas specifically designed for this configuration. Using a slot-horn antenna connected via a coplanar line, we measure terahertz emission figures of 100 \muW over the range 100–500 GHz, with 50 \muW available at 750 GHz. We also present a novel planar double-horn antenna and show that with suitable use of terahertz “optics” this offers broadband through-substrate emission from 200 GHz to over 1 THz, with 10 \muW terahertz power emitted at 1.004 THz. [ABSTRACT FROM PUBLISHER]

In this paper, a global and geometry-independent approach is proposed for accurate analysis of edge-coupled continuous wave (CW) traveling-wave terahertz photomixer sources. All major physical phenomena involved in the operation of such devices are included in three interconnected solvers, which are combined as a unified analysis tool. A photonic solver is developed to find the optical intensity across the fast photoabsorbing region from which the carrier generation rate is determined. A semiconductor solver is used to study the charge carrier transport inside the photoconductive region through drift-diffusion model, and to predict the generated photocurrent with the beat frequency of two CW lasers. An electromagnetic solver is introduced to rigorously calculate the coupled terahertz signal into the guiding transmission line through a Lorentz reciprocity theorem. Theoretical formulation behind each solver is discussed in detail, and numerical results from each solver are presented. The proposed approach is a powerful tool for global optimization of the photoconductive sources, especially for maximizing the optical-to-terahertz power conversion. [ABSTRACT FROM AUTHOR]

This paper presents the design of terahertz Yagi-Uda antennas with high input resistance. The proposed Yagi-Uda antennas can achieve much higher input resistance than existing THz antennas by using a full-wavelength straight-line dipole and a full-wavelength U-shaped dipole as driver elements. Current leakage into the bias line was minimized by applying photonic bandgap structures at the bias line. By designing the antennas on a thin substrate, end-fire radiation patterns with high antenna resistance can be obtained even when the substrate has a high dielectric constant. We expect that the proposed Yagi-Uda antennas can achieve increased terahertz output power by improving their capacity for impedance matching with a photomixer. [ABSTRACT FROM AUTHOR]

We have devolved 1064 nm high-power monolithic distributed feedback lasers which operate simultaneously on two longitudinal modes. These modes correspond to the fundamental and first-order lateral mode and arise from a 7.5 mum width ridge waveguide supporting both of them. They are further stabilized by a first-order grating built into an InGaP/GaAs/InGaP multilayer structure. The threshold current of the laser is 66 mA, the slope efficiency is 0.5 W/A, and an output power of ~500 mW is reached. Detailed investigations of the intensity distribution of lateral and vertical far fields and the spectral behavior are shown. The longitudinal mode spacing at 260 mW is 0.56 nm corresponding to approximately 150 GHz. THz generation is demonstrated by mixing the two-line laser emission in a LT-GaAsSb photomixer. [ABSTRACT FROM PUBLISHER]

The terahertz region is one of the unexplored bands. This paper first reviews the present status of conventional high-speed devices, especially InP-based high electron mobility transistors (HEMTs), and addresses the technological problems facing the goal of terahertz operation. As an alternative approach to solve these problems, we developed a plasmon-resonant photomixer for realizing a coherent terahertz continuous-wave source. Preliminary results on electromagnetic response to impulsive photoexcitation at room temperature are reported briefly. [ABSTRACT FROM AUTHOR]

Abstract: A spectrometer operating in the 100–2000GHz range and allowing for absolute line strength measurements has been developed. The continuous wave terahertz radiation is generated by mixing two Ti:Sapphire laser beams in a vertically integrated low temperature grown GaAs (LTG-GaAs) photomixer. Pure rotational lines of 16O12C32S in the ground vibrational state have been considered for J values up to 90. Observed self-broadening parameters are in agreement with those deduced from infrared experiments. For the first time in the submillimeter range, absolute line strengths have been determined, allowing for a determination of the electric dipole moment in good agreement with the value previously obtained from Stark effect measurements. [Copyright &y& Elsevier]

We report on a completely coherent, tunable, continuous-wave THz system where, for the first-time, both the transmitter and receiver are log-periodic-antenna coupled LTG-GaAs based finger-photomixers. This compact room-temperature system exhibits signal-to-noise ratios (> 103) comparable to or better than what is reported in the literature, and has potential applications in high-resolution spectroscopy and imaging. For the purpose of demonstration, we also present results of spectroscopy measurements carried out on fused silica, which are in agreement with previously published THz-TDS measurements. [ABSTRACT FROM AUTHOR]

A tunable CW-THz system with a LTG-GaAs based THz source, which consists of an interdigitated finger photomixer integrated log-periodic antenna, is presented. The performance is compared against that of several other broadband CW-THz systems with LTG-GaAs based emitters, incorporating bow-tie and log-spiral antenna geometries. This comparison shows that our maximum output THz power level is within an order of magnitude of that of the state-of-the-art. [Copyright &y& Elsevier]

A slot fed terahertz dielectric resonator antenna driven by an optimized photomixer is proposed, and the interaction of the laser and photomixer is studied. It is demonstrated that in a continuous wave terahertz photomixing scheme, the generated THz power is proportional to the 4th power of the surface electric field of photocondutive layer. Consequently, the optical to THz conversion efficiency of the proposed photomixer has an enhancement factor of 487. This is due to the fact that the surface electric field of the proposed photomixer with a 2D-Photonic Crystal (PhC) superstrate has been improved from 2.1 to 9.9 V/m, which represents a substantial improvement. Moreover, the electrically thick Gallium-Arsenide (GaAs) supporting substrate of the device has been truncated to create a dielectric resonator antenna (DRA) that offers a typical radiation efficiency of more than 90%. By employing a traditional coplanar strip (CPS) biasing network, the matching efficiency has been improved to 24.4%. Therefore, the total efficiency has been considerably improved due to the enhancements in the laser-to-THz conversion, as well as radiation and matching efficiencies. Further, the antenna gain has been improved to 9dBi at the presence of GaAs superstrate. Numerical comparisons show that the proposed antenna can achieve a high gain with relatively smaller dimensions compared with traditional THz antenna with Si lens. [ABSTRACT FROM AUTHOR]

Millimeter-wave (MMW) frequencies (30–300 GHz), located between the microwave and infrared (IR), are promising solutions for the increasing demand of high data rate applications, UHD multimedia, HD gaming, security, surveillance, and the emergence of 5G Internet of Things (IoT). In this article, we experimentally demonstrated MMW wireless communication link using InGaAs p-i-n photomixer and commercially available telecom components at W-band (75–110 GHz). The photomixer was excited by two 1.5 µm lasers via standard telecom fiber optics, to generate frequency difference at W-band. QPSK modulated signal transmitted by the photomixer and received horn antenna integrated MMW mixer and analyzed using a spectrum analyzer and Vector Signal Analyzer (VSA) software. [ABSTRACT FROM AUTHOR]