Ha lets’oao le phahameng la frequency/microwave radio frequency le kenngoe ka har’a PCB potoloho, tahlehelo e bakoang ke potoloho ka boeona le thepa ea potoloho e tla hlahisa mocheso o itseng. Ha tahlehelo e kholoanyane, matla a fetang ka har’a lisebelisoa tsa PCB a phahame, ‘me mocheso o moholo o hlahisoa. Ha mocheso o sebetsang oa potoloho o feta boleng bo lekantsoeng, potoloho e ka baka mathata a mang. Ka mohlala, parameter e tloaelehileng ea ts’ebetso ea MOT, e tsejoang haholo ho li-PCB, ke mocheso o phahameng ka ho fetisisa oa ho sebetsa. Ha mocheso oa ts’ebetso o feta MOT, ts’ebetso le ts’epahalo ea potoloho ea PCB e tla sokeloa. Ka ho kopanya mohlala oa motlakase le litekanyo tsa liteko, ho utloisisa litšobotsi tsa mocheso oa RF microwave PCBs ho ka thusa ho qoba ho senyeha ha ts’ebetso ea potoloho le ho senyeha ha ts’epo ho bakoang ke mocheso o phahameng.

Ho utloisisa hore na tahlehelo ea ho kenya e etsahala joang lisebelisoa tsa potoloho ho thusa ho hlalosa hantle lintlha tsa bohlokoa tse amanang le ts’ebetso ea mocheso oa lipotoloho tse phahameng tsa PCB. Sehlooho sena se tla nka potoloho ea microstrip transmission line e le mohlala ho buisana ka mekhoa ea khoebo e amanang le ts’ebetso ea mocheso oa potoloho. Potolohong ea microstrip e nang le sebopeho sa PCB se mahlakoreng a mabeli, tahlehelo e kenyelletsa tahlehelo ea dielectric, tahlehelo ea conductor, tahlehelo ea radiation le tahlehelo ea ho lutla. Phapang pakeng tsa likarolo tse fapaneng tsa tahlehelo e kholo. Ntle le mekhelo e ‘maloa, tahlehelo ea ho lutla ha li-circuits tsa PCB tse phahameng hangata e tlase haholo. Sehloohong sena, kaha boleng ba tahlehelo ea ho lutla bo tlase haholo, bo tla hlokomolohuoa hajoale.

Ho lahleheloa ke mahlaseli

Radiation loss depends on many circuit parameters such as operating frequency, circuit substrate thickness, PCB dielectric constant (relative dielectric constant or εr) and design plan. As far as design schemes are concerned, radiation loss often stems from poor impedance transformation in the circuit or electromagnetic waves in the circuit. The difference in transmission. Circuit impedance transformation area usually includes signal feed-in area, step impedance point, stub and matching network. Reasonable circuit design can realize smooth impedance transformation, thereby reducing the radiation loss of the circuit. Of course, it should be realized that there is the possibility of impedance mismatch leading to radiation loss at any interface of the circuit. From the point of view of operating frequency, usually the higher the frequency, the greater the radiation loss of the circuit.

Mekhahlelo ea lisebelisoa tsa potoloho e amanang le tahlehelo ea radiation haholo-holo ke dielectric khafetsa le botenya ba thepa ea PCB. Ha karolo e nyenyane ea potoloho e teteaneng, ho na le monyetla o moholo oa ho baka tahlehelo ea mahlaseli; ha εr ea thepa ea PCB e tlase, tahlehelo e kholo ea mahlaseli a potoloho. Litšobotsi tse lekanyang ka botlalo, tšebeliso ea li-circuits tse tšesaane li ka sebelisoa e le mokhoa oa ho fokotsa tahlehelo ea radiation e bakiloeng ke lisebelisoa tse tlase tsa εr. Tšusumetso ea botenya ba potoloho ea substrate le εr ho tahlehelo ea mahlaseli a potoloho ke hobane ke ts’ebetso e itšetlehileng ka makhetlo. Ha botenya ba substrate ea potoloho bo sa fete 20mil mme maqhubu a ts’ebetso a le tlase ho 20GHz, tahlehelo ea mahlaseli a potoloho e tlase haholo. Kaha boholo ba mehlala ea potoloho le maqhubu a litekanyo sehloohong sena a tlase ho 20GHz, puisano e sehloohong sena e tla hlokomoloha tšusumetso ea tahlehelo ea mahlaseli ho futhumatsa potoloho.

After ignoring the radiation loss below 20GHz, the insertion loss of a microstrip transmission line circuit mainly includes two parts: dielectric loss and conductor loss. The proportion of the two mainly depends on the thickness of the circuit substrate. For thinner substrates, conductor loss is the main component. For many reasons, it is generally difficult to accurately predict conductor loss. For example, the surface roughness of a conductor has a huge influence on the transmission characteristics of electromagnetic waves. The surface roughness of copper foil will not only change the electromagnetic wave propagation constant of the microstrip circuit, but also increase the conductor loss of the circuit. Due to the skin effect, the influence of copper foil roughness on conductor loss is also frequency-dependent. Figure 1 compares the insertion loss of 50 ohm microstrip transmission line circuits based on different PCB thicknesses, which are 6.6 mils and 10 mils, respectively.

The simulation results are obtained using Rogers Corporation’s MWI-2010 microwave impedance calculation software. The MWI-2010 software quotes the analytical equations in the classic papers in the field of microstrip line modeling. The test data in Figure 1 is obtained by the differential length measurement method of a vector network analyzer. It can be seen from Fig. 1 that the simulation results of the total loss curve are basically consistent with the measured results. It can be seen from the figure that the conductor loss of the thinner circuit (the curve on the left corresponds to a thickness of 6.6 mil) is the main component of the total insertion loss. As the circuit thickness increases (the thickness corresponding to the curve on the right is 10mil), the dielectric loss and the conductor loss tend to approach, and the two together constitute the total insertion loss.

The circuit material parameters used in the simulation model and the actual circuit are: dielectric constant 3.66, loss factor 0.0037, and copper conductor surface roughness 2.8 um RMS. When the surface roughness of the copper foil under the same circuit material is reduced, the conductor loss of the 6.6 mil and 10 mil circuits in Figure 1 will be significantly reduced; however, the effect is not obvious for the 20 mil circuit. Figure 2 shows the test results of two circuit materials with different roughness, namely Rogers RO4350B™ standard circuit material with high roughness and Rogers RO4350B LoPro™ circuit material with low roughness.

For thinner substrates, the use of smooth copper foil can significantly reduce the insertion loss. For the 6.6mil substrate, the insertion loss is reduced by 0.3 dB due to the use of smooth copper foil at 20GHz; the 10mil substrate is reduced by 0.22 dB at 20GHz; and the 20mil substrate, the insertion loss is only reduced by 0.11 dB.

This means that when the circuit is fed with a certain amount of RF microwave power, the thinner the circuit will generate more heat. When comprehensively weighing the issue of circuit heating, on the one hand, a thinner circuit generates more heat than a thick circuit at high power levels, but on the other hand, a thinner circuit can obtain more effective heat flow through the heat sink. Keep the temperature relatively low.

E le ho rarolla bothata ba ho futhumatsa ha potoloho, potoloho e tšesaane e loketseng e lokela ho ba le litšobotsi tse latelang: tahlehelo e fokolang ea thepa ea potoloho, koporo e boreleli e mosesaane, e tlaase εr le conductivity e phahameng ea mocheso. Ha ho bapisoa le lisebelisoa tsa potoloho tse phahameng εr, bophara ba conductor ea impedance e tšoanang e fumanoang tlas’a boemo ba tlaase εr e ka ba kholoanyane, e leng molemo ho fokotsa tahlehelo ea mokhanni oa potoloho. Ho ea ka pono ea ho felloa ke mocheso oa potoloho, le hoja likarolo tse ngata tse phahameng tsa maqhubu a PCB li na le mocheso o fokolang haholo o amanang le li-conductor, mocheso oa mocheso oa thepa ea potoloho e ntse e le parameter ea bohlokoa haholo.

Lipuisano tse ngata mabapi le conductivity ea mocheso oa li-circuits tsa potoloho li hlalositsoe lihloohong tse fetileng, ‘me sehlooho sena se tla qotsa liphetho le tlhahisoleseding e tsoang lihloohong tse fetileng. Ka mohlala, equation e latelang le Setšoantšo sa 3 li thusa ho utloisisa lintlha tse amanang le ts’ebetso ea mocheso oa thepa ea potoloho ea PCB. Ho equation, k ke mocheso oa mocheso (W / m / K), A ke sebaka, TH ke mocheso oa mohloli oa mocheso, TC ke mocheso oa mohloli o batang, ‘me L ke sebaka se pakeng tsa mohloli oa mocheso le mohlodi o batang.