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A slim and semi-flexible UHF RFID tag antenna, which has a compact dimension of 40 mm $\times $ 5 mm $\times $ 3.2 mm ( $0.1221\lambda \times 0.0153\lambda \times 0.0098\lambda $ ), is proposed for tagging on metallic industrial tools with a narrow footprint. For a metal-mountable tag antenna, the unwanted electromagnetic antenna-metal interaction can deteriorate the tag read performances and it is particularly pronounced when the tag is attached to a narrow industrial tool. To achieve a size-reduction, the proposed tag is made of an inlay comprising a very compact 3-layer structure with two radiating patches. The currents on the top and middle patches can be made in phase for enhancing the radiated fields. Digital serrations, inductive stubs, and open slots loading have been studied for optimizing the antenna resonant frequency efficiently. With the use of the tuning mechanisms, when being tested on a narrow-body metal tool, the antenna impedance can be fully matched with the RFID microchip impedance, resulting in a good power transmission coefficient of ~ 1. Despite its compactness, the proposed tag antenna is readable from 11.0 m with an EIRP of 4W. To the best of our knowledge, the proposed tag antenna has a much better aspect ratio between its read distance and tag volume than most of the commercially available on-metal tags and it can be used for tagging on narrow metallic surfaces.

A new type of tag antenna, which is made by placing four identical planar inverted-L antennas (PILAs) in rotational symmetry constellation, is proposed for designing a miniature on-metal tag antenna. It shows good omnidirectional characteristics in the azimuth plane. In the design, the directive radiation beams of the respective PILAs are tactfully combined to form a stable omnidirectional pattern. The proposed tag is compact with a small size of 40 mm $\times40$ mm $\times1.6$ mm ( $0.122\,\,\lambda \times 0.122\,\,\lambda \times 0.005\,\,\lambda $ ). Here, all the PILAs are inductively excited by a circular loop, which also introduces additional reactance for improving the impedance matching. The proposed tag antenna is able to achieve a stable read distance of 5.9 m on metal in the azimuth plane when it is tested using equivalent isotropic radiated power of 4 W. The operating frequency of the tag is stable and it is not affected much by changes in the backing metal.

For the first time, the folded crossed-dipole structure is explored for designing a compact metal tag (40 mm $\times $ 40 mm $\times $ 1.6 mm) that can be read in all boresight directions. The tag structure consists of a pair of folded crossed-dipoles which are orthogonally displaced for achieving polarization diversity, where the angular reading range has been extended by removing the null points. In the design, a parasitic metal ring is loaded beneath the radiator for tuning down the tag resonant frequency effectively. Good impedance matching with high power transmission is achievable by employing additional tuning mechanisms such as slotting the radiating dipole arms and adding rectangular patches beneath the slots. Design schemes for optimizing the impedance matching between the antenna and the chip have also been thoroughly discussed. Conjugate impedance match is found to be easily achievable by tuning the design parameters. To understand the impedance characteristics, an equivalent circuit has been derived for the proposed tag antenna. When tested using a linearly polarized reader antenna with a transmitting power of 4 W EIRP, the tag antenna is detectable from 5.6 m to 7.7 m in the boresight and it can be read in all directions.

In this paper, a pair of differentially fed coplanar waveguides is employed for exciting a folded patch antenna for designing a metal-mountable UHF RFID tag. The proposed tag has a compact size of 30 mm $\times \,\,25$ mm $\times \,\,3.0$ mm. Multiple slots are incorporated into the patch for tuning the resonant frequency and optimizing the impedance matching between the chip and the antenna. Two inductive stubs are introduced at two corners of the radiating patch to enable further frequency tuning. An equivalent circuit has been given for characterizing the tag’s impedance characteristics. When tested on a 20 cm $\times\,\,20$ cm metal plate, the read range of the proposed tag can achieve 8.9 m (4 W EIRP) using the Monza R6 microchip (with chip sensitivity of −20 dBm). Also, it has been found that the resonant frequency of the proposed tag antenna is stable and it does not shift much when the size of the backing metal is varied. The read distance is also more than 4 m when the proposed tag is attached to various dielectric materials with permittivity $\varepsilon _{r}$ in the range of 1–12.4.

A miniature folded radio frequency identification (RFID) tag antenna which has an embedded artificial magnetic conductor (AMC) structure is proposed for the first time. The AMC occupies no footprint virtually as it is embedded inside the antenna itself. By incorporating an interlayer AMC in between a dipolar patch and its ground plane, the tag resonant frequency can be easily scaled down to the useful ultrahigh frequency (UHF) band with good realized gain and far read distance. The proposed tag antenna can be easily fabricated on a single piece of a thin flexible polyethylene terephthalate (PET) substrate by using the standard printed-circuit-board (PCB) processes. With a compact size of only 30 mm $\times50$ mm $\times3.35$ mm $(0.092 \lambda \times 0.153 \lambda \times 0.010\lambda)$ , the proposed tag is able to achieve a far read distance of 9.8 m when it is measured using an effective isotropic radiated power (EIRP) power of 4 W. The tag resonant frequency is proven to be very stable and insensitive to the variations of the backing metal.

A compact tag antenna, which has a geometrical dimension of 20 mm $\times18$ mm $\times1.7$ mm ( $0.0615\lambda \times 0.0553\lambda \times 0.0052\lambda$ ), is proposed for metal-insensitive applications in the UHF radio frequency identification (RFID) band. The antenna structure comprises of a pair of dipolar patches, which are loaded with a non-resonating ring underneath. Changing the ring size is found to be able to tune the tag antenna’s resonant frequency and its impedance effectively. Capacitive and inductive effects introduced by the loading ring are useful for lowering the tag’s resonant frequency down to the useful UHF RFID band. The proposed tag is able to achieve more than 80% of power transmission coefficient, where the antenna impedance can match to the chip impedance quite well. Measurements show that the proposed tag antenna is readable from 6.62 m on metal with an effective isotropic radiation power (EIRP) power of 4 W. The tag’s resonant frequency is insensitive to changes in the backing object, which is advantageous for designing a stable RFID tag.

For the first time, a planar and low-profile magnetic loop antenna is proposed for designing an omnidirectional metal-mountable radio frequency identification (RFID) tag antenna. The proposed tag antenna, which consists of an annular slot exciter, a shorted patch, two shorting stubs, and four notches, can be easily made on one side of a flexible polyimide film. It has a dimension of 38 mm $\times \,\, 38$ mm $\times \,\, 1.6$ mm ( $0.116\lambda \times 0.116\lambda \times 0.0049\lambda$ ). The tag antenna is able to generate stable omnidirectional read patterns when placed on metal. The notches are not only employed for bringing down the tag’s resonant frequency to the ultrahigh (UHF) RFID band, but they can also be used for effectively reducing the gain fluctuation in the azimuth plane. Good maximum power transmission of ~90% is attainable. Measurements are conducted with reference to a transmitting power of 4W EIRP, and it has been shown that the proposed tag antenna is able to generate omnidirectional radiation patterns with a stable read distance of 5.29–5.65 m on metal in all directions in the azimuth plane. The tag’s resonant frequency is also very stable with a maximum fluctuation of only 0.22%.

In this research, a Coulomb force-assisted heat pump (CF-HP) dryer was invented for the purpose of improving the drying characteristics and product quality of biomaterials. As compared to HP drying...

A compact folded-patch antenna with a dimension of 45 mm $\times45$ mm $\times3.2$ mm ( $0.137\lambda \times 0.137\lambda \times 0.0097\lambda$ ) is proposed for on-metal applications. A T-shaped L-probe is employed for feeding the top-loaded radiating folded patch. It is found that good impedance matching can be easily achieved between the tag antenna and the microchip with the use of the T-shaped feeder. Also, the maximum power transmission coefficient can be significantly enhanced from 0.45 to 1. By adjusting some of the design parameters, the tag’s footprint area can be effectively reduced by 50% while maintaining considerably good read performance. The proposed tag antenna can not only radiate efficiently with a high radiation efficiency of 73.8% but also be read from a long read distance of 19 m when placed on a 20 cm $\times20$ cm metal plate with reference to a transmitting power of 4 W EIRP.

A single-layer or multilayer wall with thickness can be modeled accurately and efficiently as one infinitesimally thin patch in ray tracing by using correction factors to compensate for the ray path errors. This communication presents the correction factors to be used with the classical multiple-dielectric-interface reflection and transmission coefficients, for reflected, transmitted, and diffracted ray paths. It is shown that, with the aid of the correction factors, the ray-tracing simulation of an indoor scene with a penetrable hollow wedge formed by multilayer walls can produce results that match the 3-D full-wave results.

A highly miniaturized semi-flexible tag antenna, with dimensions 23 mm $\times \,\, 7.5$ mm $\times \,\, 3.2$ mm ( $0.0702\lambda \times 0.0229\lambda \times 0.0098\lambda $ ), is designed for tagging small metallic objects. It consists of three patches and two foams which are tactfully folded to form a very compact three-layer structure. Multiple slots are etched on the top and middle patches for increasing the current paths, where the slots on the top patch are made orthogonal to those in the middle one so that the currents on the two patches do not affect each other. This enables the currents on the two patches to be tuned independently without affecting the tag performances. Despite its small size, the proposed tag is able to generate sufficient antenna resistance to match the impedance of the microchip. As a result, it is able to achieve a good conjugate match with a power transmission coefficient of ~1. The tag has a very compact size of $\sim \lambda $ /14. It can be read from a distance of 5.0 m when tested on a metal surface with reference to a transmitted power of 4 W effective isotropic radiated power. To the best of our knowledge, as compared to most of the contemporary tags, this is the best performing tag antenna in terms of size-ratio (read distance/tag volume).

A compact tag antenna, which has a geometrical dimension of 40 mm $\times40$ mm $\times3.048$ mm ( $0.1224\lambda \times 0.1224\lambda \,\,\times 0.0093\lambda$ ), is proposed for metal-mountable applications in the UHF band. The antenna structure comprises a pair of semicircular microstrip dipolar patches which are orthogonally loaded with another pair of similar patches on the top. Rotating the orientation of the top-loading patch is found to be able to effectively tune the tag antenna’s resonant frequency and its impedance. The capacitive and inductive effects introduced by the top-loading patches are crucial for bringing the resonant frequency of the tag antenna down to the useful UHF band. Conjugate impedance matching is achieved between the antenna and the microchip. An equivalent circuit has been constructed to study the impedance characteristics. Measurements show that the proposed tag antenna is able to achieve a read distance of 12.25 m at the Effective Isotropic Radiated Power of 4 W. The operating frequency of the patch-loaded dipolar patches is found to be insensitive to changes in the size of the backing metal plate, which is very useful for designing a stable radio frequency identification (RFID) tag.

A compact UHF tag antenna, which consists of a bowtie-shaped folded patch antenna and two split ring resonators (SRRs), is proposed for on-metal applications. This antenna is made by using a flexible substrate and it is electrically small, having a circuit size of 40 $\text {mm} \times 40\,\,\text {mm} \times 3.18$ mm ( $0.122\lambda \times 0.122\lambda \times 0.010\lambda$ ). The SRRs introduce additional capacitance and inductance to the tag antenna’s impedance for achieving a conjugate match with the chip’s impedance. It is also found that the SRRs improve the radiation efficiency of the proposed tag antenna. The proposed tag antenna is able to achieve a far read distance of 9.5 m on metal when tested at EIRP power of 4 W. Most importantly, the resonant frequency of the proposed tag is stable and it is not affected much by the size and curvature of the backing metallic object.

A planar inverted-S antenna (PISA) is proposed for designing a compact ultrahigh frequency (UHF) radio frequency identification (RFID) tag for on-metal applications. For the first time, a U-shaped arm is embedded into the middle layer of the tag structure for effectively miniaturizing the footprint. Here, a serpentine patch is tactfully placed on top of the U-shaped arm to achieve a higher level of miniaturization. A compact UHF tag ( $25\,\,\text {mm} \times 25\,\,\text {mm} \times 3.2\,\,\text {mm}$ ), with a good power transmission coefficient of 99.7% and a long read distance of greater than 11 m, has been successfully demonstrated. It is also shown that our tag size can be further reduced to $15\,\,\text {mm} \times 15\,\,\text {mm} \times 3.2\,\,\text {mm}$ by simply adjusting the geometrical parameters, without sacrificing the power transmission coefficient much. With reference to a 4 W EIRP reader output power, the proposed tag antenna can be read from 11.9 m. For the tag with a footprint of $15\,\,\text {mm} \times 15\,\,\text {mm}$ , the read range is estimated to be at least 7 m.

A new type of C-shaped antenna, which is designed by combining a loop antenna and a planar inverted-L antenna, is proposed for designing a miniature tag antenna for on-metal applications. The proposed tag antenna can be easily made by folding a piece of flexible substrate. It is electrically small and low in profile, with a circuit size of 40 mm $\times40$ mm $\times1.6$ mm ( $0.122\lambda \times 0.122\lambda \times 0.005\lambda$ ). The antenna consists of five patch segments, which can be adjusted for achieving multiple degrees of tuning freedom. By tuning the antenna impedance, a conjugate match can be easily obtained. When mounted on a $20 \times 20$ cm2 metal plate, the proposed tag antenna is able to achieve a maximum read distance of 9.2 m with equivalent isotropic radiated power of 4 W, which is much better than the conventional loop antenna. The operating frequency of the proposed tag antenna is found to be very stable and it is not affected much when the dimensions of the backing metal object are varied.

A compact folded patch antenna, which has a dimension of 42 mm $\times50$ mm $\times1.6$ mm ( $0.128\lambda \times 0.152\lambda \times 0.0049\lambda $ ) is proposed. Multiple C-shaped slotlines are incorporated for tuning down the resonant frequency of the folded patch. A pair of double-T-slots, which acts as the impedance matching network, is etched at the center of the patch for achieving conjugate match between the antenna and the chip. By combining the analytical method and the particle swarm optimization algorithm, an equivalent circuit model is constructed for analyzing the impedance characteristics of the proposed tag antenna. With the use of 4 W EIRP, a maximum read distance of 11.5 m is achievable by placing the proposed tag antenna on a dielectric object. Also, the tag antenna is found to be able to reach ~5.2 m on metal. The operating frequency of the proposed tag antenna is very stable for both the dielectric and metallic objects, which is very desirable for practical applications.

A semiflexible E-shaped folded patch with a compact footprint of 30 mm $\times30$ mm $\times3$ mm ( $0.091\lambda \times 0.091\lambda \times 0.0091\lambda $ at 912 MHz) is proposed for designing a miniature ultrahigh frequency tag for on-metal applications. The proposed tag antenna is simple in structure, and it has eight design parameters to achieve different levels of tuning. By changing the parameters, coarse and fine tunings can be easily performed to vary the tag’s resonant frequency. In spite of its compactness, the proposed tag antenna is able to provide sufficient resistance and inductive reactance to enable conjugate match with the chip. Due to conjugate match, the proposed tag antenna has achieved a power transmission coefficient of ~1 and a maximum read distance of 14.5 m (with 4 W equivalent isotropic radiated power) on metal even it is electrically small. It has a radiation efficiency of 53%.

This paper describes two important improvements to a 3-D shooting-and-bouncing-polygon (SBP) ray tracer for radio propagation modeling. It introduces a way to trace diffracted–reflected (D–R) rays in the SBP framework and improves SBP accuracy when the D–R rays play an important role. It also introduces a better space partitioning scheme for the use with SBP and improves the SBP’s computation efficiency by more than $10\times $ in some applications. The numerical results are compared against published measurements and 3-D full-wave solutions. They show that the improved SBP ray tracer is a good multipurpose 3-D ray tracer which can be used to simulate urban street canyon (without double over-rooftop diffraction), indoor, and tunnel propagation environments.

A compact folded dipole antenna that consists of two C-shaped arms, which are placed in the antipodal constellation, is proposed for designing a metal-mountable miniature tag antenna in the UHF band. Here, each of the dipole arms is composed of four unequal line segments for reducing the current crowding effect and for improving the tag’s performance. Two inductive shorting stubs are introduced for tuning the tag’s resonant frequency. The proposed tag antenna is made using a flexible substrate and it is electrically small, having a circuit size of 50 mm $\times30$ mm $\times1.6$ mm ( $0.153\lambda \times 0.092\lambda \times 0.005\lambda$ ). It has been found that conjugate match can be easily obtained by adjusting the dimensions of the C-shaped arms and the inductive shorting stubs. When mounted on metal, the proposed tag antenna is able to achieve a maximum read distance of 9.1 m at the equivalent isotropic radiated power of 4 W. The proposed tag antenna is found to be platform insensitive and it can read beyond 7 m when placed on dielectric objects.

A low profile and metal-mountable ultrahigh frequency (UHF) tag antenna, which has a geometrical dimension of 47 mm $\times47$ mm $\times0.8128$ mm ( $0.143\lambda \times 0.143\lambda \times 0.0025\lambda$ ), is proposed. It has four identical open stubs attached to the circumference of a circular patch for performing coarse- and fine-tunings on the tag’s resonant frequency without affecting the read performances. At the center of the patch, a rectangular slot of $0.121\lambda \times 0.009\lambda \times 0.0025\lambda $ is etched for accommodating a microchip. Good impedance matching between the tag antenna and the microchip can be easily achieved by changing the dimensions of the center slot. It is also found that the introduction of the slot is crucial for bringing down the tag’s resonant frequency to the UHF band. In this paper, an equivalent circuit is also derived for studying the impedance characteristics of the proposed tag antenna. Measurements have been carried out with the use of an effective isotropic radiated power of 4 W, and maximum read distances of 3.45 m and ~1.7 m are attainable, respectively, when the tag is placed on metal plate and dielectrics. It is found that the resonant frequency of the proposed tag antenna is stable and not affected much by its backing objects.

A miniature folded patch with a dimension of $40\,\,\text {mm} \times 40\,\,\text {mm} \times 1.6\,\,\text {mm}\,\,(0.1156\lambda \times 0.1156\lambda \times 0.0046\lambda $ at 867 MHz) is proposed for designing a passive metal-mountable tag. It consists of a square patch which is equally separated into two rectangular patches. Since the patch resonator usually has high resonant frequency, multiple tuning mechanisms are always needed to bring down the frequency so that it can be used for designing a tag antenna in the UHF band. In the proposed design, each patch is incorporated with a C-shaped slot and three thin inductive stubs for performing different levels of frequency tunings. An equivalent circuit has been built for estimating the input impedance of the antenna. Reasonable agreement is found between the measured, modeled, and simulation results. The proposed tag antenna is readable from 5 m with an EIRP of 3.28 W when placed on a 20 cm $\times20$ cm metal plate.

A folded patch, which is centrally fed by a coplanar feedline, is proposed for designing a miniature UHF tag antenna for mounting on metal surfaces. The tag is designed using a flexible polyethylene terephthalate substrate with a very compact size of 25 $\text {mm} \times 40\,\,\text {mm} \times 3$ mm ( $0.0767\lambda \times 0.123\lambda \times 0.0092\lambda$ ). Conjugate match is attainable between the antenna and the microchip and it is able to achieve a maximum read distance of 10.7 m at the effective isotropic radiated power of 4 W. In the design, two notches have been incorporated with an inductive stub for tuning of the tag’s resonance over a larger frequency range. Also, a simple equivalent circuit has been derived to characterize the impedance of the tag antenna. The resonant frequency of the proposed tag antenna is found to be insensitive to various sizes of the backing metal object, which is a very desirable feature for tag design. The proposed tag can achieve a read distance of greater than 10 m when placed on metal. It is able to be read beyond 5 m when it is placed on dielectrics with permittivity in the range of 1–5.8.

A single-layer microstrip patch unit element, which is loaded with eight concentric L-shaped slots, is proposed for reflectarray design. In this case, the lengths of the inner and outer slots are varied concurrently to function as the phase-shifting geometrical parameters. The reflection characteristics of the element are analyzed using the waveguide method, and the simulation results have been verified with experiments. A broad reflection phase range of 631.83° with slow gradient has been successfully achieved with the use of the slotted patch with constant size. Parametric analysis has been performed and it is found that the S-curve can be easily fine-tuned by changing some of the design parameters.

A pair of complementary planar inverted-F antennas (PIFAs), which are tactfully integrated, is employed for designing a compact on-metal tag. Here, two complementing PIFAs that are placed into antipodal style are found to be able of introducing reactive loading effects for reducing the overall size of a UHF RFID tag to 40 × 40 × 3.18 mm3. Despite being electrically small, this antenna is able to achieve a long read distance of 10 m (4 W EIRP) when it is tagged on metal. Worth-mentioning is that additional matching network is not required as varying the dimensions of the stubs and narrow slot are already sufficient to tune the antenna impedance for achieving good impedance matching.

In this paper, a microwave transmission line sensor is investigated and used for bulk liquid permittivity measurement. A microstrip type transmission line is designed and analysed for a frequency range of 150 kHz to 8 GHz. The transmission coefficient magnitude of the microstrip line covered with different liquid samples is calculated numerically and compared with the measurement results. The calculated transmission coefficient magnitudes show good agreement with the normalized measurement results for the sample with a dielectric constant of less than 30 and a frequency range up to 6 GHz. A specific focus of the work is to study the transmission response of the microstrip line sensor when it is implemented on a curved substrate instead of the traditional planar substrate. A semi-flexible microstrip line is designed using a semi-rigid substrate for different curvature and its transmission coefficient is calculated numerically. The curved microstrip line sensor shows good agreement between the calculated and the measured results with minimum effect on the curvature. Furthermore, dielectric constant empirical models are formed and tested for unknown liquid samples. The results show a good match between the microstrip line sensor and the commercial dielectric probe for the determination of dielectric constant at frequency range less than 0.5 GHz and 4 to 8 GHz. The study demonstrated that the empirical models applied for the dielectric constant determination can be developed for low dielectric constant liquid despite of the sensor structure is curved or planar.

A compact folded patch is proposed for designing an on-body UHF RFID tag. Stretchable polymer such as PDMS (polydimethylsiloxane) has been employed as a substrate to increase the flexibility of the antenna, and it allows conformal mounting on human body. It has small footprint ( $25\times 25\ \text{mm}^{2}$ ) and low profile (3 mm). For the proposed antenna design, its operating frequency can be easily tuned by adjusting the geometrical dimensions of the two shorting stubs. A ground layer has been incorporated into the design for achieving platform isolation. The proposed tag antenna has hemi-omnidirectional radiation patterns and it is able to achieve a maximum realized gain of −5 dBi when tested on a phantom that imitates human tissue.

A linearly polarized single-layer single-resonator reflectarray, which is designed using a simple circular patch loaded with two unequal rectangular slots, is investigated for the first time. For the proposed design, the linearity and sensitivity of the phase curve (S-curve) can be easily optimized by adjusting the ratio of the two unequal slots changeable according to a simple design equation. Here, the patch radius serves as a phase-shifting geometrical parameter and it is able to achieve a wide phase range of more than 458° with low phase sensitivity and a low reflection loss of less than 0.5 dB. With the use of the optimized phase curve, an offset-fed 13 × 13 full-fledged reflectarray with a square aperture is designed, fabricated and measured. Measurement results show that a −1-dB gain bandwidth of 11.8% and an antenna gain of 23.4 dBi are realizable at the center frequency of 9.3 GHz. Also, the proposed reflectarray has an aperture efficiency of 42% and a radiation efficiency of 98%. The proposed reflectarray has a simple structure and it is able to achieve smooth phase curve, low cross-polarized radiation field and low sidelobes.

A low-profile folded patch antenna is proposed for UHF meta-mountable RFID tag design. The proposed tag has overall size of 32 mm × 32 mm × 1.6 mm (0.098λ × 0.098λ × 0.005λ), which miniaturization of tag can be achieved by etching a narrow Z-shaped slot on the radiating patch and stub-shorting the patch to ground. Measurements are conducted with EIRP of 4W. The proposed tag is readable at distance of 8 m away from the reader antenna. Resonant frequency of the proposed tag antenna is very stable and it is insusceptible to the changes of the backing metal plate size.

In this research, a Coulomb force assisted heat pump (CF-HP) dryer was invented for the purpose of improving the drying characteristics and product quality of biomaterials. As compared to heat pump drying alone, the assistance of Coulomb force in heat pump dryer enhanced the drying rates and effective moisture diffusivity of lemon slices up to 26%, which eventually shortened the total drying time to 40%. This saved the total energy consumption of HP drying by 31.5%. High retention of vitamin C and TPC were also found in CF-HP dried slices due to mild drying temperature and fast drying rate. Keywords: Coulomb force; Heat pump drying; Drying rate; Vitamin C; Total Phenolic Content (TPC).

A UHF RFID wristband tag is designed using a planar inverted-F antenna (PIFA). With the use of the folding technique and the PP-2 soft foam substrate, the tag can be made compact, light-weight, and flexible for electronic package. The tag's footprint is only 900 mm2 with almost 100% power transmission. From simulation, the wristband tag has a theoretical read range of 8.3 m at 923 MHz when placed on a rectangular phantom. With a 3.28 W EIRP, it is also experimentally demonstrated that the wristband tag can be read from 5.1 m when it is tested on minced meat.

A simple folded patch antenna is proposed to be used as a metal mountable UHF tag antenna. Two parallel slots are introduced on the radiating patch for increasingits electrical length, causing this antenna to have a small size of 35 35 1.6 mm $^3$ (0.107$\lambda$ $\times$0.107$ \lambda$ $\times$0.005 $\lambda$). Antenna’s input impedance can be easily matched to the complex conjugate of the chip’s impedance by varying the stub’s width and position. Fabrication of the tag antenna by using flexible foam as a substrate permits the application of this tag antenna on curved metallic surfaces. The maximum achievable read distance of the tag antenna is $ sim$9.5 m at resonant frequency of 915 MHz.

Six-port reflectometer is well-known for its abil- ity to measure magnitude and phase-shift of microwave signal using four power detectors that perform magnitude- only measurements. This paper presents the development of an innovative symmetric ring junction as four-port re- flectometer for complex reflection coefficient measure- ments. It reduces the number of required detectors to two. Design optimization, new calibration modeling and algo- rithm are discussed in details for this four-port reflectome- ter. The developed four-port reflectometer is compared to five-port reflectometer and vector network analyzer. It is found that the measured magnitude and phase-shift show good performance in comparison with the commercial vector network analyzer and the five-port reflectometer.

A miniature folded patch antenna, which has a dimension of 30 mm × 30 mm × 1.6 mm (0.092λ × 0.092λ × 0.0047λ), is proposed for designing a passive ultra-high frequency (UHF) tag. Tag miniaturization can be easily achieved by stub-shorting two triangular patches to the ground and by inserting two narrow notches on both sides of the patches. Maximum realized gain of −9.97 dB is obtainable at the resonant frequency of 920 MHz. When placed on a dielectric object with permittivity value in the range of 1–12.4, the tag has very little fluctuation in the resonant frequency.

A linearly polarized (LP) Yagi-Uda-like transmitarray element, which consists of multiple strips in parallel, has been proposed for achieving broad phase range. A 6-layer unit element has been demonstrated using the Floquet method to achieve a transmission phase range of 364o. The element is then used to design a 5×5 full-fledged transmitarray to generate an antenna gain of ∼ 17dBi, a broad 1-dB bandwidth of 11.86%, and an aperture efficiency of 44.3%. To ease the design procedure, a curve-fitted equation is also provided.

A dual open ended coaxial sensor system to determine complex permittivity was studied in detail. This paper focuses on determination of a reflection coefficient phase from two magnitudes using modified capacitance model from 300 kHz to 8 GHz. The phase information can then be used for calculation of the sample's complex permittivity. Factors such as range and limitation of the model, sample's permittivity, operating frequency, and size of sensor were investigated. Sensitivity of calculated phase with respect to small changes in measured magnitude was carried out.

Common mode current induced on cable attached to a PCB has been a well-known source of unintentional radiated emissions. The coupling mechanism of the common mode current to the cable can be divided into two types: voltage-driven and current-driven. In voltage-driven mechanism, the common mode current is induced by electric fleld that couples from traces on PCB to the cable. Previous work showed that these radiated emissions can be estimate based on the self-capacitance of the trace and the signal return plane but the method is only reasonably accurate at lower frequency. This paper develops a model which gives an extended frequency range up to 800MHz. The formulation for the equivalent common-mode voltage source is improved by taking into account the driving point impedance of the cable which behaves as a wire antenna. The radiated emissions estimated by the improved model match well with the values from 3D electromagnetic simulation of the original PCB with attached cable. It represents an improvement compared to earlier model by 11dB at 400MHz to 16dB at 700MHz for board size of 10cm £ 16cm and cable length of 3m. Similar improvements are obtained for other combinations of board size and cable length. The results show that the cable length is an important factor, in addition to the board area as suggested by earlier work, in determining the magnitude of the equivalent common-mode voltage source. Resonant of the wire antenna afiects not only the radiated electromagnetic fleld but also the common- mode voltage source magnitude due to varying antenna impedances.

A new microstrip structure for realization of wideband phase shifter has been designed and fabricated. The proposed design uses edge-coupled semi-elliptical structure and an elliptical defected ground plane to increase the coupling coe-cient and operating bandwidth. Simulation performed using CST Microwave Studio and measured results conflrm the good performance of the proposed design. The phase deviation is better than §4 - , insertion loss less than 0.6dB and return loss better than 10dB over a wide frequency range. The achievable bandwidth is more than 2.3 : 1.

A power divider with ultra-wideband (UWB) performance has been designed. The quarter-wave transformer in the conventional Wilkinson power divider is replaced by an exponentially tapered microstrip line. Since the tapered line provides a consistent impedance transformation across all frequencies, very low amplitude ripple of 0.2dB peak-to-peak in the transmission coe-cient and superior input return loss better than 15dB are achieved over an ultra-wide bandwidth. Two additional resistors are added along the tapered line to improve the output return loss and isolation. Simulation performed using CST Microwave Studio and measured results conflrm the good performance of the proposed circuit. The return loss and the isolation between the output ports are better than 15dB across the band 2{ 10.2GHz. Standard ofi-the-shelf resistance values can be selected by optimizing the physical locations to mount the resistors. Better performance can be achieved with more isolation resistors added. Hence, the number of isolation resistors to be used may be selected based on the desired bandwidth and level of isolation and return loss speciflcations.

A circulator is needed in a C-band airborne synthetic aperture radar system which employs single antenna configuration. The circulator provides full-duplex capability to transmit high-power RF signal and receive the echo signal via the same antenna simultaneously. Commercially available circulators with moderate isolation are inadequate for this application. An innovative Cancellation Network (CN) has been designed to enhance the performance of the conventional circulator. This paper highlights the conceptual design and measurement results of the CN. An improvement of more than 27 dB has been achieved

The generation of the picture out of the SAR raw data is a computational intensive task. Both range compression and azimuth compression utilized Fast Fourier Transform (FFT) algorithms and Inverse Fast Fourier Transform (IFFT) in order to perform convolution with respective reference signal. Thus FFT and IFFT occupied about 70% of the total computation operation in SAR image formation. In this paper a modified algorithm based on conventional FFT is proposed to optimize the computation performance. It is shown that the proposed algorithm can essentially achieve better performance with minimum computational burden compare to conventional FFT.